| Acceleration of our country's urbanization process aggravated the deterioration of water environment, while weak economic strength limited our country's substantive input for wasterwater treatment. So, it was very inporment for promoting continuable development of national wastewater treatment cause to develop economical and efficient wastewater treatment technology. This article, based on the characteristics of activated sludge process and ultrasonic technology, introduced low intensity ultrasound into sewage treatment process of activated sludge technology, and the experimental study on feasibility and mechanism of improving activated sludge for sewage treatment with low intensity ultrasonic irradiation is introduced. The main conclusions are as follows:â‘ Ultrasonic pretreatment with different parameter combination has great influence to performance of activated sludge degradate organics. The results show that low intensity ultrasonic irradiation can change the property of sludge and the reaction system, affect the process of organic adsorbed by sludge. The adsorption of sludge is enhanced by appropriate parameters of ultrasonic irradiation at the frequency of 28 kHz, input power of 20W with exposure time of 10 min,but inappropriate ultrasound parameters can inhibit the initial activated sludge adsorption ability of wastewater organic. Adsorption of sludge is most affected the power factor, followed by irradiation time, the smallest is the frequency.â‘¡Low intensity ultrasonic irradiation with appropriate parameters can effectively enhance sludge activity, increase sewage organic removal rate of activated sludge. The results show, after pretreatment of the sludge ( MLSS of operation sludge is 6000mg/L ) by low intensity ultrasonic with frequency of 21kHz and input power density of 20W/L for 5 min, mixed with sewage, after 6h's aeration, the supernatant SCOD removal rate (97.7%) of the reactor was increased by 3.8% compared with that of the control one (93.9%).â‘¢By analysing ERIC- PCR fingerprint diagram, it shows that low intensity ultrasonic pretreatment will not immediately change the composition of microbial population, But perhaps some microbial growth will be inhibited, which leads to obvious variation of the sludge extracellular polymeric substances (EPS) components content, thereby changing micro-environment for sludge growth. An important phenomenon has been observed that when the sludge was pretreated by ultrasonic at the frequency of 21 kHz and 28 kHz, input power density of 20 W/L and 40W/L) with exposure time of 10 min, the polysaccharose concentration in the sludge EPS is less than that in the control one and consists of 77.6%~90.4% of the latter, but the protein content is more and consists of 110.0%~133.5% of the control sample, and MLVSS/MLSS ratio of the Sludge gradually increased, which indicate synthesis ablity of microbe was strengthened. So improvement of the wastewater treatment process with low intensity ultrasonic irradiation is a comprehensive result of enhancing and inhibiting action.â‘£Low intensity ultrasonic irradiation enable activated sludge structure loose, minish average sludge floc size, increase surface area of sludge, lead to augment contact area between solid and liquid, intensify micro-transfer of oxygen, enhance biological activity of sludge ,in order to improve wastewater treatment.
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