Encyclopedia of Environmental Science and Engineering, Volume I and II

1246 WATER AND WASTE MANAGEMENT SYSTEMS IN SPACE

(a potassium monopersulfate compound) combined with sul-

furic acid, or hypochlorite (bleach) before distillation.

Thermoelectric Integrated Membrane

Subsystem (TIMES)

This was the original baseline water recovery subsystem for

the space station (Figure 2). Wastewater is heated to 66
C

in a heat exchanger, and is then pumped through bundles of

small diameter hollow Nafion fiber membranes in the evap-

orator module. The Nafion allows only water, gases, and

small neutral molecules to pass through. The pressure on the

exterior of the membrane is reduced to 17 kPa (2.5 psi) to

assist in both transport through the membrane, and subse-

quent evaporation. The water vapor is then condensed, and

the latent heat of condensation is conducted to the input heat

exchanger. The TIMES system was found to produce poorer

quality water than the VCD. 4,5

Vapor Compression Distillation (VCD)

The VCD process involves spreading a thin film of the waste-

water on the inside wall of a thin-walled rotating drum under

low pressure, typically about 4.8 kPa (0.7 psi). The VCD is

shown in Figure 3, and in-depth discussions may be found

in Refs. 4, and 6–11. The system operates at 35
C which is

slightly above ambient temperature. Heat is applied to the

outside of the wall causing the thin film of water to boil. The

vapor is extracted from the drum interior and compressed

by a pump. The compressed vapor is then condensed on the

exterior wall of the drum. The compressed vapor condenses

at a higher temperature than that at which it had originally

evaporated. The latent heat of condensation thus supplied

the heat required to evaporate the original feed water in the

inside of the drum. The unevaporated brine, heavily loaded

with contaminants, is recycled back to the inflow stream, or

passed to another subsystem.

TABLE 2 (continued)

QUALITY PARAMETERS Shuttle Potable EPA Current SSF Potable SSF Hygiene

MICROBIAL None Viable — — —

BACTERIA (CFU/100 mL) ————

TOTAL COUNT — — 1 1

ANAEROBES — — 1 1

COLIFORM — 1 1 1

ENTERIC — — — —

VIRUS (PFU/100 mL) — — 1 1

YEAST and MOLD

(CFU/100 mL)

—— 11

RADIOACTIVE CONSTITUENTS

(pCi/L)

NRC LIMITS (see Note3) ——

ORGANIC PARAMETERS (mg/L) (See

Note 2)

————

TOTAL ACIDS — — 500 500

CYANIDE

(total including organic cyanides)

— — 200 200

HALOGENATED HYDROCARBONS — 0.1 (THM)* 10 10

TOTAL PHENOLS — — 1 1

TOTAL ALCOHOLS — — 500 500

TOTAL ORGANIC CARBON (TOC) Reference only — 500 10000

UNCHARACTERIZED TOC (UTOC) — — — —

(see Note 4) — — 100 1000

ORGANIC CONSTITUENTS (mg/L) — — — —

(see Notes 2 and 5) — — — —

Note 1: No detectable gas using a volumetric gas vs. fluid measurement system. This excludes CO 2 used for aesthetics

purposes.

Note 2: MCLs considered independently of others.

Note 3: The maximum contaminant levels for radioactive constituents in potable and personal hygiene water shall

conform to Nuclear Regulatory Commission (NRC) regulations (10CFR20, et al.). These maximum contaminant levels

are listed in the “Federal Register Vol 51, No: 6, 1986, Appendix B, Table 2.

Note 4: Total organic carbon minus identifiable organic contaminants.

Note 5: MCLs for others, if found, will be established as necessary.

* THM = Trihalomethanes

SSF = Space Station Freedom

Source: Ref 3.

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