A systematic approach for selecting an optimal strategy for controlling VOCs emissions in a petrochemical wastewater treatment plant

This study assessed the fate of benzene, toluene, and styrene in a full-scale petrochemical wastewater treatment plant (WWTP) with respect to the selection of an efficient and cost-effective control strategy. To prepare input parameters for TOXCHEM, wastewater samples were collected from the inlet of treatment units. Subsequently, the resultant emission rates were applied in AERMOD to study the dispersion patterns of the target volatile organic compounds (VOCs). Based on the TOXCHEM results, the overall emission of benzene, toluene, and styrene was 123,935g/day, of which 73.4, 13.3, and 13.4% were benzene, toluene, and styrene, respectively. The results indicated that up to 99.5% of the target VOCs were removed from wastewater by volatilization and biodegradation mechanisms. Also, more than 85% of the VOCs emission occurred from the primary treatment units (American Petroleum Institute oil separator, equalization basin, and dissolved air flotation system). In some cases, the concentration distribution profiles resulting from AERMOD showed higher values than EPA reference concentrations (RfC) around the study area. The most affected area was near the WWTP with maximum 1-h concentrations of 8166, 1267, and 1228g/m(3) of benzene, toluene, and styrene, respectively. Based on the modeling results, the most applicable and available methods for separating and ultimately disposing of VOCs were investigated and compared with the aim of reducing emission rates to meet ambient air quality standards. The results revealed that steam stripping is the most efficient and cost-effective VOCs control strategy in the studied plant. Moreover, thermal incineration was marked as the first choice for ultimate disposal of the contaminated air streams.