The treatment of a toxic nitrgenous-containing organic compound by supercritical water oxidation and wet air oxidation processess [i.e. processes] : operating conditions and reaction kinetics
Hydrothermal. oxidation processes at high pressure and temperature can be operated at
conditions below or above the critical point of water (374.2'C and 221 bar). The former, is
known as Wet Air Oxidation (WAO) and the latter is often referred to as Supercritical Water
Oxidation (SCWO). The researchp resentedin this thesisa imed at investigatingt he viability
of SCWO and WAO in treating 1,8- diazabicyclo [5.4.0] undec-7-ene (DBU)-containing
wastewaterp roducedf rom pharmaceuticaal pplications.D BU was selecteda s a recalcitrant
nitrogenous compound of industrial interest, which is difficult to treat by conventional
treatmentm ethodso f industrial wastewatersI.n principle, the two processesc an be regarded
to a certaine xtenta s the samep rocessw ith the main differenceb eing the conditionso f water.
Among many other implications( will be discussedin the thesis),t his resultsi n the existence
of two phasesin the subcriticalr angew hile it is monophasica t the supercriticalr ange.
In SCWO, a laboratory scale system consisting of a plug-reactor was employed for
acquisition of novel kinetic data in the supercritical region by investigating the effect of
several operating parameters namely temperature, pressure, oxidant-to-organic ratio, organic
concentration and residence time. The possible reactions by-products were also investigated
by following the fates of carbon and nitrogen at various reaction conditions.
A laboratorys cales emi-batchs ystemc onsistingo f a stirredt ank reactorw as employedf or the
WAO studies to obtain novel kinetic data of the destruction of DBU in the subcritical region.
The investigation was focused on the effect of reaction temperature, pressure, organic concentration and the speed of impeller. No studies on oxidant-to-organic ratio were
undertakena s the systemo peratedin vast excesso f oxidant.
The kinetic data acquired in both sub- and supercritical systems were consequently
incorporatedin the semi-batcha nd continuousr eactore quationsfo r WAO and SCWO system
respectively to develop kinetic rate expressions for both processes.
It was found that the global rate expressions uccessfullyd escribedt he kinetics of SCWO in a
plug flow continuous reactor, while the WAO semi-batch process was modelled by the
pseudo-first order expression. Complete organic carbon removal was achieved in the SCWO
system, but incomplete removal was observed in the WAO system even at extreme operation
conditions. Significant proportion of nitrogen component from the waste was converted to
ammonia rather than nitrogen gas.