Waste Management xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Waste Management journal homepage: www.elsevier.com/locate/wasman
Scum sludge as a potential feedstock for biodiesel production from wastewater treatment plants Wang Yi a,⇑, Feng Sha a, Bai Xiaojuan a, Zhao Jingchan b, Xia Siqing a,c a
School of Environmental and Municipal Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China College of Chemistry & Materials Science, Northwest University, Xi’an 710069, China c School of Environmental Science and Engineering, Tongji University, Shanghai 200092, China b
a r t i c l e
i n f o
Article history: Received 17 January 2015 Revised 19 June 2015 Accepted 24 June 2015 Available online xxxx Keywords: Wastewater treatment plant Scum sludge Biodiesel production
a b s t r a c t The main goal of this study was to compare the component and yield of biodiesel obtained by different methods from different sludge in a wastewater treatment plant. Biodiesel was produced by ex-situ and in-situ transesterification of scum, primary and secondary sludge respectively. Results showed that scum sludge had a higher calorific value and neutral lipid than that of primary and secondary sludge. The lipid yield accounted for one-third of the dried scum sludge and the maximum yield attained 22.7% under in-situ transesterification. Furthermore the gas chromatography analysis of fatty acid methyl esters (FAMEs) revealed that all sludge contained a significant amount of palmitic acid (C16:0) and oleic acid (C18:1) regardless of extraction solvents and sludge types used. However, the difference lay in that oleic acid methyl ester was the dominant component in FAMEs produced from scum sludge while palmitic acid methyl ester was the dominant component in FAMEs from primary and secondary sludge. In addition, the percentage of unsaturated fatty acid ester in FAMEs from scum sludge accounted for 57.5–64.1% of the total esters, which was higher than the equivalent derived from primary and secondary sludge. In brief, scum sludge is a potential feedstock for the production of biodiesel and more work is needed in the future. Ó 2015 Published by Elsevier Ltd.
1. Introduction Scum is a floatable material skimmed from the surface of primary and secondary settling tanks, especially from the surface of grit chamber in wastewater treatment plants. The origin of scum is mainly from fats, oil, and grease, which are washed into the plumbing system through kitchen sinks and floor drains and are eventually conveyed to wastewater treatment plants downstream. Animal oil, vegetable oil, and grease from restaurants and fast-food outlets that do not implement adequate grease control measures are the main contributors to the fats, oil, and grease of wastewater treatment plants. According to a survey conducted by the National Renewable Energy Laboratory (NREL) in 30 US metropolitan areas, fats, oil, and grease are generated at a rate of approximately 1.9 gallons/person/year (Wiltsee, 1998). Fats, oil, and grease are difficult to recover once it has been mixed with raw sewage and the NREL study likely overestimates the recoverable quantity (Long et al., 2012). Another type of nonpolar oils and greases that is not readily biodegradable is that generated from petroleum ⇑ Corresponding author. E-mail address: [email protected] (Y. Wang).
products or other industries (Jarde et al., 2005; Durand et al., 2004). This type of grease also pours into wastewater treatment plants by storm runoff or pipes. Scum has some detrimental impacts on the operation of wastewater treatment plants. It can clog wastewater treatment systems and result in the flotation of sludge in thickening units. Significant amounts of fats, oil, grease or lipid in sludge can affect both aerobic and anaerobic processes (Chipasa and Medrzycka, 2006), inhibit methanogenesis during anaerobic digestion (Luostarinen et al., 2009; Carucci et al., 2005), and clog sludge dewatering equipment when scum is pumped to the waste sludge treatment system along with the sludge. Thus, scum must be skimmed off the surface of the wastewater at the beginning of the wastewater treatment process using the grit chambers. However, the treatment and disposal of scum are invariably overlooked compared with that of primary and secondary sludge in the wastewater treatment plants, which spend 20–60% of total wastewater treatment plants’ operating costs (Chipasa and Medrzycka, 2008). Some scum sludge is recycled to the inlets of wastewater treatment plants in consideration of its slow microbial degradation (Andreoli et al., 2007), which often leads to a higher concentration of lipid in the effluent. Some scum sludge is
http://dx.doi.org/10.1016/j.wasman.2015.06.036 0956-053X/Ó 2015 Published by Elsevier Ltd.
Please cite this article in press as: Wang, Y., et al. Scum sludge as a potential feedstock for biodiesel production from wastewater treatment plants. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.06.036
2
Y. Wang et al. / Waste Management xxx (2015) xxx–xxx
discarded into garbage cans as municipal trash and directly disposed in landfills. The disposal scum landfills not only increases the cost of treatment facilities, but also causes many environmental problems. For instance, the Metropolitan Wastewater Treatment Plant at St. Paul. MN (Metro Plant) spends $100,000 a year just for land filling the scum (Bi et al., 2015). Furthermore, the landfill could rise to underground water pollution because of the landfill leachate. Therefore, the alternative approach is needed to improve the disposal situation of scum, which is also consummated the management of sewage sludge in wastewater treatment plants. Actually, the treatment and disposal of sewage sludge are significant environmental challenges these years since the amount of this sludge is expected to increase in the future as a result of increasing urbanization and industrialization, especially in China. The use of sludge as fertilizer is restricted in many countries given its bad odor and the presence of heavy metals, toxic substances, and pharmaceutical chemicals. Moreover, sludge incineration generates emissions that contain heavy metals and dioxins (Angerbauer et al., 2008; Kargbo, 2010; Woon and Lo, 2014; Samolada and Zabaniotou, 2014). Thus, the feasible approach to treat and dispose sewage sludge must be established and a new disposal method is proposed to utilize sewage sludge as a biodiesel feedstock because of the rapid increase in fuel demand worldwide, reduced fossil fuel reserve, and the high cost of feedstock for present biodiesel production over the past decade (Haas et al., 2007; Meng et al., 2009; Devereaux and Lee, 2009; Tao and Aden, 2009; Marufuzzaman et al., 2014). Previous studies have demonstrated the potential of primary and secondary sludge from municipal wastewater treatment plants as biodiesel feedstock. For instance, Dufreche et al. (2007), Mondala et al. (2009), Revellame et al. (2010) and Olkiewicz et al. (2015) reported that the biodiesel generated from wastewater treatment plants sludge mainly contains methyl esters of palmatic acid (C16:0), palmitoleic acid (C16:1), stearic acid (C18:0), oleic acid (C18:1), and linoleic acid (C18:2). This biodiesel composition is similar to that of some vegetable oil biodiesel such as olive, corn and rapeseed (Ramos et al., 2009), which had the better properties because of the greater monounsaturated content. In theory, scum sludge is mainly composed of fats, oil, and grease, which is a waste product rich in free fatty acids (Marufuzzaman et al., 2014) and has high lipid content (Bi et al., 2015; Sangaletti-Gerhard et al., 2015). Thus, it is more beneficial to biodiesel production than primary and secondary sludge. Unfortunately, little research has been conducted on the application of scum sludge to biodiesel production to date, although fats, oil, and grease have recently been recovered for use as a biodiesel feedstock (Sangaletti-Gerhard et al., 2015; Pastore et al., 2014). The main objective of this paper is to introduce scum sludge to biodiesel production and to compare the biodiesel yield of scum sludge with that of primary and secondary sludge through ex-situ and in-situ production systematically. The research is important to the management of scum sludge in wastewater treatment plants and to the scope widening of the potential feedstock for production of second-generation biofuels.
