Characterization and Recovery of In Situ Transesterifiable Lipids (TLs) as Potential Biofuel Feedstock from Sewage Sludge Obtained from Various Sewage Treatment Plants (STPs)

Abstract

This study purposed to characterize the sewage sludge from various sewage treatment plants (STPs) as a biodiesel feedstock. Crude biodiesel was produced from each dried primary sludge (PS) and waste activated sludge (WAS) via in situ transesterification process. The average yield of transesterifiable lipid (TL) was 77.8% and 60.4% of the total lipid content from PS and WAS, respectively. The TL yield had a greater margin among WAS than PS samples due to differences in the biological processes adopted in each treatment plant. The TL recovered from PS and WAS contained 54.2% and 40.1% fatty acid methyl esters (FAMEs), respectively, which were mostly made up of palmitic acid (C16:0) and stearic acid (C18:0). The FAME composition of the biodiesel in the WAS sample was highly associated with a microbial community that grows otherwise, depending on the purpose of the biological treatment process. In particular, the increase in the proportion of nitrifying bacteria that grow predominantly under a relatively longer solid retention time (SRT) contributed significantly to the improvement in FAME content.Energies 2019, 12, 3952 2 of 12 fuel with potential for use in vehicles [6][7][8][9]. Sewage sludge, represented by primary sludge (PS) and waste activated sludge (WAS), has many benefits as a biodiesel feedstock; it is a low-cost feedstock, with abundant and consistent generation during sewage treatment, and the lipid content (necessary for conversion to fuel) in both types of sewage sludge is significant [9]. Sewage sludge as an alternative feedstock could contribute to drastically reducing the material costs of biodiesel production which account for 70-85% of the overall cost [10]. In addition, the generation of sewage sludge is plentiful and consistent on a yearly basis; thus, it can stably supplement the lack of feedstock for biodiesel. Assuming that biodiesel is produced from the total amount of sewage sludge, biodiesel production is estimated to be more than three times the current capacity in the US [11]. Various lipids, including fats, oil, and fatty acids, present in the sewage sludge are biodiesel precursors. The triglycerides (TG) and phospholipid fatty acids (PLFAs), which are the predominant lipids of sewage sludge, can be converted to biodiesel via transesterification (Equations (1) and (2)). Furthermore, PS and WAS contain 5-36% and 2-20% free fatty acids (FFAs), respectively [12,13]. The sewage sludge FFAs are also convertible to fatty acid methyl esters (FAMEs) via acid-catalyzed esterification [14].

Stimulation of Lipid Extraction Efficiency from Sewage Sludge for Biodiesel Production through Hydrothermal Pretreatment

“…The lipid recovery efficiency can vary due to the characteristics of sludge and the type of treatment plant. The observed lipid recovery efficiency is comparable to the efficiencies reported in previous studies [3,6,7,18]. Solvents with a high polarity are required to rupture the phospholipid layer and release the lipid drops.…”

“…Consequently, the calorific value of the solid by-products decreased due to the lipid extraction, but this was supplemented by hydrothermal carbonization. (2) Gobitz et al, 1999 [30]; (3) this study.…”

“…In particular, the main component of animal oil-derived biodiesel consists of saturated fatty acids such as C16 (palmitic acid) and C18 (stearic acid), and vegetable oil-derived biodiesel contains a large number of unsaturated fatty acids such as C16:1 (palmitoleic acid), C18:1 (oleic acid), and C18:2 (linoleic acid) [29]. The composition of individual FAMEs is an important factor in determining the fuel characteristics of biodiesel, such as combustion rate, ignition temperature, fluidity, and viscosity [3]. Although large amounts of saturated FAMEs found in animal fats have a high combustion rate, they can degrade the quality of biodiesel by reducing the fluidity.…”

“…Sewage sludge is a pollutant that affects human health and must be disposed of in an environmentally sound manner [1,2]. However, in recent years sewage sludge has gained attention as a promising source for biofuel production [3]. Many studies have suggested anaerobic digestion or fermentation and the direct use (through incineration after drying) of sewage sludge [4], but the low biological conversion efficiency and high energy consumption during sewage sludge drying are drawbacks of these methods.…”

Preparation and Selective Adsorption Performance of the Carboxymethyl Salix psammophila Wood Powder-Imprinted Membrane for Tetracycline

“…With the progress of human science and technology and the rapid development of the medical field, a large variety of wastewater has been produced . Among these, antibiotic wastewater has garnered significant attention in recent years.…”