Abstract
In this study, a lab-scale bioreactor experiment was conducted to investigate the fates of three aromatic hydrocarbons (benzene, toluene, and xylenes) in wastewater treatment processes, with respect to the differences among the species, together with the effects of aeration and the presence of activated sludge. The concentrations of the volatile organic compounds (VOCs) in the phases of air, water, and activated sludge in the bioreactor were analyzed to determine the respective chemical activities and to predict the possible transferring potentials of the VOCs among the three phases. Given appreciable levels of the VOCs being absorbed from the wastewater treatment plants (WWTPs) and their volatility, the directions of the transfers for these VOCs were from activated sludge to water and from water to air, indicating the importance of volatilization for the fates of VOCs in this reactor. The presence of activated sludge in the bioreactor had a positive effect on the transfers of the VOCs from air to water and from water to sludge, particularly for those VOCs with large octanol-water partition coefficients (KOW). The effect of aeration on the fates of the VOCs was affected by factors including the Henry’s law coefficients and KOW values of the VOCs, and the presence of activated sludge in the system. For the VOCs with large Henry’s law coefficients and small KOW values, aeration reduced the concentration of the VOCs in the air and water phases more significantly, resulting in positive and negative impacts on the volatilization and biosorption/biodegradation of the VOCs in WWTPs, respectively, which was unexpected based on the design of the WWTPs for VOC removal.
Highlights
Volatile organic compounds (VOCs) are organic chemicals mainly being composed of carbon atoms and can be emitted to the atmosphere as gases due to high vapor pressures resulting by their low boiling points
Given appreciable levels of the volatile organic compounds (VOCs) being absorbed from the wastewater treatment plants (WWTPs) and their volatility, the directions of the transfers for these VOCs were from activated sludge to water and from water to air, indicating the importance of volatilization for the fates of VOCs in this reactor
The objective of this study was to investigate the characteristics of the fates of the VOCs with respect to the associated effects of aeration and biological treatment, two steps widely seen in conventional WWTPs
Summary
Volatile organic compounds (VOCs) are organic chemicals mainly being composed of carbon atoms and can be emitted to the atmosphere as gases due to high vapor pressures resulting by their low boiling points Besides natural sources such as vegetation and forest fires, VOCs are used in various industrial processes and applications by different means, such as components and starting substances in industries, and are released from these sources (Nizzetto et al, 2007; Bravo-Linares and Mudge 2009; Joseph et al, 2012; Han et al, 2012; Hossain and Park 2012; Wang et al, 2012). Benzene is a chemical substance classified as a probable/ Despite those natural and industrial/commercial processes acting as sources releasing VOCs into the environment, there is a growing concern regarding the emission of VOCs from wastewater treatment plants (WWTPs) (WEF-ASCE 1995; Banat and Simandl 1996; Escalas et al, 2003; Oskouie et al, 2008; Lebrero et al, 2011). Mandated by the Clean Air Act, the public WWTPs in the U.S need to inventory and control their emissions of hazardous air pollutants in which most of them are VOCs (USEPA, 2012). Pope and Disalvo (1995) researched the VOC emission in 14 WWTPS in the U.S with different wastewater sources including residential and industrial sources, commercial facilities, hospitals, laboratories, and stormwater
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