The Effect Of COD/SO₄^2- Ratio On Methane And Hydrogen Sulfide Production And Carbon Transfer In Gravity Sewers

Methane and hydrogen sulfide production in sewers has received more and more attention because of the great global warming potential of methane and corrosive of hydrogen sulfide.Moreover,methane and hydrogen sulfide can be produced simultaneously because of the coexistence of methanogens?MA?and sulfate reducing bacteria?SRB?in sewer,especially from biofilms adhered to sewers.Aerobic,anoxic,anaerobic environment and long hydraulic retention time make MA and SRB coexist in sewers.During the production of methane and hydrogen sulfide,hydrogen and acetate act as the electron donors for MA and SRB.This results in competition between MA and SRB for these electron donors in sewers.The competition of SRB and MA is influenced by many factors and COD/SO₄^2-ratio play the major role.This study mainly focused on the effect of COD/SO₄^2-ratio on methane and hydrogen sulfide production and the competition between MA and SRB for same electron donors in gravity sewers.Therefore,three independent pilot systems were set up to simulate the practical operation of sewers,corresponding to COD/SO₄^2-ratios of 3,6.08 and 9.Methane,hydrogen sulfide,and carbon dioxide in gas phase were measured using a Shimadzu GC-9A Gas Chromatograph equipped with an FID.Based on the experimental data,a model taking into the COD/SO₄^2-ratio was developed to predict the production of methane and hydrogen sulfide in gravity sewers.When the experiment was accomplished,the biofilm microorganism community was explored using high throughput sequencing?HTS?.In addition,the utilization of acetate and propionate by SRB in gravity sewers was also analysed in this study.The main achievements of this article are summarized as follows:?1?Although species number of MA and SRB were similar,amount of MA was far more than the SRB present at all three COD/SO₄^2-ratios.At a COD/SO₄^2-ratio of 3,6 classified MA and 7 SRB were detected,the amount of MA were least while SRB were greatest,Methanobacterium,Terrestrial-Miscellaneous-Gp-TMEG and Methanothermobacter were predominant in MA and Desulfitobacterium was predominant in SRB.At a COD/SO₄^2-ratio of 6.08,6 classified MA and 6 SRB were detected,Methanobacterium and Methanosarcina were predominant in MA and Desulfotomaculum,Desulfovibrio and Desulfitobacterium were predominant in SRB.When COD/SO₄^2-ratio was 9,6 classified MA and 5 SRB were detected the amount of MA was greatest while SRB was least,Methanosarcina was completely predominant in MA and Desulfitobacterium was predominant in SRB.?2?The effect of COD/SO₄^2-ratio on methane production was obviously greater than hydrogen sulfide production in gravity sewers,the least methane production was less 172% than the greatest while the least hydrogen sulfide production was just less 72% than the greatest.At three COD/SO₄^2-ratios,the methane production were obviously greater than the amount of hydrogen sulfide produced.The most methane produced was 118.45 mg at a COD/SO₄^2-ratio of 9.Whereas the most hydrogen sulfide produced was just 27.65 mg at a COD/SO₄^2-ratio of 3.?3?At the same conditions,the ability of SRB to utilize propionate was stronger than acetate.At three COD/SO₄^2-ratios,the consumptions of propionate were all obviously greater than acetate and the hydrogen sulfide production originated from which SRB utilized propionate was greater than acetate.At a COD/SO₄^2-ratio of 3,0.02 mg hydrogen sulfide per mg of acetate and 0.028 mg of hydrogen sulfide per mg of propionate was produced.At a COD/SO₄^2-ratio of 6.08,0.007 mg of hydrogen sulfide per mg acetate and 0.015 mg hydrogen sulfide per mg propionate was produced.At a COD/SO₄^2-ratio of 9,0.006 mg hydrogen sulfide per mg of acetate and 0.011 mg hydrogen sulfide per mg of propionate was produced.When COD/SO₄^2-ratio was 3,SO₄^2-concentration was 333.3mg/L,SRB could effectively utilize acetate and propionate at the same time.When COD/SO₄^2-ratios were 6.08 and 9,the SO₄^2-concentration was 164.5mg/L and 111.1 mg/L,the activity of SRB decreased and would preferentially utilize propionate.?4?At three COD/SO₄^2-ratios,carbon resources utilized by MA were all greater than which utilized by SRB.A high COD/SO₄^2-ratio is essential for MA outcompete SRB.At a COD/SO₄^2-ratio of 9,MA is completely dominant in competition between MA and SRB.When COD/SO₄^2-ratio was 3,although there were enough electron donor,SRB was still not completely dominant in competition between MA and SRB,and in the later period of experiment,MA was outcompete SRB.?5?a model predicted methane and hydrogen sulfide production was developed and the R2 of model developed and validated were both more than 0.90,indicating this model was reasonable and reliable.COD/SO₄^2-ratio and other hydraulic conditions were considered in this model.This model could forecast methane and hydrogen sulfide production in gravity sewers and had a significance in control of methane and hydrogen sulfide.