2. Materials and methods 2.1. Sludge collection and preparation Scum, primary, and secondary sludge were collected from the grit chamber, primary clarifier, and secondary clarifier of a municipal wastewater treatment plants in Xi’an, China. The raw sludge was first sieved ( C18:1 > C18:0 > C18:2 > C16:1 > C14:0. Each profile maintained a relatively stable percentage. Palmitic acid (C16:0), oleic acid (C18:1), stearic acid (C18:0), and linoleic acid (C18:2) accounted for more than 40%, 25%, 11%, and 5% of total biodiesel, respectively. Thus, the percentage of unsaturated fatty acid ester in biodiesel obtained from each extracted lipid was between 35.3% and 37.7%, with an average of 36.2%. The fatty acid profiles constructed from secondary sludge using various extraction methods were sequenced as follows: C16:0 > C18:1 > C16:1 > C18:0 > C18:2 > C14:0. Each profile also
Fig. 1. Effects of different co-solvents on the lipid yield from various types of dried sludge and the FAME yield from extracted lipid: a. Effect of different co-solvent ratios on the lipid yield from various types of dried sludge; b. Effect of different co-solvents on the FAME yield from extracted lipid.
Please cite this article in press as: Wang, Y., et al. Scum sludge as a potential feedstock for biodiesel production from wastewater treatment plants. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.06.036
Y. Wang et al. / Waste Management xxx (2015) xxx–xxx
5
Fig. 2. Composition of FAMEs derived from the exsitu production of different sludge types when lipids were extracted by co-solvents at different volume ratios: a. 20:60:20; b. 40:40:20; c. 60:20:20; d. 80:20:0.
maintained a relatively stable percentage. Palmitic acid (C16:0) and oleic acid (C18:1) remained the dominant components and constituted 37.0–39.2% and 21.3–22.9% of total biodiesel, respectively. This percentage range was slightly lower than that of the FAMEs obtained from primary sludge using the same extraction method. The content of palmitoleic acid (14.5–16.9%) ranked third and was higher than that of stearic acid (11.8–12.4%). Therefore, the percentage of unsaturated fatty acid ester in biodiesel generated from each extracted lipid was between 43.7% and 46.3%, with an average of 45.0%. Similarly, the fatty acid profiles in biodiesel from scum sludge under various co-solvent ratios were sequenced as C18:1 > C16:0 > C18:2 > C18:0 > C16:1 > C14:0. However, this arrangement differed from those of primary and secondary sludge in that oleic acid became the dominant component of the fatty acids and palmitic acid ranked second. Meanwhile, the percentage of each methyl ester in biodiesel varied widely. For example, the percentage ranges of oleate methyl and palmitate methyl were 35.9–42.1% and 25.5–30.8%, respectively. Moreover, these percentages were positively correlated with those of n-hexane and methanol in the co-extraction system. The contents of linoleate methyl and stearic acid methyl ester in the biodiesel were 18.0–20.2% and 6.9–8.3%. In short, the percentage of unsaturated fatty acid ester from each extracted lipid was increased when scum sludge was used as the sludge source. The variation in the percentage range of unsaturated fatty acid ester from each extracted lipid ranged from 57.5% to 64.1%, and the percentage of unsaturated fatty acid increased when the co-extraction system contained more hexane and less methanol.
In brief, all of the sludge types possessed significant amounts of palmitic acid (C16:0) and oleic acid (C18:1) regardless of the co-solvent used. Palmitic acid methyl was the dominant component in the FAMEs produced from primary and secondary sludge and accounted for approximately 45% and 37% of total biodiesel, respectively. Meanwhile, oleic acid methyl was the dominant component in the FAMEs produced from scum sludge and it constituted more than 35% of total biodiesel. In this experiment, all sludge had a similar fatty acid composition (i.e., C16 and C18 acids) as the sludge fatty acid profiles generated with various extraction methods were compared with each other and with that of the profile of non-edible-based biodiesel (Ashraful et al., 2014). Mohammad Fauzi and Saidina Amin (2013) reported that palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2), and linolenic acid (C18:3) were the common fatty acids in vegetable oils. Thus, the fatty acids in sludge and vegetable oil could similarly produce biodiesel. Nonetheless, the biodiesel derived from vegetable oil contained the linolenic acid (C18:3) missing from that derived from sludge. Furthermore, the quality of biodiesel and its fuel properties depend strongly on the relative percentage of fatty acid composition in the fuel blend. Sahoo and Das (2009) reported that fuel cetane number, cloud point, and stability increased when saturated fatty acid alkyl ester was introduced into fuel blends. Biodiesel viscosity and freezing point increase with the increase in carbon chain length and decrease with the increase in double bond chains. In the current study, the percentage of unsaturated fatty acid ester in biodiesel produced by the ex-situ transesterification of scum sludge ranged from 57.5% to 64.1%. This range was comparable to the 61% in the
Please cite this article in press as: Wang, Y., et al. Scum sludge as a potential feedstock for biodiesel production from wastewater treatment plants. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.06.036
6
Y. Wang et al. / Waste Management xxx (2015) xxx–xxx
biodiesel derived from soybeans. This percentage may also generate biodiesel with poor oxidation stability and improved cold flow properties (Canakci and Sanli, 2008). Nevertheless, the percentages of unsaturated fatty acid ester in the biodiesel produced through the ex-situ transesterification of primary and secondary sludge were low at 35.3–37.7% and 43.7–46.3% respectively.
