Catalytic wet air oxidation (CWAO), which was
developed in 1980s based on wet air oxidation (WAO), is considered to be
effective to the degradation of highly concentrated contaminants as an emerging
technique. With the assistance of catalysts under high temperature and
pressure, the organics could be mineralized or converted into easily
biodegraded products by the oxidation of air. The advantages of CWAO process
relative to other techniques include the possibility of simultaneous removal of
organics and nitrogen/sulfur compounds in only hours, a compact plant design
for low space requirements and no secondary pollutants including sludge and
ashes. Compared with WAO, the employment of efficient catalysts in CWAO makes
it possible to achieve better results under the relaxed conditions. Therefore,
CWAO is always utilized to treat various wastewaters with complex composition
and highly concentrated refractory compounds discharged from the industries
such as coking, petrochemistry, pesticide manufacturing and food processing.
CWAO reaction is generally
carried out at temperatures between 150 and 320 oC under pressures ranging from
5 to 200 bars in the presence of heterogeneous catalyst. The economical
efficiency of CWAO depends on the characteristics of wastewater and treatment
requirements. The running cost of CWAO is close to being competitive with or
even lower than that of biological process from the view of the reduced CODCr
per kilogram per unit time, especially for the wastewater with high COD value
of over ten thousands. The wastewater with COD of over 20,000 mg/L could be
treated without supplying any auxiliary fuel that significantly reduces the
investment and running costs.