Evaluation of fenton-like oxidation coupled with struvite precipitation for the enhanced treatment of Cu-contaminated ammoniacal nitrogen-rich wastewater

Abstract

Discharging highly concentrated ammonia-containing wastewater directly to the environment causes significant environmental degradation. This work has enlightened the recovery of ammoniacal nitrogen from copper-containing Nitrogen-rich wastewater (Cu-NWW) through struvite precipitation followed by a Fenton-like copper oxidation process (CFO). Initially, Cu-NWW was treated through the CFO process by adding 10 mM of H₂O₂ (30 % w/v) and Nanoporous Activated Carbon (NAC) as a heterogeneous catalyst at an optimized reaction time of 120 min. CFO process exhibited the removal of Chemical Oxygen Demand (COD), 82 %; Biochemical Oxygen Demand (BOD₅), 73 %; and Total Organic Carbon (TOC), 78 % in Cu-NWW. It also noted that the elimination of COD and TOC by the CFO process increases the purity of struvite crystal. The presence of copper was removed before struvite precipitation by adding 10 % Na₂S solution. Further, the stoichiometric molar ratio of Mg²⁺, NH₄⁺, and PO₄³⁻ ions was optimized for struvite precipitation. The struvite precipitation was then carried out with and without removing Cu ions in Cu-NWW, and the reaction time, the addition of magnesium oxide (MgO), Spent phosphoric acid (SPA), and reaction pH were optimized. The second-order rate reaction follows the rate of the formation of struvite. The integrated CFO process and struvite precipitation achieved 92 % COD removal, 97 % ammoniacal nitrogen removal, and over 99 % Cu removal. This treatment approach is highly suitable for industries generating waste streams containing a combination of COD, ammoniacal nitrogen, and metal ions.