| Due to the difference of physical geography and economic activity,the organic matter content of municipal sludge?MS?is variable over China.This is mainly because separate sewer systems are designed to convey sewage and stormwater in separate pipes in some cities,and the organic matter content of MS can be up to 70%.In other district with combined sewers,this value is usually lower than 50%.In recent years,anaerobic digestion?AD?has been widely used for the treatment of MS with high organic content matter,and methane is obtained as the byproduct.Methane,the major constituent of natural gas,can help alleviate the dual crisis of the energy and the environment.However,the MS with low organic matter content?<50%?leads to less methane production and lower degradation efficiency accompanied with long hydraulic retention time?HRT?,which restricts its application.So in this study,substrates were selected for anaerobic co-digestion?Aco D?with low organic sludge.Then,the inhibitors and the resistance in AD with different substrates were investigated.After that,the influence of pretreatment on the performance of AD was evaluated.Subsequently,the optimization of anaerobic digestion of multiple matrix?MM?was carried out by response surface methodology?RSM?.Finally,the performance of MM in the continously stirred tank reactors?CSTR?was studied.The main results were:?1?Other substrates were determined by the specific methane production?SMP?and its kinetics in the batch experiments of Aco D.The biochemical methane potential?BMP?of the raw substrates was determined.The order of SMP was:food waste?FW?>swine manure?SW?>MS>banana straw?BS?.Based on the kinetics,the Modified Gompertz?MG?model is more suitable for AD system with raw substrates,even with a certain delay.The synergistic effect of MS and FW in Aco D experiment was not obvious.Compare to SW,the synergistic effect and the anaerobic digestion performance of BS were relatively better in the Aco D.However,the synergistic effect has not been maximized.?2?BMP experiment,equation simulation and 16s r DNA high throughput sequencing technology were used to explore the main inhibitors and resistance of anaerobic digestion in different substrates.Ammonia and long-chain fatty acids?LCFA?were mainly considered as the inhibitors in the AD.Accordingly,the synergistic effect among inhibitory factors was revealed.The tolerance concentration threshold of ammonia inhibition was greatly increased during the synergistic anaerobic digestion of MM.The order of LCFA inhibition for the inoculum of the anaerobic digestion system was:linoleic acid>oleic acid>palmitic acid>stearic acid.The resistance concentration of LCFA inhibition was increased by synergistic anaerobic of MM,but not obviously changed in case of FW.The values of SMP showed that the increase of LCFA could not reduce the inhibition of ammonia nitrogen,but induced a co-inhibition effect.The results of 16s r DNA high throughput sequencing further showed that the relative abundance of two dominant archaea,Methanosaeta and Methanobacterium,decreased from 56.5%to about 20%,when ammonia and LCFA were inhibited in AD of MM.The lower abundance of Syntrophomonas was indicated less degradation of LCFA.?3?Aiming at the limitation of hydrolysis speed in the unpretreated matrix,High temperature thermal hydrolysis pretreatment?HTHP?and alkali pretreatment methods were applied to sludge and banana straw,respectively,and the optimal pretreatment method was selected according to the SMP and organic degradation characteristics,which improved the hydrolysis efficiency.In the combining system,the methane yields of MS,BS and their mixture were388 m L·g-1VS,372 m L·g-1VS and 537 m L·g-1VS,respectively,which indicated a significant synergistic effect of MS and BS during the digestion.The results of HTHP were more effective compared to alkali pretreatment,which can be recommended as pretreatment.The SMP of MS,FW and BS mixture could reach a maximum of 608 m L·g-1VS with an increase of 66.3%when the VS ratio was 1:2:2 in AD with HTHP,which showed the maximum significant synergistic effect.By adding banana straw,organic matter content in AD system can be increased,C/N ratio can be adjusted,and inhibition effect can be alleviated.These are the main mechanism of the synergistic effect of MM in the AD system.?4?The RSM was used to optimize the digestion process and determine the optimal conditions in MM anaerobic digestion experiment.The optimal conditions of RSM for AD were:TS=15%,C/N=25,inoculation ratio?IR?=50%.The results indicate the effects of these factors on the methanogenesis of the MM are extremely significant,and the order is C/N>IR>TS.The 16s r DNA high throughput sequencing results showed that the dominant bacteria was acid-vegetative methanogens,which means higher SMP can be obtained.Most importantly,the Syntrophomonas,which determine the rate of?oxidation by LCFA,has increased exponentially.The LCFA in the AD system was effectively degraded and methane production was further increased.?5?Semi-continuous stirred tank reactor?CSTR?experiment and 16S r DNA high throughput sequencing method were used to explore the mechanism of anaerobic co-digestion of MM in semi-continuous statue.As the important parameters for the control of the anaerobic digestion process of MM in semi-CSTR,the organic loading rate and C/N were 4 kg VS·?m3·d?-1and 25,respectively.Under these conditions,the cumulative SMP of the MM pretreatment group could be stabilized at about 500 m L·g-1VS,which could maintain the anaerobic digestion reactor in a good performance and utilization level.When FAN and LCFA concentration were lower than 600 mg·L-1and 6.2g·L-1,respectively,no inhibitory effect was observed.The results of 16s r DNA high throughput sequencing showed that the dominant archaeal species were the Methanobacterium and Methanosaeta under the optimal OLR and C/N conditions.The increase of vadin BC27 and Syntrophomonas were more obvious,which promoted the decomposition of cellulose,accelerated the?oxidation of LCFA,and improved SMP correspondingly. |
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