NAMS 2002 Workshop - ICOM 2008

the current treatment line. A lab-scale adsorption unit followed the filtration.
Chlorine components were monitored; in particular, combined chlorine was
measured, which gave the concentration of disinfection by-products in the water.
Chemical water quality was followed depending on the number of swimmers and
activity. It appears that disinfection by-products concentration increases rapidly
with pool usage. However with the high variability of the number of swimmers
and the difficulty of quantifying their activity, no correlation was found between
those parameters. Combined chlorine concentration at the end of the day often
exceeds the French standard legislation, showing the non efficiency of the
classical treatment. Pool usage also has a high influence on the membrane
permeability. A constant and high number of swimmers during one day or baby
swimmer activity during 4 hours can involve a permeability decrease of 2.4 L h -1
m -2 bar -1 with each hour of filtration. After 18 months, optimal ultrafiltration
operating conditions were found to be at a transmembrane pressure (TMP) of
0.45 bar and a filtration time (Tf) of 60 min for the entire range of each water
quality parameter studied. Backwashes appear to be sufficient to maintain
membrane permeability when pollution is introduced during a short period. The
closure of the pool during night and holidays when combined with
filtration/backwashes cycles can lead to the full recovery of permeability. On the
contrary, when the pool is subjected to a constant high usage, like during the
summer months, backwashes are not sufficient and the permeability constantly
decreases. However, permeability never decreased less than 160 L h -1 m -2 bar -1 .
The adsorption step limited the concentration of combined chlorine in water to
0.35 ppm, well below the limit given by the French legislation (0.6 ppm). When
the adsorption material is fresh, active chlorine is readily adsorbed to the surface,
but after 24 hours this effect is reduced to less than 50% and the active chlorine
standard is maintained.
This hybrid ultrafiltration adsorption process responds well to all the three
required criteria of swimming pool water treatment by disinfecting and clarifying
while simultaneously reducing the concentration of combined chlorine.