Enhancement of co-conversion of endogenous carbon and nitrogen of dairy wastewater in mesophilic hydrolysis-acidification coupled microalgae culture system by rhamnolipid

In order to evaluate the efficiency of co-conversion of endogenous carbon and nitrogen of dairy wastewater in mesophilic hydrolysis-acidification coupled microalgae culture system by rhamnolipid (RL), the effects of RL dosages on the coupled system were investigated. RL can significantly increase volatile fatty acids (VFAs) production in hydrolysis-acidification liquor (HAL) (maximum VFAs production reached 11,484.38 mg COD/L in 2.5 g/L RL test at 144 h). A macrogenome sequencing revealed that the proportion of acidobacteria increased with the increasing dosage of RL. Furthermore, the effect of RL enhanced HAL on microalgae (Chlorella pyrenoidosa) growth, nutrient removal of the microalgae culture system were investigated. The harvested biomass concentration, the removal rates of ammonia nitrogen (NH4+-N), chemical oxygen demand (COD) were positively correlated with RL dosage. The maximum removal rates of NH4+-N (98.10%), COD (76.17%) which higher than those of the control (77.27% and 59.44%, respectively) were recorded. Furthermore, protein, carbohydrates, and higher heating value (HHV) outputs were also enhanced by RL treatment. More in-depth analysis found that, compared with the control test, RL can exactly enhance the endogenous C, N assimilation, the maximum promotion rates of C and N assimilation yield can reach 156% and 145%.