Research On The Preparationand Characterization Of Sludge-based Biocharand Its Application Of Soil

With the development of the business of urban wastewater treatment, theproblem of sludge treatment and disposal emerged. Sewage sludge contains largeamounts of organic matter and the elements which are necessary for plant growth, soit can be used as biomass. Sludge pyrolysis is one of the research hotpots. Pyrolysisproducts as soil amendments applied to the soil can improve the physical, chemistryand biological properties of the soil, and reduce the effectiveness of soil contaminants.The experimment prepared the biochar by pyrolysising sludge. In thisexperimment the following three parts were studied:(1) characterization of biochar,(2) effecting of biochar on chemical, physical and biological properties of the soil,(3)effecting of biochar on growth of ryegrass. By biochar characterization, analysis theeffect of pyrolysis temperature on product properties; through ryegrass potexperiments, analysis the effect of materials, pyrolysis temperature and applicationrate on soil properties and the growth of ryegrass.Raw material showed acidic, and higher the pyrolysis temperature the products’alkaline was more strongly. The pH of the850℃sludge-based biochar was9.28. Asthe pyrolysis temperature rising sludge-based biochars’ CEC firstly decreased,reaching a minimum value3.84cmol/kg at650℃, then rised to5.12cmol/kg at850℃. As the temperature increasing, the sludge-based biochars’ surface areas and porevolumes firstly decreased, then increased. Sludge had rich surface functional groupscontaining alcoholic hydroxyl group, phenolic hydroxyl group and carboxylic acids,etc.; after the pyrolysis just exsited a small amount of phenolic hydroxyl group,carboxyl group and aromatic ring. For sludge with pyrolysis temperature increasing,H/C, O/C fell. Biochar’s O/C decreasing mean decrease of oxygen-containingfunctional groups; decreasing H/C indicated that the higher is the temperature, thehigher is the degree of aromatic biochar, and the stability is stronger.By ryegrass pot experiment the effects of biochar on soil pH, CEC and enzymeactivity of H2O2were studied. The soil itself was acidic, applying biochar improvedsoil pH, the higher the proportion of biochar was, the greater pH increased.550℃,650℃and750℃sludge-based biochars applied to the soil obviously increasedsoil’s pH relative to the blank soil. When850℃sludge-based biochar was applied tosoil with the ratio of2%,5%and10%, pH value stabilized between7.2to7.4; whilethe ratio reached15%pH value increased to7.4.550℃sludge-based biochar slightlyincreased soil CEC,650℃sludge-based biochar reduced soil CEC. Low proportion of 850℃sludge-based biochar improved the soil CEC, but when the proportion reached15%, CEC was decreased than the blank soil. After850℃sludge-based biochar and750℃rice husk-based biochar were applied to the soil, enzyme activity of H2O2changed as followed:15%<blank soil <2%<5%<10%.After550℃sludge-based biochar applied to soil, plants were almost impossibleto grow,650℃sludge-based biochar also inhibited the growth of ryegrass; just wasratio of5%of750℃sludge-based biochar applied to the soil, plant fresh weight abovethe blank soil0.0084g. The ratio of850℃sludge-based biochar ranged from2%to15%, compared to the blank soil, fresh weight respectively increased58.15%,73.92%,76.56%and-0.82%. Therefore850℃sludge-based biochar played a good role inpromoting and enhancing the growth of ryegrass and the proportion of10%got thebest effect.