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Efficiency assessment of water reclamation processes in milk protein concentrate manufacturing plants: A predictive analysis
Journal of Food Engineering 272 (2020) 109811
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Journal of Food Engineering journal homepage: http://www.elsevier.com/locate/jfoodeng
Efficiency assessment of water reclamation processes in milk protein concentrate manufacturing plants: A predictive analysis Julien Chamberland *, 1, Amandine Bouyer 1, Scott Benoit, C�eline Provault, Am�elie B�erub�e, Alain Doyen, Yves Pouliot STELA Dairy Research Center, Institute of Nutrition and Functional Foods (INAF), Department of Food Science, Universit�e Laval, Qu�ebec, G1V 0A6, Canada
A R T I C L E I N F O
A B S T R A C T
Keywords: Efficiency Dairy processing Milk protein concentrate Reverse osmosis Water reclamation Predictive analysis
Milk protein concentrates (MPC) are increasingly used as protein fortifiers in food formulations, as a means to increase cheese yield, and in the manufacture of Greek-style yogurt. However, manufacturing of MPC requires significant volumes of input water and generates polluting by-products such as permeates and/or diafiltrates. Reverse osmosis was suggested to reduce the impact of both issues by reclaiming water from dairy fluids, thereby reducing the volumes of by-products to be treated. Filtration performance data was obtained from the reverse osmosis of dairy fluids, namely skim milk and ultrafiltration permeate, and from the polishing process of their respective permeates. It allowed the comparison of various water reclamation scenarios through a predictive analysis, which revealed that, without increasing operational costs, preconcentrating the skim milk prior the MPC manufacture would reduce the use of water and electricity by 35% and 10%, respectively, compared to a traditional process that consists in the concentration of skim milk by ultrafiltration, followed by the concen tration of the resulting retentate by reverse osmosis.
1. Introduction The dairy industry supplies a number of food sectors (bakery, beverage, snacks and ready to eat goods) with powdered dairy-based ingredients (e.g., whey or milk protein concentrates, caseinate, permeate powder) that possess functional properties such as water binding, emulsification, foaming, gelation, color or flavor development (O’Regan et al., 2009). Of these dairy ingredients, the milk protein concentrate (MPC) is gaining in popularity with a growing production of 40–270 � 106 kg from 2000 to 2012 (Patel and Patel, 2014), and year-over-year growth of 4% is expected by 2023, due to the high de mand for protein-rich food products (Technavio, 2019). Compared to the well-known skim milk powder (SMP), MPC has higher protein (40%–85% w/w), and lower lactose and mineral contents (Lagrange et al., 2015; Patel and Patel, 2014). The MPCs are thus interesting ingredients for standardizing the protein content of milk used to manufacture fermented dairy products such as cheese or yogurt, since their low lactose content limits the risk of excessive acidification by starter culture (acid or texture defect) (Shakeel-Ur-Rehman et al.,
2003), or occurrence of browning reactions compared to SMP (Sharma et al., 2012). The different MPC types differ in their protein content, which is indicated by the number in their name (e.g., MPC80 contains 80% w/w of proteins) (Lagrange et al., 2015; Patel and Patel, 2014). The MPC with the greatest market share in the USA is MPC56 (U.S. Dairy Export Council, 2012). These ingredients are manufactured by concen trating skim milk through ultrafiltration (UF), where milk proteins are concentrated in the retentate while lactose and minerals are transmitted in the permeate. The UF retentate might also be subjected to diafiltration (DF) to increase the protein content of the MPC. Diafiltration involves diluting the retentate with potable water, and reconcentrating by UF to remove more lactose and minerals from the retentate. The degree pro tein purification, and the levels of lactose and mineral removal levels are proportional to the number of diavolumes (DV) that correspond to the volume of water added to perform the DF (Novak, 1992). The manu facture of MPC may thus require substantial use of water if a DF is performed (Gavazzi-April et al., 2018; Novak, 1992). It also generates significant volumes of milk UF and DF permeates, even under optimized conditions (Foley, 2006; Gavazzi-April et al., 2018; Lipnizki et al., 2002). For example, manufacturing around 60 � 103 kg of dried MPC80
* Corresponding author. E-mail addresses: [email protected] (J. Chamberland), [email protected] (A. Bouyer), [email protected] (S. Benoit), Celine. [email protected] (C. Provault), [email protected] (A. B�erub� e), [email protected] (A. Doyen), [email protected] (Y. Pouliot). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.jfoodeng.2019.109811 Received 3 September 2019; Received in revised form 7 November 2019; Accepted 8 November 2019 Available online 9 November 2019 0260-8774/© 2019 Elsevier Ltd. All rights reserved.
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Journal of Food Engineering 272 (2020) 109811
Abbreviations BOD COD CP CR E P DF DV Fp: J Mi MP MPC
MPC56
Biochemical oxygen demand (mg O2/L) Chemical oxygen demand (mg O2/L) Concentration in the permeate (% w/w) Concentration in the retentate (% w/w) Energy consumption (Wh) Active power (W) Diafiltration Diavolume Permeation flux (kg/h) Permeate mass flow rate (kg/h.m2) Mass of the feed (kg) Mass of permeate collected (kg) Milk protein concentrate
MRR NPN R RO S SEC SMP TMP TN TP TS UF
or MPC85 from 1500 � 103 kg of milk would require between 243 and 871 kg of potable water during DF, and would generate between 1476 � 103 to 1973 � 103 kg of combined UF and DF permeates (Gav azzi-April et al., 2018). In addition to UF/DF, membrane cleaning op erations also require substantial volumes of water (approximately 99.3 L per m2 of membrane) (Chamberland et al., 2019). The use of reverse osmosis (RO) could reduce the impact of both issues by concentrating or lowering the volumes of dairy fluids at a low investment and operating costs (Loutatidou et al., 2014; Su� arez et al., 2015). Reverse osmosis generates high-quality water, thus reducing the use of potable water from municipal networks or groundwater sources ~o et al., 2019; Sua �rez et al., 2015; Vourch et al., 2008). During the (Bria MPC manufacturing process, RO can be performed on skim milk prior to UF, on milk retentate following UF to replace, in part, the traditional energy-demanding evaporation (Christiansen, 2017), or on UF and DF permeates. However, there are no data to support the selection of which dairy fluid should be subjected to RO to maximize the water recovery, and minimize energy input and operating costs of the MPC manufacturing process. Indeed, the reclamation of water should require less energy when used on permeates, rather than milk, due to the lower total solids (TS) and true protein (TP) content of the permeates (Hiddink et al., 1980). Alternatively, preconcentration of the milk by RO may be more efficient, since it could reduce both the volume to be concentrated by UF and the volume of permeates to be treated. Consequently, the novelty of this study was to generate technical and economic data in order to determine which water reclamation pro cessing scenario is the most efficient during the manufacture of MPCs. In the first part of the study, filtration performance data were generated at a pilot scale during the RO of skim milk and UF permeate. In the second phase, these data were used to compare different RO processing sce narios during the manufacture of MPC56, using a predictive analysis.
Milk protein concentrate with a protein content of 56% w/ w Mass reduction ratio Non-protein nitrogen Rejection rate (%) Reverse osmosis Apparent power (kVA) Specific energy consumption Skim milk powder Transmembrane pressure Total nitrogen Total protein Total solids Ultrafiltration
2.1.2. RO filtration experiments and reverse osmosis membranes The RO experiments were performed on a pilot-scale filtration unit (NIRO GEA, Hudson WI), consisting of a stainless steel tank (65 L), a feed pump (D/G-10, 576 V, 5 HP Wanner International Ltd., Minneapolis, MN, USA), two pressure gauges to monitor inlet and outlet pressures, and one spiral-wound membrane module. Two types of RO membranes (thin-film composite [TFC]) were used to mimic the two-passes RO systems used in the dairy industry to reclaim food grade water (Koyuncu et al., 2000). The first type, RO2 (RO22540, Parker-Hannifin Corpora tion, Cleveland, OH, USA), was used to pre-treat the dairy fluids, and generate non-food grade water. The other type, ROH (ROH2540, Parker-Hannifin Corporation, Cleveland, OH, USA), was used to polish this permeate generated using the RO2 membrane (Fig. 1). Both mem branes had an active filtration area of 2.09 m2. Briefly, the difference between the RO2 and the ROH membranes is that the ROH is less permeable (higher salt rejection), and supports a higher operating pressure. 2.1.3. Membrane cleaning Prior to RO experimentations, distilled water flux was measured for each membrane at a TMP of 1.2 MPa at 25 � C. A conditioning step was performed with an alkaline cleaning solution (0.5% v/v; Membra-base 210, Sani-Marc Inc., QC Canada) in the full-recycle mode (10 min, 45 � C, minimal TMP). Following RO experiments, the system was rinsed with distilled water until the water flow was clear. A clean-in-place procedure was run successively with an alkaline cleaning cycle (clean ing solution identical to that used for conditioning), and an acid cleaning cycle (0.2% v/v; Ultrasil 75, Ecolab Inc., Saint Paul, MN, USA) in a full recycling mode (30 min per cycle, 45 � C, minimal TMP). Between cleaning steps, the filtration system was rinsed with distilled water at 25 � C until neutral pH was reached at the system outlet. The RO mem branes were stored at 4 � C in an acid solution containing preservatives (0.5% v/v; Ultrasil MP, Ecolab Inc., Saint Paul, MN, USA).
2. Materials and methods 2.1. Generation of filtration data, and pilot-scale RO experiments
2.1.4. Determination of optimal transmembrane pressure Effects of the TMP on filtration performance of the RO2 membrane were determined with skim milk and UF permeate. Both dairy fluids were concentrated in a full recycling mode with an inlet pressure increasing by 0.35 MPa every 10 min, from 1.38 MPa to 3.45 MPa. Once the optimal and the critical TMP were determined, fluids were processed in concentration mode until no further permeation was possible. The same experiments were conducted with the ROH membrane used to concentrate RO2 permeates. The initial feed temperature was set to 15 � C, but increased slightly to a mean temperature of 22 � C and 25 � C with the RO2 and the ROH membrane, respectively, despite the use of a cooling unit in the feed tank.
2.1.1. Milk and UF-permeate sources Pasteurized skim milk (“skim milk” will be used for simplicity) was purchased from a local dairy and stored at 4 � C until RO concentrations. A fraction of the milk was filtered by UF (transmembrane pressure [TMP] of 465 kPa, 20 � C) using a 10 kDa polysulfone spiral-wound membrane element (Koch membrane systems, Wilmington, MA, USA) to generate milk UF permeate (“UF permeate” will be used for simplicity). Three different batches of milk were obtained to perform filtration experiments (RO concentrations, and generation of permeate through UF) in triplicate.
