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V. WASTE TREATMENT PROCESS SUMMARIES
The following pages summarize briefly the salient features of each of the treatment
process considered. More complete process descriptions are provided in Part Two.
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ADSORPTION, CARBON
I. CONCLUSIONS AND RECOMMENDATIONS
Carbon adsorption should be given serious consideration whenever it is desirable to
remove mixed organics, or to recover select organic or inorganic species from aqueous
waste streams with adsorbate concentrations less than 1%.
II. PROCESS DESCRIPTION
A large variety of organic solutes, and a more limited number of inorganic solutes can
be removed from aqueous waste streams by adsorption onto activated carbons with a high
absorptive surface area (500-1500 m2/g). Adsorption of organic solutes is commonly
followed by thermal regeneration of the carbon and simultaneous destruction of the absor-
bates. In a few cases, the carbon may be regenerated and the adsorbate recovered by treat-
ment with acid, base, steam, or solvent.
III. APPLICATIONS TO DATE
There are about 100 full-scale carbon adsorption systems currently in use for industrial/
municipal wastewater treatment. In general, the process works best with chemicals that have
a low water solubility, high molecular weight, low polarity, and low degree of ionization.
The concentration of adsorbates in the influent should be less than 1%, and suspended solids
must be low (^50 ppm) for most systems. Recovery is possible if the adsorbate may be
easily volatilized or dissolved off the carbon. Thermal regeneration (with organic adsorbates)
is economical if the carbon usage is above about 1000 Ib/day.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy requirements include electricity for pumps and fuel for the regeneration
furnace. Energy costs may be around 25% (or higher) of the total operating costs where
concentrated waste streams are being treated and the carbon is thermally regenerated.
Energy may constitute no more than 5% of total operating costs if regeneration is accom-
plished by non-thermal means.
Capital costs for a 100,000-gpd facility would be in the neighborhood of $1,000,000.
Total operating costs would be in the range of $5-20/1000 gal.
If spent carbon is not regenerated, it presents a problem for disposal. If it is thermally
regenerated, the regeneration furnace will usually require an afterburner, a scrubber, and
perhaps a dust filter.
V. OUTLOOK FOR WASTES
For aqueous waste streams containing up to 1% of refractory or toxic organics, carbon
adsorption is an excellent, proven process. For more concentrated waste streams, solute
removal would be even more efficient, but the more frequent regeneration required would
significantly increase costs. Development of new methods of regeneration, particularly
ones that allow recovery of the adsorbate, could greatly expand potential applications of
the process.
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ADSORPTION, RESIN
I. CONCLUSIONS AND RECOMMENDATIONS
Resin adsorption, like carbon adsorption, is a useful process for extraction of organic
solutes from aqueous waste streams. Resin adsorption will generally be preferred when it
is desirable to recover the adsorbate. Carbons are usually thermally regenerated with de-
struction of the adsorbate. Resins are always chemically regenerated (with caustic or organic
solvents).
II. PROCESS DESCRIPTION
Resin adsorption uses synthetic resins (which can vary significantly in their chemical
and physical nature) to extract and recover, if desired, dissolved organic solutes from
aqueous waste streams. Resins with either (or mixed) hydrophobic or hydrophylic natures
are available, and can be used to extract, respectively, hydrophobic or hydrophylic solutes.
Resins are always chemically regenerated. When organic solvents are used as the regenerant,
solute recovery is generally via distillation.
III. APPLICATIONS TO DATE
Current industrial waste treatment applications include: phenol recovery; color re-
moval; and fat removal from aqueous waste streams. The phenol concentration can be as
high as 8% by weight in the feed.
Proposed waste treatment applications (near-term) include removal of toxic chemicals
from munitions facilities' effluents; removal of pesticides from aqueous streams; carcinogen
removal from laboratory waste waters; and removal of phenolics; and removal of chlorinated
hydrocarbons.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy requirements are small when the regenerant is not recycled. When both solvent
and solute are recovered, the steam requirements for distillation (up to three stills required)
will be significant. If the regenerant is not recycled, it must be disposed of. If the regenerant
is recycled (e.g., by distillation), the still bottoms must be disposed.
Capital costs are moderately large; while no furnace is needed for regeneration (an
expensive item with carbon systems), resins costs are high. Operating costs may be below
$1/1000 gal in some applications, but may reach $5-20/100 gal when concentrated waste
streams are treated and the solute recovered. Credit for recovered solute can allow a system
to operate at a profit in favorable cases.
V. OUTLOOK FOR WASTES
Resin adsorption is particularly attractive for removing organics from aqueous waste
streams when material recovery is desirable, and when the waste stream contains high levels
of dissolved inorganic salts. Applications appear to be expanding.
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BIOLOGICAL TREATMENT: ACTIVATED SLUDGE
I. CONCLUSIONS AND RECOMMENDATIONS
Activated sludge treatment is extensively used in industry, and is probably the most
cost-effective method of destroying organics present in an aqueous waste stream. Neutraliza-
tion and equalization of the waste stream, as well as suspended solids removal, should
precede the activated sludge system. It is a safe and reliable process which is relatively
uncomplicated to operate and relatively inexpensive. Improved understanding of activated
sludge microbiology and enzyme catalysis will improve process operating efficiencies in the
future.
II. PROCESS
Aqueous organic waste streams having less than 1% suspended solids have flocculated,
biological growths continuously circulated and contacted in the presence of oxygen. Since
the process was introduced at the turn of the century it has been modified through
improved methods of maintaining aerobic conditions under varying organic loadings.
The process involves an aeration step, followed by solids-liquid separation, with recycle
of a portion of the solids. The basic system has an open tank for the mixture of the active
biomass with influent wastewater and air, followed by a clarifier. Bacteria in activated
sludge systems serve to perform hydrolysis and oxidation reactions.
III. APPLICATIONS TO DATE
The activated sludge process has been applied extensively to treat wastewater from
municipal sewage plants, canneries, paper and pulp mills, refineries, breweries, and steel,
textile, petrochemical, pharmaceutical, and timber processing plants. It has also been
applied to photo processing wastes and to the propylene glycol wastewater from polyvinyl
chloride production.
IV. ENERGY, ENVIRONMENT, ECONOMICS
The activated sludge system is energy-intensive, with over 10% of total operating cost
based on energy needed for pumping, aeration and clarification. The system is basically
environmentally sound; no chemicals are added and natural degradation takes place.
Capital costs are about 10^ per 1,000 gallons for a 10 mgd facility. These costs increase
to over $ 1 for facilities handling less than 1 mgd. Processes handling dilute wastewaters are
reported to have total costs of 10-40^ per 1,000 gallons.
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V. OUTLOOK FOR WASTES
Activated sludge systems are employed in at least two facilities for treatment of
hazardous wastes. The system is environmentally sound because it employs natural micro-
bial metabolic processes; no chemicals are added.
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BIOLOGICAL TREATMENT: AERATED LAGOONS
I. CONCLUSIONS AND RECOMMENDATIONS
The aerated lagoon biological treatment process decomposes organics in wastewater
containing less than 1% solids, employing essentially the same microbial reactions as
activated sludge. The aerated lagoon, however, does not have a sludge recycle system for
continuous circulation of microorganisms, and microbial strains do not acclimatize to the
same extent. BOD removal efficiencies range from 60 to 90%. The process is not as
attractive for industrial waste treatment as the activated sludge process; removal efficiencies
are not as high and the process is less flexible in maintaining effluent limitations under
varied influent loading.
II. PROCESS
The aerated lagoon technique developed from adding artificial aeration to existing
waste stabilization ponds. Usually the lagoon is an earthen basin with sloping sides and
about 6-17 feet depth. For the treatment of industrial wastes, it may be necessary to line
the basin with an impermeable material. Because wastewaters in aerated lagoons are generally
not as well mixed as those in activated sludge basins, a low level of suspended solids is
maintained. If mixing and aeration are not complete, a portion of the solids settles to the
bottom and undergoes anaerobic microbial decomposition. Retention times are slightly
longer than for activated sludge; and where anaerobic decomposition is encouraged, the time
is even longer.
III. APPLICATIONS TO DATE
The process has been successfully used for petrochemical, textile, pulp and paper mill,
cannery, and refinery wastewaters.
IV. ENERGY, ENVIRONMENT, ECONOMICS
For comparable treatment efficiency, energy requirements are comparable to those for
activated sludge treatment; but generally the aerated lagoon employs less energy for aeration
and longer retention periods. Chemical requirements are essentially limited to addition of
nutrients. As in activated sludge treatment, the effluent is a clarified liquid and a biomass
sludge residue; the biosolids are more difficult to flocculate and settle from the mixed liquor
because of the longer retention time.
Total costs range from 10 to 30(//1000 gallons of dilute influent; if basin lining and
high aeration is required, treatment costs may be nearly $2/1000 gallons.
V. OUTLOOK FOR WASTES
The process is not as attractive as activated sludge treatment for a wastewater influent
with highly variable organic and metal concentrations.
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BIOLOGICAL TREATMENT: ANAEROBIC DIGESTION
I. CONCLUSIONS AND RECOMMENDATIONS
Anaerobic digestion is a biological treatment process for the degradation of simple
organics in an air-free environment. Part of the carbon substrate is used for cell growth and
the other is converted to methane and carbon dioxide gas. The microbiology is complex and
still not well understood. Two types of interdependent organisms are present, and steady-
state environmental conditions must be maintained to keep them balanced. Because of this
delicate balance, the process is not suitable for treatment of most industrial processing
sludges. Oil, fat, and grease are also troublesome.
II. PROCESS
The organic sludges and biomass sludges from primary clarification and biological
treatment are processed to reduce their volume and improve their stability. In the conven-
tional process, the waste stream is fed into the middle zone of a closed tank with no
agitating mechanism. The solids are digested by the organisms, gas rises, bringing scum to
the surface, and the gas is collected from the roof of the tank. Usually this gas is used to
maintain the temperature of the installation and sometimes to heat other parts of the plant.
The digested sludge settles to the bottom of the tank after 30 to 60 days. There is only a
small volume of digested sludge, which is stable and inert and can be disposed of for land
reclamation or by ocean dumping. The bacteria are sensitive to pH, temperature, and the
composition of the waste, but usually with time the system will achieve its own balance.
Modifications have been made for some installations, usually involving agitation or heating,
shortening the process to several days to two weeks.
III. APPLICATIONS TO DATE
Most installations have been for the digestion of sewage sludge, as the final step in a
complete municipal waste treatment facility. Boston and Chicago both use anaerobic
digesters: Boston disposes of the waste by ocean dumping; Chicago, whose plant is the
world's largest, treating a billion gallons of wastewater per day, uses the waste for land
reclamation. In the past 20 years, the system has been studied for meat packing wastes, and
there are several plants operating commercially. It has also been studied for cotton kiering
liquor, brewery wastes and alcohol distillery wastes.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy demands are relatively low; some electric power is needed to mix the reactor
contents, recycle some of the effluent sludge to the reactor and heat the incoming sludge.
Essentially all of the power for the heat exchanger is provided through production of
methane gas.
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The presence of arsenate or mercury in anaerobic digesters could lead to formation of
toxic compounds.
In municipal wastewater treatment plants, costs for anaerobic digestion are difficult to
segregate. Estimates for a facility treating 100,000 gal/day of sludge with 5% solids would
be: capital investment, $1.25 million,annual fixed costs would be $219,000, and variable
costs $171,000. The cost for treating 103 gallons would be $10.69.
