| A large amount of excess sludge is being produced by municipal sewage treatment plants and it is becoming a more and more serious environmental and social problem. The excess sludge disintegration ruptures floc structure and bacterial cell wall, then extracellular and intracellular components are set free which results in the organic matter transfers from the refractory solid phase to the degradable liquid phase and realizes sludge minimization and reclamation.The exploratory research of sludge disintegration by high-pressure jet flow(HPJF) is one part of this paper. For this disintegration process, cycle-index, spray pressure, plate-to-nozzle distance, mixed liquor suspended solid(MLSS) and nozzle spray angle are considered to be the influencing factors of sludge disintegration performance and used to determine the optimum disintegration condition. However, as to ultrasonic cavitation(USC) disintegration method, through orthogonal test, the relation among ultrasonic time, frequency, power and impulse ratio are studied, and the optimum disintegration condition is determined. For the disintegration degree(DDcoD) of HPJF and USC are inferior, the combination of both disintegration methods are investigated by comparing DDCOD, detecting particle diameter and examining TEM micrographs’characteristics in this paper, then finally to determine the better combination mode and to analyse its mechanism.The results of quality determination of cracked sludge supernatant show that, under the same experimental condition, to disintegrate excess sludge twice can greatly enhances the DDCOD, but the improvement is not obvious when keeps increasing cycle-indexes. The DDCOD of 0°pray angle nozzle prior to 15°, and the 15° better than 40°; the optimum plate-to-nozzle distance of 0°,15° and 40° spray angle nozzle are 25cm,5cm and 10cm, respectively. The DDCOD increases with the enhancement of spray pressure and remarkably decreases when the MLSS over 10000mg/L. The HPJF orthogonal analysis indicates that prioritization of influencing factors here increase in the order MLSS>plate-to-nozzle distance>spray pressure>spray angle. Meanwhile, the optimum disintegration condition is 7510mg/L of MLSS,25cm of plate-to-nozzle distance,6MPa of spray pressure,15° of spray angle.For the USC disintegration method, the prioritization of ultrasonic factors here increase as follows:ultrasonic time>ultrasonic frequency>ultrasonic power>ultrasonic impulse ratio, and the corresponding optimal standard of those factors is 10min of ultrasonic time,20kHz of ultrasonic frequency,600 W of ultrasonic power,1:2 of ultrasonic impulse ratio, respectively.Between the combination of HPJF and USC, the optimum disintegration condition of HPJF+USC is 8MPa,10cm,15°,11810mg/L, 10min,1:1,15kHz, however, for the USC+HPJF, it gets the highest DDcod when the experimental condition is 8MPa,10cm,15°, 6942mg/L, 10min,1:1,40kHz. The different combination sequences of HPJF and USC make those influencing factors have diverse prioritization.The optimal DDCOD of HPJF, USC, HPJF+USC and USC+HPJF is 17.62%,13.21%, 20.59% and 27.23%, respectively; and the versus energy consumption(Es) is 2.60,20.09, 18.68 and 25.55MJ/kgMLSS, then the DDCOD/Es is 6.54,0.65,1.07 and 1.06kgMLSS/MJ, respectively. Through particle diameter comparison and electron microscopy observation, the explanation of USC+HPJF gets the highest DDCOD is achieved. Once excess sludge is disintegrated by USC, a portion of micro-organisms cell wall is ruptured, and finally makes cell inclusion dissolve out by HPJF, then the DDCOD enhanced. |
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