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Convective sludge drying by rotary drum dryer using waste steam for palm oil mill effluent treatment
Journal of Cleaner Production 240 (2019) 117986
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Convective sludge drying by rotary drum dryer using waste steam for palm oil mill effluent treatment Mohammed Abdillah Ahmad Farid a, Ahmad Muhaimin Roslan a, *, Mohd Ali Hassan a, b, Farhana Aziz Ujang a, Zarry Mohamad a, Muhamad Yusuf Hasan b, c, Shirai Yoshihito d a
Department of Bioprocess Technology, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, 43400, UPM Serdang, Selangor, Malaysia Department of Process and Food Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400, UPM Serdang, Selangor, Malaysia c Section of Bioengineering Technology, Universiti Kuala Lumpur Branch Campus, Malaysian Institute of Chemical and Bio-Engineering Technology (UniKLMICET), 78000, Alor Gajah, Melaka, Malaysia d Graduate School of Life Sciences and System Engineering, Kyushu Institute of Technology, 808-0196, Hibikino 2-4, Wakamatsu-ku, Kitakyushu-shi, Fukuoka, Japan b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 February 2019 Received in revised form 5 July 2019 Accepted 9 August 2019 Available online 14 August 2019
Achieving a more sustainable wastewater treatment plant has never been so important. Issues around energy consumption and pollutants removal efficiency are of growing importance in the context of production costs and pollution control. In the palm oil industry, more than 85% mills are managing their palm oil mill effluent (POME) via lagoons, yet the system considered less effective as the quality of the effluent hardly achieved the permissible limits. It is therefore in the best interest of the industry to employ a better practice. Convective sludge drying (CSD) has been shown to have exceptional efficiency in high-strength wastewater treatment. In this study, CSD epitomized the zero-emission of POME treatment due to the fact that; 1) It operates on low-grade steam discharged by the mill instead of electricity, leading to a huge cut on energy consumption, 2) Production of secondary micronutrientsenriched solids by-product (i.e., calcium and magnesium) that can be repurposed as fertilizer, and 3) The decoction produced can potentially be reused to irrigate the existing oil palm plantation for nutrient cycling. The treatment resulted in substantial removal of the chemical oxygen demand (COD), biological oxygen demand (BOD), suspended solids (SS), ammoniacal nitrogen (AN), and oil and grease (OG) down to 2 mg/L, 67.7 mg/L, 40.0 mg/L, <0.01 mg/L, and <1 mg/L, respectively, which meets the Standard-A of Malaysia Environmental Quality Regulation (2009), making it sourceable for domestic usage. Reported groundworks demonstrated that CSD was superior to other physicochemical methods in POME treatment, with >99% of BOD, COD, SS, OG, and AN removal efficiency. The operating cost was valued at USD 1.91 per m3 POME. The pilot-scale operation proved CSD is a viable alternative to the lagoons. © 2019 Elsevier Ltd. All rights reserved.
Handling Editor: CT Lee Keywords: Palm oil mill effluent Wastewater treatment Convective sludge drier Rotary drum dryer Zero-emission
1. Introduction Palm oil has the highest global demand for oils and fats as compared to other edible oils. The palm oil industry is likely to extensively develop in order to meet the ever-growing demand for
* Corresponding author E-mail addresses: [email protected] (M.A. Ahmad Farid), ar_muhaimin@ upm.edu.my (A.M. Roslan), [email protected] (M.A. Hassan), [email protected] (F. Aziz Ujang), [email protected] (Z. Mohamad), [email protected] (M.Y. Hasan), [email protected]. jp (S. Yoshihito). https://doi.org/10.1016/j.jclepro.2019.117986 0959-6526/© 2019 Elsevier Ltd. All rights reserved.
crude palm oil (CPO). At present, Indonesia and Malaysia are dominating the global CPO production at 85e90%, combined (Choong et al., 2018). To sustain this, however, there would be an imminent threat of environmental pollution due to the huge amount of industrial palm oil mill effluent (POME) generated. It has been reported that POME is the major contaminating effluent, contributing to approximately 80% of the total palm oil industrial pollution. Statistically, 3 tons of POME is generated per ton of CPO (Taha and Ibrahim, 2014). In Malaysia, POME production is estimated at 60 million tons per annum (MPOB, 2017). This has led to the critical environmental concern voiced by the local authorities who have been calling for an immediate response to deal with such
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steaming capacity of 20e30 ton/hour, and power generation for roughly 77% of the total factory’s electricity consumption (Chavalparit et al., 2006), releasing approximately 165,900e240,900 ton/year of spare steam (Yoshizaki et al., 2013) that could potentially be utilized as heat source instead of electricity. This novel configuration prevails over the lagoons due to the fact that it greatly reduces the electricity use, leading to a huge cut on energy consumption, as well as proven to have far-better pollutant removal efficiency (Ahmad Farid et al., 2019). Various laboratory-scale studies have been carried out on biological and chemical treatments of POME, but hardly any on physical treatments especially at industrial scale (Zhang et al., 2019). This paper explores the ways in which zero-emission of POME treatment possibly be integrated into the current system. A total solution is proposed which allows the spent steam produced by the mill to be utilized and concurrently reused all of the byproducts generated into value-added purposes. Thus, for the first time, a sizeable RDD system was assembled at Keningau Palm Oil Mill (KPOM), Sabah, Malaysia to investigate its feasibility to treat raw POME. The resulting condensate and decoction were examined against the standard quality prescribed by the Malaysian Department of Environment (DOE). The dewatered sludge produced was analyzed for nutrient contents in order to determine its suitability as a soil conditioner. The methodological process was also assessed from economic perspectives.
an environmental threat. At present, more than 85% palm oil mills manage their POME via lagoons, which is a sequence of ponds designed for cooling, mixing (de-oiling) and anaerobic and aerobic digestions (Wu et al., 2010). These ponds are made up of earthen structures with no lining at the bottom, making it a cheap and preferred system by the industry (Ahmed et al., 2015). The relative importance of the lagoons system, however, has been subject to considerable discussion since it requires a massive treatment area and emits greenhouse gases. Approximately 28 m3 methane (CH4) is generated for every ton of anaerobically treated POME (Ng et al., 2012). The simplicity of the process posed another downside as it caused the treatment to be ineffective and concomitantly resulted in discharging effluent above permissible limits (Ohimain and Izah, 2017). For that reason, many types of research are being undertaken to improve POME treatment. Table 1 summarizes the currently available treatments of POME. POME is a colloidal suspension containing 4e5% total solids. Therefore, sludge drying technology offers an effective solution in achieving a remarkable dry solids removal which is easier to handle for disposal or utilization (Deng et al., 2019). The technological progress in developing a physical treatment for wastewater has been focusing on convective sludge drying (CSD) in which indirect or direct heating is used to evaporate the wastewater, leaving the solid impurities available for removal (Bantle and Eikevik, 2014). One of the commonly used CSD technologies is rotary drum dryer (RDD), best known for its exceptional performance in quickly removing solids from wastewater. RDD operates on convective sheat transfer between liquid and gas (Bennamoun et al., 2013) without direct contact between the heating media and sludge. As the wastewater rolls in the pre-heated rotating drum, condensation occurs thereby producing decoction and solids. The technology represents an innovation in sludge dewatering technology as it improves energy efficiency by consumption of low-grade steam for the drying process (Horttanainen et al., 2017). However, CSD faces less implementation due to high-energy consumption (Bennamoun, 2012). Fortunately for the palm oil industry, this drawback could be avoided. At present, palm oil mills operate on cogeneration of steam for fresh fruit bunch (FFB) sterilization at a
2. Materials and methods 2.1. POME characterization Raw POME is a colloidal suspension containing a small fraction of oil and solids and derived from three main sources, i.e. sterilizer condensate, separator sludge, and hydrocyclone wastewater. By practice, KPOM produces POME using the open lagoon system. Two-liter of POME were collected from the sterilizer pit and stored in the refrigerator at 5 C. The sample was then analyzed in accordance with the Standard Methods for Examination of Water and Wastewater (APHA, 2005) for chemical oxygen demand (COD), biological oxygen demand (BOD), suspended solids (SS), volatile
Table 1 Various treatments of palm oil mill effluent (POME). Methods
Types of treatment
Advantages
Disadvantages
References
Aerobic
Biological
i. ii. iii. iv.
