Effect Mechanism Of The Iron Source On Extracellular Polymer Substances Of Sludge During Bioleaching Sludge Dewatering

Sludge extracellular polymer substances?EPS?have extremely high viscosity,which can adsorb the impurities such as suspended matters,viruses and organic matters in sewage,and form a zooglea structure with an extremely high water content which leads to high moisture content and difficult dewatering in excess sludge.Bioleaching technology can improve sludge dewatering performance and achieve sludge reduction through physiological and biochemical reactions of microorganisms.Iron source is one of the important energy substrates of bioleaching microorganisms.Different iron sources and their dosages will affect their metabolism,which will lead to changes in EPS of sludge,and then affect the efficiency of sludge dewatering.Therefore,in this study,bioleaching method was used to treat the deep dewatering of excess sludge,to explore the influence of the iron source on EPS structure and component migration/transformation,and to find a reasonable iron source supply mode,aiming to provide a reference for bioleaching to promote sludge deep dewatering.The bioleaching experiment was carried out with single iron source?Fe SO₄ and Fe Cl₂?and iron source combined with sulfur source?Fe SO₄+S⁰,Fe SO₄+Na₂S₂O₃,Fe Cl₂+S⁰,and Fe Cl₂+Na₂S₂O₃?as energy substrates under the condition of temperature at 28?and the rotation speed at 180 rpm.The results show that:?1?When iron source was used as the energy substrate,the proportion of TB-EPS in sludge EPS is the highest?68.15%-95.47%?followed by S-EPS?2.69%-30.36%?.During the bioleaching process,the increase of TB-EPS and S-EPS content is unfavorable for sludge dewatering.?2?The proportion of protein in TB-EPS,S-EPS,and LB-EPS?47.18%-98.73%?was all the highest followed by polysaccharides?0.73%-42.96%?.Three-dimensional?3D?excitation-emission matrix?EEM?fluorescence spectroscopy of the sludge EPS during the bioleaching process showed that,the EPS mainly showed five fluorescence peaks of proteinoid,tryptophan,polysaccharide,polycyclic aromatic hydrocarbon humic acid,and carboxylic acid humic acid substances.Among them,proteinoid and tryptophan characterize the protein substances in sludge EPS,which have the strongest correlation with sludge dewatering performance.?3?Pearson correlation analysis showed that protein and polysaccharide in TB-EPS were positively correlated with SRF;proteins in S-EPS was highly positively correlated with SRF,polysaccharides were highly negatively correlated with SRF;the protein and polysaccharide in LB-EPS were negatively correlated with SRF;there was no significant correlation between DNA and SRF.?4?Decrease in protein and polysaccharide content in TB-EPS was beneficial to promote sludge dewatering;the decrease of protein content and the increase of polysaccharide content in S-EPS were beneficial to promote sludge dewatering;the increase of protein and polysaccharide contents in LB-EPS was beneficial to promote sludge dewatering.When a single iron source was added,the correlation between the sludge EPS and sludge specific resistance of filtration?SRF?of the Fe SO₄ group was stronger than that of the Fe Cl₂ group;when the composite energy substrates were added,the correlation between the EPS and SRF of the sludge in the Fe SO₄+S⁰ group was relatively significant.?5?Compared with the composite energy substrate,when Fe SO₄ was used as the energy substrate,the SRF decreased from 5.82×10¹² m/kg to 3.58×10¹¹m/kg,and the sludge changed from difficult dewatering state to easy dewatering state,with the highest SRF reduction rate of 93.85%.From the perspective of sludge dewatering,the optimal iron source was Fe SO₄.With Fe SO₄ as the energy substrate,the bioleaching experiment was conducted under the condition of the dosage of 2g/L-8 g/L.It showed that with the increase of Fe SO₄ dosage,the sludge dewatering performance was improved.When the dosage was 6g/L,the sludge dewatering performance was the best.