V. OUTLOOK FOR WASTES
There seems to be a potential for disposal of feed lot wastes, culture material from
pharmaceutical processing, and food processing wastes. For industrial processing sludges, the
method may be suitable if there is a steady volume and flow, oil and grease are removed,
and soluble metal content is low.
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BIOLOGICAL TREATMENT: COMPOSTING
I. CONCLUSIONS AND RECOMMENDATIONS
Composting provides a means of achieving aerobic digestion of organic wastes by
microorganisms inthepresenceoftheirownreleasedheat.lt is the only biological treatment
process relatively insensitive to toxicants and it encourages adsorption of metals. Costs are
higher than for other biological processes, but lower than for incineration.
II. PROCESS
Composting basically involves piling ground waste in windrows and aerating the piles
by periodic turning. All that need be done is scheduling of spreading and turning with
earthmoving equipment, adding some nutrients and alkalis if necessary, and providing for
collection of leachate and runoff water to protect groundwater. There are over 30 process
modifications involving rotating drums, forced aeration, etc. Complete digestion of most
organic wastes take place in three or four months, although refinery wastes or other difficult
organics may take up to a year.
III. APPLICATIONS TO DATE
Systematic composting has been widely used in Europe, where there is a ready market
for composted waste as an organic soil conditioner. Most of the demonstration projects in
the United States have closed for lack of a market for humus, but some cities use this
cost-effective disposal technique for municipal refuse and give the compost away. Chicago
uses the system to dispose of high-strength organic sludges, and several petroleum refineries
use it for refinery wastes. It has also been used for cannery solids, pharmaceutical and meat
packing sludges.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy demand is low, limited primarily to fuel costs to operate earthmoving equip-
ment and pumps.
The only emissions from composting are carbon dioxide, steam, a liquid effluent
containing partially oxidized organics and a barnyard smell indicative of healthy microbial
activity.
Costs for composting are about $30/thousand gallons of influent, exclusive of land
acquisition or further treatment of collected leachate. The capital expenditure to handle
100,000 gpd would be $1.5 million; fixed costs $275,000 annually and variable costs
$802,500.
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V. OUTLOOK FOR WASTES
Composting is applicable to high-organic wastes, including oils and tars and industrial
processing sludges.
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BIOLOGICAL TREATMENT: ENZYME TREATMENT
I. CONCLUSIONS AND RECOMMENDATIONS
Enzyme treatment of industrial processing wastes is totally impractical. Enzymes
catalyze specific reactions and cannot adapt well to the varying composition of typical
waste streams. Furthermore, enzyme production is very expensive.
II. PROCESS DESCRIPTION
Enzymes are highly selective chemical catalysts which act on specific molecules. The
urease enzyme, for example, breaks down urea into carbon dioxide and ammonia. A
hydrolase enzyme derived from yeast has been shown to oxidize phenol to carbon dioxide
and water. The cellulose enzyme, produced by a stream of fungus, Trichoderma viridi,
catalyzes the hydrolysis of cellulose to glucose.
III. APPLICATIONS TO DATE
There are no known full-scale applications of enzyme treatment processes in hazardous
waste management. There are commercial applications in meat tenderizing, de-hairing of
hides prior to tanning, cheese-making, pharmaceutical manufacture, and detergent
production.
The Army's Natick Research and Development Command is operating a 1000 Ib/mo.
pilot plant to convert waste paper into glucose. A number of Government, university, and
industrial laboratories are investigating the use of lactose for recovery of monosaccharides
from cheese whey. Groups at Oak Ridge National Laboratories and the University of
Pennsylvania have studied the enzyme decomposition of phenol.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Due to the specificity of enzyme reactions and the fact that current waste treatment
applications are limited in number and lab scale, no useful generalizations can be made
about energy, economics, or potential environmental impacts.
V. OUTLOOK FOR WASTES
Enzyme treatment may be useful for specialized industrial applications, particularly
in cases where salable reaction products result. Enzymes have little or no potential in
general waste treatment.
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BIOLOGICAL TREATMENT: TRICKLING FILTERS
I. CONCLUSIONS AND RECOMMENDATIONS
The trickling filter process is a proven technology for the decomposition of organics in
waste streams with less than 1% suspended solids. The process brings the wastewater in
contact with aerobic microorganisms by trickling the water over media supporting the
microorganisms. BOD removal efficiencies range from SO to 85%. The process is used in
industry to accept wastewater loading variations and provide a relatively uniform effluent
for treatment by other biological processes, such as activated sludge.
II. PROCESS
Wastes are sprayed through the air to absorb oxygen, and then allowed to trickle
through a bed of rock or synthetic media coated with a slime of microbial growth. Process
modifications employ various media and depths to retain the microorganisms under varying
hydraulic and effluent recycle conditions. The primarily metabolic processes are aerobic, and
the microbial population is similar to the activated sludge population. However, because of
the relatively short contact time, the percentage removal of organics is not as great.
The process involves open tanks or towers to house the filter packing, followed by
effluent clarifiers. Recycle pumps may be used to recirculate filter effluent. A rotating spray
dosing system feeds influent wastewater to the filter surface.
III. APPLICATIONS TO DATE
Trickling filters have been extensively used in sewage treatment and in treatment of
refinery wastewaters containing oil, phenol, and sulfide. They are applicable to the same
industrial waste streams as the activated sludge process, including cannery, pharmaceutical,
and petrochemical wastes.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy demands are low, as little as one-tenth that of activated sludge treatment.
Dilute wastewater is treated at a total cost between 10 to 30^ per 1000 gallons; for
concentrated waste requiring filter recycle the cost may be $2 per 1000 gallons. The process
effluents are a liquid wastewater from which a major portion of the dissolved organics have
been removed and a biomass sludge.
V. OUTLOOK FOR WASTES
The process could be used in sequence with other biological treatment, such as
activated sludge, but it is not generally efficient enough to use as the sole method of
biodcgradation.
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BIOLOGICAL TREATMENT: WASTE STABILIZATION PONDS
I. CONCLUSIONS AND RECOMMENDATIONS
Waste stabilization ponds utilize natural biodegradation reactions in wastewaters con-
taining less than 0.1% solids with low concentrations of organics. The process is more
sensitive to concentrations of inorganics and suspended solids than any of the other
biological treatments discussed in this report. It is suitable for industrial wastes only where
preliminary treatment has removed most contaminants and final effluent polishing is needed
before discharge to a receiving water.
II. PROCESS
Waste stabilization ponds are large shallow basins where wind action provides aeration
and a mixed autotrophic and heterotrophic microbial population provides decomposition of
organics over a long retention time. Deep ponds, more than 4 feet deep, may promote
anaerobic decomposition of settled sludge.
III. APPLICATIONS TO DATE
Waste stabilization ponds have been widely used for sanitary sewage and dilute
industrial wastes, mostly to provide final effluent polishing. Industries using the method
include meat and poultry packing, canneries, dairies, iron and steel works, paper and pulp
mills, textile mills, oil refineries and petrochemical plants.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Large land acreage is the principal capital cost; energy and chemical requirements are
insignificant. Total costs for treating dilute wastewaters in unlined basins range from 5 to
15^ per 1000 gallons; for more concentrated waste streams in clay-lined basins, the cost is
about $1.70 per 1000 gallons. Energy is needed only for pumping. A polished liquid
effluent and some biomass sludge are the end-products.
V. OUTLOOK FOR WASTES
The process can be employed only where substantial land acreage is available and
where climate is suitable. Toxic inorganics must be removed before waste stabilization
ponding because of the system's high sensitivity to inhibitors. The use of the method for
final polishing provides extra insurance that final effluent guideline limitations will be met.
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CALCINATION
I. CONCLUSIONS AND RECOMMENDATIONS
Calcination is a well established process, and one of the few that can satisfactorily
handle sludges. Calcination is recommended as a one-step process for treatment of complex
wastes containing organic and/or inorganic components. The organics are destroyed; the
inorganics are generally reduced in volume and converted into a form of low leachability
suitable for landfill.
II. PROCESS DESCRIPTION
Calcination is a thermal decomposition process, generally operated around 1000°C at
atmospheric pressure. It can be applied to aqueous solutions, slurries, sludges, and tars to
drive off volatiles and to produce a dry powder or sintered solid. Typical calciners include
the open hearth, rotary kiln, and fluidized bed.
III. APPLICATIONS TO DATE
Industrial applications include production of cement, lime, magnesia, titania, and
wall plaster, and smelting of sulfide and carbonate ores. Waste treatment applications in-
clude recalculation of lime sludges from water treatment plants; coking of heavy residues and
tars from petroleum refining operations; concentration and volume reduction of liquid
radioactive wastes; and treatment of mixed refinery sludges containing hydrocarbons,
phosphates, and compounds of Ca, Mg, K, Na, S, Fe, and Al.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy requirements are generally high, but depend on the water and organic content
of the waste stream. Calcination of dry material requires about l-3xl06 Btu/ton of solid
product; calcination of a sludge or slurry with 90% water requires about 20x106 Btu/ton of
solid product. If this waste stream contains a combustible organic fraction, the energy re-
quirements are reduced.
In general, calcination systems will require fairly extensive air pollution control equip-
ment, including particulate-removal devices, wet scrubbers, and possibly final gas adsorp-
tion systems.
Capital investment costs for a calciner are in the range of $10,000-$30,000/ton of
throughput daily. Operating costs are highly variable, depending on the water and organic
content of the waste stream, and the possibilities for resource recovery credits.
V. OUTLOOK FOR WASTES
Calcination has been used widely in industrial and waste treatment applications. Its use
is likely to expand, particularly in the treatment of tars, sludges, and other residues which
present particularly difficult problems for disposal.
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CATALYSIS
I. CONCLUSIONS AND RECOMMENDATIONS
Whenever a waste stream can usefully be treated by a chemical transformation process,
the possibility of catalyzing the reaction should be considered. In general, if a transforma-
tion can be successfully catalyzed, operating costs and energy requirements will be reduced.
II. PROCESS DESCRIPTION
Catalysis is not a process in itself, but rather a modification of the rate or mechanism
of chemical reaction processes through the use of catalysts, which are themselves unchanged
at the end of a reaction.
III. APPLICATIONS TO DATE
The industrial applications of catalysts in the petroleum refining, chemical, phar-
maceutical, and textile industries are legion.
In the field of waste treatment, catalytic oxidation is used quite widely as an alternative
to incineration in the decomposition of waste organics. A number of catalytic processes
have been investigated in the laboratory for destruction or detoxification of chlorinated
pesticides, oxidation of cyanides, sulfides, and phenols, decomposition of sodium hypo-
chlorite solutions, and conversion of mixed carboxylic acid waste streams to fumaric acids
for recovery.
IV. ENERGY, ENVIRONMENT, ECONOMICS
In general, a catalytic process operates at a much lower temperature than the equiva-
lent non-catalytic process and hence consumes less energy.
Environmental impacts are generally the same as those of the non-catalytic process.
Catalytic processes may be higher in capital costs than non-catalytic processes in some
cases. However, the less severe operating conditions (lower temperatures and/or pressures)
almost always result in lower overall operating costs.
V. OUTLOOK FOR WASTES
As the use of chemical processing in waste treatment increases, the effort to develop
catalytic processes should be increased as well. A great deal of work is needed to demon-
strate the commercial practicality of catalytic reactions tested in the laboratory, and ex-
ploratory work could be useful on catalytic hydrogcnation and low-temperature air
oxidation.
