Study On EDTA Coupled Alkali Thermal To Strengthen Sludge Disintegration

Sludge,as the final product of the sewage treatment plant,is of high content of organic matter,which results in its pronounced value of resource.With the deepening of the concept of ecological civilization and environmental protection,and the continuous construction of environmental laws and regulations,it is an inevitable trend to explore an economically viable sludge deep resource treatment.At present,the resource utilization of sludge is mainly through the collection of useful contents by sludge disintegration,and the use of anaerobic fermentation to collect methane and other products.The thermal-alkali disintegration method is one of the most commonly used sludge disintegration methods,but this method uses a large amount of alkali and requires a large amount of energy input（generally>100°C）.In view of the ability of EDTA to dissolve extracellular polymers（EPS）and damage to sludge microbial cell membrane,this paper is the first time that used EDTA coupled thermal-alkali method to explore its effect on sludge disintegration effect under medium and low temperature conditions,and optimize the disintegration conditions.Under the optimal disintegration conditions,the process of disintegration sludge by thermal-alkali-EDTA coupling method was studied,and the mechanism of EDTA enhanced disintegration was speculated.It lays the foundation for the large-scale use of the thermal-alkali method for sludge disintegration to realize resource utilization.The experiment selected the five main factors of affecting sludge disintegration（pH,temperature,solid-liquid ratio,reaction time,EDTA dosage）to evaluate the single factor effect one by one,and select the factor level in the interval with large influence effect of each factor.The orthogonal test of L₁₆（4⁵）is used to optimize the disintegration conditions.The optimum conditions for the disintegration of the sludge by the thermal-alkali-EDTA coupling method are as follows:the solid-liquid ratio was 1:8.5,the pH was 12.5,and the EDTA dosage was 0.17 g/10 g wet sludge,the reaction temperature was 85°C,and the reaction time was 3 h.The factors affecting the disintegration effect are as follows:solid-liquid ratio>pH>EDTA dosage>temperature>reaction time.Further,under the optimal disintegration conditions,the process of disintegration sludge by thermal-alkali-EDTA coupling method was studied.The experimental group added with EDTA had 14.7%more SOCD dissolution than the control group,and the volatile solids（VS）content in the sludge residue was about 7%lower.cell rupture time is shortened by 15 min,which proves that the addition of EDTA improves the efficiency of sludge disintegration.The particle size analysis of the sludge flocs found that the floc size D（0.5）of the EDTA experimental group was larger than that of the control group,indicating that EDTA and the dissolved matter had significant interactions.The observation of sludge floc morphology and cell structure damage analysis showed that the cell structure damage of the EDTA experimental group was weaker than that of the control group in the early stage of the disintegration.The strengthening effect of the EDTA experimental group mainly occurred in the stage where the compact EPS began to dissolve slowly,and the disintegration was 120min.After that,73.3%of the sludge cells in the EDTA experimental group showed damage to the cell membrane,which was much higher than the 31.9%of the control group.The relative molecular mass analysis of dissolved organic matter（DOM）in the lysate found that adding EDTA made DOM easier to hydrolyze.EDTA contains a large number of hydrogen bond acceptors,and FTIR analysis has found that it forms hydrogen bonds with hydroxyl hydrogen bond donors of alcohols and phenols in EPS and DOM.Through three-dimensional fluorescence analysis of solubilized product（SP）,it was found that the organic fluorophore of protein substances was interfered by hydrogen bonding effect,and its fluorescence intensity weakened or even disappeared.Based on particle size analysis,it is speculated that the mechanism of EDTA enhanced sludge disintegration is related to the formation of hydrogen bonds between EDTA and organic matter inside and outside the cell.In summary,the thermal alkali-EDTA coupling method has the effect of strengthening sludge disintegration,and the mechanism of strengthening disintegration is related to the formation of hydrogen bonds between EDTA and the dissolved matter.