NAMS 2002 Workshop - ICOM 2008

Drinking and Wastewater Applications III – 3
Wednesday July 16, 10:45 AM-11:15 AM, Maui
Membrane Enhanced Ultraviolet Oxidation of Polyethylene Glycol
Wastewaters
D. Patterson (Speaker), Laboratory for Green Process Engineering, University of Auckland,
Auckland, New Zealand - darrell.patterson@auckland.ac.nz
T. Vranjes, Laboratory for Green Process Engineering, University of Auckland, Auckland, New
Zealand
Ultraviolet (UV) advanced oxidation is a commonly used system used to degrade
biologically recalcitrant wastewaters. It typically consists of a non selective flow-
through reactor containing ultraviolet lamps irradiating a wastewater, into which
an oxidant is dosed. The UV energy is sufficient to generate the strongly
oxidising hydroxyl free radical (HO") from the water and oxidant, which
mineralises the organic compounds in the wastewater via a series of radical
reactions. Standard UV oxidation systems do not give an efficient treatment, as
they can be non- selective and wasteful of the oxidant and other active radicals
because they have no method of ensuring that only fully oxidised compounds
leave in the effluent. This can have dire consequences: If the oxidation
technology is the sole means of treating the water, untreated waste may exit the
system, contravening the discharge consent. If the water is being pre- treated by
the oxidation technology to make it more biodegradable, then the more refractory
compounds may not be adequately oxidised, leaving them biologically
recalcitrant. Finally, the radicals (which destroy the organic waste) are always
lost with the treated effluent, creating a severe process inefficiency.
A new technology, called Membrane Enhanced Oxidation (MemOx), could
overcome these limitations. If the compounds in the water streams undergo an
order of magnitude change in size when oxidised, ionize, or change polarity, then
a membrane may be applied to selectively retain the unoxidised molecules in the
UV reactor. The membrane is chosen so that unoxidised molecules cannot
permeate through the membrane, whilst the smaller, sufficiently oxidised
molecules permeate and are discharged in the effluent. Also, by recycling
partially oxidised molecules back into the reactor, this technology can increase
the rate of reaction by synergistic rate acceleration. This is because the recycled,
unoxidised effluent contains radical species, which increase the radical
concentration in the reactor, thereby increasing the rate of reaction.
This paper will outline the preliminary work conducted at the University of
Auckland developing the MemOx process. PEG1500 was chosen as the model
organic pollutant and UV oxidised using solutions at 1 to 2 g/L using hydrogen
peroxide (at varying concentrations) as the oxidant. The oxidation was carried