The applications of modern technology to the resolution of the problem of solid wastes in space cabin environments was studied with emphasis on the exploration of operating conditions that would permit lowering of process temperatures in wet oxidation of combined human wastes. It was found that the ultimate degree of degradation is not enhanced by use of a catalyst. However, the rate of oxidation is increased, and the temperature of oxidation is reduced to 400 F

Ross, L. W.

English

NASA Technical Reports Server

Final Report
NASA Grant NGR-06-004-068
30 April 1973
DIRECT OXIDATION OF STRONG WASTE WATERS,
SIMULATING COMBINED WASTES IN EXTENDED-MISSION SPACE CABINS
Principal Investigator:
Dr. Laurence W. Ross K
Associate Professor of Chemical Engineerir4 JUL
(1ASA-C - 138607) DIRECT OXIDATION OF N74-26629
STRONG WASE WATEaS, SIMULATING COMBINED
WASES Ir EXiENDED-MISSION SPACE CABINS
Final Peport (Denver Research Inst.) Unclas
1) p HC $4.^0 CSCL C6I G3/05 41380
DENVER RESEARCH INSTITUTE
to
https://ntrs.nasa.gov/search.jsp?R=19740018516 2020-03-23T08:40:50+00:00Z
Introduction
The objective of this research was to explore applications
of modern technology to the resolution of the problem of solid wastes
in space cabin environments.
Originally, the research task consisted of an investigation
of electrolytic degradation of human wastes. However, in view of the
priority assigned by NASA to thermal methods for treating combined
wastes, it was considered desirable to conduct exploratory studies
toward the objective of identifying improved operating conditions
for thermal methods.
Accordingly, with the sponsor's approval, the objective of
NASA grant NGR-06-004-068 was shifted to exploration of operating
conditions that would permit lowering of process temperatures in wet
oxidation of combined human wastes.
Background
The two principal methods that are currently being considered
for elimination of solid wastes in spacecraft environments are both
oxidation techniques, viz.,
1) wet oxidation
2) incineration.
At present, there are three major NASA contractors who are
exploring these techniques with reference to wastes generated in
spacecraft, namely,
Lockheed Missiles and Space Company
General American Research Division (GARD) of
the General American Transportation Company
General Electric Corporation.
-1-
Lockheed is investigating wet oxidation, in which the
oxidation occurs at about 5500F under conditions of continuous flow.
GARD and GE, on the other hand, are investigating combustive systems
that essentially involve dried wastes, with the result that temperatures
are much higher (up to 11000F). The drying and pyrolysis steps in
the GARD and GE systems involve significant weight penalties, especially
in transport of solids.
The first basic investigation of wet oxidation was reported
by Fisher in 1971. 1 Fisher's principal conclusions including the
following:
a) the ultimate products of wet oxidation are
the lower fatty acids;
b) temperatures approaching the critical (~ 3500C)
are required to achieve essentially complete oxidation,
even in pure oxygen atmosphere.
The Zimmerman (or Zimpro) process had been known for many years before
Fisher's investigation, but there was little basic understanding of
its limitations, and especially the nature of its products. Dr. Paul
Schatzberg of the U.S. Navy Engineering Command has extended the under-
standing of the wet oxidation process in several investigations under
his contractual supervision. In particular, research performed for
Dr. Schatzberg has shown that wet oxidation of a strong sewage-type
waste is achieved in two fundamental stages: (1) a rapid degradation
to lower fatty acids (mainly acetic acid) followed by (2) a slow oxidation
to the ultimate oxidation products, CO2 and H20.2
The studies of Bruce Jagow at Lockheed Missiles and Space Co.3
have generally verified the Zimmerman results and Fisher's findings.
-2-
Jagow has employed oxidation catalysts, but only for the purpose of
oxidizing ammonia-nitrogen to the nitrate state. Jagow's experiments
are unique in that they are conducted under continuous-flow conditions.
Recently, interest in direct oxidation of sewage wastes has
arisen within the chemical manufacturing industry. The prospect of
converting sewage into chemical synthetic feedstocks is attractive
where the waste volume is sufficiently large. The principle of such
a conversion process is illustrated in the following sketch:
Raw _ Concentration Concentrated
waste -- step waste
Water for
recycling
Fig. 1
-3-
The recycled water stream is capable of yielding potable water.
Meanwhile, the concentrated waste stream provides a "strong" feedstock
for potential chemical processing.
Research Program
The present investigation has been concerned with a systematic
search for catalysts which would permit conversion of the "strong"
waste water stream (Fig. 1) into a useful chemical feedstock at
reasonable rates.
Initial emphasis, as in the case of Fisher's research I was
directed to absolute degradation of the waste, expressed as reduction
in COD.
A synthetic "strong waste" has been employed, .consisting of
a mixed-organic mash filtrate from the Adolph Coors brewery in Golden,
Colorado, suitably diluted to yield an initial COD of about 15,000 mg/l
for our tests.
Typical reaction conditions are summarized as follows:
