Study On The Adsorptin Of Chromium By Immobilizing Activated Sludge With Chitosan

Heavy metal pollution of point source by the past deteriorated to current non-pointsource pollution which leads to the traditional physical and chemical methods to be hardto fit with current status because of its high cost. Instead, the biological treatment hasbeen becoming the current hot pot. Starting from low-carbon green philosophy, thisstudy makes excess sludge of urban sewage plant which are difficult to deal with toresource reuse. An adsorbent named SCTS with characteristic s of high efficient andenvironmental friendly and affordable has been prepared with chitosan as carrier forembedding activated sludge cells. Specific research contents and results are as follows.1) Two kinds of candidate curing agent and five kinds of foamer have beenevaluated. Six factors were researched to ascertain the effect on the adsorption capacityand the quality of the ball of SCTS by single factor experiment. Six factors are thecuring solution concentration，the dosage of foamer, the amount of cross-linking agent，the ratio between activated sludge and chitosan and the foaming temperature. Theprincipal-secondary sequence of factors and the optimal level combination werededuced by orthogonal experiment. The results revealed the selected factors havesignificant effect on the adsorption capacity of SCTS and The adsorption rate of Crhasachieved95.7%under the condition:0.4%STPP，10%NH4HCO3，the ratio betweensludge and chitosan to be0.5, foaming temperature to be100℃and thecuringtemperature under30℃。2) The pH, temperature, ion concentration, dosage of SCTS in the adsorptionsystem were researched to discuss the effect on the removal rate of total chromium andthe hexavalent chromium reduction rate. Meanwhile, the kinetic rules andthermodynamic laws and regeneration characteristics has been investigated in this studyas well. The experiment results show that pH≤3and T≥40℃improve remarkably theremoval rate of total chromium and hexavalent chromium reduction rate. When thesolid-to-liquid ratio is to be0.75g/100ml, high removal rate can be reached40.03mg/gunder350mg/L. The kinetic and thermodynamic study show that the SCTS adsorptionprocess conform to the pseudo-second-order model and the Langmuir adsorptionisotherm and spontaneous monolayer adsorption reaction. The desorption andregeneration experiments indicate that high temperature and concentration of desorptionsolution can enhance the rate of the regeneration of SCTS. 3) This study not only has tested some physical indexs but also microstructures bySEM, FTIR, XRD. The macroscopic physical indexsshow that the SCTS basicallymeets the requirement of adsorption’s own demands. The Electronic scanning imagesand X-ray diffraction pattern proves the adsorbed behavior of chromium by SCTS. Themovement of multiple absorption peak of infrared spectrum demonstrate that aminogroup in chitosan and proteins polypeptide and carboxyl group in activated sludge andso on have involved in the adsorption process of chromium.