Research On The Operation And Optimization Of Bladder-type Anaerobic Sludge Digestion And Dewatering

With the dramatic increase in the volume of sewage treatment in China,the annual output of excess sludge is also greatly increased.If the sludge is not treated,it will lead to soil and water pollution.However,due to special climatic conditions in northern China,the operation of sludge anaerobic digesters is very unstable and has poor results.Therefore,most of the sewage treatment plants only dehydrate the sludge.Therefore,it is of practical significance to debug the bladder-type anaerobic sludge digestion reactor to make it stable,and to optimize the dewatering performance of anaerobic sludge to form a complete process with certain reference value.The start-up process of the bladder-type anaerobic sludge digestion reactor is divided into three stages.In the early stage of start-up,the methanogens in the reactor have not been matured,the acid-producing bacteria are mainly active.Therefore,the pH in the container is low.In the middle of the start-up period,the methanogens began to grow in large quantities,the pH increased,and the biogas production also increased significantly.In the late stage of the startup,the methanogens matured,the pH was around 7.1,and the biogas production rate remained at a high level.During the stable operation of the bladder-type anaerobic sludge digestion reactor,the elimination rate of organic matter was always above 45%,the pH of digestive juices was always maintained between 6.5-7.4,and the biogas production rate was also higher than the expected 0.75 m3/kg.Therefore,the bladder-type anaerobic sludge digestion reactor's operation can be considered stable and running well.The rate of water content of the sludge after digestion is about 97%,and it is difficult to dehydrate,so it is necessary to improve sludge dewatering effect through conditioning.By debugging the operating conditions of the bladder-type anaerobic sludge digestion reactor,it can be seen that with the increase of temperature,the VSS elimination rate is significantly improved,and the VSS elimination rate at 32±1? is higher than that of 26±1? by approximately 15%.Meanwhile,the biogas production rate is about 25% higher.The agitation time has little effect on the elimination rate of organic matter.With the increase of the agitation time,the biogas productivity increased first and then decreased.When the agitation time was 14 h/d,the biogas production rate was the highest,which was 25% higher than that of other conditions.With the increase of sludge load,the reduction rate of organic matter decreased by about 8%,but the gas production rate of biogas increased by about 18%.When the dehydration performance was improved by means of chemical conditioning of digested sludge,polyaluminum chloride,cationic polyacrylamide,iron sulfate,aluminum sulfate and calcium oxide are selected as flocculants.When a single agent was used,CPAM had the best effect.The best dosage is 160mg/L.When the two or more chemicals were added together,the dehydration effect was significantly better than that of the chemicals alone.The best combination of chemicals was 80 mg/L CPAM,2 g/100 m L calcium oxide,and 1.8 g/L PAC.When the dehydration performance was improved by means of compound conditioning of digested sludge,washing method conditioning and freezing conditioning are selected as pretreatment.After compound conditioning,the dosage of the sludge was significantly reduced,and the sludge dewatering effect was also significantly improved.The effect of washing method conditioning was slightly better than that of the frozen conditioning.Sludge digestion-dehydration program is determined to be performed at 32? for the bladder-type anaerobic sludge digestion reactor.The daily sludge volume is 15 t and the agitation time is 14 h/d.The crew press dewatering machine is selected as the dewatering equipment.0.08 kg CPAM is added per ton of sludge.The estimated cost per ton of sludge treatment is 51.51 yuan.