Diminish pathogens High organic pollutant removal Simple design Long life expectancy
Biological
Coagulation-flocculation
Chemical
i. ii. iii. iv. v. i.
Chemical
Physical
ii. iii. i.
i. ii. iii. iv. i. ii. iii. iv. i. ii. iii. iv.
Sensitive reaction Energy-intensive Use chemicals High operating cost Require post treatment High operating cost Short life expectancy Use adsorbents Energy-intensive Short life expectancy Require pre-treatment Unable to treat highly contained suspended solids influent
Ahmed et al. (2015); Choong et al. (2018); Zahrim et al. (2017); Ho and Tan (1983)
ii. iii. i.
Simple design Low maintenance cost Low energy requirement High organic pollutant removal Long life expectancy High organic and inorganic pollutant removal Require small area Require no post-treatment High organic and inorganic pollutant removal Short retention time Require small area High organic and inorganic pollutant removal Short retention time Require small area
High biomass production Long start-up operation Require post treatment Long retention time High operating cost High biomass production Long retention time Long start-up operation Require post treatment
Ahmed et al. (2015); Choong et al. (2018); Poh and Chong (2009); Taha and Ibrahim (2014)
Anaerobic
i. ii. iii. iv. v. i. ii. iii. iv.
Adsorption
Membrane
ii. iii.
Ahmed et al. (2015); Choong et al. (2018); Poh and Chong (2009); Taha and Ibrahim (2014); Tabassum et al. (2015)
Ahmed et al. (2015); Choong et al. (2018); Zahrim et al. (2017); Ahmad et al. (2005a)
Abdurahman et al. (2017); Liew et al. (2014); Poh and Chong (2009)
M.A. Ahmad Farid et al. / Journal of Cleaner Production 240 (2019) 117986 Table 2 Raw POME characterizations. Parameters
BOD3 (mg/L) COD (mg/L) SS (mg/L) VSS (mg/L) TN (mg/L) VFA (mg/L) pH Temperature ( C) AN (mg/L) OG (mg/L) Water content (%)
Average
Industrial discharged limits (DOE, 2010)
44,805 ± 3256 72,500 ± 7804 25,438 ± 2163 22,789 ± 1345 46 ± 9 8020 ± 581 3.6 ± 0.8 32 ± 1.8 66 ± 12 19,560 ± 1076 74% þ 0.8
Standard-A
Standard-B
20 80 50 e e e 6e9 40 10 1.0 e
40 200 100 e e e 5.5e9 40 20 10 e
solids (VS), volatile fatty acids (VFA), total nitrogen (TN), ammoniacal nitrogen (AN), and oil and grease (OG). In the present work, POME compositions are summarized in Table 2. These results indicated that the POME was high-strength organic wastewater due to its exceptional pollution levels which consisted of amino acids, organic matters, inorganic nutrients, nitrogenous compounds, and carbohydrates. The pH was acidic because of the presence of free organic acids (Wu et al., 2009). 2.2. Rotary drum dryer (RDD) design and drying strategy The drum dryer (model DR-101, NARA Machinery Co. Ltd., Japan) was cylindrical with a capacity of 0.05 m3/h, the dimension of 400 mm 500 mm and heat conductive area of 0.6 m2. The motor (model GM-DP, Mitsubishi Electric, Japan) operated at 50 Hz and 0.75 kWh, powering the roller to rotate up to 7.5 rpm. The blower (model M-47738, MUTO Denki Corporation, Japan) operated at 50 Hz and 0.4 kWh, drawing the steam at 2 m3/min from the boiler into the RDD. Inside the drum designed in the present work, metal tubes were installed longitudinally to allow the hot steam to pass through and indirectly heating up the drum. Temperature (129e137 C) and pressure (24 bar) were indicators measured before the entire drying process was initiated. Steam from the biomass-fired boiler was streamed into the drum by the action of an installed pump. The drying was initiated as an amount of POME was introduced through an inlet into a feeding pan. As the pre-heated drum rolled into the feeding pan, a thin film of POME adhered onto the drum surface and condensed. The drying rate was controlled by using a suitable speed of drum rotation (7.5 rpm), targeting the maximum output of
Side view
3
the condensate produced. The dewatered sludge was scrapped from the drum surface using a pre-installed blade, while other impurities were separated in the form of decoction. The produced condensate was then collected for quality analysis and mass balance measurement. The drying was stopped when no more condensate was being produced. All the experiments were performed in triplicates and the results were reported as mean and standard deviation. Fig. 1 illustrates the design of the proposed treatment process. Fig. 2 further shows the process flow diagram of the designed RDD in KPOM. Fibers and dry shells produced from the mill were reused as fuel for a water-tube boiler to produce heat and power through steam. Clean water was directed to heat exchanger installed inside the boiler at a controlled flow rate of 9e9.5 kg/s. The heat generated inside the combustion chamber was utilized to heat the water tubes to produce superheated steam at 222 C and power a back pressure steam turbine generator with an installed capacity of 1.6 MW. The steam turbine generator expanded and discharged the saturated steam at about 143 C, which was then channeled to a steam manifold for the sterilization process as well as convective drying system. 2.3. Condensate, decoction and dewatered sludge characterizations Water quality parameters such as BOD, COD, SS, VSS, TN, VFA, pH, AN and OG were analyzed in accordance with the Standard Methods for Examination of Water and Wastewater (APHA, 2005). In accordance with APHA 5210 B, BOD incubation was taken place for 5 days at 20 C. Through APHA 5220 D closed reflux method, COD was determined using the COD test cell (Merck, Germany), followed by spectroscopy at 600 nm. SS and VSS were determined by referring to APHA 2540 D and E, whereby the sample was filtered, dried at 105 C and further ignited at 550 C. VFA was measured according to the APHA 5560 C distillation method. The sample was first subjected to centrifugation before proceeding to titration. OG was measured through extraction using n-hexane via APHA 5520 B partition-gravimetric method. AN determination was carried out in accordance with APHA 4500-NH3 B preliminary distillation step using boric acid, followed by titration with H2SO4. TN was determined through oxidative digestion by referring to APHA 4500-N C persulfate method. The pH was monitored using a pH probe (Mettler Toledo, FE20). The results were examined against the Standard-A water quality prescribed by the Malaysian Department of Environmental (DOE, 2010). The levels of N, P, K, and heavy metals were also analyzed for the dewatered sludge to examine its quality to be used as a soil amendment.
Perspective view
Fig. 1. Side and perspective views of the designed rotary drum dryer (RDD) for palm oil mill effluent (POME) treatment.
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Fig. 2. Process flow diagram of the proposed palm oil mill effluent (POME) treatment using convective sludge drying system via rotary drum assembled at Keningau Palm Oil Mill (KPOM).
3. Results and discussion 3.1. Convective sludge drying (CSD) performance In current practice, a high volume of water is used during CPO extraction, ranging from 1.0 to 1.3 m3/ton FFB. Approximately 50e79% of this water results in POME, whereas the remaining as steam waste, mainly as exhaust gases from sterilizers. According to Yoshizaki et al. (2013), around 300,000 ton/d steam waste is generated annually in a palm oil mill. This amount of steam waste could potentially be used for CSD as a heating agent in POME treatment. This would consequently save up electricity consumption, which is one of the advantages of CSD. Besides, the condensate produced could also be reused domestically. A mass balance of wastewater treatment is an important tool for economic analysis as well as to indicate system’s efficiency, for instance, in Section 3.2, the amount of effluent produced is used as a baseline for capital and production expenditures calculations at mill’s capacity. The process input and output were measured according to the actual mass balance obtained. Based on Fig. 3, 90% of condensate was recovered from POME, leaving merely a small fraction of decoction (1%), dewatered sludge (8%), and a slight loss due to dehydration. The result signified that CSD had induced evaporation of POME, leaving decoction and solid as the byproducts. Following the treatment, the condensate color turned clear, as displayed in Fig. 4 (A), which showed the capability of CSD to remove color. The color removal could be the result of organic compound removal (Nor et al., 2015). In contrast, decoction exhibited a dark color, which could be contributed by the accumulation of soluble microbial products (SMPs), such as protein, polysaccharide, and humic substances. Dai et al. (2018) reported that the humic substances are accountable for the color as a result of the release of melanoidins and humic acid. Fig. 4 (B) shows the RDD installed at KPOM. To further characterize the resulting condensate and decoction,
Fig. 3. Mass balance of rotating drum dryer.
wastewater analyses were performed on them with permissible limits by Malaysia Environmental Quality Regulation, 2009 to establish their acceptance level as industrial discharge effluent. It is apparent from Table 3 that the condensate quality parameters were within the Standard A limits, while the decoction quality parameters exceeded the prescribed regulatory limits. These findings strengthen the idea that POME could be reclaimed as a source of clean water supply for domestic usage thereby resolving river pollution issues. In Thailand, an average of 166 m3/ton FFB of grey water (treated POME) is reused to irrigate the existing oil palm plantation for
M.A. Ahmad Farid et al. / Journal of Cleaner Production 240 (2019) 117986
(A)
5
(B) II
Fig. 4. (A) Appearance of wastewater and treated water following the convective sludge drying (CSD) treatment; (I) decoction and (II) condensate, and (B) Rotary drum dryer (RDD) used at Keningau Palm Oil Mill (KPOM).
