Application Of Membrane Distillation In Coking Wastewater Treatment

Membrane Distillation(MD)process refers to the physical separation of a mixture across a hydrophobic microporous membrane by means of a thermal driven process,it is an effective method for the separation of volatile substances such as ammonia nitrogen and phenol in organic wastewater.The vacuum membrane distillation method was used to treat high concentration wastewater in steam ammonia section and its feasibility was discussed in this paper.There were researched on the effects of different treatment parameters on the removal of ammonia nitrogen and organic matter in waste water and analyzed the mechanism of heat and mass transfer in vacuum distillation process.On the basis of this,those were studied the membrane fouling of membrane module and the scheme of membrane cleaning,conclusion as below:(1)Study on the influence of hollow fiber membrane vacuum distillation unit on different processing parameters,the results showed that with the increase of temperature,vacuum,pH and flow rate,the flux of ammonia increased,the water flux increased and the mass transfer coefficient of ammonia increased.The effect of temperature on ammonia flux and water flux is the most obvious,Ammonia nitrogen flux up to 2.67g/m~2·h,Water flux up to 1.4kg/m~2·h.PH increased from 7.4 to 11.3ammonia flux increased by 35%,pH has a great influence on the ammonia flux,the impact on the water flux is not obvious.When the vacuum degree is 0.044MPa,the ammonia flux accounts for the largest proportion of total membrane flux,the proper degree of vacuum is conducive to the separation of ammonia nitrogen and water in the distillate.Therefore,the optimal operating parameters are:P=0.044MPa,flow rate V=0.73m/s,solution pH=11.3,temperature T=75.4?,under such operating conditions for 4 hours,ammonia nitrogen in the coking wastewater can be removed by 88.3%.(2)Concentration polarization coefficient CPC is mainly affected by the flow rate of raw material liquid,when the flow rate of 0.073m/s CPC=1.001,the concentration polarization phenomenon is weakened.TPC decreases with increasing temperature and pH,and the heat utilization efficiency decreases.However,the small molecules containing hydroxyl groups in the wastewater and the aromatic compounds containing carboxyl groups affect the saturated vapor pressure of the solution and the formation of hydrogen bonds with the ammonia nitrogen molecules,thus affecting the ammonia mass transfer process.(3)Through the discussion of cleaning program,the joint cleaning scheme with0.1mol/L HCl and 0.1mol/L NaOH solution and gas blowing shell was finally determined.