Dairy wastewater treatment using integrated membrane systems

Accepted Manuscript Title: Dairy wastewater treatment using integrated membrane systems Authors: Airton C. Bortoluzzi, Julio A. Fait˜ao, Marco Di Luccio, Rog´erio M. Dallago, Juliana Steffens, Giovani L. Zabot, Marcus V. Tres PII: DOI: Reference:

S2213-3437(17)30456-6 http://dx.doi.org/10.1016/j.jece.2017.09.018 JECE 1866

To appear in: Received date: Revised date: Accepted date:

13-4-2017 30-8-2017 9-9-2017

Please cite this article as: Airton C.Bortoluzzi, Julio A.Fait˜ao, Marco Di Luccio, Rog´erio M.Dallago, Juliana Steffens, Giovani L.Zabot, Marcus V.Tres, Dairy wastewater treatment using integrated membrane systems, Journal of Environmental Chemical Engineeringhttp://dx.doi.org/10.1016/j.jece.2017.09.018 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Dairy wastewater treatment using integrated membrane systems

Airton C. Bortoluzzia, Julio A. Faitãoa, Marco Di Lucciob, Rogério M. Dallagoc, Juliana Steffensc, Giovani L. Zabotd and Marcus V. Tresd,*

a

Federal Institute of Education, Science, and Technology of Rio Grande do Sul (IFRS), Domingos Zanella St.,

104, Erechim - RS, 99713-028, Brazil E-mails: [email protected]; [email protected] b

Department of Chemical and Food Engineering, Federal University of Santa Catarina (UFSC), P.O. Box 476,

Florianópolis - SC, 88040-900, Brazil E-mail: [email protected] c

Department of Food Engineering, Integrated Regional University (URI), Sete de Setembro Av., 1621, Erechim -

RS, 99709-910, Brazil E-mails: [email protected]; [email protected] d

Laboratory of Agroindustrial Processes Engineering (LAPE), Federal University of Santa Maria, UFSM,

Presidente Vargas Av., 1958, Cachoeira do Sul - RS, 96506-302, Brazil E-mails: [email protected]; [email protected]

*Corresponding author: [email protected] (Marcus V. Tres); +55.51.3724.8433

Graphical abstract

PROCESS EVALUATION: MICROFILTRATION (MF) + REVERSE OSMOSIS (RO) 100

Treatment by conventional technologies Retentateline

Membrane

Treatment by membrane technology Direct disposalin receivingbodies

X

ü.

Relative retention (%)

DAIRY WASTEWATER

80

Color Turbidity TOC

60

TKN

40 20

Permeateline

0

MF

RO

ABSTRACT This work evaluated the performance of double-stage integrated filtration systems using membranes. The integrated systems comprise the sequential use of microfiltration (MF) plus nanofiltration (NF) and MF plus reverse osmosis (RO) under different pressures for treating dairy wastewater. The MF + NF system reduced 100% turbidity, 96% color, 58% total Kjeldahl nitrogen (TKN) and 51% chemical oxygen demand. The MF + RO system reduced 100% turbidity, 100% color, 94% TKN and 84% total organic carbon. Therefore, the MF + RO system was more efficient to retain total solids and organic matter. The performance of the systems was also evaluated in terms of permeate flux under 1 and 2 bar (MF membrane) and under 20 and 30 bar (NF or RO membranes). Overall, a flux decline was 2

3

observed in the first 30 min. Thereafter, the flux remained relatively constant until 60 min. The retention was higher in lower pressures, enabling a more purified permeate wastewater that could be disposed of in receiving water according to the Brazilian environmental regulations or reused in Cleaning In Place systems. Keywords: wastewater treatment; COD; membranes; microfiltration; nanofiltration; reverse osmosis.

1

INTRODUCTION The dairy industry is one of the most critical polluters [1-3]. The wastewater is

generally of dark/gray color and of milky/turbid appearance [4], which could present a chemical oxygen demand (COD) over than 6 g/L [5] as a consequence of the high concentrations of organic matter. This problem gets worse when the discharges are high. Commonly, approximately 0.2 – 10 L of wastewater are generated for 1 L of processed milk, having an average generation of 2.5 L of wastewater for 1 L of processed milk [6]. Considering that the world milk production has increased more than 50% in the last three decades, from 500 million tons in 1983 to 769 million tons in 2013 [7], a large volume of wastewater is generated every day. Consequently, dairy wastewater can be a crucial environmental problem when it is not treated or disposed of appropriately. Treatment processes for dairy wastewater include removal of solids, oils, and fats by primary techniques, removal of organic matter and nutrients by secondary techniques, and polishing by tertiary techniques [8, 9]. In this field, one of the most promising technologies for wastewater treatment and reuse are membrane separation technology. Membranes can be used because they provide selective separation through a compact apparatus and they present operational simplicity [10, 11]. Considering the global legislation are going to advance towards more restricting disposal and strong parameters control in the near future, the membranes are going to have more applications for enabling local wastewater treatment and reuse. Based on this context, this study was encouraged to evaluate the dairy wastewater polishing by applying integrated membrane systems. Integrated membrane systems consist of using different types of membranes in sequential stages [12]. Commonly, microfiltration (MF) membranes are used to separate

