Study On Optimization Of Phenol-Containing Wastewater Treatment Process In The Semi-Coking

The phenolic compounds content is 2264 mg/L and the content of COD is 14265 mg/L in the phenol containing the semi – coking phenolic wastewater,which belongs to the high concentration phenol containing wastewater.It is characterized by complex components,high toxicity and difficult degradation.If biochemical treatment direct can lead to microbial poisoning,it will be a great practical significance to explore the efficient treatment process of the semi – coking phenolic wastewater for economic,environmental and social benefits.At present,domestic and international the treatment methods of the phenolic wastewater are physical method,chemical method and biological method.The practice has proved that any single method of removal phenol has its advantages and limitations.The chinese government strictly controls the discharge standard of volatile phenols in phenol containing wastewater that it is less than 0.5 mg/L.Generally,if we only take a single method to deal with the phenol of wastewater,we are difficult to reach standard of the national discharge.So we can take the advantages of several methods together which it is forming a new combination process.The new combination process is a new direction which the phenol of wastewater treatment technology in the development.Basing on the semi – coking phenolic wastewater is as the research object in this paper.At following,the semi – coking phenolic wastewater is referred to as the phenol of wastewater.On the basis of treating phenolic wastewater by resin adsorption and complexation extraction separately,we combine the advantages of complexation extraction and resin adsorption techniques which develope an adsorption – complexation extraction combination new process.This paper mainly includes the optimization of the conditions in the resin adsorption process,the optimization of the conditions in the complex extraction process,and the adsorption – complex extraction combined process for removing phenol and recovering phenols.In the static resin adsorption process,orthogonal test method is used to determine the optimal process conditions that affect the static adsorption of XAD – 2 macroporous resin: room temperature is 15 ?,pH is 7,XAD – 2 macroporous resin dry base quantity is 2.5 g,the phenol of wastewater is 100 mL and adsorption equilibrium time is 5.5 h.Under optimum process conditions,the adsorption ratio for volatile phenols is 99.35 % and adsorption ratio for COD is 62.38 %.From the kinetic model,it is determined that its adsorption behavior conforms to the pseudo – second – order kinetic model which is more suitable for characterization of the resin adsorption process.Adsorption rate is mainly controlled by the chemical adsorption.The orthogonal test method is used to determine the optimal process conditions of affecting the adsorbent in the static desorption experiment: the concentration of NaOH solution is 6 %,the concentration of ethanol solution is 50 % and the concentration of HCl solution is 6 %.Under the optimal adsorption and desorption process operating conditions,10 mL 12 % NaOH solution + 10 mL absolute ethanol are used to form basic ethanol– containing 6 % NaOH and 10 mL 6 % HCl solution to desorb the phenol – rich resin.After the phenol – rich resin is regenerated by static desorption,the concentration of volatile phenol in the effluent is 16.5 mg/L,the regeneration adsorption ratio for volatile phenol is 99.27 %.In the process of resin dynamic adsorption,the orthogonal test method is used to determine the optimal process conditions of affecting in the dynamic adsorption: XAD – 2 macroporous resin bed volume is 15 mL,flow rate is 3 BV/h,and the maximum one – way treatment capacity of phenol containing wastewater is 480 mL.Under the optimal process conditions,double column series dynamic adsorption is adopted which the adsorption ratio for volatile phenols is 99.93 % and the adsorption ratio for COD is 88.92 %.On the basis of static desorption,the desorption agent is basic ethanol – containing 6 % NaOH and 10 mL 6 % HCl solution,the amount of desorption agent is 2 times the volume of XAD – 2 resin bed,the desorption flow rate is 1 BV/h,desorption time 2 h,desorption temperature is 25 ?.The phenol – rich XAD – 2 resin adsorption column is desorbed after the double – column series adsorption.When the phenol – rich resin adsorption column is regenerated by dynamic desorption,the concentration of volatile phenol in the effluent is 1.6 mg/L and the regeneration adsorption ratio is 99.93 % and the COD regeneration adsorption ratio is 88.96 %.Under the optimal conditions of the dynamic adsorption – desorption process,the selected resin is continuously subjected to 6 cycles of regeneration stability experiments which the concentration of volatile phenols in the effluent is below 10 mg/L,the average adsorption ratio for volatile phenols is 99.58 % and the average adsorption ratio of COD is 84.60 %.It is indicated that XAD – 2 macroporous resin has stable regeneration performance.In the complex extraction process,tributyl phosphate(abbreviated as TBP)is used as the extractant,and kerosene is used as the diluent.The single factor control variable method is used to determine the optimal operating conditions that affect complex extraction: pH is 6,complexation extraction temperature is 25 ?,oil/water ratio is 1:3,the volume ratio of TBP and kerosene in complex extraction agent is 3:2,the rotation speed is 625 r/min and the first – level complex extraction is carried out.The extraction ratio of volatile phenol in the raffinate phase is 97.33 %,and the extraction ratio of COD is 78.50 %.The orthogonal test method is used to determine the optimal process conditions that affected the stripping process: reverse extraction agent NaOH concentration is 10 %,number of back extraction is 2,oil / alkali ratio(V/V)is 1:1 and the temperature is 35 ?.Under the optimized process conditions of back extraction,the organic phase of the first – stage extraction is subjected to two back extractions and the recovery ratio of volatile phenols can reach 96.23 %.Under the optimized conditions of complex extraction – back extraction process,the selected complex extractant is continuously subjected to 6 cycles of regeneration stability experiment.The average extraction ratio of volatile phenol in the raffinate phase is 86.54 % and the average extraction ratio of COD is 74.07 %.It's indicated that the complex extractant has regeneration stability.Adsorption – complex extraction combined process is a combination the advantages of resin adsorption technology and complex extraction technology.The phenol – containing wastewater which is difficult to meet the discharge standards are treated in stages.In order to reduce the complexity of the operation process,under the optimal process conditions,XAD – 2 macroporous resin adsorption method is used to perform single – column dynamic adsorption and the complex extraction process is used to perform first – level complex extraction.After the phenol – containing wastewater treated by the combined adsorption – complexation extraction process,the concentration of volatile phenolic substances is 0.33 mg/L and the corresponding removal ratio is 99.99 %.According to the effect of removing phenol,the high concentration phenol – containing wastewater is treated by the combined adsorption – complexation extraction process which has reached the national discharge standard.Under the optimized dephenolization process conditions,the desorption and back – extraction of the phenol – rich XAD – 2 macroporous resin adsorption column and the complex extraction organic phase are carried out.The recovery amount of volatile phenolic compounds is 1050.1 mg and the corresponding desorption the phenol ratio is 96.66 %.Therefore,the adsorption – complexation extraction combined process is used to remove phenol from wastewater containing phenol,which not only can reduce the concentration of volatile phenolic substances in wastewater containing phenol to the national emission standard,but also can recover volatile phenols resources.In order to make this experimental program to have practical application value,a pilot test should be carried out on the basis of the need.So that the combined adsorption – complexation extraction process can be further industrialized and bring higher economic and environmental benefits for society.