Submerged attached-growth reactors as lagoon retrofits for cold-weather ammonia removal

Ammonia is one component of wastewater that needs to be removed before releasing the treated water to lakes and rivers due to its toxicity to aquatic organisms. Regulation agencies have started to pass more stringent limits on the allowable amount of ammonia released to natural waters in an effort to protect recreation and aquatic life. Large scale wastewater treatment facilities use a variety of biological methods to meet permitted ammonia limits. However, these methods typically cannot be applied in small wastewater systems, many of which operate lagoons. Additionally, biological ammonia removal is severely limited by cold-temperature which further hinders ammonia removal in lagoons. There is a need for lagoon retrofits for cold-weather ammonia removal. To support small scale wastewater treatment we investigated one lagoon retrofitted with submerged attached-growth reactors (SAGRsTM), reactors that contain attachment media submerged in wastewater and are continuously aerated. This study used historical data to analyze SAGR effectiveness and sizing. We found that SAGRs were an effective lagoon retrofit but should be reduced in size in future systems to minimize construction and maintenance costs while still effectively removing ammonia. We also collected wastewater and biofilm samples from a SAGR to investigate what process contributed to the system success. We found that increasing the amount of ammonia entering the SAGR before winter helped stimulate ammonia removal during limiting temperature conditions and that the attached-growth system selected for a diverse microbial community. This work suggests that SAGRs be used to retrofit lagoons struggling to meet cold-weather ammonia permit limits.