4

5

solids for delivering a solids-free permeate to the next processing stages. Therefore, additional treatment is usually needed. This can be accomplished by pressure driven membrane processes such as nanofiltration (NF) or reverse osmosis (RO). NF and RO membranes can retain more specific solutes than MF membrane does. In the scientific community, studies show that NF and RO are being increasingly used for treating several types of wastewaters [4, 9, 13, 14]. However, the use of MF + NF and MF + RO systems for treating dairy wastewater is scarce. High values of COD, total Kjeldahl nitrogen (TKN), total organic carbon (TOC), color, and turbidity are a problem for the dairy plants, while solutions for reducing them are continuously searched. However, information about the use of these integrated processes (MF + NF and MF + RO) for real dairy wastewater (and not for model/synthetic wastewater) was not disclosed yet in the literature. Taking into account this lacking of information, this work intends to study the integrated microfiltration plus nanofiltration and microfiltration plus reverse osmosis for dairy wastewater samples. The retention of target solutes and the permeate flux are some of the most evaluated parameters for the efficient operation separation process by membranes. Then, the performance of the systems was evaluated in terms of removal of COD, color, turbidity, TKN, and TOC, as well as the performance of the permeate flux (JP) during the filtration time. The proposal was to apply a processing condition that could enable the disposal of the treated wastewater in receiving waters or that could enable its reuse as Cleaning In Place (CIP) systems in the dairy plant, following the Brazilian environmental regulations.

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2 2.1

MATERIALS AND METHODS Wastewater Raw wastewater was obtained from a dairy company located in the North of Rio

Grande do Sul State – Brazil. Samples were collected in four different days, transported to the laboratory, homogenized and stored in sanitized bottles at -18°C. Before the treatments, the raw wastewater was characterized as turbidity, color, TOC, TKN, COD, settleable solids (SS), lactose, and five-day biochemical oxygen demand (BOD5) (Table 1). The description of the analyses is presented in section 2.7. 2.2

Membranes A hollow-fiber-type polymeric membrane (PAM Membranas Seletivas Inc., Brazil)

was used for MF process. Such membrane was composed of a poly(ether sulfonate) / poly(vinyl pyrrolidone) (PES/PVP) mixture with a 0.20 μm pore diameter. Polymeric-flattype membranes (Dow-Filmtec, Canada) were used for NF and RO processes. Such membranes were composed of polyamide composites (Table 2). The work pressures were selected based on the restrictions provided by the manufacturers. 2.3

Experimental apparatus The experimental apparatus (Fig. 1) was composed of a thermostatic bath (Marconi,

Model MA 083, Brazil) with ± 0.1°C temperature precision, a gear pump (Cole-Parmer, model Micro pump 72211-15, USA) for MF process or a piston pump (Lab Alliance, model Series III, USA) for NF and RO processes, a pressure gauge (Salvi, model Standard, Brazil) and a flowmeter (Conaut, model 440, Brazil). The work pressure was controlled by a pressure regulator valve (Swagelok, series KPB, USA).

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2.4

Membrane conditioning Before being used for NF and RO processes, the polymeric membranes were

immersed in ethyl alcohol (Merck, ACS Reagent, Brazil) for 24 h at 25°C. After this period, the membranes were immersed in deionized water for 24 h at 25°C [15]. In order to maintain the transporting characteristics of membranes, they were washed with distilled water and submitted to 30 bar until stabilizing the permeate flux. 2.5

Wastewater treatment For each assay, a 1.5 L sample was thawed to room temperature (approximately

25°C), homogenized and filtered using a 25 μm quantitative filtering paper (J Prolab, model JP40, Brazil). Preliminary filtration was performed for removing solids that could damage the membranes. Membrane separation processes were applied in two filtration stages. In the first stage, the MF was done as a pre-treatment for the second filtration stage in an independent form with NF and RO membranes (Table 3). In the first stage, the MF process was evaluated at 1 and 2 bar with a feeding flow rate equal to 1 L/min at 25°C. In the second stage, the NF or RO processes were evaluated at 20 and 30 bar with a feeding flow rate equal to 9 mL/min at 25°C using the permeate from the MF process. The flow rates were selected based on the operational limitations of the pumps. During the wastewater treatment, the retained and permeate streams returned to the feeding volume for maintaining the homogeneity of samples. The performance of the membranes was evaluated in terms of permeate flux (JP, L/h.m2) given by the ratio between the volumetric flow rate (Q, L/h) and membrane’s filtration area (A, m2), (Eq. 1) [16]. JP 

