CATALYTIC WET AIR OXIDATION OF BLACK LIQUOR

Abstract

Today, the survival of process industries is becoming increasingly dependent upon the environmental sustainability of their technologies. Most industrial processes produce a waste stream that may contain high concentrations of ammonia, hydrogen sulphide and other noxious gases. The pulp and paper industry has been brought under the list of 17 most polluting sectors as identified by the central pollution control board. The wastewaters from these mills have high BOD, COD, pH, temperature and colour. However, rising general awareness, stricter implementation of environmental regulations and the need to survive in a highly competitive market are slowly forcing the mills to upgrade and improve practices. The choice of treatment method for a particle effluent stream- is governed by factors such as the organic or inorganic constituent, their concentration, toxicity and environmental discharge standards. Wet Air Oxidation (WAO) is a newly emerging technique for the aerobic oxidation of an organic wastewater under high temperature and pressure. The WAO is used as a pretreatment step so that the resulting solution can be treated biologically. The Catalytic Wet Air Oxidation (CWAO) is an alternative to WAO techniques, efficiently removes organics from an industrial stream using catalyst to obtain the better oxidation rates at lower temperatures and pressures. In present work, CWAO of black liquor, effluent from pulp and paper mill was carried out at atmospheric pressure and temperature of 70-98°C to remove the toxic organics from the effluent. The catalysts used for the tests include different compositions of CuO/Mn02, The removal of organics was found to occur through two steps: hydrolysis and wet oxidation. CuO/Mn02 having a composition of 50:50 by weight of two oxides was found to be the best with almost 85% COD removal at 95 °C using a catalyst concentration of 3 gm/1 at pH 6.0 after 6 hours of reaction time.