Effects Of Fe₂?SO₄?₃ On Anaerobic Digestion Of Pig Manure And Straw

Livestock manure and straw are mainly organic solid wastes generated during agricultural production.With the large-scale development of livestock and agricultural straw banned burning policy promulgated,livestock and poultry manure and agricultural straw resources have been increasing year by year,putting tremendous pressure on ecological environment management.Heavy metals in livestock and poultry manure can cause serious soil heavy metal pollution with the application of organic fertilizers.In order to study the effect of different doses of Fe2(SO4)3 on the gas production characteristics during anaerobic fermentation process mixing agricultural organic solid wastes and heavy metal passivation effect in biogas slurry,Pig manure and straw were selected as fermentation materials.The initial doses of Fe2(SO4)3 were set as 0.5%,1%,3%,6%and 9%respectively(based on the total solids of fermented feedstock).The fermentation temperature was(35+1)? and the duration was 30 days.The results showed that the biogas and methane production in the 3%addition group was the highest.The total gas production was 25.65 L and the cumulative methane production was 12.30 L.The total gas production respectively increased by 32.01%and 51.48%when Fe2(SO4)3 dosages were 1%and 3%.However,when Fe2(SO4)3 dosages were 6%and 9%,the total gas production decreased by 10.50%and 11.73%respectively.These datas indicated low dose of Fe2(SO4)3 promotes gas production but high dose restrains.VFA accumulated and pH value decreased in the 9%addition group,which may explain the lower gas production.The first order kinetic equation of biological gas production was used to evaluate the effect of gas production.The results showed that adding Fe2(SO4)3 significantly improved gas production efficiency.Additionally,the addition of 1%and 3%Fe2(SO4)3 improved but the addition of 6%and 9%Fe2(SO4)3 reduced theoretical gas production.During anaerobic fermentation,high concentration of sulfates can cause sulfate-reducing bacteria competing for organics with methanogens,which will affect the function of methanogens and result in reduced gas production.Gas component analysis showed that Fe2(SO4)3 significantly influenced the contents of main gases such as CH4 and CO2,while the content of N2 was less affected.In addition,the introduction of sulfate increased the concentration of H2S in biogas.The results of XRD analysis indicated that Fe2(SO4)3 promoted the decomposition of cellulose.Pig manure was used as raw material in the anaerobic fermentation.Fe2(SO4)3 was added to study the anaerobic digestion ability and heavy metal passivation effect.The initial dosage of Fe2(SO4)3 was 0%,0.5%,3%,90%(according to the fermentation material TS),Experimental results show that:medium and low doses can stimulate gas production,high doses impede gas production.Compared with the control,0.5%and 3%additions increased the total gas production by 9.16%and 26.95%,while in the 9%addition group,VFA accumulation were observed,and gas production decreased by 6.53%.At the same time,Fe2(SO4)3 additions reduced the exchangeable distribution rate of Cu and Zn,and the distribution ratio of residual state increased,The passivation effect was obvious.The MF value was used to evaluate the bioavailability of heavy metals.The results showed that the lower bioavailability of Cu and Zn was 0.5%and 9%respectively,the effect of adding Fe2(SO4)3 on the bioavailability of Cd was weak.XRD analysis of biogas residue showed that the addition of Fe2(SO4)3 promoted the decomposition of cellulose,and stimulated sulphur and various heavy metals transforming into metallic sulfide mineral.The precipitation and sorption of these minerals can fix the activated heavy metals and sulfur in feedstocks and reduced the risk of sulfur to release into the environment in the form of H2S.