Encyclopedia of Environmental Science and Engineering, Volume I and II

1250 WATER AND WASTE MANAGEMENT SYSTEMS IN SPACE

Discussions on these and related topics may be found in

Refs. 24–27.

Immobilized Cell or Enzyme Bioreactors

Immobilized microorganisms convert contaminants into

simpler molecules at near ambient temperatures. The immo-

bilized cells can treat a wide variety of contaminants. This

technology is under development, but it may have significant

terrestrial uses. 28 – 30 These biological systems require little

energy, and may leave little waste residue. Prototype reactors

were tested using a packing of diatomaceous earth. When

tested with feed containing 10 and 100 mg/L phenol in an

oxygenated solution, they were able to produce an effluent

with phenol content below the detection limit of 0.01 mg/L.

The report did not say what organisms were used, nor how

they were arranged for the test.^30 Immobilized microbial cell

bioreactors have been used in industrial wastewater treatment

applications. In a comparative test processing feed from a

coal tar plant, a reactor using a porous polymeric biomass

support achieved effluent phenol levels 100 times lower than

those achieved by a commercial bioreactor utilizing a non-

porous polyethylene support. Similar results were observed

for minor contaminants, and the sludge output was about

20% of that from the nonporous system.

A bioreactor test using a consortium of enriched aero-

bic microorganisms immobilized in packed bed reactors

was conducted, utilizing a simulated wastewater feed.

A porous polymeric biomass support was used in the reactor.

Influent concentrations were nominally 600 mg/L COD, and

1000 mg/L urea. COD reductions of 95% or more, and urea

reductions of 95–99% were achieved when using hydraulic

retention times of 24 or 48 hours. Effluent total suspended

solids ranged from 1 to 3 mg/L.^28

Tests have shown that low-molecular weight, polar, non-

ionic contaminants can be removed from solution by immobi-

lized enzymes which catalyze the oxidation of various organic

compounds, such as alcohols, aldehydes, and so on, to organic

acids, for subsequent removal by ion exchange. Hence exist-

ing ion exchange technology (multifiltration Unibeds) can be

Electrolysis + Electrodialysis

RO Brine

Stream

Bleed to waste

Anion

Exchange

Membrane

Cation

Exchange

Membrane

RO Recycle

Stream

Negative

Electrode

Positive

Electrode

Brine

Drain

FIGURE 5 Electrooxidation—combined electrolytic and electrodialytic cell. Source: Ref. 7.

C023_001_r03.indd 1250C023_001_r03.indd 1250 11/18/2005 1:29:12 PM11/18/2005 1:29:12 PM