Water Science & Technology: Water Supply Vol 1 No 2 pp 131–140 © IWA Publishing 2001
Removal of natural organic matter (NOM) using different coagulants and
lightweight expanded clay aggregate filters
B Eikebrokk* and T Saltnes**
*
SINTEF Civil and Environmental Engineering, Dept. Water and Wastewater,
N-7465 Trondheim, Norway
Department of Hydraulic and Environmental Engineering,
Norwegian University of Science and Technology, Trondheim, Norway
**
Department of Hydraulic and Environmental Engineering,
Norwegian University of Science and Technology, Trondheim, Norway
Optiroc a.s, Oslo, Norway
ABSTRACT
Chitosan and lightweight expanded clay aggregates were investigated as
alternatives to traditional metal coagulants and anthracite in pilot
scale coagulation-filtration experiments for the removal of natural
organic matter (NOM) from drinking water. The raw water tested covered
a range of colour and organic carbon of 15–50 mg Pt/L and
2–5 mg NPOC, respectively. Aluminium sulphate, poly aluminium
chlorides with different calcium content, iron chloride sulphate, and
chitosan coagulants were tested. The dual media filter bed was built
with 0.6 m of 0.8–1.6 mm lightweight expanded clay aggregates
(Filtralite) above 0.35 m of 0.4–0.8 mm sand. A conventional
anthracite-sand filter with the same layer depths and grain sizes was
used as a reference. In general, the maximum permissible concentration
level of 0.1-mg Me/L controlled the minimum coagulant dose requirements
when metal-based coagulants were used (Norwegian water quality standard).
Typical NOM removal efficiencies obtained with metal coagulantswere in the range of 75–90% and 40–70% with respect to colour
and organic carbon, respectively. Chitosan was able to remove colour
quite effectively, but this coagulant was less effective with respect
to organic carbon removal. Lightweight expanded clay aggregate was a
good alternative to anthracite, with lower rates of head loss build-up,
and increased filter run length and filter storage capacity. Only
small differences in effluent water quality were detected with the two
filters.
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