Wet Air Oxidation: Applicability and Safety Design When One Standard Is Annulled and One Is a Draft

1. Framing: the Standard Supply Situation for Wet Air Oxidation

In China, wet air oxidation (WAO) and catalytic wet air oxidation (CWAO) currently have no corresponding national engineering specification. The only written documents available are two group standards, and the status of each must be verified first.

• T/SEESA 005-2020, Technical Specification for High Concentration Organic Wastewater and Sludge Treatment by Wet Air Oxidation Technology, issued 15 January 2020 and effective 1 February 2020, covering design, process, construction, acceptance, operation and management for refractory high-strength organic wastewater (including landfill leachate) and organic sludge (industrial and municipal). According to the National Digital Standard Library record, this standard was annulled on 21 July 2026.
• T/TMAC, Technical Specification for Catalytic Wet Oxidation of Industrial Wastewater (draft for comment), under the China Technology Market Association, number to be assigned, eight pages, specifying work requirements, work flow, work steps, technical requirements and test methods, applicable to industrial wastewater treatment and especially to wastewater containing high concentrations of organic pollutants.

Read together the conclusion is direct: as of this writing there is no currently valid dedicated standard for wet air oxidation. Any design document citing T/SEESA 005-2020 must first verify its annulment, and any use of the T/TMAC text must be marked as a draft for comment.

2. Applicability Boundaries: Design Parameters from T/SEESA 005-2020

That standard gives one common set of conventional design parameters for both the sludge line and the high-strength organic wastewater line.

• Reaction temperature 180 degrees Celsius to 320 degrees Celsius.
• Reaction time 30 min to 120 min.
• Reaction pressure 2.5 MPa to 15 MPa.
• COD removal above 50 percent.

For the sludge route it adds two hard indicators.

• Clause 5.4: where the process can be energy self-sustaining without external heat, and without impairing sludge fluidity, the sludge concentration should be above 2.5 percent, and higher is better; excess sludge must be pre-thickened in a sludge thickener to the required concentration before entering the main reactor.
• Clause 7.4.2: feed sludge solids content shall be not less than 2.5 percent, and sludge mass reduction shall be not less than 70 percent.

Clause 5.7 further states that the main reactor consists of a pressure vessel made of special metallic materials, including heat exchangers, a reaction vessel and a gas-liquid separator, with materials selected according to wastewater and sludge characteristics and treatment requirements.

One caution: the widely circulated statement that the scope is "COD 15,000 to 100,000 mg/L with salinity below 5 percent" has no corresponding clause number in the public information of the standard information service platform and must not be written into design documents as a basis.

3. Quantified Parameters for Catalytic Wet Oxidation (T/TMAC Draft)

Table 1 of the draft gives a complete parameter set - the most detailed written values currently obtainable (note: draft for comment, not mandatory provisions).

• Feed: initial COD 3,000 mg/L to 50,000 mg/L; wastewater flow 1 L/min to 5 L/min.
• Reaction conditions: reaction temperature 150 degrees Celsius to 300 degrees Celsius; working pressure 2 MPa to 15 MPa; contact time 30 min to 90 min (adjusted to pollutant type and concentration); initial pH 6 to 9 (adjusted with alkali solution depending on catalyst type).
• Catalyst: CuO, Fe2O3, CeO2 or MnO2; catalyst loading 10 wt% to 20 wt%.
• Oxidant: oxygen partial pressure 0.5 MPa to 2 MPa; H2O2 concentration 0.5 mol/L to 2 mol/L.
• Removal performance: COD removal not less than 70 percent within 3 h; at 40 min COD removal above 80 percent and colour removal above 90 percent; overall COD removal not less than 90 percent, NH3-N removal not less than 99 percent, and BOD/COD ratio not less than 0.3; effluent organic and NH3-N removal not less than 99 percent.

The BOD/COD not less than 0.3 requirement deserves particular attention: it shows that CWAO is frequently positioned to improve biodegradability rather than to achieve complete mineralisation, and is normally followed by a biological unit rather than direct discharge.

