Industrial by-products in treatment of metals from polluted water
Abstract: Water treatment can be carried out effectively by passive, low cost methods, as an addition or alternative to existing advanced technology. Energy and resource use can be optimized (i.e. minimized) by reusing by-products from local or regional manufacturing of timber and steel. The ability of pine bark and blast furnace slag to treat metal contaminated water, primarily landfill leachate, has been evaluated. Several issues of concern were addressed in laboratory experiments and pilot scale measurements at a landfill site, including metal adsorption capability, saturation, variables influencing the adsorption process and potential leaching of organic toxicants from pine bark. The data was analyzed using kinetic modeling, regression and multivariate data analysis, i.e. PCA. These experiments showed that pine bark and blast furnace slag have great potential to retain metals from solution. Pine bark could also be used to treat solutions with high concentrations (>200 mg/l) and containing several heavy metals simultaneously (Cu, Pb, Zn, Cr and Ni). A constructed pilot plant showed poor retention of metals, which was somewhat improved by increased contact time, a variable which was found to be important in one of the laboratory experiments. Studies of organic content in landfill leachate, primarily dissolved organic carbon (DOC), showed that this could limit adsorption to pine bark. Another important finding, which is in contrast to the suggestions of other researchers, was that leaching of phenols from pine bark constituted only a small fraction of the DOC and was not toxic to the test-organism Daphnia Magna at neutral pH. In order to understand more about the relationships between the different variables, a multivariate approach (PCA) was applied to data on the treatment of landfill leachate with pine bark. This study showed that the metal concentration of the leachate was the variable most strongly related to metal adsorption. The concentration of DOC had only a minor effect according to PCA. Overall, pine bark and blast furnace slag can be used as adsorbents, but with caution and preferably in effluents of moderate metal concentration and low DOC.
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