Study On The Culture Of Anaerobic Alginate Degradation Consortium And The Properties Of Its Degradation For Extracellular Polymeric Substance

Alginate(Alg)is polymerized by?-L-guluronate(G)and?-D-mannuronate(M).Approximately 10%of alginate exopolysaccharides(ALE)are present in aerobic sludge,which often ignored as an important component of sludge flocculates and extracellular matrix.And these refractory extracellular polymeric substance(EPS)are one of the rate-limiting steps in the anaerobic digestion of sludge.Therefore,the selection and enrichment of alginate-degrading bacteria(ADB)or consortium(ADC)and their application in the anaerobic digestion of municipal sludge are expected to improve the efficiency of anaerobic digestion of sludge and promote the resource utilization of sludge.This study includes:1)With algnate as the sole carbon source,ADB and ADC were enriched and screened by plate drawing method and subculture method,respectively.The generation cycle and alg degradation ability of ADC were much better than that of the pure strain ADB.After high-throughput sequencing of 16S r RNA gene,it was found that Fimicutes,which is responsible for VFAs production,dominated the ADC,accounting for more than 96%on Day 360.2)The factors affecting the growth of ADC were optimized by single factor experiment design.The optimal growth and gas production conditions of ADC were as follows:10 g/L sodium alginate concentration,10%inoculation amount,p H7,80 rpm,30?.3)Through the growth curve in the process of anaerobic degradation of alginate and gas accumulation curve,intermediate metabolites,gas,enzyme activity,molecular weight and concentration of alginate,s COD et al.quantitative and qualitative analysis,found the ADC growth lag phase is short,66 hr namely plateauing,and almost all the sodium alginate into metabolites VFAs,CO₂ and CH₄ etc;The extracellular enzyme activity(2.72 U/m L)was higher than the intracellular enzyme activity(0.4 U/m L)in the logarithmic phase of ADC.The mixed consortium ADC has a strong ability to produce VFAs,which inhibits the process of methane production,and the gas production is mainly CO₂.In the final anaerobic system,acetate(1000-1500 mg/L),butyrate(450-650 mg/L)and isobutyrate(116 mg/L)were abundant.Because ADC is acid-producing bacteria,the highest degradation rate of s COD(66hr)is only 21%.Through the measurement of metatranscriptome in the logarithmic phase and stable phase,it is speculated that the degradation path of alginate under the digestion of ADC is:uncultured bacterium utilizes alginate lyase(EC 4.2.2.3)and oligo-alginate lyase(EC:4.2.2-)rapidly converts alginate into small molecule polysaccharides and DEH monomers firstly,and then Clostridium enters the pyruvate cycle through Embden-Meyerhof-Parnas(EMP)and Entner-Doudoroff(ED)pathways,and further converts acetyl-Co A into a large amount of acetate,a small amount of butyrate and CO₂,while some acetate is converted into CO₂ through methanation.Compared with the traditional alginate methane-converted strains,the functional ADC for VFAs with high purity,high yield and higher economic value was obtained.4)The mixed bacteria ADC was added to the municipal aerobic sludge EPS with10% inoculation amount for anaerobic digestion.It was found by 3D-EEM fluorescence spectrum that the dissolved substances(region?)metabolized by microorganisms accounted for the highest proportion.Through the degradation experiment,it was found that the mixed bacteria ADC played a certain role in promoting the acid production(mainly acetate),gas production(mainly CH₄)and the degradation of _SCOD of EPS,especially for TB-EPS with high organic concentration.It was found that ADC had the ability to degrade not only the tryptophan protein(region?)of TB-EPS,but also the by-products of non-protein soluble microbial metabolites(region?)and the humic acid(region?).