Study On The Effects Of Organic Components Transformation On Dewatering Performance And Carbon Source Utilization During Sludge Pre-oxidation

Sludge,a byproduct of biological wastewater treatment,contains a large amount of organic components.Various changes in characteristics of organic components were achieved during different pretreatments,consequently improving the sludge dewatering performance and resource utilization efficiency.Due to the complex composition of organic components in sludge,in this thesis,the changes of the characteristics of organic components in sludge pretreated by different pre-oxidation processes were investigated,the complexation mechanisms between cations and components in sludge were explored,and the influences of organic components transformation on sludge dewatering performance and carbon source utilization were explored.The main research contents and results are presented as follows:1.Study on the transformation of organic components in sludge pretreated by the pre-oxidation processA comparative study of the dewatering performances and the transformations of organic components in sludge pretreated by the pre-oxidation process with three oxidants（Oxone,H₂O₂ and Na Cl O）was presented.It was found that the sludge dewatering performances were deteriorated during the pre-oxidation with oxidant alone.When the dose of oxidant was 4mmol/g VS（Volatile solid）,the sludge dewatering performances were slightly deteriorated with the addition of Oxone and H₂O₂.And compared with the raw sludge,the capillary suction time（CST）increased by 21.4%and 54.1%,respectively;and the specific resistance to filtration（SRF）increased by 20.3%and 53.2%,respectively.However,the sludge dewatering performance was significantly deteriorated with the addition of Na Cl O with an increase of 382.7%and 195.6%in CST and SRF,respectively.The destructions of organic components of extracellular polymeric substance（EPS）in sludge caused by different oxidants were different.The organic components structures of the bound EPS（B-EPS）were significantly destroyed and the releases of organic components（especially protein）and hydrophilic amino acids in the soluble EPS（S-EPS）were significantly promoted during the oxidation of Oxone.The less effects on organic components in B-EPS and the releases of organic components and hydrophilic amino acids to S-EPS were observed during the oxidation of H₂O₂.Compared with the raw sludge,with the addition of Oxone and H₂O₂（at4 mmol/g VS）,the total dissolved organic carbon（TOC）contents of S-EPS increase by 342.9%and 75.8%,respectively,and the hydrophilic amino acids contents increased by 430.4%and76.3%,respectively.While the excessive release of organic components in both S-EPS and B-EPS and hydrophilic amino acids were significantly promoted during the oxidation of Na Cl O,and the TOC contents of S-EPS and B-EPS in sludge increased by 1642.7%and159.5%,respectively,and the hydrophilic amino acids contents increased by 620.3%.2.Study on the complexation mechanisms and coagulation effects of cations with dissolved organic matter in sludgeThe complexation mechanisms of different cations（Fe（III）,Al（III）,Fe（II）and Ca（II））with dissolved organic matter（DOM）in sludge were compared.The binding order of different cations with fluorescent components in DOM of sludge were preferentially protein-like components,followed by humic acid-like components.And the complexation of different cations with proteins were stronger than that of humic acids.Fe（III）and Al（III）were preferentially binding to hydrophilic groups,while Fe（II）and Ca（II）were preferentially binding to hydrophobic groups.Fe（III）and Al（III）formed more stable complexes with DOM in sludge,and their complexation constants with DOM in sludge were 9.64×10⁴ M^-1 and3.89×10⁴ M^-1,respectively,which were significantly higher than those of Fe（II）and Ca（II）.Compared with Fe（II）and Ca（II）,Fe（III）and Al（III）were more likely to make the sludge floc shape regular and form larger stable agglomerates.At the 10 min of coagulation,the floc equivalent diameter increased by 67.5%and 33.1%,respectively,and the shape factor decreased by 25.8%and 22.8%,respectively.The coagulation effects of Fe（III）and Al（III）were more beneficial to improve the settling performance of sludge.3.Behavior of organic components and the migration of heavy metals by advanced oxidation