3.3. Production of biodiesel from sludge by in-situ transesterification 3.3.1. FAMEs yield from the transesterification of dried sludge An examination of the biodiesel from various sludge types showed that the in-situ conversion of lipids to FAMEs yielded higher overall biodiesel than the ex-situ conversion of lipids to FAMEs did. Fig. 3 depicts the average FAMEs yield through in-situ production from different sludge types. Biodiesel yield was maximized at 22.7% via the in-situ transesterification of scum sludge, followed by those of primary and secondary sludge at 9.0% and 1.9%, respectively. By contrast, the yields of the ex-situ conversion of scum (9.1%), primary (5.0%), and secondary (1.5%) sludge to FAMEs were maximized when the co-solvent ratios were 20:80:0, 60:20:20, and 20:60:20, respectively. Dufreche et al. (2007) yielded 27.4% (w/w dry sludge) lipid after the extraction of lipid from primary and activated sludge, which was obtained from a municipal wastewater treatment plants. Subsequent transesterification of the lipid extracts yielded 4.4% biodiesel (w/w dry sludge). Using sewage sludge obtained from the same WWTPs, Mondala et al. (2009) reported maximum biodiesel yields of 14.5% and 2.5% (w/w dry sludge) via the in situ transesterification of primary and activated sludge, respectively. Moreover, Revellame et al. (2010) obtained a maximum biodiesel yield of 4.79% (w/w dry sludge) from activated sludge under optimum in-situ transesterification conditions. The biodiesel yields obtained in our experiment from primary and secondary (activated) sludge processed through in-situ and ex-situ transesterification were slightly lower than those of the aforementioned studies. Our study differed from the previous ones not only in terms of sludge source origin but also in terms of transesterification conditions. This implied biodiesel yield of 22.7% from scum sludge via in-situ transesterification exceeded the expectation and was a reasonable value. Thus, the results indicated that the overall biodiesel yields of all three sludge types were considerably higher under in situ conversion than under ex-situ conversion. This result agreed with those of previous reports and may be ascribed to the access of the reagents to all lipids in the sludge instead of to the extracted lipids alone.
Fig. 3. FAMEs yield by in-situ production from different sludge types.
3.3.2. FAMEs composition of biodiesel produced by the in-situ transesterification of dried sludge The FAMEs analysis of biodiesel obtained via acid-catalyzed in-situ esterification and the transesterification of dried sludge is presented in Fig. 4. The FAMEs compositions of biodiesel generated by in-situ and ex-situ production were highly similar. The fatty acid profiles in biodiesel produced in situ from primary sludge were sequenced as follows: C16:0 > C18:1 > C18:0 > C18:2 > C16:1 > C14:0. Methyl palmitate, methyl oleate, stearic acid methyl ester, and methyl linoleate accounted for more than 44.6%, 26.3%, 12.0%, and 6.4% of total biodiesel, respectively. These percentages were higher than those in the corresponding composition of biodiesel produced by ex-situ production. On the basis of the content of FAMEs, the percentage of unsaturated fatty acid ester was 38.5%, which was slightly higher than that obtained by ex-situ production. The fatty acid profiles in biodiesel generated in-situ from secondary sludge were sequenced as follows: C16:0 > C16:1 > C18:1 > C18:0 > C18:2 > C14:0. Methyl palmitate remained the dominant component and constituted approximately 38.1% of total biodiesel. The contents of methyl palmitoleate and methyl oleate were very close at approximately 17.5%. The percentage of unsaturated fatty acid ester in FAMEs from secondary sludge was significantly higher (44.4%) than that of unsaturated fatty acid ester in FAMEs derived from primary sludge through in situ production. The fatty acid profiles in biodiesel produced in situ from scum sludge were arranged as follows: C16:0 > C18:1 > C18:2 > C18:0 > C16:1 > C14:0. Methyl palmitate was also the dominant component of the FAMEs and accounted for 37.3% of total biodiesel. Oleate methyl and linoleate methyl were ranked second and third and constituted 30.1% and 15.1%, respectively, of the biodiesel. The total percentage of unsaturated fatty acid ester in FAMEs from scum sludge was 49.1%. In short, the analysis of fatty acid profiles in biodiesel generated in-situ from sludge and indicated that the percentage of unsaturated fatty acid ester in FAMEs from scum sludge was higher than those from primary and secondary sludge. Moreover, the former accounted for one-half of the total esters. 4. Conclusion The paper introduced scum sludge to biodiesel production and compared the biodiesel yield of scum sludge with that of primary and secondary sludge through ex-situ and in-situ production systematically. The results had shown that scum sludge had almost twice calorific value of primary and secondary sludge under freeze-drying. However, all sludge types contained a significant
Fig. 4. FAME composition by in-situ production from different sludge types.
Please cite this article in press as: Wang, Y., et al. Scum sludge as a potential feedstock for biodiesel production from wastewater treatment plants. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.06.036
Y. Wang et al. / Waste Management xxx (2015) xxx–xxx
amount of palmitic acid (C16:0) and oleic acid (C18:1) regardless of the co-solvent used in extraction. Palmitic acid methyl ester was the dominant component in the FAMEs and accounted for approximately 45% and 37% of total biodiesel produced from primary and secondary sludge respectively. However oleic acid methyl ester was the dominant component in the FAMEs produced of scum sludge and constituted more than 35% of total biodiesel. It was also found in this study that the neutral lipid was dominant in scum sludge and the maximum lipid yield accounted for one-third of the dried scum sludge when the extraction was performed with the co-solvent containing a high percentage of hexane (60%). In addition, the percentage variation of unsaturated fatty acid ester in biodiesel by the ex-situ transesterification of scum sludge ranged in 57.5–64.1%, while the equivalent value were 35.25–37.72% and 43.67–46.3% in the biodiesel produced from primary and secondary sludge, respectively, using the same methods. Therefore, the percentage of unsaturated fatty acid ester in the FAMEs from scum sludge accounted for more than one-half of the total esters, which was higher than the equivalent derived from primary and secondary sludge. As for the difference of biodiesel yield by ex-situ and in-situ transesterification, it was obvious that the maximum yield from scum sludge, primary and secondary sludge was 22.7%, 9.0% and 1.9% respectively, which was higher than the corresponding yield gained through ex-situ transesterification. In conclusion, scum sludge was a potential resource for the production of biodiesel, which had a higher calorific value and neutral lipid than that of primary and secondary sludge. The lipid yield accounted for one-third of the dried scum sludge and the maximum yield was 22.7% by in-situ transesterification of scum sludge. Oleic acid methyl ester instead of palmitic acid methyl ester, which was the dominant component in the biodiesel produced from primary and secondary sludge, was the dominant component in the biodiesel produced of scum sludge. Acknowledgements This work was funded by the Education Department of Shaanxi Province [Grant numbers 2013JC20 and 13JS046] and State Key Laboratory of Pollution Control and Resource Reuse Foundation (No. PCRRF14013). The research was also supported by the innovative research team of Xi’an University of Architecture and Technology. The authors wish to express their gratitude to the No. 4 Wastewater Treatment Plant of Xi’an for supporting this study. In addition, we thank reviewers for their valuable suggestions to improve this manuscript. References Andreoli, C.V., Sperling, M.V., Fernandes, F., 2007. Sludge treatment and disposal. Biological wastewater treatment series, vol. 6. IWA Publishing, BeloHorizonte, London, New York Belo Horizonte, Brazil, London, New York. Angerbauer, C., Siebenhofer, M., Mittelbach, M., Guebitz, G.M., 2008. Conversion of sewage sludge into lipids by Lipomyces starkeyi for biodiesel production. Bioresour. Technol. 99, 3051–3056. Ashraful, A.M., Masjuki, H.H., Kalam, M.A., Rizwanul Fattah, I.M., Imtenan, S., Shahir, S.A., Mobarak, H.M., 2014. Production and comparison of fuel properties, engine performance, and emission characteristics of biodiesel from various non-edible vegetable oils: a review. Energy Convers. Manage. 80, 202–228. Barber, W.P.F., 2015. Influence of wastewater treatment on sludge production and processing. Water Pract. Technol. 10, 178–186. Bi, C., Min, M., Nie, Y., Xie, Q., Lu, Q., Deng, X., Anderson, E., Li, D., Ruan, R., 2015. Process development for scum to biodiesel conversion. Bioresour. Technol. 185, 185–193.
