Emission characteristics and associated health risk assessment of volatile organic compounds from a typical coking wastewater treatment plant.

Abstract

Coking wastewater is a typical industrial wastewater and contains a number of toxic and harmful organic pollutants which threaten human health. However, emission of volatile organic compounds (VOCs) from coking wastewater treatment plants (WWTPs) is rarely studied. Here, the emission characteristics of VOCs were investigated in a full-scale coking WWTP composed of an anaerobic-oxic-oxic (A-O1-O2) treatment system. Furthermore, the potential health risks were assessed in this study. VOC emission rates were estimated at each unit of the coking WWTP and the influencing factors of emissions were discussed. Seventeen VOCs were identified in the air phase by gas chromatography-mass spectrometry combined with Tenax adsorption-thermal desorption method; benzene, toluene, and xylenes were predominant, and the concentration of total VOCs decreased gradually from the raw water tank (857.86 ± 131.30 μg m-3) to the effluent tank (28.56 ± 3.96 μg m-3). The total VOC emission rate from all units was 1773.42 g d-1, corresponding to an annual emission of 0.65 tons year-1. Since the treatment capacity of this coking WWTP was about 1500 m3 d-1, it was estimated that 1.18 g of VOCs are emitted during the treatment of 1 m3 wastewater. Influencing factors of VOC emission mainly include the background concentration of VOCs in wastewater, operational parameters of the treatment processes, and physicochemical properties of VOCs. The carcinogenic risk of VOCs for workers in this coking WWTP ranged from 3.0 × 10-5 to 7.8 × 10-4, which exceeded an acceptable level (1.0 × 10-6). The non-carcinogenic risk hazard ratio of benzene exceeded 1, indicating that benzene has an obvious non-carcinogenic risk. Understanding VOCs emission characteristics and emission rates can help to identify the adverse effects of coking WWTPs on human health and provide relevant information for policy-making.