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CENTRIFUGATION
I. CONCLUSIONS AND RECOMMENDATIONS
Centrifugation is a well-developed liquid/solid separation process being used in a
variety of full-scale applications for material processing and waste treatment. In treating
hazardous wastes, centrifugation can be used to greatest advantage to increase the solids
concentration, and thereby reduce the volume, of a high concentration liquid/solid mixture
(sludge) by partially separating the liquid and solid phases ("sludge dewatering").
Centrifugation is generally technically and economically competitive with other sludge
dewatering processes (e.g., vacuum filtration or the use of filter presses) and should be
considered as a potential process for concentrating hazardous waste sludges and slurries.
Equipment is commercially available in a large variety of sizes and configurations.
II. PROCESS
Centrifugation is a physical process whereby the components of a fluid mixture are
separated mechanically by the application of centrifugal force, applied by rapidly rotating
the mass of fluid within the confines of a rigid vessel. Centrifugal forces acting on the
revolving mass of fluid cause the solids suspended in the fluid to migrate to the periphery of
the vessel where they can be separated. The particles are removed as a liquid/solid mixture
significantly more concentrated than the original liquid.
III. APPLICATIONS TO DATE
Some common applications of centrifugation are in separating oil and water mixtures;
clarification of viscous gums and resins; classification and removal of oversize particles and
unground pigment from lacquers, enamel and dye paste; clarification of essential oils,
extracts, and food products, such as homogenized milk and fruit juices; separation of
micro-organisms from fermentation broths, recovery of finely divided metal such as silver
from film scrap and platinum from spent catalyst; separation of acid sludges from the acid
treatment of petroleum; recovery of crystalline solids from brine; dewatering of fibrous
solids such as paper pulp and chemical fibers; dewatering and removal of starch from potato
fibers, etc. Probably the main application for centrifuges at present is the dewatering of
waste sludges.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Power requirements for centrifugation are typically 0.3-1.2 horsepower per gallon per
minute of inlet waste feed. Power consumption is equal to or slightly greater than for other
sludge dewatering processes.
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For most sludge dewatering purposes, centrifugation is generally cost-competitive with
other dewatering processes such as vacuum filtration or press filtration.
A conveyor bowl type centrifugation system capable of dewatering 6 tons per day of
sludge (dry basis) will have an installed capital cost of approximately $140,000 and a total
operating cost (including amortization) of $34.50 per ton of solids dewatered. In most
applications, costs range from $20-$45/ton.
V. OUTLOOK FOR WASTES
The major application of centrifugation to waste treatment is the dewatering of waste
sludges generated by water pollution control systems. Centrifuges have for many years been
used on biological sludges from municipal treatment plants and from pulp and paper mills.
Some expect the technique to replace vacuum filtration as the most common dewatering
technique, especially for sticky or gelatinous sludges. It will also find further application in
removing soluble metals from wastewater, as from the wet scrubbers used in the steel
industry, to dewater sludges generated from sulfur dioxide air pollution control systems,
etc.
Because it is capable of totally closed operation, centrifugation is particularly well
suited to treating liquids that are volatile, flammable, or otherwise pose health and/or safety
hazards to operating personnel.
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CHLORINOLYSIS
I. CONCLUSIONS AND RECOMMENDATIONS
Chlorinolysis is capable of converting most liquid chlorinated hydrocarbons completely
to carbon tetrachloride. It is not really a waste treatment process, but a manufacturing
process that uses chlorocarbon waste streams and residuals as feedstocks. The process has
excellent resource recovery potential (sufficient wastes are generated in the Gulf Coast
region to support at least one 25,000 ton/yr chlorinolysis plant) if there is a market for the
carbon tetrachloride. There may be, however, legal and institutional problems that might
hinder transfer of wastes from generators to an operating chlorinolysis unit.
II. PROCESS
At temperatures around 500°C and pressures of about 200 atm in the presence of
excess chlorine, the carbon-carbon bonds of hydrocarbons can be broken, and the molecules
recombined to react with chlorine to form carbon tetrachloride. Because liquid chlorine is
highly reactive, reactors and piping must be high-purity nickel, surrounded by a stainless
steel jacket. The organic feedstock and preheated chlorine are introduced to the reactor,
which is heated to initiate chlorinolysis; subsequently the process provides its own heat. At
the end of the process, the pressure is released and the products are cooled and drawn off.
Subsequent processing by distillation yields carbon tetrachloride, the principal product for
sale.
III. APPLICATIONS TO DATE
This is not a waste treatment process, but a production process that can utilize waste
streams. A semicommercial plant to produce 6000-8000 tons/year has been operating in
Germany and a 50,000 ton/year plant is planned for the same site.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Electricity and fuel requirements per ton of carbon tetrachloride are relatively small —
135kWh and 794 Btu, respectively. Chlorinolysis offers the opportunity of resource re-
covery, but the process involves hydrochloric acid and phosgene gas effluents. Neutraliza-
tion of the effluent streams will produce sodium hypochlorite, which is toxic to aquatic life.
Capital and operating costs for a plant processing 25,000 metric tons/year of mixed
chlorinated hydrocarbon wastes are estimated at $19,700,000/year; the process could
produce carbon tetrachloride at 10.24 per Ib, and the selling price is now 19
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DIALYSIS
I. CONCLUSIONS AND RECOMMENDATIONS
Dialysis is one of the earliest membrane processes. It can separate salts and low mole-
cular weight organics from colloids and high molecular weight solutes in aqueous waste
streams. However, both of the output streams are more dilute than the feed stream, and
neither is likely to be more suitable for disposal or recovery than the feed stream. Hence,
dialysis has little or no potential for general waste treatment applications.
h. PROCESS DESCRIPTION
A solute-containing feed stream is passed across one free of a semi-permeable mem-
brane and a higher volume wash stream is passed across the opposite face. Small solute
molecules are transferred to the wash stream by diffusion across the membrane. Larger
molecules and colloids are retained in the feed stream.
III. APPLICATIONS TO DATE
The best known current application of dialysis is hemodialysis, which removes salts,
urea, and other wastes from the blood of people suffering from chronic kidney failure.
Since the 1920's, dialysis has been used in the rayon industry to separate caustic soda from
hemicellulose wastes. There are also other smaller scale applications in pharmaceutical and
biochemical laboratories for special production and purification. Dialysis equipment is
available commercially.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy requirements are low, being limited to the pumping of feed and wash streams.
The two diluted product streams could prevent difficult disposal problems if not
reusable.
Capital costs depend more on the amount of material to be separated than on the
waste stream throughput. A commercial dialyzer separating 1000 Ib/day of solute would
cost about $3000.
V. OUTLOOK FOR WASTES
Dialysis is a mature technology; no major new developments are expected which would
make the process at all useful for hazardous waste treatment.
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DISSOLUTION
I. CONCLUSIONS AND RECOMMENDATIONS
Dissolution is a first step that removes major or minor constituents from solids. The
process is applicable to any solids that can be wetted by a suitable liquid. We recommend
that more emphasis be placed on more complete characterization of solids to aid in
specification and testing of possible dissolution processes. Efforts should also be made to
utilize lower quality or waste reagents where possible.
II. PROCESS
Dissolution may be defined as the complete or partial transfer of one or more
components from a solid to a liquid phase in contact with the solid. The reaction involves
some degree of chemical transformation, such as solvation, ionization, or oxidation. The
solids are contacted by the reagent in a mixer, following which the slurry is separated. Heat
may be applied to speed the process and provide increased solubility. Solids can be treated
sequentially with different reagents to remove components selectively. The products are a
wastewater stream that requires further treatment, and residual solids that may be suitable
for disposal, reuse, or further treatment.
III. APPLICATIONS TO DATE
Dissolution has been widely used in metallurgy since the early 1800's and in the
synthetic chemical industry since its beginning. Many of these applications (e.g., separation
of metals from ores) are closely related to treatment of inorganic wastes, but there appears
to be little large-scale application to waste treatment. One installation involves production
of chemicals for agriculture and other use from galvanizing wastes and flue dust. Another is
used for recovery of metallic copper from scrap, and a semi-commercial plant is being
considered for recovery of metal from plating slimes. Several pilot and laboratories studies
are now going on.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy requirements are limited to electricity for mixing and pumping, and heat, if
required. Emissions to water are not harmful if the liquors used and produced are conveyed
to the next process step without inadvertent losses. No land disposal problems are antici-
pated if leached solids are adequately washed to remove leach liquor. Emissions to air will
be significant only when gas is evolved in the process, or where an unintended reaction takes
place (e.g., reaction of traces of sulfides in water to give off hydrogen sulfide).
The diversity of materials potentially suitable for dissolution and the circumstances of
reaction vary considerably. The process is especially sensitive to chemical and labor costs.
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An approximate cost for dissolving a hypothetical metal finishing sludge waste using fresh
sulfuric acid reagent would be: $61 per ton of input solids or $300 per ton of desired metal
removed; the cost of sulfuric acid is $24 per input ton.
V. OUTLOOK FOR WASTES
Further applications for waste treatment depend on cost-sensitive factors, such as
utilization of waste reagents, and on better understanding of composition of sludges and
mixed metal compounds.
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DISTILLATION
I. CONCLUSIONS AND RECOMMENDATIONS
Distillation is a unit operational process that is fully developed commercially and is
often employed to separate or purify liquid organic product streams. It is a non-destructive
process, and practical limitations are primarily economic. With more stringent limitations on
air, liquid effluents, and land site disposal, and with the rising cost of organic chemicals,
distillation could become more competitive with other methods for recovery of useful
materials from waste streams.
II. PROCESS
The basic principle of distillation is as simple as it is old: when a mixture of liquids is
boiled, the vapcr usually differs in composition from the liquid that remains. Only since the
19th century, however, has distillation been conducted on a large scale as a steady-state
operation.
In general, a feedstock is charged to a large vessel (still) which is heated, and vapors are
removed as they are formed, and then condensed. There are a number of variations on this
basic process.
III. APPLICATIONS TO DATE
Distillation has wide industrial application in petroleum fractionation, organic chemical
purification, organic chemical intermediate manufacture, solvent recovery, and cryogenic air
separation to produce oxygen, nitrogen, and argon.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Because of the variables involved, there is no such thing as a typical cost on a unit
product or unit feed basis.
Distillation creates no air or liquid effluent problems.
An economic analysis of a system that might be used for different types of organic
liquid waste streams was made, based on a capacity of 8000 Ib 20% acetone in water
waste/day. The solvent recovery cost in this system would be 4.2
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oil. The process is not suitable for treatment of thick, polymeric materials, slurries, sludges,
or tars that can cause operational problems. The types and quantities of organic solvent and
chemical wastes that are treated by distillation will increase as effluent regulations become
more stringent.
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ELECTRODIALYSIS
I. CONCLUSIONS AND RECOMMENDATIONS
Electrodialysis has not been employed on a full-scale basis for any hazardous waste
problem, per se. Nevertheless, it may have applicability where it can be tied into further
concentration or reuse schemes. It will profit by the fact that it is a mature technology with
well-known performance characteristics and price, and therefore can be easily evaluated as a
potential component of any multi-process treatment being considered.
II. PROCESS
The general principle of electrodialysis is the separation of an aqueous stream under
the action of an electric field into two streams, one enriched and one depleted. Success
depends on synthetic membranes, usually based on ion-exchange resins, which are permea-
ble only to a single-charge type of ion. Cation exchange membranes permit passage of only
positive ions, while anion membranes permit only negatively charged ions to pass through.
The feed water passes through compartments formed by the spaces between alternating
cation-permeable and anion-permeable membranes held in a stack. At each end of the stack
is an electrode having the same area as the membranes. A d-c potential applied across the
stack causes the positive and negative ions to migrate in opposite directions. Feed material is
first filtered to remove suspended particles that could clog the system. An operating plant
usually contains many recirculation, feedback and control loops and pumps to optimize the
concentrations and pH at different points for most efficient operation.
