Advanced treatment of hydraulic fracturing flowback water using a novel combined process

Abstract

A novel process was proposed for treating heavily polluted hydraulic fracturing flowback water from oil/gas production with an initial chemical oxygen demand (COD) of 8850 mg/L. The process was comprised of gel breaking, cavitation-impinging stream/iron-carbon micro-electrolysis (CIS/ICME) and electro-Fenton. The viscosity of the wastewater was reduced from 6.20 to 1.09 mPa•s after 90 min of gel breaking treatment using sodium hypochlorite at a dosage of 3.0 g/L. The CIS technology solved the passivation and hardening problems of traditional ICME technology, enhancing COD abatement by 48.2% points and increasing iron utilization from 36.8% to 82.4%. The results show that, under the optimum conditions, the effluent COD was reduced to around 170 mg/L with a removal efficiency of 98.1%, and the reduction ratios of oil, color, corrosion rate and suspended solids reached 100%, 95.2%, 94.0% and 97.7%, respectively. The quality of final effluent could meet the national discharge standard of China. The CIS/ICME process removed a considerable proportion of COD and oil, while the electro-Fenton unit played an important role in post-polish of final effluent. This study shows that the hybrid system has the potential to be applied for the advanced treatment of high-strength oilfield wastewater.