Chapter 3
NUTRIENT REQUIREMENTS
AND
WATER MANAGEMENT
1. Introduction
Nutrition is an important aspect, as it determines the space, water and
energy necessary for agriculture sustaining a colony’s population. Rational
diets should be proposed in order to determine the nutrient requirements of a
population. This is necessary for determining the food requirement of the
colony and thus designing its agriculture. Water consumption is another
important aspect. It includes domestic water consumption, agriculture
consumption and industry consumption. Determining exactly what is the balance
between comfort and cost is the essential aspect for modeling water
consumption. What is acceptable in terms of comfort for a non-permanent space
station or shuttle may not be acceptable for a permanent space colony. People
living in the colony would expect a comfort similar to what they get on Earth.
Ensuring water quality both from aesthetic and health points of view is
a vital aspect. Water quality and monitoring is discussed in the fourth section
of the chapter.
STATE OF THE ART
Previous designs considered that water consumption onboard the
settlement should be the same as on a non-permanent space station (the values
presented in other projects were given in [4]). The solution proposed in [4]
has been adopted in [14, 17]. Extremely low water consumption has been proposed
in [13] (20L per day per capita). However, the space settlement has a permanent
character. People will not be attracted to settle if the comfort is low. Living
with just 
of water per year is
fine in terms of comfort for a period of two years or less (non-permanent
character of space station) but is not acceptable for a permanent
settlement. Moreover, the designs that follow [4] neglected the water
consumption of industry and agriculture. I propose a water consumption model
that includes industry, agriculture consumption and a fair level of comfort.
The proposed model is compared with the consumption of England (one of the
lowest water consumers) and Canada.
Some designs [13,14] proposed that water tank capacity should include
the amount of water necessary for one week. Some recycling processes are
continuous - such as recycling water vapor from the atmosphere. The proposed
capacity was for one month, for recycling and safety reasons.
Water quality and monitoring has been discussed in other projects [13,
14]. Project [13] proposes the usage of ozone for water disinfection. [15, 17]
do not discuss water quality/monitoring. Project [14] proposes chlorine
dioxide, ozone, iodine and silver as effective disinfectants. All solutions are
analyzed, along with advantages and disadvantages (such as disinfection
by-products). However, project [14] only deals with ensuring water quality such
that it will not affect health. Physical quality is an important aspect (how
people rate water based on what they feel) and is analyzed. Physical quality of
water also influences its utility.
Water disinfection methods used onboard spacecraft are also discussed,
such as the MCV [7, 9] used onboard the space shuttle.
For the nutrition section of the chapter, the approach was to determine
the needed quantity of proteins, lipids and carbohydrates for various activity
profiles and the oxygen consumption. This approach is different, as it focuses
on the energetic needs of a diet, rather than naming the aliments included in
the diet. Without analysis of the energetic needs for a specific activity
profile, the aliments included in the diet cannot be stated exactly. Previous
projects [13] named aliments included in the diet, but did not the energetic
analysis. Project [14] did the nutrient need analysis, but did not state the
oxygen consumption for a given activity profile. In [15, 17] the matter was not
discussed.
Ozone used as a disinfectant has not been discussed in detail. The
analysis in [5] states that Bromate is a possible by-product of disinfection
using ozone, other by-products were not determined up to now. This degree of
uncertainty hinders the analysis.
2. Nutrient and oxygen requirements
THEORETICAL ASPECTS
An adequate diet must be ensured for people living onboard the space
settlement and for the workers and builders in the lunar extraction/processing
facility. Diets vary with occupation, age, sex, height, weight and location, as
discussed in this section.
An adequate diet comprises providing the body with sufficient energy,
carbohydrates, essential fatty acids and proteins, vitamins and water.
Subsequently, the body needs for normal digestion cellulose fibers (the
so-called “roughage”).
Metabolism is defined as the conversion of chemical energy of food into
heat and mechanical work and partly the synthesis of endogenous substances.[1]
BMR (Basal Metabolic Rate) is defined as the minimal consumption of
energy needed for survival in ideal environment conditions [1]. This comprises
resting and thermal comfort. Any supplementary activity would require
additional energy. For any energy consumption above the BMR we will define the
“Working Metabolic Rate” (known as WMR, [1]). Both the BMR and the WMR vary
with age, body weight, height and sex. The WMR varies with the occupation.
The BMR is averaged for a 70kg adult at 
[1].
