Characteristics And Anaerobic Digestion Process Of Alkaline Thermal Pretreatment WWTP Sewage Sludge

With the acceleration of urbanization, the number of wastewater treatment plants(WWTP) is increasing, and the amount of sewage sludge has increased dramatically.Therefore sludge treatment and stability become an indispensable step. The WWTPsludge as the research object, using Biochemical Methane Potential (BMP) test tocarried out the effects of sludge lysing, anaerobic digestion and the performance ofdewatering of alkaline thermal pretreated sewage sludge; On this basis, used theCompletely Stirred Tank Reactors (CSTRs) to discuss the effect of anaerobic digestionwhich pretreated by short-term low temperature pretreatment on mixed sludge andprimary sludge, respectively. The results were as follows:1. In the study of alkaline thermal pretreatment by orthogonal test to determine thebest pretreatment conditions of alkalis, dosage and hydrolysis time, then through themesophilic BMP test and thermophilic BMP test to determine the pretreatmenttemperature and to assess the anaerobic digestion performance. Different dosage(0,0.05,0.10,0.15,0.20g/g TS) of NaOH and CaO were added to the sludge samplesseparately, at70℃treated2h and9h, and then using the above obtained suitablepretreatment parameters, at different temperatures (50℃,60℃,70℃,80℃,90℃)to pretreate the sludge, then the pretreated sludge as the base material for themesophilic BMP test and thermophilic BMP test. The results showed that the optimalpretreatment condition for mesophilic anaerobic digestion was0.05gNaOH/gTS and70℃treated9h; the optimal pretreatment condition for thermophilic anaerobicdigestion was0.05gNaOH/gTS and90℃treated9h. 2. In order to dewatering effectively, the sewage sludge pretreated by alkaline+lowtemperature. The sludge from the thickener as the research object treated by70℃for1h,2h and9h after the sludge were added different dosage of CaO (20,30,40,50%TS,as a percentage of the dry mass of sludge to vote plus) and different dosage of FeCl3(3,5,7,9,11%TS), and then measured the dewatering indexes through plate and framefilter press dewatering test. The results showed that there were a great degree of celldamage and significant colloid properties in the alkaline+thermal pretreated sludge,and the colloid properties were not conducive for subsequent dewatering. In contrast,after a single alkaline treatment the sludge got better results for dewatering, and theoptimal condition was CaO dosing40%TS, ferric dosing11%TS, the moisture contentof the sludge changed from96.6%to68.8%.3. Themophilic anaerobic digestion of short time low temperature thermal pretreatedmixed and primary sludge were investigated using completely stirred tank reactors(CSTRs) at (55±1)℃. The concentrated sewage sludge was thermal pretreated at90℃for30minutes. The results showed that the performance of primary sludge anaerobicdigestion was better than mixed sludge which relate to the amount of organic matter inthe sludge; whether gas production or VS gas production rate, R2(primary sludge)were higher than R1(mixed sludge), the biogas production rate of R1and R2were(343±9.8) mL/gVSaddedand (365±20.5)mL/gVSadded, respectively; solid organic matterdegradation rate and degradation rate of R2were also higher than R1, the VS removalrate of R2was15%higher than R1, the average VS removal rate of R2maintained at(45.8±2.3)%.