| Sludge pyrolysis for biochar preparation is a way of resource utilization of sludge,which provides more options for raw materials in biochar preparation.The application potential of biochar in soil carbon sequestration makes it one of the efficient ways to reduce greenhouse gas emissions and solve the problem of global climate change.However,there is little research on related issues about how the physical and chemical properties of sludge biochar will change and how it affects soil microorganisms after applied in the soil.In this study,sludge from municipal,pharmaceutical and steel mill wastewater treatment plant,as well as chicken manure,were pyrolyzed at 500℃,600℃,and 700℃,respectively,for biochar preparation.The physical,chemical and microbial responding properties of sludge biochar were studied in the processes of chemical,physical,and biological aging.The chemical aging method selected in this experiment is hydrogen peroxide oxidation;the physical aging is the freeze-thaw cycle;and the biological aging is the mixed cultivation of soil and biochar.Results show that these sludge biochar have strong capacity of carbon sequestration and resistance of oxidation and weathering,and can ameliorate acid soil.In summary,these conclusions can be drawn:(1)As the pyrolysis temperature increases,the carbon content in the sludge biochar decreases,the degree of carbonization increases,and the inorganic components are gradually concentrated and retained in the sludge biochar.Sludge yield showed a significant negative correlation with pyrolysis temperature,which of sludge biochars was higher than that of chicken manure;ash content was significantly positively-relative with the temperature,which of sludge biochars were higher than that of chicken manure.p H was positively correlated significantly with pyrolysis temperature and ash content.(2)The property of the sludge determined the property of the biochar.Sludge biochar has complex inorganic ingredients,which have wide varieties and high contents.During the processes of aging,Fe dissolution rate of biochars from still mill plant reached2.61-24.71 g/kg,which was greatly higher than that of biochars with other origins.Dissolution rate of Al and Ca were relatively lower.The rest toxic element,such as Cu,As,Pb,Cr and Zn,have dissolution rates lower than 1 ppm;(3)The interaction of inorganic and organic compounds can immobilize the carbon in the biochar,which may strengthen stability of the biochar,including resistance capacity to chemical and physical aging,good carbon sequestration and soil amelioration ability.This high immobilization of carbon may be caused by the formation of inorganic and organic compounds;(4)The sizes of the biochars decreased with the process of physical aging,except biochars with pharmaceutical origin.The sizes of biochars from municipal wastewater treatment plant and chiken manure were higher than that of the rest biochars,which indicated that these two kinds of biochars may have lower migration abilities and stably exist in the soil.(5)Microbial organisms might not survive after mixed with biochars due to the high p H and inorganic content of biochars.Therefore,the application of sludge biochars should be paid great attention in the soil with high bioconcentration,such as the roots of crops. |
