Microbial degradation of hydrocarbons in aqueous systems.

There is a vast worldwide consumption of petroleum hydrocarbons and accidental release in to the environment is common. For example petroleum forecourt retail outlets have 'interceptors' to prevent release of hydrocarbons into the environment. The aim of this study was to investigate options for in-situ bioremediation of the hydrocarbon substrates within these 'interceptors' in a laboratory model. The initial studies on bioremediation were undertaken with diesel as the substrate. It was shown that the addition of nitrogen and phosphorus to the system increased hydrocarbon mineralisation by a factor of 16, resulting in increased carbon dioxide evolution. There was strong evidence indicating that nitrogen and phosphorus were the limiting factor for hydrocarbon metabolism in this aqueous system. Trichoderma harzianum and a soil bacterial isolate LFC D1 FI were assessed and shown to degrade hexadecane and pristane. The positive affect of adding a cosubstrate was evident in flask studies; the rates of degradation by LFC D1 FI and T. harzianum were approximately doubled and tripled respectively in the presence of glucose compared to treatments without glucose. Previous attention has focused on the ability of Phanerochaete chrysosporium to degrade polycyclic aromatic hydrocarbons; in this study the degradation of aliphatics was investigated. Spores from P. chrysosporium induced on the hydrocarbon substrate were found to be necessary to degrade hexadecane. Pseudomonas putida was unable to grow in liquid media containing hydrocarbons, however on solid media and in an aqueous environment containing acid-washed sand, degradation of hydrocarbons was evident, hi the presence of sand P. putida degraded both hexadecane and pristane by 70% of the initial concentration added; in the absence of sand no degradation in the aqueous system was seen. This suggests surface attachment plays an important role in hydrocarbon degradation by P. putida. The attachment and use of the sessile P. putida in aliphatic hydrocarbon degradation is discussed