(646a) Waste Activated Sludge Valorization for Short-Chain Fatty Acids Production By Integrated Electro-Alkaline Treatment

A significant amount of waste activated sludge (WAS) is generated during the wastewater biological treatment process, which needs to be properly treated before disposal. The disposal cost of WAS approximately accounts for 50–60% of the total operation cost of a wastewater treatment plant. Due to the increase in wastewater treatment capacity, the disposal of a huge volume of WAS has become a serious environmental and economic issue. On the other hand, WAS has been considered as a sustainable resource owing to a high organic matter content (>40%, consist of mostly proteins and carbohydrates) with an average calorific value of 6094 kcal/kg. Therefore, harnessing bioenergy from WAS could simultaneously address environmental and economic concerns imposed by the growing amount of WAS.

Short-chain fatty acids (SCFAs) (e.g., acetic acid, propionic acid, butyric acid, etc.) are the intermediate chemicals in anaerobic digestion. SCFAs are more valuable (600-3815$/ton) than biogas (150$/ton) and need shorter retention time (< 2d). The production of SCFAs from waste activated sludge has attracted growing attention in wastewater treatment plants (WWTPs) because SCFAs could be utilized for a wide range of applications including biohydrogen production, bioplastics (polyhydroxyalkanoate (PHA)), and biological removal of nutrients from wastewater.

It has been confirmed that electrochemical treatment is a powerful and environment-friendly pathway to disrupt sludge floc and sludge disintegration to produce SCFAs through oxidation of the complex organic compounds on the surface of the electrode. On the other hand, it has been reported that SCFAs production at alkaline pH was significantly higher than that at neutral or acidic pH because the alkaline medium is more favorable for protein and carbohydrate destruction. Moreover, it results in increased SCFA accumulation by mitigating the methanogenesis reactions.

In this study, the combined alkaline-electrochemical treatment was utilized in a single chamber electrolysis cell at low operating temperatures (22-55 °C) to investigate the synergetic effect of alkaline and electrochemical treatment on the solid reduction and SCFAs production. The effect of applied potential, electrode materials, operating temperature, and alkaline agent concentration on SCFAs production was evaluated. The sludge solid before and after treatment was characterized by thermogravimetric analysis (TGA), Scanning electron microscope (SEM), and elemental analysis techniques. The liquid filtrate after treatment was analyzed with gas chromatography- flame ionization detector (GC-FID) to evaluate the SCFAs concentration. In this presentation, the results from this work will be provided including volatile solid removal, SCFAs concentration, and solid residue characterization.