EXPERIMENTAL INVESTIGATION OF BIODEGRADATION OF SYNTHETIC WASTEWATER IN AN ANAEROBIC TANK REACTOR USING MICROALGAE

Abstract

The objective of this study was to investigate the viability of microalgae biomass (Chlorella vulgaris) as a substrate for anaerobic digestion using synthetic wastewater as well as evaluate the biogas production improvement and the microalgae cultivation rate. The experimental procedure lasted for 700 hours, where a mixture of synthetic wastewater and microalgae were used in the BE4 anaerobic tank reactor. Based on the process parameters (pH and temperature), the degradation phases (hydrolysis, acidogenesis (fermentation acidification), acetogenesis, methanogenesis) were successfully separated from each other. A drop in pH was detected from 7 to 4.5 in the acidogenesis phase, which resulted in a delayed decrease in the total chlorophyll concentration and the microalgae activity rate. In the methanogenesis phase, the pH slightly returned to neutral and caused a relatively low biogas yield (0.15 L in total), which can be explained by the unbalanced carbon/nitrogen rate (C : N) in relation to the substrate. The increase in total chlorophyll concentration was observed by the end of the process as a result of the increasing pH. It was found, that the concentration of major chemical constituents and the COD can be described well by logarithmical curves according to the nutrient consumption of microalgae. The COD decreased from the initial value of 5077 mg·L-1 O2 to 1592 mg·L-1 O2, which refers to anintensive anaerobic degradation process.

Keywords

• anaerobic degradation
• wastewater
• microalgae
• tank reactor
• water quality
• biogas