III. APPLICATIONS TO DATE
Electrodialysis has been used for desalination since the 1950's. The largest number of
installations is in the production of potable water from brackish well or river water.
Hundreds of such units, some of which can handle more than one million gallons per day,
are in use throughout the world.
In the food industry, electrodialysis is used for desalting whey and de-ashing sugar. The
chemical industry uses the technique for enriching or depleting solutions, and for removing
mineral constituents from product streams.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Electrical requirements vary, but conventional systems take about 5 kWh of energy for
each 1000-ppm reduction of salt in each 1000 gal. purified product water and up to 3 kWh
to pump each 1000 gal. products.
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The product streams must be recycled, sold, or otherwise disposed of. Electrodialysis
may generate low levels of toxic or flammable gases that might present a hazard in an en-
closed space.
The capital costs for electrodialysis are modest, about 20-25% of the total cost of
water treatment. Both capital and direct operating costs are dependent on the volume of
water treated and on the salts removed. Total water production costs of less than $.50/103
gal are reported for salt reduction from 2000 ppm to 500 ppm in plants treating 106 gal/day
or more. Other plants may have higher costs or may receive significant credits for reclaimed
material.
A typical electrodialysis system to treat rinse tanks from an acid nickel plating line
might cost about $6.00/103 gal.
V. OUTLOOK FOR WASTES
Pilot operations have been carried out in the desalting of sewage plant effluent,
sulfite-liquor recovery, and acid mine drainage treatment. Treatment of plating wastes and
rinses, particularly to salvage chromium, may have some potential.
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ELECTROLYSIS
I. CONCLUSIONS AND RECOMMENDATIONS
Electrolytic processes may be considered for reclaiming heavy metals, including toxic
metals from concentrated aqueous solution and for polishing dilute metallic wastewaters.
They are not generally useful for dissolved organics, organic waste streams or viscous and
tarry liquids.
II. PROCESS
Electrolysis refers to the reactions of oxidation or reduction that take place at the
surface of conductive electrodes immersed in an electrolyte, under the influence of an
applied potential.
III. APPLICATIONS TO DATE
Electrolysis, including electroplating and anodizing, has been an important process of
industrial chemistry for many years. Chlorine production, for example, depends on elec-
trolysis, and many commercial metals are refined by electrolytic processes. Metals may be
obtained from primary ores, and magnesium and aluminum are processed by electrolysis in
molten salt baths. Electrolysis for waste treatment has been employed to a limited extent
depending largely on costs. The most frequent application is the partial removal of
concentrated metals such as copper from waste streams for recycle or reuse. Other applica-
tions which have been successfully piloted include oxidation of cyanide wastes and separ-
ation of oil-water mixtures.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Electrical energy costs range from 10 to 35% of total operating costs, with treatment
of concentrated metals at the low end, and dilute streams or cyanide treatment at the high
end.
Gaseous emissions may exist; some may be vented to the atmosphere, others may have
to be scrubbed or otherwise treated. The process wastewater may be reusable or disposable,
or may have to undergo further processing.
Costs are highly dependent on the concentration and nature of the undesirable
material. Electrolysis may offer significant trade-offs between capital and operating costs,
depending on chemical and economic variables.
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ELECTROPHORESIS
I. CONCLUSIONS AND RECOMMENDATIONS
No suitable equipment for electrophoretic treatment of hazardous wastes is available.
Many critical problems would have to be solved before such equipment could be developed,
and even if the design problems were solved, there is no assurance that the process would be
operationally practical. Further consideration of electrophoresis cannot therefore be
justified.
II. PROCESS DESCRIPTION
Electrophoresis is the transport of electrically charged particles under the influence of
a DC electric field. The charged particles (generally colloids in the 1-20/u size range)
migrate to a collecting membrane for subsequent removal.
III. APPLICATIONS TO DATE
Electrophoresis is used extensively as a laboratory tool in the analysis and separation of
proteins, polysaccharides, and nucleic acids. It has also been used commercially for creaming
of rubber latex, and for fractionation of animal sera for veterinary vaccines. Numerous
proposed applications have been researched and shown to be technically feasible. These in-
clude deposition of paints, polymers, ceramics, and metals. The process has also been con-
sidered for water purification (e.g., for separation of emulsions, and for color, virus, and
algae removal).
IV. ENERGY, ENVIRONMENT, ECONOMICS
In aqueous systems, the electrical energy requirements are of the order of 7 kWh/
1000 gal.
The process may evolve gases from electrode reactions. Both the concentrated sludge
and the "treated" liquid may require subsequent disposal.
Capital costs would be lower than the costs for electrodialysis. Operating costs might
be in the range of $0.50-2.00/1000 gal, depending on the application.
V. OUTLOOK FOR WASTES
At least 5-10 years of effort would be required to develop electrophoresis equipment
for waste treatment. In view of the lack of scientific and practical guides available, and the
very significant problems of controlling electrode reactions, pH, conductivity, flow, tem-
peratures, and membrane plugging, there is even some question whether an R&D effort
would be successful.
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EVAPORATION
I. CONCLUSIONS AND RECOMMENDATIONS
Evaporation is a well-defined well-established process, used throughout industry. It is
capable of handling liquids, slurries, sludges, both organic and inorganic, containing sus-
pended or dissolved solids or dissolved liquids where one of the components is nonvolatile.
It is energy-intensive, and specialized equipment can be expensive.
II. PROCESS
The process and equipment for applying heat to the solution are similar to that for
distillation, except that the vapor is not separated. Open, direct-fired pans or solar evapora-
tion from ponds are still used in some applications, but most evaporators are heated by
steam condensing on metal tubes, through which the solution flows. Usually the steam is at
low pressure and the boiling liquid is under a moderate vacuum. There are numerous
variations on equipment and processes, depending on the application.
III. APPLICATIONS TO DATE
In the chlor-alkali industry, evaporation is used to concentrate caustic soda and to
produce calcium chloride. Evaporation of saline water to provide fresh water is well
established; U.S. plants have a capacity of about 67 million gpd. Concentration of sulfuric
and hydrochloric acids, citrus fruit juice, phosphates, and milk whey; crystallization of salts,
sugar; dehydration of Glaubers salt, sulfur sludges are all well established.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy requirements vary considerably within a range of 100 to 1100 Btu/lb liquid
evaporated, with the average closer to the lower figure.
There are generally no pollution problems with evaporation vapors. Where the vapors
contain organics, the liquid is condensed and either disposed of or recovered by another
process, such as distillation.
Economic analysis of an operation to concentrate 100,000 gallons per hour of kraft
black liquor shows capital investment of $1.3 million. Yearly operating costs would be
$1.06 per 1000 Ibs of water.
V. OUTLOOK FOR WASTES
Evaporation is already used in the treatment of radioactive wastes, and is very effective
where suspended solids content is high and other methods are difficult. A combination of
evaporation and simultaneous combustion is used to dispose of TNT wastes. Other
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applications include photographic chemicals, papermill wastes, molasses distillery wastes,
and pickling liquors. Evaporation is not suitable for tars, solids, dry powders, or gases.
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FILTRATION
I. CONCLUSIONS AND RECOMMENDATIONS
Filtration is a well-developed liquid/solid separation process currently applied to the
full-scale treatment of many industrial wastewaters and waste sludges. For the treatment of
hazardous wastes, filtration can be used to perform two distinctly different functions:
1) Removal of suspended solids from a liquid (usually aqueous) waste stream
with the objective of producing a purified liquid.
2) Increasing the solids concentration, and thereby reducing the volume, of a
high concentration liquid/solid mixture (sludge) by removing liquid from the
mixture ("sludge dewatering")-
As a wastewaier treatment process, filtration is usually most applicable when following
some form of flocculation and/or sedimentation. As a sludge dewatering process filtration is
usually technically and economically competitive with other dewatering processes.
We recommend that filtration be considered as a potentially applicable process for
hazardous waste treatment applications requiring the separation of liquid and solid phases.
II. PROCESS
Filtration is a physical process whereby particles suspended in a fluid are separated by
forcing the fluid through a porous medium. As the fluid passes through the medium, the
suspended particles are trapped on the surface of the medium and/or within the body of the
medium. Filter media can be a thick barrier of a granular material, such as sand, coke, coal,
or porous ceramic; a thin barrier, such as a filter cloth or screen; a thick barrier composed of
a disposable material such as powdered diatomaceous earth or waste ash. The pressure
differential to move the fluid through the medium can be induced by gravity, positive
pressure, or vacuum. The intended application has a great influence on both the type of
filter and its physical features.
III. APPLICATIONS TO DATE
The inorganic chemicals industry employs various forms of filtration to separate
precipitated product from waste material. They are commonly used in the manufacture of
titanium dioxide, sodium dichromate, aluminum sulfate, and magnesium. The organic
chemicals industry also employs filter techniques, e.g., removal of acetylene carbon particles
fiom aqueous quench streams, and removal of dye particles from the reaction bath. Rotary
vacuum filters are used to remove impurities in the processing of sugar. Vacuum filtration is
often used to remove impurities from lube oils. Boiler feed water and many types of
industrial process water have stringent specifications on suspended solids. Filtration is often
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used in conjunction with precipitation, flocculation, and sedimentation to remove these
solids. Filtration is also used as the final step in many industrial wastewater treatment
plants.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy requirements for filtration are relatively low. A vacuum filtration system
capable of dewatering 36,000 gal/day of sludge containing 6 tons of solids will have a power
requirement of only 25 horsepower.
The cost of treatment for both vacuum filtration and press filtration is usually within
the range of $20-$45/ton of solids treated (dry basis). For liquid purification the cost of
filtration by granular media filters usually varies from $0.10-$0.50 per 1000 gallons of
wastewater treated.
V. OUTLOOK FOR WASTES
Major applications are and will be in the removal of suspended solids from wastewater
streams and in the volume reduction (dewatering) of waste sludges and slurries. As more and
tighter restrictions are placed on wastewater discharge, filtration will often be used after
precipitation, flocculation, and sedimentation.
Decreased availability of solid waste disposal sites will further encourage the de-
rins of sludees nrinr to Hisnnsal.
watering of sludges prior to disposal.
Non-aqueous liquids can be subjected to filtration for removal of suspended solids, but
highly viscous semi-liquids such as tars are generally not amenable to filtration.
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FLOCCULATION, PRECIPITATION, AND SEDIMENTATION
I. CONCLUSIONS AND RECOMMENDATIONS
Flocculation, precipitation, and sedimentation are fully-developed processes currently
used in a wide variety of industrial processing and waste treatment applications. While
flocculation, precipitation, and sedimentation are individual process steps, they are inter-
related, and are often combined into a single overall treatment process. They can be quite
readily applied to a variety of aqueous hazardous wastes for the removal of precipitable
substances, such as soluble heavy metals and for the removal of solid particles suspended in
the liquid. We recommend that these processes be given serious consideration for removal of
heavy metals and/or suspended solids from an aqueous waste stream. Although the process
theoretically can be used to treat non-aqueous liquids, such applications are very rare.
Precipitation, flocculation, and sedimentation are generally unsuitable for treating heavy
slurries, sludges, and tars.
II. PROCESS
Flocculation is the process whereby small, unsettleable particles suspended in a liquid
are made to agglomerate into larger more settleable particles. Precipitation is a physico-
chemical process where some or all of a substance in solution is removed from the solution
and transformed into a second (usually solid) phase. Sedimentation is a purely physical process
whereby particles suspended in a liquid are made to settle by means of gravitational and
inertial forces acting on both the particles suspended in the liquid and the liquid itself.