Table 3 Condensate and decoction qualities when compared against the quality standards. Parameters
BOD3 (mg/L) COD (mg/L) SS (mg/L) VSS (mg/L) TN (mg/L) VFA (mg/L) pH AN (mg/L) OG (mg/L)
Condensate
2±1 67.5 ± 12 40.0 ± 8 4.0 ± 2 5.0 ± 3 0.7 ± 0.3 6.5 ± 1 <0.01 <1
Decoction
75 ± 21 860 ± 32 310 ± 18 128 ± 24 56.0 ± 16 162.1 ± 24.3 7±1 75 ± 15 30 ± 11
Industrial discharged limits (DOE, 2010) Standard-A
Standard-B
20 80 50 e e e 6 to 9 10 1
40 200 100 e e e 5.5 to 9 20 10
nutrient cycling, which is a profound increase from 53 m3/ton FFB in 2010 (Suttayakul et al., 2016), while in Malaysia the industry has started utilizing treated POME for land irrigation as a means to compensate for the rainfall shortage (Patel, 2015). According to this study, there was merely a small fraction of decoction produced, making it likely to be reused for irrigation. Macro- and micronutrients are necessarily important for plant growth and metabolism. Therefore, a viable option to enhance the use of dewatered sludge for crop plants appeared to be appealing due to low-cost (Tarpani and Azapagic, 2018). Table 4 presents the results obtained for macro- and micronutrients of the dewatered sludge obtained in the present work. Closer inspection of the data reveals that the dewatered sludge contained a high amount of Table 4 Dewatered sludge characterizations. Test parameters Primary macronutrients Total nitrogen (TN) Phosphorus (P) Potassium (K) Secondary macronutrients Calcium (Ca) Magnesium (Mg) Micronutrients Aluminium (Al) Copper (Cu) Iron (Fe) Manganese (Mn) Sodium (Na) Nickel (Ni) Zinc (Zn)
Methods
Values (mg/L)
APHA 4500 APHA 3120 B EPA 6020 A
7.7 ± 0.2 5.6 ± 0.2 34.8 ± 3.3
EPA 6020 A
118.1 ± 11.7 318.2 ± 24.1
EPA 6020 A
2.2 ± 0.1 1.2 ± 0.1 71 ± 6.8 5.8 ± 0.4 7 ± 0.3 0.2 ± 0.1 1 ± 0.3
secondary macronutrients such as calcium (Ca) and magnesium (Mg). Secondary macronutrients play a vital role to correct soil’s acidity, and this finding opens up the possibility to utilize the dewatered sludge as fertilizer. Grobelak et al. (2017) evaluated the effects of sewage sludge applications on a barren and contaminated soil to immobilize harmful trace metals and obtain sustainable plant cover. The results brought about outstanding benefits to soil fertility by helping to remediate the soil, which allows the growth of various species of grasses, dicotyledonous plants, spontaneous growth of birch plant, and biomass of trees (mainly spruce and pine). Different technologies reveal different pollutant removal efficiencies. Therefore, a comparison with other physicochemical treatments of POME is summarized in Table 5. It is apparent that the method employed in the present work yielded excellent performance where BOD, COD, SS, OG and AN reduction recorded satisfactory results of higher than 99%, outperforming other established methods.
3.2. Economic assessment for convective sludge drying (CSD) technology at the palm oil mill Besides system efficiency, knowing the capital and operating costs are vital in providing facts and figures for the industry to assess in the context of actual expenditures. That being said an economic profile is equally important to maintain a technology application in the long run, and a larger production dimension contributes to more detailed aspects (Farid et al., 2017). Therefore, in order to generate a critical budgetary overview, a pilot-scale approach was undertaken. The preliminary economic evaluation was investigated by taking into account capital (CAPEX) and operation (OPEX) expenditures. For a typical palm oil mill, approximately 23.6 ton/h of POME is produced (Yoshizaki et al., 2013). In line with this production capacity, this value was set as the baseline in the economic evaluation. Both CAPEX and OPEX calculated were referred to as engineering economic multiplier values (Peters et al., 2003). The financial data of CSD in KPOM is shown in Table 6. For CAPEX, the total plant cost (TPC) monopolized the largest spending, constituting about 47% of the total capital investment (TCI). This expenditure includes the cost of equipment, building, installation, yard improvement, process piping, and electrical system which was worth approximately USD 2.9 mil. With the addition of the contractor’s fee, the TCI amounted to USD 3 mil. For OPEX, the total fixed cost (TFC) also monopolized the largest
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M.A. Ahmad Farid et al. / Journal of Cleaner Production 240 (2019) 117986
Table 5 Comparison with other physicochemical treatment methods of palm oil mill effluent (POME). Method
Centrifugation Coagulation Coagulation-flocculation and adsorption
Flocculation Flotation Adsorption Ultrafiltration Drum dryer
Treatment descriptions
Treatment performances
10,000 g for 60 min Use alum at a dosage of 8 g/L for 30 min at 100 rpm 1) Coagulation-flocculation: Use alum/profloc CX822 at a dosage of 1.4% (v/v)/0.03% (w/v) for 5 min at 600 rpm 2) Adsorption: Use fixed bed activated carbon at a flow rate of 4L/min Use polyacrylamides at a dosage of 36 mg/L for 1 min at 100 rpm, and 20 min at 15 rpm, consecutively Use colloidal gas aphrons at 300 cm3 of LUX flakes sparged for 10 min Use chitosan at a dosage of 0.5 g/L for 15 min at 100 rpm Use polysulphone UF membrane of 20 kDa at 0.8 MPa Convective drying at a steam rate of 2 m3/min
Table 6 Financial data for convective sludge drying (CSD) technology assembled at Keningau Palm Oil Mill (KPOM). The currency exchange rate used is 1 USD ¼ 4.19 MYR. Items Capital expenditures (CAPEX) Equipment Building Installation Yard improvement Process piping Electrical system Total plant cost (TPC) Contingency Total capital investment (TCI) Operation expenditures (OPEX) Basic labor costs (4 persons) Fringe benefits Supervision Total labor costs (TLC) Laboratory/QC/QA Total variables cost (TVC) Depreciation Maintenance and repair Total fixed cost Total production cost Unit-production cost per m3
Values (USD) 1,421,715.79 142,171.58 454,949.05 213,257.37 497,600.53 142,171.58 2,871,865.90 143,593.29 3,015,459.19 23,113.20 9245.28 4622.64 36,981.12 2311.32 39,292.44 286,468.62 60,309.18 346,777.81 386,070.25 1.91
spending in the total production cost (TPC) amounting up to 90% of the annual operating cost. The total labor cost (TLC), which involved basic labor cost, fringe benefits, and supervision, summed up to annual overhead expenses of USD 36,981.12. In the present work, the treatment plant is run for two shifts per day (17 h) with four operators assigned. The basic salary was calculated according to the Malaysia national minimum wages policy (Cheah et al., 2017). The total variables cost (TVC) is estimated at USD 39,292.44 for laboratory/QC/QA expenses. By taking into account TLC and TVC, the TPC amounted to USD 386,070.25. The operating cost per m3 POME incurred by the proposed CSD at KPOM is USD 1.91. 3.3. Challenges to establishing convective sludge drying (CSD) in palm oil mill The strategy to modernize the current POME treatment has always been under consideration for many years. In conjunction with the expansion of knowledge, the concept can be actualized to reap the benefits via CSD technology. However, a leap forward in technology is not always a leap forward in benefit. A major issue in establishing CSD technology in palm oil mill is massive capital
