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Membrane-aerated biofilm reactors (MABRs) have emerged as a potential nitrogen removal technology for high-strength, nitrogen dominant waste streams (TOC:N 500mg/L). In particular, the unique properties of a MABR are well suited for extreme and/or isolated environments with carbon limited wastes such as a lunar habitation scenario. Among many other features, the ability of MABRs to degrade carbonaceous and nitrogenous pollutants concomitantly via simultaneous nitrification and denitrification (SND) in a single-stage vessel has posed this technology as a well-suited candidate for space-based water reuse applications. Relatively untouched by current MABR research, nitrogen dominant waste streams have been deemed outside the range for significant SND in a MABR without the supply of exogenous consumables; however, experimental research has not been conducted in order to confirm or disprove this hypothesis. The goal of this current work was to explore the performance limits of treating a space-based waste stream with the MABR technology using experimental studies and mathematical modeling efforts. The experimental studies entailed investigating the performance of a traditionally designed MABR and a modified MABR (mMABR). The mMABR combined oxygen permeable membranes in tandem with inert attachment media theoretically supporting nitrification on the former and denitrification on the latter. The traditionally designed MABR reported average carbon and total nitrogen (TN) removal rates as high as 0.33 g-C/m2-d and 0.14 g-N/m2-d, respectively, whereas the mMABR achieved mean carbon and TN removal rates reaching 0.26 g-C/m2-d and 0.22 g-N/m2-d, respectively. The most notable difference between the two reactors was the ability of the mMABR to support denitrification, which was attributed to the mMABRs combination of co- and counter-diffusion biofilms. The mathematical modeling study aimed to identify the inherent differences that could be propagated by the range of assumed nitrification and denitrification biochemical pathways for one-dimensional membrane-aerated biofilm models. The overarching conclusion reached as a result of this study was that mathematical simulation results vary based upon the assumed biopathway applied to the model. The results of this study were used to understand the underlying processes that occurred during the MABRs treatment of a space-based waste. |
