Comparative Analysis of Boron Removal by Electrocoagulation in Synthetic and Local Real Produced Waters

Abstract

The presence of boron in oil and gas wastewater (produced waters) is a potential challenge for reuse of these waters for irrigation and agricultural uses. Boron is an essential micronutrient, but also toxic to plants at relatively low concentrations. It is also typically present as neutrally charged boric acid (H3BO3) in solution which is difficult to remove by conventional treatment technologies. In previous studies, electrocoagulation using an aluminum anode effectively removed boron from synthetic produced water solutions. Boron removal proceeded primarily through borate (B(OH)4-) ion interactions with Al(OH)3, with optimal results at pH 8. The present study extends this work to examine the impacts of real produced water composition (including dissolved organic matter and high divalent cation concentrations) on boron removal by electrocoagulation and treated water quality. Similar levels of boron removal were achieved in produced water samples from Douglas County and Reno County, Kansas. Periodically adjusting the pH of these waters was found to be a key factor in significant removal of boron. Consistent with previous studies using synthetic solutions, both increased boron removal and a faster rate of removal were observed in real produced waters with increased current loading. The presence of high concentrations of Ca and Mg in the produced water resulted in low bulk pH values throughout the process and greater formation of solid products. However, boron removal did not decrease with this lower bulk pH, as it had in the synthetic solution. This suggests there may be sorption interactions with Mg and Ca solids forming due to localized high pH conditions near the carbon electrode. The presence of organic matter from different sources (humic matter, phenol, and oilfield DOM) had minimal impact on boron removal. The removal of DOC from produced waters during the electrocoagulation process was also minimal. The use of iron as an alternative sacrificial electrode produced poor boron removal in comparison to aluminum. Further work should assess the impact of produced water suspended solids and the integration of electrocoagulation into an integrated treatment process for produced water conditioning and desalination.