References
pH
BOD removal (%)
COD removal (%)
SS removal (%)
OG removal (%)
AN removal (%)
e 4.5 6
46 86.3 e
40 e 85
100 89 99.9
50 99 95
50 e e
Ho and Tan (1983) Ahmad et al. (2006) Ahmad et al. (2005b)
e
e
54
98.7
e
e
Ariffin et al. (2005)
5
e
e
96
e
e
Hashim et al., 1995
4.5 8.4 6.5
e e 99.9
e 98 99.9
99.8 98 99.8
99 e 99.9
e 61.9 99.9
Ahmad et al. (2006) Wu et al. (2007) The present work
inflow, which scares the industry to invest into the CSD system as compared to other technologies that could reduce the cost by approximately five-fold (Ibrahim et al., 2017). Based on the treatment efficiency, around 1.2 tons of steam waste was consumed for every ton of POME treated. Thus, the likelihood of implementing the CSD technology in palm oil mill is less favorable due to high steam consumption of 679.7 ton/d while the steam waste generation approximated at 501.4 ton/d (Yoshizaki et al., 2013) which was able to cover only 88.4% of the total POME produced. Alternative to cater the issue is either to outsource a steam generator to supply the remaining 12% of steam needed or integrate CSD with the current lagoons system. Knowingly, the system can only reach up to ~90% of POME capacity, so much so the sustainability. Perhaps, further effort to enhance the system’s efficiency is warranted in the future to attain a higher amount POME treated within a shorter time at the current rate of steam waste generation, so that the system is capable of accommodating the entire POME production. 4. Conclusion The objective of the present work has been successfully achieved. Approximately 90% of condensate was recovered from POME, while the rest were 8% solids (dewatered sludge) and 1% decoction. The system demonstrated excellent performance in which 99.9% biological oxygen demand (BOD), 99.9% chemical oxygen demand (COD), 99.8% suspended solids (SS), 99.9% oil and grease (OG) and 99.9% ammoniacal nitrogen (AN) removal efficiencies were recorded, outperforming other established methods. The final BOD, COD, SS, AN and OG were 2 mg/L, 67.5 mg/L, 40.0 mg/L, <0.01 mg/L and <1 mg/L respectively, which meets the Standard-A of industrial effluent discharged of 20 mg/L for BOD, 80 mg/L for COD, 50 mg/L for SS, 10 mg/L for AN and 1 mg/L for OG making it suitable for domestic usage. Also, the dewatered sludge has the potential to be utilized as fertilizer as it was rich in secondary macronutrients, helping to correct soil’s acidity as well as improving plant’s overall health and growth. The operating cost incurred per m3 POME was USD 1.91, which is considered economical for a highly effective wastewater treatment system. Nevertheless, there is still room for improvement in establishing a viable CSD technology to be adopted by the palm oil mills in the near future. Acknowledgments The authors would like to acknowledge the Science and
M.A. Ahmad Farid et al. / Journal of Cleaner Production 240 (2019) 117986
Technology Research Partnership for Sustainable Development (SATREPS) funding by Japan Science and Technology Agency, Japan International Cooperation Agency and Ministry of Education Malaysia (Vot No: 6300156), and Keningau Palm Oil Mill (KPOM) for all-inclusive supports given. References Abdurahman, N.H., Azhari, H.N., Said, N., 2017. An integrated ultrasonic membrane anaerobic system (IUMAS) for palm oil mill effluent (POME) treatment. Energy Procedia 138, 1017e1022. Ahmad, A.L., Sumathi, S., Hameed, B.H., 2005a. Adsorption of residue oil from palm oil mill effluent using powder and flake chitosan: equilibrium and kinetic studies. Water Res. 39 (12), 2483e2494. Ahmad, A.L., Ismail, S., Bhatia, S., 2005b. Membrane treatment for palm oil mill effluent: effect of transmembrane pressure and crossflow velocity. Desalination 179 (1e3), 245e255. Ahmad, A.L., Sumathi, S., Hameed, B.H., 2006. Coagulation of residue oil and suspended solid in palm oil mill effluent by chitosan, alum and PAC. Chem. Eng. J. 118 (1e2), 99e105. Ahmed, Y., Yaakob, Z., Akhtar, P., Sopian, K., 2015. Production of biogas and performance evaluation of existing treatment processes in palm oil mill effluent (POME). Renew. Sustain. Energy Rev. 42, 1260e1278. Ariffin, A., Shatat, R.S.A., Nik Norulaini, A.R., Mohd Omar, A.K., 2005. Synthetic polyelectrolytes of varying charge densities but similar molar mass based on acrylamide and their applications on palm oil mill effluent treatment. Desalination 173 (3), 201e208. Bantle, M., Eikevik, T.M., 2014. A study of the energy efficiency of convective drying systems assisted by ultrasound in the production of clipfish. J. Clean. Prod. 65, 217e223. onard, A., 2013. Review on fundamental aspect of Bennamoun, L., Arlabosse, P., Le application of drying process to wastewater sludge. Renew. Sustain. Energy Rev. 28, 29e43. Chavalparit, O., Rulkens, W.H., Mol, A.P.J., Khaodhair, S., 2006. Options for environmental sustainability of the crude palm oil industry in Thailand through enhancement of industrial ecosystems. Environ. Dev. Sustain. 8 (2), 271e287. Cheah, K.W., Yusup, S., Singh, H.G., Uemura, Y., Lam, H.L., 2017. Process simulation and techno economic analysis of renewable diesel production via catalytic decarboxylation of rubber seed oil e a case study in Malaysia. J. Environ. Manag. 203, 950e961. Choong, Y.Y., Chou, K.W., Norli, I., 2018. Strategies for improving biogas production of palm oil mill effluent (POME) anaerobic digestion: a critical review. Renew. Sustain. Energy Rev. 82, 2993e3006. Dai, Q., Ma, L., Ren, N., Ning, P., Guo, Z., Xie, L., Gao, H., 2018. Investigation on extracellular polymeric substances, sludge flocs morphology, bound water release and dewatering performance of sewage sludge under pretreatment with modified phosphogypsum. Water Res. 142, 337e346. Deng, W., Ma, J., Xiao, J., Wang, L., Su, Y., 2019. Orthogonal experimental study on hydrothermal treatment of municipal sewage sludge for mechanical dewatering followed by thermal drying. J. Clean. Prod. 209, 236e249. DOE, 2010. Malaysia Department of Environment (DOE), Environmental Quality (Industrial Effluents) Regulations 2009, eleventh ed. Ministry of Natural Resources and Environment, Malaysia. 2010. Farid, M.A.A., Hassan, M.A., Taufiq-Yap, Y.H., Shirai, Y., Hasan, M.Y., Zakaria, M.R., 2017. Waterless purification using oil palm biomass-derived bioadsorbent improved the quality of biodiesel from waste cooking oil. J. Clean. Prod. 165, 262e272. Farid, M.A.A., Zakaria, M.R., Hassan, M.A., Mohd Ali, A.A., Othman, M.R., Ibrahim, I., Samsudin, M.H., Shirai, Y., 2019. A holistic treatment system for palm oil mill effluent by incorporating the anaerobic-aerobic-wetland sequential system and a convective sludge dryer. Chem. Eng. J. 369, 195e204. Grobelak, A., Placek, A., Grosser, A., Singh, B.R., Almås, Å.R., Napora, A., Kacprzak, M., 2017. Effects of single sewage sludge application on soil phytoremediation. J. Clean. Prod. 155, 189e197.
