Ammonium Removal from Alkaline Groundwater Using A Dropping Nitrification Unit with Sponge or Biofringe Material

Abstract

Ammonium (NH₄⁺) contamination makes groundwater undrinkable. The dropping nitrification unit, a simple and low-cost biological unit, has been found to be effective for NH₄⁺-removal from contaminated groundwater at a near-neutral pH. However, the pH of groundwater varies widely and is highly alkaline (pH 8.7−10) in some areas of the world, which could negatively affect the biological nitrification process. The objectives of this study were to investigate the NH₄⁺-removal from alkaline groundwater using dropping nitrification units with sponge or biofringe material, compare their removal efficiencies, and characterize the effect of alkaline groundwater on the growth and activity of nitrifying bacteria. Synthetic alkaline groundwater (50 mg-NH₄⁺-N L⁻¹; pH 9.4 ± 0.1) was dropped from the top of 1-m long hanging units at 3 mL min⁻¹ for 56 days. The NH₄⁺-removal efficiency of sponge units (> 88%) was significantly higher than that of biofringe units (56−89%). The abundance of amoA gene of ammonia-oxidizing bacteria increased significantly over 56 days and was significantly higher in sponge units than in biofringe units, resulting in higher NH₄⁺-removal in sponge units than that in biofringe units. This study demonstrated that dropping nitrification units can be used effectively for NH₄⁺-removal from groundwater having a neutral to alkaline pH.