SAND FILTER TESTS AND PROCEDURE
The following procedures and tests were completed by Headwaters Engineering on two small scale sand filters to demonstrate the filtration capabilities of this design. The filters had different particle size fine sand media to determine which system would be most efficient. The overall setup of the filters is shown in the figure below. The filter on the right was not used. The procedure is then detailed in the following pictures/captions and the results are shown. All tests were completed in the Environmental Engineering Lab at Montana State University.
PROCEDURE
1)The sieve stacks in the Geotechnical lab are prepared to filter the soil.
2)The desired media captured in the sieves are sorted into two buckets. One contains the sand captured between the No. 100 and No. 50 (.0059 in through .0117in or .15 mm through .3 mm) sieve while the other has the sand captured between the No. 50 and No. 40 sieve (.0117in through .0165in or .3mm through .435 mm).
3)Gravel caught on the 3/8-inch sieve is used for the underdrain and is also placed on top of the filter to dissipate energy from the poured water and creating an even distribution of flow.
4)The pea gravel caught on the No. 8 sieve is used beneath the fine sand layer to keep that sand from sifting into the underdrain.
5)The gravel and sand are then placed in the filters. The 3/8- inch gravel (9.5mm) is placed on the bottom 2 inches (5 cm) of the filter, followed by 4 inches (11 cm) of the pea gravel and 22 inches(56 cm) of the fine sand.
6)Iron water iscreated by aerating a steel wool pad suspended in a large container of water. This is done until the mixture is completely saturated with iron and the steel wool no longer oxidizes.
7)The saturated iron solution is then diluted using three parts of water to one part of the created iron solution. The amount of diluted solution used in each of the tests was 1.2 gallons (4.5 liters).
A sample of the diluted solution before it is added to the filters
8)The diluted solution is then added to each of the filters. The effluent is captured in containers for further observation.
These pictures show the water after filtration. These are samples from the first and second tests using the filter loaded with the No. 50 (.0117 in or .3 mm) filter media.
The filtered water from the first and second tests using the filter loaded with the media captured on the No. 100 sieve (.0059 in or .15 mm)
RESULTS
The only results of this initial experiment are from general observation. An iron and pH combination test kit was recently purchased by Headwaters Engineering.
It is apparent from these initial tests that the slow sand filter is successful at removing the iron from the water. The color, odor, and taste of the water had no obvious traces of iron after purification. The purified water is still significantly turbid. This can be attributed to the fact that the fine sand media was not properly cleaned before being added to the filter. The excess particles of dirt/dust/mud are now suspended in the water causing the strong turbidity. By properly cleaning the sand before placing in the filter, the turbidity of the water will be reduced.
The flow rate of the filter also significantly decreased between the first and second tests. The pore spaces in the sand are being clogged rapidly due to the excess dirt and iron particles. Additional tests on the filters (with clean fine sand media) may result in larger and more consistent flow rates.