Combined Freezing-based Method Study On High-salt And High-organic Wastewater Treatment

Industry has always promoted the development of social production.However,with the increase of people’s material and cultural needs,industrialization is developing faster and faster,and the pollution caused by pollutant discharge of wastewater is becoming a rigorous test.In the face of increasingly complex industrial wastewater,especially the wastewater with high concentrations of salt and organic matters which is difficult to biodegrade,the treatment efficiency of traditional methods has been unable to meet the increasing economic and environmental needs.Advantages of the freezing method have attracted the interest of researchers for its application in wastewater treatment.In this thesis,the model wastewater with high concentrations of salt and organic matters is taken as research object.Three parts of experimental research were carried out based on the progressive freezing process of refrigerator.The first part is the experiment of freezing method(FM)for wastewater treatment.The effects of freezing time and heat transfer mode on the removal efficiencies of pollutants were studied.In the unidirectional freezing experiment,based on the freezing time,the comparison of the separation ability of solutes on single-component solution and mixing solution were studied.Then,multidirectional freezing experiments were conducted for mixing solution,and the variety of ice formation rate,the removal efficiencies of chemical oxygen demand(COD)and salt under different heat transfer modes were explored.The second part is the experiment of wastewater treatment applied by combined freezing,watering and centrifugal method(FWCM).In the work,the multi-directional freezing method was used to make ice rapidly,and the original wastewater was used as the solution injected into the ice fines.The effects of the key watering parameters,including the mass proportion and temperature on removal efficiencies of salt and COD and on ice yield rate were investigated.The third part is the experiment of wastewater treatment applied by combined freezing,soaking and centrifugal method(FSCM).In the work,the multi-directional freezing method was used to make ice rapidly,and the original wastewater was used as the soaking liquid.The influences of soaking-related parameters,such as the soaking medium temperature,the duration and ice to soaking medium ratio(ice to soaking medium ratio is the ratio of initial mass of ice samples to soaking solution’s mass)on removal efficiencies of COD and salt as well as on ice yield rate were studied.The main conclusions of the experiment are as follows:1)For FM experimental research,with the increase of freezing time,the ice formation rate increased and the pollutant removal efficiency showed a change trend of first increasing and then decreasing.The ice formation rate in unidirectional freezing is much lower than that in multidirectional freezing,and the maximum salt and COD removal efficiencies are higher than that in multidirectional freezing.2)Under the same ice formation rate,the salt removal efficiency of Na Cl solution and the COD removal efficiency of glucose solution are only slightly higher than those of the mixed solution.Therefore,freezing method can be used to remove salt and organic matter from wastewater at the same time.3)For FWCM experimental research,the results show that it is an effective way to improve the removal efficiencies of salt and organic matters through increasing the mass ratio of added wastewater.When the temperature of wastewater fluctuates due to the seasonal change,the higher the water temperature is,the better the purification effect of ice sample achieves.Therefore,in order to maintain better removal efficiencies of salt and COD,the mass ratio of the added solution should be increased when the water temperature is low.4)After FSCM treatment,the pollutant removal efficiencies of all samples are more than 90%,and the highest is about 96%.The removal rates of salt and COD increase with the increase of soaking time,soaking liquid temperature and the mass ratio of ice to soaking liquid.But the ice yield rate reduces due to more ice crystals melting in the soaking liquid.5)Compared with the FM treatment,the combined freezing-based method(FCM,FWCM and FSCM)used in the paper is facilitate further separate the ice crystals from wastewater.Since the wastewater with high concentrations of salt and organic matters generated by different industries varies greatly,the operating parameters and treatment effects of the composite methods applied to the actual wastewater need to be further studied.