Study On Sludge Aerobic Digestion Promoted By Low Ultrasound Radiation

Having fully grasped a variety of processes for sludge treatment and the up-to-day developing trend of ultrasonic technology in bioengineering,author fist time introduced the biological technique of ultrasonication with low energy into sludge aerobic digestion and puted forward the process of low dose of ultrasound radiation promoting sludge aerobic digestion, with the aim of improving the condition of lacking the stabilization facilities seriously for sludge in most sewage plant of medium and small scale in China.Furthermore,it was studied how does low dose of ultrasound radiation effect physical and chemical properties of sludge,the metabolism activity of micoorganism and sludge aerobic digestion.Physical and chemical properties, biological activity and its lasting of waste active sludge of different age was measured after ultrasound radiation with different intensity and time.It was concluded that the variation of sludge property shows three different stages during ultrasonication.It is displayed in the first stage that to decrease the size of floes, increase biological activity and solve soluable organic compounds in sludge flocs.In the second stage biological activity is restrained in short time and then gradually recovers.Finally,ultrasound radiation gives a fatal damage to microorganisms so that oxygen uptake rate, number of active bacteria, enzymes activity and dehydrogenase activity all have a considerable decrease.The intensity of 0.05w/ml is more economical from saving energy and two to ten minutes is better for ultrasound radiation.According to the variation of sludge properties during ultrasound radiation,aerobic digestion of sludge with ultrasound radiation was studied by means of alterating inputed energy,inputed number, inputed energy each time and sludge concentration,with the result that three aspects of conclusions were achieved as follows.(1) Ultrasound radiation is able to improve the aerobic digestion of sludge,for it can shortened the digestion time of five to seven days and increase the romoved ratio of TVSS by 30-50%.In this process,variations of concentration of COD,NH4+-N,NO"3-N and TP in supernatant are similar to control sample and aren't interfered with by the way of ultrasound radiation.In addition,ultrasound radiation can decrease SVI value of ultimate products in aerobic digestion of sludge and make SVI value stable in shorter time , and inputed energy is more, the stabilization is more quick.(2) The way of ultrasound radiation has an important effect on the time for aero-bic digestion to stabilize sludge.The order of importance about intensity,inputed energy each time,inputed times is that intensity is first,inputed energy each time second,inputed times third.(3) Having analysed the dynamics of sludge aerobic digestion with ultrasound radiation,author believed that the process of sludge aerobic digestion with low ultrasound radiation still abides by the first order dynamic model,and approximately, the reaction rate is an index function of inputed energy when it was less than the greatest reaction rate.