Q V  A tA

(1)

8

Where: V is the permeate volume (L); t is the time needed to permeate the feeding volume (h). The membranes used in this study, including the pre-conditioned ones, were submitted to flux measuring with distilled water under different pressure levels. The hydraulic permeability (LP, L/h.m2.bar) for each membrane was measured taking into account the JP and pressure (P, bar) (Eq. 2) [11]. The LP was calculated to verify the cleaning efficiency of the membranes after each assay (Table 4). LP 

JP Q V   P A P t  A P

(2)

Species removal or retention efficiency (Ef, %) was calculated as Eq. (3) based on the concentrations of a determined species in the permeate (CP, g/L) and in the feeding (CF, g/L) [10].  C E f  1  P  CF

   100 

(3)

Consequently, the remaining concentration (Rc, %) of each parameter evaluated after membrane separation process (relative to the initial concentration) was calculated as Eq. (4): Rc  100  E f

2.6

(4)

Membrane cleaning MF membrane cleaning was performed following the recommendations of the

manufacturer. The MF membrane was washed with distilled water and maintained soaked in a commercial enzymatic descaling solution for 2 h. Afterward, the MF membrane was washed again with distilled water. The NF and RO membrane cleaning was performed with distilled water (1 L) at room temperature (approximately 25°C) and pressure (approximately 1 bar). Washing was also done with pressurized distilled water (0.5 L) at 30 bar. This procedure was

9

able to restore the membrane hydraulic permeability. All the remaining water from the cleaning and hydraulic permeability tests was removed from the system aiming at reducing or eliminating the dilution of fed samples. 2.7

Analyses The characteristics of the raw wastewater, preliminarily filtered wastewater, and

permeates from the MF, NF and RO processes were evaluated in terms of eight parameters. The responses taken into account were: color, turbidity, pH, TOC, TKN, COD, BOD5, and SS. The analyses followed the methodologies described in the Standard Methods for the Examination of Water and Wastewater [17]. Color and turbidity were measured using a colorimeter (Hach, model DR870, USA) at 25°C and 420 nm wavelength and at 25°C and 720 nm wavelength, respectively. Turbidity determination was based on the method 2130 B. The pH was measured at room temperature (approximately 25°C) using a potentiometer (Metrohm, model 827 pH Lab, Switzerland). Lactose was measured using a spectrophotometer (Agilent Technologies, model 8453E, USA) at 570 nm following the methodology described by Miller [18]. BOD5 was measured according to standard methodology [17]. TOC determination was based on the method 5310 B using a TOC equipment (Shimadzu, model TOC-V CSH, Japan). COD was measured using the 5220 D method. The readings were done in a colorimeter (Hach, model DR870, USA) at 600 nm wavelength and in a spectrophotometer (Logen Scientific, model LS-7052BIV, Brazil) at 420 nm wavelength.

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3

RESULTS AND DISCUSSION

3.1

Wastewater treatment Raw wastewater (dairy wastewater) was near to a dark-gray color with a pungent

smell and an acid pH. Before treatments, the raw wastewater presented high values of turbidity, color, TOC and COD (Table 1). The composition of wastewater regarding these parameters was similar to the composition of raw dairy wastewater evaluated elsewhere [4, 8]. In this work, after being filtered in the 25 μm quantitative filtering paper (preliminary treatment), the wastewater was submitted to three membrane filtration systems (Table 3): MF + NF90, MF + NF and MF + RO. Then, in the next sections, results regarding membrane separation processes are presented and discussed. 3.1.1 Treatment using MF + NF90 system MF + NF90 system was performed in two stages. Firstly, the MF membrane was applied for pre-treating the previously filtered samples. Secondly, the NF90 membrane was applied for improving the separation performance. Two pressures in the NF process were evaluated: 20 bar and 30 bar. After this treatment, parameters as color, turbidity, COD, pH and TKN (Table 5) were taken into account. MF permeate maintained the same pH when comparing with the filtered wastewater. COD was almost unaffected by this first stage of membrane filtration, maintaining its value near to 3 g/L. A few reduction of TKN was observed. However, for both pressures, color and turbidity were reduced to a large extent (efficiencies up to 78%). Color and turbidity removal by MF process is associated with the removal of powdered materials as fat globules. According to James, et al. [19], fat globules could be larger than 0.5 μm, thus they could be retained during MF process. Furthermore, we infer the low COD removal could be associated

