Photocatalytic industrial effluent treatment
Photocatalysis has been considered for a number of years to be an ideal technique for the treatment of industrial effluents. However, until now the cost of the process has been prohibitive for all but the most intractable problems. Recently Photox Bradford has developed a new approach to the application of the technique based around a new catalyst developed at the University of Bradford and a much simpler reactor design.
Chemists at the University of Bradford have researched the suitability of
photocatalysts as an effective water treatment process for the part 20
years. They have accumulated expertise in the treatment of various organic
compounds as well as the removal of heavy metals from industrial process
water. Examples examined have included the destruction of dyes, pesticides
(OPs and SPs) phenols, cyanide, chromium removal, COD reduction,
surfactants, greases and oils.
Because the process gradually breaks down the contaminant molecule, no
residue of the original material remains and therefore no sludge requiring
disposal to landfill is produced. This results in considerable savings and a
simpler operation of the equipment involved.
Additionally, because the contaminant is attracted strongly to the surface
of the catalyst, the process will continue to work at very low
concentrations allowing sub part-per-million consents to be achieved.
Taken together, these two advantages mean that the product water may be
recycled, resulting in savings in the cost of input water and effluent
Traditionally, in order for photocatalysis to be effective the catalyst has
been added to the effluent as an extremely fine dust. This makes the
catalyst efficient in its use of the UV light energy but the extremely fine
powder is difficult and expensive to recover from the effluent stream. This
has meant that approximately 90 per cent of the cost of treating process
effluents using this method has been due to the use of sophisticated solid
recovery methods usually an expensive membrane and catalyst release
system. Quotes from a small US supplier have indicted that the approximate
capital cost for a typical UK dyer for example would be in the region of
As a result of the research conducted by Dr Bickley and Dr Hogg at the
University of Bradford, a catalyst with an activity that is comparable to
that of a fine dust but has an average particle size that is nearly 100
times larger has been developed. In practice, this means that instead of
using a custom-built form of ceramic membrane filtration system to remove
the catalyst at a cost of approximately £1 million per 10m3/hr capacity, a
standard off-the-shelf separator is able to remove the new, coarser catalyst
at a cost of approximately £6,000 per 10m3/hr capacity.
The system itself consists of a series of interconnected tanks and trays
above which are mounted standard UV lamps. A single pump is used to
reticulate the catalyst slurry via the separator and is the only moving
component in the flow system.
Following its formation in 1997, Photox has completed a number of successful
trials on a range of process effluents ranging from the removal of chromium
ions (15pm to 0ppm) to the complete removal of colour from screen printing
In the summer of 1998, Photox won an innovation award from the Department of
Trade and Industry’s Smart Competition. This has been used to fund the
development, through a firm of engineering subcontractors, of a full-scale
production unit that can be transported to industrial sites to demonstrate
the effectiveness of the process on waste streams up to 10m3/hr. The unit is
modular and the process takes place at ambient temperatures and pressures.