Effects And Mechanisms Of Exogenous Substance Addition For Improving Acid Suppression Of Anaerobic Digestion Of High Concentration Organic Wastewater

Anaerobic biological treatment has become an important means for high concentration organic wastewater treatment.The acid accumulation in the process leads to acid inhibition,which seriously affects anaerobic digestion.Solving acid inhibition is the key and difficult point to improve anaerobic treatment.In this paper,zeolite,zero-valent iron and their composite were added to the anaerobic biological treatment system as exogenous substances to the anaerobic biological treatment system of high-concentration organic wastewater,and and the effects of the addition on the stability of the anaerobic biological treatment system and the improvement of the internal environment of the system were investigated.The effects of dosage,type and particle size of exogenous substances on anaerobic biological treatment system were analyzed,and its mechanism of action was explored.It was applied in an upflow anaerobic sludge bed reactor.Different kinds of exogenous substances all promoted the anaerobic biological treatment process of high concentration organic wastewater.With the suitable zeolite,zero-valent iron and composite dosage,the biogas production increased by 421.7%,378.4%,438.7%,respectively.And the acid inhibition problem was effectively solved after the addition of exogenous substances.The highest VFA concentration with exogenous substances addition was lower than that of control.The COD removal with the exogenous substances addition reached to 95%,and the system pH maintained at 6.5-7.5.The composite material combined the advantages of zeolite and zero-valent iron.The suitable dosage of composite was reduced by 25%.The biogas production of anaerobic system was higher,and the COD removal rate was over 99.5%.Zeolite ensured the stability of anaerobic system,which was beneficial to methanogens to maintain the activity.The addition of zeolite affected the relative abundance of microorganisms in the anaerobic system.The hydrophilic methanogen Methanobacterium was dominant,but its relative abundance decreased from 84.9%to 54.39%.While acetotropic methanogen Methanosaeta became another dominant species,and its relative abundance increased from 6.19%to 30.42%,which is beneficial to VFA transfer.The addition of zero-valent iron changed the content of polysaccharides and protein.Under a zero-valent iron dosage of 0.4 g/L,the protein content increased from 40%to 72%,and the polysaccharide content increased from 41%to 54%.The dominance of hydrophilic methanogen Methanoregula was strengthened,and its relative abundance increased from 56.50%to 69.26%,which contributed to more efficient biotransformation of VFA.The addition of composite materials reduced the adsorption capacity of zero-valent iron to granular sludge.Lowering zero-valent iron dosage might weaken the disrupture effect of anaerobic methanogens from zero-valent iron.The addition of composite material to upflow anaerobic sludge bed reactor for high concentration organic wastewater ensured that the upflow anaerobic sludge bed reactor system ran basically in normal operation for a long term.The internal pH of anaerobic system was maintained between 7.2 and 8.6,which solved the acid inhibition problem,which easily occurred when treating the high concentration organic wastewater.The COD removal was more than 80%,the daily gas production and methane production were about 3.2 and 1.8 L/d,respectively,and the highest methane production per unit organic matters was 318 mL CH4/gCOD.