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with carbohydrate degradation, mostly from lactose, which could produce lactate ion and ethanol. Those organic molecules have low molecular weight, thus permeating through the MF membrane. Furthermore, values of lactose were almost null after the filtrations (Table 5). NF90 permeate also maintained the same pH when comparing with filtered wastewater and with MF permeate. Otherwise, color and turbidity reduced to values near to 4 – 15% relative to their initial concentrations (Fig. 2), indicating that the reductions achieved 95% for color and 96% for turbidity. This means the integrated system (MF + NF90) is effective for removing organic matter and color, with a slightly better performance when using 20 bar in the NF process. This behavior might be associated with the increase in the concentration polarization on the membrane surface, which increasing the pressure from 20 to 30 bar hampered the retention efficiency of the solutes. Suárez, et al. [20] reported a similar behavior for solute retention when evaluating different pressures with a spiral-wound polyamide NF membrane. COD and TKN reductions were slightly better when using 20 bar in the NF process (Table 5 and Fig. 2). For 20 bar, the relative concentrations for COD and TKN were 49% and 42%, respectively. NF process was responsible for the main reduction of these two parameters. Such findings might be linked with the NF membrane capacity of removing dissolved solutes and organic compounds of high molar mass, as well as nutrients (nitrogen). As reported in the literature [12], NF process is effective when used as a polishing step, especially in a treatment system for secondary or tertiary effluents aiming at the generation of water for industrial, agricultural, or indirect potable reuse. In the case of permeate flux (JP), the MF process at 1 bar (in the MF + NF90 system) presented the lowest values (Fig. 3, circles). The JP ranged from 48.8 L/m2.h to 31.7 L/m2.h for the dairy raw wastewater. Concentration polarization occurred during the filtration. The

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concentration of retained solutes became higher near the surface of the MF membrane than within the bulk solution as a consequence of the convective transport and the accumulation of solutes. The decrease in the permeate flux was attenuated after 20 min. Concentration polarization has been reported not only in dairy wastewater but in other cases as in the treatment of chloride-rich steel plant effluent [14], in hybrid coagulation-nanofiltration membrane process for water treatment [21], and in the desolventizing of Jatropha curcas and soybean oil from azeotropes of solvents [22, 23]. When evaluating the JP for the integrated processes (MF followed by NF (NF90 model)), it ranged from 54.7 L/m2.h to 38.8 L/m2.h and from 21.2 L/m2.h to 11.8 L/m2.h at 30 and 20 bar, respectively, for the previously filtered wastewater (Fig. 4A). For both pressures, the JP was almost constant after 20 min of filtration. However, the JP was approximately 3 times higher when using 30 bar. With higher pressure, some solutes permeate the membrane more easily. When comparing the JP for the MF membrane under 1 bar (Fig. 3, circles) and for NF90 membrane under 30 bar (Fig. 4A, open circles), the kinetic values were quite similar. It suggests the pressure acted to overcome the resistance generated by the smaller pore diameter of the NF90 membrane. 3.1.2 Treatment using MF + NF system Similarly to the MF + NF90 system, the MF + NF system was performed in two stages (Table 3). The difference, in this case, stands for the NF membrane characteristics (Table 2). Parameters as color, turbidity, COD and TKN (Table 6), and JP (Fig. 3 and Fig. 4B) were also taken into account. Color and turbidity reduced to values near to 0 – 11% relative to their initial concentrations (Fig. 2), indicating that the reductions achieved 96% for color and 100% for turbidity. COD and TKN reduced to values near to 56 – 78% relative to their initial

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concentrations. Overall, the characteristics of the NF membrane whether compared with NF90 membrane include a slight higher MgSO4 rejection and a lower pH range. As a consequence, the slight differences between them were seen to influence the process performance. The COD was reduced, but not to a large extent. The COD was still over 1 g/L and the TKN was approximately 44 mg/L after performing the processes defined in the MF + NF system (Table 6). Considering the highest established patterns for releasing treated wastewaters in receiving waters, the dairy treated wastewater with such COD and TKN does not meet the environmental requirements stated by the State Council for the Environment (CONSEMA) 128/2006 Resolution Number [24]. Based on these aspects, another system was evaluated (MF + RO), as discussed in the section 3.1.3. Considering the JP for the MF process at 1 bar (in the MF + NF system), it ranged from 63.4 L/m2.h to 31.7 L/m2.h for the dairy raw wastewater. The main reduction was occurred from 10 to 30 min, thus being almost constant after this period (Fig. 3, squares). It suggests an initial obstruction of the MF membrane pores, which caused the initial flux decline. This behavior might be associated with membrane fouling, which is caused by the adsorption of solutes in the membrane structure. Thereafter, the flux was lower but constant. Otherwise, the JP for the MF process at 2 bar was higher and nearly a constant (Fig. 3, diamond). Less membrane fouling could occur in such condition as a consequence of the higher pressure. When evaluating the JP for the integrated processes (MF followed by NF (NF model)), the JP ranged from 74.1 L/m2.h to 45.9 L/m2.h and from 52.9 L/m2.h to 42.3 L/m2.h at 30 and 20 bar, respectively, for the previously filtered wastewater (Fig. 4B). Overall, the flux was larger for both pressures. The influence of the pressure was less significant than for MF + NF90 system. Only in the first 30 min the NF membrane submitted to 30 bar provided a larger difference of JP. Regardless the pressure, the similar behavior after 30 min could be associated

