Electrochemical Valorization of Waste Activated Sludge for Short-Chain Fatty Acids Production

Abstract

During the wastewater biological treatment process, a significant amount of waste activated sludge (WAS) is produced, which must be properly treated before disposal. The cost of WAS disposal accounted for nearly 50–60% of a wastewater treatment plant’s operating costs. The disposal of a large amount of WAS has become a serious environmental and economic problem as wastewater treatment capacity has increased. Furthermore, WAS has been considered as a sustainable resource due to a high organic matter content (>40%, mainly proteins, and carbohydrates) with an average calorific value of 6094 kcal/kg. As a result, harnessing bioenergy from WAS could resolve both environmental and economic issues raised by the growing amount of WAS.The intermediate chemicals in anaerobic digestion are short-chain fatty acids (SCFAs) (e.g., acetic acid, propionic acid, butyric acid, etc.). SCFAs are more beneficial (600-3815$/ton) than biogas (150$/ton) and produced in a shorter period (less than 2d). SCFAs production from waste activated sludge is getting popular in wastewater treatment plants (WWTPs) because SCFAs can be used for a variety of applications, including biohydrogen production, bioplastics (polyhydroxyalkanoate (PHA), and biological nutrient removal.Electrochemical treatment has been shown to be a powerful and environmentally friendly method of disrupting sludge floc and sludge disintegration to create SCFAs by oxidizing complex organic compounds on the electrode surface. On the other hand, the alkaline pH is more favorable for protein and carbohydrate destruction which results in a substantial increase in SCFAs production. Furthermore, methanogenesis reactions are mitigated in alkaline media, so that more SCFAs accumulate as a final product.In this study, the electrochemical treatment under an alkaline environment was utilized in a single chamber electrolysis cell at low operating temperatures (25-55 °C) to achieve solid reduction and SCFAs production. The effect of the operating condition such as applied potential, electrode materials, operating temperature, and alkaline agent concentration on SCFAs production was investigated. The waste activated sludge solid before and after treatment was characterized by thermogravimetric analysis (TGA), Scanning electron microscope (SEM), and elemental analysis techniques. The supernatant liquid after electrochemical treatment was evaluated with gas chromatography- flame ionization detector (GC-FID) to analyze the SCFAs concentration. In this presentation, the results from this research study will be provided including volatile solid removal, SCFAs concentration, and solid residue characterization.