Application Of Cetyltrimethylammonium Bromide Bentonite-titanium Dioxide Photocatalysis Technology For Pretreatment Of Aging Leachate

Organobentonite-photocatalysis technology was applied to pretreat agingleachate containing refractory pollutants.The organobentonite was synthesized by organic modifiercetyltrimethylammonium bromide (CTMAB) and natural bentonite. Incharacterization experiments, we could confirm that organic functional groups ofcetyltrimethylammonium (CTMA+) cations were successfully loaded on the surface ofbentonite. Through contrasting some physical parameters of natural bentonite andCTMAB2.5, it was not difficult to find three facts. First, the porosity of CTMAB2.5was much higher than that of natural bentonite. Second, Zeta potential changed fromthe negative of natural bentonite to the positive of CTMAB2.5. Third, the organiccarbon content of CTMAB2.5was much greater than that of natural bentonite. So theadsorption of CTMAB2.5was better than that of natural bentonite.While using CTMAB2.5alone to pretreat leachate, we found that COD removalincreased with the advance of CTMAB2.5dosage, but it decreased with improving pHvalue. And NH3-N removal increased with the advance of CTMAB2.5dosage and pHvalue. With overall consideration of the removal of COD and NH3-N, under theoptimal operation condition of CTMAB2.5dosage=7.5g/L and pH=3.5, the removal ofCOD and NH3-N arrived at38%and23%, respectively.While using TiO2alone to pretreat leachate, we found that COD removal went upwith the advance of TiO2dosage, but it declined with improving pH value. AndNH3-N removal increased with the advance of TiO2dosage and pH value. In addition,pH also affected decolourization ration of the leachate. The decolourization rationdecreased with increasing the pH. With overall consideration of the removal of CODand NH3-N, under the optimal operation condition of TiO2dosage=3.88g/L andpH=6.5, the removal of COD and NH3-N arrived at41%and29%, respectively.The combination of CTMAB2.5adsorption and TiO2photocatalysis was superiorto either running separately. Furthermore, removal efficiency of simultaneouslyutilizing CTMAB2.5and TiO2was better than them in succession.The combination technology was optimized by response surface methodology(RSM) with COD and NH3-N removal rate as the target responses. In30setsexperiments, under the different operation conditions, the removal rate of COD and NH3-N could be up to89%and61%respectively. The optimal operation conditionscalculated from the regression equations were CTMAB2.5dosage of7.5g/L, pH at3.5, TiO2dosage of1.63g/L, and reaction time for60.02min, which maintained theremoval of COD and NH3-N at82%and37%, respectively. According to the optimaloperation condition, demonstration test showed that the removal rate of COD andNH3-N could be86%and41%respectively.After the pretreatment under the optimal operation condition, the quality and thebiodegradability of effluent got improved obviously, which created the goodconditions for the following biochemical progress. By estimation, if CTMAB2.5andTiO2were reused two or three times, the treatment cost was about10yuan/t. Thus, thecombination technology was feasible.