Study of alternatives for the design of a mobile unit for wastewater treatment by supercritical water oxidation

Abstract

Supercritical water oxidation (SCWO) has been shown to be an appropriate technology for the treatment of water containing toxic and hazardous substances, because it provides high destruction ef®ciencies. This paper reports a study of alternatives, and optimisation of various parameters and conditions, which are applied to the design of a mobile treatment unit. Phenol was selected as a model organic compound present in the feed stream and NaCl was selected as a model polar compound for solid separation. Pilot plant results show that ef®ciencies above 99.9% in phenol destruction are reached, at an operation temperature of about 650°C, with stoichiometric amounts of air. Feed streams with a wide range of heating values (lower limit 530 and upper limit 930 kJ kg À1 ) can be handled, because these values allow both thermal and mechanical energy recoveries, which are the key factor for economic feasibility. The unit is capable of handling wastewater containing toxic, recalcitrant or nonbiodegradable compounds that cannot be treated with global streams at the wastewater treatment plant of a factory. It is speci®cally proposed for use in industries in which wastewater contains solvent mixtures of ®ne chemicals and pharmaceuticals. # 2001 Society of Chemical Industry Keywords: supercritical water oxidation; mobile unit; salt separation; mass and energy balances 1 INTRODUCTION Supercritical water oxidation (SCWO) is a new clean technology for the ultimate destruction of varied organic wastes to generate CO 2 and H 2 O as the ®nal products. Water above its critical point (Tc = 374°C, Pc = 22 MPa), is a suitable medium to oxidise organics because it provides a very high solubility for both organics and gases and because the relatively high temperatures provide rapid oxidation rates. Detailed information on SCWO processes 1±4 and the properties of supercritical water are found in the literature.