Lighting strategy drives removal of ammonia nitrogen and phosphate in microalgae-bacteria consortia under tetracycline hydrochloride exposure

Microalgae and bacteria interactions play an important role in nutrient absorption and utilization. Lighting strategies are extremely crucial factors for the interaction of microalgae-bacteria consortia for the deep treatment of swine wastewater containing antibiotics. In this study, a co-culture system of Chlorella sorokiniana and Paracoccus pantotrophus was constructed to explore the effects of lighting strategy and tetracycline hydrochloride (TCH) on ammonia nitrogen (NH4+-N) and phosphates removal. The results showed that the co-culture system overtly increased the removal of NH4+-N and phosphate, with the maximum removal efficiencies of 85.75 % and 75.5 %, respectively. The photosynthetic activity (Fv/fm) of C. sorokiniana in the co-culture system was measured by a handheld algal fluorescence meter, and the value increased from 0.47 to 0.61 in comparison to the monoculture. Under complete darkness, the NH4+-N removal efficiency was only 67.46 %, while the light/dark ratio increase from 12:12 to 24:0 promoted the NH4+-N removal efficiency to a maximum of 87.66 %. Meanwhile, the activities of glutamate synthase (GS) and glutamine synthetase (GOGAT) assayed according to the enzyme activity detection kit were the highest with 8696 and 411 U/g prot, respectively. When TCH concentration increased from 0.5 to 2.0 mg/L, the NH4+-N removal efficiency decreased from 84.07 % to 71.48 %, which might be due to the toxic effect of TCH on bacteria, leading to a decrease in the activities of GOGAT and GS in the co- culture system. In addition, the co-culture system also had a well removal on TCH, with the maximum removal efficiency reaching 93.33 %. The co-culture system performed well in the removal of pollutants (NH4+-N, PO4+-P and TCH), which provided a feasible and sustainable technology for the advanced treatment of swine wastewater.