| Organic nitrogen (ON) is a significant fraction of the effluent total nitrogen (TN) in wastewater treatment plants (WWTPs) that remove nitrogen to low levels. Further reduction of effluent TN to lower levels must consider the significance of effluent ON. The ON fraction includes the particulate ON (PON), colloidal ON (CON), and dissolved ON (DON). CON and DON are the subjects of research in this dissertation. The key research issues addressed are the measurement, fractionation, fate and biodegradability/bioavailablity of ON in WWTPs.;This research showed that sample digestion to measure ON with persulfate digestion is an efficient method yielding as high as 100 percent N recovery when urea, mixed amino acids, and EDTA were used as nitrogen standards. Second derivative ultraviolet spectroscopy following digestion is a better method to measure low TN (TN<3 mg N/L) wastewater effluent samples with as low as 0.05 mg N/L sensitivity and detection limit. Investigation of nitrogen fractions in samples collected from different unit processes and operations in four nutrient removal WWTPs was undertaken by conducting serial filtration with 1.2, 0.45, 0.22 mum pore-sized filters, and flocculation and filtration (FF). Generally, 1.2-mum filtrate contained highest ON concentration and conventional filtration with 0.45 mum filtrate contains colloidal fraction. True DON can be determined by FF method. Final effluents from WWTPs contained as high as 27% of ON as CON and the remaining is true DON. It was found that majority of CON and DON in the influent was removed in the biological process of a WWTP. However, some DON production was observed in the primary anoxic zone of the biological process, possibly due to biomass metabolic and catabolic activities.;Bioavailability of DON ranges from 22 to 61 percent DON in low TN effluents. The results from algal and bacterial bioavailable DON (ABDON) and bacterial biodegradable DON (BDON) protocols did not show a significant difference in DON utilization. However, the DON degradation rate in ABDON protocol was higher than that in BDON protocol. Slower DON degradation was found when nitrate was present in the effluents, demonstrating that nitrate competes with DON utilization by microorganisms. |
