Coupling FeMgAl-LDH and sludge biofilm for simultaneous and effective removal of nitrate and ammonium in water

The existence of redundant nitrate (NO3−) and ammonium (NH4+) in water caused negative impacts on the ecosystem's stability while the simultaneous removal of these nitrogenous substances has become a challenging task. The intimately coupled photocatalysis and biodegradation (ICPB) system has shown great potential in the efficient removal of aquatic pollutants. In this study, the FeMgAl layered double hydroxide (FeMgAl-LDH) capable of removing NO3− and NH4+ concurrently through adsorption and photocatalysis was successfully synthesized based on the hydrothermal method. The characterization of the material has verified its lamellar structure and the inclusion of metal oxide phases. Then, the ICPB system was constructed by coupling FeMgAl-LDH and biofilm from activated sludge onto a polyurethane carrier. After 12-hour water treatment, the ICPB system could realize 54.45 % and 42.57 % of the NO3− and NH4+ removal rates at a pH of 7 and dissolved oxygen (DO) of 2 mg/L, which was superior to the single photocatalysis and biological treatment. The removal performances of the ICPB system under different pH and DO levels were assayed. Meanwhile, microbial activities, community variation, and relational genes were studied to analyze the microbial mechanisms. The microorganisms in the ICPB system possessed high activity to form extracellular polymeric substances (EPSs), nitrogen transformation, and electron transfer. In all, this study constructed a new ICPB system and revealed its mechanism to simultaneously remove the NO3− and NH4+ from the water.