Effect And Mechanism Of Cationic Surfactants On Sludge Dewater Ability

As the rate of municipal and industrial wastewater treatment goes up,the amount of sludge produced in the treatment process increases increase.Since the sludge contain large proportiomn of water,and its dewaterability is poor,thus resulting in the increasement of cost of sludge treatment and disposal.As a result,how to enhance the dewaterability of sludge and reduce the cost of sludge treatment becomes an important research in the world.Using physical,chemical and biological methods to pretreat sludge can change the physical characterization and chemical composition of sludge flocs,destroy the sludge colloid structure and reduce the affinity between water and colllid particles,thus improving the dewaterability of sludge.The medicament conditioning becomes a common method because of simple operation and low cost.At present,the sludge conditioners are mostly cationic macromolecular flocculants which can bring about good solid-liquid separation through bridging and charge neutralization effects.According to this situation,with the purpose of removing the water in the sludge flocs,the main purpose of experiment is moving the water in the sludge flocs.Sludge was mixed by two cationic surfactants including CTMAB and TMAB which belong to quaternary ammonium salt and study the effects and improvement of cationic surfactants on the dewaterability of sludge were discussed.Cationic surfactants are chemical matters which are combined through covalent bond between hydrophobe groups and hydrophilic groups with positive charge.Generally, hydrophobe groups of cationic surfactants contained alkyl;hydrophilic groups were constituted with groups containing nitrogen,phosphorus and sulfur atoms which could take positive charge.The length of hydrophobe chain present in CTMAB was longer than that of TMAB.Their functional theory could explained through Laplace-young equation.When the activated sludge was treated with cationic surfactants,the interfacial tension between gas and liquid could be reduced and the contact antenna could be advanced;on the other hand, the sludge dewaterability was improved through heightening the capillary radius and minishing the capillary sop pressure.The cationic surfactants could improve the separated efficiency between solid and liquid through adsorbed combination and electrical nentralisaion;besides this,the hydrophobe intensity was strengthened by the long hydrophobe chain of surfactants molecule;consequently the combinative water content reduced.Experimental results indicated that CTMAB can improve dewaterabilitiy of sludge evidently rather than TMAB.The results also showed that when the additive quantity was the same.when the additive quantity of CTMAB was 25%of the dry weight of sludge,the quantity of extra-cellular polymeric substance of sludge was released more than TMAB and was about 231mg/L.Besides these,the capillary sop time(CST)of sludge can be reduced to 73s;after centrifugal effect,the turbulence of top clean liquid of sludge was reduced to 15.9 and the water content of sludge was only 73.2%;when the additive quantity of TMAB and CTMAB was more the 15%of the dry weight sludge,SRF of sludge become dewater easily after vacuum filtration;the effects of CTMAB and TMAB on the sedimentation of sludge were unevidently.During the experiment,research on risk assessment and resource utilization of sludge was carried out;in order to illuminate property of sludge and probability of recycle,the organical matters,pathogens and bacteria groups contained in original sludge and treated sludge were discussed.Experimental results indicated that with the increase of additive quantity of TMAB.The COD of sludge gradually reduced from 1356mg/L to 1267 mg/L,1154 mg/L,1049 mg/L,891 mg/L,775mg/L and 734 mg/L;when using same dosage of CTMAB,COD of sludge gradually reduced from1356 mg/L to1247 mg/L,1084 mg/L, 957 mg/L,837 mg/L,734mg/L,623mg/L;besides this,the ratio of BOD and COD of the top clean water of sludge incessantly incresced,when the additive quantity of TMAB was 30%of the dry weight of sludge,the ratio increased from 0.4 to 0.55;when the additive quantity of CTMAB was 30%of the dry weight of sludge,the ratio increased from 0.4 to 0.59.The phenomenon indicated that the two kind of surfactant not only influenced COD and BOD of top clean water of sludge,but improved the simultaneously the BOD/COD. The wastewater treatment can deal with the supernatant liquor easily.But the,effect of TMAB and CTMAB on pathogens and vector attraction in sludge didn't accorded with the control of certain standard,so it was harm to environment if it was used as resource directly.