4. Equipment and Control Accuracy Requirements

• 4.3.1.1: the main reactor shall be resistant to high temperature (not less than 300 degrees Celsius) and high pressure (not less than 15 MPa) and comply with GB/T 150.1.
• 4.3.1.2: precise temperature control and a pressure regulating valve shall be provided.
• 4.3.1.3: the oxidant dosing system shall include corrosion-resistant piping, a flow control valve and a return line.
• 4.3.1.4: the off-gas treatment unit shall include a gas-liquid separation stage with separation efficiency not less than 95 percent.
• 4.3.1.5: the solids-liquid separation system shall have sedimentation and filtration efficiency not less than 90 percent.
• 4.3.2.1: temperature control accuracy within plus or minus 1 degree Celsius; pressure control within plus or minus 0.1 MPa.
• 4.3.2.2: oxidant flow control error within plus or minus 2 percent.
• 4.3.2.3: emissions from the off-gas unit shall meet GB 16297, Integrated Emission Standard of Air Pollutants.
• 4.3.2.4: all equipment shall be calibrated periodically and calibration records kept for not less than one year; Table 1 additionally sets a calibration interval of every 3 to 6 months for the temperature control system and pressure regulator.

5. Safety Design: the Pressure Vessel Is the Central Risk

5.1 The version reference must be pinned down

Clause 4.3.1.1 of the draft says only "comply with the relevant provisions of GB/T 150.1" and does so as an undated reference. According to the national standard information public service platform, GB/T 150.1-2011, Pressure Vessels - Part 1: General Requirements (issued 21 November 2011, effective 1 March 2012, under the National Technical Committee on Boiler and Pressure Vessel Standardization), was annulled on 1 February 2025. Design documents must state the specific version adopted together with its current status, and may not simply write "GB/T 150.1".

5.2 Environment and personnel

• 4.1.1: the work area shall be well ventilated and the oxidant dosing location shall have dedicated ventilation.
• 4.1.2: ambient temperature 5 to 35 degrees Celsius and humidity 30 to 70 percent RH.
• 4.1.3: fire and explosion protection shall comply with GB 50016, Code for Fire Protection Design of Buildings (2018 edition).
• 4.1.4: the wastewater storage area shall have anti-seepage facilities and corrosion-resistant flooring.
• 4.2.2: operators shall hold an industrial wastewater treatment qualification; engineers shall hold intermediate professional titles or equivalent; at least one senior engineer shall be responsible for monitoring and adjusting process parameters.
• 4.2.3: personnel at oxidant dosing and equipment maintenance posts shall wear protective equipment (gloves, gas masks).
• 4.2.4: all operators shall be familiar with emergency response plans and drill regularly.

5.3 Start-up, shutdown and discharge

• 6.3: heat up gradually, raise pressure gradually to the process range and confirm gas tightness, then admit oxidant uniformly while monitoring agitation rate.
• 6.4.3: monitor off-gas pressure stability to avoid excessive discharge or leakage.
• 6.5: stop oxidant feed and reduce reactor temperature and pressure gradually before starting the discharge system; suspended solid catalyst shall be separated and recovered by settling or filtration.
• 6.6: off-gas is collected by the gas-liquid separator and sent to the off-gas polishing unit; solid residue is classified; regenerable catalyst returns to the system and waste is disposed of as hazardous waste.
• 6.7: flush periodically, check catalyst condition, keep operating logs, and service heating, pressurisation and oxygen supply equipment regularly.

6. Test Methods and the List That Must Be Determined by Testing

Table 2 of the draft maps each test item to a standard: initial COD and NH3-N per GB/T 31962; temperature and pressure measurement per GB/T 32327; catalyst performance per GB/T 38602, Test Method for Activity of Catalysts for Catalytic Wet Oxidation of Organic Wastewater; oxygen partial pressure and oxidant concentration per HJ/T 399; COD removal analysis per GB 8978 and GB/T 31962; initial and dynamic pH per GB/T 6920; off-gas polishing efficiency and residue handling performance per GB 16297; BOD5 per GB/T 7488; effluent per GB 18918 and HJ 535.

The following parameters have no values in available written documents and must be determined by testing:

• specific catalyst selection and service life (Table 1 gives only four candidate compounds and a loading range of 10 to 20 wt percent);
• salinity ceiling and chloride corrosion allowance;
• vessel material grade and wall thickness (the document requires only "special metallic materials" and compliance with GB/T 150.1);
• control limits for volatile organic compounds and odour in off-gas (it points to GB 16297 without giving values);
• energy consumption per tonne of water and heat recovery rate.

Sources: clauses 4.1 to 4.3, 6.1 to 6.7, Table 1 and Table 2 of the draft Technical Specification for Catalytic Wet Oxidation of Industrial Wastewater; the standard information page of T/SEESA 005-2020 including its annulment record; the standard information page of GB/T 150.1-2024.