Abstract:
The Kilinochchi water treatment plant (KWTP) which has a Roughing Filter, an Aerator
and Slow Sand Filters (SSF-KWTP) had been designed to meet the increasing water demand of
Kilinochchi district. The Source for the KWTP is Dry Aru which is fed by Iranamadhu reservoir.
Huge seasonal fluctuation of turbidity and the algal population in Dry Aru affect the performance
of the KWTP and the plant shut down for several months. The decision has been taken to
incorporate the coagulation flocculation treatment system to KWTP to improve the treatment
efficiency. Slow sand filtration works primarily through biological activity on the sand bed and it
is a chemical free treatment system. Adding pre-treatment chemical may affect the biofilm layer
as well as the performance of the slow sand filter. Hence the purpose of the study is to evaluate
the filtration efficiency of the slow sand filter after pretreatment with poly aluminium chloride
(PACL) coagulant chemical. Real Slow sand filter model (SSF-Model) has been built and
connected with coagulation flocculation system. Turbidity reduction percentage of the SSF-Model
and SSF-KWTP was in the range of 75- 97.05% and 90.63-97.30% respectively. Average colour
reduction % of the SSF-Model was 83.87%. Algal removal efficiency of the SSF-Model was 58%
and the SSF-KWTP was 63.7%. There was no significant difference in performance of SSF-Model
in terms of Turbidity (4%), Manganese (3.9%), Total iron (0.4%) and Algal removal (5.6%)
efficiency compared with the SSF-KWTP. Colour removal efficiency (14%) of SSF-Model was
significantly lower than SSF-KWTP. It can be concluded that coagulation flocculation treatment
system with pretreatment chemical as PACL can be incorporated to improve the treatment
efficiency to KWTP