III. APPLICATIONS TO DATE
The processes have long been widely used for a variety of industrial applications, such
as in the manufacture of many organic chemicals, the preparation of metal ores, and the
preparation of sugar.
Practically every industry that discharges a process wastewater stream contaminated
with suspended and/or precipitable pollutants employs some form of precipitation, floccula-
tion and/or sedimentation. Examples are: removal of heavy metals from iron and steel
industry wastewater; removal of fluoride from aluminum production wastewater; removal of
heavy metals, from wastewaters from copper smelting and refining, and from the metal
finishing industry.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Hnergy consumption is very low compared to other processes. The processes produce a
waste sludge, which can often present a serious disposal problem.
A large (over 5 million gallons per day) system employing only sedimentation with no
flocculating chemicals will typically treat wastewater at a cost of $0.10-$0.50 per 1000
gallons treated.
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A moderate size (0.5-5 million gallons per day) system employing precipitation,
flocculation, and sedimentation and using moderate dosages of precipitating/flocculating
agents will usually treat wastewater at a cost of $0.50-$3.00 per 1000 gallons.
Small, especially designed systems (less than 0.5 million gallons per day) using high
dosages of precipitating/flocculating agents can have costs that are higher, but these will
rarely exceed $6.00 per 1000 gallons.
V. OUTLOOK FOR WASTES
Precipitation, flocculation, and sedimentation are generally practical, effective, and
relatively low-cost processes for the removal of precipitable soluble substances and sus-
pended particles from aqueous waste streams. The processes are particularly suitable for the
treatment of high volume/low concentration waste streams.
In determining the applicability of precipitation, flocculation, and sedimentation to
specific waste streams, true research and development is usually unnecessary. Past experi-
ence and simple laboratory treatability tests are usually all that is necessary in determining
applicability.
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FLOTATION
I. CONCLUSIONS AND RECOMMENDATIONS
Flotation is a physical-chemical method of separating solid particles suspended in a
liquid, when the valuable products to be separated constitute less than 10% of the total
solids. Although flotation has found only limited application outside the mineral industry, it
is our belief that, with further research and development, the technique could be used to
separate many types of components from mixtures of solids.
II. PROCESS DESCRIPTION
The material is crushed or ground, mixed with water and reagents into a slurry or pulp,
and agitated. Air bubbles carry the selected materials to the surface to form a stabilized
froth, which is then skimmed off, while the waste materials remain. By using the correct
reagents, it is possible to separate similar materials from each other. Some installations
separate only one valuable component from waste; others separate two, three, or even four
products.
III. APPLICATIONS TO DATE
Although flotation has been applied principally to mineral processing to separate
valuable ore from tailings, a few other applications seem to have potential. When cellulose is
recycled from paper, flotation can be used to remove ink, pigments, and coatings. A few
years ago three plants in the United States treated about 25,000 tons of paper per year in
this manner.
Other possible applications outside the mineral industry, though there are no commer-
cial plants, are as a means of removing cyanide from solutions or mixed suspensions. In one
test, about 95% of the cyanide could be removed. Research also shows that microorganisms
can be floated, concentrated, and removed from a suspension.
IV. ENERGY, ENVIRONMENT, ECONOMICS
The typical conventional flotation plant is a relatively large consumer of energy,
averaging about 15 kWh/ton milled. Only about 15% of the total is consumed in the
flotation step, with most of the energy used for crushing and grinding.
Air emissions are not significant, since flotation is a wet process. Dust emissions occur
at the ore crusher and at conveyor transfer points but are controlled with collecting hoods
and water sprays. The waste effluent goes to a tailings dam from which water may be
recycled, especially in arid areas.
Costs depend on the size and nature of the process. Operating costs for sulfide ore
flotations vary from $4/ton ore processed for a 500T/day plant to $1.50/ton fora 10,000
T/day plant.
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V. OUTLOOK FOR WASTES
The best application for the flotation process would be for separating a hazardous solid
from one that is not. Another application would be to separate all solid materials in a slurry;
however, it is difficult to see any reason for doing it this way, when the simpler process of
thickening and filtration would accomplish the same purpose. Heavy metal ions (copper,
nickel, cadmium) and cyanides might be amenable to removal by this process, as well as
such inorganics as carbonyls and fluorides. As far as we know, however, no work has been
done to utilize the process.
On the other hand, some of the reagents commonly used for mineral and ore
processing are themselves hazardous and, if used carelessly, may appear in the tailings. Care
must be exercised in their use and control.
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FREEZE-CRYSTALLIZATION
I. CONCLUSIONS AND RECOMMENDATIONS
Freeze-crystallization has been successfully tested for desalination of brackish waters
in pilot plants. It has been demonstrated in the laboratory for hazardous waste treatment,
and is expected to find commercial applications in the near future.
II. PROCESS DESCRIPTION
Freeze-crystallization involves formation of "pure" ice crystals from a solution, and
concentration of dissolved solutes in a residual brine. The ice crystals may be separated
mechanically from the brine, washed, and melted to yield fresh water (or solvent). The brine
must be treated further, or otherwise disposed of.
III. APPLICATIONS TO DATE
A number of freeze-crystallization processes were developed for desalination, but none
have become commercial. Waste treatment applications tested in the laboratory include:
sulfite liquors; plating liquors; paper mill bleach solutions; arsenal redwater; solutions con-
taining acetic acid, methanol and aromatic acids; ammonium nitrate wastes; and cooling
tower blowdown.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Electrical energy requirements are in the range of about 60-75 kWh/1000 gal of pro-
duct water.
The major environmental problem is associated with further treatment, or disposal
of the brine. Some emissions of refrigerant (e.g., butane or freon) are possible.
Capital costs are estimated to be in the range of $600,000-$800,000. Operating costs
might be in the range of $6-12/1000 gal of product water.
V. OUTLOOK FOR WASTES
Freeze-crystallization appears to be a very promising process for treatment of aqueous
waste streams containing 1-10% TDS. Commercial applications are certainly anticipated
within the next five years. Applications to some non-aqueous waste streams could probably
be developed.
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FREEZE-DRYING
I. CONCLUSIONS AND RECOMMENDATIONS
Freeze-drying (lyophilization) has no apparent potential for treating hazardous indus-
trial wastes. Although freeze-drying is used, commercially for desiccating biological and
sensitive materials, it does not appear adaptable to economical waste processing on a large
scale. The process is slow, costly, and energy-dntensive, with limited use for removing water.
II. PROCESS DESCRIPTION
Freeze-drying is a process for subliming frozen water from a material under high
vacuum. Basic equipment consists of a vacuum chamber, a vacuum source, and appropriate
refrigeration and heating equipment. Suitable feeds include wet solids, sludges, and slurries.
III. APPLICATIONS TO DATE
The largest current use of this process is.in the preparation of freeze-dried coffee which
commands a premium price in the marketplace. It is also used in the manufacture of phar-
maceutical and biological preparations.
There are no known applications to waste treatment, and none is under development.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Freeze-drying is energy-intensive and costly to operate. Capital equipment costs range
from $300,000-500,000. Its pollution potential is low, except for secondary effects of energy
generation.
V. OUTLOOK FOR WASTES
Freeze-drying development aimed at waste treatment is unknown and will probably
remain so due to the serious limitations of the process.
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FREEZING, SUSPENSION
I. CONCLUSIONS AND RECOMMENDATIONS
Freezing of sludges can aid in the agglomeration of suspended particles, which then
tend to separate rapidly on thawing, leaving a clean supernatant. There are no practical
applications at this time.
II. PROCESS DESCRIPTION
Suspension or simple freezing (dewatering) of sludge causes the suspended solids to
agglomerate and form relatively large floe particles which are more easily removed. Freezing
is accomplished naturally outdoors or through use of a refrigerant. Flocculants may be used
to accelerate coalescence of suspended solids during freezing. Separated solids are screened
or filtered off, and the water is further treated if necessary.
III. APPLICATIONS TO DATE
No commercial suspension freezing or freeze dewatering applications exist. Freezing
alum sludges typical of waste water treatment plants has been the center of interest in the
laboratory. Development of freezing for other materials is not being advanced.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy requirements for natural freezing outdoors are small. Mechanical refrigeration
requires large energy expenditures. Suspension freezing is essentially a phase separation
process, and both the separated solids and the supernatant liquid would generally require
further treatment prior to disposal.
Reliable cost data are not available, but are expected to be relatively high.
V. OUTLOOK FOR WASTES
Unless energy considerations are proven to be acceptable and a broader usage of sus-
pension freezing can be found, it will remain limited in application to sludge dewatering.
Its value as a viable waste treatment process remains to be demonstrated on a commercial
scale.
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HIGH-GRADIENT MAGNETIC SEPARATION (HGMS)
I. CONCLUSIONS AND RECOMMENDATIONS
High-gradient magnetic separation (HGMS) should be considered for removal of
magnetic materials, or recovery of certain high-value, nonmagnetic materials, from waste
streams. The process is particularly attractive for high-volume applications. Aqueous or
non-aqueous liquids, slurries, solids, and dry powders may be treated.
II. PROCESS DESCRIPTION
HGMS is a technique for separating magnet or weakly paramagnetic particles and other
nonmagnetic materials (down to colloidal particle size) from slurries, sludges, and (after
chemical treatment) from solutions. The feed stream is passed through a fine ferromagnetic
filter which, when magnetized, collects the magnetic material. The filter is periodically
cleaned, with the magnetic material then recovered by a simple wash procedure. The re-
moval of nonmagnetic material requires the feed to be treated with a magnetic seed (e.g.,
magnetite).
III. APPLICATIONS TO DATE
Current applications include clay whitening (removal of a small colored magnetic
fraction), and upgrading of low-grade iron ore.
Applications currently being investigated, but not yet commercial, include: beneficia-
tion of other ores, coal desulfurization, removal of flue dusts in air streams from blast
furnaces, and wastewater treatment (including municipal wastes and steel mill wastewaters).
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy requirements may be relatively large, especially if high magnetic fields are
required. Electromagnets, used to generate fields of up to 20 kOe, have power ratings of
around 400 kW for the larger machines. Disposal of the filter wash solution, if the material
is not recovered, and additional treatment of treated stream may also be required.
Capital costs may be as high as $800,000, if high magnetic fields are required; they
may be as low as $5,000, if the material being removed is ferromagnetic. Operating costs
for high-volume applications are expected to be around 10-50^/1000 gal for removal of
ferromagnetic materials, and of the order of $1-5/1000 gal for removal of weakly para-
magnetic materials.
V. OUTLOOK FOR WASTES
HGMS has attractive possibilities for the removal of ferromagnetic and paramagnetic
particulates from liquids or slurries (where seeding is not required). When other non-
magnetic particles are present, the magnetic material should constitute only a small fraction
of the total solids; total solids, however, may be as high as 10-15% by volume of the waste
stream. Economics are probably favorable only for large-volume streams. The time frame for
development is of the order of 5-10 years.
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HYDROLYSIS
I. CONCLUSIONS AND RECOMMENDATIONS
Hydrolysis is potentially applicable to a wide range of waste forms and compositions.
There are currently very few actual waste treatment applications, but the process does
appear promising for detoxification and recovery of organics. Expanded R&D activity is
recommended.