2
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Journal of Food Engineering 272 (2020) 109811
Fig. 1. Experimental design for the reclamation of water from skim milk and milk UF permeate.
2.1.5. RO performance characterization
function of the pump load and varied with the viscosity of the fluid processed. It was calculated as function of the pump load, according to manufacturer’s data (M�ethot-Hains et al., 2016).
2.1.5.1. Permeation flux. For both RO membranes, permeation flux (Fp, kg/h) was determined every 10 min by weighing permeate collected for 30 s. Permeate mass flow rate (J, kg/h.m2) was reported per active membrane surface area (A, m2) (Eq. (1)). J¼
Fp A
P ¼ S � cosðφÞ
The energy consumption (E, Wh) was finally calculated using Eq. (7). It is a function of the active power (Pi, Wh) required to pump the dairy fluid during a time interval (i) and the duration of this time interval (Δti (min).
(1)
2.1.5.2. Rejection coefficient. The rejection coefficients (R, %) of min erals, lactose, and proteins were calculated from their concentrations in the retentate (CR) and in the permeate (CP) using Eq. (2) (Balannec et al., 2005): � � Cp R¼ 1 � 100 (2) CR
E ¼ Pi �
Mi Mi
SECi ¼
Water recovery ¼
Mp � 100 Mi
(7)
Ei Mp
(8)
Total specific energy consumption (SECtot, Wh/kg of permeate) was calculated from the energy consumptions (E, Wh) reported for the mass of permeate (Mp, kg) obtained throughout filtration (Eq. (9)). R tf n X E dt Ei SECtot ¼ to ¼ Δti (9) Mp Mp i¼1
(3)
Mp
Δti 60
2.1.5.5. Specific energy consumption. The energy consumption and the mass of permeate generated during time interval i were used to calculate the specific energy consumption (SEC, Wh/kg of permeate) (Eq. (8)).
2.1.5.3. Mass reduction ratio and water recovery. The mass reduction ratio (MRR, Eq. (3)) and the water (or permeate) recovery (%, Eq. (4)) were calculated as described by Vourch et al. (2008), from the initial mass of the feed (Mi, kg) and the mass of RO permeate (Mp) generated for each concentration experiment. MRR ¼
(6)
The SECtot is the energy required for the pump to generate one kg of permeate, throughout the entire fluid concentration process. The values were calculated for both the end of the filtration for both dairy fluids (Fp ¼ 0 with the RO2 membrane, maximal MRR with the ROH mem brane). They were also calculated for the highest common MRR reached in concentration mode as milk and UF permeate did not reach the same maximal MRR.
(4)
2.1.5.4. Energy consumption. The pump power and electrical energy consumption of the filtration system were calculated as described by M�ethot-Hains et al. (2016). Briefly, voltage (U, V) and current (I, A) measurements were recorded in situ every minute during filtration with a voltmeter (V3000FC, Fluke, Everett, WA, USA) and three ammeters (A3001FC, Fluke, Everett, WA, USA) connected to the 3-phase asyn chronous motor powering the system. These data were recorded in real time and used to determine apparent power (S, kVA) for the duration of the experimentation (Eq. (5)). pffiffi S¼ 3�U �I (5)
2.1.6. Chemical analyses The TS content of dairy samples was measured using the forced-air drying method (AOAC International 990.20). Total nitrogen (TN) and non-protein nitrogen (NPN) contents were determined with the Kjeldahl method (AOAC International 991.20 and 991.21, respectively). The TP content was calculated by subtracting the NPN value from the corre sponding TN content, and using a nitrogen-to-protein conversion factor of 6.38. Lactose content was determined by HPLC (IDF 198:2007). Mineral (Ca2þ, Mg2þ, Naþ, Kþ, Cl , Total P) contents were determined
Apparent power values allowed the calculation of the active power (P, W) required for the pump (Eq. (6)). The power factor (cos(φ), %) is a 3
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Journal of Food Engineering 272 (2020) 109811
systems was 99.3 L per m2 of membrane area, which corresponds to the most conservative value predicted by Chamberland et al. (2019) to clean a UF system generating skim milk retentate at an MRR of 3.0. This value included the water used to rinse the systems and to make the cleaning solutions (12.2 L of cleaning solutions to be discarded daily per m2 of filtration area). All filtration systems modelled for this study were in a multi-stage configurations. The performance of these was predicted, as suggested by Cheryan (1998) and GEA (2016), by linear extrapolation of the data obtained for the RO systems in this study and of the data obtained by Gavazzi-April et al. (2018) for UF systems. The permeation flux (kg/h. m2), membrane area requirement (m2), and specific energy consump tion (Wh/kg of permeate) of each stage was determined from the MRR and the TS of the retentate at the outlet of each stage.
with an inductively coupled plasma-optical emission photometer (Op tima 4300, dual view, PerkinElmer, Norwalk, CT, USA). The electrical conductivity of the permeates was measured every 10 min during RO using an electrical conductivity meter (Orion star A122, Thermo Fisher Scientific, Waltham, MA, USA). Biochemical oxygen demand (BOD) and chemical oxygen demand (COD) were quantified according to the methods ASTM 5210B, and ASTM 5220C (ASTM International, 2017), respectively (AgroEnviroLab, La Pocati�ere, QC, Canada). 2.1.7. Statistical analysis As mentioned above, all RO experiments (milk, UF permeate, and RO permeates concentration) were performed in triplicate. Significant ef fects (p < 0.05) on the feed, RO retentate, permeate compositions, and processing performance (maximal MRR, RO permeate recovery, SEC) caused by the fluids filtered were determined by conducting a one-way analysis of variance (ANOVA).
3. Results and discussion 3.1. Impact of type of dairy fluid on the composition of RO permeates
2.2. Predictive analysis of water reclaiming scenarios in a MPC56 plant
Table 1 shows the compositional characteristics of skim milk and UF permeate, and their respective permeates obtained following RO2 and ROH concentrations. Major differences were observed between both initial feeds, especially for the TS, TP and mineral contents. Since the UF permeate was obtained from UF of skim milk, it contained only traces of proteins (TP of 0.01 � 0.00% w/w, compared to 3.99 � 0.03% w/w in skim milk). The TS content was also lower in UF permeate (5.30 � 0.21% w/w) than in the skim milk (8.82 � 0.09% w/w) (p < 0.05), but skim milk had a higher mineral content (Ca2þ, Mg2þ, Naþ, Kþ, Cl , and total P) (p < 0.05). For example, skim milk had a Ca2þ concentration of 1019 � 16 mg/kg, whereas the UF permeate had just 109 � 8 mg/kg. The BOD and COD of the skim milk (63,525 � 106 mg O2/L, and 106,900 � 6364 mg O2/L, respectively) were twice as high as in UF permeate (29,650 � 11,667 mg O2/L, and 56,050 � 1344 mg O2/ L, respectively) (p < 0.05), in line with the higher TS of the skim milk (Menchik et al., 2019). These were similar to values presented elsewhere for skim milk (Bylund, 2003), or milk UF permeate (Wang et al., 2009). The lactose content was similar in both fluids, between 4.67 � 0.33% w/w and 4.69 � 0.30% w/w (p > 0.05), since the UF membranes do not retain lactose (Cheryan, 1998). The chemical compositions of RO2 permeates obtained from skim milk and UF permeate were similar. Both had low TS contents, and traces of TP or lactose (Table 1). The electrical conductivity of the RO2 permeate obtained from skim milk was lower than the UF permeate (81.9 � 6.6 μS/cm vs. 96.3 � 3.5 μS/cm at p < 0.05). The quality of the
From the experimental data obtained, predictive analysis was used to compare the concentration process in three MPC56 manufacturing sce narios using RO to reclaim water from dairy fluids (Fig. 2). In all sce narios, 1000 � 103 kg of skim milk was used to manufacture milk retentate containing 56% protein on a dry basis (MPC56 prior to evap oration and drying) in 20 h in a virtual plant. In the first scenario, the skim milk is preconcentrated by RO to a MRR of 1.40, and the resulting retentate is concentrated by UF, and purified by DF, with water reclaimed by the previous RO process (Scenario 1, blue lines, Fig. 2). In the second scenario, the milk is also preconcentrated by RO, but the UF is performed at a higher MRR rather than conducting DF (Scenario 2, red lines, Fig. 2). In the third scenario, the traditional way of manufacturing MPC 56, the milk is primarily concentrated by UF until reaching a TP/TS ratio of 56%, and the resulting retentate is concentrated by RO prior to evaporation (Scenario 3, green lines, Fig. 2). For all of the three sce narios, the MRR reached during ROH operations was equivalent to the mean maximal MRR (4.0) obtained for the concentration of RO2 per meates obtained from skim milk or permeate in the experimental part. The final retentate of the three scenarios has a TS content of 19.88% w/ w, which was the highest TS obtained when concentrating milk with the RO2 membrane. In all the scenarios, water is reclaimed from the UF permeates and diafiltrates. The skimming, evaporation and drying pro cesses were not included since they did not differ between the compared scenarios. The predictive analysis focused only on the membrane filtration processes. The volume of water used to clean the filtration
Fig. 2. Comparison of the three scenarios used to manufacture liquid MPC56. These include (blue and red lines) or exclude (green lines) the preconcentration of milk by RO. 4
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Journal of Food Engineering 272 (2020) 109811
Table 1 Mean compositional characteristics of dairy fluids during the water reclamation process performed from skim milk and UF permeate. Skim milk scenario Total solids (% w/w) True proteins (% w/w) NPN (% w/w) Lactose (% w/w) Minerals (mg/kg) Ca2þ Mg2þ Naþ Kþ Cl Total P BOD (mg/L) COD (mg/L) EC (μS/cm)
UF permeate scenario
Skim milk
RO2 permeate
ROH permeate
UF permeate
RO2 permeate
ROH permeate
8.82 � 0.09a 3.99 � 0.03a 0.20 � 0.01a 4.69 � 0.30
0.04 � 0.00 N.D. N.D. N.D.
0.01 � 0.00 N.D. N.D. N.D.
5.30 � 0.21b 0.01 � 0.00b 0.15 � 0.01b 4.67 � 0.33
0.06 � 0.00 N.D. N.D. N.D.
0.01 � 0.00 N.D. N.D. N.D.
