Research On The Pretreatment Of Pharmaceutical Wastewater By Iron-carbon Micro-electrolysis-Fenton Combined Process

The discharge of wastewater not only results in a waste of valuable resources, but also causes serious environmental pollution if the wastewater is sent into rivers. Wastewater of resveratrol production is a pharmaceutical wastewater, which has characteristics with high concentration, high bio-toxic and complexity of components. Generally, it should be pretreated before the biological treatment. The key points of pretreatment which directly affect the effect of biological treatment are how to reduce the concentration of organics, especially the refractory organics, remove or reduce toxicity, and change the water qualities. In order to improve the biodegradability of the wastewater, change the property of pollutants in wastewater, so as to make the following treatment much easier, iron-carbon micro-electrolysis followed by Fenton oxidation method was used in the pretreatment research in this paper. Firstly, the process parameters and main factors were obtained through the pretreatment experiments of the wastewater. Then, based on the research of the combined process, the optimum experimental conditions of the combined process were determined. Finally, the pretreatment cost was obtained through the price calculation of the basic processes.Based on the basic principles of iron-carbon micro-electrolysis, iron scrap and activated carbon powder were used as materials of micro-electrolysis to pretreat the wastewater of resveratrol production. Orthogonal and single-factor experiment methods were used to get the key factors affecting the process, the factors, such as electrolysis time, the iron-carbon dosage, pH, iron-carbon ratio and so on, which affect COD removal rate of the wastewater were discussed. The results showed that under the conditions of pH 2.5, electrolysis time was 3 hours, iron-carbon ratio (volume ratio) was 2:3, iron-carbon dosage was 1300g/L, COD removal rate of the wastewater reached 83.8%. Orthogonal analysis results showed that the order of various main factors affecting the effect of the iron-carbon electrolysis was electrolysis time > iron-carbon dosage> pH> iron-carbon ratio.In this study, 30% hydrogen peroxide and ferrous sulfate solution were selected as the materials of Fenton reagent, through single factor and orthogonal experiments, the main factors of treatment of resveratrol wastewater by Fenton reagent were studied and the optimum conditions were obtained, The main factors included pH, oxidation time, Fe²⁺ / H₂O₂ molar ratio, H₂O₂ dosage and so on. The results showed that pH3.5, oxidation time was 40 minutes, molar ratio of Fe²⁺ and H₂O₂ was 2:45, oxidant dosage (30% H₂O₂) was 27mL/L were determined as the optimum conditions of the Fenton oxidation process, under these conditions, COD removal rate reached 52%. pH as the most important factor has been determined by orthogonal experiments,COD removal rate and pH changes showed a significant linear relationship by fitting, which had direct relationship with the fixed speed steps of H₂O₂ decomposition to produce activity .OH. The order of various main factors affecting the effect of the Fenton oxidation process was pH> Fe²⁺ / H₂O₂ molar ratio > H₂O₂ dosage.Through preliminary studies, we could see that COD of the resveratrol production wastewater still stayed high after the iron-carbon micro-electrolysis treatment, in order to further reduce the COD value of the wastewater, reduce the load of equipments in subsequent biological treatment, and accelerate the degradation of organic matter, in this study, iron-carbon micro-electrolysis treatment followed by Fenton oxidation treatment was used to enhance the treatment result of the wastewater. The results showed that, by adjusting the original waste water's pH to 2.5, adding iron-carbon 1300g/L with the volume ratio 2:3, and after electrolysis for 3 hours, adjusting water's pH to 3.5, then adding 8mL/L H₂O₂ as the oxidant, while adding additional 20% Fe²⁺ solution about 0.74 mL/L as catalyst, at last, after oxidation for 40 minutes, adjusting water's pH to 8.5 ⁹, then COD removal rate reached 96% . After the pretreatment process, the water became clarification, COD reduced to about 1200mg/L, the odor was basically removed and no suspended particles were observed, achieving the requirement of biological treatment.