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

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.