Filamentous Bulking Control By Slowly Biodegradable Organic Substances In Activated Sludge System

Filamentous bulking is still a headache problem in the operation of state-of-the-artwastewater treatment plants (WWTPs), which can cause deterioration of effluent quality,sludge washout and even the collapse of the overall system. The experiment wasperformed in a lab-scale fed batch reactor. Glucose and sweet potato starch werealternatively used as model substrate of soluble and particulate substrate. The aim ofthis study is to evaluate the bulking controlling ability of slowly biodegradable substrateand investigate the effects of slowly biodegradable substrate on the proliferation offilamentous organisms. The main research methods and results are as follows:(1) After5days cultivation with glucose, SV30, SVI and TEFL rapidly increasedto73.8%,311mL/g and55.3km/g-SS, respectively. The typical filamentous bulkingwas triggered. However, the sludge settleability was significantly improved afterconverting substrate into sweet potato starch. The SV30、SVI and TEFL rapidlydecreased to21.5%,139mL/g and29.5km/g-SS on11day. The results indicated thatthe filamentous bulking in the lab-scale fed batch reactor can be induced by glucose andcured by sweet potato starch.(2) In both stages, the readily biodegradable substrate concentrations in bulksolution were very low (15.3mg-COD/L with glucose,22.1mg-COD/L with starch). Itindicated that the low substrate concentration was not the intrinsic reason for the sludgebulking and micro-gradient of substrate inside the flocs was the real cause for the sludgebulking.(3) The results of morphology observation and FISH analysis showed thatMicrothrix parvicella was the dominant filamentous organisms in the seed sludge fromthe wastewater treatment plant and Type1851was responsible for the sludge bulking in this experiment.(4) The bounded EPS contained in sludge was much related to the type of substrate.The content of protein, polysaccharide and DNA in EPSglucosewere26.31mg/g-VSS,16.84mg/g-VSS and5.75mg/g-VSS, while that in EPSstarchwere57.14mg/g-VSS,32.28mg/g-VSS and5.80mg/g-VSS. The content of protein and polysaccharide inEPSstarchis higher than that in EPSglucose. It is mainly attributed to the accumulation ofextracellular enzyme and hydrolysis products in EPSstarch.(5) The results of FISH analysis and DAPI counterstaining showed that Tpye1851still proliferated inside the flocs when filamentous bulking was cured and more compactand shear resistant floc was developed.(6) A physical model was proposed to interpret the evolution of sludge bulkingcaused by soluble substrate and cured by particulate substrate.