Abstract: With batch experiment and continuous-running bioreactor, this paper studied the decay of the population size of genetically engineered microorganisms (GEMs) in activated sludge. The decay models and their parameters were obtained, and several affecting factors were analyzed. The results showed that both in batch experiment and in continuous-running bioreactor, the population size of the GEMs decreased rapidly initially, and then tended to keep constant. The dynamics of decay could be fitted well by Logistic model and Gompertz model, and no difference was observed between the fit goodness of the models. Under different conditions, the value ranges of the parameters in batch experiment were decay coefficient r′=0.5—0.6 h^-1 and stable population size K′=10⁴—10⁵ cfu·ml^-1 for Logistic model, and initial decay coefficient b=0.6—1.2 h^-1 and specific decay coefficient a=0.02—0.09 h^-1 for Gompertz model. The initial population size had a little effect on the decay, but affected stable population size remarkably. Mixed liquor suspended solid (MLSS) and temperature both affected remarkably, i.e., the decay became faster but got larger when MLSS was smaller, whereas the decay became faster and got smaller when temperature was lower. Nutrient conditions and predation by protozoa and metozoa were also the important affecting factors of decay. In continuous-running membrane bioreactor and conventional activated sludge reactor, Logistic model could also fit the dynamics of decay well, and the values of parameters were in the ranges obtained from batch experiment.

Key words: Camellia rosthorniana, Bionomic strategies, Fitness, Reproductive value