Emission rates of aromatic hydrocarbons and chlorinated hydrocarbons at a wastewater treatment plant

The emission of aromatic hydrocarbons (benzene, toluene, and xylene) and chlorinated hydrocarbons (chloroform, carbon tetrachloride, trichloroethylene, and tetrachloroethylene) at a municipal wastewater treatment plant in Harbin was studied to calculate their seasonal emission rates from screen room, primary clarifier, biochemical tank (anaerobic and oxic stages), and secondary clarifier by applying different mathematical models. The highest emission rates of aromatic hydrocarbons and chlorinated hydrocarbons were observed for the biochemical tank, which were 1.92~5.22 g/s for benzene and 16.94~18.8 g/s for trichloroethylene, respectively. The emission rates of aromatic hydrocarbons failed to meet the criteria of Integrated Emission Standard of Air Pollutants (GB16297-1996). The emission of aromatic hydrocarbons decreased quickly along biochemical tank, while that of chlorinated hydrocarbons kept constant. The lowest emission rates of aromatic hydrocarbons and chlorinated hydrocarbons were observed for the screen room, which were 12.94×10 ^-6~17.24×10 ^-6 g/s for xylene and 1.88×10 ^-6~2.58×10 ^-6 g/s for chloroform, respectively. In the primary and secondary clarifiers, the average emission rates of aromatic hydrocarbons and chlorinated hydrocarbons in spring were 1.7 times of those in summer. In Spring, the emission rates of benzene, toluene and xylene in the secondary clarifier were 59.2%, 53.3%, and 4.5% of those in the primary clarifier, while the average emission rates of chlorinated hydrocarbons in the secondary clarifier was increased by 13%.