For various occupations, the WMR is [1]:
·
For
office work: 
[average]
·
For
women performing heavy work: 
[average]
·
For
men performing heavy work: 
[average]
·
Maximum
energy consumption [heaviest work]: 
The energy needs are covered by three basic nutrients, namely
carbohydrates, proteins and fats. A minimal quantity of proteins is needed to
provide the essential amino acids. For humans, there are nine essential amino
acids that cannot be synthesized by the organism: valine, threonine,
phenylalanine, leucine, lysine, histidine, methionine, tryptophan and
isoleucine. The majority of plant proteins are deficient in one or more of the
essential amino acids. The minimal protein intake should be 
per kilo of body
weight, but the functional minimal intake is twice the minimal amount. Half of
the functional minimal intake should be supplied in the form of animal proteins
to ensure that the essential amino acids are furnished to the body.
The energy requirement is largely satisfied by degradation of
carbohydrates and fats. Fats are largely superfluous – except for the essential
fatty acids (linoleic acid, for example) and for fat-soluble vitamins.
Fat-soluble vitamins (A, D, E and K) are necessary for a healthy organism, as
lacks in these vitamins have severe effects – night blindness (A avitaminose),
rickets (D avitaminose) and disturbances in blood clotting (K avitaminose).
Fats have the largest caloric value out of all nutrients, 
. Carbohydrates have a caloric value of 
(approximately equal to that of proteins) and comprise sugars
and glycogens. For a normal diet, the energetic contribution of fats is 25-30%,
but the requirements may rise up to 40% in physically demanding conditions. The
energetic contribution of carbohydrates is normally 60%. The minimal
contribution is 10%.
Other dietary requirements are comprised of mineral substances – calcium
(
minimal requirement), iron (
m.r. in males, 
in females), iodine (
m.r.) and trace elements (
). Notice that trace elements are vital, but are poisonous if
administrated in large amounts.
Vitamins are vital in metabolism – they activate enzymes and some are
coenzymes. Vitamins cannot be synthesized in sufficient amounts by the body.
The vital vitamins are: 
, folic acid, niacinamide and pantothenic acid.
The average energy consumption is 25% for fats, 12% for proteins and 63%
for carbohydrates [2]. The average caloric values for fats, proteins and
carbohydrates are:
;
;
.
The physical caloric value is
defined as the utilizable energy content of the food made available by its
combustion (breakdown into molecules of 
and 
with consumption of 
). It is denoted by 
.
Fats and carbohydrates are completely oxidized, while proteins can only
be broken down to urea. The physiological caloric value is defined as the
quantity of energy released in the organism after combustion of a specific
nutrient (protein, fat, carbohydrate). It is denoted by 
. In all computations, we use for nutrients the value of 
.
Notice that 
for fats and
carbohydrates, while for proteins 
.
The Caloric Equivalent (CE) is the oxygen volume required to
oxidize various nutrients (reveals the oxygen consumption). The average CE for
carbohydrates is 
, for fats 
, while for proteins 
.
Note: The metabolic rate can be computed
as 
, where 
is the oxygen volume. The respiratory quotient (RQ) is defined as 
and shows the ratio
between the number of resulted 
mol and the number of
mol required for the
oxidation process. As an example, let’s consider the oxidation of the glucose:
,
for which 
.
NUMERICAL RESULTS – ACTIVITY PROFILES
The energy requirements for fats/proteins/carbohydrates and 
consumption per day are
computed for three different activity profiles[2].
The energetic needs for various workloads and the oxygen consumption
have been computed. The method I used is better suited for such computations
because it offers flexibility for computing various cases. The accuracy of the
computations has been checked with results from literature.
I.
Office work
Office work (or similar light
work) implies a total energy consumption of 
. The total intake of fats, proteins and carbohydrates in a normal
diet and the required oxygen volume are presented in Table III.1.
Table III.1. Nutrient and Oxygen requirements per day for people
performing office/light work [averages].
Notice that the volume of 
required for
degrading a specific nutrient is obtained as:
[Energy
intake/day]/CE (1)
For example, the required Oxygen volume/day/person for fats, for a
person performing light work is:
.
Computations for the required Oxygen volume per nutrient/day are based
on (1).
II.
Women performing
heavy work
Heavy work implies a total energy consumption of 
for women (as they
have a slower metabolism than men). The total intake of fats, proteins and
carbohydrates in a normal diet and the required oxygen volume for this activity
profile are presented in Table III.2.
Table III.2. Nutrient and Oxygen requirements per day for women
performing heavy work.
