Encyclopedia of Environmental Science and Engineering, Volume I and II

WATER AND WASTE MANAGEMENT SYSTEMS IN SPACE 1249

heat to evaporate the feed, condensing to form the product

water. The residual concentrated feed, or brine, is sent to a

supercritical water oxidizer (SWCO) to remove the remain-

ing contaminants. Bacterial growth is suppressed because

bacteria do not thrive in the concentrated brine due to the

buildup of both toxic compounds and of heavy metals in the

brine. The vapor phase provides a barrier to non-airborne

micro-organisms.^10

Plant Transpiration and Water Recovery

The use of plants to produce clean water by transpiration

is being examined by NASA. It is believed that plants can

process wastewater, and transpire it with minimal contami-

nants. However, any volatile contaminants must be removed

first, so that they cannot evaporate directly from the wastewater

into the air. The type of pretreatment required will depend

upon the waste steam being treated. Plant nutrients will have

to be added to the water. Preliminary experiments using

only a plant nutrient solution indicated that the amount of

total organic carbon (TOC) in transpired water vapor from

unstressed plants was very low, about 1.4 mg/L in the water

that was collected in condensers outside the plant cham-

ber. Water collected in the plant chamber had higher TOC

values, averaging 2.5 mg/L. Stressed plants transpired water

with TOC values of up to 7 mg/L. The average TOC level

of tap water was 1.6 mg/L. Insect infestation stressed the

plants, causing higher TOC levels in the transpired water.

It was not clear if any of the increased TOC was derived

from the insects themselves. There are many questions about

the feasibility of using a compact growth facility to treat the

wastewater. These questions need to be examined carefully.

TOP OF

UNIBED

MEDIA

TYPE

PROCESS FUNCTION

BOTTOM OF

UNIBED

Diatomaceous

Earth Coarse

Diatomaceous

Earth Fine

MCV

Iodinated Resin

Dowex-1

Mixed Bed Resin

DIRECTION OF FLOW

Carbon/Adsorbent

Silicalite Mixture

Weak Base Anion

MCV

Iodinated Resin

+30 US Mesh

-30 US Mesh

Iodinated

SBA Anion

Dowex-1

SBA Anion

Coarse

Filtration

Fine Filtration

Iodine

Injection

Absorption

Cleansing

Agents

Ion

Exchange

Turbidity Removal

Turbidity Removal

Microbial Control

Organic

Scavenging

Reduction

Inorganic Salts

Mixed

Resin

SAC/SBA

Adsorbant

Section

Methacrylic

Weak Base Gel

Type Resin

Iodinated

SBA Anion

Adsorption

Ion Exchange

Weak Organic

Acids

Iodine Injection

TOC

Removal/Reduction

Reduction

Organic acids

Microbial Control

FIGURE 4 Multifiltration unibed schematic and process details. Source: Ref. 15.

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