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Hashim, M.A., Gupta, B.S., Kumar, S.V., 1995. Clarification of yeast by colloidal gas aphrons. Biotechnol. Tech. 9 (6), 403e408. Ho, C.C., Tan, Y.K., 1983. Centrifugal fractionation studies on the particulates of palm oil mill effluent. Water Res. 17, 613e618. Horttanainen, M., Deviatkin, I., Havukainen, J., 2017. Nitrogen release from mechanically dewatered sewage sludge during thermal drying and potential for recovery. J. Clean. Prod. 142, 1819e1826. Ibrahim, I., Hassan, M.A., Abd-Aziz, S., Shirai, Y., Andou, Y., Othman, M.R., Ali, A.A.M., Zakaria, M.R., 2017. Reduction of residual pollutants from biologically treated palm oil mill effluent final discharge by steam activated bioadsorbent from oil palm biomass. J. Clean. Prod. 141, 122e127. Liew, W.L., Kassim, M.A., Muda, K., Loh, S.K., S.K., Affam, A.C., 2014. Conventional methods and emerging wastewater polishing technologies for palm oil mill effluent treatment: a review. J. Environ. Manag. 149, 222e235. MPOB, 2017. Malaysian palm oil board (MPOB), Malaysia production of crude palm oil. Accessed 4.20.18 (2017). http://bepi.mpob.gov.my/index.php/en/statistics/ production/177-production-2017/792-production-of-crude-oil-palm-2017. html. Ng, W.P.Q., Lam, H.L., Ng, F.Y., Kamal, M., Lim, J.H.E., 2012. Waste-to-wealth: green potential from palm biomass in Malaysia. J. Clean. Prod. 34, 57e65. Nor, M.H.M., Mubarak, M.F.M., A Elmi, H.S., Ibrahim, N., Wahab, M.F.A., Ibrahim, Z., 2015. Bioelectricity generation in microbial fuel cell using natural microflora and isolated pure culture bacteria from anaerobic palm oil mill effluent sludge. Bioresour. Technol. 190, 458e465. Ohimain, E.I., Izah, S.C., 2017. A review of biogas production from palm oil mill effluents using different configurations of bioreactors. Renew. Sustain. Energy Rev. 70, 242e253. Patel, P., 2015. Zero discharge of palm oil mill effluent through outdoor flash evaporation at standard atmospheric conditions. Oil Palm Bull. 71, 14e24. Peters, M.S., Timmerhaus, K.O., West, R.E., 2003. Plant Design and Economics for Chemical Engineers, fourth ed. McGraw-Hill, Singapore. Poh, P.E., Chong, M., 2009. Development of anaerobic digestion methods for palm oil mill effluent (POME) treatment. Bioresour. Technol. 100, 1e9. Suttayakul, P., H-Kittikun, A., Suksaroj, C., Mungkalasiri, J., Wisansuwannakorn, R., Musikavong, C., 2016. Water footprints of products of oil palm plantations and palm oil mills in Thailand. Sci. Total Environ. 542, 521e529. Tabassum, S., Zhang, Y., Zhang, Z., 2015. An integrated method for palm oil mill effluent (POME) treatment for achieving zero liquid discharge e a pilot study. J. Clean. Prod. 95, 148e155. Taha, M.R., Ibrahim, A.H., 2014. COD removal from anaerobically treated palm oil mill effluent (AT-POME) via aerated heterogeneous Fenton process: optimization study. J. Water Process Eng. 1, 8e16. Tarpani, R.R.Z., Azapagic, A., 2018. Life cycle costs of advanced treatment techniques for wastewater reuse and resource recovery from sewage sludge. J. Clean. Prod. 204, 832e847. Wu, T.Y., Mohammad, A.W., Jahim, J.M., Anuar, N., 2007. Palm oil mill effluent (POME) treatment and bioresources recovery using ultrafiltration membrane: effect of pressure on membrane fouling. Biochem. Eng. J. 35 (3), 309e317. Wu, T.Y., Mohammad, A.W., Jahim, J.M., Anuar, N., 2009. A holistic approach to managing palm oil mill effluent (POME): biotechnological advances in the sustainable reuse of POME. Biotechnol. Adv. 27 (1), 40e52. Wu, T.Y., Mohammad, A.W., Jahim, J.M., Anuar, N., 2010. Pollution control technologies for the treatment of palm oil mill effluent (POME) through end-of-pipe processes. J. Environ. Manag. 91 (7), 1467e1490. Yoshizaki, T., Shirai, Y., Hassan, M.A., Baharuddin, A.S., Abdullah, N.R., Sulaiman, A., Busu, Z., 2013. Improved economic viability of integrated biogas energy and compost production for sustainable palm oil mill management. J. Clean. Prod. 44, 1e7. Zahrim, A.Y., Dexter, Z.D., Joseph, C.G., Hilal, N., 2017. Effective coagulationflocculation treatment of highly polluted palm oil mill biogas plant wastewater using dual coagulants: decolourisation, kinetics and phytotoxicity studies. J. Water Process Eng. 16, 258e269. Zhang, H., Rigamonti, L., Visigalli, S., Turolla, A., Gronchi, P., Canziania, R., 2019. Environmental and economic assessment of electro-dewatering application to sewage sludge: a case study of an Italian wastewater treatment plant. J. Clean. Prod. 210, 1180e1192.
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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Convective sludge drying by rotary drum dryer using waste steam for palm oil mill effluent treatment Mohammed Abdillah Ahmad Farid a, Ahmad Muhaimin Roslan a, *, Mohd Ali Hassan a, b, Farhana Aziz Ujang a, Zarry Mohamad a, Muhamad Yusuf Hasan b, c, Shirai Yoshihito d a
Department of Bioprocess Technology, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, 43400, UPM Serdang, Selangor, Malaysia Department of Process and Food Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400, UPM Serdang, Selangor, Malaysia c Section of Bioengineering Technology, Universiti Kuala Lumpur Branch Campus, Malaysian Institute of Chemical and Bio-Engineering Technology (UniKLMICET), 78000, Alor Gajah, Melaka, Malaysia d Graduate School of Life Sciences and System Engineering, Kyushu Institute of Technology, 808-0196, Hibikino 2-4, Wakamatsu-ku, Kitakyushu-shi, Fukuoka, Japan b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 February 2019 Received in revised form 5 July 2019 Accepted 9 August 2019 Available online 14 August 2019
Achieving a more sustainable wastewater treatment plant has never been so important. Issues around energy consumption and pollutants removal efficiency are of growing importance in the context of production costs and pollution control. In the palm oil industry, more than 85% mills are managing their palm oil mill effluent (POME) via lagoons, yet the system considered less effective as the quality of the effluent hardly achieved the permissible limits. It is therefore in the best interest of the industry to employ a better practice. Convective sludge drying (CSD) has been shown to have exceptional efficiency in high-strength wastewater treatment. In this study, CSD epitomized the zero-emission of POME treatment due to the fact that; 1) It operates on low-grade steam discharged by the mill instead of electricity, leading to a huge cut on energy consumption, 2) Production of secondary micronutrientsenriched solids by-product (i.e., calcium and magnesium) that can be repurposed as fertilizer, and 3) The decoction produced can potentially be reused to irrigate the existing oil palm plantation for nutrient cycling. The treatment resulted in substantial removal of the chemical oxygen demand (COD), biological oxygen demand (BOD), suspended solids (SS), ammoniacal nitrogen (AN), and oil and grease (OG) down to 2 mg/L, 67.7 mg/L, 40.0 mg/L, <0.01 mg/L, and <1 mg/L, respectively, which meets the Standard-A of Malaysia Environmental Quality Regulation (2009), making it sourceable for domestic usage. Reported groundworks demonstrated that CSD was superior to other physicochemical methods in POME treatment, with >99% of BOD, COD, SS, OG, and AN removal efficiency. The operating cost was valued at USD 1.91 per m3 POME. The pilot-scale operation proved CSD is a viable alternative to the lagoons. © 2019 Elsevier Ltd. All rights reserved.