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with the hydraulic permeability of NF membrane (Table 4), which is almost 1.4 times higher than NF90 membrane. This characteristic could favor the flux of solutes even though in lower pressure (20 bar). The concentration polarization was not too evidenced in such experimental run (Fig. 4B, filled circles). However, at enhanced pressure (Fig. 4B, open circles) in the beginning of filtration, more solutes are transferred towards the NF membrane surface due to enhanced driving force, leading to increased concentration polarization and marked JP decline. High initial JP with subsequent flux decline is also the characteristic of other cases, as for whey filtration [20], for treating wastewater contaminated with ions [14] or for general purification of surface water [25]. 3.1.3 Treatment using MF + RO system MF + RO system was also performed in two stages (Table 3). Parameters as color, turbidity, TKN and TOC (Table 7), and JP (Fig. 3 and Fig. 4C) were also taken into account. The MF + RO system was evaluated for improving the efficiencies obtained in those other two systems (MF + NF90 and MF + NF), as previously described. As in the other systems, the pattern for color and turbidity removal was maintained or improved. At 20 bar, all color and turbidity were removed (Table 2). The RO process was also demonstrated to be better efficient for color and turbidity removal during the desalination of membrane bioreactor wastewater [13]. Regarding this work, the decoloration might be linked with the removal of total solids, mostly composed of finely dissolved solids. One interesting aspect is that the decoloration is not always related to the organic matter removal in a proportional trend. Some reports in the literature show the absence of correlation [26, 27]. However, in this study the MF + RO system was able to remove up to 94% TKN and 84% TOC, indicating a correlation among TKN and TOC removal and color and turbidity reductions. Moreover, TKN and TOC removal was larger in the MF + RO

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system if compared with the MF + NF and MF + NF90 systems. These results are most likely associated with the amino acids removal and other organic compounds removal, which could be removed to a larger extent when using the MF + RO system. This behavior was also reported by other studies [13, 28, 29]. Then, the dairy wastewater treated by this integrated system can now be disposed of in a receiving water because it meets the standard required by the Brazilian legislation [24]. For example, the TKN was measured as 3.08 ± 0.06 mg/L, which was 6.5 times lower than the maximum limit permitted by the legislation (20 mg/L). Moreover, the treated water could be used again in the local industry, as in the heating and cooling processes. The JP for the MF process at 2 bar (in the MF + RO system) using raw wastewater reached 114.6 L/m2.h (Fig. 3). Otherwise, the JP for the integrated processes (MF followed by RO) using the filtered wastewater did not exceed 17.6 L/m2.h (Fig. 4C). Behind these findings, we infer the RO membrane retained finely dissolved solids as well as most organic matter and nutrients. As a consequence, all these compounds deposited themselves on the surface of the RO membrane, which caused a blockage of the pores. Polysaccharides, amino acids, and proteins play an important role as membrane fouling and blocking agents. Therefore, the flux was low, representing approximately 4 times lower than the flux for NF membrane. Pressure also influenced the RO process. The JP was approximately twice for 30 bar than 20 bar. It means the higher is the pressure the larger is the permeation of solutes. Even though some partial blockage was formed, higher pressure could disrupt such blockage, thus enhancing moderately the flux. At 30 bar, a marked decrease in the flux was observed until 30 min. The polarization concentration affected the filtration, especially in this period. However, at 20 bar, the flux was constant during the filtration time course, indicating the resistance did not change with the potential retention of solutes. As an integrated analysis, the

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JP was the lowest (Fig. 4C) mostly likely because the removal efficiency (Fig. 2, presented as a relative concentration for MF + RO system at 20 bar) was the highest amongst the conditions studied in this work.

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CONCLUSION After performing a dairy wastewater treatment using MF + NF90, MF + NF and MF +

RO systems in two sequential stages, some inferences are provided: 1) Pressure and solids deposition on the membrane surface played an important role in the permeate flux in all systems evaluated, especially in the beginning of the filtration. Overall, a marked reduction in the flux occurred in the first 30 min. Thereafter, the flux was almost a constant regardless the pressure. 2) MF membrane removed suspended solids to a large extent, thus reducing up to 82% color and 78% turbidity. When evaluating the reduction of COD (0 – 6%), TKN (5 – 17%) and TOC (0 – 9%), the MF membrane acted as a pre-treatment process for the second stage; 3) MF + NF90 and MF + NF systems were both effective to reduce color (up to 100%) and turbidity (up to 96%). Even the other parameters were reduced if compared to the MF process alone, the environmental requirements stated by the CONSEMA for disposing of treated wastewater in receiving water were not met when using those systems. 4) MF + RO system was efficient for treating dairy wastewater. Reductions of 100% turbidity, 100% color, 94% TKN and 84% TOC were reached. Therefore, wastewater treated by the integrated processes (microfiltration plus reverse

17

osmosis) could meet the environmental requirements stated by the CONSEMA. Furthermore, these results could encourage the water reuse in the dairy plant itself as in cooling and heating processes.

