Study On The Stabilization Of Polyphenols And Collagens In Tannery Wastewater

Leather processing is actually the process of turning raw hide into stable material through tanning agent,which involves the interaction of polyphenols and collagen and other substances.The associated water-soluble and refractory organic matter restricts the treatment efficiency of tannery wastewater,which is difficult to meet the increasing wastewater discharge standards.In the present study,various spectroscopic and physicochemical methods including ultraviolet visible(UV-Vis)spectra,fourier transform infrared(FTIR)spectra,three-dimensional fluorescence excitation-emission matrix(3DEEM)spectra,solid-state 13C NMR,gel permeation chromatography(GPC)and elemental analysis were used to investigate the stabilization process of polymers formed by the interaction of typical components such as collagens and tannins in tannery wastewater under catalytic conditions;Escherichia coli(E.coli)was selected as the representative of the fast isooxygenated microorganism,and the stable organic matters were used as the matrix.The effects on E.coli were elucidated by the characteristics of intracellular and extracellular fluorescence;Furthermore,the degradation rule of the stabilized organic matters in activated sludge system was studied by 3DEEM,UV-Vis analysis and the detection of CODCr,TOC and SUVA and other indicators.As a result,tannins and typical biomolecules in tannery wastewater would interact to form typical high molecular weight refractory oranic polymers,in which tannin played an important role.Humic acid-like 0(HAL0)of simple phenol-Maillard system with small organic matters as precursors had higher aromaticity(H/C=1.16),which was different from the spectral characteristics of humic acid like(HAL)products of polyphenol-amino acid/protein system.Humic acid-like 2(HAL2)with protein as the precursor had the highest nitrogen content(7.5%)and aliphatic structures(H/C=1.53).Under the acute exposure(3 day-1000 mg/L)of the organic polymers produced by the interaction of typical components in tannery wastewater,the fluorescence intensity of the intracellular organic matter of E.coli in the protein area increased significantly.With the increase of exposure time,the fluorescence intensity of organic matters in the protein region decreased,while that in the humic acid region increased,especially at high concentration(2000 mg/L).With the addition of microorganism,the fluorescence peak of low concentration organic polymers would shift blue and the fluorescence intensity decreased,while the fluorescence intensity of high concentration organic polymers increased.The removal efficiency of the stabilized organics by biosorption was not high,the maximum removal rate was only 29.67%at 0.5 h,and the biodegradation efficiency was also low.The removal efficiency of the high concentration organic polymers was only 29.66%,and the CODCr was 437.5 mg/L,which was far from the wastewater discharge standard.With the progress of activated sludge treatment,the SUVA value of the effluent of each treatment showed an upward trend.The SUVA value of the effluent of the treatment with the stabilized organic matter as the substrate reached the maximum of 6.87 L/(mg·m),and the humification degree was the highest.The results of 3DEEM of dissolved organic matter(DOM)in effluent showed that high concentration of organic polymers could also stimulate the formation of microbial products such as proteins and humic acids.The results of 3DEEM of extracellular polymeric substance(EPS)showed that high concentration of organic polymers in wastewater increased the content of humic acid in loosely bound EPS(LB-EPS)and decreased the content of polysaccharides in tightly bound EPS(TB-EPS).Therefore,the typical biomolecules in tannery wastewater interacted with tannins to form typical high molecular weight humus-like polymers,which was not only difficult to biodegrade,but also had potential risks to the activated sludge treatment system,making it difficult for wastewater to reach the standard.