Conor Pacific Environmental Technologies Inc. (CPET) has the global rights to a patented wet oxidation technology (originally developed by a Danish consortium consisting of RISO National Laboratory and NKT Research Center (NKT/RISO)) used for destroying hazardous and non-hazardous material contained in liquids and soils. CPET also has the Canadian rights for the Eco Waste Technologies (EWT) supercritical wet oxidation technology and various other technologies under development, including catalyzed wet oxidation technologies.

The technologies have effective applications for the treatment of organic contaminants in water, soil, sludge and sediment remediation, for various industries including the pulp and paper, chemical, and petrochemical industries.

The technologies used by CPET are based on the principle of using unique combinations of temperature, pressure, flow and exposure to gaseous oxygen in a pipe reactor to decompose contaminants in liquid form or as a slurry. Depending on the compounds requiring treatment, the degree of destruction is controlled to the most economical level.

Wet oxidation is defined as the process where organic contaminants in liquids, or solids, are extracted into water where they are contacted with an oxidant under conditions that promote their rapid destruction, which in this case are, 220-290° C or over 374° C and at pressures of 100 - 250 bar.

The general configuration of the reactor systems includes a feed preparation and analysis tank, feed pump, heat recovery, preheater, oxygen injection/reactor system and heat recovery and discharge separation as shown schematically in Figure 1.

The NKT/RISO process is a subcritical wet oxidation carried out at pressures of 100-170 bars and between 220-300° C in a continuous pipe reactor under turbulent flow conditions. Oxygen is injected and dissolved in the reactor at various predetermined points and in measured amounts to achieve the optimum reaction kinetics. The process is exothermic but some heat is required at start-up and, thereafter, cooling is required to overcome heat buildup. This is accomplished using heat exchangers that typically allow an overall energy recovery of 80%. The reactor is a closed system and, therefore, gaseous waste product emission is controlled. Where complete oxidation takes place, carbon dioxide and water are the by-products. Due to the controlled oxygen addition, pressures and temperatures, the reactor and process equipment can be easily constructed from unique combinations of readily available materials, so the overall capital costs are low.

The EWT process is a super critical wet oxidation process carried out at temperatures above 374° C and at pressures of over 220 bar where changes in the physical properties of water make organics highly soluble. Under these conditions the organic materials are easily dissolved in water and contact with oxygen allows oxidation to proceed rapidly. Compared to the NKT/RISO process the reaction proceeds much faster so a smaller reactor system is required. Due to the higher temperatures and pressures the materials of construction are more exotic and expensive, resulting in overall higher capital costs than the NKT/RISO system.

Large organic molecules are broken down into carbon dioxide and smaller oxygen-rich organic compounds, mainly carboxylic acids or, if oxidation is complete, to carbon dioxide and water. Where complete oxidation is not cost-effective or required, the degree of destruction can be regulated so that compounds containing sulphur, chlorine or nitrogen are converted to sulphate, chloride, and ammonium nitrate or gaseous nitrogen respectively. These compounds are generally very water-soluble, and in the case of soils, are easily separated from the soil matrix where after-treatment of the discharge liquids may be completed using a conventional biological process.

Transportable liquids demonstration plant, Edmonton, Alberta.

Pulp and paper companies have shown particular interest in the technologies for site remediation associated with previous wood treatment activities and treatment of high organic content streams to close bleach plants, and to increase chemical recovery capacity and treat contaminated sludges and waterways.

In particular the technologies have been used to:

• Reduce high concentrations of organics, both hazardous and non-hazardous, to levels that are easily biologically polished (municipal sewer dischargable). The NKT/RISO process is typically most cost-effective for this application.
• Completely destroy high concentrations of organics and discharge fully treated waters (cleaner than raw receiving water standard). The EWT process is typically most cost-effective for this application, depending on the contaminants and treatment targets.
• Extract and destroy organic contaminants in soils and sludges. For example, coal tar and PAH contaminated soils or sludges treated to CCME residential park land standards. For this application, either the NKT/RISO or EWT process can be cost-effective depending on the contaminants and treatment targets.
• Destroy organic contaminants mixed with inorganic chemicals allowing chemical recovery. The NKT/RISO or EWT process can be used, depending on the contaminants and treatment targets.

CPET believes that the best motivation for any company or industry to reduce or eliminate an environmental liability is a clear-cut economic benefit.

Where the economic benefit is not immediately apparent, delays may occur. By offering a range of treatment options on an all-in cost basis, companies are able to easily understand the alternatives and select the most cost- and regulatory-effective option. The end results desired are most importantly selected on the basis of what is required. Typical examples of the treatment levels that have been demonstrated and contracted for with the technologies include:

• 99.9%+ destruction of hazardous organics and 70-90%+ reduction in COD,
• 99.999%+ destruction of all C-H-O-N organics,
• destruction of restricted organic contaminants to CCME dischargeable levels,
• sufficient organic destruction to allow cost-effective chemical recovery.

The treatment costs for the technologies are dependent on the contaminants, their concentrations, the level of destruction required and volumes requiring treatment. Due to the significant differences changes in these variables can have, cost comparisons are only relevant on a clearly defined case, or on a relative basis. In general, the technologies are most applicable for feed organic concentrations of 5,000-300,000 PPM, under conditions where the contaminants are in wet conditions such as contaminated liquids, lagoon sludges, or wet soils.

Feed contaminant types, concentrations and treatment levels are agreed to and the materials are accepted for treatment in a feed pile or feed tank. The materials are treated on site and returned, treated to the target levels and to a discharge pile or pipe at a cost per tonne (all costs in) basis.

In comparison to incineration, the technologies are easier to permit and are less affected by high moisture contents and the destruction efficiencies are more insensitive to variations in fuel values of the waste stream.

In comparison to biological systems the technologies are compact and can treat hazardous wastes and biologically toxic materials at high concentrations and at high destruction levels. Case studies have shown treatment cost reductions of up to 50% compared to existing treatment options.

Typical examples of all-in treatment costs including capital, return on capital, maintenance, labour and all utilities, are:

• $0.02-0.25/litre using the NKT/RISO process with discharge of municipally acceptable wastewaters to a municipal waste treatment system including municipal charges or a biological polishing system.
• $0.08-0.50/litre using the EWT supercritical process, discharging waters that are cleaner than the raw receiving waters.
• $75-200/tonne for treating contaminated soils and/or sludges to CCME levels acceptable for final disposition of the solids at the site they were removed from.

Costs for chemical recovery are so dependent on the contaminant and residual levels that can be accepted in the chemicals being recovered that no general numbers are meaningful. It can be stated, however, that the economics of wet oxidation for chemical recovery have proven cost-effective.