II. PROCESS DESCRIPTION
Hydrolysis generally refers to double decomposition reactions with water of the type:
XY + H2O >• HY + XOH. The reactions are usually carried out at elevated temperatures and
pressures, often with acid, alkali, or enzyme catalysts. Suitable feed streams include aqueous
or non-aqueous solutions, slurries, sludges, or tars.
III. APPLICATIONS TO DATE
The oldest application of hydrolysis is in the production of soap from heated fats in
the presence of caustic (known as saponification). Hydrolysis is also used commercially for
the manufacture of a variety of organics (e.g., production of phenol from chlorobenzene;
production of ethylene oxide from ethylene glycol or ethylene chlorohydrin).
Waste treatment applications are not widespread. However, in the petroleum industry,
the sludge from acid treatment of light oils is often hydrolyzed to recover sulfuric acid for
reuse; the other product, a tarry acid oil, may be concentrated and burned as fuel.
Hydrolysis has also been used for detoxification of waste streams containing carbamates,
organophosphorus compounds, and other pesticides.
Hydrolytic waste treatment processes that have shown promise in the laboratory
include acid hydrolysis of waste paper to sugar; conversion of organic sludge to animal feed;
and decomposition of polyurethane foam to toluene diamine and a polyol.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy requirements vary considerably with the application, but are generally high.
Steam requirements for production of fatty acids approximate 120 Btu/lb of product.
Production of TiO2 from Ti(SO4)2 requires about 1500 Btu steam/lb of TiO2 produced.
The products of hydrolysis of a complex waste stream are not readily predictable and
may be toxic.
The capital investment and operating costs are highly dependent on the specific process
details. Capital investment figures for different processes range from about$2500-20,QOO/
ton of material handled daily. Operating costs might range from 0.3-1.5^/lb.
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V. OUTLOOK FOR WASTES
Although not in widespread use as a waste treatment process, hydrolysis presents no
fundamental problem. Handling of strong acids and alkalies requires care, and performing
reactions at high temperatures and pressures necessitates close control and monitoring.
For hazardous wastes, hydrolysis can be adapted to handle liquids, gases, or solids. It
does not appear promising for inorganic materials, but is suitable for a wide range of
aliphatic and aromatic organics.
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ION EXCHANGE
I. CONCLUSIONS AND RECOMMENDATIONS
Ion exchange is well suited for general and selective removal of heavy metals and toxic
anions from dilute aqueous waste streams. The upper concentration limit for efficient
operation is about 4000 mg/1. Research on the use of polymer beads impregnated with
liquid ion exchange materials has some promise for extending the concentration limits.
II. PROCESS DESCRIPTION
Ion exchange involves the interchange of ions between an aqueous solution and a solid
material (the "ion exchanger"). After removal of the solution, the exchanger is then
exposed to a second aqueous solution of different composition which removes the ions
picked up by the exchanger. The process is most frequently carried out by pumping the
solutions through one or more fixed beds of exchanger.
III. APPLICATIONS TO DATE
Full-scale operations include cleanup of dilute solutions from electroplating and other
metal-finishing operations, recovery of effluents from fertilizer manufacturing, and indus-
trial deionization. Promising applications include removal of cyanides from mixed streams
and use of newer exchangers for selective removal of heavy metals.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy requirements are low, consisting primarily of electricity for pumping solutions.
The dilute purified product stream is dischargeable to sewers. The regenerant stream
requires further treatment for recovery or disposal. Minor amounts of exchange materials
will require disposal occasionally.
Capital costs are expected to be in the range of $200,000-$350,000, with a substantial
investment in resin. Operating costs might be in the vicinity of $2-8/1000 gal.
V. OUTLOOK FOR WASTES
Ion exchange is a well developed process, which promises to be used more widely for
recovery of heavy metals, and removal of both heavy metals and cyanides.
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LIQUID ION EXCHANGE
I. CONCLUSIONS AND RECOMMENDATIONS
Liquid ion exchange (LIE) is a process with demonstrated potential for removal of
heavy metals and hazardous anions from aqueous waste streams. It covers a much wider
concentration range than conventional ion exchange. Development of new applications and
reagents for waste treatment may require special economic incentives, since historically such
research has been stimulated principally by high-volume hydrometallurgical applications.
II. PROCESS DESCRIPTION
Liquid ion exchange involves, first, the extraction of inorganic species (principally
ionic) from an aqueous stream into an immiscible organic stream containing special reagents
to facilitate the extraction, and then subsequent transfer of the species to a second aqueous
stream of different composition from the feed. Process equipment is that commonly used
for liquid-liquid extraction: mixer-settlers, differential columns, or centrifugal contactors.
III. APPLICATIONS TO DATE
Full-scale commercial operations include removal of molybdenum and acids from
metal pickling baths, zinc from textile production effluents, and copper from various
streams. Promising applications include removal of cyanides and treatment of hydroxide
slimes from electroplating.
IV. ENERGY, ENVIRONMENT, ECONOMICS
The LIE process has very low energy consumption, consisting principally of electricity
for pumping and mixing.
The cleaned feed stream will contain 10-50 mg/1 of the organic extraction solvent. The
regenerative solution into which hazardous components are stripped from the extraction
solvent will require further treatment.
Capital costs depend upon the application. Values in the literature range from $10,000
(almost certainly too low) to $600,000. Total costs for treating dilute streams are estimated
to be around $4/1000 gal. For concentrated stream, costs are highly variable, ranging from
$0.20-$3.00/lb of metal removed.
V. OUTLOOK FOR WASTES
This method is well-developed, and particularly applicable to recovery of high-value
metals from waste streams.
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LIQUID-LIQUID EXTRACTION OF ORGANICS
I. CONCLUSIONS AND RECOMMENDATIONS
Liquid-liquid extraction should be considered for the recovery of organic solutes from
fairly concentrated aqueous and non-aqueous solutions.
II. PROCESS DESCRIPTION
Liquid-liquid extraction is the separation of the constituents of a liquid solution by
contact with another (immiscible) liquid. If the substances comprising the original solution
distribute themselves differently between the two liquid phases, a certain degree of separa-
tion will result. This may be enhanced by the use of multiple contacts. A total recovery
process based on liquid-liquid extraction usually requires the use of other unit processes,
such as stripping or distillation for solvent and solute recovery.
III. APPLICATIONS TO DATE
Current actual or proven areas of applicability include:
1. Extraction and recovery from aqueous solution of:
• phenol;
• acetic acid, and other aliphatic organic acids;
• salicylic and other hydroxy aromatic acids; and
• oils.
2. Extraction (without recovery) of:
• phenol from foul waters near a refinery.
3. Extraction and recovery from organic solvents of:
• methylene chloride (from isopropyl alcohol);
• freons (from oils and acetone, or alcohols); and
• mixed chlorinated hydrocarbons (from acetone or alcohols).
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy requirements are usually quite small for just the extraction step. Where solute
and solvent recovery require stripping or distillation, steam requirements will be significant.
The only major environmental issues relate to (1) possible need for disposal of
recovered solutes if such are not reusable, (2) the probable need for a polishing treatment on
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the raffinate, following extraction from water, and (3) the possible need for disposal of
unwanted fractions following extraction of organic solutions.
Costs cannot be generalized usefully. However, capital investment might be in the
vicinity of $1 million. Total operating costs (without credit for resource recovery) might
range from well under $1/1000 gal to more than $5/1000 gal.
V. OUTLOOK FOR WASTES
The process is most attractive for treatment of concentrated, selected, and segregated
waste streams where material recovery is possible and desirable. Organic solutes, of almost
any nature, may be economically removed if concentrations are in the range of a few
hundred ppm to a few percent from aqueous waste streams. Organic solutions containing
water-soluble and non-water-soluble components may be economically separated by extrac-
tion with water.
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MICROWAVE DISCHARGE
I. CONCLUSIONS AND RECOMMENDATIONS
Microwave discharge treatment of hazardous wastes is currently in the research
stage. Early results are very promising.
II. PROCESS DESCRIPTION
High-frequency microwave power is used to establish a plasma or gaseous discharge in
which neutral molecules are partially decomposed into metastable, atomic, free radical and
ionic species. The decomposition products typically recombine to form a variety of stable
molecules, some of higher molecular weight and of higher toxicity than this feed. Plasmas
may be initiated in low-pressure gases of all kinds, and solids and liquids exposed to the
reactive species in plasmas generally undergo chemical change. Toxic vapors and liquids
introduced into an oxygen plasma undergo reactions similar to those of incineration, but at
much lower temperatures.
III. APPLICATIONS TO DATE
Commercial microwave discharge instruments are used in analytical chemistry, particu-
larly for plasma or low-temperature ashing. The only large-scale applications are for
photoresist removal and plasma etching in semiconductor device fabrication. Most research
has been concentrated on polymer film deposition and organic synthesis. Lockheed is
currently investigating the use of microwave plasmas, particularly oxygen plasmas for the
treatment of organic vapors and liquids characteristic of waste streams.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Line power requirements for microwave discharge treatment are estimated as roughly
14 kWh/lb of waste treated.
In an oxygen plasma, organic waste components are converted to products similar to
those of complete combustion.
Capital costs for a 100 Ib/hr facility might be in the neighborhood of $100,000.
Operating costs are estimated to be on the order of $1.00/lb.
V. OUTLOOK FOR WASTES
The process should be considered for small quantities of highly toxic materials that
cannot be handled by any other means, or for recovery of high-value components.
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NEUTRALIZATION
I. CONCLUSIONS AND RECOMMENDATIONS
Neutralization (or more generally pH control) is a technically and economically proven
process, currently in full-scale use in many industries. It has wide applicability to waste
streams of diverse physical and chemical compositions, and would have to be available in
almost any waste treatment facility.
II. PROCESS DESCRIPTION
Neutralization is a liquid-phase chemical reaction between an acid and a base which
produces a neutral solution. It may be carried out in batch or continuous flow. It requires
reaction tanks, agitators, monitoring and control capability, pumps, and ancillary equipment
for handling solids and/or liquids, and storage facilities. The treated stream undergoes no
change in physical form, other than solids dissolution (or precipitation) or gas evolution.
The process can be used on aqueous and non-aqueous, liquids, slurries, and sludges.
III. APPLICATIONS TO DATE
The process is in full-scale use throughout many industries, e.g., pulp and paper,
petroleum refining, and inorganic chemicals. It is used to treat acid exhausts, pickle liquors,
plating wastes, and acid mine drainage. It can be used on almost any stream requiring pH
adjustment.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy requirements are primarily for electricity used to run pumps and stirrers.
Treated streams may contain precipitated solids which require additional handling. The
solids must be recovered or sent for disposal as a solid waste. There is the possibility of toxic
gas being evolved, particularly if sulfides or cyanides are present in the waste stream. Capital
investment requirements are highly variable, depending upon the size of the stream to be
treated. Operating costs range from $0.20/1000 gal to $4/1000 gal.
V. OUTLOOK FOR WASTES
Neutralization is and will continue to be a routine and accepted part of industrial
processing waste management.
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OXIDATION, CHEMICAL
I. CONCLUSIONS AND RECOMMENDATIONS
Chemical oxidation and the technology for its large-scale application are well estab-
lished. Oxidation-reduction, or "Redox" reactions are those in which the oxidation state of
at least one reactant is raised while that of another is lowered. We recommend that chemical
oxidation be considered for dilute aqueous streams containing hazardous substances or for
removing residual traces of contaminants after treatment. Chemical oxidation should be
considered as a first treatment step when the waste contains cyanide, when it contains
constituents not amenable to other treatment methods, or as a final step to remove traces
of contaminants after other treatment.
