Effects Of Added Iron On Combined Anaerobic Hydrogen And Methane Production From Kitchen Waste And Municipal Sludge

Municipal sludge and kitchen waste are two kinds of urban organic solid wastes,among which the output of municipal sludge increases year by year.If these two solid wastes are not treated,the environment and human health will be damaged.The above two kinds of organic solid wastes can be stabilized and recycled by anaerobic digestion technology.When two organic solid wastes are mixed for anaerobic digestion,they have disadvantages such as long residence time and low gas production efficiency.Adding iron to the anaerobic system can enter the stable period of gas production in advance,which also improves the gas production performance of the system.The effect of adding zero valent iron and scrap iron on anaerobic digestion of municipal sludge and kitchen waste were discussed in this paper.Firstly,the effect of zero valent iron（i.e.iron powder dosage）on anaerobic digestion of mixed solid waste was investigated.Under the condition of iron powder dosage of 20 g/L,the cumulative methane production was330.07 mL/g VS,which was 41%higher than that of the blank group.The concentration of H₂S in the system was also significantly lower than that in the blank group,and excessive acidification in the system was alleviated.When the dosage of scrap iron was 20 g/L,the cumulative gas production of scrap iron group and pure iron powder group was 26025 ml（630.24 mL/g VS）and 25120 ml（619.18 mL/g VS）,respectively,which was 51%and 45%higher than that of the blank group.The concentration of VFA in the scrap iron group and pure iron powder group reached its peak on the 10th day,reaching 11051 mg/L and 10800mg/L,respectively,which was 16%and 12%higher than that in the blank group.The infrared spectrum and thermogravimetric analysis showed that there were various forms of iron in the scrap iron,such as hydroxyl oxidize iron,ferric oxide and zero valent iron.The gas production and methane production of scrap iron group were better than that of iron powder group.The effect of scrap iron on hydrogen production by anaerobic fermentation was discussed.It was found that the hydrogen production rate reached its peak at 16h.The hydrogen production rate of scrap iron group was 22.67 mL/g VS,which increased by 59%compared with the blank group.At 20h,the hydrogen concentration of both groups reached the maximum.At this time,the hydrogen concentration of scrap iron group was 61.42%,which was 15%higher than that of the blank group.At 24h,the cumulative hydrogen production of the scrap iron group was 1548 mL,which was 56%higher than the blank group.The volatile organic acids of the two groups gradually increased with time.At 24h,the VFA of the scrap iron group was 2675 mg/L,which was 16%higher than that of the blank group.At 12h,SCOD concentration in the reactors of the two groups reached the maximum.The SCOD concentration in the scrap iron group was 7140 mg/L,which was 11%higher than that of the blank group.The addition of scrap iron increases the substrate content consumed by the hydrogen-producing bacteria and the hydrogen-producing efficiency of the anaerobic fermentation system.