Combined treatment of organic material in oilfield fracturing wastewater by coagulation and UV/H2O2/ferrioxalate complexes process

Organic material is considered to be a main component of oilfield fracturing wastewater (OFW). This work is intended to optimize the experimental conditions for the maximum oxidative degradation of organic material by coagulation and the UV/H2O2/ferrioxalate complexes process. Optimal reaction conditions are proposed based on the chemical oxygen demand (COD) removal efficiency. The overall removal efficiency of COD reached 83.8% when the dilution ratio of raw wastewater was 1:2, the pH was 4 and the FeCl3 loading was 1,000 mg/L in the coagulation process; the dosage of H2O2 (30%, v/v) was 0.6% (v/v) and added in three steps, the n(H2O2)/n(Fe2+) was 2: 1, n(Fe2+)/ n(C2O42-) was 3:1 and the pH was 4 in the UV/H2O2/ferrioxalate complexes process; the pH was adjusted to 8.5-9 with NaOH and then 2 mg/L of cationic polyacrylamide (CPAM) was added in the neutralization and flocculation process. The decrease in COD during the coagulation process reduced the required H2O2 dosage and improve efficiency in the subsequent UV/H2O2/ferrioxalate complexes process. Furthermore, there was a significant increase of 13.4% in the COD removal efficiency with the introduction of oxalate compared with UV/Fenton. Experimental results show that the coagulation and UV/H2O2/ferrioxalate complexes process could efficiently remove the organic material dissolved in OFW. An optimal combination of these parameters produced treated wastewater that met the GB8978-1996' Integrated Wastewater Discharge Standard' level III emission standard.