BIOAVAILABILITY OF DISSOLVED ORGANIC NITROGEN IN TREATED EFFLUENTS

The objective of this study was to assess the bioavailability of dissolved organic nitrogen (DON) in wastewater effluents from a total nitrogen removal plant and a nitrification only plant. The bioavailability of DON was assessed using bacterial and algal inocula in a 14-day bioassay developed using existing methods in limnology and oceanography literature. Nitrogen species, dissolved organic carbon, chlorophyll a, and biomass (as TSS and culturable cell counts) concentrations were measured to assess bioavailability during the bioassays. An increase in the concentration of chlorophyll a in the algal samples with a concurrent increase in algal biomass over time, and an increase in bacterial counts over time and a decrease in DON concentration over time, and increase in the C: N ratio at the end of the 14-day incubation period could be considered as indicators of DON bioavailability to algae and bacteria. The experimental results showed that 18 to 61% of the DON in low TN wastewater effluent sample was bioavailable in the 14-day bioassays. The DON results suggested that bacteria and algae uptake DON as well as release DON to the culture medium as a result of their metabolic activities during their growth.