Handling Editor: CT Lee Keywords: Palm oil mill effluent Wastewater treatment Convective sludge drier Rotary drum dryer Zero-emission
1. Introduction Palm oil has the highest global demand for oils and fats as compared to other edible oils. The palm oil industry is likely to extensively develop in order to meet the ever-growing demand for
* Corresponding author E-mail addresses: [email protected] (M.A. Ahmad Farid), ar_muhaimin@ upm.edu.my (A.M. Roslan), [email protected] (M.A. Hassan), [email protected] (F. Aziz Ujang), [email protected] (Z. Mohamad), [email protected] (M.Y. Hasan), [email protected]. jp (S. Yoshihito). https://doi.org/10.1016/j.jclepro.2019.117986 0959-6526/© 2019 Elsevier Ltd. All rights reserved.
crude palm oil (CPO). At present, Indonesia and Malaysia are dominating the global CPO production at 85e90%, combined (Choong et al., 2018). To sustain this, however, there would be an imminent threat of environmental pollution due to the huge amount of industrial palm oil mill effluent (POME) generated. It has been reported that POME is the major contaminating effluent, contributing to approximately 80% of the total palm oil industrial pollution. Statistically, 3 tons of POME is generated per ton of CPO (Taha and Ibrahim, 2014). In Malaysia, POME production is estimated at 60 million tons per annum (MPOB, 2017). This has led to the critical environmental concern voiced by the local authorities who have been calling for an immediate response to deal with such
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steaming capacity of 20e30 ton/hour, and power generation for roughly 77% of the total factory’s electricity consumption (Chavalparit et al., 2006), releasing approximately 165,900e240,900 ton/year of spare steam (Yoshizaki et al., 2013) that could potentially be utilized as heat source instead of electricity. This novel configuration prevails over the lagoons due to the fact that it greatly reduces the electricity use, leading to a huge cut on energy consumption, as well as proven to have far-better pollutant removal efficiency (Ahmad Farid et al., 2019). Various laboratory-scale studies have been carried out on biological and chemical treatments of POME, but hardly any on physical treatments especially at industrial scale (Zhang et al., 2019). This paper explores the ways in which zero-emission of POME treatment possibly be integrated into the current system. A total solution is proposed which allows the spent steam produced by the mill to be utilized and concurrently reused all of the byproducts generated into value-added purposes. Thus, for the first time, a sizeable RDD system was assembled at Keningau Palm Oil Mill (KPOM), Sabah, Malaysia to investigate its feasibility to treat raw POME. The resulting condensate and decoction were examined against the standard quality prescribed by the Malaysian Department of Environment (DOE). The dewatered sludge produced was analyzed for nutrient contents in order to determine its suitability as a soil conditioner. The methodological process was also assessed from economic perspectives.
an environmental threat. At present, more than 85% palm oil mills manage their POME via lagoons, which is a sequence of ponds designed for cooling, mixing (de-oiling) and anaerobic and aerobic digestions (Wu et al., 2010). These ponds are made up of earthen structures with no lining at the bottom, making it a cheap and preferred system by the industry (Ahmed et al., 2015). The relative importance of the lagoons system, however, has been subject to considerable discussion since it requires a massive treatment area and emits greenhouse gases. Approximately 28 m3 methane (CH4) is generated for every ton of anaerobically treated POME (Ng et al., 2012). The simplicity of the process posed another downside as it caused the treatment to be ineffective and concomitantly resulted in discharging effluent above permissible limits (Ohimain and Izah, 2017). For that reason, many types of research are being undertaken to improve POME treatment. Table 1 summarizes the currently available treatments of POME. POME is a colloidal suspension containing 4e5% total solids. Therefore, sludge drying technology offers an effective solution in achieving a remarkable dry solids removal which is easier to handle for disposal or utilization (Deng et al., 2019). The technological progress in developing a physical treatment for wastewater has been focusing on convective sludge drying (CSD) in which indirect or direct heating is used to evaporate the wastewater, leaving the solid impurities available for removal (Bantle and Eikevik, 2014). One of the commonly used CSD technologies is rotary drum dryer (RDD), best known for its exceptional performance in quickly removing solids from wastewater. RDD operates on convective sheat transfer between liquid and gas (Bennamoun et al., 2013) without direct contact between the heating media and sludge. As the wastewater rolls in the pre-heated rotating drum, condensation occurs thereby producing decoction and solids. The technology represents an innovation in sludge dewatering technology as it improves energy efficiency by consumption of low-grade steam for the drying process (Horttanainen et al., 2017). However, CSD faces less implementation due to high-energy consumption (Bennamoun, 2012). Fortunately for the palm oil industry, this drawback could be avoided. At present, palm oil mills operate on cogeneration of steam for fresh fruit bunch (FFB) sterilization at a
2. Materials and methods 2.1. POME characterization Raw POME is a colloidal suspension containing a small fraction of oil and solids and derived from three main sources, i.e. sterilizer condensate, separator sludge, and hydrocyclone wastewater. By practice, KPOM produces POME using the open lagoon system. Two-liter of POME were collected from the sterilizer pit and stored in the refrigerator at 5 C. The sample was then analyzed in accordance with the Standard Methods for Examination of Water and Wastewater (APHA, 2005) for chemical oxygen demand (COD), biological oxygen demand (BOD), suspended solids (SS), volatile
Table 1 Various treatments of palm oil mill effluent (POME). Methods
Types of treatment
Advantages
Disadvantages
References
Aerobic
Biological
i. ii. iii. iv.
Diminish pathogens High organic pollutant removal Simple design Long life expectancy
Biological
Coagulation-flocculation
Chemical
i. ii. iii. iv. v. i.
Chemical
Physical
ii. iii. i.
i. ii. iii. iv. i. ii. iii. iv. i. ii. iii. iv.
Sensitive reaction Energy-intensive Use chemicals High operating cost Require post treatment High operating cost Short life expectancy Use adsorbents Energy-intensive Short life expectancy Require pre-treatment Unable to treat highly contained suspended solids influent
Ahmed et al. (2015); Choong et al. (2018); Zahrim et al. (2017); Ho and Tan (1983)
ii. iii. i.
Simple design Low maintenance cost Low energy requirement High organic pollutant removal Long life expectancy High organic and inorganic pollutant removal Require small area Require no post-treatment High organic and inorganic pollutant removal Short retention time Require small area High organic and inorganic pollutant removal Short retention time Require small area
High biomass production Long start-up operation Require post treatment Long retention time High operating cost High biomass production Long retention time Long start-up operation Require post treatment
Ahmed et al. (2015); Choong et al. (2018); Poh and Chong (2009); Taha and Ibrahim (2014)
Anaerobic
i. ii. iii. iv. v. i. ii. iii. iv.
Adsorption
Membrane
ii. iii.
