Potential application of coastal biofilm-coated gravel particles for treating oily waste

This paper reports on hydrocarbon-degrading microbial consortia immobilized in biofilms on gravel particles in the intertidal zone of the Arabian Gulf coast. These microorganisms contribute to the self-cleaning of the coasts and, in addition, could potentially be used for cleaning oily industrial waste before its disposal in the open environment. Each gravel particle was found coated with about 100 mg biofilm of blue-green biomass. The predominant phototrophs were the cyanobacteria Dermocarpella and to a lesser degree Lyngbya sp. The most dominant hydrocarbondegrading bacterium in this consortium was Acinetobacter calcoaceticus; minor bacteria included Micrococcus and nocardioforms. The biofilm-coated gravel particles were used in 5 successive cycles of purification of oily sea water. This immobilized microflora was efficient during all cycles in hydrocarbon consumption. In contrast, bacteria adhering to biomass-uncoated gravel particles brought about hydrocarbon degradation in the first few cycles, but then gradually lost their cleaning potential, apparently due to their successive washing out from the particles during successive cycles.