Effects Of Alkaline Heat Treatment On Dehydration Performance And Hydrogen Production By Pyrolysis Of Municipal Sludge

With the increasing attention paid to the treatment of water environmental pollution in China,the number of sewage treatment plants is increasing day by day,which leads to a sharp increase in the number of sludge but the treatment method can not meet the current demand for severe problems.The disposal of sludge should be based on the principles and objectives of reduction,harmlessness and resource conservation,among which reduction is the primary premise of sludge treatment.Alkali heat treatment conditions of this test by adjusting the different treatment temperature and treatment time,alkali dosing amount,and studied the characteristics of the effects of these factors on the efficiency of sludge dewatering,and analyzed the sludge particle apparent morphology,the sludge particle specific surface area and particle size distribution,to analyze the nature of the alkali treatment of sludge floc structure change,on the basis of general alkali heat treatment and sludge pyrolysis process were studied.The main research results are as follows:?1?The best alkali conditions for heat treatment for the processing temperature of210?to 60min,and mixed with sludge dry base quality 40%CaO powder,can make the moisture content of sludge from 80.57%to 62.48%.?2?The structure of sludge flocs was destroyed by alkaline heat treatment.Under the combined action of temperature and time,the sludge flocs were fully hydrolyzed.The addition of Ca²⁺can reduce the resistance of the cell wall of sludge flocs under high temperature conditions,and Ca²⁺also reduces the repulsion force of the double electric layers in the sludge flocs,helping the bound water in the cells to be converted into free water in a larger proportion,so that the treated sludge flocs can lose more water in centrifugal dehydration.?3?After the alkaline heat treatment,the sludge changed from solid state to liquid state,and the melanoid-like substance generated by maillard reaction gradually changed the color of the supernatant after centrifugal dehydration to brown and black.By scanning electron microscopy?SEM?observations show that the sludge particles are destroyed,appears to be a massive pore surface.The average particle size decreased from 78.75?m to 24.43?m.The BET specific surface area of the original sludge was 0.27m²/g,the Langmuir specific surface area was 0.36m²/g,the BET specific surface area reached5.97m²/g after the thermal alkali treatment,and the Langmuir specific surface area reached 8.24m²/g.?4?Alkaline thermal pretreatment can effectively damage the internal structure of sludge flocs,increase the number of pores,enhance the hydrolysis effect of hydrothermal,change the moisture occurrence state in the sludge,increase the proportion of moisture that can be separated,and effectively improve the dehydration performance of sludge.?5?Alkaline heat treatment can effectively destroy the structure of sludge flocs,enhance the adsorption of sludge particles,and improve the gas production efficiency of sludge after pyrolysis reaction.CaO powder used in alkali heat treatment can also act as Ca based catalyst in the pyrolysis process,which can not only accelerate the initial pyrolysis reaction of sludge,but also improve the secondary cracking of intermediate product tar and water-gas conversion reaction and improve the content of hydrogen in pyrolysis gas.Under the condition of 210?to 60min of alkali heat treatment results show that the hydrogen gas in the pyrolysis gas proportion increased from the original45.48%to 59.48%.