Odour Emission and Dispersion from a Cold Region Municipal Wastewater Treatment Plant

Abstract

Hydrogen sulphide (H2S) and ammonia (NH3) are two important odourants that are regularly emitted from conventional municipal wastewater treatment plants. The main objective of this research was to determine H2S and NH3 emission rate estimates (EREs) from open-to-air treatment processes at the Saskatoon Wastewater Treatment Plant (SWTP), Saskatchewan, Canada. Laboratory-scale reactors were developed to assess H2S and NH3 EREs from possible emission sources including clarifiers, anaerobic, anoxic, and aerobic basins. Experiments were conducted at 13 and 17 °C to simulate the operating temperatures at the SWTP which are impacted by highly variable seasonal temperatures in Saskatoon (from −40 to 30 °C). The EREs were used as the input for air dispersion modelling by AERMOD to evaluate the ambient air concentrations in downwind directions from the SWTP. Results indicate that the NH3 and H2S EREs in winter from the open-to-air emission sources were negligible. However, temperature rise led to higher activities for anaerobic processes in summer that increased H2S emission in primary clarifiers, anaerobic reactors, and anoxic reactors to average EREs of 1.17, 0.870, and 0.264 kgH2S/d, respectively. Atmospheric dispersion modelling by AERMOD showed that the maximum 24-h average ambient H2S concentration exceeded the limit of 5.0 µg/m3 set by Saskatchewan Ambient Air Quality Guideline in several episodes over the year.