1019 � 16a 100 � 2a 411 � 4a 1391 � 59a 1014 � 79a 836 � 17a 63,525 � 106a 106,900 � 6,364a 5277 � 45b
N.D. N.D. 36 � 3 131 � 9 159 � 8 N.D. 127 � 78 135 � 106 81.9 � 6.6b
N.D. N.D. N.D. N.D. 19 � 7 N.D. 2�0 8�7 1.8 � 0.2
109 � 8b 17 � 2b 162 � 22b 337 � 86b 259 � 48b 118 � 5b 29,650 � 11,667b 56,050 � 1,344a 5933 � 191a
N.D. N.D. 38 � 6 132 � 24 134 � 18 11 � 5 356 � 328 748 � 417 96.3 � 3.5a
N.D. N.D. N.D. N.D. 11 � 4 N.D. 4�4 11 � 6 2.4 � 0.5
BOD: Biochemical oxygen demand, COD: Chemical oxygen demand, EC: Electrical conductivity, N.D.: Not detected, NPN: Non-protein nitrogen. 1 Different superscript letters in a same row, for a same fluid type (initial feed, RO2 permeate or ROH permeate) indicate significant differences (one-way ANOVA, p < 0.05, n ¼ 3, �standard deviation (SD)).
non-linear at 15.1 kg/L.m2 (critical flux obtained at a TMP of 2.28 MPa) (Fig. 3A). As similar permeation fluxes were obtained for both dairy fluids under a TMP of 2.07 MPa, this pressure was selected for filtrations performed in concentration mode. In concentration mode, the permeation fluxes were always higher during the RO of UF permeate (Fig. 3B). At the beginning of filtration, the permeation flux was of 17.6 kg/L.m2, compared to 10.7 kg/L.m2 during skim milk concentration (Fig. 3B). A maximal MRR of 2.5 was finally reached with UF permeate, compared to 2.2 with skim milk. A non-linear increase of the electrical conductivity of the permeates and of the electricity consumption was observed throughout the concentration experiments (Fig. 3C and D). The fluid type had a lower impact on the performance of the ROH membrane. The effect of TMP on the permeation flux of the ROH membrane was similar for RO permeates generated from skim milk or UF permeate RO (Fig. 4A). At a TMP between 1.29 MPa and 3.37 MPa in full recycling mode, the permeation fluxes increased linearly with the TMP, from 9 to 37 kg/L.m2 (Fig. 4A). Since the ROH membrane did not reach critical flux during experiments performed in full recycling mode, a TMP near the maximal operating pressure recommended by the membrane manufacturer (3.37 MPa) was selected for filtrations con ducted in concentration mode. In concentration mode, an increase in the permeation flux was observed for the concentration of both RO permeates filtered as function of the MRR (Fig. 4B). This increase was due to an increase in tempera ture and a decrease in the viscosity of the feed during this high-pressure concentration, as revealed by a reduction in consumption of electricity
RO2 permeates did not meet discharge water quality standards (COD higher than 125 mg/L), and required further RO treatment with a pol ishing membrane (ROH) in order to be reused (Balannec et al., 2002; ~o et al., 2019; Koyuncu et al., 2000). Bria After the second RO treatment (ROH membrane), the compositions of all permeates were similar to that of pure water. The combined treatments with RO2 and ROH membranes in series reduced the skim milk and UF permeate BOD and COD by 99.99%. The conductivities of the ROH permeates obtained from milk and UF permeate were lowered by 99.97% and 99.96%, respectively. Their low Ca2þ (not detectable) and electrical conductivity (<40 μS/cm) would allow their reuse in boiler or cooling tower (Mavrov et al., 2001). Like the water generated from whey by Meneses and Flores (2016), these ROH permeates might be suitable for DF or cleaning purposes but further analyses, such as total organic carbon (TOC) and microbiological analysis (total aerobic plate count, coliforms, E. coli), would be needed to determine whether they could reach drinking water quality. Heat treatment, UV disinfection, or chlorination would also be mandatory prior to reuse in industrial pro cesses (Lindgaard-Jørgensen et al., 2018; Mavrov and B�eli� eres, 2000; Meneses and Flores, 2016). 3.2. Impact of the type of dairy fluid on the performance of RO processes In full recycling mode, the permeation flux of the RO2 membrane increased linearly with the TMP to a TMP of 3.38 MPa with UF permeate, reaching a maximal value of 32.0 kg/h.m2 (Fig. 3A). When concentrating skim milk, the increase of the permeation flux became
Fig. 3. Performance of the RO2 membrane with skim milk and UF permeate. A) Permeation flux (J) in the full-recycle mode, B) J in the concentration mode at a TMP of 1.93 MPa, C) Electrical conductivity of the permeates, and D) Electricity consumption in the concentration mode as function of mass reduction ratio (MRR) (n ¼ 3, �SD). 5
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Journal of Food Engineering 272 (2020) 109811
Fig. 4. Performance of the ROH membrane. A) Permeation flux (J) in the full-recycle mode, B) J in the concentration mode at a TMP of 3.37 MPa, C) Electrical conductivity of the permeates, and D) Electricity consumption during the polishing of the RO2 permeates in the concentration mode as function of mass reduction ratio (MRR) (n ¼ 3, �SD).
as function of the MRR (Fig. 4D). This permeate flux increase was not observed with the RO2 membrane, despite a similar temperature in crease, because of the greater membrane fouling of this membrane concentrating dairy fluids. The electrical conductivity of the permeates did not increase during the concentration with the ROH membrane (Fig. 4C).
with diluted feed (e.g., 5 Wh per kg of water reclaimed from dairy ef fluents [Koyuncu et al., 2000]), or those obtained from industrial multi-stage RO systems (e.g., 7.5 and 9.6 Wh per kg of water reclaimed from milk and cheese whey, respectively (Pepper and Orchard, 1982; Stabile, 1983). Industrial systems are equipped with recirculation loops that reduce membrane fouling incidence (higher feed velocity), increase permeation flux, and allow further concentration of the feed (Pepper and Orchard, 1982). In the present study, skim milk was concentrated at a maximal TS content of 19.88% w/w, whereas a concentration of 29.4% w/w was reported by Christiansen (2017). This adds-up with the ROH limitations mentioned above. Consequently, it is assumed that this study may have overestimated energy consumption and membrane re quirements compared to industrial performance, but the relative dif ferences observed between the performance of the filtered fluids are consistent since they were processed using the same filtration system. Overall, the concentration of RO permeates obtained from skim milk and UF permeate resulted in similar water recoveries of 74.8 � 3.1%, and 75.4 � 3.6%, respectively, and similar energy use of 73 � 3 Wh, and 74 � 4 Wh per kg of permeate collected, respectively (p > 0.05) (Table 2). Contrary to the RO performed with the RO2 membrane, the limitation was not the final permeation flux, but the size of the feed tank. With a larger a larger feed tank (approximately 15 times), a higher water recovery up to an MRR of 64 might have been possible, as reached by ~o et al. (2019) with dairy rinse water. Bria
3.3. Overall process efficiency of the water reclamation processes The RO2 membrane produced RO permeate conversions of 59.2% and 54.5% of the initial mass of UF permeate and skim milk, respectively (Table 2). Neither the maximal MRR, nor the permeate recovery were significantly different between skim milk and UF permeate experiments (p > 0.05). However, as shown in Table 2, the recovery of RO permeate from UF permeate required less energy than permeate recovered from skim milk (99 vs. 160 Wh per kg of permeate, p < 0.05). The same conclusion was obtained by calculating the SEC at the highest common MRR of 2.2 (SEC2.2), reached in concentration mode (Table 2). Since RO membranes retain low molecular weight molecules such as salts, any of the dairy solids act as foulants in the membrane polarization layer (Drioli and Macedonio, 2012). Consequently, RO performance is strongly affected by the TS content (Aydiner et al., 2014; Hiddink et al., 1980; Vourch et al., 2005), and is limited by the presence of constituents affecting the osmotic pressure of the feed, such as minerals, lactose, and proteins. Minerals, however, have the greatest impact on osmotic pres sure (Cheryan, 1998). Indeed, the UF permeate, which had the lowest TS and mineral contents, had the best performance with the RO2 mem brane (higher flux, lower SEC). The highest water recovery rate for RO2 and ROH membranes in series was obtained with UF permeate (44.7% vs. 40.8%, Table 2). This scenario led to a water quality similar to that from skim milk, but it consumed 28% less electricity per kg of water reclaimed (205 Wh per kg of reclaimed water compared to 286 Wh with skim milk, Table 2). These electricity demands are high compared to other processes measured
3.4. Where should water be reclaimed in a MPC manufacturing plant? The results from this study indicated that better performance is observed when reclaiming water from UF permeate than from skim milk. However, in the case study of an MPC manufacturing plant where water can be reclaimed by RO at several points — (1) from milk prior to UF, (2) from UF retentate, or (3) from UF permeate — the decision to reclaim water from permeate may not be as evident. One consideration is that extracting water from skim milk reduces the volume of milk to be
Table 2 Performance of the RO2 and ROH membranes for the concentration of skim milk, UF permeate, and their respective RO permeates, and the predicted performance of a combined system (RO2 and ROH membranes in series). Indicatora Maximal MRRb RO permeate recovery (%) SECtot to reach MRR max (Wh/kg of permeate) SEC2.2c (Wh/kg of permeate)
RO2 membrane
RO2 and ROH in seriesc
ROH membrane
Skim milk
UF permeate
Skim milk RO permeate
UF permeate RO permeate
Skim milk
UF permeate
2.2 � 0.1 54.5 � 1.3 159.7 � 1.9a 159.7 � 1.9a
2.5 � 0.2 59.2 � 2.7 98.6 � 7.7b 78.8 � 31.3b
4.0 � 0.5 74.8 � 3.1 72.5 � 3.3 –
4.1 � 0.6 75.4 � 3.6 74.1 � 1.1 –
– 40.8 286.0 –
– 44.7 204.9 –
a
Different superscript letters in the same row, for the same fluid type (initial feed, RO2 permeate or ROH permeate) indicate significant differences (one-way ANOVA, p < 0.05, n ¼ 3, �SD). b MRR: Mass reduction ratio, SECtot: Total specific energy consumption, SEC2.2: Specific energy consumption at the uppermost common MRR reached in the concentration mode (2.2). c Values obtained by interpolation. 6
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Journal of Food Engineering 272 (2020) 109811
ultrafiltered, and the volumes of UF permeate to be treated. Since the manufacture of MPC may also require water to perform DF, it might be beneficial to reduce the input water by generating DF water from skim milk prior to UF. Consequently, the data obtained in the previous ex periments were used to perform a predictive analysis of the scenarios presented in Fig. 2. The processing needs (milk, membranes, electricity and water) of three scenarios are presented in Table 3, whereas the economic balance of those scenarios is presented in Table 4. Reclaiming water from the unconcentrated milk, followed by an UF to concentrate the milk without DF (Scenario 2, red scenario, Fig. 2) was the most efficient scenario, having the lowest electricity (101.2 MWh) and water (95 m3) consumptions (Table 3). The scenarios reclaiming water from UF retentate (Scenarios 1 and 3, or blue and green scenarios, respectively, Fig. 2) required higher membrane surface area and pumping energy. Reverse osmosis is the most energy demanding of all the filtration processes because it requires the highest operating pressure (de Boer, 2014). Consequently, the most efficient water reclamation scenarios are those that use RO to process the most diluted fluids, and, ideally, lower volumes of feed. In the scenarios 2 and 3, 1000 � 103 kg of skim milk (TS ¼ 9.0%), and 200 � 103 kg of UF retentate (TS ¼ 13.9%) were, respectively, concentrated by RO at an MRR of 1.4. As a lower permeation flux was expected with the latter feed (higher TS content and viscosity), it required 18% more RO2 membranes, and had similar electricity consumption, despite a five-fold lower volume to be concentrated. Furthermore, as milk was preconcentrated in the scenario 2 (RO/UF scenario), there was a lower volume of milk to be ultrafiltered and a lower volume of permeate was generated compared to the scenario 3 (UF/RO scenario) (391 m3 vs. 555 m3 of UF permeate, respectively). Ultimately, the scenario 2 used only 36.1 MWh while the UF/RO sce nario used 66.1 MWh to generate water from UF permeate (RO2 and ROH combined). Both scenarios reclaimed the same volume of water, but the scenario 3 had more membrane surface area to clean, which
Table 4 Processing costs for three processing scenarios to manufacture MPC56 from 1000 � 103 kg of skim milk. Indicator
Skim milka
Skim milk
Unit
Membranesb Cleaning solutionsc
Scenario 2 (RO/UF)
Scenario 3 (UF/RO)
� 103 kg
1000
1000
1000
Electricityd Electrical power4 Fresh watere
m2
1798
1665
1688
m2 m2
2630 1001
2187 635
2584 684
Cleaning solutions Polishing retentate
MWh
12.6
11.8
6.3
MWh MWh MWh
36.0 39.3 38.2
36.0 – 27.2
– 33.0 44.8
MWh
26.8
17.4
7.7
MWh
14.1
8.6
20.6
Total
MWh
167.0
100.9
112.4
Operating cost
m3
525
347
343
3
237 539
– 445
– 492
Balance a
m m3 m3
251
98
17.88 $Can/ 100 kg
178,800
178,800
178,800
0.60 $Can/ m2.day 50.84 $Can/m3
3203
2647
2925
3367
2783
3074
5478
3310
3687
3591
2170
2417
324
127
193
0.97 $Can/ m3 0.97 $Can/ m3
64
53
59
170
112
111
$Can
194,997
190,002
191,266
0.0328 $Can/kWh1 0.43 $Can/ kW.day 1.29 $Can/ m3
The skim milk price was calculated from the price of protein and solids of the class 5B in Quebec (Canada) in January 2019. It does not include the price of fat. b It was assumed that membranes were replaced after 18 months. c The cost of cleaning solutions included the price of caustic and acid cleaning chemicals (Chamberland et al., 2019). d The price of electricity was that of Hydro-Qu� ebec in 2019 for business cus tomers with a contract power of more than 5000 kW (rate L). e The price of water was that calculated by MAMROT (MAMROT, 2015) for production and distribution of drinking water in Quebec in 2012 (Canada). f The wastewater disposal cost was that by MAMROT (MAMROT, 2015) for wastewater collection and treatment in Quebec in 2012 (Canada).
