PAENIBACILLUS-LIKE SPP. AND SLUDGE BULKING

Previously, we reported that PAENIBACILLUS-like spp. were a probable cause of non-filamentous sludge bulking in an industrial activated sludge system treating a waste stream from a dairy food processing plant (Oerther et al. 2002). Our results were based upon the use of the “full-cycle 16S rRNA approach” which showed that up to 30% of total DAPI stained cell counts in samples removed from the activated sludge system were PAENIBACILLUS-like spp. To confirm the role of PAENIBACILLUS-like spp. in non-filamentous sludge bulking, we operated four laboratory-scale activated sludge bioreactors for a period of eighty days. All four systems were operated in batch mode with a cycle time of 24 hours. The influent to all four systems consisted of a synthetic dairy wastewater prepared daily. To mimic completely mixed conditions, two systems were fed continuously and reacted for a period of 23 hours. To mimic plug flow conditions, two systems were fed for ten minutes and reacted for a period of 23 hours. All four systems were allowed to settle for 40 minutes before decant of effluent. One completely mixed system and one plug flow system were bioaugmented on a daily basis with 400 mg volatile suspended solids of a pure culture of Paenibacillus polymyxaT. A modified sludge volume index test was used to track sludge bulking. The completely mixed system bioaugmented with P. polymyxa demonstrated poor sludge settling characteristics; whereas the completely mixed system that was not bioaugmented demonstrated a well-settling sludge throughout the eighty days of operation. Both plug flow systems demonstrated a well-settling sludge throughout the experiment. These results support our previous hypothesis that PAENIBACILLUS-like spp. are a cause of non-filamentous sludge bulking in completely mixed activated sludge systems. Furthermore, we demonstrated that either the elimination of bioaugmentation of PAENIBACILLUS-like spp. from the influent or conversion to a bioreactor with a plug flow characteristic would be successful to eliminate non-filamentous sludge bulking due to PAENIBACILLUS-like spp. These results are useful for industrial activated sludge systems treating waste streams from dairy food processing plants. Furthermore, these results demonstrate the value of combining molecular biology techniques for identifying microorganisms with bioprocess engineering to solve operating problems for biological treatment of wastes.