| Base on the researches on sludge digestion process of the others, sludge ultrasonic pretreatment was introduced into sludge anoxic/aerobic digestion process in this paper, for searching a low-cost, short period, high efficiency sludge reduction process.First, the sludge ultrasonic pretreatment experiment was taken in this paper. The impact of ultrasonic density and time on sludge pretreatment efficiency has been studied at certain ultrasonic frequency (28 kHz) and sludge concentration (10 g/L). Both the sludge oxygen uptake rate (SOUR) and the degree of disintegration (DDCOD) have been analysized, and used to evaluate the sludge pretreatment efficiency. The results have showed that disintegration degree and sludge activity were improved significantly under appropriate ultrasound treatment condition. And the optimum operating parameters of ultrasonic energy density and ultrasonic time were 0.1 W/mL×15min and 0.15W/mL×10min. At those cases, DDCOD reached 18.74% and 17.03% respectively,△SOUR reached 11.6872mg02/gMLSS·h and 12.55mg02/gMLSS·h respectively, and specific energy consumption was 9.47kJ/gSS.Secondly, sludge ultrasonic pretreatment was introduced into sludge anoxic/aerobic digestion process for researching the operating parameters. An experimental program of orthogonal design was carried out to determine the most effective treatment conditions of the ultrasonic density, time and interval on the waste activated sludge anoxic/aerobic digestion. The results have showed that the max removal rate of MLVSS reached 50.9% after 9d's digestion with ultrasonic treatment,14.4% higher than that without ultrasonic treatment, and the optimal treatment conditions were ultrasonic density at 0.15 W/mL. ultrasonic time at 10 min. ultrasonic interval at 12 h. Among the three factors, ultrasonic interval is the most influencing factor, next is ultrasonic density and the last is ultrasonic time.Finally, ultrasonic-anoxic/aerobic digestion process simulation test was taken. A reactor with a volume of 30L was designed and specialized for the ultrasonic anoxic/aerobic digestion. The pretreatment tests were carried out at the following conditions:ultrasonic frequency of 28 kHz. ultrasonic density of 0.15 W/mL, ultrasonic time of 10 min. ultrasonic interval of 12 h. and pretreated sludge proportion of 30%. The results have shown that the ultrasonic pretreatment can reduce the digestion time of sludge and improve the digestion efficiency significantly. Sludge reached the discharge standard after 10 days'digestion.12 days shorter than that without ultrasonic pretreatment. The maximum removal rate of MLVSS was increased by 11%, up to 55.10%. In addition, the ultrasonic pretreatment had a significant effect on the change trend of soluble COD (SCOD) of supernatant digestion liquid, but a little on that of pH. ammonia nitrogen and TP.
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