Hythane Production From Rice Straw And Pig Manure In A Two-phase Anaerobic Co-Digestion

The use of non-renewable fossil fuels will cause environmental problems such as acid rain and ozone layer destruction,so it is imperative to find sustainable and environmentally friendly new energy sources.Livestock manure and crop stalks are two major agricultural solid wastes,and their annual output is up to 3.8 billion tons and 900 million tons respectively,among them,rice straw and pig manure have larger annual output.Since both wastes contain large amounts of organic matter,they can be used as a substrate for anaerobic digestion to produce biogas.Hythane(a mixed gas of 5-25%by volume of hydrogen and 75-95%methane)have the advantages of hydrogen and methane,and the use of hythane will not release oxides of nitrogen,sulfur and other substances,so hythane are considered to be good alternative to fossil fuels.Two-phase anaerobic digestion can separate the hydrogen production process and methane production process of single-phase anaerobic digestion,and realize the simultaneous recovery of hydrogen and methaneIn this study,firstly,batch test of rice straw and fresh pig manure co-fermentation to hydrogen production were tested,which determined the best mixing ratio of rice straw and fresh pig manure,the best inoculum pretreatment method and the hydrogen production time.Secondly,a continuous experiments of two-phase anaerobic co-digestion of rice straw and fresh pig manure were operated under different processes,which determined the optimal process of hythane production form rice straw and fresh pig manure.Finally,a continuous experiments of hythane production from different substrate composition were carried out,which determined the optimal substrate composition by rice straw and pig manure.The best process for two-phase anaerobic digestion of hythane from rice straw and pig manure judged by methane yield,hydrogen and methane ratio,energy yield,and COD balance,organic matter removal rate and other aspects comprehensively.The main research content and results are as follows:(1)Firstly,a batch fermentation test of rice straw and fresh pig manure was used to produce hydrogen.Five kinds of fermentation substrates with TS=3%were prepared from rice straw and fresh pig manure,which were rice straw:pig manure=1:0,5:1,3:1,1:1,and 0:1(TS).Then,inoculate the inoculum after acid,alkali and heat pretreatment respectively,and take the untreated anaerobic sludge as a control,and then conduct the hydrogen production test at 55℃.The result shown that the 5:1 mixing of rice straw and pig manure was the optimal mixing,the best inoculum pretreatment was acid pretreatment,and the hydrogen production time did not exceed 3.5d.Under the optimal conditions,the hydrogen yield is 44.59 mL/g VS added,the TCOD removal rate and conversion rate are 18.12%and 2.12%,respectively.At the same time,it will not cause ammonia nitrogen inhibition(<670 mg/L)and metabolites under these conditions.Mainly butyric acid;(2)Continuous experiments on the production of hythane by rice straw and fresh pig manure under different technological processes.On the basis of the first phase process parameters(inoculum acid pretreatment,rice straw:fresh pig manure=5:1 and HRT=3.0d)determined by batch experiment,the rice straw and fresh pig manure to product hythane under the four process processes(mesophilic-thermophilic(M-T),digestive juice reflux mesophilic-thermophilic(M-T(R)),thermophilic-mesophilic(T-M)and digestive fluid reflux thermophilic-mesophilic(T-M(R)).Experiments show that the T-M has good hythane production performance,its total hydrogen production rate is 13.63±1.50 mL/L/d,and its total methane production rate is 161.55±8.47 mL/L/d,the ratio of hydrogen to methane is as high as 8.45±1.01%,and its energy yield is also the highest(7.26±0.44 kJ/g VS added);the Thermoanaerobacterium(32.24%)and Clostridium(27.47%)was the major hydrogen producing bacteria in the first phase and the(36.00%)and Methanobacterium(46.00%)was the major methanogens in the second phase;(3)Continuous experiments on the production of hythane by rice straw and pig manure under different substrate composition.The best composition of rice straw and pig manure for continuous to production hythane was tested under the optimal mixing ratio of rice straw and fresh pig manure(5:1)determined by batch experiments and the optimal process for producing hythane determined by continuous experiments(T-M).The experimental results show that the best substrate composition is rice straw:fresh pig manure=5:1,and substrate concentration is TS=6%,the total hydrogen generation rate is as high as 115.50±4.41 mL/L/d,and the total methane generation rate is as high as 369.60 25.46 mL/L/d,the ratio of hydrogen to methane is 31.4±2.61%,and the energy yield is 9.30±0.34 kJ/g VS added.The Clostridium(18.00%)was the major hydrogen-producing bacteria in the first phase and the Methanosaeta(50.00%)was the major methanogens in the second phase.Our work was determined the optimal process parameters for hythane production by two-phase anaerobic co-digestion of rice straw and pig manure,which realized the reclamation,reduction and innocuity of rice straw and pig manure.Our study provided a new idea for the disposal of crop straw and livestock manure,and laid a theoretical foundation and practical test for the development of environmentally friendly and sustainable energy sources.