Food Waste And Dairy Manure Anaerobic Fermentation Process And Microbial Diversity During The Process

Biogas anaerobic fermentation technology is one of the effective means for the resource utilization of food waste(FW)and dairy manure(DM).However,the fermentation process of FW is easily affected and fluctuated by the accumulation of organic acid,when DM has low gas production efficiency due to the high contain in cellulose,lignin and other refractory materials.In order to improve the resource utilization of FW and DM,the study of FW and DM co-anaerobic fermentation through the optimization of fermentation conditions and improvement of fermentation process was carried out.Based on the optimization of the two phase anaerobic fermentation conditions by batch experiment,the influence of application of fixed bed reactor(FBR)and continuous stirred-tank reactor(CSTR)on FW and DM co-anaerobic fermentation were evaluated by semi continuous experiment,at the same time,microorganisms diversity in CSTR and FBR was analysis through the miseq high-throughput sequencing technology.The effect of organic loading(OLR)on the FBR treatment of mixed materials was studied under a constant mixed materials concentration,and the changes of microbial population in the process were analyzed by using PCR-DGGE technique.The main results are as follows:1)Experiments were conducted in 1 L anaerobic digestion reactors at 35 with volatile solid ?(VS)ratios of 3:1,2:1,1:1,1:2 and 1:3(FW/DM)when the VS of FW was 16 g VS in the digestion system.The p H value first decreased and then increased during digestion process.With a higher proportion of DM added,p H value decreased within a smaller limit and recovered faster,total methane production increased significantly and methane production rate decreased obviously.Compared to the sum of methane production of FW anaerobic digestion and that of DM anaerobic digestion,methane production of the mixed anaerobic of FW and DM was higher.When the ratio of DM to FW was 2,the increased methane production reached to the highest value and the increased rate was 52.4%.2)The optimum acidification conditions were as follows: 7.6 h of the acidification time,10.4% of substrate concentration,and 35 ?of acidification temperature.Under the optimum condition,methane production rate was 290.5m L/g VS,which was 17.9% higher than 246.3m L/g VS of un-pretreatment anaerobic digestions.3)The optimum fermentation conditions were as follows: 36.6? of fermentation temperature,and 5% of the substrate concentration.Under this condition,the methane yield of the mixture was 312.3 m L/g VS,which increased by 7.5% compared with that under the best condition from single factor test.4)The addition of carbon fiber carrier improve the mixture anaerobic fermentation biogas production and methane yield by 4.9% and 13.9% at the hydraulic retention time(HRT)of 10 days,respectively.Carbon fiber carrier ensured the stable and consistent operation of the FBR at the HRT of 5 days.Miseq high-throughput sequencing results showed that microbial composition in FBR and CSTR was obviously different.Syntrophomonas(5.25% in carbon fiber carrier(FF)and 6.04% in feed liquid(FL)),Lactobacillus(5.15% in FF and 3.34% in FL)and Clostridium(3.11% in FF and 8.32% in FL)were the dominate bacteria in the FBR when Prevotella(66.93%)and Faecalibacterium(2.58%)dominate the CSTR.Methanobrevibacter(50%)and Methanobacterium(25%)were Hydrogenotrophic Methanogens,which dominate in the CSTR.when Hydrogenotrophic Methanosarcina(35.1% in FF and 67.2% in FL)and Methanobacterium(35.6% in FF and 6.9%in FL)and acetate-utilized Methanosaeta(8.6 in FF and 21.8% in FL)were dominant in the FBR.5)In the OLR range of 2.0-10.0 g VS/(L·d),the reactor operated stably.Volume biogas production rate and methane yield reached maximum of 1553.4 m L/(L·d)and 1106.4 mg/L at a OLR of 10.0 g VS/(L·d),When the methane yield and methane content reached the maximum value of 270.5 m L/g VS and 75.5% at a OLR of 3.3 g VS/(L·d).VFAs accumulation reached 5579mg/L when OLR increased to 12.5 g VS/(L·d),then biogas production from the reactor stopped.PCR-DGGE results indicate that microbial diversity was high in the OLR range of 2.0-10.0g VS/(L·d).The dominant bacterial were syntrophomonas,Lactobacillus and Clostridium,when the dominant Archaea bacteria were Methanosarcina,Methanosaeta,methanobrevibacter and Methanobacterium.When OLR was raised to 12.5 g VS/(L·d),the microbial diversity in FBR decreased significantly.Dominant bacteria were Faecalibacterium and Prevotella,when dominant archaeal changed to Methanobrevibacter and Methanobacterium.This study provides the evidence that the mixed anaerobic of FW and DM could enhanced the buffer capacity of the digestion system and improved the anaerobic digestion efficiency.Using two-phase anaerobic fermentation and anaerobic fermentation conditions optimization improved the mixture methane production.Carbon fiber carrier was used to fix the major microbial groups for acidification and methane production.Compared with CSTR,the microbial diversity in FBR was rich,with an efficient organic matter degradation,VFAs conversion and methane production,which ensured the stability of methane production process.The anaerobic fermentation of mixed materials can be improved by using a fixed bed anaerobic fermentation process.