Ahmed et al. (2015); Choong et al. (2018); Poh and Chong (2009); Taha and Ibrahim (2014); Tabassum et al. (2015)
Ahmed et al. (2015); Choong et al. (2018); Zahrim et al. (2017); Ahmad et al. (2005a)
Abdurahman et al. (2017); Liew et al. (2014); Poh and Chong (2009)
M.A. Ahmad Farid et al. / Journal of Cleaner Production 240 (2019) 117986 Table 2 Raw POME characterizations. Parameters
BOD3 (mg/L) COD (mg/L) SS (mg/L) VSS (mg/L) TN (mg/L) VFA (mg/L) pH Temperature ( C) AN (mg/L) OG (mg/L) Water content (%)
Average
Industrial discharged limits (DOE, 2010)
44,805 ± 3256 72,500 ± 7804 25,438 ± 2163 22,789 ± 1345 46 ± 9 8020 ± 581 3.6 ± 0.8 32 ± 1.8 66 ± 12 19,560 ± 1076 74% þ 0.8
Standard-A
Standard-B
20 80 50 e e e 6e9 40 10 1.0 e
40 200 100 e e e 5.5e9 40 20 10 e
solids (VS), volatile fatty acids (VFA), total nitrogen (TN), ammoniacal nitrogen (AN), and oil and grease (OG). In the present work, POME compositions are summarized in Table 2. These results indicated that the POME was high-strength organic wastewater due to its exceptional pollution levels which consisted of amino acids, organic matters, inorganic nutrients, nitrogenous compounds, and carbohydrates. The pH was acidic because of the presence of free organic acids (Wu et al., 2009). 2.2. Rotary drum dryer (RDD) design and drying strategy The drum dryer (model DR-101, NARA Machinery Co. Ltd., Japan) was cylindrical with a capacity of 0.05 m3/h, the dimension of 400 mm 500 mm and heat conductive area of 0.6 m2. The motor (model GM-DP, Mitsubishi Electric, Japan) operated at 50 Hz and 0.75 kWh, powering the roller to rotate up to 7.5 rpm. The blower (model M-47738, MUTO Denki Corporation, Japan) operated at 50 Hz and 0.4 kWh, drawing the steam at 2 m3/min from the boiler into the RDD. Inside the drum designed in the present work, metal tubes were installed longitudinally to allow the hot steam to pass through and indirectly heating up the drum. Temperature (129e137 C) and pressure (24 bar) were indicators measured before the entire drying process was initiated. Steam from the biomass-fired boiler was streamed into the drum by the action of an installed pump. The drying was initiated as an amount of POME was introduced through an inlet into a feeding pan. As the pre-heated drum rolled into the feeding pan, a thin film of POME adhered onto the drum surface and condensed. The drying rate was controlled by using a suitable speed of drum rotation (7.5 rpm), targeting the maximum output of
Side view
3
the condensate produced. The dewatered sludge was scrapped from the drum surface using a pre-installed blade, while other impurities were separated in the form of decoction. The produced condensate was then collected for quality analysis and mass balance measurement. The drying was stopped when no more condensate was being produced. All the experiments were performed in triplicates and the results were reported as mean and standard deviation. Fig. 1 illustrates the design of the proposed treatment process. Fig. 2 further shows the process flow diagram of the designed RDD in KPOM. Fibers and dry shells produced from the mill were reused as fuel for a water-tube boiler to produce heat and power through steam. Clean water was directed to heat exchanger installed inside the boiler at a controlled flow rate of 9e9.5 kg/s. The heat generated inside the combustion chamber was utilized to heat the water tubes to produce superheated steam at 222 C and power a back pressure steam turbine generator with an installed capacity of 1.6 MW. The steam turbine generator expanded and discharged the saturated steam at about 143 C, which was then channeled to a steam manifold for the sterilization process as well as convective drying system. 2.3. Condensate, decoction and dewatered sludge characterizations Water quality parameters such as BOD, COD, SS, VSS, TN, VFA, pH, AN and OG were analyzed in accordance with the Standard Methods for Examination of Water and Wastewater (APHA, 2005). In accordance with APHA 5210 B, BOD incubation was taken place for 5 days at 20 C. Through APHA 5220 D closed reflux method, COD was determined using the COD test cell (Merck, Germany), followed by spectroscopy at 600 nm. SS and VSS were determined by referring to APHA 2540 D and E, whereby the sample was filtered, dried at 105 C and further ignited at 550 C. VFA was measured according to the APHA 5560 C distillation method. The sample was first subjected to centrifugation before proceeding to titration. OG was measured through extraction using n-hexane via APHA 5520 B partition-gravimetric method. AN determination was carried out in accordance with APHA 4500-NH3 B preliminary distillation step using boric acid, followed by titration with H2SO4. TN was determined through oxidative digestion by referring to APHA 4500-N C persulfate method. The pH was monitored using a pH probe (Mettler Toledo, FE20). The results were examined against the Standard-A water quality prescribed by the Malaysian Department of Environmental (DOE, 2010). The levels of N, P, K, and heavy metals were also analyzed for the dewatered sludge to examine its quality to be used as a soil amendment.
Perspective view
Fig. 1. Side and perspective views of the designed rotary drum dryer (RDD) for palm oil mill effluent (POME) treatment.
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Fig. 2. Process flow diagram of the proposed palm oil mill effluent (POME) treatment using convective sludge drying system via rotary drum assembled at Keningau Palm Oil Mill (KPOM).
3. Results and discussion 3.1. Convective sludge drying (CSD) performance In current practice, a high volume of water is used during CPO extraction, ranging from 1.0 to 1.3 m3/ton FFB. Approximately 50e79% of this water results in POME, whereas the remaining as steam waste, mainly as exhaust gases from sterilizers. According to Yoshizaki et al. (2013), around 300,000 ton/d steam waste is generated annually in a palm oil mill. This amount of steam waste could potentially be used for CSD as a heating agent in POME treatment. This would consequently save up electricity consumption, which is one of the advantages of CSD. Besides, the condensate produced could also be reused domestically. A mass balance of wastewater treatment is an important tool for economic analysis as well as to indicate system’s efficiency, for instance, in Section 3.2, the amount of effluent produced is used as a baseline for capital and production expenditures calculations at mill’s capacity. The process input and output were measured according to the actual mass balance obtained. Based on Fig. 3, 90% of condensate was recovered from POME, leaving merely a small fraction of decoction (1%), dewatered sludge (8%), and a slight loss due to dehydration. The result signified that CSD had induced evaporation of POME, leaving decoction and solid as the byproducts. Following the treatment, the condensate color turned clear, as displayed in Fig. 4 (A), which showed the capability of CSD to remove color. The color removal could be the result of organic compound removal (Nor et al., 2015). In contrast, decoction exhibited a dark color, which could be contributed by the accumulation of soluble microbial products (SMPs), such as protein, polysaccharide, and humic substances. Dai et al. (2018) reported that the humic substances are accountable for the color as a result of the release of melanoidins and humic acid. Fig. 4 (B) shows the RDD installed at KPOM. To further characterize the resulting condensate and decoction,
Fig. 3. Mass balance of rotating drum dryer.
wastewater analyses were performed on them with permissible limits by Malaysia Environmental Quality Regulation, 2009 to establish their acceptance level as industrial discharge effluent. It is apparent from Table 3 that the condensate quality parameters were within the Standard A limits, while the decoction quality parameters exceeded the prescribed regulatory limits. These findings strengthen the idea that POME could be reclaimed as a source of clean water supply for domestic usage thereby resolving river pollution issues. In Thailand, an average of 166 m3/ton FFB of grey water (treated POME) is reused to irrigate the existing oil palm plantation for
M.A. Ahmad Farid et al. / Journal of Cleaner Production 240 (2019) 117986
(A)
5
(B) II
Fig. 4. (A) Appearance of wastewater and treated water following the convective sludge drying (CSD) treatment; (I) decoction and (II) condensate, and (B) Rotary drum dryer (RDD) used at Keningau Palm Oil Mill (KPOM).
Table 3 Condensate and decoction qualities when compared against the quality standards. Parameters
BOD3 (mg/L) COD (mg/L) SS (mg/L) VSS (mg/L) TN (mg/L) VFA (mg/L) pH AN (mg/L) OG (mg/L)
Condensate
2±1 67.5 ± 12 40.0 ± 8 4.0 ± 2 5.0 ± 3 0.7 ± 0.3 6.5 ± 1 <0.01 <1
Decoction
75 ± 21 860 ± 32 310 ± 18 128 ± 24 56.0 ± 16 162.1 ± 24.3 7±1 75 ± 15 30 ± 11
Industrial discharged limits (DOE, 2010) Standard-A
Standard-B
20 80 50 e e e 6 to 9 10 1
40 200 100 e e e 5.5 to 9 20 10
nutrient cycling, which is a profound increase from 53 m3/ton FFB in 2010 (Suttayakul et al., 2016), while in Malaysia the industry has started utilizing treated POME for land irrigation as a means to compensate for the rainfall shortage (Patel, 2015). According to this study, there was merely a small fraction of decoction produced, making it likely to be reused for irrigation. Macro- and micronutrients are necessarily important for plant growth and metabolism. Therefore, a viable option to enhance the use of dewatered sludge for crop plants appeared to be appealing due to low-cost (Tarpani and Azapagic, 2018). Table 4 presents the results obtained for macro- and micronutrients of the dewatered sludge obtained in the present work. Closer inspection of the data reveals that the dewatered sludge contained a high amount of Table 4 Dewatered sludge characterizations. Test parameters Primary macronutrients Total nitrogen (TN) Phosphorus (P) Potassium (K) Secondary macronutrients Calcium (Ca) Magnesium (Mg) Micronutrients Aluminium (Al) Copper (Cu) Iron (Fe) Manganese (Mn) Sodium (Na) Nickel (Ni) Zinc (Zn)
Methods
Values (mg/L)
APHA 4500 APHA 3120 B EPA 6020 A
7.7 ± 0.2 5.6 ± 0.2 34.8 ± 3.3
EPA 6020 A
118.1 ± 11.7 318.2 ± 24.1
EPA 6020 A
2.2 ± 0.1 1.2 ± 0.1 71 ± 6.8 5.8 ± 0.4 7 ± 0.3 0.2 ± 0.1 1 ± 0.3
secondary macronutrients such as calcium (Ca) and magnesium (Mg). Secondary macronutrients play a vital role to correct soil’s acidity, and this finding opens up the possibility to utilize the dewatered sludge as fertilizer. Grobelak et al. (2017) evaluated the effects of sewage sludge applications on a barren and contaminated soil to immobilize harmful trace metals and obtain sustainable plant cover. The results brought about outstanding benefits to soil fertility by helping to remediate the soil, which allows the growth of various species of grasses, dicotyledonous plants, spontaneous growth of birch plant, and biomass of trees (mainly spruce and pine). Different technologies reveal different pollutant removal efficiencies. Therefore, a comparison with other physicochemical treatments of POME is summarized in Table 5. It is apparent that the method employed in the present work yielded excellent performance where BOD, COD, SS, OG and AN reduction recorded satisfactory results of higher than 99%, outperforming other established methods.
