The effects of carbon nitrogen ratio and salinity on the treatment of swine digestion effluent simultaneously producing bioenergy by microalgae biofilm

In order to remove high concentrations of ammonia nitrogen (NH4+-N) and refractory sulfamethazine (SM2) from swine digestion effluent, different carbon/nitrogen (C/N) ratios and salinity were used to determine the effects of pollutants removal in the microalgae biofilm system. Microalgae biofilm treatment under optimal environmental conditions in synthetic swine digestion effluent were C/N ratio of 20 and salinity of 140 mM. In order to make the actual swine digestion effluent discharge up to the standard, three different two-cycle treatments (suspended microalgae, microalgae biofilm, microalgae biofilm under the optimal conditions) were studied. The results showed that after two-cycle treatment with microalgae biofilm under the optimal conditions, the actual swine digestion effluent levels of total nitrogen (TN), NH4+-N, total phosphorus (TP), chemical oxygen demand (COD), SM2 were 22.65, 9.32, 4.11, 367.28, and 0.99 mg L-1, respectively, which could satisfy the discharge standards for livestock and poultry wastewater in China. At the same time, first-order kinetic simulation equations suggested a degradation half-life of 4.85 d for SM2 under optimal conditions in microalgae biofilm, and microbial community analysis indicated that the dominant genus was Halomonas. Furthermore, 35.66% of lipid, 32.56% of protein and 18.44% of polysaccharides were harvested after two-cycle in microalgae biofilm treatment under optimal environmental conditions. These results indicated that the regulation of C/N and salinity in microalgae biofilm for the treatment of swine digestion effluent was a high-efficiency strategy to simultaneously achieve wastewater treatment and bioenergy production.