Urea Responsible for Aggregation in Bacterial Strains Commonly Found in Activated Sludge

Dissolved organic nitrogen (DON) in wastewater effluent discharge could cause major water quality concerns in receiving waters. Existing wastewater treatment processes only partially biodegrade or ammonify DON, and complete ammonification can take weeks. During preliminary experiments, bacterial aggregation was observed in the presence of DON compounds, suggesting that DON plays a role in promoting aggregate formation in bacteria. Aggregation is a process by which microorganisms attach to each other via extracellular material. This study investigated the effect of pure bacterial cultures commonly found in activated sludge on DON. Three bacterial species, Alcaligenes faecalis, Comamonas testosterone, and Pseudomonas putida were grown separately on urea, glutamic acid, and glycine. The growth of freely suspended bacteria and aggregated bacteria was monitored by determining the concentrations of adenosine triphosphate using the BacTiter™-Glo microbial cell viability assay. Bacterial aggregations were observed to depend upon the type and concentration of DON compound. Bacteria formed aggregates after approximately 30 h of incubation when exposed to urea (1,200 mg-N/L), wastewater influent and effluent. Glycine and glutamic acid concentrations of 50 mg-N/L resulted in the formation aggregates in 100 h. Understanding of aggregate formation in the presence of DON compounds will help understand and improve biodegradation processes.