Emission and spatial variation characteristics of odorous pollutants in the aerobic tank of an underground wastewater treatment plant (UWWTP) in southern China

Abstract

In this study, the spatial concentration of odorous pollutants in the aerobic tank of an underground wastewater treatment plant (UWWTP) in southern China is monitored. The odour activity value, odour contribution rate, and chemical concentration contribution rate are used to evaluate the degree of contribution of odorous substances. Computational fluid dynamics (CFD) simulations of odorous pollutant diffusion are also established. The study shows that the odorous substances detected in the aerobic tank mainly included ammonia (NH₃), hydrogen sulfide (H₂S), trimethylamine (C₃H₉N), and methanethiol (CH₃SH), and their concentrations are 1.160, 0.778, 0.022, and 0.0006 mg/m³, respectively. The total odour activity value of the aerobic tank is 450.72 (dimensionless), of which the odour activity value of H₂S is 432.22, and the contribution rate reaches 95.9%. H₂S is the main contributor to odour and a key controlled substance. The air inlets and exhaust outlets in the aerobic tank are cross-arranged at the top of the space, and the CFD model of odorous pollutant diffusion shows that the gas flow organization determines the odorous pollutant diffusion. The spatial distribution of gas flow and odorous substances in the aerobic tank is relatively uniform, and the odour collection efficiency is higher. The production flux and production coefficient of H₂S in the aerobic tank are calculated as 25.831 mg/(m²·h) and 14.149 mg/t, respectively. This study determines the reasonable air supply and exhaust design of the aerobic tank, the number of odour pollutants, and the key controlled substances. These findings offer guidance and serve as useful references for the prevention and control of odour pollution in aerobic tanks of the same type of UWWTPs.

Keywords: Aerobic tank; CFD model; Emission characteristics; Odorous pollutants; UWWTP.