III.
Men performing
heavy work
Heavy work implies a total energy consumption of 
for men. The total
intake of fats, proteins and carbohydrates in a normal diet and the required
oxygen volume are presented in Table III.3.
Table III.3. Nutrient and Oxygen requirements per day for men performing
heavy work.
Note: To these nutrient quantities,
cellulose fibers or other “roughage” should be added, considering a 50%
quantity of the total nutrient quantity. For example, men performing heavy work
would require additionally 500.305[g] of fibers to ensure proper digestion.
DISCUSSION
In past designs, such as the NASA 1975 Summer Study [12], the average
space diet included significant quantities of meat (40g per person per day) and
approximately 0.5 eggs per day in prepared food. According to the Study, a
person would require 24g of egg per day. An egg weights in average 54g. Thus a
person would need per day approximately 
eggs in prepared
food. According to the same study, a hen lays five eggs per week in average. If
we consider that people will only eat eggs five days per week, then the ratio
is 1 egg per 1 hen per day. The total egg consumption for a population of
100’000 is about 44’444. That means that we need over 40’000 laying hens! The
space required is so high, that only if we send the poultry on an annex station
(just for growing poultry, for example), separate to the torus, it will be
feasible. We consider as feasible a value of 1 egg per person per ten days. An
alternative source of proteins has to be found in order to compensate animal
proteins’ lack.
We consider that animal protein will be largely substituted by soy.
Soy has been proven by various studies as a good protein alternative. It
contains 38% proteins and 15% fibers (the “roughage” necessary for a normal
digestion). High concentrations of iron, calcium, zinc, B vitamins and E
vitamin are found in soy. It has been recognized in over 150 studies as an
alternative to proteins found in meat, eggs and milk. Moreover, consumption of
soy instead of meat ensures a healthy diet – lower levels of cholesterol and
provides the body with an anti-carcinogen (phytoestrogen). Tofu has been used
in space meals (on the ISS, for example). Soy represents a feasible, cheap
alternative to animal proteins. A regular diet on the space settlement should
be based on soy, rather than on meat.
3. Water consumption computation
Water is the basic ingredient of life. The water content of the body has
to be strictly regulated. The water balance comprises that all water losses
must be counter-balanced by water intake and production. Water results from
metabolism processes. Water balance is achieved via the ECF
(Extra-Cellular-Fluid).
The average water intake consists of [1]:
·
Drinks
;
·
Water
in the composition of solid food 
;
·
Water
resulting from metabolism processes 
.
The average water output consists of:
·
Urine 
;
·
Water
contained in feces 
;
·
Water
lost in expired air/sweating 
.
The average water intake/output in normal conditions is 
.
The per capita water consumption may be computed using the following
categories:
·
Domestic
water
·
Water
required for agriculture
·
Water
used in industrial processes
·
Commercial
and institutional water.
The quantity per capita for each category is computed considering the
municipal water needs for various locations, presented in different surveys.
Data has been collected from the Canadian survey [3] and has been compared to
Britain’s average water consumption. All values state for water consumption per
capita per day.
The minimal water requirement onboard a spacecraft is 31L per capita per
day. This value has been computed in [4] taking into account that the people stay
onboard a spacecraft or onboard a non-permanent space station less than two
years. The space settlement has a permanent character, so consumption needs are
different. We look at the settlement as a nice place to live and work in, where
people afford a normal life with all utilities. 5,5 Liters for shower per day
per capita for a lifetime is not acceptable. Moreover, the Space Station
Freedom water requirements do not include any industry/agriculture water (see
Table III.4).
Table III.4. Water requirements of Space Station Freedom (NASA SSP
30362, 1990). This represents a minimal domestic water requirement per day per
person. From http://oregonstate.edu/~atwaterj/io.htm,
[4].
Some previous space settlement designs adopted this model ([14]), while
some designs used extreme water consumption, of only 20L/day ([13]). It is not
realistic, as it doesn’t meet the requirements of an industry, agriculture and
it solely meets the minimal requirements for domestic consumption. The space settlement has to allow its
inhabitants a life close to that on Earth. Water consumption on the station
should be of the same magnitude as on Earth. The values from the Canadian water
consumption survey and from the British survey have been compared. Taking into
account all of modern society needs and comparing the water consumption of two
countries (Canada, UK), we have proposed a model for the settlement’s water
consumption. The proposed model ensures the minimal industry consumption and
comfort for a permanent residence.