affected the final water balance. The scenario 3, which is the most common processing strategy in the industry, required 50% more (48 m3) input water than the scenario 2 (Table 3). Rather than using RO, UF retentate could also be concentrated by vacuum evaporation (de Boer, 2014), but this latter process would require eight times more energy than RO (Cheryan, 1998). For the scenario 1, even if DF water is generated at the plant, the DF can be done only if necessary, because it requires additional membrane surface to operate (which increases electricity consumption) and clean (which increases water consumption). This scenario generated the highest volume of water (531 m3) because more permeate was gener ated from the DF permeate, but it was also the most water-demanding scenario (247 m3 of input water due to the water used for DF and membrane cleaning). This strategy of generating DF water remains interesting as a way to reduce the environmental impact of the industry but should be reserved for the manufacture of MPC with a higher protein concentration (e.g., MPC85), which requires substantial purification by DF. Table 4 reports the comparative analysis of processing costs for the three scenarios. The operating costs were similar between the scenarios, as the skim milk was the major expenditure (92–94% of total expendi tures). Nevertheless, the scenario reclaiming water from the uncon centrated milk, followed by an UF to concentrate the milk without DF (scenario 2, red scenario, Fig. 2) had slightly lower total operating costs of 190,002 Can$. It must also be emphasized that this scenario resulted in lower costs for all expenditures considered (membranes, cleaning solutions, resources and energy, and wastewater disposal). Although
Water balance Water generated Water used Diafiltration (DF) Membrane cleaning
Scenario 3 (UF/RO)
a
Electricity use UF and DFa RO2 Skim milk Milk retentate UF permeate ROH Permeate from milk RO Permeate from permeate RO
Scenario 2 (RO/UF)
Wastewater disposalf
Membrane surface Ultrafiltration (UF) and diafiltration (DF)a RO2 ROH
Scenario 1 (RO/DF)
Resources and energy
Scenarios Scenario 1 (RO/DF)
Scenarios ($Can)
Filtration systems
Table 3 Prediction of the membrane, electricity, and water requirements for three pro cessing scenarios to manufacture of MPC56 from 1000 � 103 kg of skim milk. Indicator
Price
149
Diafiltration was only performed in the scenario 1. 7
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these costs are relatively minor in absolute value on a daily basis, they represent significant cost savings on a longer-term basis (e.g., 1 year) when compared to the other scenarios.
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In: New Applications of Membrane Processes, IDF Special Issue 9201. International Dairy Federation (IDF), Brussels, pp. 51–66. O’Regan, J., Ennis, M.P., Mulvihill, D.M., 2009. Milk proteins. In: Phillips, G.O., Williams, P.A. (Eds.), Handbook of Hydrocolloids. Woodhead Publishing Limited, pp. 298–358. https://doi.org/10.1533/9781845695873.298. Patel, H., Patel, S., 2014. Milk protein concentrates: manufacturing and applications technical report. U.S. Dairy Export Counc. Dairy Res. Inst. Pepper, D., Orchard, A.C.J., 1982. Improvements in the concentration of whey and milk by reverse osmosis. Int. J. Dairy Technol. 35, 49–53. https://doi.org/10.1111/ j.1471-0307.1982.tb02712.x. Shakeel-Ur-Rehman, Farkye, N.Y., Considine, T., Schaffner, A., Drake, M.A., 2003. Effects of standardization of whole milk with dry milk protein concentrate on the yield and ripening of reduced-fat cheddar cheese. J. Dairy Sci. 86, 1608–1615. https://doi.org/10.3168/jds.S0022-0302(03)73746-1. Sharma, A., Jana, A.H., Chavan, R.S., 2012. Functionality of milk powders and milkbased powders for end use applications-A review. Compr. Rev. Food Sci. Food Saf. 11, 518–528. https://doi.org/10.1111/j.1541-4337.2012.00199.x. Stabile, R.L., 1983. Economics of reverse osmosis and multistage evaporation for concentrating skim milk from 8.8 to 45% solids. J. Dairy Sci. 66, 1765–1772. https://doi.org/10.3168/jds.S0022-0302(83)82004-9. Su� arez, A., Fern� andez, P., Ram� on, J., Iglesias, E., Riera, F.A., 2015. Cost assessment of membrane processes : a practical example in the dairy wastewater reclamation by reverse osmosis. J. Membr. Sci. 493, 389–402. https://doi.org/10.1016/j. memsci.2015.04.065. Technavio, 2019. Global Milk Protein Concentrates Market 2019-2023, Growth Analysis and Forecast. https://www.businesswire.com/news/home/20190425005460/en/. (Accessed 5 June 2019). Vourch, M., Balannec, B., Chaufer, B., Dorange, G., 2005. Nanofiltration and reverse osmosis of model process waters from the dairy industry to produce water for reuse. Desalination 172, 245–256. https://doi.org/10.1016/j.desal.2004.07.038. Vourch, M., Balannec, B., Chaufer, B., Dorange, G., 2008. Treatment of dairy industry wastewater by reverse osmosis for water reuse. Desalination 219, 190–202. https:// doi.org/10.1016/j.desal.2007.05.013. Wang, S., Chandrasekhara Rao, N., Qiu, R., Moletta, R., 2009. Performance and kinetic evaluation of anaerobic moving bed biofilm reactor for treating milk permeate from dairy industry. Bioresour. Technol. 100, 5641–5647. https://doi.org/10.1016/j. biortech.2009.06.028.
4. Conclusion Significant water consumption in the dairy industry could be reduced through the use of RO to reclaim water in-plant from dairy fluids. A case study of an MPC56 manufacturing process revealed that preconcentrating the milk prior to traditional manufacturing processes lowers the volume of subsequent fluids to be processed, and the use of water and energy. Further work at the industrial scale will determine realistic water reclamation cost in dairy processing plants, and include the operating cost of the whole process (notably MPC drying). An optimization of operating filtration parameters is also essential to generate water that meets drinking water quality requirements. Declarations of competing interest None. Acknowledgments Funding: NSERC-Novalait Research Chair on Process Efficiency in Dairy Technology [grant numbers IRCPJ 46130-12, 2014–2019 to Yves Pouliot]. The authors are thankful to Barb Conway for editing this manuscript. References ASTM International, 2017. ASTM D6238-98(2017), Standard Test Method for Total Oxygen Demand in Water. https://doi.org/10.1520/D6238-98R17. West Conshohocken. Aydiner, C., Sen, U., Topcu, S., Ekinci, D., Altinay, A.D., Koseoglu-Imer, D.Y., Keskinler, B., 2014. Techno-economic viability of innovative membrane systems in water and mass recovery from dairy wastewater. J. Membr. Sci. 458, 66–75. https:// doi.org/10.1016/j.memsci.2014.01.058. Balannec, B., G�esan-Guiziou, G., Chaufer, B., Rabiller-Baudry, M., Daufin, G., 2002. Treatment of dairy process waters by membrane operations for water reuse and milk constituents concentration. Desalination 147, 89–94. https://doi.org/10.1016/ S0011-9164(02)00581-7. Balannec, B., Vourch, M., Chaufer, B., 2005. Comparative study of different nanofiltration and reverse osmosis membranes for dairy effluent treatment by deadend filtration. Separ. Purif. Technol. 42, 195–200. https://doi.org/10.1016/j. seppur.2004.07.013. Bri~ ao, V.B., Salla, A.C.V., Miorando, T., Hemkemeier, M., Favaretto, D.P.C., 2019. Water recovery from dairy rinse water by reverse osmosis : giving value to water and milk solids. Resour. Conserv. Recycl. 140, 313–323. https://doi.org/10.1016/j. resconrec.2018.10.007. Bylund, G., 2003. Dairy Processing Handbook. In: http://www.dairyprocessinghand book.com/. (Accessed 11 May 2019). Chamberland, J., Benoit, S., Harel-Oger, M., Pouliot, Y., Jeantet, R., Garric, G., 2019. Comparing economic and environmental performance of three industrial cheesemaking processes through a process simulation. J. Clean. Prod. 239 https:// doi.org/10.1016/j.jclepro.2019.118046. Cheryan, M., 1998. Ultrafiltration and Microfiltration Handbook, second ed. CRC press, Boca Raton. Christiansen, M.V., 2017. Physical-chemical Characterisation of Skim Milk Concentrates Produced by RO Filtration. University of Copenhagen. Dairy Export Council, U.S., 2012. Child Nutrition: Global Follow-On Formula, GrowingUp Milk Report (Arlington, vol. A). de Boer, R., 2014. Vital membrane processes. In: de Boer, R. (Ed.), From Milk ByProducts to Milk Ingredients: Upgrading the Cycle. John Wiley & Sons, Hoboken, pp. 141–167. https://doi.org/10.1002/9781118598634.ch6. Drioli, E., Macedonio, F., 2012. Membrane engineering for water engineering. Ind. Eng. Chem. Res. 51, 10051–10056. https://doi.org/10.1021/ie2028188. Foley, G., 2006. Water usage in variable volume diafiltration: comparison with ultrafiltration and constant volume diafiltration. Desalination 196, 160–163. https://doi.org/10.1016/j.desal.2005.12.011.
