Effect Of Biochar Addition And Hydrothermal Pretreatment On Anaerobic Digestion Of Fish Processing Waste, Tofu Residue And Rice Straw

Anaerobic digestion is an efficient way of treating animal wastes and biomass byproducts to reduce its pollution threat and produce renewable bioenergy in the form of methane（biogas）.Among the potential bioenergy resources,fish processing waste and lignocellulosic biomass has been identified as cheap and effective feed-stocks for biogas production.China had a total fisheries production of 49.2 million tons in 2016,which was about 62%of the global inland fishery production.Fish processing waste（FPW）,including fish viscera,fish fat,bladder,bone,fin,and scales,is the major byproduct during fish processing and it represents more than 10%of the fish weight,which means more than 4.9 million tons of fish processing waste was generated in China in 2016.Traditionally,FPW is disposed by landfills and incineration,but those disposal methods are expensive and cause more environmental problems.Landfill occupies large amount of land resource and the leachate of the landfills pollutes groundwater,while incineration emits greenhouse gases and toxic gases.Tofu residue（TR）is a major by-product derived from tofu production or their derivatives such as soy bean curd and soy beverages.In general,every 1000 L of soy milk produces about 250 kg of tofu residue.It was estimated that approximately 14million tons of tofu residue was generated all over the world each year,bringing environmental burden.In addition,rice straw is one of the most abundant lignocellulosic agricultural crop wastes in China.However,lignocellulosic materials are naturally recalcitrant and have structure that is more complex.Pretreatment or co-digestion with manure is needed for rice straw treatment to improve the anaerobic digestion efficiency for biogas production.Hydrothermal pretreatment is an attractive approach for lignocellulosic biomass pretreatment.This approach is very cost effective,low-energy requirement,environment friendly and low formation of toxic materials.The research focused on the application of bamboo residue hydrothermal carbonization on anaerobic digestion with fish processing waste and tofu residue.The effects of bamboo hydrochar,co-digestion of fish processing waste with liquid fraction of hydrothermal carbonization,hydrothermal pretreatment of tofu residue and rice straw were studied to maximize the biogas production,methane yield and net energy output.The theoretical basic for engineering application of the technique was provided.The research contents and the main results are as follows:1)The effect of hydrothermal carbonization（HTC）temperature and bamboo hydrochar（BHC）addition on biogas production in anaerobic digestion of FPW was studied.HTC temperature（200-280°C）had significant effects on methane yield and content,while the BHC had little effects.The maximum biogas yield observed with HTC at 200°C and a BHC adding ratio of 1:2（dry mass ratio of FPW to BHC）reached 292m L/g volatile solids（VS）,which were 64%higher than the control group with only FPW,with the maximum methane yield of219m L/g-VS and highest net methane energy yield of 3410 k J/kg-VS.The obtained results can be used to design an efficient anaerobic digestion process for treating and effectively utilize fish processing waste.2)The effects of different mixing ratios of FPW with the liquid fraction（LF）of hydrothermal carbonization（HTC）of bamboo residues on biogas and methane yield was investigated.The different mixing ratio（FPW+LF）and HTC temperature（200–280°C）had significant effects on biogas and methane production.The anaerobic co-digestion of the various mixing ratio of FPW and LF of bamboo residues did not enhance the methane yield compared to the AD of FPW alone.However,a mixture of75FPW+25LF（220）presented a similar methane production（133 m L/g VS）to that achieved with 100FPW（142 m L/g VS）,only increased by 6.4%.The ratio of75FPW+25LF（220）increased the biogas yield by 81%compared with the control group of 100LF（220）.The mixing ratio of 75 FPW+25LF（220）did not require clean water input to dilute FPW for biogas production,which is a practical waste management method.3)The influences of tofu residue hydrothermal pretreatment and the addition of hydrochar on anaerobic digestion for biogas production.The highest VS/TS of tofu residue was 98.25±0.25%with a hydrothermal pretreatment temperature of 140°C.HPTR-140 had the highest cumulative biogas production yields,which was improved cumulative biogas production yield by 23.8%compared with the control.And the highest cumulative biogas production yields was observed with hydrochar 200（4g/L）among the various addition amounts of hydrochar,with an increase of 18.9%compared with the control.Moreover,the highest methane production yields was observed during anaerobic digestion with HPTR-140,which increased by33.9%compared with the control.It was found that hydrothermal pretreatment at temperature140°C and additive hydrochar-200（4g/L）were the most efficient for tofu residue anaerobic digestion for biogas production.4)The effects of hydrothermal pretreatment of rice straw and tofu residue on anaerobic co-digestion for biogas production and methane yield was studied.Hydrothermal pretreatment of rice straw（100-180°C）has the effect on biogas production and methane yield on anaerobic co-digestion,the optimal HTP condition was at temperature of 160°C for rice straw.The maximum biogas production and methane yield was observed with HTP at 140°C for tofu residue,reached 306 m L biogas/g VS and 200.1 m L CH₄/g VS,respectively.The results can be used to design an effect anaerobic co-digestion management process and effectively utilize rice straw and tofu residue for renewable bio-energy production.