APPROXIMATE CALCULATION OF N2O FORMATION IN HETEROTROPHIC DENITRIFICATION PROCESSES OF WASTEWATER DURING BIOLOGICAL TREATMENT

Abstract

This article addresses the important ecological issue of quantitatively determining greenhouse gas emissions – nitrous oxide – from municipal wastewater treatment facilities, which is a factor in global climate change. Data from scientific research indicate that deep biological treatment of nitrogen compounds at wastewater treatment facilities significantly contributes to the gross emissions of nitrous oxide from industrial facilities. Direct measurements of nitrous oxide emissions from biological treatment facilities in Ukraine have not been conducted. The aim of this study is to assess the potential emissions of the greenhouse gas N2O during the biological treatment of municipal wastewater in aeration tanks operating under the traditional, non-zoned scheme in Ukraine, which ensures deep nitrification. The study was conducted at municipal wastewater treatment facilities equipped with 3-channel aeration tanks. The process of wastewater treatment in aeration tanks operating under the traditional non-zoned scheme is fully aerobic and characterized by deep nitrification. Measurements of hydrochemical indicators of wastewater composition (BOD5, N–NH4, N–NO2, and N–NO3, Kjeldahl nitrogen) were carried out using certified methods in an accredited laboratory. It was found that biological treatment of municipal wastewater exclusively under aerobic conditions does not effectively remove nitrates from the wastewater. The nitrogen balance in incoming and treated wastewater was calculated, and the formation of N2O in the processes of suppressed denitrification was quantitatively determined. The consumption of nitrogen for the formation of excess activated sludge biomass, the efficiency of nitrification to nitrates, and the probable formation of N2O as a result of inhibition of the final heterotrophic denitrification reaction (reduction of N2O to N2) were calculated. The results showed that the maximum value of the N2O emission coefficient (the ratio of formed N2O to the concentration of total nitrogen entering the treatment process) at the studied facility could range from 3.24 % to 6.47 %, which is consistent with direct measurement data conducted at operating treatment facilities by foreign scientists. The study results confirm that modern technologies for deep biological wastewater treatment should consider not only effective removal of biogenic elements but also the minimization of greenhouse gas emissions.