What if we make fuel oil from our sanitary sewage? The ramifications of this question posed a decade ago turned out in various research areas such as resource recovery, wastewater treatment, chemical reaction engineering, catalysis, bioprocessing, separation processes, modeling-simulation, systems integration, and supply chain. The enhancement and extraction of oil from microbial consortia of activated sludge (AS) generated by wastewater treatment facilities have been studied with the potential as viable platform for organic waste-to-fuels and organic waste-to-chemicals transformation. The fundamental principles of this technology emulate the principles of single cell oil technology and resource recovery from wastewater treatment. The technology was established in 2005 through a project on biodiesel and value-added chemicals extraction from wastewater sludges [1]. Significant amounts of AS microbial oil were extracted and trans-esterified to biodiesel [2], but the enhancement of oil content is needed to make the technology economically feasible [3]. The oil content of AS was then enhanced using the principles of single cell oil technology in which high carbon to nitrogen ratio (mole C/mole N) triggers generation of structural lipids (phospholipids, sphingolipids, etc.) and reserve lipids (mainly TAGs) [4]. With sugars such as glucose and xylose as model carbon sources, researchers established that activated sludge oil can be enhanced and that the microbial process has similar microbial kinetics to that of a single cell oil accumulation [5, 6]. The commercialization of the aerobic lipid accumulation by AS, however, is challenged by the relatively high cost of the typical sugar substrates glucose and xylose. Several studies explored alternative carbon sources for microbial lipid accumulation and suggested the use of short chain fatty acids (SCFAs) such as acetic acid, propionic acid and butyric acid as substrates [7, 8]. These SCFAs are considered cost-effective because they are intermediate compounds in anaerobic digestion, a common wastewater treatment process [9]. Recent studies indicated that the microbial consortia of AS feeding on acetic acid (an SCFA) can accumulate lipids [10, 11]. This talk assesses the maturity of the technology in terms of the findings and the pertinent questions yet to be answered. On-going studies are also presented in order to set the immediate directions of some active research paths.
[1] Zappi ME, French WT, Hernandez R, Dufreche ST, Sparks DJ. Production of biodiesel and other valuable chemicals from wastewater treatment plant sludges Mississippi State University, US Patent, 2009.
[2] Dufreche S, Hernandez R, French T, Sparks D, Zappi M, Alley E. Journal of the American Oil Chemists' Society 2007;84(2):181-187.
[3] Mondala A, Liang K, Toghiani H, Hernandez R, French T. Bioresource Technol. 2009;100(3):1203-1210.
[4] Papanikolaou S, Aggelis G. European Journal of Lipid Science and Technology 2011;113(8):1031-1051.
[5] Mondala A, Hernandez R, Holmes W, French T, McFarland L, Sparks D, Haque M. AICHE J. 2013;59(11):4036-4044.
[6] Mondala AH, Hernandez R, French T, McFarland L, Santo Domingo JW, Meckes M, Ryu H, Iker B. AICHE J. 2012;58(4):1279-1290.
[7] Fei Q, Chang HN, Shang L, Choi J-d-r, Kim N, Kang J. Bioresource Technol. 2011;102(3):2695-2701.
[8] Fontanille P, Kumar V, Christophe G, Nouaille R, Larroche C. Bioresource Technol. 2012;114:443-449.
[9] Chang HN, Kim N-J, Kang J, Jeong CM. Biotechnol. Bioprocess Eng. 2010;15(1):1-10.
[10] Fortela DL, Hernandez R, French WT, Zappi M, Revellame E, Holmes W, Mondala A. Renew. Energ. 2016;96, Part A:11-19.
[11] Fortela DL, Hernandez R, Zappi M, WT French, Bajpai R, Chistoserdov A, Revellame E, Holmes W. J. Bioprocess. Biotech. 2016;6(4):275.
