Factors impacting electrocoagulation treatment of hydraulic fracturing fluids and removal of common fluid additives and scaling ions

This research presents 56 experiments on hydraulic fracturing flowback and produced waters to evaluate common factors affecting electrocoagulation (EC) removal of turbidity, chemical oxygen demand (COD), dissolved organic carbon (DOC) and final pH. Additionally, qualitative reductions in the common fluid additives polyethylene glycols (PEGs) and polypropylene glycols (PPGs), which can interfere with reuse in hydraulic fracturing, were evaluated by mass spectrometry for the first time. Design of experiments tested five EC process control factors: electrode material, current, initial pH, treatment time, and number of electrodes. Turbidity reductions were high (>90 %), and a maximum of 37.4 % of COD and 54.0 % of DOC was removed. Due to low variability, no factors were significant for turbidity reduction, while current, treatment time, and numbers of electrodes were significant factors for COD and DOC reduction. pH increased with iron electrodes and was neutralized with aluminum electrodes. Both PEGs and PPGs were removed, and PPGs were removed to a greater extent. Removal of these compounds increased as they became more hydrophobic as suggested by their logKow values. Some analysis was done on removal of common scaling ions (Ba, Ca, Mg, Sr) with removal possibly related to the pH of the water.