The synergistic effect of a consortium of protozoan isolates (Paramecium sp., Vorticella sp., Epistylis sp. and Opercularia sp.) on the biodegradation of petroleum hydrocarbons in wastewater

Abstract

Many bioremediation studies have demonstrated that bacteria, fungi, algae and even protozoan counterparts possess catabolic abilities that may be applied for the remediation of soil and water contaminated with polycyclic aromatic hydrocarbons (PAHs). The aim of this study was to investigate the synergistic effect and toxicity tolerance of a consortium of protozoan species (Paramecium sp., Vorticella sp., Epistylis sp. and Opercularia sp.) during the biodegradation of petroleum hydrocarbons in wastewater. During this study, the synergistic indices were calculated and the toxicity of petroleum hydrocarbons and their degradation products present in wastewater were tested, in terms of LD50 at 24 h. The individual isolates were able to biodegrade approximately >65% with a consortium having biodegradation capabilities of <70%. Based on the synergistic effect of the isolates, most of these microbes were able to have a positive interaction during biodegradation from the 2nd to the 16th day with synergistic indices of>0.5. However, after the 16th day of the study period, either no interactions or negative and fewer activities were observed amongst the target microbes. Minimal or no toxicity (<10%) of the petroleum hydrocarbons to the individual isolates as well as the consortium of isolates was observed, especially during the first two days. However, as the study progressed, the toxicity gradually increased from <10% to <40% [calculated as percentage of inhibition (%E)] up to the 16th day of the study period.