7
Canakci, M., Sanli, H., 2008. Biodiesel production from various feedstocks and their effects on the fuel properties. J. Ind. Microbiol. Biotechnol. 35, 431–441. Carucci, G., Carrasco, F., Trifoni, K., Majone, M., Beccari, M., 2005. Anaerobic digestion of food industry wastes: effect of codigestion on methane yield. J. Environ. Eng. 131, 1037–1045. Chipasa, K.B., Medrzycka, K., 2006. Behavior of lipids in biological wastewater treatment processes. J. Ind. Microbiol. Biotechnol. 33, 635–645. Chipasa, K.B., Medrzycka, K., 2008. Characterization of the fate of lipids in activated sludge. J. Environ. Sci. (China) 20, 536–542. Devereaux, C., Lee, H., 2009. Biofuels and certification. A Workshop at the Harvard Kennedy School of Government. Summary Report. Dufreche, S., Hernandez, R., French, T., Sparks, D., Zappi, M., Alley, E., 2007. Extraction of lipids from municipal wastewater plant microorganisms for production of biodiesel. J. Am. Oil Chem. Soc. 84, 181–187. Durand, C., Ruban, V., Ambles, A., Oudot, J., 2004. Characterization of the organic matter of sludge: determination of lipids, hydrocarbons and PAHs from road retention/infiltration ponds in France. Environ. Pollut. 132, 375–384. Haas, M., Scott, K., Foglia, T., Marmer, W., 2007. The general applicability of in situ transesterification for the production of fatty acid esters from a variety of feedstocks. J. Am. Oil Chem. Soc. 84, 963–970. Huynh, L.H., Kasim, N.S., Ju, Y.H., 2010. Extraction and analysis of neutral lipids from activated sludge with and without sub-critical water pre-treatment. Bioresour. Technol. 101, 8891–8896. Jarde, E., Mansuy, L., Faure, P., 2005. Organic markers in the lipidic fraction of sewage sludges. Water Res. 39, 1215–1232. Kargbo, D.M., 2010. Biodiesel production from municipal sewage sludges. Energy Fuels 24, 2791–2794. Li, M., Xiao, B., Wang, X., Liu, J., 2015. Consequences of sludge composition on combustion performance derived from thermogravimetry analysis. Waste Manage. 35, 141–147. Long, J.H., Aziz, T.N., Reyes III, F.L.d.l., Ducoste, J.J., 2012. Anaerobic co-digestion of fat, oil, and grease (FOG): a review of gas production and process limitations. Process Saf. Environ. Prot. 90, 231–245. Luostarinen, S., Luste, S., Sillanpaa, M., 2009. Increased biogas production at wastewater treatment plants through co-digestion of sewage sludge with grease trap sludge from a meat processing plant. Bioresour. Technol. 100, 79– 85. Marufuzzaman, M., Eksßiog˘lu, S.D., Hernandez, R., 2014. Environmentally friendly supply chain planning and design for biodiesel production via wastewater sludge. Transp. Sci. 48, 555–574. Meng, X., Yang, J., Xu, X., Zhang, L., Nie, Q., Xian, M., 2009. Biodiesel production from oleaginous microorganisms. Renew. Energy 34, 1–5. Mohammad Fauzi, A.H., Saidina Amin, N.A., 2013. Optimization of oleic acid esterification catalyzed by ionic liquid for green biodiesel synthesis. Energy Convers. Manage. 76, 818–827. Mondala, A., Liang, K., Toghiani, H., Hernandez, R., French, T., 2009. Biodiesel production by in situ transesterification of municipal primary and secondary sludges. Bioresour. Technol. 100, 1203–1210. Olkiewicz, M., Fortuny, A., Stüber, F., Fabregat, A., Font, J., Bengoa, C., 2015. Effects of pre-treatments on the lipid extraction and biodiesel production from municipal WWTP sludge. Fuel 141, 250–257. Pastore, C., Lopez, A., Mascolo, G., 2014. Efficient conversion of brown grease produced by municipal wastewater treatment plant into biofuel using aluminium chloride hexahydrate under very mild conditions. Bioresour. Technol. 155, 91–97. Ramos, M.J., Fernández, C.M., Casas, A., Rodríguez, L., Pérezángel, 2009. Influence of fatty acid composition of raw materials on biodiesel properties. Bioresour. Technol. 100, 261–268. Revellame, E., Hernandez, R., French, W., Holmes, W., Alley, E., 2010. Biodiesel from activated sludge through in situ transesterification. J. Chem. Technol. Biotechnol. 85, 614–620. Sahoo, P.K., Das, L.M., 2009. Process optimization for biodiesel production from Jatropha, Karanja and Polanga oils. Fuel 88, 1588–1594. Samolada, M.C., Zabaniotou, A.A., 2014. Comparative assessment of municipal sewage sludge incineration, gasification and pyrolysis for a sustainable sludgeto-energy management in Greece. Waste Manage. 34, 411–420. Sangaletti-Gerhard, N., Cea, M., Risco, V., Navia, R., 2015. In situ biodiesel production from greasy sewage sludge using acid and enzymatic catalysts. Bioresour. Technol. 179, 63–70. Tao, L., Aden, A., 2009. The economics of current and future biofuels. In Vitro Cell. Dev. Biol.-Plant 45, 199–217. Wiltsee, G., 1998. Waste grease resource in 30 US metropolitan areas. In: The Proceedings of Bioenergy 98 Conference, Wisconsin, pp. 956–963. Woon, K.S., Lo, I.M.C., 2014. Analyzing environmental hotspots of proposed landfill extension and advanced incineration facility in Hong Kong using life cycle assessment. J. Clean. Prod. 75, 64–74.
