Effects of bacterivorous ciliated protozoans on degradation efficiency of a petrochemical activated sludge process

The aim of this work was to adapt protozoans to a saline and crude-oil contaminated petrochemical sewage. Wild type protozoans were isolated from different marine locations and from a municipal-refinery mixed sewage treatment plant. In batch culture the micro-organisms were adapted by slowly increasing concentrations of sodium chloride and hydrocarbons. No wild type strain survived in the saline sewage. Using selected type strains of protozoans as inocula, Cohnilembus rheniformis and Uronema marinum were found to adopt to the brine. In a 20 l-batch culture U. marinum grow up to a number of 14.000 cells•ml−1. Since the yield was recognized to be to small for further scale-up, additional experiments were done in continuous culture. In a lab-scale 2-step continuous culture, inoculated with natural activated sludge mixed populations of protozoans, one single species of a ciliated protozoan could be enriched and identified as Uronema nigricans. The effluent turbidity, measured as optical density (OD600), of the lab-scale activated sludge plant decreased dependent on the increase of U. nigricans count. In addition, chemical oxygen demand degradation efficiency was found to be 45.8%, compared to 35.4% in activated sludge mixed cultures missing protozoans.