Kinetic study of chlorobenzene degradation by isolated microbes from wastewater

Abstract

The performance of microbial consortia from wastewater to degrade chlorobenzene (CB) was investigated. The consortia were initially exposed to high CB concentration (i.e. 0.2mg/L) for seven months in order to isolate the most dominant survivor(s). The two survivors were known as ‘Yellow Colony’ or YC, and ‘White Colony’ or WC. In batch culture, the maximum specific CB degradation rate, or Qs (g CB degraded/g cell per hour) of WC, YC, mixture of WC and YC, were compared. The mixture of WC and YC gave three times greater Qs than individual WC and YC, combined. This synergistic effect has never been reported so far. Study in a continuous culture indicated that nitrogen-enriched feed has resulted in greater critical dilution rate, Dc (i.e. 0.11h-1) than the unsupplemented one (i.e. 0.08h- 1). This proved that the nitrogen limiting could not be ignored. It was also discovered that a short term (i.e. two days) adaptation of the consortia on CB prior to the degradation test in continuous cultures, as employed in some published works, was insufficient to produce significant result in this study. Data in batch study revealed that high aeration and temperature close to ambient (versus 37 oC) doubled the microbial growth in CB degradation. The batch study also showed that the CB degradation rate obeyed the first order kinetic. However, no degradation was witnessed below 0.0006 mg/L of CB. Below this threshold level, CB was almost undetectable by microbes. The outcomes of this study have not only proved the potential of employing microbes from wastewater to solve chlorobenzene contamination problem, but also provided useful parameter estimates for future up scaling works, or on site trial.