The Study Of Process Paramerters During Anaerobic Digestion Of Pig Carcass After Hydrothermal Pretreatment And The Mechanism For Ammonium Recovery By Hydrochar Additon

As large amounts of dead pig carcass were generated along with the potential bacterial pathogens issues through intensive breeding,how to safety handle the dead pig carcass become a research question.The incineration by incinerator or open air are the current methods for pig carcasses disposal but they are not environmental friendly.Hydrothermal pretreatment and anaerobic digestion could be a better way for the treatment as they are environmental friendly and simultaneously can produce biogas.This study demonstrated the feasibility of anaerobic digestion of hydrothermal treated dead pig carcass and explained the effect of hydrochar on biogas production by optimizing the process parameters and adding rice straw hydrochar in the system.This will provide the theoretical basis and technical support for dealing with dead pig carcass in a nontoxic way and provide energy source.The detail of the study content,methodology and experimental results are listed as follows.1)Effects of degradability of pork were studied by varying feedstock concentration(10?50%,wet weight)and temperature(140?180?)in HTP.Results showed that for the pork products after different feedstock concentrations HTP at 140?,the wet weight of solid residue(SR)reduced about 50%;the lipid content of SR decreased from 24.6%to 3.3%;the protein content of SR decreased from 16.4%to 15.3%;COD concentration of liquid product(LP)increased to 305 g/L.During HTP,the increase in feedstock concentration had no impact on enhancing the degradability efficiency,the rise in temperature from 140 to 180? was available to promote decomposition of organic matters,the solid residues dropped from 55.6%to 27.3%.The protein decomposition rate accelerated after 160?.The highest concentration COD(642 g/L)was obtained at 170?.2)The biogas potential of the pork products after HTP was studied in batch reactors.Through batch anaerobic digestion(37?),biogas potential of SR was increasing with the VS content decreasing from 2.4%to 3.3%.The highest biogas potential in mono-digestion of SR and LP was 464 mL/g-VS and 826 mL/g-COD,respectively.The methane content of biogas from the pork products after HTP could reach 73.4%.3)This study successfully mitigated the inhibition in anaerobic digestion of carcasses by hydrochar addition(2?10 g/L)and by co-digestion with RS and HRS(10?50%,d.b.,based on VS).Biogas production in mono-digestion of SP was inhibited by the ammonia nitrogen and biogas production yield is only 236 mL/g-VS.After adding the RS,the specific biogas production was enhanced to 428 mL/g-VS;after adding the hydrochar(6 g/L),the specific biogas production was achieved to 451 mL/g-VS.The methane content was also increased from 57.5%to up to 69.8%after hydrochar addition,higher than 63.3%in co-digestion of SP and RS.4)We studied the effect of different temperatures(220?280?)on the hydrochar production and different concentrations of hydrochar addition(2?8 g/L)on biogas production of LP.The biogas production decreased from 264 to 119 mL/g-COD with the increase in organic load in mono-digestion of LP.After adding hydrochar,the consumption of lactate was enhanced and the biogas production was increased by 5.1?27.6%.With the carbonization temperature increased from 220 to 280?,the intensity of functional groups on the surface of hydrochar was reinforced,while the BET surface area of hydrochar did not show significant difference.260? would be the suitable temperature for hydrothermal carbonization of rice straw.The optimal hydrochar concentration was 6 g/L in anaerobic digestion.5)The mechanism for the promotion effect of hydrochar on biogas production was explained.The addition of hydrochar strengthened the intensity of functional groups on the surface of inoculated sludge and provided the habitat for the microorganisms.The alkaline environment of hydrochar enhanced the buffering capacity of the system.Hydrochar could remove part of ammonium and VFA by surface adsorption.1 g/L of hydrochar removed 11 mg/L of ammonium nitrogen and 10 mg/L of VFA.6)We studied the hydrochar addition effect on hydrothermal treated carcasses in semi-continuous digestion,the cumulative biogas yield and VS removal efficiency was enhanced by 28.6%and 17.1%through hydrochar addition,respectively.The running time which the organic load exceed 10 g-VS/L exceeded 20 d,the tolerance value for organic load was 14.76 g-VS/L.The threshold for ammonium inhibition was enhanced from 1766 to 2584 mg/L after hydrochar addition.The microorganism tolerance of ammonia nitrogen increased from 2678 to 3383 mg/L.When acetate percentage was more than 40%of the total fermentation liquid,the biogas production was active;when the acetate range from 25-40%,the biogas production was stable;when acetate content waslower than 25%,the biogas production slowed down.