Dissolved organic nitrogen in wastewater effluents: Occurrence, fate, and bioavailability

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 μm pore-sized filters, and flocculation and filtration (FF). Generally, 1.2-μm filtrate contained highest ON concentration and conventional filtration with 0.45 μm 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

Nutrient and dissolved organic carbon removal from natural waters using industrial by-products

Attenuation of excess nutrients in wastewater and stormwater is required to safeguard aquatic ecosystems. The use of low-cost, mineral-based industrial by-products with high Ca, Mg, Fe or Al content as a solid phase in constructed wetlands potentially offers a cost-effective wastewater treatment option in areas without centralised water treatment facilities. Our objective was to investigate use of water treatment residuals (WTRs), coal fly ash (CFA), and granular activated carbon (GAC) from biomass combustion in in-situ water treatment schemes to manage dissolved organic carbon (DOC) and nutrients. Both CaO- and CaCO3-based WTRs effectively attenuated inorganic N species but exhibited little capacity for organic N removal. The CaO-based WTR demonstrated effective attenuation of DOC and P in column trials, and a high capacity for P sorption in batch experiments. Granular activated carbon proved effective for DOC and dissolved organic nitrogen (DON) removal in column trials, but was ineffective for P attenuation. Only CFA demonstrated effective removal of a broad suite of inorganic and organic nutrients and DOC; however, Se concebtrations in column effluents exceeded Australian and New Zealand water quality guideline values. Water treated by filtering through the CaO-based WTR exhibited nutrient ratios characteristic of potential P-limitation with no potential N- or Si-limitation respective to growth of aquatic biota, indicating that treatment of nutrient-rich water using the CaO-based WTR may result in conditions less favourable for cyanobacterial growth and more favourable for growth of diatoms. Results show that selected industrial by-products may mitigate eutrophication through targeted use in nutrient intervention schemes. Crown Copyright (c) 2012 Published by Elsevier B.V. All rights reserved