Treatment Efficiency Of Anaerobic Sludge Irradiated By Low Intensity Ultrasound In Anaerobic Baffled Reactor

Low intensity ultrasonic irradiation is a very promising new technology to improve biologic activity thus to promote wastewater biological treatment efficiency.The paper is specific to low specific growth rate of anaerobic micro-organism as well as low specific degradation rate of ground substance caused by low temperature and low organic matter concentration gradient existing at low-concentration wastewater treatment of anaerobic organism;the effective mixing of mixed liquor can not be achieved due to the small gas production rate,as well as the low solid-liquid mass transfer efficiency;the harsh living conditions of methane bacteria and long multiplication rate will lead to low microbial activity as well as long reactor start-up period etc.Through combining with low intensity ultrasonic irradiation technology,it can promote enzyme and substrate contacting,modify conformation of enzyme molecules thus to improve biologic activity of the enzyme,and significantly improve biological activity to strengthen the wastewater biological treatment.The paper studied the influence of different ultrasonic parameters on promoting the activity of anaerobic sludge under 20 KHz low intensity ultrasonic irradiation;investigated action mechanism of periodic ultrasonic irradiation anaerobic sludge on wastewater organic matter degradation as well as the biological activity of activated sludge in the reactor;relying on molecular biology,it revealed the influence of low intensity ultrasonic radiation on sludge microbial community structure.The main research contents include:First of all,through bench scale experiment of lab beaker,by setting anaerobic sludge of ABR technology as research object and adopting coenzyme F420 and dehydrogenase activity as representation,it studied activity changes of anaerobic sludge within the ultrasound input power density of 0.02~0.4 W/mL,and irradiation time of 0~60 min.The research detected that the application ranges of ultrasonic irradiation parameters optimization for different characteristics of sludge are narrow.Appropriate intensity of ultrasonic irradiation can strengthen the adsorption capacity at early stages of the anaerobic sludge.It has obvious promotion effect on biological treatment of wastewater anaerobic degradation of organic matter.Secondly,it carried out ultrasonic irradiation researches with different characteristics.It has detected that when sludge concentration reached 40 g/L will improve the mixture cavitation threshold thus to weaken the reinforcement effects.Low wastewater organic concentration is more advantageous to improve the activity of anaerobic sludge compared to high wastewater organic concentration.However,when the chemical oxygen demand of wastewater is less than 200 mg/L will weaken sludge activity strengthening effects.The intermittent agitation can improve irradiation effects of anaerobic sludge during ultrasonic process.And then,based on ultrasonic optimization parameters at early stage of the beaker experiment,the two groups adopt ABR technology for parallel running to control inflow COD concentration to approximately 600 mg/L.The irradiation cycle of ABR in ultrasound is 24 h.Under the circumstance of irradiation sludge ratio as 10%,it has been detected through ABR comparative experiment in control group that,the ultrasonography group can better adapt to the changes in the environment.Low power ultrasound irradiation can shorten starting time of ABR low-concentration wastewater treatment and improve wastewater COD removal rate.Continuous periodic ultrasonic effects will change the compositions of sludge extracellular polymers.Ultrasonic action will suppress the polysaccharide microbial metabolism in the process of transformation.It is possible that ultrasonic can result in changes of microbial flora and reduce the contents of polysaccharide in EPS.The mechanical effect and steady-state cavitation effect of ultrasonic can instantly cause damage to the surface of sludge cells.The wound caused by low intensity and short irradiation is small in size,which can hardly be self-repaired by the microorganism.The secretion of protease as well as sludge activity can be enhanced during the repairing process.Periodic ultrasonic effects make the DNA released by the microorganism will greater than the control group.Continuous ultrasound could cause quicker contabescence of some microbes thus to release more DNA.In order to further optimize the process operating parameters of ultrasonic combining with ABR wastewater treatment,it has been detected through experiment with different irradiation and irradiation sludge ratio after successful starting up of reactor that the removal rate can be up to 81.6% when the irradiation cycle is 16 h and the irradiation sludge ratio is 7% with a 6 percentage points improvement compared to that of control group.It has been detected through shock resistance and load experiment that compared to control group,the ultrasonography group has better organic load impact resistance performance.However,its hydraulic impact load resistance performance is weaker.By adopting 12 h nitrobenzene poison impact experiment,it has been approved that periodic ultrasonic irradiation can promote the microbes inside the reactor to produce more EPS,and stimulate it to produce more extracellular hydrolytic enzymes thus to make the reactor of ultrasound group has greater toxicant resistance ability.After running the test for one month at low temperature condition that the COD removal rate of ultrasound group is 8.63 percentage points higher than that of control group which indicates that ultrasound can better promote microbial activity.The low temperature will weaken catalytic function.Furthermore,ultrasound can make the conformation of enzyme become more reasonable.Anaerobic biological treatment of wastewater can be enhanced by stimulating the enzyme activity as well as accelerating the reaction.Eventually,To explore ultrasonic promoting mechanism,it studied the changes of anaerobic sludge characteristics during ultrasonic irradiation process.Through microscope and scanning electron microscope,it detected that ultrasonication can decrease the average grain diameter of sludge particulate,and will cause dispersive floc structure,overall size decreasing,relatively rough surface,invisible boundary,more bumps and dents on surface of the floc.However,due to the reduction between flocs,in most cases,polysaccharide cellophane tape glue materials can be detected on most of the floc surface.It's sedimentation performance will drop within 30 min.after ultrasonic treatment.However,with continuation of time,its sedimentation function will be higher than control group 2 h later.The Zeta electric potential on sludge surface will increase due to the ultrasonic treatment which will improve the adsorption capacity of anaerobic sludge.PCR-DGGE technology has been adopted to analyze anaerobic microbial flora structure.Direct ultrasonic irradiation will not change the dominant population composition of sludge.However,continuous periodic ultrasonic irradiation can make the microorganism flora which are sensitive to the reactor being knocked out and certain dominant bacterial community to concentrate together thus to change the structure of the whole microbial flora in the reactor,and affect its degradation rate to organic matters.