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The growth of mineral crystals on surfaces is a challenge across multiple industrial processes. Membrane-based desalination processes, in particular, are plagued by crystal growth (known as scaling), which restricts the flow of water through the membrane, can cause membrane wetting in membrane distillation, and can lead to the physical destruction of the membrane material. Scaling occurs when supersaturated conditions develop along the membrane surface due to the passage of water through the membrane, a process known as concentration polarization. To reduce scaling, concentration polarization is minimized by encouraging turbulent conditions and by reducing the amount of water recovered from the saline feed. In addition, antiscaling chemicals can be used to reduce the availability of cations. Here, we report on an energy-efficient electrophoretic mixing method capable of nearly eliminating CaSO4 and silicate scaling on electrically conducting membrane distillation (ECMD) membranes. The ECMD membrane material is composed of a percolating layer of carbon nanotubes deposited on porous polypropylene support and cross-linked by poly­(vinyl alcohol). The application of low alternating potentials (2 Vpp,1Hz) had a dramatic impact on scale formation, with the impact highly dependent on the frequency of the applied signal, and in the case of silicate, on the pH of the solution.

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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].