A more exhaustive study should be made of the potential for treatment of waste
containing hazardous materials. Most of the literature deals only with very dilute waste
streams, or with the preparation of materials from basic raw materials via chemical oxidative
techniques, and little has been published relative to treatment of concentrated hazardous
wastes.
II. PROCESS
The first step of the chemical oxidation process is adjustment of the pH of the
solution. The oxidizing agent is added gradually and mixed thoroughly. The agent may be in
the form of a gas (e.g., chlorine), a liquid (e.g., hydrogen peroxide), or a solid (e.g.,
potassium permanganate). Because some heat is liberated, concentrated solutions may
require cooling, or may require careful measurement and handling to avoid violent reactions.
III. APPLICATIONS TO DATE
Application to industrial wastes is well developed for cyanides and for phenols, organic
sulfur compounds, etc., in dilute waste streams. The primary application has been in
converting and destroying cyanides from plating and metal finishing operations.
The chlor-alkali industry uses chemical oxidative techniques to remove mercury from
ores, as well as from cell wastes. Mercury removal rates of over 99% are claimed for
concentrated ores, and residual mercury levels of less than 0.1 ppm for chlor-alkali sludge.
The technique is also used to remove organic residues from drinking water, or to
remove residual chlorine after chlorine treatment. Gases have been treated by scrubbing
with oxidizing solutions to destroy odorous substances. Chemical oxidation is also used for
odor destruction in the manufacture of kraft paper and in the rendering industry.
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IV. ENERGY, ENVIRONMENT, ECONOMICS
Total energy consumption is low; the only requirements are for pumping and mixing.
A disadvantage of chemical oxidation for waste treatment is that it introduces new
metal ions into the effluent that might require further treatment. The only waste that
appears troublesome is the sludge that can develop in the oxidation treatment of cyanides
when iron and some other ions are present. A facility for chemical oxidation of 103 gpd of
highly concentrated cyanide waste from a plating operation, using batch alkaline chlorina-
tion would require a capital investment of $100,000. Fixed costs would be $18,300
annually and variable costs $36,700, giving a unit cost of $229.20/103 gal. For a less highly
concentrated waste (100 ppm copper cyanide and 100 ppm sodium cyanide), the operating
cost would be about $170/103 gal. Costs could be lowered if the daily flow rate were to
increase and the treatment operation could be continuous rather than batch.
V. OUTLOOK FOR WASTES
In addition to the already-established applications for removal of hazardous substances,
chemical oxidation may be used to remove chlorinated hydrocarbons and pesticides from
dilute streams. Laboratory and pilot studies have demonstrated the potential for this
application.
The extent to which the technique can be used to remove hazardous substances from
industrial sludges may be limited because of inefficiency and incompleteness of the reaction.
The use of chemical oxidation for concentrated wastes should have careful evaluation
for reasons of economics, process safety, and the addition of chemicals that may add to the
pollutant load.
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OZONATION
I. CONCLUSIONS AND RECOMMENDATIONS
Technology for large-scale ozone application is well developed. Feasibility has been
demonstrated for treatment of cyanides and phenols, and laboratory and pilot studies
indicate potential for chlorinated hydrocarbons, polynuclear aromatics, and pesticides.
We recommend that ozonation be considered for treatment of aqueous or gaseous
waste streams containing less than 1% oxidizable hazardous components and as a prelimi-
nary treatment for more concentrated wastes not amenable to other techniques. We also
recommend ozonation as a final treatment process where more complete removal of
oxidizable substances is required.
A more exhaustive study should be made of the literature on the susceptibility of
various compounds to ozonation. Laboratory studies are needed to evaluate the effectiveness
of treatment of pollutants of current concern. Additional research and development aimed
at more efficient ozone generation and ozone/water mixing should be supported.
II. PROCESS
Since ozone is a powerful oxidizing agent and an extremely reactive gas that cannot be
shipped or stored, it must be generated on site immediately prior to use. Ozone generated at
a concentration of <2% and a pressure of <15 psi from a stream of air or oxygen
previously dried to a dewpoint of -50°C or lower is introduced into a contact chamber
designed to ensure good mixing with the waste stream. For aqueous wastes, a venturi
injector, a porous diffuser, or an impeller is used to mix ozone and liquid at high velocity
for 10 minutes or more. Liquid depth is at least 15 feet, and two or more reactors are
frequently employed. For gaseous waste streams, a porous diffuser is used if ozonized air is
generated at positive pressure; at atmospheric pressure, a wet scrubbing process is used, with
a fine mist of ozone-saturated water sprayed into a contact chamber. Contact times for
gaseous streams is 5-60 seconds.
III. APPLICATIONS TO DATE
Ozone, besides being a powerful reducing agent, has antibacterial and antiviral proper-
ties. This disinfecting power has been responsible for most large-scale applications. The
process is widely used in Europe to purify and improve drinking water, and there have been
a number of installations in the United States for treatment of municipal sewage plant
effluents. It has also been used to remove sulfide and other odors from rendering plant
effluent; fermentation odors from a pharmaceutical plant; treatment of liquid effluent
containing cyanides, sullldes, sulfites and other hazardous components after biological
treatment; reduce cyanide levels from effluent of a tire plant, a chemical plant, and an
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electroplating facility. In combination with activated carbon adsorption, ozonation has been
used to remove color from waste dyeing water. Oxidation of phenols in coke oven wastes,
wood products waste and biologically treated refinery waste.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Ozonation can be expensive, but may be economically competitive for treatment of
dilute waste streams. Generation of ozone is the dominant cost component in terms of
capital and power. With air feed, energy requirements are from 7.2 to 9.0 kWh/lb of ozone
generated. Power requirements are half this figure if oxygen is used for feed. Any improve-
ment in ozone demand or efficiency would improve economics; the catalytic effect of UV
light can extend the effect of ozonation dramatically and can reduce ozone demand by a
factor of two. Labor and space requirements are low.
Concentrations of ozone leaving the contact chamber are carefully monitored; some-
times the ozonized air is cycled to provide pretreatment of incoming aqueous waste. The
waste stream effluent is also monitored, and the dosage increased if necessary. Gaseous
effluent is discharged directly to the atmosphere; aqueous effluent may be discharged to a
sewer or natural body of water where the oxygen-rich water is beneficial.
V. OUTLOOK FOR WASTES
Complete oxidation to CO2 can sometimes be achieved; in other cases, oxidized
intermediates may be formed that resist further ozonation. Whether a given degree of
oxidation constitutes satisfactory treatment depends on the criteria for the particular waste
stream or disposal site. Slurries, tars, sludges and solutions in oxidizable liquids are
generally not suitable for ozonation. Although ozone itself is a toxic substance, the risk of
exposure to toxic levels is small.
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PHOTOLYSIS
I. CONCLUSIONS AND RECOMMENDATIONS
Technology for large-scale application of photolysis to wastes is not highly developed.
Further laboratory studies of photolysis of selected candidate waste streams (for example,
pesticide contaminated solvents) should be conducted. Pure photolysis is not likely to be a
practical industrial waste treatment process within the next 5-10 years, but UV-assisted
ozonation and chlorination are promising in the near term.
II. PROCESS DESCRIPTION
In photolysis, chemical bonds are broken under the influence of UV or visible light.
Products of photodegradation vary according to the matrix in which the process occurs, but
the complete conversion of an organic contaminant to CO2, H2O, etc., is not probable.
Equipment required includes a source of UV/visible radiation, such as a mercury arc. Re-
actor geometry and materials of construction must allow adequate penetration of the light
into the waste.
III. APPLICATIONS TO DATE
Pure photolysis has been investigated only in laboratory-scale studies. Combined UV/
ozonolysis and UV/chlorination have been used in pilot and full-scale applications in the
hazardous waste area.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Any photolysis process is relatively energy-intensive. There are not sufficient data to
allow estimation of either process economics or environmental issues. In general, the process
effluent is a stream with physical characteristics similar to those of the input stream, but
with different chemical characteristics. Organic hazardous components are not completely
degraded and the residues may still pose hazard.
V. OUTLOOK FOR WASTES
Applications are probably highly specialized, detoxification of pesticide-contaminated
solvents is one possibility. However, pure photolysis requires research and testing at labora-
tory and pilot-scale to demonstrate applicability to hazardous waste.
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REDUCTION, CHEMICAL
I. CONCLUSIONS AND RECOMMENDATIONS
Reduction reactions are among the most common chemical processes; reduction-
oxidation or "Redox" reactions are those in which the oxidation state of at least one
substance is raised while another is lowered. The technology for large-scale reduction of
some industrial wastes, sometimes allowing recovery of metals, is well developed. We believe
that the process could well be adapted to remove hazardous substances from dilute wastes,
to pretreat wastes that have constituents not amenable to other methods, and to remove
traces of contaminants.
II. PROCESS
The equipment for reduction processes is simple: only storage, metering, mixing,
pumping and instrumentation, with the major cost for reducing chemicals. The economics
vary with the substance being treated. Introduction of foreign ions into the stream is a real
or potential disadvantage; otherwise it is straightforward.
III. APPLICATIONS TO DATE
The application to industrial wastes is already well established for dilute waste streams,
especially those containing chromium (VI), and other hazardous substances, such as lead
and mercury. In addition to detoxifying hazardous substances, the process sometimes allows
recovery of metals. The plating and tanning industries use the process to reduce highly toxic
chromium (VI), to chromium (III), which is less hazardous and can be precipitated for
removal.
The process also finds application in the chlor-alkali industry for removal of mercury
from effluents. It appears to have potential for removing other hazardous substances, e.g.,
cadmium and antimony, in diluted streams.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Total energy consumption is low; the only requirements are for pumping and mixing.
A disadvantage of chemical reduction for waste treatment is that it may introduce new
ions into the effluent that might necessitate further treatment. Air emissions are not
significant. There may be problems with land disposal or residues, especially those sus-
ceptible to acid leaking. A facility for chemical reduction of 2,000 gpd of chromium (VI)
waste from a plating operating, using batch sulfur dioxide treatment would require a capital
investment of $230,000. Variable operating costs would be S51,400 and fixed costs
$41,600 annually. Unit costs would be $193.80/103 gal. Costs could be lowered if the daily
flow rate were to increase and the treatment operation could be continuous rather than
batch.
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V. OUTLOOK FOR WASTES
We believe there should be a more exhaustive study of the potential for reduction
processes for concentrated hazardous wastes. It should certainly be considered as a treat-
ment step whenever chromium VI is a constituent of the effluent. It may be a method for
treating wastes that have constituents not amenable to other treatment, and as a final
polishing step for removing traces of contaminants.
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REVERSE OSMOSIS
I. CONCLUSIONS AND RECOMMENDATIONS
Reverse osmosis (RO) should be considered for treatment of aqueous waste streams
containing organic and inorganic species in solution. Total dissolved solids in the feed
stream may be as high as 34,000 ppm.
II. PROCESS DESCRIPTION
The heart of the reverse osmosis process is a semipermeable membrane which is per-
meable to solvent, but impermeable to most dissolved species, both organic and inorganic.
Separation is brought about by means of an applied pressure gradient. To protect the mem-
branes for chemical attack and plugging, oxidants, iron and manganese salts, and oils and
greases are generally removed prior to application of RO.
III. APPLICATIONS TO DATE
There are about 300 full-scale plants worldwide using reverse osmosis for desalination
of sea or brackish water. Reverse osmosis has been used very successfully in the treatment of
electroplating rinse waters, not only to meet effluent discharge standards, but also to re-
cover concentrated metal solutions for reuse. A limited number of other full-scale uses can
be found in the treatment of sulfite streams from the paper industry and in food processing.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Energy requirements are of the order of 10 kWh/1000 gal of product water.
