Studies On The Effects Of Flocculants And Coagulants On Sludge Dehydration Performance And Sticky Properties In Sludge Conditioning

30 years of reform and opening up,China's economy has developed a lot,with a large quantity of waste water discharged.The sewage sludge produced in the WWTP contains a large number of pathogenic bacteria,heavy metals and other harmful substances.If they are not well treated,it'll be easy to result to soil,water,air pollution,and will be dangerous to human health and environmental safety.The moisture content of excess sludge is quite high,and it's difficult to meet the requirements of sludge disposal,so mechanical dewatering,and even heat drying is necessary before disposal.In the process of sludge dewatering,the sludge is likely to adhere on the wall or cohere together,which increases the operating load of the machine and the energy consumption,decreases the efficiency,and easily brings some safety hazards.In this paper,the effects of additives on the dewatering and sticky properties of sludge were studied.Three kinds of agents were selected,including ferric chloride,polyferric chloride and polyacrylamide.In the experiment of dewatering performance,the effects of additives were studied from three aspects:water content of the centrifuged sludge,zeta potential of the supernatant and sludge particle size.In the sticky property testing experiment,based on the peeters adhesion tester,an experimental apparatus was developed for the measurement of adhesion and adhesion of sludge.Adhesion and cohesion tests were carried out on sludge with different concentrations of coagulant and flocculant to study the sticky Characteristics.The results showed that the optimal dosage of inorganic coagulant was more than that of organic high-molecular flocculant,and had a neutralization effect on the surface charge of sludge particles.The organic flocculant used in this experiment is non-ionic,so it has little effect on the surface charge of floc particles,but with the increase of flocculation,it can effectively increase the floc particle size and promote the flocculation of sludge.In the experiment of dehydration,the water content of centrifuged sludge was affected by the agent.The sludge treated with inorganic cation coagulant had lower moisture content when the absolute value of zeta potential was at the lowest value,and the water content of the sludge treated by organic macromolecule flocculant firstly decreased and then increased with the increase of dosage.The dosage of organic cationic coagulant and organic macromolecule flocculant can be determined separately.In the experiment of sticky properties,both the inorganic cation coagulant and the organic macromolecule flocculant have great influence on the sticky properties of sludge.The adhesion shear stress decreases with the increase of coagulant and flocculant dosage.With the increase of coagulant and flocculant dosage,the cohesion shear stress firstly decreased and then increased.In order to reduce the adhesion and cohesion shear stress of sludge,an optimal dosage should be chose.Compared with the experiment of dewatering,when the cohesion and adhesion shear stress are at the lowest value,the dehydration is best improved.The proper dosage of coagulant and flocculant can improve the sludge dewatering performance while reducing sludge sticky shear stress.