Nitrogen removal and changes to microbial communities in model flood/drain and submerged biofilters treating aquaculture wastewater

Abstract

This study investigated nitrogen removal from aquaculture wastewater in laboratory-scale biofilters treating saline aquaculture wastewater. Alongside the monitoring of water chemistry, changes to the total bacterial communities and ammonia oxidizing bacterial (AOB) communities were characterised using DNA based techniques. Three replicate flood/drain biofilters were compared with three replicate submerged biofilters under different treatments. Performance of a combined flood/drain and submerged biofilter was also investigated. No difference in nitrogen removal was seen between submerged and flood/drain biofilters when water had a single passage. However, when wastewater was recirculated, more organic nitrogen and ammonia removal, but less nitrate and nitrite removal, was observed in the flood/drain wetlands compared with the submerged biofilters. Terminal restriction fragment length polymorphism (T-RFLP) analysis revealed a greater degree of similarity among bacterial communities from the submerged biofilters than the flood/drain biofilters. AOB communities in the flood/drain biofilters were dominated by bacteria belonging to the Nitrosomonas aestuarii/Nitrosomonas marina lineage. The dominant nitrifier in the submerged biofilters could not be identified by T-RFLP.