| Compared with conventional solid content anaerobic digestion and mesophilic anaerobic digestion of sludge of municipal wastewater treatment plants,high solid thermal hydrolysis pretreatment following thermophilic anaerobic digestion(THP-TAD)presents advantages in efficient energy recovery and methane production rate.However,the stability of the THP-TAD system hinders its full-scale application,especially by the ammonia inhibition and volatile fatty acids(VFAs)accumulation during the start-up stage.Therefore,achieving THP-TAD is to balance the accumulation and consumption of VFAs and hydrogen during the start-up stage,in addition,by strengthening the performance of syntrophic acetate oxidation coupled with hydrogenotrophic methanogenesis(SAOHM).At present,it has been proved that a variety of regulatory methods can be used to realize SAO-HM.In this study,2% conventional solids thermophilic anaerobic digestion sludge and 10% high solids thermal hydrolysis mesophilic anaerobic digestion sludge were used as inoculated sludge to analyze the kinetic rate changes and ammonia inhibition characteristics of each anaerobic digestion step under different anaerobic digestion environments.Continuous operation tests were conducted to analyze the methane production performance and the kinetics and microbial community structure of the two inoculated sludge,to explore the feasibility of ammonia concentration control and solids rate control strategies for THP-TAD,in order to provide a theoretical basis for efficient treatment and resource utilization of sludge in wastewater treatment plants.The main findings are as follows:(1)The metabolic characteristics of inoculated sludge under different anaerobic digestion environments showed that specific methanogenic activities of acetic acid,propionic acid,butyric acid and thermal hydrolysis sludge decreased by 65.34,83.76,69.95 and 71.88% with increasing ammonia concentration,respectively,while the hydrogen utilization rate and syntrophic acetate oxidation rate were not significantly affected.Under thermophilic conditions,the methanogenic activity of all groups decreased to 1.53,4.04,22.92 and 11.59% of the maximum activity,respectively.The maximum decrease in hydrogen utilization rate and syntrophic acetate oxidation rate were60.11 and 77.74%,respectively.For conventional thermophilic anaerobic digestion inoculated sludge,the SMA of acetic acid,propionic acid,butyric acid and thermal hydrolyed sludge decreased by 28.05,57.89,61.27 and 13.33% with the increase of ammonia nitrogen concentration,respectively,while hydrogen utilization rate and syntrophic acetate oxidation rate were not significantly affected.Therefore,the results of hydrogen utilization rate and syntrophic acetate oxidation activity under high ammonia environment indicate that it is feasible to achieve THP-TAD by the above two inoculated sludge.(2)The feasibility analysis of ammonia concentration control to achieve THP-TAD showed that the continuous load shock test of thermophilic anaerobic digestion at HRT of 20,15,10 and 5 could operate stably,the high solids mesophilic sludge was regulated from ammonia concentration 3051.92 ± 78.47 to 2476.11 ± 58.22 mg/L,although the VFAs concentrations were as high as 85.90 ± 9.40、96.32 ± 7.49、100.42 ± 7.85 and192.50 ± 11.86 g COD/L,the reactors p H of each group was maintained at 7.77 ± 0.27 and the volumetric gas production rate recovered to 0.47 ± 0.12,0.57 ± 0.09,1.01 ± 0.23 and 0.79 ± 0.18 L/(L·d).The THP-TAD sludge,which operated stably after ammonia concentration regulation,still showed good metabolic rate after returning to thermophilic environment,the SMA of acetic acid,propionic acid,butyric acid and thermal hydrolysis sludge all increased to different degrees and hydrogen utilization rate was also increased by 22.87,44.62,48.21 and 45.74%,respectively.The results of 16 S r RNA gene sequencing showed that the relative abundance of Defluviitoga,Tepidimicrobium,Anaerobaculum,Symbiobacterium and Syntrophaceticus,which possess syntrophic acetate oxidation function,all became the dominant genera in the regulated sludge.the relative abundance of Methanosarcina after the switch decreased from 72.48% to 42.05± 19.37%and Methanomassiliicoccus increased from 6.54% to 13.31 ± 10.29%,while the relative abundance of Methanothermobacter increased from 0.12% to 42.78 ±27.64%.Therefore,ammonia concentration regulation can effectively increase the proportion of methane production from syntrophic acetate oxidation in the anaerobic system and promote the construction of SAO-HM system.(3)The feasibility analysis on solids rate regulation for THP-TAD showed that The results of the continuous load impact test of thermophilic anaerobic digestion at HRT of20,15,10 and 5 showed that the volumetric gas production rates were 0.40 ± 0.09,0.61 ±0.12,0.95 ± 0.17 and 1.79 ± 0.22 L/(L·d),respectively,when the conventional solids content of thermophilic anaerobic digestion sludge(2%)was regulated to a high solids content(10%).When the organic load was as high as 14 g COD/(L·d),the free ammonia reached 665.65 ± 121.29 mg/L and the system still showed that COD removal capacity(27.99 ± 3.66%)and stability(p H 7.74 ± 0.09).The hydrogen utilization rate of sludge at different HRT was increased by 91.60 ± 41.54 % after solids content regulation.The results of 16 S r RNA gene sequencing showed that the relative abundance of Coprothermobacter,Anaerobaculum,Tepidimicrobium and Syntrophomonas genera increased after the regulation,the acetic acid trophic methanotrophic Methanothrix was eliminated,and the SAO-HM process could be involved in The relative abundance of Methanosarcina increased from 16.52% to 58.75 ± 7.28% and Methanothermobacter increased from 2.69% to 37.17 ± 7.36%.Therefore,the solid content regulation strategy is an effective strategy to achieve THP-TAD,which can changed the methanogenic pathway from acetoclastic methanogen(AM)to SAO-HM. |
PDF Full Text Request