| With the increase of wastewater collection and treatment efficiency, How toproperly handle sewage sludgeand avoid secondary pollutionhas become to the public of environmental problems, crying for solutions.The study was based on municipalsludge from municipal sewage treatment plants, through microwave pyrolysis to produce biochar, studying its characteristic and potential application. Exploring the influence on biochar characteristic under different pyrolysis temperatures and different chemical impregnation as well as variation of heavy metal speciation during microwave pyrolysis.Temperature dramatically affected biochar preparation by microwave pyrolysisin low temperature(300-450℃). With the increase of pyrolysis temperature, biochar organic matter content is reduced from 74.33% of raw sludge to 51.99% of biochar prepared under 450℃, while the ash content increased from 27.2% of raw sludge to 49.06%. Carbon element content was increased from 35.33wt.% to 45.48 wt.%. In the meantime, the surface appearance and its proportion of biochar was changed by the pyrolysis temperature and pyrolysis conditions.After studying the microwave pyrolysis affecting on the form of heavymetals in sludge and its biochar, with the extraction methods, the find is microwave pyrolysis can turn the soluble and reducible heavy metals in the sludge, which have high environmental ecological risk in the sludge into theresidual states which with low environmental ecological risk in the biochar. Using the three kind methods to evaluate the potential ecological risk of heavy metals of biochar, it finds that there are differences amongdifferent pyrolysis temperaturesand different kinds of heavy metals element, the As, Cu, Ni, Znin biochar were remarkablely less risk to evironment, but Cr, Pb were not was not significant.The biochar BET surface area significant increase after chemical impregnation. The largest BET surface area was 467.21 m2/g which preparation under 700℃within KOH impregnation. In the same pyrolysis temperature, different chemical activators affectedthe biochar BET surface area were as follow is KOH>ZnCl2>H2SO4>citric acid>H3PO4. The biochar adsorption test results show that biochar adsorption capability for MB was relevant with its surface area. Under the same condition, the order was KOH>ZnCl2>H2SO4>H3P04>Citric acid, in the case of different chemical impregnation agent. Most biochar adsorbing to MB was in accordance Freundlich isotherm adsorption, which shows MB in the surface of biochar is not only monolayer adsorption.The adsorption of MB by biochar was better meet the second level dynamics adsorption of Lagergren. Also it is more closer to the equilibrium adsorption capacity by experiment accords with the second level dynamics equation.Through testing the perennial ryegrass seed germination, found that the sludge biochar was benefited to perennial ryegrass germination. The germinationrate reached 98.15% in group SC350, which has 9.26% morethan the soil groupwhose rate was 88.89%. By planting perennial ryegrass, found that the sludge biochar addition, had no negative effect on growth of perennial ryegrass, on the contrary, comparingwith the direct added sludge, the perennial ryegrass grow well in group of added biochar.It chould be realize sludge reduce, recyle, reuse through microwave pyrolysis. The biochar preparation from microwave pyrolysis not only reduce the sludge ecological risk for agricultural purposes, while at the same time could be used as a low-cost adsorbent by chemical impregnation method, has a good application prospect. |
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