Impacts of ammonia loading and biofilm age on the prevalence of nitrogen-cycling microorganisms in a full-scale submerged attached-growth reactor.

This study reports the impacts of seasonal ammonia load changes and biofilm age on the quantity of biomass and on the prevalence of ammonia- and nitrite-metabolizing organisms within a submerged attached-growth reactor (SAGR™) following lagoon treatment. Ammonia (NH ) loadings (0.12-3.17 kg/d) in the primary SAGR were measured over 223 days from May to December in 2017. Adjustment of the wastewater flow path on September 1 successfully increased NH loading to the primary SAGR, which subsequently caused reactor biomass to increase. The NH removal rate in October (0.5 kg/d) was greater than rates in June and July (0.3 and 0.2 kg/d) despite a water temperature decrease from >24 to 15.6°C. This elevated removal rate in October, and the sustained removal rate in December (0.4 kg/d, 5.3°C) were associated with a measured increase in microbial biomass. The relative abundance of the anammox organism C. Brocadia was 5 times greater in the mature biofilm after 686 days of growth, and the genus Pseudomonas increased sevenfold. The presence of Pseudomonas, which contains denitrifying species, and anammox suggests a high potential for removal of total nitrogen in SAGRs. PRACTITIONER POINTS: Pseudomonas prevalence and the presence of anammox suggest a high potential for total nitrogen removal in mature SAGR biofilms. The abundance of the anammox microorganism C. Brocadia was greater after 686 days of biofilm growth compared with 33 days. Simple operational changes can increase biomass in the SAGR to maintain, or even increase, NH transformation rates during cold weather.