An Alternative Approach

The elemental composition of food consumed by astronauts is well defined. The major elements carbon, hydrogen, oxygen, nitrogen and sulfur are taken up in large amounts and these are often associated with the organic fraction (carbohydrates, proteins, fats etc) of human tissue. On the other hand, a number of the elements are located in the extracellular fluids and can be accounted for in the liquid and solid waste fraction of humans. These elements fall into three major categories cationic macroelements (e.g. Ca, K, Na, Mg and Si), anionic macroelements (e.g. P, S and CI and1 7 essential microelements, (e.g. Fe, Mn, Cr, Co, Cu, Zn, Se and Sr). When provided in the recommended concentrations to an adult healthy human, these elements should not normally accumulate in humans and will eventually be excreted in the different human wastes. Knowledge of the partitioning of these elements between the different human waste fractions is important in understanding (a) developing waste separation technologies, (b) decisionmaking on how these elements can be recovered for reuse in space habitats, and (c) to developing the processors for waste management. Though considerable literature exists on these elements, there is a lack of understanding and often conflicting data. Two major reasons for these problems include the lack of controlled experimental protocols and the inherently large variations between human subjects (Parker and Gallagher, 1988) We have used the existing knowledge of human nutrition and waste from the available literature and NASA documentation to build towards a consensus to typify and chemically characterize the various human wastes. It is our belief, that this could be a building block towards integrating a human life support and waste processing in a closed system. INTRODUCTION In a healthy adult, one would expect the intake of elements to be equal to the output in the form of human wastes (feces, urine, respiration, sweat, semen and menstrual fluid). Schroeder (1 973) reports “The body has marvelously exact mechanisms for maintaining homeostasis of inorganic elements. Unfortunately it has relatively poor mechanisms for maintaining the organic elemental content of the carbon, hydrogen and oxygen which is built up and deposited as fat”. There are wellestablished isports that have defined calcium and phosphate homeostasis, based on the understanding of these processes [3, 111. Wastes in healthy humans are well characterized by human physiological processes such as defined absorption rates of elements at the intestinal level, defined elemental transfer and mobilization at the kidney and sweat functions. Despite this assumption, the authors are not aware of reports to demonstrate this partitioning empirically. An excellent study of input/output mass metabolic rates (MMR) was presented in the form of a computer simulation model to predict mass of urine and feces produced in a closed system[4]. The paper demonstrated that both feces and urine production were functions of Energy expenditure rate (EER) which in turn was a function of the inputloutput MMR. This paper made an assumption that the solid feces mass flow rate is some production ratio (dfs) of the dry food input and liquid feces mass flow rate as being dependent on the total water input. Using the dry food input and liquid input, they were able to predict both solid and liquid fecal rates at different EER’s. They carried out similar studies to estimate liquid urine and solid urine outputs as a function of EER. Our attempt will be to use physiological knowledge to predict elemental output. Further, if combined with the https://ntrs.nasa.gov/search.jsp?R=20040010359 2017-10-28T13:45:28+00:00Z