Evaluation of proteins and organic nitrogen in wastewater treatment effluents

Proteins represent a large portion of organic nitrogen and carbon in wastewater treatment effluents, but their detailed characteristics and their role and fate in receiving waters are virtually unknown. We used two protein fractionation techniques to characterize effluent proteins and proteolytic enzymes in three activated sludge plants, as a first step to elucidate the fate and role of proteins in receiving water environments. The quantitative data first showed that the protein concentration in primary and secondary effluents was significantly correlated with organic nitrogen and could comprise up to 60% of effluent organic nitrogen. Protein separation results showed that some proteins persisted through secondary treatment, while others were produced during biological treatment. Despite a high similarity of protein and enzyme profiles in primary effluent across three facilities, those in secondary effluent were consistently different, suggesting that effluent proteins could serve as markers of different wastewater treatment works. These profile fingerprints can be used to track effluent proteins in laboratory bioassays, or directly in receiving waters, and may permit the determination of the fate of effluent proteins, and thus a significant fraction of effluent organic nitrogen, in the environment.