Experimental Studies On Combined Ultrasonic And Calcium Hydroxide Disintegration Technology Of Sewage Sludge

There are two major problems during the wastewater treatment process in China:one is the poor denitrification efficiency caused by low C/N ratio, the other one is alarge quantity of sewage sludge can’t be proper treated. The denitrification carbonresource developed by sewage sludge can achieve the sludge’s recycling andreduction. And the combined pretreatment of ultrasonic-alkaline can improve thecarbon resource production and lower the cost.The sewage sludge from Yaozhuang wastewater treatment was selected as theresearch object. The sludge was treated by low energy density ultrasonic, Ca(OH)2and combined method to analysis the effect of these treatments and investigate theoptimal disintegration condition. The results showed that:(1) Ca(OH)2can enhance the sludge’s disintegration efficiency and restrain thephosphorus releasing. When Ca(OH)2was applied in the sludge, the pH of sludgeincreased which caused the higher disintegration degree, while the protein releasingwas inhibited by Ca2+. The disintegration degree(DD) reached the maximum, which is7.48%, when the sludge was treated by0.04mol/L Ca(OH)2for60min. In thesupernatant of sludge which was treated by Ca(OH)2, the concentration of totalphosphorus and orthophosphate were all lower than the control group’s.(2) Low energy density ultrasonic can promote the sludge disintegrationefficiency and the concentrations of all dissolved compounds rised with theincreasing of ultrasonic energy density and the treatment time during the sludgedisintegration process. The DD reached the maximum, which is5.39%, when thesludge was treated by ultrasonic energy density of0.10W/mL.(3) The combined pretreatment of ultrasonic and Ca(OH)2can greatly improvethe sludge disintegration degree and control the phosphorus releasing. With theincrease of the Ca(OH)2dosing quantity, the SCOD and the concentration of proteinin the supernatant of sludge showed a decreasing trend after first, while theconcentration of polysaccharide continued to rise. When the sludge was treated by0.03mol/L Ca(OH)2the dissolution rate of organic matter reached the maximum,which means it was a higher economic method than other treatment. When theultrasonic energy density was0.10W/mL, the SCOD/TN and SCOD/TP value washigher than other treatments’, which reduced the pressure of follow-up treatment.(4) The SOUR, which characterizes the microbial activity of sludge, haveincreased to0.294mg/(g·min) when the sludge was treated by0.04W/mL ultrasonic and0.01mol/L Ca(OH)2for60min. When Ca(OH)2dosage exceeded to0.03mol/L,sludge activity reduced to0quickly.(5) The distintegration effect of combined pretreatment of ultrasonic-Ca(OH)2was superior to the effect of two separate methods. The DD was fitted based on theactual value to a second order polynomial equation: DD=-2.660-0.057A+484.738B-0.048C+0.441AB+2.233×10-3AC-0.088×BC+2.909×10-4A2-6055.000B2+2.117×10-4C2, and A is ultrasonic energy density, B is the dosage level of Ca(OH)2and C iscombined application time and DD respectively. During the process of disintegration,ultrasonic has a synergistic reaction with Ca(OH)2.