8
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Journal of Food Engineering journal homepage: http://www.elsevier.com/locate/jfoodeng
Efficiency assessment of water reclamation processes in milk protein concentrate manufacturing plants: A predictive analysis Julien Chamberland *, 1, Amandine Bouyer 1, Scott Benoit, C�eline Provault, Am�elie B�erub�e, Alain Doyen, Yves Pouliot STELA Dairy Research Center, Institute of Nutrition and Functional Foods (INAF), Department of Food Science, Universit�e Laval, Qu�ebec, G1V 0A6, Canada
A R T I C L E I N F O
A B S T R A C T
Keywords: Efficiency Dairy processing Milk protein concentrate Reverse osmosis Water reclamation Predictive analysis
Milk protein concentrates (MPC) are increasingly used as protein fortifiers in food formulations, as a means to increase cheese yield, and in the manufacture of Greek-style yogurt. However, manufacturing of MPC requires significant volumes of input water and generates polluting by-products such as permeates and/or diafiltrates. Reverse osmosis was suggested to reduce the impact of both issues by reclaiming water from dairy fluids, thereby reducing the volumes of by-products to be treated. Filtration performance data was obtained from the reverse osmosis of dairy fluids, namely skim milk and ultrafiltration permeate, and from the polishing process of their respective permeates. It allowed the comparison of various water reclamation scenarios through a predictive analysis, which revealed that, without increasing operational costs, preconcentrating the skim milk prior the MPC manufacture would reduce the use of water and electricity by 35% and 10%, respectively, compared to a traditional process that consists in the concentration of skim milk by ultrafiltration, followed by the concen tration of the resulting retentate by reverse osmosis.
1. Introduction The dairy industry supplies a number of food sectors (bakery, beverage, snacks and ready to eat goods) with powdered dairy-based ingredients (e.g., whey or milk protein concentrates, caseinate, permeate powder) that possess functional properties such as water binding, emulsification, foaming, gelation, color or flavor development (O’Regan et al., 2009). Of these dairy ingredients, the milk protein concentrate (MPC) is gaining in popularity with a growing production of 40–270 � 106 kg from 2000 to 2012 (Patel and Patel, 2014), and year-over-year growth of 4% is expected by 2023, due to the high de mand for protein-rich food products (Technavio, 2019). Compared to the well-known skim milk powder (SMP), MPC has higher protein (40%–85% w/w), and lower lactose and mineral contents (Lagrange et al., 2015; Patel and Patel, 2014). The MPCs are thus interesting ingredients for standardizing the protein content of milk used to manufacture fermented dairy products such as cheese or yogurt, since their low lactose content limits the risk of excessive acidification by starter culture (acid or texture defect) (Shakeel-Ur-Rehman et al.,
2003), or occurrence of browning reactions compared to SMP (Sharma et al., 2012). The different MPC types differ in their protein content, which is indicated by the number in their name (e.g., MPC80 contains 80% w/w of proteins) (Lagrange et al., 2015; Patel and Patel, 2014). The MPC with the greatest market share in the USA is MPC56 (U.S. Dairy Export Council, 2012). These ingredients are manufactured by concen trating skim milk through ultrafiltration (UF), where milk proteins are concentrated in the retentate while lactose and minerals are transmitted in the permeate. The UF retentate might also be subjected to diafiltration (DF) to increase the protein content of the MPC. Diafiltration involves diluting the retentate with potable water, and reconcentrating by UF to remove more lactose and minerals from the retentate. The degree pro tein purification, and the levels of lactose and mineral removal levels are proportional to the number of diavolumes (DV) that correspond to the volume of water added to perform the DF (Novak, 1992). The manu facture of MPC may thus require substantial use of water if a DF is performed (Gavazzi-April et al., 2018; Novak, 1992). It also generates significant volumes of milk UF and DF permeates, even under optimized conditions (Foley, 2006; Gavazzi-April et al., 2018; Lipnizki et al., 2002). For example, manufacturing around 60 � 103 kg of dried MPC80
* Corresponding author. E-mail addresses: [email protected] (J. Chamberland), [email protected] (A. Bouyer), [email protected] (S. Benoit), Celine. [email protected] (C. Provault), [email protected] (A. B�erub� e), [email protected] (A. Doyen), [email protected] (Y. Pouliot). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.jfoodeng.2019.109811 Received 3 September 2019; Received in revised form 7 November 2019; Accepted 8 November 2019 Available online 9 November 2019 0260-8774/© 2019 Elsevier Ltd. All rights reserved.
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Abbreviations BOD COD CP CR E P DF DV Fp: J Mi MP MPC
MPC56
Biochemical oxygen demand (mg O2/L) Chemical oxygen demand (mg O2/L) Concentration in the permeate (% w/w) Concentration in the retentate (% w/w) Energy consumption (Wh) Active power (W) Diafiltration Diavolume Permeation flux (kg/h) Permeate mass flow rate (kg/h.m2) Mass of the feed (kg) Mass of permeate collected (kg) Milk protein concentrate
MRR NPN R RO S SEC SMP TMP TN TP TS UF
or MPC85 from 1500 � 103 kg of milk would require between 243 and 871 kg of potable water during DF, and would generate between 1476 � 103 to 1973 � 103 kg of combined UF and DF permeates (Gav azzi-April et al., 2018). In addition to UF/DF, membrane cleaning op erations also require substantial volumes of water (approximately 99.3 L per m2 of membrane) (Chamberland et al., 2019). The use of reverse osmosis (RO) could reduce the impact of both issues by concentrating or lowering the volumes of dairy fluids at a low investment and operating costs (Loutatidou et al., 2014; Su� arez et al., 2015). Reverse osmosis generates high-quality water, thus reducing the use of potable water from municipal networks or groundwater sources ~o et al., 2019; Sua �rez et al., 2015; Vourch et al., 2008). During the (Bria MPC manufacturing process, RO can be performed on skim milk prior to UF, on milk retentate following UF to replace, in part, the traditional energy-demanding evaporation (Christiansen, 2017), or on UF and DF permeates. However, there are no data to support the selection of which dairy fluid should be subjected to RO to maximize the water recovery, and minimize energy input and operating costs of the MPC manufacturing process. Indeed, the reclamation of water should require less energy when used on permeates, rather than milk, due to the lower total solids (TS) and true protein (TP) content of the permeates (Hiddink et al., 1980). Alternatively, preconcentration of the milk by RO may be more efficient, since it could reduce both the volume to be concentrated by UF and the volume of permeates to be treated. Consequently, the novelty of this study was to generate technical and economic data in order to determine which water reclamation pro cessing scenario is the most efficient during the manufacture of MPCs. In the first part of the study, filtration performance data were generated at a pilot scale during the RO of skim milk and UF permeate. In the second phase, these data were used to compare different RO processing sce narios during the manufacture of MPC56, using a predictive analysis.
Milk protein concentrate with a protein content of 56% w/ w Mass reduction ratio Non-protein nitrogen Rejection rate (%) Reverse osmosis Apparent power (kVA) Specific energy consumption Skim milk powder Transmembrane pressure Total nitrogen Total protein Total solids Ultrafiltration
2.1.2. RO filtration experiments and reverse osmosis membranes The RO experiments were performed on a pilot-scale filtration unit (NIRO GEA, Hudson WI), consisting of a stainless steel tank (65 L), a feed pump (D/G-10, 576 V, 5 HP Wanner International Ltd., Minneapolis, MN, USA), two pressure gauges to monitor inlet and outlet pressures, and one spiral-wound membrane module. Two types of RO membranes (thin-film composite [TFC]) were used to mimic the two-passes RO systems used in the dairy industry to reclaim food grade water (Koyuncu et al., 2000). The first type, RO2 (RO22540, Parker-Hannifin Corpora tion, Cleveland, OH, USA), was used to pre-treat the dairy fluids, and generate non-food grade water. The other type, ROH (ROH2540, Parker-Hannifin Corporation, Cleveland, OH, USA), was used to polish this permeate generated using the RO2 membrane (Fig. 1). Both mem branes had an active filtration area of 2.09 m2. Briefly, the difference between the RO2 and the ROH membranes is that the ROH is less permeable (higher salt rejection), and supports a higher operating pressure. 2.1.3. Membrane cleaning Prior to RO experimentations, distilled water flux was measured for each membrane at a TMP of 1.2 MPa at 25 � C. A conditioning step was performed with an alkaline cleaning solution (0.5% v/v; Membra-base 210, Sani-Marc Inc., QC Canada) in the full-recycle mode (10 min, 45 � C, minimal TMP). Following RO experiments, the system was rinsed with distilled water until the water flow was clear. A clean-in-place procedure was run successively with an alkaline cleaning cycle (clean ing solution identical to that used for conditioning), and an acid cleaning cycle (0.2% v/v; Ultrasil 75, Ecolab Inc., Saint Paul, MN, USA) in a full recycling mode (30 min per cycle, 45 � C, minimal TMP). Between cleaning steps, the filtration system was rinsed with distilled water at 25 � C until neutral pH was reached at the system outlet. The RO mem branes were stored at 4 � C in an acid solution containing preservatives (0.5% v/v; Ultrasil MP, Ecolab Inc., Saint Paul, MN, USA).
