Use of a Slime Producing Microorganism to Enhance Biomass Settleability in Activated Sludge and ASB System, 1998 Environmental Conference Proceedings

A novel microbial organism has been identified which produces a large quantity of polysaccharide slime in wastewater systems. The organism, Bacillus sp. 4MA12.2E, demonstrated an ability to produce this flocculating slime in low F:M aerobic, biological systems. Since the polysaccharide had the potential to act as a cationic flocculant, it was decided to evaluate the organism in wastewater systems. In particular, applications were chosen with filamentous bulking. The challenge was to introduce the microorganism in a ASB, or activated sludge basin system. Steady state kinetic models assume microbial population is adequate for the substrate present. To establish a new strain in an ASB one must create a transition condition where biomass growth is limited. This is accomplished by using biomass chlorination or by increased wasting. In one case sodium hypochlorite was used to suppress filaments prior to inoculation with the selected bacterial strain. Two (2) field tests were conducted during 1997. One was an ASB system, and one was an activated sludge unit. Both had settling problems. The first ASB was a Canadian mill which had three lagoons. This sulfite mill experienced periodic Thiothrix sp. filamentous infestations due to septicity upstream of the biosystem. Prior attempts to chlorinate the filaments had resulted in loss of BOD5 removal. In January, 1997 a reoccurrence of the Thiothrix sp. filaments led to a trial with a two phase control approach. This time sodium hypochlorite was applied until the filaments were significantly damaged. Then the 4MA12.2E strain was applied in a concentrate culture. Improved flocculation occurred within 24 hours of application and continued until effluent TSS was reduced from 180 mg/L to less than 50 mg/L in 48 hours. During 1997 chlorination was repeated to control TSS. Subsequent analysis showed settling could often be improved without having to resort to chlorination. After this positive experience the settling culture was applied at an activated sludge system with filamentous bulking and an ASB with non-filamentous bulking. The Activated sludge system, with a 20 mgd flowrate, used the culture to suppress Thiothrix, N. Limicola, and Type 021N filamentous infestations. This resulted in a 25% improvement in SV30 and over 40% reduction in secondary polymer costs. Both applications were successful in improving settling and effluent TSS. Data is presented from both cases to illustrate the field experience.