A pilot study on the removal of ammonia from aqueous solution using the integration of struvite synthesis and breakpoint chlorination

Abstract

Herein, a pilot study on the removal of ammonia from surface water using the integration of struvite precipitation and breakpoint chlorination is reported. A two staged pilot plant with a capacity of 1000 liters (1 m3) per run (LPR) was utilized, of which Stage 1 comprised struvite precipitation and Stage 2 comprised breakpoint chlorination. Optimum conditions (i.e., Stage 1) for struvite precipitation were 110 mg/L of Mg and P dosage (concentration), 150 rpm of mixing speed, 60 minutes of contact time, and lastly, 120 minutes of sedimentation, while optimum condition for the breakpoint chlorination (i.e., Stage 2) were 30 minutes of mixing and an 8:1 Cl2-NH4+ weight ratio. The synergistic effects of this hybrid system proved to be effective, with Stage 1 increasing the pH from 6.8 to 10.1, reducing Mn (≥97.0%) and Fe (≥99.6%) concentrations steeply, and concomitantly deactivated E coli and TPC to ≥ 99% and ≥91%, respectively, while ammonia was reduced from 5.4 mg/L to 2.7 mg/L-N (51.8 %). In Stage 2, i.e., breakpoint chlorination, ammonia was reduced from 2.7 mg/L to 0.02 mg/L-N whilst fully depleting residual microorganisms. Finally, the OPEX amounted to $ 0.31/m3; however, there is a potential for cost savings (≈53.2%) by replacing Kh2PO4 with waste phosphoric acid. Lastly, the results from this techno-economic evaluation study showed great potential compared to similar technologies, making this approach a game-changer towards the prudent management of elevated levels of ammonia amongst other problematic contaminants.

Keywords

• operational expenditure (opex) analysis
• hybrid approach
• struvite synthesis
• breakpoint chlorination
• ammonia removal
• calcium hypochlorite (hth)
• real surface water treatment