2. Materials and methods 2.1. Generation of filtration data, and pilot-scale RO experiments
2.1.4. Determination of optimal transmembrane pressure Effects of the TMP on filtration performance of the RO2 membrane were determined with skim milk and UF permeate. Both dairy fluids were concentrated in a full recycling mode with an inlet pressure increasing by 0.35 MPa every 10 min, from 1.38 MPa to 3.45 MPa. Once the optimal and the critical TMP were determined, fluids were processed in concentration mode until no further permeation was possible. The same experiments were conducted with the ROH membrane used to concentrate RO2 permeates. The initial feed temperature was set to 15 � C, but increased slightly to a mean temperature of 22 � C and 25 � C with the RO2 and the ROH membrane, respectively, despite the use of a cooling unit in the feed tank.
2.1.1. Milk and UF-permeate sources Pasteurized skim milk (“skim milk” will be used for simplicity) was purchased from a local dairy and stored at 4 � C until RO concentrations. A fraction of the milk was filtered by UF (transmembrane pressure [TMP] of 465 kPa, 20 � C) using a 10 kDa polysulfone spiral-wound membrane element (Koch membrane systems, Wilmington, MA, USA) to generate milk UF permeate (“UF permeate” will be used for simplicity). Three different batches of milk were obtained to perform filtration experiments (RO concentrations, and generation of permeate through UF) in triplicate.
2
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Journal of Food Engineering 272 (2020) 109811
Fig. 1. Experimental design for the reclamation of water from skim milk and milk UF permeate.
2.1.5. RO performance characterization
function of the pump load and varied with the viscosity of the fluid processed. It was calculated as function of the pump load, according to manufacturer’s data (M�ethot-Hains et al., 2016).
2.1.5.1. Permeation flux. For both RO membranes, permeation flux (Fp, kg/h) was determined every 10 min by weighing permeate collected for 30 s. Permeate mass flow rate (J, kg/h.m2) was reported per active membrane surface area (A, m2) (Eq. (1)). J¼
Fp A
P ¼ S � cosðφÞ
The energy consumption (E, Wh) was finally calculated using Eq. (7). It is a function of the active power (Pi, Wh) required to pump the dairy fluid during a time interval (i) and the duration of this time interval (Δti (min).
(1)
2.1.5.2. Rejection coefficient. The rejection coefficients (R, %) of min erals, lactose, and proteins were calculated from their concentrations in the retentate (CR) and in the permeate (CP) using Eq. (2) (Balannec et al., 2005): � � Cp R¼ 1 � 100 (2) CR
E ¼ Pi �
Mi Mi
SECi ¼
Water recovery ¼
Mp � 100 Mi
(7)
Ei Mp
(8)
Total specific energy consumption (SECtot, Wh/kg of permeate) was calculated from the energy consumptions (E, Wh) reported for the mass of permeate (Mp, kg) obtained throughout filtration (Eq. (9)). R tf n X E dt Ei SECtot ¼ to ¼ Δti (9) Mp Mp i¼1
(3)
Mp
Δti 60
2.1.5.5. Specific energy consumption. The energy consumption and the mass of permeate generated during time interval i were used to calculate the specific energy consumption (SEC, Wh/kg of permeate) (Eq. (8)).
2.1.5.3. Mass reduction ratio and water recovery. The mass reduction ratio (MRR, Eq. (3)) and the water (or permeate) recovery (%, Eq. (4)) were calculated as described by Vourch et al. (2008), from the initial mass of the feed (Mi, kg) and the mass of RO permeate (Mp) generated for each concentration experiment. MRR ¼
(6)
The SECtot is the energy required for the pump to generate one kg of permeate, throughout the entire fluid concentration process. The values were calculated for both the end of the filtration for both dairy fluids (Fp ¼ 0 with the RO2 membrane, maximal MRR with the ROH mem brane). They were also calculated for the highest common MRR reached in concentration mode as milk and UF permeate did not reach the same maximal MRR.
(4)
2.1.5.4. Energy consumption. The pump power and electrical energy consumption of the filtration system were calculated as described by M�ethot-Hains et al. (2016). Briefly, voltage (U, V) and current (I, A) measurements were recorded in situ every minute during filtration with a voltmeter (V3000FC, Fluke, Everett, WA, USA) and three ammeters (A3001FC, Fluke, Everett, WA, USA) connected to the 3-phase asyn chronous motor powering the system. These data were recorded in real time and used to determine apparent power (S, kVA) for the duration of the experimentation (Eq. (5)). pffiffi S¼ 3�U �I (5)
2.1.6. Chemical analyses The TS content of dairy samples was measured using the forced-air drying method (AOAC International 990.20). Total nitrogen (TN) and non-protein nitrogen (NPN) contents were determined with the Kjeldahl method (AOAC International 991.20 and 991.21, respectively). The TP content was calculated by subtracting the NPN value from the corre sponding TN content, and using a nitrogen-to-protein conversion factor of 6.38. Lactose content was determined by HPLC (IDF 198:2007). Mineral (Ca2þ, Mg2þ, Naþ, Kþ, Cl , Total P) contents were determined
Apparent power values allowed the calculation of the active power (P, W) required for the pump (Eq. (6)). The power factor (cos(φ), %) is a 3
J. Chamberland et al.
Journal of Food Engineering 272 (2020) 109811
systems was 99.3 L per m2 of membrane area, which corresponds to the most conservative value predicted by Chamberland et al. (2019) to clean a UF system generating skim milk retentate at an MRR of 3.0. This value included the water used to rinse the systems and to make the cleaning solutions (12.2 L of cleaning solutions to be discarded daily per m2 of filtration area). All filtration systems modelled for this study were in a multi-stage configurations. The performance of these was predicted, as suggested by Cheryan (1998) and GEA (2016), by linear extrapolation of the data obtained for the RO systems in this study and of the data obtained by Gavazzi-April et al. (2018) for UF systems. The permeation flux (kg/h. m2), membrane area requirement (m2), and specific energy consump tion (Wh/kg of permeate) of each stage was determined from the MRR and the TS of the retentate at the outlet of each stage.
with an inductively coupled plasma-optical emission photometer (Op tima 4300, dual view, PerkinElmer, Norwalk, CT, USA). The electrical conductivity of the permeates was measured every 10 min during RO using an electrical conductivity meter (Orion star A122, Thermo Fisher Scientific, Waltham, MA, USA). Biochemical oxygen demand (BOD) and chemical oxygen demand (COD) were quantified according to the methods ASTM 5210B, and ASTM 5220C (ASTM International, 2017), respectively (AgroEnviroLab, La Pocati�ere, QC, Canada). 2.1.7. Statistical analysis As mentioned above, all RO experiments (milk, UF permeate, and RO permeates concentration) were performed in triplicate. Significant ef fects (p < 0.05) on the feed, RO retentate, permeate compositions, and processing performance (maximal MRR, RO permeate recovery, SEC) caused by the fluids filtered were determined by conducting a one-way analysis of variance (ANOVA).
3. Results and discussion 3.1. Impact of type of dairy fluid on the composition of RO permeates
2.2. Predictive analysis of water reclaiming scenarios in a MPC56 plant
Table 1 shows the compositional characteristics of skim milk and UF permeate, and their respective permeates obtained following RO2 and ROH concentrations. Major differences were observed between both initial feeds, especially for the TS, TP and mineral contents. Since the UF permeate was obtained from UF of skim milk, it contained only traces of proteins (TP of 0.01 � 0.00% w/w, compared to 3.99 � 0.03% w/w in skim milk). The TS content was also lower in UF permeate (5.30 � 0.21% w/w) than in the skim milk (8.82 � 0.09% w/w) (p < 0.05), but skim milk had a higher mineral content (Ca2þ, Mg2þ, Naþ, Kþ, Cl , and total P) (p < 0.05). For example, skim milk had a Ca2þ concentration of 1019 � 16 mg/kg, whereas the UF permeate had just 109 � 8 mg/kg. The BOD and COD of the skim milk (63,525 � 106 mg O2/L, and 106,900 � 6364 mg O2/L, respectively) were twice as high as in UF permeate (29,650 � 11,667 mg O2/L, and 56,050 � 1344 mg O2/ L, respectively) (p < 0.05), in line with the higher TS of the skim milk (Menchik et al., 2019). These were similar to values presented elsewhere for skim milk (Bylund, 2003), or milk UF permeate (Wang et al., 2009). The lactose content was similar in both fluids, between 4.67 � 0.33% w/w and 4.69 � 0.30% w/w (p > 0.05), since the UF membranes do not retain lactose (Cheryan, 1998). The chemical compositions of RO2 permeates obtained from skim milk and UF permeate were similar. Both had low TS contents, and traces of TP or lactose (Table 1). The electrical conductivity of the RO2 permeate obtained from skim milk was lower than the UF permeate (81.9 � 6.6 μS/cm vs. 96.3 � 3.5 μS/cm at p < 0.05). The quality of the
From the experimental data obtained, predictive analysis was used to compare the concentration process in three MPC56 manufacturing sce narios using RO to reclaim water from dairy fluids (Fig. 2). In all sce narios, 1000 � 103 kg of skim milk was used to manufacture milk retentate containing 56% protein on a dry basis (MPC56 prior to evap oration and drying) in 20 h in a virtual plant. In the first scenario, the skim milk is preconcentrated by RO to a MRR of 1.40, and the resulting retentate is concentrated by UF, and purified by DF, with water reclaimed by the previous RO process (Scenario 1, blue lines, Fig. 2). In the second scenario, the milk is also preconcentrated by RO, but the UF is performed at a higher MRR rather than conducting DF (Scenario 2, red lines, Fig. 2). In the third scenario, the traditional way of manufacturing MPC 56, the milk is primarily concentrated by UF until reaching a TP/TS ratio of 56%, and the resulting retentate is concentrated by RO prior to evaporation (Scenario 3, green lines, Fig. 2). For all of the three sce narios, the MRR reached during ROH operations was equivalent to the mean maximal MRR (4.0) obtained for the concentration of RO2 per meates obtained from skim milk or permeate in the experimental part. The final retentate of the three scenarios has a TS content of 19.88% w/ w, which was the highest TS obtained when concentrating milk with the RO2 membrane. In all the scenarios, water is reclaimed from the UF permeates and diafiltrates. The skimming, evaporation and drying pro cesses were not included since they did not differ between the compared scenarios. The predictive analysis focused only on the membrane filtration processes. The volume of water used to clean the filtration
Fig. 2. Comparison of the three scenarios used to manufacture liquid MPC56. These include (blue and red lines) or exclude (green lines) the preconcentration of milk by RO. 4
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Journal of Food Engineering 272 (2020) 109811
Table 1 Mean compositional characteristics of dairy fluids during the water reclamation process performed from skim milk and UF permeate. Skim milk scenario Total solids (% w/w) True proteins (% w/w) NPN (% w/w) Lactose (% w/w) Minerals (mg/kg) Ca2þ Mg2þ Naþ Kþ Cl Total P BOD (mg/L) COD (mg/L) EC (μS/cm)
UF permeate scenario
Skim milk
RO2 permeate
ROH permeate
UF permeate
RO2 permeate
ROH permeate
8.82 � 0.09a 3.99 � 0.03a 0.20 � 0.01a 4.69 � 0.30
0.04 � 0.00 N.D. N.D. N.D.
