| Description |
Bacteriophages are viruses that infect bacteria and are known to be a very important component of microbial ecology in aquatic environments. Bacteria are involved in removing organics, ammonia and phosphorus in activated sludge processes. Frequent upsets, however, were found in the activated sludge process such as nitrification failure and filamentous bulking, causing the deteriorated effluent quality. Those upsets are caused by either unwanted bacterial growth or the death of key bacteria in an activated sludge bioreactor. The prophage on the bacterial genome remains dormant, but can cause cell lysis under certain environmental conditions. The effect of various environmental stress factors was examined on the ammonia oxidation and prophage induction in a model ammonia oxidizing bacterium, Nitrosospira multiformis. The factors included in the study were pH, temperature, organic carbon, the presence of heavy metal and toxicity. The selected environmental factors are commonly encountered in wastewater treatment processes, where ammonia oxidizing bacteria play a pivotal role of converting ammonia into nitrite. All of the factors could induce prophage from N. multiformis, demonstrating that cell lysis due to prophage induction could be an important mechanism contributing to the frequent upset in ammonia oxidation efficiency in full-scale treatment plants. The lytic phage could be applied to control biomass bulking in the activated sludge process using model filamentous bacteria. The lytic phage especially infecting model iv filamentous bacteria was isolated from the mixed liquor of a wastewater treatment plant. Significant reduction of sludge volume index (SVI) was observed after the isolated phage addition. The phages were considerably stable after exposure to high temperature and pHs, emphasizing that phage can withstand the seasonal/operational fluctuations. The isolated phage showed no cross infectivity with other bacteria most commonly found in activated sludge systems, thus validating its suitability for biocontrol of filamentous bulking caused by filamentous bacteria. Following the application of bacteriophage-based biocontrol, successful reduction in SVI was achieved, indicating improved biomass settling. The phage application did not affect the nutrient removal efficiency of the biomass. The phage-based biocontrol, therefore, holds a great potentiality for large-scale applications as an economic agent in the mitigation of several water, wastewater and environmental problems. |