Temperature 4000F
Pressure (02) 300 psig
Reaction time 2 hours.
Heating to the reaction temperature level is performed under nitrogen
atmosphere.
Oxidation is conducted in a Parr pressure reaction apparatus,
constructed of 316 stainless steel, with a reaction chamber 1 liter in
volume. A sample of 200 ml is used, under conditions of continuous
stirring. COD measurements are performed according to standard proce-
dures. Reaction temperature is controlled by an on-off controller
-4-
actuated by a chromel-alumel thermocouple.
Reaction conditions include the following parameters of
interest to the investigation:
Temperature
Catalyst
pH.
In particular, the investigation has sought to identify a catalyst
which permits maximum conversion at lowest temperature. However, the
question of conversion products is still to be considered, i.e.,
whether the products of oxidation are useful as feedstocks for organic
chemical synthesis.
The catalyst systems examined to date in the present investi-
gation are summarized in Table 1. Catalysts employed fall into two
categories:
1) free-radical generators
2) supported metals.
Parameters for investigation include pH and temperature.
Although several metal compounds have been employed, the list is by
no means exhaustive, because our objective was merely to determine
the potential gains to be obtained from catalysis, in oxidation of
strong organic wastes. Furthermore, the cost of the metals will be
an economic factor in the process, even if the metals are recovered.
Results
At the expiration date of the grant, only preliminary results
had been obtained. However, these results-were sufficiently promising
to warrant continued investigation, and the study has been continued
-5-
under sponsorship of the University of Denver. The study will be
concluded about June 1974.
The principal finding of the investigation to date is that
the ultimate degree of degradation is not enhanced by use of a catalyst.
This is evident in Fig. 2. In fact, the degradation may be suppressed
(Table 1). However, several catalysts were found which increased the
rate of degradation.
Some results seem to verify Dr. Paul Schatzberg's findings
(see above) with respect to a two-stage mechanism.2 That is, a drop
in COD followed by an increase in COD has been observed in two cases.
This can be explained by a fast degradation of organic materials to
lower fatty acids followed by a slower degradation of these acids to
CO2 and H20.
Another important finding is that most catalysts lead to a
clear liquid product that possesses a faintly ethereal odor, while
identical treatment in absence of catalyst produces a brown-colored
liquid with a distinct odor of char. With catalyst, the suspended solids
settle rapidly into a thin layer of light brown color after reaction;
without catalyst, solids settle slowly, and possess a dark color.
These findings are suggestive of different product compositions, but
they have not yet been supported by quantitative chemical analysis.
Conclusions
The use of catalysts can alter the composition of products
from oxidation of strong chemical waste waters, and can increase the
-6-
rate of oxidation. In addition, the temperature of oxidation can be
reduced to 4000F, compared to a typical temperature of 5500 F in con-
ventional "wet oxidation" processes. It is possible that the optimum
conversion to useful products, as opposed to complete degradation, may
be achieved at much lower temperatures.
Future Work
No other catalyst combinations are planned for investigation.
Future work will revolve around determination of optimum pH and minimum
temperature. In addition, the nature of the products as a function
of catalyst and temperature will be studied by chemical analysis.
References
1. W. J. Fisher, Water Research 5, 187-201 (1971).
2. Paul Schatzberg, personal communication.
3. R. B. Jagow, Paper presented to 1972 Environmental Control/Life
Support Conference, San Francisco. ASNE paper no. 72-ENAv-3.
-7-
Table 1
Organic Degradation Achieved by Various Catalyst
Systems in Two Hours of Oxidation
Catalyst System COD Reduction
1. Ferrous Sulfate + Hydrogen Peroxide 65.8
2. Ferrous Sulfate + Benzoyl Peroxide 92.2
3. Cobalt Sulfate + Hydrogen Peroxide 85.8
4. Cobalt Sulfate + Benzoyl Peroxide 75.6
5. Ceric Sulfate + Hydrogen Peroxide 91.0
6. Ceric Sulfate + Benzoyl Peroxide 79.7
7. Silver Sulfate + Hydrogen Peroxide 84.7
8. Silver Sulfate + Benzoyl Peroxide 82.5
9. Chromic Sulfate + Hydrogen Peroxide 83.0
10. Chromic Sulfate + Benzoyl Peroxide 73.0
11. Nickel Sulfate + Copper Sulfate + Hydrogen Peroxide 88.8
12. Nickel Sulfate + Copper Sulfate + Benzoyl Peroxide 89.5
13. Mercuric Sulfate + Hydrogen Peroxide 79.4
14. Mercuric Acetate 67.3
15. Ferric Acetate 79.7
16. Ferrous Sulfate + Benzoyl Peroxide + 2-4 Dimethyl-
aniline 61.5
17. Sodium Perborate 92.0
18. Raney nickel (W-2) 79.2 (90 minutes)
19. Platinum Black 67.8 (70 minutes)
20. No catalyst 90.2
-8-
0.8 g NiS04 +
100 0.2 g CuS04 +
0.5 g benzoyl peroxide
80 _ 0
S-No catalyst
0.2 g sodium
0 perborate
bUO-
o /
40
20
0 30 60 90 120 150
Reaction time, minutes
Fig. 2. Typical patterns of COD reduction, with and without
addition of catalyst.


Direct oxidation of strong waste waters, simulating combined wastes in extended-mission space cabins

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