Effect of HRTs of Wastewater After Anaerobic Digestion on Growth of Desmodesmus sp.

Abstract.

Current thesis used the anaerobic digested wastewater (ADW) to cultivate Desmodesmus sp. to find a proper concentration of ADW and hydraulic retention time (HRT) in a semi-continuous cultivation. The optimal concentration of wastewater to accumulate biomass was 5%, where the dry cell weight of Desmodesmus sp. was 0.382 g/L, biomass productivity was 27.28 mg/L/d. Lipid content was 18.54%~20.96%, decreased with higher biomass accumulation. Untreated wastewater was used to cultivate microalgae in semi-continuous mode where HRT was set as 3, 5 and 7 days. After 22 days of cultivation, higher dry cell weight was observed in longer HRT. The biomass productivity was among 50~87 mg/L/d, which was 2 times as much as that cultivated in batch mode. Lipid content was 17.61%~21.80% and lipid productivity was 8.96~18.97mg/L/d, which both decreased with longer HRT. Less than 50% of TAN was utilized in semi-continuous cultivation, leading to higher quality of effluent in longer HRT system. Components of harvested algae were tested which showed that ash content (1.42%~2.86%), and protein content (10.57%~22.57%) decreased with long HRT, while polysaccharides (13.26%~16.45%) increased with HRT. In conclusion, proper HRT can be chosen from practical concern.