3.2. Economic assessment for convective sludge drying (CSD) technology at the palm oil mill Besides system efficiency, knowing the capital and operating costs are vital in providing facts and figures for the industry to assess in the context of actual expenditures. That being said an economic profile is equally important to maintain a technology application in the long run, and a larger production dimension contributes to more detailed aspects (Farid et al., 2017). Therefore, in order to generate a critical budgetary overview, a pilot-scale approach was undertaken. The preliminary economic evaluation was investigated by taking into account capital (CAPEX) and operation (OPEX) expenditures. For a typical palm oil mill, approximately 23.6 ton/h of POME is produced (Yoshizaki et al., 2013). In line with this production capacity, this value was set as the baseline in the economic evaluation. Both CAPEX and OPEX calculated were referred to as engineering economic multiplier values (Peters et al., 2003). The financial data of CSD in KPOM is shown in Table 6. For CAPEX, the total plant cost (TPC) monopolized the largest spending, constituting about 47% of the total capital investment (TCI). This expenditure includes the cost of equipment, building, installation, yard improvement, process piping, and electrical system which was worth approximately USD 2.9 mil. With the addition of the contractor’s fee, the TCI amounted to USD 3 mil. For OPEX, the total fixed cost (TFC) also monopolized the largest
6
M.A. Ahmad Farid et al. / Journal of Cleaner Production 240 (2019) 117986
Table 5 Comparison with other physicochemical treatment methods of palm oil mill effluent (POME). Method
Centrifugation Coagulation Coagulation-flocculation and adsorption
Flocculation Flotation Adsorption Ultrafiltration Drum dryer
Treatment descriptions
Treatment performances
10,000 g for 60 min Use alum at a dosage of 8 g/L for 30 min at 100 rpm 1) Coagulation-flocculation: Use alum/profloc CX822 at a dosage of 1.4% (v/v)/0.03% (w/v) for 5 min at 600 rpm 2) Adsorption: Use fixed bed activated carbon at a flow rate of 4L/min Use polyacrylamides at a dosage of 36 mg/L for 1 min at 100 rpm, and 20 min at 15 rpm, consecutively Use colloidal gas aphrons at 300 cm3 of LUX flakes sparged for 10 min Use chitosan at a dosage of 0.5 g/L for 15 min at 100 rpm Use polysulphone UF membrane of 20 kDa at 0.8 MPa Convective drying at a steam rate of 2 m3/min
Table 6 Financial data for convective sludge drying (CSD) technology assembled at Keningau Palm Oil Mill (KPOM). The currency exchange rate used is 1 USD ¼ 4.19 MYR. Items Capital expenditures (CAPEX) Equipment Building Installation Yard improvement Process piping Electrical system Total plant cost (TPC) Contingency Total capital investment (TCI) Operation expenditures (OPEX) Basic labor costs (4 persons) Fringe benefits Supervision Total labor costs (TLC) Laboratory/QC/QA Total variables cost (TVC) Depreciation Maintenance and repair Total fixed cost Total production cost Unit-production cost per m3
Values (USD) 1,421,715.79 142,171.58 454,949.05 213,257.37 497,600.53 142,171.58 2,871,865.90 143,593.29 3,015,459.19 23,113.20 9245.28 4622.64 36,981.12 2311.32 39,292.44 286,468.62 60,309.18 346,777.81 386,070.25 1.91
spending in the total production cost (TPC) amounting up to 90% of the annual operating cost. The total labor cost (TLC), which involved basic labor cost, fringe benefits, and supervision, summed up to annual overhead expenses of USD 36,981.12. In the present work, the treatment plant is run for two shifts per day (17 h) with four operators assigned. The basic salary was calculated according to the Malaysia national minimum wages policy (Cheah et al., 2017). The total variables cost (TVC) is estimated at USD 39,292.44 for laboratory/QC/QA expenses. By taking into account TLC and TVC, the TPC amounted to USD 386,070.25. The operating cost per m3 POME incurred by the proposed CSD at KPOM is USD 1.91. 3.3. Challenges to establishing convective sludge drying (CSD) in palm oil mill The strategy to modernize the current POME treatment has always been under consideration for many years. In conjunction with the expansion of knowledge, the concept can be actualized to reap the benefits via CSD technology. However, a leap forward in technology is not always a leap forward in benefit. A major issue in establishing CSD technology in palm oil mill is massive capital
References
pH
BOD removal (%)
COD removal (%)
SS removal (%)
OG removal (%)
AN removal (%)
e 4.5 6
46 86.3 e
40 e 85
100 89 99.9
50 99 95
50 e e
Ho and Tan (1983) Ahmad et al. (2006) Ahmad et al. (2005b)
e
e
54
98.7
e
e
Ariffin et al. (2005)
5
e
e
96
e
e
Hashim et al., 1995
4.5 8.4 6.5
e e 99.9
e 98 99.9
99.8 98 99.8
99 e 99.9
e 61.9 99.9
Ahmad et al. (2006) Wu et al. (2007) The present work
inflow, which scares the industry to invest into the CSD system as compared to other technologies that could reduce the cost by approximately five-fold (Ibrahim et al., 2017). Based on the treatment efficiency, around 1.2 tons of steam waste was consumed for every ton of POME treated. Thus, the likelihood of implementing the CSD technology in palm oil mill is less favorable due to high steam consumption of 679.7 ton/d while the steam waste generation approximated at 501.4 ton/d (Yoshizaki et al., 2013) which was able to cover only 88.4% of the total POME produced. Alternative to cater the issue is either to outsource a steam generator to supply the remaining 12% of steam needed or integrate CSD with the current lagoons system. Knowingly, the system can only reach up to ~90% of POME capacity, so much so the sustainability. Perhaps, further effort to enhance the system’s efficiency is warranted in the future to attain a higher amount POME treated within a shorter time at the current rate of steam waste generation, so that the system is capable of accommodating the entire POME production. 4. Conclusion The objective of the present work has been successfully achieved. Approximately 90% of condensate was recovered from POME, while the rest were 8% solids (dewatered sludge) and 1% decoction. The system demonstrated excellent performance in which 99.9% biological oxygen demand (BOD), 99.9% chemical oxygen demand (COD), 99.8% suspended solids (SS), 99.9% oil and grease (OG) and 99.9% ammoniacal nitrogen (AN) removal efficiencies were recorded, outperforming other established methods. The final BOD, COD, SS, AN and OG were 2 mg/L, 67.5 mg/L, 40.0 mg/L, <0.01 mg/L and <1 mg/L respectively, which meets the Standard-A of industrial effluent discharged of 20 mg/L for BOD, 80 mg/L for COD, 50 mg/L for SS, 10 mg/L for AN and 1 mg/L for OG making it suitable for domestic usage. Also, the dewatered sludge has the potential to be utilized as fertilizer as it was rich in secondary macronutrients, helping to correct soil’s acidity as well as improving plant’s overall health and growth. The operating cost incurred per m3 POME was USD 1.91, which is considered economical for a highly effective wastewater treatment system. Nevertheless, there is still room for improvement in establishing a viable CSD technology to be adopted by the palm oil mills in the near future. Acknowledgments The authors would like to acknowledge the Science and
M.A. Ahmad Farid et al. / Journal of Cleaner Production 240 (2019) 117986
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