Survey on Odorous Mineral Gases in the Air Around the Wastewater Treatment Plant: A Case Study in a Stabilization Pond

Malodors are one of the problems of water and wastewater treatment plants, especially in the vicinity of residential areas. Mineral compounds like hydrogen sulfide (H۲S) and ammonia (NH۳) produce unpleasant smells in the wastewater treatment plants. These gases also have adverse effects on both humans and the environment. After field visits around the plant, a number of ۱۲ sampling stations were determined. Sampling stations were selected from ۴ cardinal directions with regard to permanent trade winds and on distances of ۰, ۲ and ۴ km from the plant. Sampling was performed in the morning and evening during the four seasons. Jacob and Indophenol methods were used for measuring the concentration of H۲S and NH۳. According to analysis of variance (ANOVA) and Tukey test, and concentrations of NH۳ and H۲S during different seasons, the emissions were more significant in the warm seasons and caused more malodors (P = ۰.۰۱۱, P = ۰.۰۰۴ for NH۳ and H۲S, respectively). Moreover, there was a significant relationship between the concentration of NH۳ and sampling sites (P = ۰.۰۰۰). However, the relationship between the concentration of H۲S and sampling stations was not significant (P = ۰.۱۷۹).According to the results, the concentrations of H۲S and NH۳ in all the seasons except for winter were within the threshold limits. The concentration of H۲S in the summer and the concentration of NH۳ in all the seasons were higher than USEPA standards and World Health Organization (WHO) guidelines.