Study On The Pre-Treatment Of High Concentration Pharmaceutical Wastewater By Coagulation-Fenton Process

High concentration pharmaceutical wastewater is one kind of refractory industry wastewater due to complicated components, high quantity organic compounds, deep color and low biodegradability. Conventional biological processes are not effective for it, so unable to meet the discharge standard. Thus, for the subsequential biological process, it is necessary to improve the biodegradability and to reduce the organic load of the pharmaceutical wastewater via the pre-treatment. The combined coagulation-Fenton oxidation process was adopted for the pre-treatment of high concentration pharmaceutical wastewater which was originated from a workshop of Pharmaceutical General Factory of Harbin (COD 14700¹7600mg/L; BOD5/COD(B/C) ratio 0.25⁰.26). The influencing factors of each unit were investigated.The coagulation effects of six kinds of coagulant were compared. The results indicated that Polyferric Sulfate (PFS) was the best compared to the others, so it was chosen as the coagulant for the pharmaceutical wastewater. The effect of PFS dosage, initial pH, agitation time and precipitation time in coagulation were investigated. The optimal operation parameters of coagulation were determined as follows: PFS dosage of 200mg/L, initial pH of 4, high speed agitation of 300 r/min with 1min, low speed agitation of 50r/min with 12min and precipitation time of 60min. After coagulation, 62.2% COD and 88.2% SS removal were achieved, and the organic load was evidently decreased, but B/C ratio only increased from 0.25 to 0.28.To further improve the biodegradability and reduce the organic load of pharmaceutical wastewater, Fenton oxidation process was selected for the sequencing treatment of the effluent of coagulation with consideration of pH of the effluent was 3.5⁴ and Fe²⁺/Fe³⁺ presented. The effects of the effluent of coagulation treatment with Fe³⁺/Fe²⁺/H₂O₂/UV/C2O42-, Fe³⁺/Fe²⁺/H₂O₂/UV and Fe³⁺/Fe²⁺/H₂O₂ processes were compared. The results showed that COD removal efficiency followed the decreasing order: Fe³⁺/Fe²⁺/H₂O₂/UV/C2O42-> Fe³⁺/Fe²⁺/H₂O₂/UV>Fe³⁺/Fe²⁺/H₂O₂. Fe³⁺/Fe²⁺/H₂O₂ process was selected at last because the COD removal efficiency of Fe³⁺/Fe²⁺/H₂O₂ process was only about 10% lower than that of Fe³⁺/Fe²⁺/H₂O₂/UV/C2O42- process, moreover, the cost of Fe³⁺/Fe²⁺/H₂O₂ process was lower and the process had the most application in reality.Optimum conditions of Fe³⁺/Fe²⁺/H₂O₂ process for treating the effluent of coagulation were determined as: adjusting initial pH of wastewater about 3, controlling initial Fe²⁺ concentration of 1200mg/L, adding half the stoichiometric calculated quantities(Qth) of H₂O₂, using air as carrier gas, reacting for 1h, pH was then adjusted to 7⁷.5, in which Fe²⁺ and H₂O₂ were added every 20 minutes during the first hour of reaction. Under these conditions, 69.2% COD removal was obtained, and B/C ratio increased to 0.79. Continuous running was also evaluated. COD removal efficiency was 54.8%⁵7.9% and B/C ratio was about 0.7 when hydraulic rentention time(HRT) was 3h. The combined coagulation-Fe³⁺/Fe²⁺/H₂O₂ process was effective for pre-treatment of high concentration pharmaceutical wastewater. The total COD removal efficiency was more than 80.0%, and B/C ratio improved from 0.25 to over 0.7. Therefore the combined process was benefit for the subsequential biological process, and had the promising application in the field of high concentration pharmaceutical wastewater pre-treatment.