(86f) Concoction of Bacteria for Biodegradation of Btex

Authors: 
Nagarajan, K., National University of Singapore
Loh, K. C., National University of Singapore


Industrial progress, in the last few decades, has dramatically increased the release of toxic xenobiotics into the environment, endangering the eco-balance of Mother Earth. One of the most commonly cited environmental pollutant is the mono aromatic group of hydrocarbons BTEX - Benzene, Toluene, Ethyl Benzene and o-Xylene (BTEX). For pollution abatement, these volatile organic compounds are generally removed through physico-chemical methods such as adsorption, extraction and stripping. These methods, however, suffer from high operating cost, difficulty in operation and production of secondary pollutants. Biodegradation involving the use of naturally occurring microorganisms presents an alternative, yet better approach for the degradation of BTEX.

Hitherto, biodegradation studies on BTEX have been focussed on describing metabolic pathways, modeling kinetics and biodegradation using an isolated consortium from contaminated sites or using pure cultures. In actual application of biodegradation, a mixed bacterial community or microcosm plays a vital role in the degradation and there has been minimum focus on concocting a mixed culture for a stable consortium.

The biodegradation potential of three pure cultures ? Pseudomonas putida F1, Rhodococcus zopfii and Pseudomonas stutzeri was studied individually as well as in combinations. The overall objective was to combine the 3 species into a bacterial concoction that can effectively biodegrade BTEX. It was found that in the pure substrate systems, Pseudomonas putida F1 and Rhodococcus zopfii degraded toluene, benzene and ethyl benzene, while Pseudomonas stutzeri degraded toluene, benzene and o-xylene as sole sources of carbon. In the mixed substrate systems, a biodegradation hierarchy was found to exist, with toluene being the most easily degraded compound followed by benzene, ethyl benzene and o-xylene for all the three species.

Based on the biodegradation profiles of the individual substrate and mixed substrates by the pure cultures, parameters such as substrate range of the species, metabolic pathway, specific growth rate and degradation time were selected to formulate a set of guidelines for mixing the 3 species. Based on this, cocktails of the three species were formulated for different concentration levels of the BTEX compounds. The mixed culture?mixed substrate study revealed that the initial inoculum size and the relative composition of the species in the formulated microcosms contributed significantly towards efficient and faster removal of the BTEX compounds. It was also found that the mixed community of the three species had better biodegradation capability than the individual pure cultures. Further studies on the population dynamics of the mixed culture during biodegradation will shed light on the substrate and microbial interactions, stability of the consortium composition for different concentration levels of BTEX and the contribution of each species towards the degradation of the individual compounds in a mixed substrate system.