Canada has the average per capita water consumption per year of 1600
cubic meters. Britain has the average of 300 cubic meters. The values presented
in survey [3] have been analyzed. Taking into account that a very limited water
quantity for the settlement is affordable, the averages considered as providing
sufficient comfort for permanent residence in space are presented in Table
III.5.
The total per capita yearly water consumption for the settlement’s
inhabitants is lower than UK’s, which in turn is one of the lowest three water
consumers in the world, about 6.3 times lower than the consumption in Canada.
However, the consumption per capita for the inhabitants of Space Station
Freedom is 11.3 cubic meters per year. The comfort ensured by this consumption
is good for periods of less than two years, but it is not suitable for a
permanent residence.
Table III.5. Average per day per capita water consumption for each
category; total water consumption per month per person, for a population of
1000 people and for a final population of 100’000 people.
Water recycling takes about one month. Some processes are continuous,
such as recycling the water vapor present in the atmosphere. Therefore, the
water reservoir should include enough water for sustainment of the settlement
for a period of one month. Water tank capacity should be computed taking into
account this aspect.
Figure III.1. Water consumption repartition [in percentages]. Notice
that the domestic water comprises most of the water consumption, followed by
the water used in irrigation (agriculture) and the institutional water.
4. Water quality and monitoring
Water quality defines good drinking water from both health and aesthetics
points of view. It depends on:
·
Microbial
quality
·
Chemical
quality
·
Radiological
quality
·
Physical
quality.
The first three categories impact health. Physical quality is related to
the appearance, taste and odor of water. The physical properties of water also
include its hardness, pH, turbidity and percentage of dissolved oxygen. Each
category will be discussed and explained, along with monitoring concerns.
The goal is to provide the settlements inhabitants with clean water that
has good aesthetic properties and that can be used in all activities (domestic
water, industry water, agriculture water and so on).
Monitoring of water quality depends on:
·
Which
characteristics are analyzed (e.g. chemical composition, microbial composition);
·
Sample
collection frequency and variation of collection point;
·
The
usage of more than one sampling technique;
·
Comparison
and evaluation of sample results;
·
Rapid
decisions if any problem is depicted.
The sample locations should be:
·
Storage
tanks;
·
Pipe
leaving the disinfection facility;
·
Various
distribution points and major pipes.
There are three possibilities to disinfect water:
·
Chemical
disinfection (by usage of chlorine, iodine or ozone, silver ions [6]);
·
Radiation
disinfection (usage of UV);
·
Thermal
disinfection.
Chemical disinfection is widely used
and has been proven to work in various space applications. It is – at the
present state of art – the cheapest disinfection method. Only this disinfection
method is analyzed in detail.
MICROBIAL
QUALITY
A common health risk is the presence
of microorganisms in drinking water. Disease-causing microorganisms (bacteria,
viruses and protozoa) may be found in water as a result of contamination.
Microorganisms may be eliminated from the water supply by treatment processes –
water filtration and disinfection. The easiest (at the present date) way of
determining whether a water supply has suffered contamination is to check it
for indicator microorganisms. Such organisms can be determined rather easily
and show if the water is contaminated. Water contamination is determined by the
presence of thermotolerant coliforms (E. Coli, for example) or coliforms, which
produce infectious gastrointestinal diseases. These two groups of bacteria are
complementary. However, their absence does not guarantee that the water is not
contaminated with other health-threatening microorganisms. Some cyano-bacteria
produce toxins that may remain in the water even after the microorganisms have
been removed. “Nuisance” micro-organisms do not prejudice health, but modify
the physical properties of water.
Monitoring and prevention
The most common contamination prevention method is to eliminate
microorganisms using chlorine or iodine. However, water should be tested for
the presence of toxins resulting from algae. Such toxins may cause asthma,
neuro-muscular disorders or liver damages. The number of cyano-bacteria should
be less than 1000/mL. Australian experts advised in [5] at least twice a week
inspections for microbial contamination.
Prevention methods:
·
Ensure
that the settlement’s visitors/newcomers do not have any infectious disease
that may be transmitted via water/air;
·
Filtration
and settling of water;
·
Periodic
checks of integrity of distribution system;
·
Proper
disinfection of water before it enters the distribution system;
·
Maintenance
of a residual disinfectant throughout the distribution system;
Samples should be checked at least twice per week for indicator
microorganisms. The results should be averaged over a period of 12 months. The
performance is satisfactory if 95% of all samples did not contain any
thermotolerant coliforms and if 98% of all samples did not contain any
coliforms. If the results were poorer, the disinfectant concentration should be
raised. In extreme cases, iodine may be used as a disinfectant. [5]
CHEMICAL
QUALITY
Some inorganic chemicals and some organic compounds prove of concern if
present in large quantities in drinking water, as they are either toxic, have
adverse health effects (some are carcinogenic), or change the aesthetic
qualities of water.
