| Anaerobic fermentation(AF)process can decompose organic matter in waste activated sludge(WAS)and convert it into volatile fatty acids(VFA).Redox mediators(ROMs),also known as electron shuttles,are a class of organic molecules that can be reversibly oxidized and reduced.VFA production during AF can be promoted with the help of the electron transport and biocatalytic function of ROMs.This study presented for the first time to improve the production of VFA by adding ROMs during AF of WAS.The influences of different ROMs on VFA production,organic matter release and microbial community structure during AF of WAS were investigated.On this basis,the experiments of VFA production by ROMs combined with FeCl3 addition and ROMs combined with alkali pretreatment were carried out,and the influence of its synergistic effect on the production of VFA and organic matter during AF was analyzed.The main research results are as follows:(1)The type and dosage of ROMs affect the production of acid in anaerobic fermentation.After adding 1 mmol/L anthraquinone-2-sulfonate sodium(AQS),the maximum concentration of VFA in the system reached the maximum on day 5,which were 473.81 mg/L,2.14 times of that in the Control group.The VFA concentration of 100 μmol/L sodium 1,2-naphthoquinone-4-sulfonate(NQS)was 1.07 times that of the Control group.In addition,VFA production decreased with the increase of ROMs dosage.The addition of biochar(BC)inhibited the production of VFA in the anaerobic process,and the VFA production was only 24.86%-44.36%of the Control group.The acetic acid proportion in the control group was 10.53%.The addition of ROMs increased the proportion of acetic acid,and with the increase of AQS dosage,the proportion gradually increased.In the AQS 4 group,the proportion of acetic acid reached 43.33%.(2)Both AQS and NQS could promote the release of organic matter during AF.When 4 mmol/L AQS was added,the concentration of SCOD,protein and polysaccharide in supernatant and were 4.20,4.25 and 2.87 times of those in the Control group,respectively,while BC could inhibit the release of organic matter.The addition of AQS,NQS and BC could increase the microbial abundance and diversity during AF,and the enrichment effect of acid producing bacteria was the best when the dosage of AQS was 1 mmol/L.(3)The synergistic treatment of ROMs and FeCl3 could further promote the production of acid during AF of WAS.The VFA concentrations in the FeCl3 400+AQS and FeCl3 400+NQS groups reached the maximum on day 5,which were 71.34%and 59.35%higher than that in Control group,and 11.90%and 4.07%higher than that in FeCl3 400 group,respectively.After the synergistic treatment of ROMs and FeCl3,the proportion of acetate increased to 45.59%～65.98%.The addition of AQS and FeCl3 had a synergistic promoting effect on protein and polysaccharide release,while the addition of NQS and FeCl3 only had a synergistic effect on the release of polysaccharides.(4)The synergistic treatment of ROMs and alkali significantly improve the efficiency of VFA production.The VFA concentration in pH 11+AQS and pH 11+NQS groups reached the maximum on day 4,which were 616.63 mg/L and 679.04 mg/L,respectively.These values are 4.46 times and 4.91 times higher than those of the control group,and 1.25 times and 1.37 times higher than those of the pH 11 group,respectively.After synergistic treatment of ROMs and alkali pretreatment,the proportion of acetate increased to 50.97%～62.97%.ROMs and alkali synergistic pretreatment had a significant promoting effect on the release of organic matter,and the SCOD concentration in pH 11+AQS and pH 11+NQS groups were 5.03 and 4.41 times those of the Control group,respectively. |
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