| From 2007 to 2017,Chinese large-scale broiler farms with an annual output of more than500,000 chickens rose from 320 to 1950,and the large-scale layer farms with an annual inventory of more than 500,000 chickens increased from 6 to 69.The number of large-scale chicken farms and breeding in my country has been increasing year by year.The amount of chicken manure produced is also increasing,which brings great pressure to environmental pollution control.Anaerobic digestion technology for dealing with chicken manure and producing biogas and biogas fertilizer is an economical and feasible method.Chicken manure is high-solid with low C/N,which leads ammonia inhibition more easily to occur in anaerobic digestion.Therefore,adding water to dilute the feed produces excessive biogas slurry and reduces the nutrition of biogas slurry.How to achieve stable and efficient high-solid anaerobic digestion of chicken manure has always been a challenge.In this paper,a continuous stirred-tank reactor operated for more than 150 days without adding auxiliary substances.Compared with the conventional chicken manure anaerobic digestion feed(TS < 10%),the total solid was increased to TS 15%,and the hydraulic retention time(HRT)was set as 20,40 and 60 d.The effect of HRT on high-solid anaerobic digestion was studied.The main conclusions obtained are as follows:(1)Under the conditions of HRT 20 and 40 d,the anaerobic digesters could not operate stably for a long time.Under the condition of HRT 60 d,the digester could maintain stable operation,and the methane conversion efficiency of volatile solids(VS)reached 326 m L/g-VS,similar to conventional low-solid anaerobic digestion performance.Under the condition of HRT 60 d,the total solid(TS)removal efficiency reached 64%,the volatile solid(VS)removal efficiency reached68%,with the best organic conversion effect.(2)Under the condition of HRT 60 d,the average concentration of total ammonia nitrogen and free ammonia reached 7527 and 2610 mg/L,respectively.Anaerobic microorganisms could adapt to the environment of high ammonia nitrogen.The average concentration of total VFA was only 552 mg/L.(3)Compared with the digester under HRT 40 d,the acetic methanogenic activity of HRT 60 d anaerobic sludge maintained a higher level,and the propionic metabolic activity was also significantly improved.The gas production potential of the digester showed that the effect and stability of the HRT 60 d digester was better than that of two digesters with shorter HRT.(4)Operating under high ammonia nitrogen conditions for long-term,bacteria and hydrogenophilic methanogens that tolerated high ammonia nitrogen environments were domesticated.The dominant genus of methanogenic archaea changed from Methanobacterium(48.45%)at HRT 40 d to Methanoculleus(83.14%)at HRT 60 d.By extending HRT,the bacteria became more evenly distributed and the archaea abundance became higher in the digester.By carrying out a long-term continuous experiment,the effect of HRT on the performance of chicken manure high-solid anaerobic digestion process was studied.The results showed that more than 50% water consumption and more than 30% of biogas slurry and biogas residue discharge could be reduced in the chicken manure biogas engineering,with appropriately extended HRT and the invariable load.The burden of biogas slurry and biogas residue was reduced.A broader application prospect for livestock and poultry waste biogas engineerings was provided. |
