OPERATION PARAMETERS AFFECTING THE SURVIVAL OF GENETICALLY-ENGINEEREDMICROORGANISMS IN ACTIVATED-SLUDGE PROCESSES

The survival of genetically engineered microorganisms (GEMs) harboring recombinant plasmid pBH500, containing catechol 2,3-oxygenase encodin g gene, in model activated sludge processes was investigated. Escheric hia coli C600 (pBH500) and Pseudomonas putida BH(pBH500) were inoculat ed into activated sludge and cultivated in the fill and draw (FD) and continuous how (CF) systems under different conditions. In both system s, the populations of introduced GEMs declined rapidly during the init ial period (5-10 days for the FD system and 5-15 days for the CF syste m), after which they remained relatively stable. In the FD system, the larger the inoculum size, the higher the population level at which th e GEMs remained stable. However, in the CF system, repeated inoculatio n did not improve the survival of P. putida BH(pBH500). The sludge ret ention time (SRT) affected the survival of GEMs considerably in both s ystems; as the SRT of the system was decreased, the survival populatio ns of GEMs increased. The presence of phenol, which can support the gr owth of P. putida BH(pBH500), did not influence its survival.