Improving Sludge Anaerobic Digestion Performance By Pretreatment

With the founding of an increasing number of sewage treatment plants with strongerprocessing capacity, how to handle the massive residual sludge in the process of productionhas become a hot spot in the field of wastewater treatment. Anaerobic digestion is consideredas the best way to decreasing and reusing waste activated sludge. But the hydrolysis of sludgesolid is the key step of sludge aerobic digestion. As an effective pretreatment technology ofexcess sludge treatment, alkaline thermal hydrolysis method not only was good at cellsdisintegration, but also can enhance the treatment results of anaerobic digestion. Comparedwith traditional heating，microwave technology have advantages of efficiency and fast,andcan break the cells fast.Effects of microwave-alkaline treatment on characteristics of sewage sludge wereinvestigated in this paper. The effects of different operation, such as microwave power,irradiation time, dosages of alkali were mainly investigated to optimize the treatmentcondition.The concentration of SCOD, TN, TP, NH4+-N, protein and sugar in sludge solutionafter microwave irradiation-alkaline treatment were compared with the raw sludge.And theeffects of anaerobic digestion after microwave irradiation-alkaline preprocessing were alsoinvestigated. Effect of pretreatment on the biogas production and the SCOD、TCOD、VSS、VFA and alkalinity of sludge solution were analyzed,too.The result s showed that microwave irradiation combined with NaOH treatmentaccelerated the lysis of sewage sludge. In the optimal operation,800W microwave irradiationpower,microwave irradiation time of110s,the NaOH dosage of0.14g per gram SS,thesludge dissolving ratio increased to46%.In this operation, more microbial extracellularpolymeric substances (EPS) were decomposed, and more intracellular material were releasedto the liquid phase. The concentration of SCOD increased to2487mg/L which wererespectively about12times as compared with the initial one. The concentration of TN, TPincrease1.7times and1.45times respectively than single microwave processing,The proteincontents and the sugar contents increase7.9times and0.89times respectively. As the increase of NaOH dosage, NH4+conversion to NH3and the concentration of NH4+-Ndecreased to5.7mg/L when the given dosage was0.145gNaOH/gSS. After sludge treatment,the volatile fatty acids were released to the liquid phase and the pH value decreased from10.5to9.1.Experimental results show that the pretreatment can improve the anaerobic digestibilityof sludge. After pretreatment, the average daily gas production rate was50.5mL/d，morethan the the average daily gas production rate of raw sludge increased64%in the anaerobicdigestion process. The total gas production is increased by63.7%.The removal rate of TCODduring the digestion is50.4%and the removal rate of TCOD is increased by10.4%comparedwith raw sludge. The gas production of sludge with pretreatment enhanced from215.7mL/gVSS to272.2mL/gVSS after anaerobic digestion. After pretreatment the VFAconcentration increased obviously in sludge solution, but the alkalinity also substantiallyincrease and made the system keep better buffer capacity during anaerobic digestion.