Inorganic chemicals comprise carbonates and chlorides, which may result
from addition of chemicals for disinfection (chlorine) or from corrosion of
pipes and fittings.
Organic compounds are classified in:
·
Disinfection
by-products;
·
Other
organic components (toxins produced by cyano-bacteria, for example).
Disinfection by-products pose a lower health risk than water that has
not been disinfected. Proper disinfection is an essential process in rendering
the water safe to drink.
Inorganic chemicals are chlorine, chlorine dioxide and iodine. All are
disinfectants. Iodine should be used only as an emergency disinfectant. The
aesthetic concentration for chlorine and chlorine dioxide is 
, but the ratio may rise up to 
in order to maintain
effective disinfectant residuals throughout the distribution system. Iodine may
be administrated with a maximum concentration of 
. Chlorate and chloride are by-products.
Organic by-products are chloroacetic acids, chlorophenols, chloropicrin
(all results of chlorination) and formaldehyde. Organic compounds that may
result from water industrial contamination are [5] Vynil chloride (carcinogen,
used in PVC manufacturing), Xylene (solvent for plastic bonding),
tetrachloroethene (solvent and metal degreaser). The maximal concentrations in
water of these compounds are: 
for Vynil, 
for Xylene, and respectively
for
tetrachloroethene. All these compounds are extremely toxic if found in larger
quantities. However, if the metal processing industry and the chemicals
industry are placed on the lunar facility, these compounds do not threat the
space settlement’s inhabitants. Precautions for industrial contamination of
water should apply mainly for the lunar facility.
Pesticides are extremely toxic. They include agricultural chemicals,
such as herbicides, nematicides, miciticides and rodenticides. The best
prevention method is to ensure that no pests are brought to the settlement.
Pesticides, if ever used on the settlement, should be found in concentrations
below 
[average].
WATER
DISINFECTANTS ONBOARD SPACECRAFT [6], [7], [8], [9]
Elemental iodine has been proven as a highly efficient disinfectant,
being used in all American designed water systems. [6] The Russian space
program, on the other hand, uses silver ions. Both elemental iodine and silver
ions are effective biocides.
Elemental iodine has been used to disinfect water supplies onboard
spacecraft as early as the Apollo program (began in 1969). For the lunar
module, the adopted solution was to prefill the water tanks with a
concentration if iodine of 
. The resulted residual disinfectant concentration was less
than 
. The same solution has been used for the Skylab mission, but
iodine concentrations were monitored in order to maintain the residual
disinfectant concentration between 0.5 and 
. If the concentration dropped, the water tanks would receive
additions of disinfectant. The additional disinfectant was a solution of
potassium iodide and elemental iodine in a molar ratio of two to one.
The Space Shuttle benefits of a new water disinfection system, called
the MCV (stating for Microbial Check Valve). This device controls the release
of elemental iodine in water. The Space Shuttle produces high purity water
(resulting from the fuel cells). That water is then passed through an MCV unit,
which provides a residual iodine concentration ranging between 0.5 and 
.
Iodine has been proven to work as an excellent disinfectant in various
space missions. Iodine may be used as a primary disinfectant for the
settlement’s water supply. However, Australian specialists (in report [5])
recommend that it should only be used as an emergency disinfectant, and that
chlorine (or chlorine dioxide) is currently used widely for water disinfection.
As both solutions have been proven viable, we consider them both feasible as
applied to the space settlement.
Monitoring and prevention
·
Daily
water chemical composition checks[3];
·
Maintenance
of (when possible) an “aesthetic” concentration limit of disinfectants;
·
Specific
checks on industrial chemicals and by-products, and, if used, on pesticide
concentrations in water.
RADIOLOGICAL
QUALITY
Drinking water (in normal conditions) will contribute only a very low
proportion to a person’s total radiation exposure. The health hazard related to
radiation is cancer.
The guidelines for determining radiological quality have followed levels
for gross alpha and beta concentrations [5]:
·
Gross
alpha activity concentration should be below 
;
· Gross beta activity concentration should be below