| With the development of social economy and the acceleration of urbanization, the emission and thetreatment of domestic sewage increase rapidly. As the by-product of urban sewage treatment, sludge isbeing discharged increasingly. The qualitative and quantitative determination of pollutants in sludge, aswell as their treatment and disposal, have become an important issue in the field of environmentalengineering.In the present work, detail experimental studies were conducted on the sludges which came from Westand East sewage treatment plant of Kaifeng(named A, B).3kinds of electric heating board digestionsystems (HNO3-HF-HClO4, HNO3-HCl-HClO4, H2O2-HNO3-HCl) and2kinds of microwave systems(H2O2-HNO3-HCl, H2O2-HNO3-HCl-HF) were selected to pretreat the sludges.11metals, such as Cu, Pb,Cd, Cr, Zn, Mn, etc, were determined by Inductive Coupled Plasma Atom Emission Spectrometer(ICP-AES). Results suggested that5kinds of digestion systems were all efficient for the determination ofmetals. The complete dissolution of heavy metals could be realized with the microwave digestion systemusing H2O2-HNO3-HCl-HF, by which the recovery rates of Cu, Pb, Cr, and Ni could reach96%-104%andRSD were in0.160%-3.48%. This method shows good precision, high accuracy, less acid consumption,easy and safe operation, displaying great applicability to the analysis of heavy metals in sludge. Bothsludge contain higher concentration of Fe and Ba, while the amounts of Cu, Zn, Pb, Cd, and Ni are lowerthan standard limit (CJ/T309-2009).The chemical forms, as well as the bioavailability and the related environmental effects of heavymetals in both sludges were investigated using selective sequential extraction procedure which wasdeveloped by Tessier. The results showed Fe and Ba in the both sludges mainly existed in residue state,which could not be absorbed and used easily by creature and caused less harm to environment. The mainexisting forms of Cu, Cr, Pb, Ni, Zn, and Mn are organic-bound state, which belong to the potentialeffective state and might cause environmental pollution under certain conditions. A small part of Mn, Niand Pb exist in exchangeable state, in particular the proportions of biological effective state of Mn, Ni andPb are25.21%,26.56%and26.81%respectively, which are easy to be accumulated and absorbed in living body and lead to serious damage to environment.The sludge-based adsorbents were prepared by modifying the sludge from West sewage treatmentplant with cetyltrimethylammonium bromide (CTAB) combined with hydrochloric acid. The adsorbentsand the raw sludge were characterized by FT-IR, BET and so on. FT-IR result showed CTAB weresuccessfully grafted onto the sludge; BET indicated the total specific surface area of the adsorbentincreased slightly compared with the raw sludge. The sludge-based adsorbents were efficient to removeCr(VI) up to91%from simulate wastewater under the conditions of20mg·L-1Cr(VI), pH=2.0,8g·L-1ofadsorbent dosage,30minutes of contact time, and25oC for absorption temperature.In a certain range of temperature and concentration, the adsorption of Cr(VI) by modified sludge couldbe much more preferably described by Langmuir isotherm models with the correlation coefficients of0.9991, indicating the priority was monolayer adsorption. The correlation coefficients ofpseudo-second-order kinetics equations were up to0.9990, and the experimental qewas calculated to be9.64mg·g-1, which was close to the theoretical value of9.68mg·g-1, what’s more, it could have a betterdescription of the whole adsorption process, and the adsorption of Cr(VI) consisted of physical adsorptionand chemical adsorption. The negative△G0indicated the adsorption process can occur spontaneously withexothermic characteristic, the negative values of△H0and△S0demonstrated that the process wasexothermic and the disorder of the whole system reduced after the adsorption reaction. |
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