Effects Of Biosurfactant And Its Combination With Chemical Surfactants On Dewaterability Of Activated Sludge

With the accelerating of the urbanization, as the by-product of the sewagetreatment, large amounts of municipal sewage sludge has been produced. In order tofacilitate the accompanying treatment and disposal of sludge, it is necessary todecrease the water content of sludge and improve the dewaterability.In this study, effect of biosurfactant rhamnolipid on dewaterability of activatedsludge has been investigated. And effects of rhamnolipid and the anionic chemicalsurfactant sodium dodecyl sulfate (SDS) on dewaterability of activated sludge havebeen compared. Besides, effect of biosurfactant co-conditioned with ordinarychemical surfactants, including SDS and cetyltrimethyl ammonium bromide (CTAB),on sludge dewaterability have also discussed. In this investigation, Capillary SuctionTime (CST) and the water content of dewatered sludge cakes were measured tocharacterize the sludge dewaterability, while Zeta potential, the ExtracellularPolymeric Substances (EPS) content in supernatant and turbidity were determined toanalyze the mechanism of the experimental phenomena.Firstly, effect of biosurfactant rhamnolipid on dewaterability of activated sludgewas investigated. The results show that more and more EPS was solubilized from thesurface of sludge flocs and dissolved into aqueous phase. The surface tension of thesludge could decreased significantly at low dosage. And Zeta potential increased withadding rhamnolipid. The dosage of rhamnolipid couldn’t improve the dewatering rateof activated sludge, while could decrease the water content of dewatered sludge cakes,The optimum dosage of rhamnolipid was0.10g/gDS (Dry Sludge). Then theexperiment compared effect of rhamnolipid with SDS on dewaterability of activatedsludge. Compared with rhamnolipid, SDS would deteriorate the dewatering rate moresignificantly, in terms of more increase of CST. Compared with the raw sludge,adding SDS could reduce the water content of dewatered sludge cakes too. Butcompared with activated sludge conditioned with rhamnolipid, rhamnolipid drew drierdewatered sludge cakes at the same concentration.Compared with adding any surfactant alone, the dewatering rate of the sludgepretreated with the combination of rhamnolipid and SDS deteriorated. When theproportion of the combination system was3:1, CST didn’t increase greatly comparedwith rhamnolipid alone. Compared with rhamnolipid alone, the water content of centrifuged sludge decreased significantly when the the combination rate ofrhamnolipid and SDS were3:1and2:1, and increased with the percentage of SDS incombination system rising. Compared with rhamnolipid or CTAB alone, thecombination of rhamnolipid and CTAB within proportions of1:2or1:3,could notonly decrease the water content of dewatered sludge cakes, but also improve thedewatering rate of activated sludge. And with the proportion of CTAB increasing, thedewaterability improved more obviously.