Boron (B) is a vital micronutrient for plants, but also toxic at high concentrations depending on plant species. Boron at high concentrations commonly exists in oil and gas produced water, preventing its reuse as irrigation water without proper treatment. Under typical conditions, aqueous B is present as boric acid (H<sub>3</sub>BO<sub>3</sub>), which is neutrally charged, and thus, B can be particularly challenging to remove. Coagulation is a traditional method for water treatment where a coagulant, in this case an aluminum or iron salt, is added to contaminated water to allow charged particles to clump together and settle out, which has the potential to adsorb and remove B from water. The goal of this research was to test B removal using electrocoagulation (EC), and to compare it against B removal by chemical coagulation (CC). An aluminum electrode and powdered aluminum sulfate were used for Al floc generation in EC and CC, respectively. For both methods, B removal increased with increased Al concentration, but high EC current intensity limited B removal. The critical current intensity is being investigated under varying conditions. EC removed B better than CC when they produced the same Al floc concentration in the solution. It was found that high B removal (&gt; 60%) requires a large aluminum floc concentration (&gt; 3 g/L as Al) at a pH of 8 for CC method, but an Al floc concentration of only 1 g/L produced the same B removal using EC. The possible reason is the size of Al floc generated by EC is much smaller than that generated by CC method, so that EC floc has a higher surface area for B. For both methods, boron removal is best at pH 8, corresponding to a lightly positive zeta potential for aluminum hydroxide and a small but significant fraction of negatively charged B species. At higher pH the zeta potential becomes negative, and at lower pH the fraction of negatively charged B species becomes increasingly miniscule. It was also found that total dissolved solids (TDS) in the produced water tend to reduce boron removal by CC method at high Al concentrations. However, high TDS improves EC performance because high TDS increases the critical current intensity.

Boron removal from water by electrocoagulation, and comparison with chemical coagulation

2019 Spring National Meeting

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