Oil and gas production in the United States generates more than 20 billion barrels (3.2 trillion liters) of wastewater (produced water or PW). The environmental impacts of PW disposal, which has been linked to increased seismic activity, has led to a renewed interest in developing cost-effective methods for treatment and reuse of PW. Agriculture could be a major avenue for reusing PW. However, boron is often present in these waters at concentrations toxic to plants, limiting reuse opportunities.<br/>Previous studies have shown that electrocoagulation (EC) using an aluminum anode can effectively remove boron from synthetic produced waters. EC provides several advantages for PW treatment, including increased effectiveness at high salinity and the potential to simultaneously remove other constituents (oil, TSS). Boron removal through EC is achieved by adsorption and/or incorporation to aluminum oxide precipitates generated in-situ, with optimal results at pH 8. However, studies in real produced waters have shown reduced boron removal and differences in pH trends during EC.<br/>In this study, we present results of studies linking boron removal in produced waters to changes in produced water composition, specifically the concentrations of divalent cations. EC experiments were carried out using synthetic solutions with varying levels of four different divalent cations (Ca, Mg, Ba, Sr) often found in produced waters, both alone and in combination. The composition of both the produced waters and the settled flocs were examined following EC. Presence of elevated levels of magnesium, depresses solution pH compared to other cations while presence of cations also play a role in the consistency of floc produced. These experimental results are being used to develop a general mechanism for boron removal as a function of PW composition, and to generate an economic model for EC pre-treatment that will address the impact of produced water composition on treatment cost and effectiveness.

Impacts of divalent cations on boron removal through electrocoagulation

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