Research On Enhanced Anaerobic Digestion Of Sludge And Its Mechanism Based On Iron/iron-carbon Dosing

Anaerobic digestion is one of the key technologies to realize sludge reduction,stabilization and resource recovery.Currently,zero-valent iron has been considered as an effective additive to enhance sewage sludge anaerobic digestion.In order to further realize the industrial application of zero-valent iron in enhancing anaerobic digestion of sludge,the effect and mechanism of zero-valent iron on mesophilic anaerobic digestion of sludge with different total solid contents,microwave pretreatment and thermal hydrolysis pretreatment at low and high dosages of zero-valent iron addition were systematically studied.Results showed that;(1)the main role of zero-valent iron addition is to promote the methane production rate of different types of sludge in the early stage of anaerobic digestion.For example,the methane production rate of sludge with microwave pretreatment was further increased by 11.02%(at 2 day of anaerobic digestion)when zero-valent iron was added.The total methane production rate of the thermal hydrolyzed sludge in the initial stage of anaerobic digestion(1-11d)was improved by 13.55%;(2)the increase of methane production rate is closely related to the release of dissolved organic matter and the degradation of volatile fatty acids(VFAs)under zero-valent iron addition.For example,in the easoluble rly stage of sludge anaerobic digestion after microwave pretreatment,the release of protein increased by 21.16%compared to that in the pretreatment group without zero-valent iron addition;(3)zero-valent iron tends to precipitate with phosphate and sulfide,which may be an important reason for the limited enhancing efficiency of zero-valent iron on anaerobic digestion of sludge.How to quickly restore the methane production efficiency of anaerobic digestion which is in unstable state is particularly important.This study verified that zero-valent iron could significantly accelerate the restoring rate of methane production in the inhibitory state under excess ammoniaconcentration.The anaerobic digestion was completed about 15 days earlier.Under ammonia inhibition,a large amount of VFAs accumulated,and the addition of zero-valent iron could accelerate the degradation of VFAs and promoted the biochemical reaction rate.After the zero-valent iron addition,the dissolved iron content increased by 48.60%compared with the control,which increased the relative abundance of functional microorganisms(Methanosarcina)and rapidly restored the anaerobic digestion process.The combined addition of iron and carbon matrial could further restore metabolic activity of methanogens under ammonia inhibition.Results showed that the activated carbon,graphite,iron and iron-carbon composite material could further improve the restoring efficiency of methane production under ammonia inhibition,made lag phase of methane production decreased by 66.67%?61.01%and 59.54%compared to the single zero valent iron addation,thus relieved ammonia inhibition.This may be the result of increased electron transfer efficiency between microbes with iron-carbon addition.After adding zero-valent iron and carbon,oxidation reduction potential(ORP)and conductivity of anaerobic digestion system was decreased,which was benefit for increasing metabolic activity of methanogens and methanogenesis.