Treatment Of Coal Washing And Petroleum Refinery Wastewater In Northern Shaanxi Region

As an important energy and chemical industry base in China,northern Shaanxi region is rich in energy resources but lacks water resources,which plays an essential role in energy and chemical production.However,the energy and chemical enterprises occupy the limited water resources to maintain production while discharge plenty of industrial wastewater,which means that if the industrial wastewater can not be treated and recycled in northern Shaanxi region,it will lead to serious ecological pollution and even bring about negative effect on the sustainable development of the energy and chemical industry base.In order to make the industrial wastewater treated and recycled in northern Shaanxi region,on the basis of the actuality of the energy and chemical industry base,coagulants and PAFC flocculants were prepared from fly ash to treat coal washing wastewater,vacuum evaporation and three-dimensional electrodes-electrical Fenton were used to treat petroleum refinery wastewater respectively in this study.The mechanism and the operating condition in the process of wastewater treatment were studied in hopes that the industrial wastewater in northern Shaanxi can be treated and recycled in the light of its own water quality and local condition.The concrete research contents are summarized as following:The solid waste,fly ash was leached by hydrochloric acid to convert into a kind of coagulant which can be used to treat coal washing wastewater,in the process of which,the effects of coagulant after calcined and Na2C03 activated on coal washing wastewater treatment were studied,the influences of the operating conditions on the leaching rate of A13+ in fly ash,including Na2CO3 dosages,HCl concentration,the leaching time and the leaching temperature were investigated,the optimal condition of preparing the coagulant and the wastewater treatment by coagulant were discussed,and the mechanism of coal washing wastewater treatment by the coagulant was also analyzed.The results showed that the pH,chemical oxygen demand(COD)and suspended solids(SS)of coal washing wastewater reached the wastewater discharge standard at dosages of 10 g L-1,initial pH of 9 by introducing CaO,which attribute to the reason that the fly ash based coagulant for coal washing wastewater treatment is a kind of multi-component coagulant that is rich in A13+ and Fe2+/Fe3+.Although this process reached the goal of"treat waste with waste",the argillation of the coal slimes was found in the process of treatment due to the coagulant added,which means that the coal slimes cannot be recycled,resulting in the waste of the coal slimes and preventing the application of this method from coal washing wastewater treatment.Basing on the result of the first part,the acid leaching filtrate of fly ash was titrated by NaOH solution to prepare PAFC flocculant for coal washing wastewater treatment in this part due to its richness in Al3+ and Fe3+.The effect of the PAFC flocculant prepared in different pH value,reaction temperature and reaction time on coal washing wastewater treatment was studied,the prepared PAFC flocculant was compared with the PAC flocculant used in the industry,and response surface methodology was employed to assess the optimal condition of preparing PAFC flocculant and the optimal dosages of the prepared PAFC flocculant cooperated with PAM for coal washing wastewater treatment.Residue of fly ash after acid leaching was also characterized.The result showed that the prepared PAFC flocculant is a kind of flocculant with polymer of aluminum,iron properties.The COD and SS of coal washing wastewater can reached the grade I of wastewater discharge standard,and the coal slimes can be recycled after dried as well when coal washing wastewater treated by the prepared PAFC flocculant cooperation with PAM.Furthermore,Residue of fly ash has a certain surface area and adsorption properties,which means that the prepared PAFC flocculant for coal washing wastewater treatment can not only save the agent cost in coal washing wastewater treatment,but also comprehensive utilization of resources.In the third part,vacuum evaporation(VE)was utilized for treatment of petroleum refinery wastewater that was characteristic of high temperature and salinity.The effect of various common promoters like kaolin,H2SO4,FeC13 and NaOH on the water quality of condensate were investigated to get the proper promoter,the water quality and environment estimation were tested before and after treatment.The influences of the operating conditions,such as vacuum degree,the initial pH and feeding process during the treatment were also studied.In addition,the processes by using tureen and falling film evaporator to treat petroleum refinery wastewater with high salinity was designed at last.The results showed that NaOH promoted VE displayed higher efficiency in treatment of refinery wastewater than other systems,and make the refinery wastewater achieve complete "zero emission",because it can change phenolic compounds and sulphides in petroleum refinery wastewater into nonvolatile salts.The treated water can be used to irrigate gardens,and the treatment process can be operated continuously at operation vacuum degree of-0.085 MPa,initial pH of 11.Furthermore,the process by using the tureen for treatment of the wastewater needs a large number of devices and occupies too much space,while the process by using the falling film evaporator has a better effect of heat transfer,shorter resident time,higher evaporation speed and smaller temperature differences.Thus,the falling film evaporator can be utilized as a proper vacuum evaporation process for treatment of high saline refinery wastewater.In the forth part,three-dimensional electrodes-electrical Fenton process was adopted to treat petroleum refinery wastewater,in which the role of iron particles packed and aeration in the electrochemical process was verified.The influences of the operating conditions,such as electrolyte type,electrolyte dosage,the initial pH,the electrolysis voltages and Fe particle dosage on wastewater treatment were studied,and response surface methodology was employed to assess the optimal operating condition.In addition,the quality of treated water and the energy consumption after treatment was also analyzed.The results showed that the iron particles packed and aeration in the electrochemical process had build the three-dimensional electrodes-electrical Fenton system,which makes the refinery wastewater treated after pH adjusted,iron particles packed and aeration have a good treatment effect.When the refinery wastewater was treated under the best operating condition,all of the water quality such as COD、NH3-N、conductivity reached the grade Ⅱ of wastewater discharge standard.Finally,this process have low energy consumption,indicating that three-dimensional electrodes-electrical Fenton process have reached the real standard of "energy saving and emission reduction",is an economical and effective technology to treat the refinery wastewater.