Nutrient removal and microbial communities' development in a young unplanted constructed wetland using Bauxsol™ pellets to treat wastewater

Municipal wastewater was treated over a six month period in an unplanted constructed wetland with a lower soil layer and an upper Bauxsol™ pellet layer. The interactions between Bauxsol™ pellets, soil, effluent and microbial communities demonstrated a positive influence on contaminant removal. Bauxsol™ treated effluent showed > 95% phosphate removal and ~ 26% nitrogen removal during the trial. Substantial quantities of nitrate, trace-metals and Colwell P were bound to the pellets, whereas only ammonium was bound to the soil. The structure of microbial communities analysed by denaturing gradient gel electrophoresis (DGGE) showed distinct bacterial communities attached to Bauxsol™ pellets and soil owing to differences in geochemistry and micro-environmental conditions. Polymerase chain reaction (PCR) amplification of specific marker genes (i.e. bacterial and archaeal amoA genes, nosZ gene, and hzo gene) was used to evaluate the presence of microbial communities associated with nitrogen transformation. Data revealed the co-existence of aerobic ammonia-oxidising bacteria, anaerobic ammonia-oxidising bacteria (anammox) and denitrifiers attached to Bauxsol™ pellets and ammonia-oxidising bacteria and archaea attached to soil. This study successfully demonstrates that Bauxsol™ pellets are a suited alternative media for constructed wetland to treat wastewater effectively removing phosphate and serving as biomass support particles for bacterial communities associated with nitrogen-cycling.