Abstract

NASA has been developing and testing a water recovery system for over two decades to minimize the amount of water required for long duration human space missions. A key system component is the total organic carbon analyzer (TOCA) that determines if the recovered water is below the toxicology-defined health limit of 5 mg/L TOC and is safe to drink. The TOCA is composed of a liquid phase loop and a gas phase loop. The TOCA employs an oxidizer to convert the organics in the liquid phase to carbon dioxide (CO₂) and a liquid–gas separator to isolate the CO₂ for measurement in the gas phase by infrared spectroscopy. In an effort to reduce the consumables, mass, volume, and power of the system, we investigated the ability of surface-enhanced Raman spectroscopy (SERS), and Raman spectroscopy to measure 5 mg/L carbon in water. The SERS measurement employed silver colloids to increase sensitivity, while the Raman measurements used multiple mirrors to increase sensitivity. Here, we present SERS measurements of carbonate (CO₃=) at 3 mg/L carbon and Raman measurements of CO₂ at 9 mg/L carbon in the effluent water of a new oxidizer being developed for a future TOCA. Both SERS and Raman techniques can determine TOC in the liquid phase, eliminating the need for the gas phase loop and associated supplies and replacement components, which could effectively decrease the size and weight of the current TOCA by as much as 50%.

© 2022 The Author(s)

Highly sensitive Raman system for dissolved gas analysis in water

Dewang Yang, Jinjia Guo, Qingsheng Liu, Zhao Luo, Jingwen Yan, and Ronger Zheng
Appl. Opt. 55(27) 7744-7748 (2016)

Dissolved organic matter in bovine slaughterhouse wastewater using fluorescence spectroscopy associated with CP/PARAFAC and PCA methods

Murillo Cruz Matos, Amanda Maria Tadini, Fernando Rodrigues da Conceição, Amilcar Machulek Junior, Carlos Renato Menegatti, Stéphane Mounier, Anderson Rodrigues Lima Caires, and Gustavo Nicolodelli
Appl. Opt. 61(22) 6590-6598 (2022)

Quantitative measurements of CO₂ and CH₄using a multipass Raman capillary cell

William F. Pearman, J. Chance Carter, S. Michael Angel, and James W-J. Chan
Appl. Opt. 47(25) 4627-4632 (2008)

Reagent- and separation-free measurements of urine creatinine concentration using stamping surface enhanced Raman scattering (S-SERS)

Ming Li, Yong Du, Fusheng Zhao, Jianbo Zeng, Chandra Mohan, and Wei-Chuan Shih
Biomed. Opt. Express 6(3) 849-858 (2015)

Spectrophone measurements of isotopes of water vapor and nitric oxide and of phosgene at selected wavelengths in the CO and CO₂ laser region

Walter Schnell and Gaston Fischer
Opt. Lett. 2(3) 67-69 (1978)