Study On Treatment Of Coking Wastewater By Vacuum Membrane Distillation

Coking wastewater is considered as a kind of waste water contain numbers of complex organic matter and high concentration ammonia nitrogen released from coking plant,the gas cooling and the refining process of chemical products.Due to the large emissions,strong toxicity and pungent odour,coking wastewater has become a prevalent research in sewage treatment industry.Vacuum membrane distillation?VMD?technique is regarded as an innovative membrane separation technique possessed the advantages of high efficiency of separation,covering small area,simplicity of operator and low cost of investment et al.Huge application potential is performed for this technique in treating dyeing wastewater,pharmaceutical wastewater and petrochemical wastewater et al.At present,there's still lack of systematic research using VMD treating coking wastewater,therefore,the VMD treatment of coking wastewater was studied in this paper comprehensively,and here is the main contents and results:?1?In regard to the simulated coking wastewater,the influence of process parameters?feed temperature,velocity,vacuum?and quality of wastewater?pH,NH3-N,organic matters?on the performance of VMD was studied.?1?The results indicated membrane flux and ammonia flux,removal,mass transfer coefficient and selectivity coefficient influenced greatly,flux velocity inconspicuously.In this research,the performance of VMD treatment was obviously affected by feed temperature and decompress vacuum,while feed velocity not significantly.In addition,increasing temperature,vacuum and velocity were beneficial to VMD treatment of coking wastewater,but the effect of velocity was not obvious.?2?The most suitable parameters for VMD treatment were 80?feed temperature,0.09 MPa vacuum and 350 L/h feed velocity.?3?The VMD treatment was not influenced by the quality of wastewater significantly,especially pH and the concentration of NH₃-N.In this research,with the increase of pH and NH₃-N,the flux,removal rate,mass transfer coefficient and selectivity coefficient of ammonia were improved,more favorable for denitrification,but water flex decreased.The denitrification performance and the quality of penetrant were declined with the increase of organic matters in wastewater.Therefore,in VMD treatment of actual coking wastewater,besides regulating pH value and concentration of NH₃-N,we need to decrease the concentration of organic matter as possible.?2?To investigate the effect of treating real coking waste-water using pretreatment or not with distillation vacuum membrane according to the technological conditions determined from chapter,the results showed that:?1?Pretreatment of wastewater is demonstrated as a powerful measure to enhance stability of operation and effect of treatment in the process of real coking wastewater treated by VMD;?2?Based on different pretreatment methods,the treatment of coking wastewater express diverse effects,and purification result of adsorption pretreatment is superior to that of coagulation pretreatment;?3?High treatment performance was revealed from homemade-Fe₂O₃-adsorbent,after pretreating through Fe₂O₃-adsorbent,the stability of continuous operation utilizing VMD treating real coking waste-water was improved up to 10 h from 4 h,and the removal rate of COD was enhanced overtop95%,the desalination rate is above 98%,the removal rates of turbidity and chromaticity almost approach to 100%,and the recovery rate of ammonia is up to94.5%;?4?the organic matter contained in real coking waste-water was comprised mainly by aromatic proteins,analogous fulvic acids and HULIS et al.The organic substance removed by pretreatment methods of coagulation and adsorption was principal HULIS,and the rust adsorption pretreatment method is more effective than that of coagulation method;the main organic compounds in permeation generated by VMD are aromatic proteins,which restrained the removal rate of COD in wastewater.?3?The characteristics and causes of membrane pollution in the treatment of coking wastewater by vacuum membrane distillation and the cleaning scheme of membrane fouling were studied.The results showed that:?1?The surface roughness of membrane was magnified,the structural uniformity,porosity of membrane and the hydrophobicity of membrane were all decreased significantly that bring about membrane fouling in the process of treating coking wastewater using VMD.?2?According to the analysis of the elements on the membrane surface,the membrane pollution in the VMD process of coking wastewater are caused by the organic matter and inorganic salts such as Ca and Mg deposited on the membrane surface,the membrane hole was blocked and the hydrophobicity of membrane was destroyed.?3?The stability and recoverability of membrane were affected by the method,period and time of membrane cleaning.The solution that combines acid and alkali was better than uses acid or alkali respectively,and decreasing the cleaning period and increasing the cleaning time appropriately were beneficial for the stability and recoverability of membrane.?4?The best cleaning solution for VMD treatment of coking wastewater was 0.5%NaOH+0.5%HCl,6-hour cleaning period and15-minute cleaning time.In this condition,the recover rate of membrane was 93.9%after cleaning.