Wet air oxidation is applicable to industrial wastewaters containing organics and oxidizable inorganics such as cyanide. The process is typically used to oxidize sewage sludge, regenerate spent activated carbon, and treat process wastewaters. Wastewaters treated using this technology include pesticide wastes, petrochemical process wastes, cyanide containing metal finishing wastes, spent caustic wastewaters containing phenolic compounds and some organic chemical production wastewaters. WAO can be used to treat wastewaters that have higher organic concentrations than are normally handled by biological treatment, carbon adsorption and chemical oxidation, but may be too dilute to be effectively treated by thermal processes such as incineration. WAO is most applicable for waste streams containing dissolved or suspended organics in the 500 to 15,000 mg/l range. Below 500 mg/l, the rates of WAO of most organic constituents are too slow for efficient application of this technology. WAO can be applied to wastes that have significant concentrations of metals (approximately 2 %) whereas biological treatment, carbon adsorption, and chemical oxidation may have difficulty treating such wastes.

WAO proceeds as a series of reaction steps and the intermediate processes are not always as readily oxidized as are the original constituents. Therefore the process does not always achieve complete oxidation of the organic constituents. As a result it is important to evaluate the process to assess the potential products of incomplete oxidation prior to implementing the technology.

WAO technology is well-developed and demonstrated for treating several hazardous wastes such as spent non-halogenated solvents and still bottoms, sludges from electroplating operations, and spent cyanide bath solutions. Successful bench scale WAO studies have been conducted on energetics [hydrazine based rocket fuel wastewater and OTTO fuel (used in torpedo propellant) wastewater], chemical agent surrogates and TNT red water. In addition, the EPA recommends WAO as the "Best Demonstrated Available Technology" for a variety of hazardous wastes.

Typical results of wet air oxidation of organic compounds in industrial wastewaters are presented in the following table:

Wet Air Oxidation of Organic Compounds In Industrial Wastewater*
Concentration, mg/l

* wet air oxidation temperature = 495°F, pressure >700 psi, residence time = 83 minutes.

The U.S. Army Construction Engineering Research Laboratories (USACERL) has completed WAO batch studies on TNT red water which is the wastewater from the manufacturing of trinitrotoluene. Major pollutants in red water include the products formed during the sellite purification of crude TNT and other by-products formed during various stages of the production process. The U.S. Environmental Protection Agency (EPA) classifies TNT red water as RCRA hazardous waste K047 due to its reactivity. The lack of a cost-effective, environmentally acceptable treatment for red water impairs the Army's mission readiness for TNT production. Results indicate that WAO can be used for successfully treating red water. Information on waste destruction rates and other performance evaluation parameters has been obtained. Toxicity of the WAO-treated red water to activated sludge and other bacteria have also been evaluated. A USACERL technical report on the feasibility, kinetics, and toxicity studies is available.

The use of a wet air oxidation system can help facilities meet pretreatment standards for discharges of industrial wastewater to a POTW (40 CFR 403) or meet effluent limits of a NPDES permit (40 CFR 122). A WAO system may also decrease the amount of hazardous waste generated which helps facilities meet the requirements of waste reduction under RCRA, 40 CFR 262, Appendix. It may also help facilities lessen the amount of regulations they must comply with for the management of hazardous waste (i.e., recordkeeping, reporting, inspections, transportation, accumulation) under RCRA, 40 CFR 262.

The compliance benefits listed here are only meant to be used as a general guideline and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g. the amount of workload involved.

Consult your local Industrial Health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing any of these technologies.

• A variety of chemical compounds can be treated at the same time in the one step process.
• Wastes are destroyed in liquid phase. As a result, the problems associated with air pollution are reduced.
• The process is less energy intensive than incineration and is less likely to produce oxides of nitrogen as by-product air pollutants.

• Waste must be in the liquid phase.
• Limited to wastewaters containing oxidizable organic and inorganic compounds. For example, WAO cannot destroy PCBs, some halogenated aromatics and some pesticides.

Assumptions:

• WAO System for treating TNT red water costs $12 million for a 16,000 gallon per day system.
• Operation and maintenance costs $974,000 per year.
• WAO system runs 200 days per year.
• Disposal of hazardous waste costs $1.17 per gallon.
• Labor of 100 man-hours a year for disposal of hazardous waste at $45 per hour.
• WAO system runs at 340°C and 1 hour contact time.

Economic Analysis Summary

Annual Savings for WAO: $2,774,500
Capital Cost for Diversion Equipment/Process: $12,000,000
Payback Period for Investment in Equipment/Process: 4.3 years

Click Here to view an Active Spreadsheet for this Economic Analysis and Enter Your Own Values. To return from the Active Spreadsheet, click the reverse arrow in the Tool Bar.

*There are multiple MSDSs for most NSNs.
The MSDS (if shown above) is only meant to serve as an example.

US Filter, Zimpro Division, Inc.
301 W. Military Road
Rothschild,  WI   54474
Phone: (715) 359-7211