Research On Disruption Behavior Of Microbial Cells Within Urban Waste Activated Sludge Under Microsecond Pulsed Electric Field

With the development of urbanization and environmental awareness in China,the discharge and treatment of waste water is increasing rapidly.The production of urban waste activated sludge(WAS)also gets a dramatic growth as one of the most common by-product of sewage treatment,which seriously affects environment and people’s health.Nowadays,anaerobic digestion(AD)is widely used for sludge treatment.However,the efficiency of AD is limited due to that most of the organic matters are bounded in microbial cell membrane.It is therefore very important to achieve the disruption of microbial cells so as to enhance the efficiency of AD.In this work,microsecond pulsed electric field(μs-PEF)has been utilized to disrupt microbial cells by means of PEF induced electroporation.Research on disruption behavior of microbial cells within WAS under different conditions has been carried.The main conclusions are summarized as follows:1.A high voltage pulse generator of exponential decay waveform has been developed.The generator is designed on the base of resistor isolated Marx generator.With the trigger signal from Single-Chip microcomputer controlling IGBTs,the pulses which meet the test standards are obtained.The parameters of output are as follows: rise time τr =5μs,pulse width τw=45μs,repetition frequency fmax=100Hz,maximum magnitude Emax =0kV~65kV.2.A set of experimental apparatus based on the parallel plate electrode is designed.Measurement of Soluble Chemical Oxygen Demand(SCOD)and calculation of the intracellular organic release index K has been performed to understand the effect of the μs-PEF magnitude,the repetition frequency and the temperature on the disruption behavior of the microbial cells in the WAS.It has been found that K increases sharply with the increase of PEF magnitude and temperature.K increases with the tension of PEF processing time.K and energy efficiency η reduces with the increase of PEF repetition frequency.Experimental results showed that the PEF magnitude and the temperature have significant influence on the disruption performance.3.Corona discharge has been formed by applying DC or AC stress between multineedle and plate electrodes.So as to pretreatment the sludge sample prior to PEF treatment.The influence of DC polarity,magnitude and AC frequency on the treatment efficiency of μs-PEF microbial cell in excess sludge has been estimated by calculation of relative change in SCOD(ΔS%).When treated under DC corona,ΔS% increases under positive DC corona and decreases under negative DC corona as the DC voltage increases.With the increase of DC voltage,ΔS% firstly increases and then decreases for positive DC corona-PEF treatment sample while increases monotonously for negative DC corona-PEF treatment.With the AC corona-PEF treatment on sludge sample,the disruption behavior of microbial cells in WAS is enhanced with frequency of AC voltage.