Side-stream Nitrogen Removal in Membrane Aerated Biofilm Reactor: NOB Suppression and Techno-economic Analysis

ZeeNAMMOX™ is a novel partial nitritation and anammox (PN/A) process on a membrane aerated biofilm reactor (MABR) platform that solves two limitations of existing side-stream treatment processes – complexity and oxygen transfer efficiency. The PN/A process is biologically efficient compared to conventional biological nitrification and denitrification (N&DN) processes (Ali and Okabe, 2015). However, current PN/A technologies still employ the fine or coarse bubble aeration that is energy intensive. In addition, issues associated with aeration control that relies on liquid-phase instruments have caused process disruptions (Lackner et al., 2014). By contrast, the ZeeNAMMOX™ process can save an additional 55% of energy due to its bubbleless aeration as compared with the existing PN/A technologies (Coutts et al., 2020a,b). ZeeNAMMOX™ takes advantages of the counter-diffusion benefits of MABR technology, forming a single biofilm that carries out the PN/A process with the coexistence of ammonia oxidation bacteria (AOB) and Anammox. The counter-diffusion of oxygen and other substrates in the biofilm provides a growing niche for AOB, preventing them from being inhibited or washed-out. A balanced AOB and Anammox population can be maintained by the precise control of oxygen supply in ZeeNAMMOX™. Since the process control can be done via sensors in the gas phase (Coutts et al., 2020a,b), ZeeNAMMOX™ maximizes the service time of sensors and simplifies the operation. The ZeeNAMMOX™ process holds great promise, however, two questions remain: is the process resilient, or more specifically, if and how can nitrite oxidizing bacteria (NOB) be suppressed; and is it cost-effective. In this paper, the operation and performance of 4 ZeeNAMMOX™ pilots that have employed novel control strategies for NOB suppression are presented with a discussion on the suppression mechanism. A preliminary life-cycle assessment (LCA) and techno-economic analysis (TEA) was then carried out to understand the business case for ZeeNAMMOX™ technology.