Photo-anammox by vacuum ultraviolet tandem chlorine.

Excessive ammonia (NH ₄ ⁺ ) discharge can lead to algal blooms and disrupt water sustainability, so its control is imperative. Although microbiology-triggered anammox process is promising, its application is limited due to time-consuming cultivation of specific microorganisms and need for skilled operation. To bypass these barriers, this study proposed and verified a photo-induced anammox technology that removes NH ₄ ⁺ and total nitrogen (TN) from water by ultraviolet (UV)/vacuum UV (VUV)/chlorine under anoxic conditions. Under the Cl/N mass ratio of 5:1, the anoxic VUV/UV/chlorine process achieved 66.8% removal of 10 mg-N/L NH ₄ ⁺ within 10 min along with 57.8% reduction in TN. Besides the evidence from TN loss, this study confirmed nitrogen gas (N ₂ ) as the primary degradation product at low dissolved oxygen (DO) concentration of 2.0 mg/L. The selective conversion of NH ₄ ⁺ into N ₂ was mainly attributed to reactive nitrogen species (RNS, 42.5%) and reactive chlorine species (RCS, 57.5%). The TN removal efficiency was insensitive to certain variations of pH (7.0-9.0), NH ₄ ⁺ concentration (1-30 mg-N/L), chloride (50-125 mg/L), and sulfate (25-100 mg/L), but sensitive to DO and bicarbonate (25-100 mg/L). Given its robustness and high efficiency, the anoxic VUV/UV/chlorine technology may serve as a potentially promising alternative for NH ₄ ⁺ and TN alleviation in wastewater.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
(Copyright © 2023 Elsevier B.V. All rights reserved.)