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

Abstract

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 (F_v/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.