Development and characteristics of microalgae-bacteria aerobic granules treating low strength municipal wastewater

Abstract

This study aims to assess the feasibility of cultivating microalgae-bacteria aerobic granular sludge using low-strength municipal wastewater (<200 mg COD/L) as a substrate. A laboratory-scale photo-sequencing batch reactor was inoculated with activated sludge and fed with municipal wastewater. The development and characteristics of microalgae-bacteria aerobic granular sludge were observed for 90 days. The average COD removal efficiency of this system was 71%. The granulation process was observed to occur on day 28, indicated by a high biomass accumulation and decreasing sludge volume index (SVI). After 90 days of cultivation, MLSS value was found to be 3.7 g/L and SVI30 at 18.9 mL/g. In addition, the diameter of the granules was significantly increased. Mature microalgae-bacteria aerobic granules were developed with an average and a maximum diameter of 0.65 mm and 6 mm, respectively. Moreover, cocci-shaped bacteria and microalgae cells were observed to reside on the granular surface during observation using field emission scanning electron microscopy (FESEM). The granules exhibited an excellent settling velocity at 80 m/h. The findings suggest the possibility of using low-strength wastewater to develop microalgae-bacteria aerobic granular sludge.