| Because of the shortage of worldwide energy and resources, sewage treatment especially aerobic biological treatment of small sized domestic sewage is constrained by economic conditions. However, with the development of third type of anaerobic technique, wastewater treatment by anaerobic bacteria becomes possible. However, the mass-transfer efficiency of organic substrate and microorganism is low, the organic matter degradation rate is slow, the activity of bacteria is not high and reactor startup cycle is long. This experiment suggests adopting ABR along with ultrasound stimulating biological activity of activated sludge to deal with low concentration domestic wastewater so as to reduce energy consumption and improve the effect of anaerobic biological treatment of low concentration domestic sewage. Main findings are as follows:1. Test in labs: launch the ABR research. Adopt fixed influent concentration to decrease the hydraulic retention time. Influent COD concentration is about 600 mg/L, and the hydraulic retention time is changed from 24 h to 12 h to finally reach 8h. What’s more, organic volumetric loading changes from 0.6 kg COD/(m3·d) to 1.8 kg COD/(m3·d). It is successfully launched based on the 44 d reaction vessel and COD removal rate is about 72%-74%, which firstly occur in two compartments occupying 90% of the total removal and the last two compartments mainly deal with stabilizing treatment. After the successful launching of the reaction vessel, all departments shall form granular sludge, and the particle size of sludge become smaller along with the flow direction and the surface structure becomes tighter with deepen color.2. Study the enhancement effect of ultrasound on anaerobic sludge through beaker experiment. The result finds out that the ultrasonic energy density and ultrasonic time are two main factors which will affect the activity of dehydrogenase sludge as well as content of coenzyme. Anaerobic sludge with the MLSS 10g/L concentration is conducted with ultrasound, and the parametric combination of 20 k Hz,0.2 W/m L,10 min plays a good role in accelerating its activity. To appropriately mix the sludge can uniform the ultrasonication to improve the parametric activity accelerating rate. When the initial COD is about 1200mg/L, the COD removal rate is increased by 12%. However, the ultrasonic parameters which can improve the anaerobic sludge activity are in a narrow range.3. To initially reveal the operating mechanism of enhancement effect of ultrasound on anaerobic sludge based on the structural form change before and after ultrasound, the change of sludge adsorbability and the polymer composition transformation. The result shows that the structure after ultrasound is loose and entirety becomes smaller while the surface becomes rough with convex and concave. But the gap between the structures becomes smaller. It proves that the low-intensity ultrasound can effectively disperse floc and add the superficial area, which also makes contributions to the adsorption degradation. With proper ultrasonic parameters, the anaerobic sludge absorption capability shall be significantly improved. Ultrasound will change the components of extracellular polymeric and stimulate more protease, but inhibit the formation of amylase. The protein content is increased by 20% while the amylase content is decreased by 10%.4. Study the effect on ABR operating caused by persistent cyclical ultrasound based on comparison test of ultrasound and control group. The result shows that when the operating is stable, the COD removal rate of ultrasound group is increased by 7%-8% comparing to the control group. |
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