Mariculture wastewater treatment using electroactive bacteria-algae biofilm coupled with siphon aeration

High-density marine aquaculture has been one of the most important ways to develop the marine economy. However, the difficult treatment of high-salinity aquaculture wastewater has restricted the marine aquaculture industry. Particularly, salinity has a significant effect on the microbial activity. Marine microorganisms can be expected to degrade the pollutants in high-salinity aquaculture wastewater. Nevertheless, it is still lacking on the large-scale marine microorganisms to treat marine aquaculture water. The main bottleneck of treatment can be attributed to the low growth and metabolism efficiency of marine microorganisms. Fortunately, the constructed wetland coupled microbial fuel cell process (CW-MFC) has been widely used in the treatment of freshwater aquaculture wastewater. CW-MFC can also make full use of membrane hanging, filtration and adsorption in constructed wetlands, combing with the electrochemical process and electrochemical microbial degradation. The efficient treatment can realize the low carbon and nitrogen ratio of aquaculture wastewater. However, the treatment of mariculture wastewater focused mainly on the membrane attachment, treatment performance, and microbial flora analysis of CW-MFC. In this study, the electroactive bacterial-algal biofilm was coupled with siphon aeration tidal current in the lab scale, in order to improve the efficiency of CW-MFC treating mariculture aquaculture wastewater. The results showed that the removal efficiencies of chemical oxygen demand, total phosphorus, ammonia nitrogen, nitrate nitrogen, nitrite nitrogen, total nitrogen, sulfamethoxazole and copper ion (Cu²⁺) in the CW-MFC by electroactive bacterial-algal biofilm and siphon aeration tidal current reached 83.49%, 93.56%, 91.26%, 96.54%, 86.11%, 92.03%, 99.25% and 98.58%, respectively. Compared with the CW-MFC group, the removal efficiency of the above pollutants increased by 33.46, 31.07, 17.44, 26.77, 16.7, 25.64, 12.83 and 25.87 percentage points, respectively. Muricauda(10.86%), Xanthomarina (10.62%) and other marine salt-tolerant bacteria in the microbial community were significantly improved under a high salt environment in the adaptation system. The electroactive microorganism (such as Geobacteraceae (10.43%) and Pseudomonas (4.12%)) and marine microalgae bacteria (such as Pseudooceanicola (12.45%) and Hoeflea (7.45%)) were highly enriched after enhancement, which promoted the electron transfer efficiency and metabolic rate, accelerating degradation of antibiotics and heavy metals. Aeration also improved the microbial activity. Siphon aeration reduced the energy loss for a better aerobic and anaerobic alternating environment, in order to ensure the reoxidation and reduction reaction, which promoted the microbial nitrification and denitrification, while the removal efficiency of microbial nitrogen and phosphorus, and the degradation efficiency of organic matter. Therefore, the electroactive biofilms coupled with the siphon aeration technique in CW–MFC can be expected to accelerate the formation of electroactive biofilm and microbial processes, such as nitrification while saving energy. The findings can provide the theoretical and technological reference for the mariculture wastewater treatment.