Declaration of interest There is no conflict of interest.

Acknowledgements The authors thank the National Council for Scientific and Technological Development (CNPq), Coordination for the Improvement of Higher Education Personnel (CAPES), Rio Grande do Sul Foundation (FAPERGS), Integrated Regional University (URI - Erechim), and the Rio Grande do Sul Federal Institute (IFRS – Erechim) for the financial support and scholarships.

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19 [18] G. L. Miller, Use of dinitrosalucylic acid reagent for determination of reducing sugar, Anal. Chem., 31 (1959) 426-428. [19] B. J. James, Y. Jyng and X. D. Cheng, Membrane fouling during filtration of milk – a microstructural study, J. Food Eng., 60 (2003) 431-437. [20] E. Suárez, A. Lobo, S. Álvarez, F. A. Riera and R. Álvarez, Partial demineralization of whey and milk ultrafiltration permeate by nanofiltration at pilot-plant scale, Desalination, 198 (2006) 274-281. [21] W. L. Ang, A. W. Mohammad, A. Benamor and N. Hilal, Chitosan as natural coagulant in hybrid coagulation-nanofiltration membrane process for water treatment, J. Environ. Chem. Eng., 4 (2016) 4857-4862. [22] N. Carniel, G. L. Zabot, M. Paliga, M. L. Mignoni, M. A. Mazutti, W. L. Priamo, J. V. Oliveira, M. D. Luccio and M. V. Tres, Desolventizing of Jatropha curcas oil from azeotropes of solvents using ceramic membranes, Environ. Technol., (2017) http://dx.doi.org/10.1080/09593330.2017.1282986. [23] J. R. M. Melo, L. Tiggeman, K. Rezzadori, J. Steffens, M. Paliga, J. V. Oliveira, M. Di Luccio and M. V. Tres, Desolventizing of soybean oil/azeotrope mixtures using ceramic membranes, Environ. Technol., 1 (2016) 1-11. [24] Brazil, State Council for the Environment - CONSEMA / Resolution nº 128 (in portuguese). http://www.sema.rs.gov.br/conselho-estadual-do-meio-ambiente-consema, 2006, accessed 28 Mar. 2017. [25] B. Govardhan, S. S. Chandrasekhar and S. Sridhar, Purification of surface water using novel hollow fiber membranes prepared from polyetherimide/polyethersulfone blends, J. Environ. Chem. Eng., 5 (2017) 1068-1078. [26] P.-F. Tee, M. O. Abdullah, I. A. W. Tan, M. A. M. Amin, C. Nolasco-Hipolito and K. Bujang, Effects of temperature on wastewater treatment in an affordable microbial fuel cell-adsorption hybrid system, J. Environ. Chem. Eng., 5 (2017) 178-188. [27] C. Ma, X. Wu and Z. Liu, Performance and fouling characterization of a five-bore hollow fiber membrane in a membrane bioreactor for the treatment of printing and dyeing wastewater, Text. Res. J., 87 (2017) 102-109. [28] M. Vourch, B. Balannec, B. Chaufer and G. Dorange, Nanofiltration and reverse osmosis of model process waters from the dairy industry to produce water for reuse, Desalination, 172 (2005) 245-256. [29] S. Alzahrani, A. W. Mohammad, P. Abdullah and O. Jaafar, Potential tertiary treatment of produced water using highly hydrophilic nanofiltration and reverse osmosis membranes, J. Environ. Chem. Eng., 1 (2013) 1341-1349.

Figure Captions Figure 1 – Schematic flux diagram for the membrane filtration apparatus. Figure 2 – Remaining concentration (Rc, relative to the initial concentration) of each parameter evaluated after the membrane separation process. Figure 3 – Permeate flux for the MF process using the raw dairy wastewater. Figure 4 – Permeate flux for the NF and RO processes using the permeate from the MF process.