Please cite this article in press as: Wang, Y., et al. Scum sludge as a potential feedstock for biodiesel production from wastewater treatment plants. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.06.036
Contents lists available at ScienceDirect
Waste Management journal homepage: www.elsevier.com/locate/wasman
Scum sludge as a potential feedstock for biodiesel production from wastewater treatment plants Wang Yi a,⇑, Feng Sha a, Bai Xiaojuan a, Zhao Jingchan b, Xia Siqing a,c a
School of Environmental and Municipal Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China College of Chemistry & Materials Science, Northwest University, Xi’an 710069, China c School of Environmental Science and Engineering, Tongji University, Shanghai 200092, China b
a r t i c l e
i n f o
Article history: Received 17 January 2015 Revised 19 June 2015 Accepted 24 June 2015 Available online xxxx Keywords: Wastewater treatment plant Scum sludge Biodiesel production
a b s t r a c t The main goal of this study was to compare the component and yield of biodiesel obtained by different methods from different sludge in a wastewater treatment plant. Biodiesel was produced by ex-situ and in-situ transesterification of scum, primary and secondary sludge respectively. Results showed that scum sludge had a higher calorific value and neutral lipid than that of primary and secondary sludge. The lipid yield accounted for one-third of the dried scum sludge and the maximum yield attained 22.7% under in-situ transesterification. Furthermore the gas chromatography analysis of fatty acid methyl esters (FAMEs) revealed that all sludge contained a significant amount of palmitic acid (C16:0) and oleic acid (C18:1) regardless of extraction solvents and sludge types used. However, the difference lay in that oleic acid methyl ester was the dominant component in FAMEs produced from scum sludge while palmitic acid methyl ester was the dominant component in FAMEs from primary and secondary sludge. In addition, the percentage of unsaturated fatty acid ester in FAMEs from scum sludge accounted for 57.5–64.1% of the total esters, which was higher than the equivalent derived from primary and secondary sludge. In brief, scum sludge is a potential feedstock for the production of biodiesel and more work is needed in the future. Ó 2015 Published by Elsevier Ltd.
1. Introduction Scum is a floatable material skimmed from the surface of primary and secondary settling tanks, especially from the surface of grit chamber in wastewater treatment plants. The origin of scum is mainly from fats, oil, and grease, which are washed into the plumbing system through kitchen sinks and floor drains and are eventually conveyed to wastewater treatment plants downstream. Animal oil, vegetable oil, and grease from restaurants and fast-food outlets that do not implement adequate grease control measures are the main contributors to the fats, oil, and grease of wastewater treatment plants. According to a survey conducted by the National Renewable Energy Laboratory (NREL) in 30 US metropolitan areas, fats, oil, and grease are generated at a rate of approximately 1.9 gallons/person/year (Wiltsee, 1998). Fats, oil, and grease are difficult to recover once it has been mixed with raw sewage and the NREL study likely overestimates the recoverable quantity (Long et al., 2012). Another type of nonpolar oils and greases that is not readily biodegradable is that generated from petroleum ⇑ Corresponding author. E-mail address: [email protected] (Y. Wang).
products or other industries (Jarde et al., 2005; Durand et al., 2004). This type of grease also pours into wastewater treatment plants by storm runoff or pipes. Scum has some detrimental impacts on the operation of wastewater treatment plants. It can clog wastewater treatment systems and result in the flotation of sludge in thickening units. Significant amounts of fats, oil, grease or lipid in sludge can affect both aerobic and anaerobic processes (Chipasa and Medrzycka, 2006), inhibit methanogenesis during anaerobic digestion (Luostarinen et al., 2009; Carucci et al., 2005), and clog sludge dewatering equipment when scum is pumped to the waste sludge treatment system along with the sludge. Thus, scum must be skimmed off the surface of the wastewater at the beginning of the wastewater treatment process using the grit chambers. However, the treatment and disposal of scum are invariably overlooked compared with that of primary and secondary sludge in the wastewater treatment plants, which spend 20–60% of total wastewater treatment plants’ operating costs (Chipasa and Medrzycka, 2008). Some scum sludge is recycled to the inlets of wastewater treatment plants in consideration of its slow microbial degradation (Andreoli et al., 2007), which often leads to a higher concentration of lipid in the effluent. Some scum sludge is
http://dx.doi.org/10.1016/j.wasman.2015.06.036 0956-053X/Ó 2015 Published by Elsevier Ltd.
Please cite this article in press as: Wang, Y., et al. Scum sludge as a potential feedstock for biodiesel production from wastewater treatment plants. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.06.036
2
Y. Wang et al. / Waste Management xxx (2015) xxx–xxx
discarded into garbage cans as municipal trash and directly disposed in landfills. The disposal scum landfills not only increases the cost of treatment facilities, but also causes many environmental problems. For instance, the Metropolitan Wastewater Treatment Plant at St. Paul. MN (Metro Plant) spends $100,000 a year just for land filling the scum (Bi et al., 2015). Furthermore, the landfill could rise to underground water pollution because of the landfill leachate. Therefore, the alternative approach is needed to improve the disposal situation of scum, which is also consummated the management of sewage sludge in wastewater treatment plants. Actually, the treatment and disposal of sewage sludge are significant environmental challenges these years since the amount of this sludge is expected to increase in the future as a result of increasing urbanization and industrialization, especially in China. The use of sludge as fertilizer is restricted in many countries given its bad odor and the presence of heavy metals, toxic substances, and pharmaceutical chemicals. Moreover, sludge incineration generates emissions that contain heavy metals and dioxins (Angerbauer et al., 2008; Kargbo, 2010; Woon and Lo, 2014; Samolada and Zabaniotou, 2014). Thus, the feasible approach to treat and dispose sewage sludge must be established and a new disposal method is proposed to utilize sewage sludge as a biodiesel feedstock because of the rapid increase in fuel demand worldwide, reduced fossil fuel reserve, and the high cost of feedstock for present biodiesel production over the past decade (Haas et al., 2007; Meng et al., 2009; Devereaux and Lee, 2009; Tao and Aden, 2009; Marufuzzaman et al., 2014). Previous studies have demonstrated the potential of primary and secondary sludge from municipal wastewater treatment plants as biodiesel feedstock. For instance, Dufreche et al. (2007), Mondala et al. (2009), Revellame et al. (2010) and Olkiewicz et al. (2015) reported that the biodiesel generated from wastewater treatment plants sludge mainly contains methyl esters of palmatic acid (C16:0), palmitoleic acid (C16:1), stearic acid (C18:0), oleic acid (C18:1), and linoleic acid (C18:2). This biodiesel composition is similar to that of some vegetable oil biodiesel such as olive, corn and rapeseed (Ramos et al., 2009), which had the better properties because of the greater monounsaturated content. In theory, scum sludge is mainly composed of fats, oil, and grease, which is a waste product rich in free fatty acids (Marufuzzaman et al., 2014) and has high lipid content (Bi et al., 2015; Sangaletti-Gerhard et al., 2015). Thus, it is more beneficial to biodiesel production than primary and secondary sludge. Unfortunately, little research has been conducted on the application of scum sludge to biodiesel production to date, although fats, oil, and grease have recently been recovered for use as a biodiesel feedstock (Sangaletti-Gerhard et al., 2015; Pastore et al., 2014). The main objective of this paper is to introduce scum sludge to biodiesel production and to compare the biodiesel yield of scum sludge with that of primary and secondary sludge through ex-situ and in-situ production systematically. The research is important to the management of scum sludge in wastewater treatment plants and to the scope widening of the potential feedstock for production of second-generation biofuels.