The concentrated brine or solute solution presents a problem for disposal, if not
recoverable.
Capital costs range from about $0.50-4/gpd of purified water output, depending on the
volume of waste to be treated. Total operating costs are in the range of $1-5/1000 gal.
V. OUTLOOK FOR WASTES
Use of RO for industrial waste treatment is growing rapidly. The process is particularly
useful for concentrating waste streams containing dissolved organics or inorganics, to
facilitate recovery, or to reduce volume.
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STEAM DISTILLATION
I. CONCLUSIONS AND RECOMMENDATIONS
Steam distillation is a proven process for removing water-immiscible, volatile com-
pounds from process or waste streams. It can be applied to any stream that can be contacted
with steam or water without reaction or decomposition. It can be used with liquids, slurries,
sludges, and solids.
II. PROCESS
Steam distillation takes advantage of the unique vapor pressure relationship of two
immiscible liquids. The additive vapor pressures allow distillation at lower temperatures. It is
usually conducted as a batch operation: the still is charged, the charge is heated to
temperature, and the distillation conducted by bubbling steam through the liquid phase. In
semi-batch operation, the charge containing a high ratio of volatiles to non-volatiles is fed to
the still continuously for a given period while the volatile component is steam-distilled from
the mixture.
III. APPLICATIONS TO DATE
The widest application is in the petroleum industry where steam and feedstock are
introduced into a multi-tray distillation column to produce gasoline, lube oil, or naphtha.
Without the use of steam or steam and vacuum together, the high distillation temperature
would result in decomposition. The process is also used for removing low boiling compo-
nents from a mixture. In the soap industry, glycerine is recovered from spent soap lye; in
the naval stores industry turpentine and gum rosin are recovered from pine gum; fatty acids
and tall oil rosin are obtained from crude tall oil, a by-product of sulfate wood pulp
production. A solvent extraction process removes organics from paper before the wood fiber
can be reused; through steam distillation the solvent is recovered. In the production of coke
from coal, quantities of aromatic hydrocarbons are also produced. The wash oils from the
ovens are steam stripped to recover the aromatic hydrocarbons.
IV. ENERGY, ENVIRONMENT, ECONOMICS
The major energy requirement is for steam. In one application, the steam requirement
would total 29,200 Ib per 3,000 gal of treated degreasing waste, or per 1,000 gal recovered
perchlorethylene. Power requirements would be 30 kWh per 3,000 gal waste.
The wastewater from condensed steam in the steam distillation process will contain
traces of volatile organics, and may have to be steam-stripped before disposal.
The fixed capital investment (new equipment) for a steam distillation unit with a
capacity of 3,000 gal/week degreasing solvent would be about $130,000. Operating costs
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would be $1,424. Credits for perchlorethylene at $2/gal and $0.05/gal for the oil/grease
mixture used for boiler fuel would more than offset treatment cost.
V. OUTLOOK FOR WASTES
Numerous industrial wastes are treated by contract disposal companies using steam
distillation to recover valuable components or reduce waste volumes. With the increase in
value of hydrocarbon solvents and increasingly strict regulations regarding landfill with
sludges containing these solvents, the use of steam distillation is expected to increase.
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STRIPPING. AIR
I. CONCLUSIONS AND RECOMMENDATIONS
Air stripping of ammonia from biologically treated domestic wastewater is being
developed as a means of reducing nitrogen content before discharge. It is suitable only for
dilute solutions, since the emission level of ammonia from a concentrated solution would be
too high. Furthermore, steam stripping would permit recovery of the ammonia from more
concentrated solutions. Application of air stripping to other gaseous compounds would
depend on the environmental impact of the resulting emissions.
II. PROCESS
Holding ponds, with or without surface agitation, and spray ponds have been investi-
gated, but the packed tower appears to be the most compact and efficient means of air
stripping. Removal efficiencies of over 90% have been obtained in pilot tests with wastewater
containing 60 ppm nitrogen. The wastewater containing ammonia and a lime slurry (lime
added for phosphate removal) are fed to a rapid mix tank, and thence to a settling basin,
where the calcium phosphate and calcium carbonate settle out. The clarified wastewater is
pumped to the top of two towers packed with a series of horizontal pipes. Air is drawn up
through the tower against the falling wastewater by large fans. After the ammonia is
removed, the wastewater flows into the recarbonation basin where compressed carbon
dioxide-rich gas from the lime recalcining furnace is bubbled through to precipitate and
recover calcium carbonate, for calcination and recycle of lime to the system.
III. APPLICATIONS TO DATE
Full-scale packed towers have been used at two locations in California for treating
domestic wastewater.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Electric power requirements for treating 15 million gpd are in the range from 1600 to
1800kWh/hr. The recalciner requires about 8 million Btu (8000ft3) natural gas/ton of
feed, or 192 million Btu/day.
When the ammonia concentration is about 23 ppm and the air-to-water ratio is
500 ft3 /gal, the concentrated ammonia in the saturated air leaving the tower is about
6 mg/m3, well below the odor threshold. Disposal of about 25 tons/day of sludge requires a
significant amount of land, but does not pose an environmental hazard.
The capital investment would be about $7.8 million; fixed costs would be $1,420,000,
and variable operating costs would be $940,000/year.
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V. OUTLOOK FOR WASTES
It is unlikely that many other applications of air stripping will be found.
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STRIPPING, STEAM
I. CONCLUSIONS AND RECOMMENDATIONS
Steam stripping should be considered whenever it is desirable to remove volatile
components (e.g., organics, H2S, NH3) from aqueous waste streams.
II. PROCESS DESCRIPTION
Steam stripping may be considered a form of fractional distillation. Live steam is
injected into the bottom of the distillation column, and carries dilute volatile components
with it. There are two aqueous output streams, one a concentrated solution of the volatile
organics and the other a dilute stream containing only residual traces of volatile organics.
III. APPLICATIONS TO DATE
Steam stripping has been used for many years to recover ammonia from coke oven
gas. It is also used to recover sulfur as H2S from refinery raw waste. Other applications
include phenol recovery, vinyl chloride monomer removal from PVC suspension resins,
and removal of organics and sulfur from Kraft mill condensates. Research work is in pro-
gress for steam stripping of light chlorinated hydrocarbons from industrial waste water.
IV. ENERGY, ENVIRONMENT, ECONOMICS
The primary energy requirements are for steam. Between 0.5 and 2.5 pounds of
steam are required per gallon of waste water. The concentrated stream containing the bulk
of the volatile organic components is processed for recovery or incinerated. If the incin-
erated stream contains sulfur, emission of SO2 must be considered. The impact of dis-
charging the treated dilute stream depends on the nature and residual concentration of
the volatile organics of the waste water.
Capital investment for a new 200-gpm, single-stage (one column) "sour water" steam
stripper would be between $500,000 for mild steel and $850,000 for stainless-steel con-
struction. Treatment cost by this system would be about $10/1000 gal. A capital investment
closer to $1,700,000, would be required for a two-stage, two-column, 200-gpm system
that would recover NH3 and H2 S for credits.
V. OUTLOOK FOR WASTES
The use of steam stripping for industrial waste treatment is growing. The most attrac-
tive applications are those that permit byproduct recovery, thus to offset fairly high
operating costs. The process is energy-intensive, with steam costs amounting to close to
X0% of operating costs.
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ULTRAFILTRATION
I. CONCLUSIONS AND RECOMMENDATIONS
Ultrafiltration is a membrane filtration process that separates high molecular weight
solutes or colloids from their surrounding media. The process has been successfully applied
to both homogeneous solutions and to colloidal suspensions that are difficult to separate by
other techniques. Commercial use has been focused on aqueous solutions.
Retained solute or particle size is one characteristic distinguishing ultrafiltration from
other filtration processes. It filters out particles as small as 10~3 to 10"2 microns. Where
solutes are being separated from solution, the process can serve as a concentration or
fractionation process for single-phase streams. It competes with adsorptive and evaporative
processes, and has the potential for broader applicability than conventional filtration.
Usually the concentrate requires further processing if a pure solute is to be recovered.
II. PROCESS
Ultrafiltration membranes have an extremely thin selective layer supported on a
thicker spongy substructure, and it is possible to tailor membranes with a wide range of
selective properties. A solution containing molecules too small to be retained by the
membrane and larger molecules that will be 100% retained is passed in a pressurized
stream. The larger molecules are collected from the upstream side and the smaller molecules
downstream.
III. APPLICATIONS TO DATE
Ultrafiltration is used for electrocoat paint rejuvenation and rinse water recovery,
protein recovery from cheese whey, and metal machining oil emulsion treatment, with
capacity to handle approximately 100 million gallons per year for each application. There
are also smaller (on the order of 10 million gpy) plants for treatment of textile sizing waste
and wash water from electronics component manufacturing, and for production of sterile
water for pharmaceutical manufacturing.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Electrical energy for pumping to maintain flow at operating pressures may be as much
as 30% of total direct operating costs.
Ultrafiltration residues are typically a concentrate of the undesirable or hazardous
components and usually require further processing unless valuable by-products can be re-
covered.
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Capital and operating costs are dependent on the specific application and the capacity
of the system. For large plants, capital costs may be $l-$4/gpd; operating costs may be
$5-$ 10 per 103 gal. Coupled with the economies of reuse of salvaged materials, these costs
are often acceptable.
V. OUTLOOK FOR WASTES
There are a number of other applications where ultrafiltration may become commercial
within the next five years. These include: treatment of dye waste, pulp-mill waste, industrial
laundry waste, and recovery of sugar from orange-juice pulp, protein from soy whey,
products from pharmaceutical and fermentation industries, and purification of power-plant
boiler feedwater and water for beverages.
Application to hazardous wastes is already well advanced, since many of the aqueous
solutions treated present severe sewage problems.
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ZONE REFINING
I. CONCLUSIONS AND RECOMMENDATIONS
Zone refining is unlikely to be useful for treatment of hazardous wastes. Although
zone refining is an effective purification technique, it has inherent limitations which make
its use for broad treatment of large quantities of waste unlikely in the near future. Zone
refining is a slow and costly operation, energy-intensive, and, at present, suitable for opera-
tion up to only about 10 kg batches.
II. PROCESS DESCRIPTION
Zone refining is a fractional crystallization technique in which a rod of impure material
is purified by heating it so as to cause a molten zone to pass along its length. Basic equip-
ment consists of a material support or ingot holder to contain the sample; a feed or travel
mechanism; and a source of heat. The process may include a cooling step. It can be used on
solids, liquids, and mixtures such as slurries. High viscosity and reactive materials are not
suitable.
III. APPLICATIONS TO DATE
Zone refining is used to purify elements, metals, semiconductor materials, oxides,
salts, and organic materials in the laboratory. Its primary commercial use is in purification
of semiconductor materials.
It is used on relatively pure materials. It is not now used for hazardous wastes, and
there are no known proposed applications for hazardous waste.
IV. ENERGY, ENVIRONMENT, ECONOMICS
Zone refining is an energy-intensive process and therefore expensive to operate.
Its pollution potential is low. Equipment costs are not presently available, most equip-
ment being engineered on a custom basis.
V. OUTLOOK FOR WASTES
Zone refining, at present, is only useful for processing small quantities (up to 10 kg) of
relatively pure material. Processing rates are under 10 cm/hr. The process is not practical
for the complex mixtures that characterize most waste streams. Even for specialized applica-
tions, the process is only operationally feasible if the distribution coefficients permit segre-
gation of impurities.
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