Research On The Conversion Of Heavy Mentals In Sludge Pyrolysis And The Effect Of Product Biochar On Soil Propertirs

In recent years,with the deepening of biochar research,pyrolysis has shown many advantages as an alternative to sewage sludge treatment: for example,pyrolysis can decompose organic pollutants and kill pathogens at high temperature,and oxygen-limited atmosphere inhibits some pollution during incineration.However,because heavy metal pollutants in sewage sludge will not disappear during the pyrolysis process,follow-up treatment applications require continuous attention.This subject takes sewage sludge with high and low concentrations of heavy metals as the research object,and investigates the conversion of heavy metals in the pyrolysis process at different temperatures and the impact of the product biocharl after pyrolysis on soil properties and release risks.The following conclusions are obtained:The characteristics of the two concentrations of sludge biochar are similar,but behave differently at different pyrolysis temperatures.When the pyrolysis temperature is high,the p H value of the sludge biochar gradually rises,the ash content increases.The lower content of C,and O,the H/C ratio and O/C ratio decrease after pyrolysis,and the surface acidic oxygen-containing functional groups decrease.The CEC values all increase slightly with the increase of temperature and then decrease.The final pyrolysis temperature rises from 300℃to 700 ℃,the types of functional groups on the surface of the sludge biochar gradually decrease,the aromatic structure is strengthened,and the surface morphology and porous structure gradually develop.Aluminum,iron,zinc,etc.are derived from inorganic components in the sludge biochar.The irregular adhesion of the pores,the specific surface area gradually increases,total pore volume gradually increases,and the pore size distribution is mainly mesopores.After the pyrolysis of the sludge with two heavy metal concentrations,the conversion law of different heavy metals is different.With the increase of pyrolysis temperature,the total amount of heavy metals in the product sludge biochar is concentrated.The DTPA-extractable content of heavy metals is greatly reduced,and the passivation effect of Cr is the most obvious.The determination of the content of various forms of different heavy metals by BCR continuous extraction method found that pyrolysis can greatly promote the conversion of Cd,Cr,Cu,and Pb from two sources of sludge from bioavailable components to stable components.The solution promotes the conversion of Zn to the residual debt state to a certain extent,but will not reduce the bioavailability of Fe and Mn,and after being converted into biochar,Mn will bring higher ecological risks.The effects of two concentrations of sludge biochar on soil physical and chemical properties are similar.The p H of the soil with pollutant sludge biochar increased to varying degrees,but it had little effect on the CEC value of the soil.The electrical conductivity of the soil is increased to different degrees after the sludge biochar is added to the soil,and as the pyrolysis temperature of the biochar added,the increase in electrical conductivity decreases,and the electrical conductivity of the soil increases after the original high-concentration sludge is added to the soil.The sludge biochar can greatly increase the organic matter content of the soil,it can also increase the urease enzyme activity and catalase activity in the soil.Two kinds of heavy metal concentrations of sludge biochar have different effects on the soil.Adding low-concentration pollutant sludge biochar can fix Pb in the original soil,and has little effect on the effective content of Cd,Cr,and Cu in the soil,but it will increase the effective content of Zn in the soil;compared with the soil added with the original high-concentration pollutant sludge,the DTPA content of heavy metals in the soil after the pyrolysis of sludge biochar is added to the soil is reduced.The determination of the content of different forms of heavy metals in the soil by the BCR continuous extraction method found that the addition of low-concentration pollutant sludge biochar can fix the mobile and effective metals Cd,Cr and Cu in the original soil,and the effect of Pb is not significant,but it will increase the bioavailable state of Zn in the soil.Compared with the soil with the original high-concentration pollutant sludge,the F3+F4value of heavy metals in the soil will increase after the sludge biochar is added to the soil.The environmental risk assessment results show that the addition of low-concentration pollutant sludge biochar can reduce the environmental risk level of the soil,and the effect of high-temperature charcoal is significant;the addition of high-concentration pollutant sludge and biochar to the soil is extremely harmful to the soil,but relatively speaking,the low temperature pyrolysis reduces this hazard to a certain extent..