Research On Sewage Sludge Reduction Technology By Microwave Digestion

Large amounts of sewage sludge were produced by activated sludge method which was aconventional sewage disposal method. The sluge which come from the sewage watercontained toxic and harmful substances such as heavy metals, water organic pollutants andspecies pathogens and so on inevitably. Also with a lot of easily decomposed andpythogenesis compositions, the sludge emits nasty smell. The organic pollutants in sludgewere potentially harmful to biology and human. As the rate of treated sewage continuousincreased, the sludge production increased rapidly. At present, traditional sludge treatmentmethods all have certain shortcoming. So, the proper handling of sewage sludge has arousedpeople’s attention. Now, researches on sewage sludge treatment mainly focused on resourcesrecovery, quantitative reduction and the innocuous treatment. Sludge microwave pyrolysistechnology combined with chemical treatment, taking advantages of fast, efficiency,energy-saving and no second pollution has become the new direction of quantitative reductiontechonolgy.Effects of microwave-alkaline treatment on characteristics of sewage sludge wereinvestigated in this paper. The effects of various conditions, such as microwave power,irradiation time, types and dosages of chemical were mainly investigated to optimize thetreatment condition. And the effects of microwave irradiation-alkaline treatment inSequencing Batch Reactor（SBR） on sludge quantitative reduction were also investigated.Effect of different reflux rate on SCOD, TN, TP and NH₄⁺-N of sludge solution have beenanalyzed.The results showed that microwave irradiation combined with NaOH treatment acceleratedthe lysis of sewage sludge. Under the optimal conditions of800w microwave irradiationpower,120s microwave irradiation time and the dosage of NaOH0.16gNaOH/gSS, thesludge dissolving ratio increased to19.7%and the concentrations of SCOD, TN, TP increasedto3107mg/L,59.9mg/L, and23.9mg/L which were respectively about12times,3.7times,and1.9times as compared with the initial one. The reduction rate of VSS was in accord with the increase trend of SCOD. As the increase of NaOH dosage, NH₄⁺conversion to NH₃andthe concentration of NH₄⁺-N decreased to3mg/L when the given dosage was0.16gNaOH/gSS. The effects of thermo-alkaline treatment and microwave irradiation-alkaline treatmenton sewage sludge were compared. The result showed when the NaOH dosage was0.16gNaOH/gSS, with the same sewage sludge reduction rate （with about20%decrement）, theformer needed0.5h while the latter only need2min. The apparent yield coefficient ofmicrowave irradiation-alkaline treatment reactor decreased by18%,16%and38%respectively when daily treated5%,10%and15%of the reactor sludge. The effluent SCODconcentration slightly increased with increasing fraction of the treated sludge, but thebiological treatment performance was maintained and the removal rate of SCOD reached to82.4%⁸4.2%. The removal rates of NH₄⁺-N in the two reactors were94.6%⁹5.9%.Nitrification capabilities were scarcely altered by microwave irradiation-alkaline treatment.Phosphorus was released into the solution after sludge decomposition and the effluentconcentrations of TP were slightly increased when the treated sludge return to biosystem.