0.01 � 0.00 N.D. N.D. N.D.
5.30 � 0.21b 0.01 � 0.00b 0.15 � 0.01b 4.67 � 0.33
0.06 � 0.00 N.D. N.D. N.D.
0.01 � 0.00 N.D. N.D. N.D.
1019 � 16a 100 � 2a 411 � 4a 1391 � 59a 1014 � 79a 836 � 17a 63,525 � 106a 106,900 � 6,364a 5277 � 45b
N.D. N.D. 36 � 3 131 � 9 159 � 8 N.D. 127 � 78 135 � 106 81.9 � 6.6b
N.D. N.D. N.D. N.D. 19 � 7 N.D. 2�0 8�7 1.8 � 0.2
109 � 8b 17 � 2b 162 � 22b 337 � 86b 259 � 48b 118 � 5b 29,650 � 11,667b 56,050 � 1,344a 5933 � 191a
N.D. N.D. 38 � 6 132 � 24 134 � 18 11 � 5 356 � 328 748 � 417 96.3 � 3.5a
N.D. N.D. N.D. N.D. 11 � 4 N.D. 4�4 11 � 6 2.4 � 0.5
BOD: Biochemical oxygen demand, COD: Chemical oxygen demand, EC: Electrical conductivity, N.D.: Not detected, NPN: Non-protein nitrogen. 1 Different superscript letters in a same row, for a same fluid type (initial feed, RO2 permeate or ROH permeate) indicate significant differences (one-way ANOVA, p < 0.05, n ¼ 3, �standard deviation (SD)).
non-linear at 15.1 kg/L.m2 (critical flux obtained at a TMP of 2.28 MPa) (Fig. 3A). As similar permeation fluxes were obtained for both dairy fluids under a TMP of 2.07 MPa, this pressure was selected for filtrations performed in concentration mode. In concentration mode, the permeation fluxes were always higher during the RO of UF permeate (Fig. 3B). At the beginning of filtration, the permeation flux was of 17.6 kg/L.m2, compared to 10.7 kg/L.m2 during skim milk concentration (Fig. 3B). A maximal MRR of 2.5 was finally reached with UF permeate, compared to 2.2 with skim milk. A non-linear increase of the electrical conductivity of the permeates and of the electricity consumption was observed throughout the concentration experiments (Fig. 3C and D). The fluid type had a lower impact on the performance of the ROH membrane. The effect of TMP on the permeation flux of the ROH membrane was similar for RO permeates generated from skim milk or UF permeate RO (Fig. 4A). At a TMP between 1.29 MPa and 3.37 MPa in full recycling mode, the permeation fluxes increased linearly with the TMP, from 9 to 37 kg/L.m2 (Fig. 4A). Since the ROH membrane did not reach critical flux during experiments performed in full recycling mode, a TMP near the maximal operating pressure recommended by the membrane manufacturer (3.37 MPa) was selected for filtrations con ducted in concentration mode. In concentration mode, an increase in the permeation flux was observed for the concentration of both RO permeates filtered as function of the MRR (Fig. 4B). This increase was due to an increase in tempera ture and a decrease in the viscosity of the feed during this high-pressure concentration, as revealed by a reduction in consumption of electricity
RO2 permeates did not meet discharge water quality standards (COD higher than 125 mg/L), and required further RO treatment with a pol ishing membrane (ROH) in order to be reused (Balannec et al., 2002; ~o et al., 2019; Koyuncu et al., 2000). Bria After the second RO treatment (ROH membrane), the compositions of all permeates were similar to that of pure water. The combined treatments with RO2 and ROH membranes in series reduced the skim milk and UF permeate BOD and COD by 99.99%. The conductivities of the ROH permeates obtained from milk and UF permeate were lowered by 99.97% and 99.96%, respectively. Their low Ca2þ (not detectable) and electrical conductivity (<40 μS/cm) would allow their reuse in boiler or cooling tower (Mavrov et al., 2001). Like the water generated from whey by Meneses and Flores (2016), these ROH permeates might be suitable for DF or cleaning purposes but further analyses, such as total organic carbon (TOC) and microbiological analysis (total aerobic plate count, coliforms, E. coli), would be needed to determine whether they could reach drinking water quality. Heat treatment, UV disinfection, or chlorination would also be mandatory prior to reuse in industrial pro cesses (Lindgaard-Jørgensen et al., 2018; Mavrov and B�eli� eres, 2000; Meneses and Flores, 2016). 3.2. Impact of the type of dairy fluid on the performance of RO processes In full recycling mode, the permeation flux of the RO2 membrane increased linearly with the TMP to a TMP of 3.38 MPa with UF permeate, reaching a maximal value of 32.0 kg/h.m2 (Fig. 3A). When concentrating skim milk, the increase of the permeation flux became
Fig. 3. Performance of the RO2 membrane with skim milk and UF permeate. A) Permeation flux (J) in the full-recycle mode, B) J in the concentration mode at a TMP of 1.93 MPa, C) Electrical conductivity of the permeates, and D) Electricity consumption in the concentration mode as function of mass reduction ratio (MRR) (n ¼ 3, �SD). 5
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Journal of Food Engineering 272 (2020) 109811
Fig. 4. Performance of the ROH membrane. A) Permeation flux (J) in the full-recycle mode, B) J in the concentration mode at a TMP of 3.37 MPa, C) Electrical conductivity of the permeates, and D) Electricity consumption during the polishing of the RO2 permeates in the concentration mode as function of mass reduction ratio (MRR) (n ¼ 3, �SD).
as function of the MRR (Fig. 4D). This permeate flux increase was not observed with the RO2 membrane, despite a similar temperature in crease, because of the greater membrane fouling of this membrane concentrating dairy fluids. The electrical conductivity of the permeates did not increase during the concentration with the ROH membrane (Fig. 4C).
with diluted feed (e.g., 5 Wh per kg of water reclaimed from dairy ef fluents [Koyuncu et al., 2000]), or those obtained from industrial multi-stage RO systems (e.g., 7.5 and 9.6 Wh per kg of water reclaimed from milk and cheese whey, respectively (Pepper and Orchard, 1982; Stabile, 1983). Industrial systems are equipped with recirculation loops that reduce membrane fouling incidence (higher feed velocity), increase permeation flux, and allow further concentration of the feed (Pepper and Orchard, 1982). In the present study, skim milk was concentrated at a maximal TS content of 19.88% w/w, whereas a concentration of 29.4% w/w was reported by Christiansen (2017). This adds-up with the ROH limitations mentioned above. Consequently, it is assumed that this study may have overestimated energy consumption and membrane re quirements compared to industrial performance, but the relative dif ferences observed between the performance of the filtered fluids are consistent since they were processed using the same filtration system. Overall, the concentration of RO permeates obtained from skim milk and UF permeate resulted in similar water recoveries of 74.8 � 3.1%, and 75.4 � 3.6%, respectively, and similar energy use of 73 � 3 Wh, and 74 � 4 Wh per kg of permeate collected, respectively (p > 0.05) (Table 2). Contrary to the RO performed with the RO2 membrane, the limitation was not the final permeation flux, but the size of the feed tank. With a larger a larger feed tank (approximately 15 times), a higher water recovery up to an MRR of 64 might have been possible, as reached by ~o et al. (2019) with dairy rinse water. Bria
3.3. Overall process efficiency of the water reclamation processes The RO2 membrane produced RO permeate conversions of 59.2% and 54.5% of the initial mass of UF permeate and skim milk, respectively (Table 2). Neither the maximal MRR, nor the permeate recovery were significantly different between skim milk and UF permeate experiments (p > 0.05). However, as shown in Table 2, the recovery of RO permeate from UF permeate required less energy than permeate recovered from skim milk (99 vs. 160 Wh per kg of permeate, p < 0.05). The same conclusion was obtained by calculating the SEC at the highest common MRR of 2.2 (SEC2.2), reached in concentration mode (Table 2). Since RO membranes retain low molecular weight molecules such as salts, any of the dairy solids act as foulants in the membrane polarization layer (Drioli and Macedonio, 2012). Consequently, RO performance is strongly affected by the TS content (Aydiner et al., 2014; Hiddink et al., 1980; Vourch et al., 2005), and is limited by the presence of constituents affecting the osmotic pressure of the feed, such as minerals, lactose, and proteins. Minerals, however, have the greatest impact on osmotic pres sure (Cheryan, 1998). Indeed, the UF permeate, which had the lowest TS and mineral contents, had the best performance with the RO2 mem brane (higher flux, lower SEC). The highest water recovery rate for RO2 and ROH membranes in series was obtained with UF permeate (44.7% vs. 40.8%, Table 2). This scenario led to a water quality similar to that from skim milk, but it consumed 28% less electricity per kg of water reclaimed (205 Wh per kg of reclaimed water compared to 286 Wh with skim milk, Table 2). These electricity demands are high compared to other processes measured
3.4. Where should water be reclaimed in a MPC manufacturing plant? The results from this study indicated that better performance is observed when reclaiming water from UF permeate than from skim milk. However, in the case study of an MPC manufacturing plant where water can be reclaimed by RO at several points — (1) from milk prior to UF, (2) from UF retentate, or (3) from UF permeate — the decision to reclaim water from permeate may not be as evident. One consideration is that extracting water from skim milk reduces the volume of milk to be
Table 2 Performance of the RO2 and ROH membranes for the concentration of skim milk, UF permeate, and their respective RO permeates, and the predicted performance of a combined system (RO2 and ROH membranes in series). Indicatora Maximal MRRb RO permeate recovery (%) SECtot to reach MRR max (Wh/kg of permeate) SEC2.2c (Wh/kg of permeate)
RO2 membrane
RO2 and ROH in seriesc
ROH membrane
Skim milk
UF permeate
Skim milk RO permeate
UF permeate RO permeate
Skim milk
UF permeate
2.2 � 0.1 54.5 � 1.3 159.7 � 1.9a 159.7 � 1.9a
2.5 � 0.2 59.2 � 2.7 98.6 � 7.7b 78.8 � 31.3b
4.0 � 0.5 74.8 � 3.1 72.5 � 3.3 –
4.1 � 0.6 75.4 � 3.6 74.1 � 1.1 –
– 40.8 286.0 –
– 44.7 204.9 –
a
Different superscript letters in the same row, for the same fluid type (initial feed, RO2 permeate or ROH permeate) indicate significant differences (one-way ANOVA, p < 0.05, n ¼ 3, �SD). b MRR: Mass reduction ratio, SECtot: Total specific energy consumption, SEC2.2: Specific energy consumption at the uppermost common MRR reached in the concentration mode (2.2). c Values obtained by interpolation. 6
