Treatment Of Salicylic Acid Wastewater By Combined Process Of Bipolar Membrane Electrodialysis And Resin Adsorption

Salicylic acid（SA）is an important fine chemical raw material which is used in the preparation of drugs such as aspirin.The production of salicylic acid produces a stream of wastewater containing high concentrations of Na₂SO₄,phenol and SA,which is a kind of typical hypersaline phenolic organic wastewater.If it is discharged directly without effective treatment,it will not only cause serious pollution to the water environment,but also lead to the waste of recoverable resources.In this paper,a combined process of bipolar membrane electrodialysis（BMED）and resin adsorption was proposed to treat salicylic acid production wastewater,and the following studies were carried out:The effects of initial p H in the feed compartments,current density,flow rate and initial salt concentration on the treatment effect of BMED were investigated adorpting simulated wastewater.The migration mechanisms of inorganic ions as well as organic matter in the wastewater were investigated.The results showed that these factors affected the final effect by influencing the morphology of organic matter,ion migration and trans-membrane transport process.When using the BMED process to treat actual SA production wastewater,it was found that the optimal operating conditions were as follows:the original p H of the wastewater around 1.3 was choosen as the proper initial p H,the current density was 50 m A/cm²,the flow rate was 5.0 cm/s and the volume ratio of 1:1.Under these operating conditions,the concentrations of H₂SO₄and Na OH solutions obtained in the acid and base compartments were 0.56 mol/L and 0.78 mol/L respectively,and the desalination rate was approximately98%.The concentrations of phenol and SA in the feed compartments were 4023.9 mg/L and503.2 mg/L respectively.After the static experiments,the AH-1 and AH-0 resin were selected as the adsorbent for the dynamic adsorption experiments and p H=4 was used as the initial p H condition.In this paper,the BMED process effluent was treated by two-stage-sorption process through the resin column.The concentrations of phenol and SA in the secondary adsorption effluents were both below 0.1 mg/L and the quality of effluent was stable,COD was 53 mg/L,and the p H was about 6～7,meeting Class I of effluent standards in the Integrated Wastewater Discharge standard（GB8978-1996）.High purity phenol and SA could be obrained in dynamic desorption effluent,which possessed high recycling value.The combined process of BMED and resin adsorption allowed the conversion of almost all Na₂SO₄in SA production wastewater into acid and base as well as the recovery of high purity phenol and SA while meeting the discharge standard,realising the resource utilization of SA production wastewater.