Effect Of Combination Of Iron Powder And Thermal Hydrolysis On Anaerobic Digestion Of Sludge

Traditional sludge anaerobic digestion has disadvantages of long digestion time,low methane production,and low removal rate of organic matter,so it is necessary to find ways to enhance the effect of anaerobic digestion.Adding iron powder and using thermal hydrolysis pretreatment are effective methods to promote anaerobic digestion of methane production.In this experiment,two variables,iron powder dosage and thermal hydrolysis temperature,were set up.Orthogonal experiments were used to organize sludge anaerobic digestion experiments to maximize the performance of sludge anaerobic digestion.The effects of iron powder,thermal hydrolysis and their combination on anaerobic digestion of sludge were investigated from three aspects: methane production,microbial community and rheological characteristics.The results are as follows:(1)Both high-temperature and low-temperature thermal hydrolysis treatments have the effect of promoting methane production,increasing by 22.9% and 4.0%,respectively,but high-temperature thermal hydrolysis is better.Anaerobic digestion with adding 30 mg/g VS iron powder increased the methane production,an increase of 18.2%,and increased the maximum methane production rate,while adding 60 mg/g VS iron powder inhibited sludge anaerobic digestion.The combination of using hightemperature thermal hydrolysis and addition of 30 mg/g VS iron powder promoted cumulative methane production,increasing by 21.9%,which was slightly lower than anaerobic digestion with thermal hydrolysis.Through orthogonal experiment analysis,it was found that the optimal dosage of iron powder is 30 mg/g VS,optimal conditions for this experimental combination were the addition of 30 mg/g VS iron powder and thermal hydrolysis at 170 °C.(2)After anaerobic digestion with high-temperature thermal hydrolysis,the apparent viscosity and yield stress of the digested sludge are reduced,the flow performance is enhanced,and the thixotropy is reduced.After anaerobic digestion with adding iron powder,the apparent viscosity and yield stress of digested sludge increased,and the fluidity and thixotropy decreased.After the combined method of anaerobic digestion,the apparent viscosity of the sludge is reduced,the fluidity is enhanced,the thixotropy is reduced,and the high-temperature thermal hydrolysis plays a leading role,which weakens the adverse effect of adding iron powder on the sludge flow.The degree of enhanced fluidity and reduced thixotropy of digested sludge with high temperature thermal hydrolysis,adding iron powder or combined of those were worse than the control group.(3)Thermal hydrolysis treatment can improve the dehydration performance of digested sludge.The effect of high-temperature thermal hydrolysis is better than lowtemperature thermal hydrolysis,and high-temperature and low-temperature thermal hydrolysis increase the dehydration performance of digested sludge by 26% and 5% respectively.The addition of iron powder reduces the dehydration performance of sludge after anaerobic digestion.Compared with the control group,anaerobic digestion with combination of thermal hydrolysis and iron powder can enhance the dehydration performance of sludge.Among the effects of combined digestion on digested sludge dewatering performance,thermal hydrolysis plays a major role.It was found that the thixotropy and dehydration of sludge corresponded to a good linear relationship.The higher the thixotropic index of sludge,the higher the solid content of centrifugal cake.The thixotropic index can be used to predict the dewatering capacity of sludge.(4)Compared with the control group,the archaea of combined anaerobic digestion have high abundance and low diversity,which is the same as the archaea of anaerobic digestion with high-temperature thermal hydrolysis.However,anaerobic digestion with adding 30 mg/g VS iron powder reduced the abundance and diversity of archaea.The dominant archaea after anaerobic digestion with high-temperature thermal hydrolysis were Methanosarcina,Methanoculleus and Methanomassiliicoccus,whose nutritional mode from acetic acid to a mixed nutritional mode of acetic acid and hydrogen.The anaerobic digestion with adding 30 mg/g VS iron powder increased the proportion of Methanoculleus,Methanomassiliicoccus and Methanobacterium,increasing the abundance of hydrogentrophic methanogens.After anaerobic digestion of the combined method,the nutritional method of archaea is two methods to hydrogen nutrition type and mixed nutrition type,which is the result of the combined action of thermal hydrolysis and iron powder.(5)Analyzed functional abundance of archaea found that the total functional abundance from large to small was anaerobic digestion with high-temperature thermal hydrolysis > combined anaerobic digestion > anaerobic digestion with adding 30 mg/g VS iron powder > control group,those regularity are the same as cumulative methane production.The functional abundance of carbohydrates,lipids,and amino acids in samples of using high-temperature thermal hydrolysis,adding 30 mg/g iron powder and those combination were higher than the control group,which is an important reason for increasing methane production.