| Citric acid is widely used in various production fields because of its advantages such as low cost,easy availability,no toxicity,and easy decomposition.The widespread use of citric acid in global has caused a large amount of citric acid wastewater to be treated every year.However,the treatment of citric acid wastewater will leave the waste sludge containing high concentration of citric acid.More and more attention has been paid to the reasonable treatment and disposal of these waste sludges.At the same time,citric acid could also be used as a strong organic acid,which is widely used in the pretreatment of municipal waste sludge.In this paper,the waste sludge is taken as the research object.The effects of citric acid on extracellular polymer destruction and cell lysis in sludge at different initial pH by measuring capillary suction time(CST),extracellular polymeric substances(EPS)and intracellular bound water and other parameters.When the ultrasonic intensity is 2W / m L and the ultrasonic time is 5 min,the EPS outside the sludge cells could be stripped out.By analyzing the changes of soluble proteins,polysaccharides,DNA and bound water before and after treatment,together with auxiliary means such as SEM and particle size analysis,the degree of EPS destruction and cell membranes lysis in the waste sludge by citric acid treatment was investigated.The effects of citric acid on sludge dewatering performance were discussed from two aspects: sludge dewatering speed and sludge dewatering degree.Through research and analysis,we could get the following conclusions:(1)The optimal treatment conditions for cell lysis of waste sludge are citric acid concentration at 0.05 g / g suspended solids(SS)and initial pH 4.Under this condition,in addition to,citric acid showed a strong effect on the slime extracellular polymeric substances(S-EPS)and the loosely bound EPS(LB-EPS)except the tightly bound EPS(TB-EPS).At the same time,the sludge cell membrane could be destroyed to release the substance in the cell.S-EPS and LB-EPS contents respectively to increase from4.92 to 41.43,2.27 to 5.49 mg / g VSS,while tightly bound EPS(TB-EPS)content to decrease from 12.35 to 5.01 mg/g VSS.(2)Citric acid could effectively destroy the sludge floc structure and release the intracellular bound water.Under the optimal treatment conditions,the intracellular bound water content decreased from 1.23 to 0.41 g / g DS,and the reduction degree reached 66.67%.After treatment with citric acid,the contents of soluble proteins,polysaccharide,and DNA in the sludge supernatant increased,and theorganic matter and humic acid in LB-EPS were also released.(3)Citric acid could effectively improve the sludge dewatering degree.It shows that after the citric acid pretreatment,the EPS floc structure is broken,the cell membrane is lysed,and a large amount of intracellular bound water and contents are released,which improves the improve the sludge dewatering degree.(4)Citric acid couldn’t enhance the sludge dewatering speed.In a series of pH experiments,the CST value increased first and then decreased.Due to of citric acid have a characteristic-deflocculation,the sludge dewatering speed with citric acid treatment alone did not enhance. |
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