20

Table 1 – Characteristics of the raw wastewater. Parameter

Average value ± standard deviation

Turbidity (FAU)

330 ± 171

Color (mg Pt-Co/L)

2244 ± 1050

TOC (mg/L)

1588 ± 351

TKN (mg/L)

75 ± 12

COD (mg/L)

3133 ± 438

pH (-)

4.67 ± 0.05

SS (mg/L)

10.00 ± 0.01

Lactose (g/L)

2.1 ± 0.5

BOD5 (mg/L)

2350 ± 1

FAU: formazin attenuation unit TOC: total organic carbon TKN: total Kjeldahl nitrogen COD: chemical oxygen demand SS: settleable solids BOD5: five-day biochemical oxygen demand

21

Table 2 – Characteristics of each membrane used in the study. Maximum temperature (°C)a

Maximum pressure (bar)a

2 – 13

55

5

0.0034

2 – 11

45

41

>99% MgSO4c

0.0034

3 – 10

45

41

> 99.5% NaClc

0.0034

2 – 11

45

41

Class

Membrane code

Material/model

Manufacturer

Pore size (μm)

MWCO Rejection (kDa)

Permeation pH range (-) area (m2)

MF

MF

PES+PVP/hollow fiber

PAM Membranas Seletivas Inc.

0.2

-

0.0120

NF

NF90

Composite polyamide/plane – NF90

Dow-Filmtec

-

0.2-0.4

NF

NF

Composite polyamide/plane – NF

Dow-Filmtec

-

-

RO

RO

Composite polyamide/plane – BW30

Dow-Filmtec

-

-

-

PES: poly(ether sulfonate) PVP: poly(vinyl pyrrolidone) MF: microfiltration NF: nanofiltration RO: reverse osmosis MWCO: molecular weight cut-off a

Operating conditions are given by the manufacturers

b

2 g/L MgSO4 at 4.8 bar and 25°C; molecular weight = 120 g/mol

c

2 g/L NaCl at 4.8 bar and 25°C; molecular weight = 58 g/mol

22

>97% MgSO4b 85-95% NaClc

Table 3 – Conditions for the wastewater treatment. 1st filtration stage System

2nd filtration stage

Membrane Feeding flow

Pressure

Membrane

Feeding flow

Pressure

code

rate (L/min)

(bar)

code

rate (L/min)

(bar)

MF + NF90

MF

1

1-2

NF90

0.009

20 - 30

MF + NF

MF

1

1-2

NF

0.009

20 - 30

MF + RO

MF

1

1-2

RO

0.009

20 - 30

MF: microfiltration NF: nanofiltration RO: reverse osmosis

23

Table 4 – Hydraulic permeability (LP) of each membrane using distilled water at 25oC with different pressures before and after the wastewater filtration. Membrane Hydraulic permeability 2

Correlation

Pressure

Feeding flow Recovery after

code

(L/h.m .bar)

coefficient [R²] (-) (bar)

rate (L/min)

cleaning (%)

MF

86.30

0.971

1, 2, 3

1

101

NF90

2.70

0.852

10, 20, 30

0.009

100

NF

4.00

0.992

10, 20, 30

0.009

95

RO

0.71

0.994

10, 20, 30

0.009

111

MF: microfiltration NF: nanofiltration RO: reverse osmosis

24

Table 5 – Characteristics of the filtered wastewater, permeate from the microfiltration process and permeate from the nanofiltration process using the NF90 membrane (MF + NF90 system). Filtered Filtration pressure

Parameter

MF permeate

NF90 permeate

wastewater

MF = 1 bar; NF = 20 bar

MF = 1 bar; NF = 30 bar

Color (mg Pt-Co/L)

1367 ± 14

327 ± 6

63 ± 15

Turbidity (FAU)

233 ± 14

53 ± 6

10.01 ± 0.01

COD (mg/L)

2725 ± 313

-

1348 ± 29

pH (-)

4.20 ± 0.10

4.20 ± 0.10

4.21 ± 0.10

TKN (mg/L)

85 ± 1

75 ± 3

35.2 ± 0.8

Lactose (g/L)

1.73 ± 0.07

0.05 ± 0.02

0.009 ± 0.003

Color (mg Pt-Co/L)

1383 ± 80

303 ± 6

163 ± 12

Turbidity (FAU)

160 ± 69

40.01 ± 0.01

23 ± 6

COD (mg/L)

3256 ± 44

3065 ± 1

2703 ± 18

TKN (mg/L)

81 ± 2

73 ± 3

59.7 ± 0.6

Lactose (g/L)

1.34 ± 0.09

0.03 ± 0.01

0.011 ± 0.004

MF: microfiltration NF: nanofiltration FAU: formazin attenuation unit TKN: total Kjeldahl nitrogen COD: chemical oxygen demand

25

Table 6 – Characteristics of the filtered wastewater, permeate from the microfiltration process and permeate from the nanofiltration process using the NF membrane (MF + NF system). Filtered Filtration pressure

Parameter

MF permeate

NF permeate

wastewater

MF = 1 bar; NF = 20 bar

MF = 2 bar; NF = 30 bar

Color (mg Pt-Co/L)

