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 cont aminated petrochemical sewage. Wild type protozoans were isolated from diff erent marine locations and from a municipal-refinery mixed sewage treatment plant. In batch culture the micro-organisms were adapted by slowly increas ing concentrations of sodium chloride and hydrocarbons. No wild type strain survived in the saline sewage. Using selected type strains of protozoans a s inocula, Cohnilembus, rheniformis and Uronema marinum were found to adopt to the brine. In a 20 l-batch culture Li. marinum grow up to a number of 1 4.000 cells ml(-1) Since the yield was recognized to be to small for furthe r scale-up, additional experiments were done in continuous culture. In a la b-scale 2-step continuous culture, inoculated with natural activated sludge mixed populations of protozoans, one single species of a ciliated protozoa n could be enriched and identified as Uronema nigricans. The effluent turbi dity, measured as optical density (OD600), of the lab-scale activated sludg e plant decreased dependent on the increase of U. nigricans count. In addit ion, chemical oxygen demand degradation efficiency was found to be 45.8%, c ompared to 35.4% in activated sludge mixed cultures missing protozoans. (C) 2000 Elsevier Science Ltd. All rights reserved.