processesA comparative study of the different advanced oxidation processes（Fe（II）-Oxone,Fe（II）-H₂O₂,and Fe（II）-Na Cl O）was carried out.With the dose of Fe（II）at 1.9 mmol/g VS and the dose of oxidant at 4 mmol/g VS,after the Fe（II）-Oxone and Fe（II）-H₂O₂treatments,sludge dewaterability was significantly improved with the reduction in CST by 87.4%and85.2%,respectively,and SRF by 80.3%and 76.3%,respectively.It was strongly correlated with the shifted organic components,particularly proteins,from B-EPS to S-EPS.However,after the Fe（II）-Na Cl O treatment,sludge dewaterability was deteriorated（CST and SRF increased by 407.8%and 351.3%,respectively）,which was strongly correlated with the over release of organic components in both S-EPS and B-EPS.Humic-like organic components were preferentially attacked over the protein-like organic components in S-EPS for both the Fe（II）-Oxone and Fe（II）-H₂O₂ treatments.While for the Fe（II）-Na Cl O treatment,protein-like organic components were preferentially attacked in both S-EPS and B-EPS.The hydrophilic functional groups may be more preferentially migrated to S-EPS in sludge for the Fe（II）-Na Cl O treatment,resulting in the deteriorated dewatering performance of sludge.The concentration of total organic carbon,particularly the concentration of proteins,may be the key factor determining the shift of Zn and Cu from solid to liquid phase in sludge,along with the high oxidation extent of organic components and close binding to CHOS and CHON compounds.4.Study on the effect of amino acids on sludge dewatering performance by advanced oxidation processA systematic study on the types and concentrations of amino acids and their correlations with characteristics of nitrogen-containing compounds during sludge conditioning by Fenton oxidation treatment was carried out.Hydrophobic tryptophane（Trp）and hydrophilic lysine（Lys）were identified as the key amino acids affecting sludge dewaterability during Fenton oxidation treatment.The content of Trp showed a strong negative correlation with bound water content in sludge（R=-0.95,p<0.05）,while the content of Lys showed a strong positive correlation with bound water content in sludge（R=0.96,p<0.01）.The amino acids may be sourced from the damage of the membrane and ribosomal proteins by hydroxyl radicals through the proteomic analysis.The peptide bonds connected with Trp had a higher charge transfer（0.337 e）interacted with hydroxyl group than other amino acids and were more inclined to be decomposed than other amino acids through the density functional theory calculation.Particularly,more amino acids of Trp could result in less necessary energy barrier for aggregation of particles.As such,the protein degradation towards production of Trp may be related with enhanced sludge dewaterability by Fenton oxidation treatment.5.Feasibility analysis of utilizing anaerobic fermentation liquid of sludge treated by different advanced oxidation processes as a carbon source for denitrificationA study on the effects of different AOPs on sludge anaerobic fermentation was investigated.It was found that Fe（II）-Na Cl O pretreatment promoted more acid production than Fe（II）-Oxone and Fe（II）-H₂O₂ pretreatments from anaerobic fermentation of sludge.The acetic acid content of fermentation liquid in sludge pretreated by Fe（II）-Na Cl O increased from 1.58 g chemical oxygen demand（COD）/L of raw sludge to 5.59 g COD/L.Fe（II）-Oxone and Fe（II）-H₂O₂ pretreatments showed significant effects on the leaching of organic components with molecular weights of 10³-10⁴ Da（Dalton）from sludge during anaerobic fermentation,while Fe（II）-Na Cl O pretreatment significantly promoted their solubilization for hydrolytic utilization during anaerobic fermentation.The greatest improvement was shown in Fe（II）-Na Cl O pretreatment with the nitrate nitrogen removal rate of 95%and denitrification capacity of 0.195 g N/g COD.Moreover,the multi-component carbon source system of fermentation liquid in sludge pretreated by AOPs was more stable than the single carbon source（sodium acetate）system.In this thesis,the characteristics of organic components in sludge pre-oxidation were explored to deeply analyze their effects on sludge dewatering and carbon source utilization,which would provide a theoretical basis for regulating the directional changes of organic components during sludge pre-oxidation.