Study On Phosphorus Release Characteristics And Recovery From Excess Sludge With Ultrasonic Combine Hydrolysis Process

Phosphorus is non-renewable and irreplaceable, which plays an important role in human activity as well as animal and plant life activities. With the increasing consumption of phosphorus, it is of great significance to alleviate the growing shortage of phosphorus resource and recover phosphorus resource. After treatment by biological method, most phosphorus in the wastewater will transfer to the sludge, which is the main factor resulting in eutrophication. Ultrasonic technology can effectively break the sludge and has been widely used in sludge treatment due to its high efficiency, no secondary pollution and so on. After treated by ultrasonic method, the organic matter, nitrogen, phosphorus and others will release from the sludge. To date, a lot of researches have focused on the release of carbon source, but few have focused on the phosphorus release. In this research, ultrasonic technology was employed to treat the excess sludge from the sequencing batch reactor (SBR). The effect of ultrasonic time, ultrasonic density, the concentration of sludge on phosphorus release and its composition were investigated, and the mechanism of action and ultrasonic combined with hydrolysis treatment for phosphorus release were explored, and the method of magnesium ammonium phosphate (MAP) was used to recycle the phosphorus resource. The main conclusions are showed as follow:(1) The result of single factor experiments and orthogonal experiments showed that the increase of ultrasonic time and ultrasonic density can promote the phosphorus release from the sewage sludge, while the sludge concentration had no obvious effect on phosphorus release; the influence significance of the three factors was in the order:ultrasonic time> ultrasonic density> sludge concentration. In this experiment, the optimal parameters for phosphorus release were 8 g/L sludge concentration,0.7 W/mL ultrasonic density and 80 min ultrasonic time.(2) After treated by ultrasonic process, the released phosphorus from sludge was most in form of PO43--P, which accounted for 59.5%-87.2% of the released total phosphorus (TP). Under the ultrasonic energy of 90-450 kJ/gMLSS, the increasing ultrasonic energy is beneficial to the phosphorus release. And at the same ultrasonic energy, the phosphorus release performed better under lower ultrasonic density and longer ultrasonic time, compared with the condition of higher ultrasonic density and shorter ultrasonic time.(3) During ultrasonic treatment on the sludge, the contribution of mechanical shear force was greater than thermal effect and HO-free radical oxidation.(4) Ultrasonic technology combined hydrolysis can effectively improve the amount of PO43--P release. Higher hydrolysis temperature can promote the phosphorus release. For example, under the condition of ultrasonic intensity of 0.4 W/mL, the ultrasonic time of 60 min, and the hydrolysis time of 10 h, when the hydrolysis temperatures were 5 ℃,25 ℃ and 50 ℃, the TP release rates were 75.9%,82.6%,90.5%, and the PO43--P release were 151.8, 178.9,202.5 mg/L, respectively.(5) MAP method was used to recycle the phosphorus in sludge supernatant after ultrasonic treatment combined with hydrolysis, the optimal condition for phosphorus recovery was the reaction time of 20 min, the initial pH of 10 and the Mg2+/PO43--P of 1.7:1, which achieved the maximum recovery rate of 93.6%.