Study On The Inactivation Of Microbe In Ballast Water By High Gradient Magnetic Separation–UV Combined Process

In order to solve the problem that ballast water and sediments bring to the marine environment,the independent designed UV equipment and high gradient magnetic separation-UV composite device were used in ballast water treatment.Meanwhile,S.aureus ATCC 25923 and E.coli ATCC 25922 was used as reference bacteria.The influence factors of HGMS process were conducted in this work,the removal rates of turbidity,particle and microorganisms were selected as detection indexes as well.The results showed that the removal rate of turbidity,particle and microorganisms increased with magnetic field strength in HGMS process,and the best results were chived when the magnetic field intensity was 10.3mT.HGMS process could remove microorganisms from ballast water,and the highest removal rate of S.aureus and E.coli were 0.928 and 0.832,respectively.The turbidity of effluent with PAC coagulant dosage increases decreases first and then increases;the optimal coagulant dosage is 100mg/L.And treatment effects of high gradient magnetic separation device were reaching the standard when the initial turbidities were from10NTU to 200NTU.It proves the mechanization of HGMS:weak magnetic particles and strong magnetic particles combine and form microbial floc formation in the promotion of flocculant,and then those strong magnetic particles drive those weak magnetic particles attached to the surface of magnetic medium.In this work,the inactivate kinetics of bacteria by ultraviolet radiation was studied.Influences of growth phases,UV dose and irradiation time were also conducted by Static UV irradiation device.Experiment results show that Biphasic model was better fit for ultraviolet disinfection under the circumstance of this experiment than Chick-Watson,Collins-Selleck and Hom models,with high R² and RMSE under 0.5.The sensitivity of microorganisms under ultraviolet radiation was in the order:in exponential phase>in stationary phase>in lag phase.The critical dosage of E.coli treated by UV were 50mJ/cm²,200mJ/cm² and 160mJ/cm² in exponential phase,stationary phase and lag phase.Besides,irradiation time have stronger influence than UV dose in UV disinfection.In regression analysis,the irradiation time F values of S.aureus and E.coli were 161.81 and423.04,which were greater than the UV intensity F value 94.36 and 212.77.It proves that the initial state of bacteria can influence the UV inactivation effect.And in the same the energy consumption,lower UV intensity and longer irradiation time could improve processing efficiency in practical application.For expound the inactivation mechanization of HGMS-UV composite method,the change caused by different treament method in removal efficiency,bacterial surface morphology,intracellular enzyme activity,membrane permeability and DNA were compared.The microorganism content in the effluent of combined method is reduced by 30%⁴0%,while the K⁺leakage rate increased by 47.9%than single UV treatment.And when the residence time was larger than 10min,the SOD enzyme treated by combined method increased 30.7%⁶6.7%than by the other two methods.Those results show that HGMS could enhance the katogene of UV on bacterial surface morphology,intracellular enzyme activity and membrane permeability.The results revealed that DNA damage caused by UV disinfection was an important reason for the microorganism inactivation and as the UV dose increased,there was greater damage caused in DNA.But there was no significant change in DNA when microorganisms were treated by HGMS.It also revealed that HGMS and UV with different mechanisms of microbial enzymes.