Study On The Mitigation Technology Of Ammonia Inhibition During Dry Anaerobic Digestion Of Chicken Manure

Large-scale chicken farms improve production efficiency,but they also produce large amounts of concentrated chicken manure,and this manure is a serious environmental hazard if it is not properly handled.Anaerobic digestion(AD)(Biogas fermentation)can degrade pollutants,and produce biogas energy and organic fertilizer.It is regarded as an effective means of treating and making use of chicken manure.In practice,wet anaerobic digestion(WAD)technology is most often used to deal with chicken manure because it produces methane which can then be utilized in other processes.The chicken manure is diluted to a total solids(TS)concentration of less than 10% before it is sent to a digester.Adding water to dilute chicken manure not only wastes water resources,but also increases heating energy consumption.Furthermore,a large amount of liquid digestion residue(biogas slurry)is produced during the WAD process and this biogas slurry with large quantity and low nutrient content requires a large area of land for utilization.There is also a high transport cost for transporting to other places.Therefore,it can be subjected to a post-treatment,which brings great challenges for biogas plants.In the dry anaerobic digestion(DAD)process,the chicken manure is not diluted,which means that the digestion residues are easy to use,so DAD has caused widespread public concern,and it is considered to be the best methane production technology for chicken manure.However,there have been no pilot-scale or full-scale cases of pure chicken manure undergoing successful dry anaerobic digestion.In the DAD system,the high nitrogen content in chicken manure is the main reason and ammonia inhibition will be produced in the AD process,which leads to the low methane production and even biogas production failure.This study focused on the problem of low biogas production efficiency caused by ammonia inhibition in DAD of chicken manure,and the screening and acclimation of DAD sludge,temperature control in DAD process,optimization of adsorbent for removing ammonia inhibition and mechanism of alleviating ammonia inhibition were studied.It is hoped to provide theoretical and technical support for the development of a high-ammonia-nitrogen DAD process for livestock and poultry manure.The main conclusions are as follows:(1)The inoculated sludge for dry anaerobic digestion(AD)of chicken manure with high ammonia nitrogen were screened from the sludges used to treat 1)pig manure from a WAD biogas plant in Qionglai(QL);2)pig manure from a DAD biogas plant in Leshan(LS);3)chicken manure from a WAD biogas plant in Beijing(BJ);4)chicken manure from a WAD biogas plant in Shangdong(SD);5)a mixture of chicken manure and other animal manure from a WAD biogas plant in Xinjiang(XJ),and the sludge used to treat chicken manure from a DAD biogas digester in the laboratory(LAB).The results showed that the WAD sludge used to treat chicken manure from a WAD biogas plant in Beijing(BJ)and the WAD sludge used to treat chicken manure from a WAD biogas plant in Shangdong(SD)had no advantage as inoculated sludge due to their low VS/TS,low organic matter content;high residual biogas production potential,more residual degraded organic matter in VS;and low specific methanogenic activity(SMA).Because of the high VS/TS,the low potential of residual biogasproduction and high SMA,the sludges used to treat 1)pig manure from a WAD biogas plant in Qionglai(QL);2)pig manure from a DAD biogas plant in Leshan(LS);3)a mixture of chicken manure and other animal manure from a WAD biogas plant in Xinjiang(XJ),and the sludge used to treat chicken manure from a DAD biogas digester in the laboratory(LAB)had the advantages of being inoculated sludge.Although QL sludge had the lowest biogas production potential and the highest SMA,the high ammonia nitrogen tolerance test showed that QL sludge had the worst ammonia nitrogen tolerance.The LAB sludge can tolerate up to 11 g/L ammonia.During the process that led to increased ammonia concentration,the SMA of the LAB sludge decreased the least compared to the other three sludges,which meant that it was the most resistant to high ammonia concentrations.Long time acclimation with high ammonia nitrogen did not show stronger tolerance to high ammonia than short time acclimation with high ammonia nitrogen.Therefore,combined with factors such as VS/TS ratio,sludge activity and ammonia tolerance,LAB sludge was most suitable for inoculation sludge in dry anaerobic digestion of chicken manure.(2)LAB sludge was used as inoculated sludge to study the effects of temperature and ammonia nitrogen concentration on the DAD of chicken manure.Temperature was the main factor affecting biogas production performance at the initial stage of AD when ammonia nitrogen had not reached the inhibition level.Low temperature reactors(15 °C and 20 °C)had the lowest biogas production rates,and the volumetric biogas production rate was always low(0.1 L/L/d).The volumetric biogas production rate of the medium and high temperature reactors can reach 0.7~1.0 L/L/d.Increasing the AD temperature did not improve biogas production when the ammonia concentration reached ~5000mg/L.The high temperature reactors(45 °C and 55 °C)had good biogas production performances during the initial stage of AD.However,as the operation time and organic load rate increased,the high ammonia nitrogen concentration led to the continuous accumulation of volatile fatty acids(VFAs).Ammonia nitrogen concentration became the main factor affecting biogas production efficiency and almost completely inhibited biogas production at the later stage.During the whole experiment process,the biogas production performance of the medium temperature reactor at 25 °C,30 °C,and 35 °C was better than the low and high temperature reactors.The reactor at 35 °C performed slightly better than that at 25 °C and 30 °C in terms of relatively good ammonia tolerance,biogas production performance and duration of ? 50% methane content.(3)This study presented a new method of adding granular activated carbon(GAC)into an AD reactor,in which the GAC packed in nylon mesh bags.The effect of adding different adsorbents to alleviate the inhibition of high ammonia nitrogen in the DAD process of chicken manure was studied at35 °C.The result shown that the addition of zeolite promoted early biogas production performance,but the addition of medical stone did not improve biogas production performance.The addition of granular activated carbon(GAC)significantly reduced the combined stress of high ammonia nitrogen and high acid levels,and improved the biogas production efficiency of the chicken manure DAD process.The reactor with added GAC had a biogas production rate of 0.19 L/kg TS and volumetric biogas production rate of 0.683 L/L/d,which was five times that of the control group.During the test process,which lastedmore than 200 days,the DAD reactor containing chicken manure produced normal levels of biogas and the methane content was more than 50%.(4)The mechanism of adding GAC to improve the DAD of chicken manure was analyzed.The GAC had a good adsorption capacity for ammonia nitrogen(the maximum adsorption capacity was19.76 mg/g).The addition of GAC increased the hydrolysis efficiency of fat and cellulose by 16.74%and 12.14% compared to the control group,respectively.However,protein hydrolysis efficiency decreased by 1.97%.Unbalanced hydrolysis of macromolecular compounds and ammonia adsorption by GAC reduced the ammonia nitrogen concentration in the reactor.The most likely reason for this was that GAC enriched syntrophic acetate oxidation(SAO)bacteria(Tepidanaerobacteris,Syntrophicacecus schinkii and Clostridium ultunense),potential SAO bacteria(Pseudomonas and Acholeplasma)and the hydrogenotrophic methanogen Methanoculleus,enhanced the ability of direct interspecific electron transfer(DIET)and promoted the syntrophic acetate oxidation-hydrogenotrophic methanogenesis(SAO-HM)pathway.