FILTRATION AND SEPARATION
The solution is clear
Loch Ascog was a water treatment
works that had been plagued with
algae problems at each loch turn
over. Twice a year filamentous algae
were drawn into the WTW causing
throughput problems and
continuous filter blockages. Filter
Clear were brought in to remove
this algae and maintain the plant
during the turn over season.
Mark Anderson explains
L
och Ascog Water Treatment Works (WTW)
consisted of two raw water intake wells
and five slow sand filters. The project was
concerned with the upgrading of the works to
satisfy the following drinking water (DW)
directives The Spruce Filter turbidity reduction
■ DW 3.1 Coliforms ■ It has a naturally high positive charge whereas ■ DW 3.1 Coliforms – average reduction after
■ DW 3.2 Manganese micro-organisms such as Cryptosporidium & Spruce Filtration 80%
■ DW 3.7 Pesticides/Taste and Odour Legionella are negatively charged. This ‘Zeta ■ DW 3.2 Manganese – average reduction after
■ DW 3.9 Turbidity Potential’ enhances the highly effective Spruce Filtration 94%
■ DW13.1 Aesthetic Quality mechanical filtration with surface adsorption to ■ DW 3.7 Pesticides/Taste and Odour – both
(Disinfection Control) remove up to 99.954% of solids down to significantly improved due to removal of algae
0.2micron, without chemical addition. ■ DW 3.9 Turbidity – average reduction after
The Spruce Filter, operating on a seasonal basis, ■ It has catalytic properties enabling significant Spruce Filtration 82% (See Graph)
was installed between the existing raw water reduction in both iron and manganese. Iron and ■ DW13.1 Aesthetic Quality (Disinfection
intake wells and the slow sand filters for the Manganese are transitional elements that when Control) – improved visible quality to extent
removal of algal, which consisted mainly of exposed to a catalyst such as the Spruce Filter never seen before by site operators
filamentous algae. Some algae are pathogenic to media change from soluble into insoluble
humans producing endotoxins that can cause through catalytic oxidation. The success of the project brought the site into
gastroenteritis, while others interfere with ■ As the filter is a deep bed filter, it has a large compliance without any additional treatment.
treatment plant operations, specifically with filter surface area for the build up of biofilm. This is The loading placed on the downstream iron
operations. The existing slow sand filters were enhanced by the natural Zeta Potential within the and manganese system was significantly
retained as they contained an activated carbon filter media. The build up of biofilm causes reduced, allowing it to run at maximum
sandwich layer. selected micro-organisms to oxidise Iron and performance.
manganese into dense precipitates; enabling
The Technology three to five times the metal retention when Conclusions
The Spruce Filter is a non-chemical deep bed compared with chemically formed precipitates. The higher filtration rates and longer filter runs
filter, capable of exceptional particle filtration, ■ The unique properties of the Spruce Media that can be obtained with the Spruce Filter has
combining mechanical and adsorptive filtration. allowed the site flowrate (45litres/sec) to be provided a substantial saving with regards to
The filter bed comprises of four layers of inert obtained in a 2m diameter vessel, with the capital expenditure against competing
particulate material. From the top layer to the benefit of a guaranteed lifespan of 15 years. technologies. When comparing the Spruce with a
bottom layer the coarseness of the particulates conventional sand filter the performance,
decrease, while the density of the particulate Results footprint and volume of wash water required to
material increases. The final adsorptive element For the WTW, the installation of the Spruce Filter clean the filter-bed allied to substantial savings
of the filter bed was significant in the success of has been of exceptional benefit. Initially installed on the civil costs, and the vastly reduced or non-
the project from several aspects. as a pre-treatment to sand, the remit of the filter existent chemical addition make the Spruce Filter
was to assist in reduction of filamentous algae, a clear winner. ■■■
■ Filtration performance down to 0.2micron at especially during the lake turnover. However, the
flowrates of up to 60m3/m2.hr and a maximum system produced results that helped with all five For further information contact
inlet solids loadings in excess 500mg/l of the key drinking water directives: mark@filterclear.com
September 2009 Water & Wastewater Treatment 21