Study On Microwave-Assisted Sludge Hydrothermal Liquefaction And Production Of Polycyclic Aromatic Hydrocarbons (PAHs)

With the rapid development of economy and society,the increasing degree of urbanization and the rapid increase of urban population,the scale of urban sewage treatment is increasing day by day,and the inevitable by-product of sludge as a sewage treatment process is also increasing year by year.However,the sludge produced by most sewage plants in China has not been well stabilized,reduced,harmless and resourced.In addition,the pyrolysis oil production technology of sludge requires high temperature and needs to dewater the sludge before pyrolysis,which increases the overall energy consumption and is not easy to be promoted and applied in industry.Hydrothermal liquefaction does not require drying of the sludge.At the same time,microwave pretreatment helps to change the organic matter in the sludge and promotes its decomposition at low temperature.Therefore,this paper takes the sludge produced by the municipal sewage treatment plant as the raw material,uses the water in the sludge as the reaction medium,and combines the microwave pretreatment and sludge hydrothermal liquefaction to oil production technology.Taking the preparation of bio-oil as the main purpose,the liquefaction behavior of bio-oil prepared by hydrothermal liquefaction of sludge after microwave pretreatment was analyzed.The effects of different liquefaction temperature,residence time and pretreatment power on the distribution of liquefied products were investigated.Exploring the product characteristics of bio-oil,biochar and gas under different microwave pretreatment powers,and analyzing the influence of microwave pretreatment on the distribution of each product component.The formation and distribution of 16 polycyclic aromatic hydrocarbons(PAHs)in bio-oil and biochar were analyzed,and the effects of microwave pretreatment on it were investigated.The results showed that temperature and residence time had a great influence on the yield of hydrothermal liquefaction products.Without microwave pretreatment,the optimal yield of bio-oil was 340℃ and 30 min,up to 30.4%.With the increase of temperature and the extension of residence time,the bio-oil yield first increased and then decreased.When microwave pretreatment was added,the addition of microwave power will cause the structural change of organic matter in the sludge,and appropriate microwave power(360W)is conducive to the conversion of organic components in the sludge into bio-oil.The addition of microwave pretreatment can improve the quality of bio-oil and reduce the production of organic acids and nitrogenous compounds in biooil,but it has no obvious effect on the characteristics of biochar and gas.In the process of direct hydrothermal liquefaction of sludge,the formation of PAHs in bio-oil was inhibited by temperature,but the prolonged residence time promoted the formation of PAHs.The addition of microwave pretreatment can inhibit the generation of polycyclic aromatic hydrocarbons(PAHs)in bio-oil.