1200 ± 50

303 ± 21

43 ± 12

Turbidity (FAU)

132 ± 55

40.00 ± 0.01

0.00 ± 0.00

COD (mg/L)

2381 ± 44

-

1853 ± 18

TKN (mg/L)

78 ± 3

71.1 ± 0.6

44.3 ± 0.8

Lactose (g/L)

1.45 ± 0.24

0.03 ± 0.02

0.007 ± 0.003

Color (mg Pt-Co/L)

950 ± 1

175 ± 12

50.00 ± 0.01

Turbidity (FAU)

150.0 ± 0.1

33.33 ± 0.01

16.67 ± 0.02

COD (mg/L)

2225 ± 1

-

1567 ± 59

TKN (mg/L)

80 ± 3

70.8 ± 0.8

51.1 ± 0.2

Lactose (g/L)

1.67 ± 0.19

0.02 ± 0.01

0.002 ± 0.001

MF: microfiltration NF: nanofiltration FAU: formazin attenuation unit TKN: total Kjeldahl nitrogen COD: chemical oxygen demand

26

Table 7 – Characteristics of the filtered wastewater, permeate from the microfiltration process and permeate from the reverse osmosis process (MF + RO system). Filtered Filtration pressure

Parameter

MF permeate

RO permeate

wastewater

MF = 1 bar; RO = 20 bar

MF = 2 bar; RO = 30 bar

Color (mg Pt-Co/L)

1208 ± 29

500 ± 25

0.00 ± 0.00

Turbidity (FAU)

175.0 ± 0.1

75.00 ± 0.03

0.00 ± 0.00

TKN (mg/L)

49 ± 2

40.3 ± 0.4

3.08 ± 0.06

TOC (mg/L)

868 ± 49

790 ± 12

138 ± 2

Lactose (g/L)

1.42 ± 0.14

0.02 ± 0.01

0.002 ± 0.001

Color (mg Pt-Co/L)

1350 ± 132

783 ± 38

80 ± 17

Turbidity (FAU)

208 ± 14

117 ± 14

10 ± 1

TKN (mg/L)

46 ± 2

43.6 ± 0.9

10.7 ± 0.2

TOC (mg/L)

815 ± 11

856 ± 28

284 ± 7

Lactose (g/L)

1.57 ± 0.12

0.04 ± 0.01

0.004 ± 0.001

MF: microfiltration NF: nanofiltration FAU: formazin attenuation unit TOC: total organic carbon TKN: total Kjeldahl nitrogen

27

28

Figure 1

Pressure regulator v alv e

Retentate line

Membrane module

Feeding

Flowmeter Thermostatic bath

Piston pump (f or NF and RO processes) or gear pump (f or MF process)

Permeate line

Pressure gauge

29

Figure 2 30 bar

100

100

80

80

Rc (%)

Rc (%)

MF + NF90 System

20 bar

60

40

40

20

20

0

0 MF

NF90

100

100

80

80

Rc (%)

Rc (%)

MF + NFSystem

FW

60

40

20

20

MF

NF

100

100

80

80

Rc (%)

Rc (%)

MF

NF90

FW

MF

NF

FW

MF

RO

0 FW

MF + ROSystem

FW

60

40

0

60

60

40

40

20

20

0

0 FW

Color (•)

60

MF

Turbidity ( )

RO

COD (! )

TKN(•)

FW: Filtered Wastew ater; MF: Microfiltration; NF: Nanofiltration; RO: Reverse Osmosis.

TOC (ª)

30

Figure 3

130

MF + NF90 system : MF at 1 bar (•)

120 110 100

MF + NF system : MF at 1 bar (!)

90

JP (L/m2.h)

80 70

MF + RO system: MF at 1 bar (")

60 50 40

MF + NF system: MF at 2 bar (#)

30 20 10

MF + RO system: MF at 2 bar (ª)

0 0

10

20

30

Time (min)

40

50

60

31

Figure 4 60

A

55

A

50

NF(NF90 model) permeate flux :at

45

JP (L/m2.h)

40

(•) 20 barfed with MF permeate at 1 bar

35 30 25

( ) 30 barfed with MF permeate at 1 bar

20 15 10 5 0 0

10

20

30

40

50

60

Time (min) 80

B

B

70

NF(NF model) permeate flux :at

JP (L/m 2.h)

60 50

(•) 20 barfed with MF permeate at 1 bar

40

( ) 30 barfed with MF permeate at 2 bar

30 20 10 0 0

10

20

30

40

50

60

Time (min) 20

C

C

18

ROpermeate flux :at

16

JP (L/m 2.h)

14

(•) 20 barfed with MF permeate at 1 bar

12 10

(•) 30 barfed with MF permeate at 2 bar

8 6 4 2 0 0

10

20

30

Time (min)

40

50

60