STUDIES ON REMOVAL OF VOC FROM WASTEWATER

Abstract

Benzene, toluene and xylene (BTX), are the major aromatic components in petroleum. BTX are widely used in industry as solvents for organic synthesis, equipment cleansing and other downstream processing purposes. They are frequently found in groundwater as a result of leaks in underground storage tanks and pipelines, improper waste disposal practices, inadvertent spills and leaching from landfills. Benzene is teratogenic and may be associated with the development of leukemia, and toluene is a suspected depressant of the central nervous system. Conventional aeration processes are commonly used in treating BTX or other VOC containing industrial wastewater. This approach to treating BTX-containing wastewater simply transfers the problem from one medium to another rather than converting the contaminants into innocuous products, as would be achieved with biodegradation. Additionally, aeration is among the most costly operational expense associated with wastewater treatment systems. Among all remediation technologies for treating BTX-contaminated water, bioremediation appears to be an economical, energy efficient and environmentally sound approach. Microorganisms are able to degrade BTEX under aerobic as well as anaerobic conditions. In general, aerobic biodegradation is considered much faster than anaerobic processes. However, aerobic treatment processes usually result in losses of the volatile organic compounds to air, rather than complete biodegradation. More recently, studies suggested that microaerobic conditions (low oxygen levels) enhanced the biodegradation abilities of toluene and possibly benzene. As a result interest has been directed toward studying BTX biodegradation under low dissolved oxygen, or microaerobic, conditions. Although these studies were conducted either with pure or subsurface cultures, the concept of microaerobic metabolism is encouraging and may provide an alternative for enhancing the effectiveness of treating wastewaters containing BTX or other volatile organic compounds (VOC). In this study a new treatment process for BTX containing wastewater is proposed by using an alternating anoxic/microaerobic sequencing batch reactor to overcome the stripping of BTX compounds into the atmosphere, as often occurs in conventional aerobic treatment processes. One of the major concerns associated with using sequencing batch reactors for wastewater treatment is the uneven oxygen demands iii encountered throughout a reaction cycle, with much higher oxygen demands at the beginning. Such an oxygen demand profile leads to either a complicated operation strategy or high peak energy consumption. This particular problem associated with sequencing batch reactors can be overcome by incorporating an anoxic environment into the reaction cycle. This paper presents a study on the biological treatment of a wastewater stream containing benzene, toluene and xylene (BTX) by using sequencing batch reactors with alternating anoxic and microaerobic conditions.