The Efficiency And Mechanism Of Hydrogen And Methane Production By Anaerobic Fermentation Of Pig Manure

The scale of pig farming is becoming increasingly large and the production of pork is rapidly increased,resulting on the by-products is increasing substantially.If a large amount of pig manure,In the absence of treatment is discharged into the external environment directly,it will inevitably cause serious pollution for soil and groundwater resources,the discharge of toxic and harmful gasesand the spread of pathogens.Therefore,it is urgent to treat pig manure innocuously and resourcefully to solve the current problems of pig manure pollution and resource waste.In this thesis,pig manure was used as the sole substrate.The granular sludge and flocculent sludge were used as co-inoculated sludge to investigate the relevant factors and mechanisms of pig manure anaerobic fermentation.In this study,seven ratios of granular sludge and flocculent sludge（0:10,1:9,4:6,5:5,6:4,9:1,10:0）were design for clarifying the effects of different sludge ratios on hydrogen and methane production from pig manure by anaerobic fermentation.The results showed that the maximum cumulative hydrogen production of 39.1 m L/g TS was achived when the ratio of granular sludge to flocculent sludge was 1:9.The acetate pathway was the main hydrogen production pathway in this system.However,the optimal sludge ratio for methane production in pig manure fermentation was 4:6（granular sludge:flocculent sludge）,whose the maximum methane production and maximum methane production rates were 39.4 m L/g TS and 10.1 m L·g TS^-1·d^-1,respectively.The SCOD removal rate reached70.2%,which was higher than that of flocculent sludge group and granular sludge group by 2.8%and 64.3%respectively.In addition,the methane was mainly generated by acetic acid cracking.Secondly,this paper investigated the effects of different initial p H on hydrogen production and methane production by anaerobic fermentation of pig manure.The results showed that hydrogen could be produced at the initial p H of 5.0～12.0.It showed a trend of first increasing and then decreasing as the increase of p H from 5.0 to 12.0.The maximum hydrogen production with 31.6 m L/g TS was observed at initial p H 8.0.Similarly,the methane production effeciency of pig manure fermentation liquid also showed a trend of first increasing and then decreasing with the increase of p H under the condition of initial p H 5.0～p H 12.0.The cumulative methane production reached a maximum of 174.7m L/g TS at the initial p H 8.0.Although peracidic and overbase（p H 5.0 and p H 12.0）did not completely inhibit the activity of hydrogen-producing and methanogenic community during the anaerobic fermentation of pig manure,the activity was low.Furthermore,redox mediators（ROMs）were used to further improve the efficiency of hydrogen production and methane production from pig manure fermentation.The results showed that humic acid,menaquinone and methyl violet improved the hydrogen production by anaerobic fermentation of pig manure.Among them,the humic acid had the most significant promotion effect,making the hydrogen yield of pig manure reaches 43.6m L/g TS.This thesis further analyzes the effects of different concentrations of humic acid on hydrogen production in pig manure fermentation.The results showed that the maximum hydrogen production efficiency of anaerobic fermentation of pig manure was observed at the humic acid of 80 mg/L.Its cumulative hydrogen production was 17.3m L/g TS,which is higher than that of the control group.The dominant bacterial genera in the system were Roseimarinus,unclassified＿Rhodobacteraceae,Bacteroidetes＿vadin HA17,unclassified＿Dysgonomonadaceae,BSV13,Bdellovibrio,unclassified＿Anaerolineaceae,[Cytophaga]＿xylanolytica＿group,OLB14 and unclassified＿Gemmatimonadaceae.The experiments about the effect of ROMs on methane production in pig manure fermentation showed that humic acid,henna quinone,menaquinone,methyl violet and AQDS were all beneficial to methane production from pig manure fermentation liquid.After 24 d of culture,their cumulative methane yields reached 194.8,206.7,191.1,180.3 and 166.6 m L/g TS,respectively.Further analysis showed that the methane production rate was significantly increased when the humic acid concentration was 25mg/L.The cumulative methane yield reached 206.7 m L/g TS.The dominant bacterial genera in the system were Methanosaeta,unclassified＿Peptostreptococcaceae,Romboutsia,Bacteroidetes＿vadin HA17,and Clostridium＿sensu＿stricto＿13,Methano-bacterium,unclassified＿Anaerolineaceae,Georgenia,OLB14,and JGI-0000079-D21.