Methods And Microbiological Mechanism Of Controlling Ammonia Inhibition In High-Nitrogen Materials Anaerobic Digestion For Biogas Production

The anaerobic methane fermentation is an effective technology for the energy conversion and resource recovery of high-nitrogen like livestock manures.However,the common problem of ammonia inhibition in high-nitrogen AD greatly reduces its overall performance.In this paper,aiming at the problem of ammonia inhibition during typical AD of livestock manure and food waste,and combining with the physicochemical property of high-nitrogen raw materials,the effects of strategies for controlling the ammonia inhibition including C/N ratio adjustment,trace elements addition and ammonia stripping on the high-nitrogen materials AD were studied.And the microbial community structure especially methanogen group was analysised,in order to explore the changes of methanogenic pathway and methanogenic bacteria during the occurrence and regulation of ammonia inhibition.In brief,main results are as follows:?1?The highest methane yields of pig manure?PM?,cow manure,chicken manure?CM?and rabbit manure were obtained at 8 g VS L^-1,with values of 409.6,269.8,377.1 and 323.2 mL CH4 g^-1VSadded,respectively.The improvement of substrate concentrations led to a decrease in methane production,biodegradation,and the percentage of methane in total gas production.In addition,high concentration substrate degraded and produced a large number of soluble inhibitors like ammonia nitrogen which inhibit methanogens activity,and due to reduced inoculum to substrate ratio,resulted in longer lag period before gas production.?2?The addition of trace elements Se and Co could improve the highest organic loading rate of food waste AD system to 3.0 g VS L^-1d^-1.At this loading,the specific methane production?SMP?was 0.486 L g^-1 VS_added,and that was 0.45 L g^-11 VS_added for control.Trace elements supplied digester with loading of 5 g VS L^-1d^-1 showed instability after 133 days of operation.The addition of Mo and Ni showed no improvement.After the addition of Fe,gas production and digestion stability returned to normal.This indicated that Se,Co,Fe are necessary trace elements for stable operation of food waste AD with high loading rate.Microbial community results demonstrated that acetoclastic methanogens played a major role in methanogenesis under optimal and sub-optimal conditions.As the increasing of ammonia nitrogen and volatile fatty acid concentration,hydrogenotrophic methanogens have become the most promising candidate for mesophilic methane production from food waste.It shows that the tolerance of hydrogenophilic methanogens to inhibitors is higher than that of acetic acid-degrading methanogens.?3?Both the highest organic loading rates of chicken manure and pig manure mono-digestion were 2.4 g VS L^-1d^-1,and the SMP were 0.279 and 0.299 L g^-11 VS_added.After the addition of rotten apple pulp,SMP improved to 0.365 and 0.322L g^-11 VSadded.And the highest organic loading rate of CM anaerobic digestion system was improved to 4.8 g VS L^-1d^-1.After the addition of corn stover?CS?,SMP were changed to 0.251and 0.301 L g^-11 VS_added.At loading 4.8 g VS L^-1d^-1,the SMP of reactors fed CM,PM,CM/AP,PM/AP were 0.237?0.253?0.329 and 0.268 L g^-11 VS_added.Fluorescence in situ hybridization revealed that the microbial community in digester fed with CM:AP mix was dominated by Methanosarcinaceae and the remaining microorganisms mainly belonged to Methanobacteriaceae,both of which reflected the tolerance of inhibitors in this system.?4?The chicken manure digestate ammonia stripping condition study showed that ammonia removal rate increased with the increasing of stripping temperature and pH value.The ammonia removal efficiency was the highest under the ammonia stripping conditions of 70°C and pH 11 and the ammonia removal rate of the fermentation was 98.4%after 86.5 h of ammonia stripping.The fitting results of the first-order kinetic model show that the feature length?increases with the temperature of the blow-off or the decrease of the pH value.The denitrification efficiency E value increases with the temperature or pH at which the ammonia is blown off.?5?The SMP of sole chicken manure AD was 0.163 L g^-1 VS_added at 3 g VS L^-1 d^-1.The adoption of ammonia stripping treatment at 35?,55?and pH 10 did not improve the AD performance of CM.Under the stripping conditions of 70?,pH 10,the highest organic loading rate of CM anaerobic digestion system can be increased from 3 VS L^-1 d^-1 to 9 g VS L^-1 d^-1 at which the SMP value as high as 0.199 L g^-1VSadded was obtained.Meanwhile,a shift from Methanosarcinaceae to Methanomicrobiales was observed in this digester,while dominant species were inhibited and decreased in other digesters.In this study,batch experiments and semi-continuous anaerobic digestion test were combined,and several ammonia inhibition control methods were adopted to treat the high-nitrogen raw materials or the digestate.The results show that all three methods,including C/N ratio adjustment,trace elements addition and digestate ammonia stripping,effectively improve methane yield and stability of livestock manure anaerobic digestion,which were ideal ways to relief ammonia inhibition.