2. Materials and methods 2.1. Sludge collection and preparation Scum, primary, and secondary sludge were collected from the grit chamber, primary clarifier, and secondary clarifier of a municipal wastewater treatment plants in Xi’an, China. The raw sludge was first sieved ( C18:1 > C18:0 > C18:2 > C16:1 > C14:0. Each profile maintained a relatively stable percentage. Palmitic acid (C16:0), oleic acid (C18:1), stearic acid (C18:0), and linoleic acid (C18:2) accounted for more than 40%, 25%, 11%, and 5% of total biodiesel, respectively. Thus, the percentage of unsaturated fatty acid ester in biodiesel obtained from each extracted lipid was between 35.3% and 37.7%, with an average of 36.2%. The fatty acid profiles constructed from secondary sludge using various extraction methods were sequenced as follows: C16:0 > C18:1 > C16:1 > C18:0 > C18:2 > C14:0. Each profile also
Fig. 1. Effects of different co-solvents on the lipid yield from various types of dried sludge and the FAME yield from extracted lipid: a. Effect of different co-solvent ratios on the lipid yield from various types of dried sludge; b. Effect of different co-solvents on the FAME yield from extracted lipid.
Please cite this article in press as: Wang, Y., et al. Scum sludge as a potential feedstock for biodiesel production from wastewater treatment plants. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.06.036
Y. Wang et al. / Waste Management xxx (2015) xxx–xxx
5
Fig. 2. Composition of FAMEs derived from the exsitu production of different sludge types when lipids were extracted by co-solvents at different volume ratios: a. 20:60:20; b. 40:40:20; c. 60:20:20; d. 80:20:0.
maintained a relatively stable percentage. Palmitic acid (C16:0) and oleic acid (C18:1) remained the dominant components and constituted 37.0–39.2% and 21.3–22.9% of total biodiesel, respectively. This percentage range was slightly lower than that of the FAMEs obtained from primary sludge using the same extraction method. The content of palmitoleic acid (14.5–16.9%) ranked third and was higher than that of stearic acid (11.8–12.4%). Therefore, the percentage of unsaturated fatty acid ester in biodiesel generated from each extracted lipid was between 43.7% and 46.3%, with an average of 45.0%. Similarly, the fatty acid profiles in biodiesel from scum sludge under various co-solvent ratios were sequenced as C18:1 > C16:0 > C18:2 > C18:0 > C16:1 > C14:0. However, this arrangement differed from those of primary and secondary sludge in that oleic acid became the dominant component of the fatty acids and palmitic acid ranked second. Meanwhile, the percentage of each methyl ester in biodiesel varied widely. For example, the percentage ranges of oleate methyl and palmitate methyl were 35.9–42.1% and 25.5–30.8%, respectively. Moreover, these percentages were positively correlated with those of n-hexane and methanol in the co-extraction system. The contents of linoleate methyl and stearic acid methyl ester in the biodiesel were 18.0–20.2% and 6.9–8.3%. In short, the percentage of unsaturated fatty acid ester from each extracted lipid was increased when scum sludge was used as the sludge source. The variation in the percentage range of unsaturated fatty acid ester from each extracted lipid ranged from 57.5% to 64.1%, and the percentage of unsaturated fatty acid increased when the co-extraction system contained more hexane and less methanol.
In brief, all of the sludge types possessed significant amounts of palmitic acid (C16:0) and oleic acid (C18:1) regardless of the co-solvent used. Palmitic acid methyl was the dominant component in the FAMEs produced from primary and secondary sludge and accounted for approximately 45% and 37% of total biodiesel, respectively. Meanwhile, oleic acid methyl was the dominant component in the FAMEs produced from scum sludge and it constituted more than 35% of total biodiesel. In this experiment, all sludge had a similar fatty acid composition (i.e., C16 and C18 acids) as the sludge fatty acid profiles generated with various extraction methods were compared with each other and with that of the profile of non-edible-based biodiesel (Ashraful et al., 2014). Mohammad Fauzi and Saidina Amin (2013) reported that palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2), and linolenic acid (C18:3) were the common fatty acids in vegetable oils. Thus, the fatty acids in sludge and vegetable oil could similarly produce biodiesel. Nonetheless, the biodiesel derived from vegetable oil contained the linolenic acid (C18:3) missing from that derived from sludge. Furthermore, the quality of biodiesel and its fuel properties depend strongly on the relative percentage of fatty acid composition in the fuel blend. Sahoo and Das (2009) reported that fuel cetane number, cloud point, and stability increased when saturated fatty acid alkyl ester was introduced into fuel blends. Biodiesel viscosity and freezing point increase with the increase in carbon chain length and decrease with the increase in double bond chains. In the current study, the percentage of unsaturated fatty acid ester in biodiesel produced by the ex-situ transesterification of scum sludge ranged from 57.5% to 64.1%. This range was comparable to the 61% in the
Please cite this article in press as: Wang, Y., et al. Scum sludge as a potential feedstock for biodiesel production from wastewater treatment plants. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.06.036
6
Y. Wang et al. / Waste Management xxx (2015) xxx–xxx
biodiesel derived from soybeans. This percentage may also generate biodiesel with poor oxidation stability and improved cold flow properties (Canakci and Sanli, 2008). Nevertheless, the percentages of unsaturated fatty acid ester in the biodiesel produced through the ex-situ transesterification of primary and secondary sludge were low at 35.3–37.7% and 43.7–46.3% respectively.