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Journal of Food Engineering 272 (2020) 109811
ultrafiltered, and the volumes of UF permeate to be treated. Since the manufacture of MPC may also require water to perform DF, it might be beneficial to reduce the input water by generating DF water from skim milk prior to UF. Consequently, the data obtained in the previous ex periments were used to perform a predictive analysis of the scenarios presented in Fig. 2. The processing needs (milk, membranes, electricity and water) of three scenarios are presented in Table 3, whereas the economic balance of those scenarios is presented in Table 4. Reclaiming water from the unconcentrated milk, followed by an UF to concentrate the milk without DF (Scenario 2, red scenario, Fig. 2) was the most efficient scenario, having the lowest electricity (101.2 MWh) and water (95 m3) consumptions (Table 3). The scenarios reclaiming water from UF retentate (Scenarios 1 and 3, or blue and green scenarios, respectively, Fig. 2) required higher membrane surface area and pumping energy. Reverse osmosis is the most energy demanding of all the filtration processes because it requires the highest operating pressure (de Boer, 2014). Consequently, the most efficient water reclamation scenarios are those that use RO to process the most diluted fluids, and, ideally, lower volumes of feed. In the scenarios 2 and 3, 1000 � 103 kg of skim milk (TS ¼ 9.0%), and 200 � 103 kg of UF retentate (TS ¼ 13.9%) were, respectively, concentrated by RO at an MRR of 1.4. As a lower permeation flux was expected with the latter feed (higher TS content and viscosity), it required 18% more RO2 membranes, and had similar electricity consumption, despite a five-fold lower volume to be concentrated. Furthermore, as milk was preconcentrated in the scenario 2 (RO/UF scenario), there was a lower volume of milk to be ultrafiltered and a lower volume of permeate was generated compared to the scenario 3 (UF/RO scenario) (391 m3 vs. 555 m3 of UF permeate, respectively). Ultimately, the scenario 2 used only 36.1 MWh while the UF/RO sce nario used 66.1 MWh to generate water from UF permeate (RO2 and ROH combined). Both scenarios reclaimed the same volume of water, but the scenario 3 had more membrane surface area to clean, which
Table 4 Processing costs for three processing scenarios to manufacture MPC56 from 1000 � 103 kg of skim milk. Indicator
Skim milka
Skim milk
Unit
Membranesb Cleaning solutionsc
Scenario 2 (RO/UF)
Scenario 3 (UF/RO)
� 103 kg
1000
1000
1000
Electricityd Electrical power4 Fresh watere
m2
1798
1665
1688
m2 m2
2630 1001
2187 635
2584 684
Cleaning solutions Polishing retentate
MWh
12.6
11.8
6.3
MWh MWh MWh
36.0 39.3 38.2
36.0 – 27.2
– 33.0 44.8
MWh
26.8
17.4
7.7
MWh
14.1
8.6
20.6
Total
MWh
167.0
100.9
112.4
Operating cost
m3
525
347
343
3
237 539
– 445
– 492
Balance a
m m3 m3
251
98
17.88 $Can/ 100 kg
178,800
178,800
178,800
0.60 $Can/ m2.day 50.84 $Can/m3
3203
2647
2925
3367
2783
3074
5478
3310
3687
3591
2170
2417
324
127
193
0.97 $Can/ m3 0.97 $Can/ m3
64
53
59
170
112
111
$Can
194,997
190,002
191,266
0.0328 $Can/kWh1 0.43 $Can/ kW.day 1.29 $Can/ m3
The skim milk price was calculated from the price of protein and solids of the class 5B in Quebec (Canada) in January 2019. It does not include the price of fat. b It was assumed that membranes were replaced after 18 months. c The cost of cleaning solutions included the price of caustic and acid cleaning chemicals (Chamberland et al., 2019). d The price of electricity was that of Hydro-Qu� ebec in 2019 for business cus tomers with a contract power of more than 5000 kW (rate L). e The price of water was that calculated by MAMROT (MAMROT, 2015) for production and distribution of drinking water in Quebec in 2012 (Canada). f The wastewater disposal cost was that by MAMROT (MAMROT, 2015) for wastewater collection and treatment in Quebec in 2012 (Canada).
affected the final water balance. The scenario 3, which is the most common processing strategy in the industry, required 50% more (48 m3) input water than the scenario 2 (Table 3). Rather than using RO, UF retentate could also be concentrated by vacuum evaporation (de Boer, 2014), but this latter process would require eight times more energy than RO (Cheryan, 1998). For the scenario 1, even if DF water is generated at the plant, the DF can be done only if necessary, because it requires additional membrane surface to operate (which increases electricity consumption) and clean (which increases water consumption). This scenario generated the highest volume of water (531 m3) because more permeate was gener ated from the DF permeate, but it was also the most water-demanding scenario (247 m3 of input water due to the water used for DF and membrane cleaning). This strategy of generating DF water remains interesting as a way to reduce the environmental impact of the industry but should be reserved for the manufacture of MPC with a higher protein concentration (e.g., MPC85), which requires substantial purification by DF. Table 4 reports the comparative analysis of processing costs for the three scenarios. The operating costs were similar between the scenarios, as the skim milk was the major expenditure (92–94% of total expendi tures). Nevertheless, the scenario reclaiming water from the uncon centrated milk, followed by an UF to concentrate the milk without DF (scenario 2, red scenario, Fig. 2) had slightly lower total operating costs of 190,002 Can$. It must also be emphasized that this scenario resulted in lower costs for all expenditures considered (membranes, cleaning solutions, resources and energy, and wastewater disposal). Although
Water balance Water generated Water used Diafiltration (DF) Membrane cleaning
Scenario 3 (UF/RO)
a
Electricity use UF and DFa RO2 Skim milk Milk retentate UF permeate ROH Permeate from milk RO Permeate from permeate RO
Scenario 2 (RO/UF)
Wastewater disposalf
Membrane surface Ultrafiltration (UF) and diafiltration (DF)a RO2 ROH
Scenario 1 (RO/DF)
Resources and energy
Scenarios Scenario 1 (RO/DF)
Scenarios ($Can)
Filtration systems
Table 3 Prediction of the membrane, electricity, and water requirements for three pro cessing scenarios to manufacture of MPC56 from 1000 � 103 kg of skim milk. Indicator
Price
149
Diafiltration was only performed in the scenario 1. 7
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Journal of Food Engineering 272 (2020) 109811
these costs are relatively minor in absolute value on a daily basis, they represent significant cost savings on a longer-term basis (e.g., 1 year) when compared to the other scenarios.
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4. Conclusion Significant water consumption in the dairy industry could be reduced through the use of RO to reclaim water in-plant from dairy fluids. A case study of an MPC56 manufacturing process revealed that preconcentrating the milk prior to traditional manufacturing processes lowers the volume of subsequent fluids to be processed, and the use of water and energy. Further work at the industrial scale will determine realistic water reclamation cost in dairy processing plants, and include the operating cost of the whole process (notably MPC drying). An optimization of operating filtration parameters is also essential to generate water that meets drinking water quality requirements. Declarations of competing interest None. Acknowledgments Funding: NSERC-Novalait Research Chair on Process Efficiency in Dairy Technology [grant numbers IRCPJ 46130-12, 2014–2019 to Yves Pouliot]. The authors are thankful to Barb Conway for editing this manuscript. References ASTM International, 2017. ASTM D6238-98(2017), Standard Test Method for Total Oxygen Demand in Water. https://doi.org/10.1520/D6238-98R17. West Conshohocken. Aydiner, C., Sen, U., Topcu, S., Ekinci, D., Altinay, A.D., Koseoglu-Imer, D.Y., Keskinler, B., 2014. Techno-economic viability of innovative membrane systems in water and mass recovery from dairy wastewater. J. Membr. Sci. 458, 66–75. https:// doi.org/10.1016/j.memsci.2014.01.058. Balannec, B., G�esan-Guiziou, G., Chaufer, B., Rabiller-Baudry, M., Daufin, G., 2002. Treatment of dairy process waters by membrane operations for water reuse and milk constituents concentration. Desalination 147, 89–94. https://doi.org/10.1016/ S0011-9164(02)00581-7. Balannec, B., Vourch, M., Chaufer, B., 2005. Comparative study of different nanofiltration and reverse osmosis membranes for dairy effluent treatment by deadend filtration. Separ. Purif. Technol. 42, 195–200. https://doi.org/10.1016/j. seppur.2004.07.013. Bri~ ao, V.B., Salla, A.C.V., Miorando, T., Hemkemeier, M., Favaretto, D.P.C., 2019. Water recovery from dairy rinse water by reverse osmosis : giving value to water and milk solids. Resour. Conserv. Recycl. 140, 313–323. https://doi.org/10.1016/j. resconrec.2018.10.007. Bylund, G., 2003. Dairy Processing Handbook. In: http://www.dairyprocessinghand book.com/. (Accessed 11 May 2019). Chamberland, J., Benoit, S., Harel-Oger, M., Pouliot, Y., Jeantet, R., Garric, G., 2019. Comparing economic and environmental performance of three industrial cheesemaking processes through a process simulation. J. Clean. Prod. 239 https:// doi.org/10.1016/j.jclepro.2019.118046. Cheryan, M., 1998. Ultrafiltration and Microfiltration Handbook, second ed. CRC press, Boca Raton. Christiansen, M.V., 2017. Physical-chemical Characterisation of Skim Milk Concentrates Produced by RO Filtration. University of Copenhagen. Dairy Export Council, U.S., 2012. Child Nutrition: Global Follow-On Formula, GrowingUp Milk Report (Arlington, vol. A). de Boer, R., 2014. Vital membrane processes. In: de Boer, R. (Ed.), From Milk ByProducts to Milk Ingredients: Upgrading the Cycle. John Wiley & Sons, Hoboken, pp. 141–167. https://doi.org/10.1002/9781118598634.ch6. Drioli, E., Macedonio, F., 2012. Membrane engineering for water engineering. Ind. Eng. Chem. Res. 51, 10051–10056. https://doi.org/10.1021/ie2028188. Foley, G., 2006. Water usage in variable volume diafiltration: comparison with ultrafiltration and constant volume diafiltration. Desalination 196, 160–163. https://doi.org/10.1016/j.desal.2005.12.011.
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