MERCER02-14
27
J.
Ionizing radiation – The adverse effects of ionizing radiation on biological systems have
been evident since its discovery, and attempts have been made to introduce radioactive
materials into antifouling coatings. Studies carried out using thallium-204 radioisotopes
demonstrated the significant antifouling capability of this material. However, the dosage
required (20 rads h
-1
) was considered too high for comfortable handling by untrained
operators. Nuclear power plants, which have highly trained operators in handling radioactive
materials, could consider this as a viable technique for control of biofouling.
K.
Chlorination
Electrochlorination – For safety and cost reasons, electrochlorination has become more
widely used for power plant fouling control. Though some safety problems are eliminated in
electrochlorination, environmental safety concerns and restrictions remain, with the addition
of a significant capital equipment investment and equipment maintenance.
Electrochlorination produces hydrogen gas, whichmust be handled/vented appropriately.
Exomotive chlorination – To overcome the problem of biofouling, long-term low-level
continuous chlorination is usually used. Such a practice is also effective in the control of
condenser slime. Thismethodwas originally started at Carmarthen power station in theU.K.
The dose employed is insufficient to kill mussels but sufficient to create an environment to
deter them from settling in the cooling water system and to cause them to move out, hence
the term exomotive chlorination. Exomotive chlorination is found to be economical and
relatively harmless to important nontarget commercial organisms.
Copper and chlorine – A recent successful use of a combination of copper and chlorine has
been reported by bothCEGB and EPRI. Results of both showed that the chlorine and copper
systemwas at least six times as effective as chlorine alone against macrofouling and three
times as effective againstmicrofoulants.
Pulsed chlorination – Periodic chlorination shock, with high doses has also been found to be
an effective approach at killing or controllingmost fouling organisms.
8.2.4. Summary
Although alternative biocides are available, sodium hypochlorite still remains themost common
method for biofouling control in cooling water systems and is often preferred to others because
of its proven effectiveness, easy availability and relatively low cost.
Three basic considerations should be kept in mind when employing chlorine, irrespective of its
source: (a) safety associated with production, transport and/or storage, (b) potential threat to
marine life, and (c) the variability in chlorine demand based on water temperature, salinity, and
organic load should be addressed to optimize the process. Intermittent or pulsed chlorination can
also be very effective if optimized andproperlymonitored.