3.3. Production of biodiesel from sludge by in-situ transesterification 3.3.1. FAMEs yield from the transesterification of dried sludge An examination of the biodiesel from various sludge types showed that the in-situ conversion of lipids to FAMEs yielded higher overall biodiesel than the ex-situ conversion of lipids to FAMEs did. Fig. 3 depicts the average FAMEs yield through in-situ production from different sludge types. Biodiesel yield was maximized at 22.7% via the in-situ transesterification of scum sludge, followed by those of primary and secondary sludge at 9.0% and 1.9%, respectively. By contrast, the yields of the ex-situ conversion of scum (9.1%), primary (5.0%), and secondary (1.5%) sludge to FAMEs were maximized when the co-solvent ratios were 20:80:0, 60:20:20, and 20:60:20, respectively. Dufreche et al. (2007) yielded 27.4% (w/w dry sludge) lipid after the extraction of lipid from primary and activated sludge, which was obtained from a municipal wastewater treatment plants. Subsequent transesterification of the lipid extracts yielded 4.4% biodiesel (w/w dry sludge). Using sewage sludge obtained from the same WWTPs, Mondala et al. (2009) reported maximum biodiesel yields of 14.5% and 2.5% (w/w dry sludge) via the in situ transesterification of primary and activated sludge, respectively. Moreover, Revellame et al. (2010) obtained a maximum biodiesel yield of 4.79% (w/w dry sludge) from activated sludge under optimum in-situ transesterification conditions. The biodiesel yields obtained in our experiment from primary and secondary (activated) sludge processed through in-situ and ex-situ transesterification were slightly lower than those of the aforementioned studies. Our study differed from the previous ones not only in terms of sludge source origin but also in terms of transesterification conditions. This implied biodiesel yield of 22.7% from scum sludge via in-situ transesterification exceeded the expectation and was a reasonable value. Thus, the results indicated that the overall biodiesel yields of all three sludge types were considerably higher under in situ conversion than under ex-situ conversion. This result agreed with those of previous reports and may be ascribed to the access of the reagents to all lipids in the sludge instead of to the extracted lipids alone.
Fig. 3. FAMEs yield by in-situ production from different sludge types.
3.3.2. FAMEs composition of biodiesel produced by the in-situ transesterification of dried sludge The FAMEs analysis of biodiesel obtained via acid-catalyzed in-situ esterification and the transesterification of dried sludge is presented in Fig. 4. The FAMEs compositions of biodiesel generated by in-situ and ex-situ production were highly similar. The fatty acid profiles in biodiesel produced in situ from primary sludge were sequenced as follows: C16:0 > C18:1 > C18:0 > C18:2 > C16:1 > C14:0. Methyl palmitate, methyl oleate, stearic acid methyl ester, and methyl linoleate accounted for more than 44.6%, 26.3%, 12.0%, and 6.4% of total biodiesel, respectively. These percentages were higher than those in the corresponding composition of biodiesel produced by ex-situ production. On the basis of the content of FAMEs, the percentage of unsaturated fatty acid ester was 38.5%, which was slightly higher than that obtained by ex-situ production. The fatty acid profiles in biodiesel generated in-situ from secondary sludge were sequenced as follows: C16:0 > C16:1 > C18:1 > C18:0 > C18:2 > C14:0. Methyl palmitate remained the dominant component and constituted approximately 38.1% of total biodiesel. The contents of methyl palmitoleate and methyl oleate were very close at approximately 17.5%. The percentage of unsaturated fatty acid ester in FAMEs from secondary sludge was significantly higher (44.4%) than that of unsaturated fatty acid ester in FAMEs derived from primary sludge through in situ production. The fatty acid profiles in biodiesel produced in situ from scum sludge were arranged as follows: C16:0 > C18:1 > C18:2 > C18:0 > C16:1 > C14:0. Methyl palmitate was also the dominant component of the FAMEs and accounted for 37.3% of total biodiesel. Oleate methyl and linoleate methyl were ranked second and third and constituted 30.1% and 15.1%, respectively, of the biodiesel. The total percentage of unsaturated fatty acid ester in FAMEs from scum sludge was 49.1%. In short, the analysis of fatty acid profiles in biodiesel generated in-situ from sludge and indicated that the percentage of unsaturated fatty acid ester in FAMEs from scum sludge was higher than those from primary and secondary sludge. Moreover, the former accounted for one-half of the total esters. 4. Conclusion The paper introduced scum sludge to biodiesel production and compared the biodiesel yield of scum sludge with that of primary and secondary sludge through ex-situ and in-situ production systematically. The results had shown that scum sludge had almost twice calorific value of primary and secondary sludge under freeze-drying. However, all sludge types contained a significant
Fig. 4. FAME composition by in-situ production from different sludge types.
Please cite this article in press as: Wang, Y., et al. Scum sludge as a potential feedstock for biodiesel production from wastewater treatment plants. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.06.036
Y. Wang et al. / Waste Management xxx (2015) xxx–xxx
amount of palmitic acid (C16:0) and oleic acid (C18:1) regardless of the co-solvent used in extraction. Palmitic acid methyl ester was the dominant component in the FAMEs and accounted for approximately 45% and 37% of total biodiesel produced from primary and secondary sludge respectively. However oleic acid methyl ester was the dominant component in the FAMEs produced of scum sludge and constituted more than 35% of total biodiesel. It was also found in this study that the neutral lipid was dominant in scum sludge and the maximum lipid yield accounted for one-third of the dried scum sludge when the extraction was performed with the co-solvent containing a high percentage of hexane (60%). In addition, the percentage variation of unsaturated fatty acid ester in biodiesel by the ex-situ transesterification of scum sludge ranged in 57.5–64.1%, while the equivalent value were 35.25–37.72% and 43.67–46.3% in the biodiesel produced from primary and secondary sludge, respectively, using the same methods. Therefore, the percentage of unsaturated fatty acid ester in the FAMEs from scum sludge accounted for more than one-half of the total esters, which was higher than the equivalent derived from primary and secondary sludge. As for the difference of biodiesel yield by ex-situ and in-situ transesterification, it was obvious that the maximum yield from scum sludge, primary and secondary sludge was 22.7%, 9.0% and 1.9% respectively, which was higher than the corresponding yield gained through ex-situ transesterification. In conclusion, scum sludge was a potential resource for the production of biodiesel, which had a higher calorific value and neutral lipid than that of primary and secondary sludge. The lipid yield accounted for one-third of the dried scum sludge and the maximum yield was 22.7% by in-situ transesterification of scum sludge. Oleic acid methyl ester instead of palmitic acid methyl ester, which was the dominant component in the biodiesel produced from primary and secondary sludge, was the dominant component in the biodiesel produced of scum sludge. Acknowledgements This work was funded by the Education Department of Shaanxi Province [Grant numbers 2013JC20 and 13JS046] and State Key Laboratory of Pollution Control and Resource Reuse Foundation (No. PCRRF14013). The research was also supported by the innovative research team of Xi’an University of Architecture and Technology. The authors wish to express their gratitude to the No. 4 Wastewater Treatment Plant of Xi’an for supporting this study. In addition, we thank reviewers for their valuable suggestions to improve this manuscript. References Andreoli, C.V., Sperling, M.V., Fernandes, F., 2007. Sludge treatment and disposal. Biological wastewater treatment series, vol. 6. IWA Publishing, BeloHorizonte, London, New York Belo Horizonte, Brazil, London, New York. Angerbauer, C., Siebenhofer, M., Mittelbach, M., Guebitz, G.M., 2008. Conversion of sewage sludge into lipids by Lipomyces starkeyi for biodiesel production. Bioresour. Technol. 99, 3051–3056. Ashraful, A.M., Masjuki, H.H., Kalam, M.A., Rizwanul Fattah, I.M., Imtenan, S., Shahir, S.A., Mobarak, H.M., 2014. Production and comparison of fuel properties, engine performance, and emission characteristics of biodiesel from various non-edible vegetable oils: a review. Energy Convers. Manage. 80, 202–228. Barber, W.P.F., 2015. Influence of wastewater treatment on sludge production and processing. Water Pract. Technol. 10, 178–186. Bi, C., Min, M., Nie, Y., Xie, Q., Lu, Q., Deng, X., Anderson, E., Li, D., Ruan, R., 2015. Process development for scum to biodiesel conversion. Bioresour. Technol. 185, 185–193.
