Study on the effect of ratio of microalgae Chlorella sp. and activated sludge to remove nutrients and organic matter for low C/N wastewater

Abstract

Microalgae and activated sludge were co-cultured in photobioreactor (PBR) systems with different ratios (1:0, 3:1, 1:1, 0:1 wt/wt) to determine an optimal ratio for organic matter and nutrient removal. The results showed that the PBR systems at 1:0 and 3:1 ratios have higher total nitrogen (TN) removal rates than at two others. The highest TN removal at the ratio of 1:0 achieved 96% and at the ratio 3:1 achieved 90% after six days of operation. In addition, the single-microalgae culture and co-culture microalgae-activated sludge systems had higher TP removal than that in the single-activated sludge one. The highest TP removal of 98.8% was achieved at 1:0 ratio after nine days. The 3:1 and 1:1 ratios had significantly higher COD removal rates than the other ratios with 131 mg/l/d and 118 mg/l/d, respectively. After four days of operation, the 3:1 ratio reached the highest specific removal rate of 132.7 mg/l/d.  This study showed that the 3:1 ratio of microalgae co-culture and activated sludge is an optimal ratio for wastewater treatment-based microalgae application.