| Livestock and poultry manure had caused serious environmental pollution to the atmosphere,water and farmland.Anaerobic digestion is an effective way to eliminate the pollution of livestock and poultry excrement,which can also recover energy from manure,it is a very promising waste treatment technology.In this paper,the effects of micro-aeration pretreatment on swine manure,zero-valent iron(ZVI)supplementation on swine manure with high ammonia nitrogen concentration,and the effects of ZVI supplementation on two-phase AD were studied to explore their effects on dissolved organic matter,biogas production and microbial community during anaerobic digestion of swine manure,which could enhance anaerobic digestion of swine manure.1)Through pretreatment of swine manure by micro-aeration(agitation)before AD,the results showed that pretreatment promoted the dissolution of large organic matter,and soluble polysaccharides,proteins and sCOD were increased by 93.9%,124.7%and 158.8%respectively;the total ammonia nitrogen after pretreatment increased significantly compared with the control,which indicated that pretreatment enhanced microbial activity in swine manure;AD experiments were carried out after pretreatments were finished,the results showed that the cumulative biogas production increased by 24.7%and the cumulative CH4 production increased by 77.8%compared with the control.2)High concentration of ammonia nitrogen could inhibit the AD process,solid NH4CI was added into swine manure to simulate the high ammonia nitrogen environment(5000mg/L)in this paper.The comparison of cumulative CH4 production between blank group(without NH4CI)and control group(with NH4Cl)showed that AD process was inhibited by high ammonia nitrogen concentration.After 30 days of AD,the cumulative CH4 production of control reactors was 109.0 mL/g-VSfed,and ZVI reactors(with NH4CI and ZVI)was 168.0 mL/g-VSfed,which was 54.1%increase than control.The results indicated that ZVI supplementation promoted CH4 production in AD of swine manure.On Day 10,the concentration of total volatile fatty acids(VFAs)in ZVI group increased by 86.87%compared with control,indicating that adding ZVI accelerated the hydrolysis-acidification of AD;ZVI supplementation increased the total alkalinity of digestion system,because ZVI could react with H+;The ORP values range was-158.0-250.0 mV after ZVI addition,which was conducive to butyric acid digestion,which promoting subsequent CH4 production process.High-throughput sequencing of microorganisms showed that adding ZVI could increase the relative abundance of Methanoculleus by 15.3%,which could tolerate the inhibition of high ammonia nitrogen,thus alleviating the inhibition of high ammonia nitrogen on methanogenesis of AD.3)Zero-valent iron(ZVI)supplementation and two-phase anaerobic digestion(AD)are enhanced ways for CH4 production in anaerobic way to convert organic wastes into renewable energy.However,the whole two-phase AD is not continuous because of the addition of methanogenesis inhibition in most of previous studies.In this study,different ZVI supplementation modes but same dosage(6g ZVI)were added during acidogenic stage(AS)or methanogenic stage(MS)in two-phase swine manure AD which was achieved by a simple pH adjustment to achieve a continuous process.The results showed that adding ZVI into both AS and MS could achieve 27.3%increase for CH4 production.ZVI supplementation during the AS would be slowly corroded,which reduces the direct contact between ZVI and methanogens and it is detrimental for methanogenesis.Microbial sequence analysis showed that adding ZVI could increase the relative abundance of Methanomassillicoccus by 39.2-92.0%.Results from this study demonstrated that ZVI should be added to make direct contact with methanogens in order to achieve higher energy recovery when treating animal manure. |
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