Study On Sewage Sludge Reduction Using Ultrasonification

As the rapid development of citify process, the treatment rate of city sewage andthe yield of excess sludge rose year by year. So the methods of excess sludgereduction attracted people's attention. In recent years, applying ultrasound to reducesludge production has been a new route and way.On this paper, based on wastewater treatment plant of Da Tan Sha for theexperiment field, the technology of sewage sludge reduction using ultrasonificationwas studied. The research included changes on ultrasonically sewage sludge,ultrasonic sludge recycle to reduce sludge production on SBR process andenhancement of sewage sludge anaerobic digestion using ultrasonification. The majorachievements in the paper are as follows:(1) When the ultrasound waves propagate through the sludge medium, thephenomenon of cavitation bubbles will occur, and the characters of sludge will beaffected. As the ultrasonic time extended, the sludge temperature promoted, thesludge flocs were destructed constantly, and the solubilisation of sludge was increased.The quantity of soluble chemical oxygen demand(SCOD) in the supernatant and thedegree of disintegrationrose linearly as the time extended. However, the increase rateof total nitrogen(TN) and total phosphorus(TP) rose linearly as the time extendedwithin 5min, thereafter rised sharply. The sludge specific resistance was increasedwith the increasing sonication time. When the sonication time was 1min, the sludgespecific resistance was increased from 0.45×109s2/g to 1.4×109s2/g, and thedewatering ability deteriorated. It is difficult to apply ultrasound as the pretreatmentmethod for dewatering.(2) Ultrasonic disintegration on sludge can enhance the sludge cryptic growth ,Based on 1 and 2 two groups of SBR process, studied the influences on the effluentquality and the production of excess sludge, after 30% excess sludge treated byultrasound for 90s was reflew into the biological reactor. Compared to the control, theeffluent values of SS,COD and TN had no obvious changes; the effluent value of TPincreased from 0.2 mg/L to 0.3mg/L, and the remove efficiency decreased by twopercent points; The finally sludge disposition decreased by 23.44%. The technologyof ultrasonic sludge recycle is feasible to reduce the excess sludge.(3) On the research about the use of ultrasound to accelerate the anaerobic digestion of sewage sludge, it has been found when the proportion of ultrasonicsludge increased, the production rate and the day production of biogas increasedsignificantly. Compared to the control which didn't add ultrasonic sludge, when theproportion of ultrasonic sludge were 30%,50%,70% and 100%,the day productionof biogas increased by 0.3,1.2,1.7and 1.9, individually. When the residence timewas 24d, after 30% ultrasonic sludge was added to the inflowing sludge, the biogasproduction and the remove efficiency of organic matters increased, so the anaerobicdigestion was accelerated.