Effects of inoculation of a genetically engineered bacterium on performance and indigenous bacteria of a sequencing batch activated sludge process treating phenol

Abstract

A genetically engineered microorganism (GEM) Pseudomonas putida BH (pS10-45), which was designed to exhibit higher phenol-degrading activity than the wild strain, was inoculated into a model activated sludge process to improve its phenol-treatment performance. The model activated sludge process was operated as a 24-h-cycle sequencing batch reactor in a shake flask, into which phenol-containing wastewater (500 mg/ l) was fed in the form of a shock loading three times at 7-d intervals and, subsequently, semi-continuously (at 100–200 mg/ l). After the shock loadings, the phenol-removal efficiency of the GEM-inoculated activated sludge was much enhanced in comparison to that of a control process without GEM-inoculation for as long as the GEM population survived at a relatively high level. During the semi-continuous feedings, the GEM-inoculated activated sludge settled much better than that in the control process, though phenol was completely removed in both processes. The improvement in the settling properties was gradually lost as the GEM population declined. It was also observed that GEM-inoculation had a considerable effect on the behavior of the indigenous phenol-degrading bacterial population, indicating that inoculation of the GEM delayed the occurrence of indigenous phenol-degraders. These results suggest that GEM-inoculation can be a useful means of improving phenol-treating activated sludge processes.