Study On Thermal Hydrolysis For Sludge Reduction And Phosphorus Recovery In AOMBR

This paper investigated the release rule of intracellular substances, thechange of sludge concentration and characteristics in sludge thermalhydrolysis process, discussed the operation mode of the effectivephosphorus recovery technology on the recovery of phosphorus released insludge thermal hydrolysis process, and studied the operation efficiency ofanoxic/aerobic membrane bioreactor （AOMBR） with thermal hydrolysisand phosphorus recovery.The influence of heating temperature, thermal hydrolysis time andinitial sludge concentration on sludge disintegration effect weresystematically investigated by batch test. On basis of the test of the bestexperimental parameters of thermal hydrolysis, the release rule ofnitrogen and phosphorus, and the change of sludge characteristics in sludgethermal hydrolysis process were explored. Then, series of experiments onthe phosphorus released in sludge thermal hydrolysis process wereperformed on to identify the best operation conditions for P recovery byemploying the calcium phosphate precipitation method.Based on the resesrch mentioned above, two laboratory scaleanoxic/aerobic membrane bioreactors （AOMBRs） with7.5L/h wereoperated in parallel to evaluate the influence of sludge thermal hydrolysis and phosphorus recovery on sludge concentration, sludge yield andpermeate quality. One of the AOMBR is with returned sludge respectively100%，75%and50%, which was treated by thermal hydrolysis andphosphorus recovery. The other is a conventional AOMBR process forcomparison. The main conclusions obtained from the research were asfollows：（1） The heating temperature, thermal hydrolysis time and initial sludgeconcentration had some influences on sludge disintegration effect. Itshowed that the initial sludge concentration of8500mg/L, the heatingtemperature of80℃, and the thermal hydrolysis time of60minutes werethe optimum operating condition of sludge thermal hydrolysis.（2） The disintegration of sludge was accompanied by massive releaseof nitrogen and phosphorus. And the release of TP was dominated mainlyby PO₄^3--P, which could be more conductive to the effective recycling ofphosphorus.（3） Thermal hydrolysis could decrease the sludge activity, reduce thepH values of sludge, and make sludge settleability and dewateringperformance worse.（4） With the mixed contact time of5minutes, initial pH of9.0andCa²⁺/PO₄^3--P of3.0, the recoveries of PO₄^3--P and TP in supernatant ofthermo-hydrolyzed sludge could reach93%and89%respectively.（5） The sludge recycle could significantly increase the sludgeconcentration of AOMBR process. When the returned sludge, which treatedby thermal hydrolysis and phosphorus recovery, was100%，75%and50%，the sludge concentration of AOMBR process increased by18.2%,9.3%and6.0%, compared with the comparison process, respectively. The bigger ofthe recycle flow rate of thermo-hydrolyzed sludge, the greater of theincreasing extent of the sludge concentration was. （6） The sludge recycle could significantly decrease the sludge yield ofAOMBR process. When the returned sludge, which treated by thermalhydrolysis and phosphorus recovery, was100%，75%and50%，the sludgeyield of AOMBR process decreased by44%,53%and32%as comparedwith the comparison process.（7） Although the sludge recycle could increase the removal rate ofCOD, NH₄⁺-N and TN, the impact is not obvious. And the removal ratecould totally meet the discharge standard, which fully embodied the highstability of MBR.（8） The sludge recycle had great influence on the removal rate of TPof AOMBR process and the influence increased with the increase of thequantity of reflux.