Diagnostic of oxidant production in under water
pulsed corona discharge
PO Box: 3640 Karlsruhe 76021 (Germany)
e-mail:
suryakant.gupta@ihm.fzk.de
Because
of undesirable side effects of chemical methods pulsed underwater corona
discharge is emerging as a potential future advanced oxidation process (A.O.P.)
for water disinfection. In Advanced Oxidation Processes the energy (chemical,
electrical or radiative) is applied into the water matrix to produce highly
reactive oxidants, which then attack and destroy the target compound(s). In
pulsed corona discharges first the formation of a plasma channel takes place,
this is a non - thermal discharge with a low degree of ionisation and electron
densities. At the tip of this plasma channel the electric field strength
reaches up to more then 20 MV/m. This strong pulse electric field produces the
electrons with energies above 10 eV.
It has been demonstrated that electrons with this energy can dissociate
water and oxygen molecule and produces various reactive radicals (OHˇ, Hˇ, Oˇ,
HO2ˇ), molecular species (H2O2, H2, O2), and ultraviolet radiation. In
addition, the expansion of the plasma channel against the surrounding water generates
an intense shock wave with pressure of the order of hundreds of MPa. The
resulting shockwave also helps to induce free radical reactions indirectly via
electrohydraulic cavitations. Among all these reactive oxidants the hydroxyl
radicals, ozone and hydrogen peroxide are the strongest oxidizers. The hydroxyl
radical is so reactive that it reacts with virtually most of organics or
bacteria in water so it could form the basis of a treatment system of general
applicability. To understand this in detail and to improve the efficiency of
the overall system there is a need of development of suitable online diagnostic
mechanism, which can quantitatively determine these short lived and highly
reactive oxidants during the pulsed underwater corona discharge process. Based
on a chain of experiments to measure the yield of oxidants quantitatively we
could successfully develop suitable diagnostic methods for the pulsed
underwater corona discharge set-up. In this paper we are going to discuss
different methods and their results for quantitative determination of OH
radicals, H2O2, and ozone in liquid as well as in the gas phase under pulsed corona
discharge conditions.