Profiling Of Amino Acids And Their Effects On Sludge Dewaterability Using Different Pretreatment Methods

The large amount of waste activated sludge produced in municipal and industrial wastewater treatment processes is considered to be an inevitable shortcoming in biological processes,and its handling and disposal has made a huge challenge to the sewage treatment plants.At present,pretreatment methods such as ultrasonic,heat,ozone and acid/alkaline conditioning and their coupling methods are often used for the study of sludge dewaterability.However,most studies have focused on the effects of changes in protein species and content but ignore the amino acids in sludge on sludge dewaterability.Comprehensive analysis and study of species and structure of hydrophilic substances in sludge can guide for the targeted removal of hydrophilic substances in sludge dewaterability.Therefore,it is especially important to study the changes of amino acid species and contents in sludge under different pretreatments,and the correlation between them and other parameters which reflect sludge dewaterability.The main research contents of this research include:1.Study on the effect of different conditioning methods on sludege dewaterabilityUltrasonic,heat,ozone and acid/alkali pretreatment methods were used to condition the waste activated sludge,and the effects of different conditioning methods on sludge dewatering performance were investigated.The results show that:?1?Ultrasonic pretreatment will deteriorate the dewaterability of sludge,and as the ultrasonic energy density increases from 0.1 W/mL to 0.4 W/mL,Capillary Suction Time?CST?and Specific Resistance to Filtration?SRF?,the particle size will gradually decrease.In addition,Loosely-bound EPS?LB-EPS?has largely increased in the content of hydrophilic substances such as proteins and polysaccharides.?2?When the temperature increased,the CST and SRF of the sludge will further increase.Tightly-bound EPS?TB-EPS?in sludge gradually converted to Soluble extracellular polymer substances?S-EPS?with temperature increased.Likewise,as the temperature increases,the sludge particles decrease.?3?As the dose of ozone increase,the SRF and CST of the sludge tend to increase gradually.In addition,the content of protein and polysaccharide in TB-EPS gradually decreased,and the content of protein and polysaccharide in S-EPS gradually increased.However,the effect of ozone on particle size of the sludge is not obvious.Ozone mainly deteriorates the dewaterability of sludge by changing the zeta potential and the protein content in S-EPS.?4?Acid treatment can significantly improve the dewaterability of the sludge.For example,under the condition of pH=2,SRF is reduced by 78.3%and CST is reduced by 29.3%.The sludge filtration performance is obviously obtained on the contrary,the alkaline treatment can significantly deteriorate the dewaterability of the sludge,and the alkaline treatment has the most obvious effect on the deterioration of the sludge compared with the ultrasonic,heat and ozone pretreatment.2.Effect of different pretreatment methods on species and contents of amino acids in sludgeBy different pretreatment methods to study the changes of amino acid species and contents in the sludge,it was found that the effects of ultrasonic,heat,ozone and acid/alkali conditioning on the content of hydrophilic amino acids in the sludge were very significant:when the ultrasonic intensity is 0.1 W/mL,the contents of amino acids released in the sludge reached to highest value;when treated at 50°C,the content of hydrophilic amino acids increased rapidly;when the ozone dose was 0.01 g/?g TS?,the sludge was released.The amino acid content reached the maximum;the acidic condition of pH=2 greatly reduced the content of hydrophilic amino acids in the sludge,and the total amino acid content decreased,while the alkaline condition conditioning of pH=10 increased the amino acid content.The effect is higher than other conditioning methods causing changes in the amino acid content of the sludge.Through the Pearson's correlation analysis,the results show that there is a significant correlation between the amino acid contents in the sludge and the dewatering characteristics of the sludge after different conditioning methods,and affect the sludge dewatering performance.The core amino acids are three hydrophilic amino acids:glycine,serine and threonine.The contents of glycine,serine and threonine were positively correlated with CST,SRF,the content of tryptophan in S-EPS and LB-EPS,protein and polysaccharides content in S-EPS,.3.Effect of core amino acids affecting sludge dewaterability on the hydrophilicity of sludge solid-liquid phaseIn order to further study the effects of core amino acids on sludge dewaterability,different contents of glycine,serine and threonine were added into the sludge,and the content of the amphiphilic functional group in the sludge was determined using Derjaguin-Landan-Venvey.-Overbeek?DLVO?theory calculates the electrostatic repulsion force,van der Waals adsorption and hydration between sludge particles before and after the addition of three hydrophilic amino acids,and uses surface thermodynamic analysis methods to draw different conditioning agent conditioning sludge.DLVO curve.The results showed that the addition of glycine,serine and threonine three amino acids?0.2 mol/L?can reduce the surface contact angle of sludge solid phase and the effect of threonine on the surface contact angle of sludge is the most significant,so that the sludge The contact angle was reduced from 85.00°to 66.23°;the three amino acids?0.2 mol/L?of glycine,serine and threonine significantly increased the proportion of carbon-containing hydrophilic functional groups in the liquid phase of the sludge compared to the original mud.The extended DLVO theory was used to calculate the three amino acids of glycine,serine and threonine to calculate van der Waals energy(W^LW),electric double layer energy(W^EL),Lewis acid base interaction energy(W^AB)and total mutual interaction between sludge particles.Function energy(W^TOT),three kinds of amino acids can increase the W^AB sharply,and the repulsion between the sludge particles increases.Compared with the original mud,the sludge after adding the amino acid shows a higher energy barrier,and the sludge particles are more It is difficult to approach each other,so the dewaterability of the sludge is deteriorated.