7
Canakci, M., Sanli, H., 2008. Biodiesel production from various feedstocks and their effects on the fuel properties. J. Ind. Microbiol. Biotechnol. 35, 431–441. Carucci, G., Carrasco, F., Trifoni, K., Majone, M., Beccari, M., 2005. Anaerobic digestion of food industry wastes: effect of codigestion on methane yield. J. Environ. Eng. 131, 1037–1045. Chipasa, K.B., Medrzycka, K., 2006. Behavior of lipids in biological wastewater treatment processes. J. Ind. Microbiol. Biotechnol. 33, 635–645. Chipasa, K.B., Medrzycka, K., 2008. Characterization of the fate of lipids in activated sludge. J. Environ. Sci. (China) 20, 536–542. Devereaux, C., Lee, H., 2009. Biofuels and certification. A Workshop at the Harvard Kennedy School of Government. Summary Report. Dufreche, S., Hernandez, R., French, T., Sparks, D., Zappi, M., Alley, E., 2007. Extraction of lipids from municipal wastewater plant microorganisms for production of biodiesel. J. Am. Oil Chem. Soc. 84, 181–187. Durand, C., Ruban, V., Ambles, A., Oudot, J., 2004. Characterization of the organic matter of sludge: determination of lipids, hydrocarbons and PAHs from road retention/infiltration ponds in France. Environ. Pollut. 132, 375–384. Haas, M., Scott, K., Foglia, T., Marmer, W., 2007. The general applicability of in situ transesterification for the production of fatty acid esters from a variety of feedstocks. J. Am. Oil Chem. Soc. 84, 963–970. Huynh, L.H., Kasim, N.S., Ju, Y.H., 2010. Extraction and analysis of neutral lipids from activated sludge with and without sub-critical water pre-treatment. Bioresour. Technol. 101, 8891–8896. Jarde, E., Mansuy, L., Faure, P., 2005. Organic markers in the lipidic fraction of sewage sludges. Water Res. 39, 1215–1232. Kargbo, D.M., 2010. Biodiesel production from municipal sewage sludges. Energy Fuels 24, 2791–2794. Li, M., Xiao, B., Wang, X., Liu, J., 2015. Consequences of sludge composition on combustion performance derived from thermogravimetry analysis. Waste Manage. 35, 141–147. Long, J.H., Aziz, T.N., Reyes III, F.L.d.l., Ducoste, J.J., 2012. Anaerobic co-digestion of fat, oil, and grease (FOG): a review of gas production and process limitations. Process Saf. Environ. Prot. 90, 231–245. Luostarinen, S., Luste, S., Sillanpaa, M., 2009. Increased biogas production at wastewater treatment plants through co-digestion of sewage sludge with grease trap sludge from a meat processing plant. Bioresour. Technol. 100, 79– 85. Marufuzzaman, M., Eksßiog˘lu, S.D., Hernandez, R., 2014. Environmentally friendly supply chain planning and design for biodiesel production via wastewater sludge. Transp. Sci. 48, 555–574. Meng, X., Yang, J., Xu, X., Zhang, L., Nie, Q., Xian, M., 2009. Biodiesel production from oleaginous microorganisms. Renew. Energy 34, 1–5. Mohammad Fauzi, A.H., Saidina Amin, N.A., 2013. Optimization of oleic acid esterification catalyzed by ionic liquid for green biodiesel synthesis. Energy Convers. Manage. 76, 818–827. Mondala, A., Liang, K., Toghiani, H., Hernandez, R., French, T., 2009. Biodiesel production by in situ transesterification of municipal primary and secondary sludges. Bioresour. Technol. 100, 1203–1210. Olkiewicz, M., Fortuny, A., Stüber, F., Fabregat, A., Font, J., Bengoa, C., 2015. Effects of pre-treatments on the lipid extraction and biodiesel production from municipal WWTP sludge. Fuel 141, 250–257. Pastore, C., Lopez, A., Mascolo, G., 2014. Efficient conversion of brown grease produced by municipal wastewater treatment plant into biofuel using aluminium chloride hexahydrate under very mild conditions. Bioresour. Technol. 155, 91–97. Ramos, M.J., Fernández, C.M., Casas, A., Rodríguez, L., Pérezángel, 2009. Influence of fatty acid composition of raw materials on biodiesel properties. Bioresour. Technol. 100, 261–268. Revellame, E., Hernandez, R., French, W., Holmes, W., Alley, E., 2010. Biodiesel from activated sludge through in situ transesterification. J. Chem. Technol. Biotechnol. 85, 614–620. Sahoo, P.K., Das, L.M., 2009. Process optimization for biodiesel production from Jatropha, Karanja and Polanga oils. Fuel 88, 1588–1594. Samolada, M.C., Zabaniotou, A.A., 2014. Comparative assessment of municipal sewage sludge incineration, gasification and pyrolysis for a sustainable sludgeto-energy management in Greece. Waste Manage. 34, 411–420. Sangaletti-Gerhard, N., Cea, M., Risco, V., Navia, R., 2015. In situ biodiesel production from greasy sewage sludge using acid and enzymatic catalysts. Bioresour. Technol. 179, 63–70. Tao, L., Aden, A., 2009. The economics of current and future biofuels. In Vitro Cell. Dev. Biol.-Plant 45, 199–217. Wiltsee, G., 1998. Waste grease resource in 30 US metropolitan areas. In: The Proceedings of Bioenergy 98 Conference, Wisconsin, pp. 956–963. Woon, K.S., Lo, I.M.C., 2014. Analyzing environmental hotspots of proposed landfill extension and advanced incineration facility in Hong Kong using life cycle assessment. J. Clean. Prod. 75, 64–74.
Please cite this article in press as: Wang, Y., et al. Scum sludge as a potential feedstock for biodiesel production from wastewater treatment plants. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.06.036
