Frequently Asked Questions and Tutorials

What materials were used?

The final materials, amounts and positioning were determined by the Control and Specifications coordination team according to the following amounts:

Final Specifications

Tube: 3’ by 1” diameter clear plastic tube

Sand: provided by soils lab (30 inches)

Fiberglass: torn-up fiberglass insulation that is put in 30 inches of tube and compacted only by the    weight of the water

Filter Depth: 2 inches gravel at bottom, 30 inches sand or fiberglass, 4 inches empty space at top.

Iron Shavings: 5.6 grams on top of the sand. Each group will rust their own shavings using  1 cup of tap water with 3 tablespoons dissolved in it. Let it rust for 48 hours.

Nylon:  ½ inch all the way on the top and ½ inch on the bottom (on top of the gravel)

Flow rate: 10 mL/hour (adjusted by measuring water going in)

Research

For iron, sand, filter depth and flow rate information:

http://web.mit.edu/watsan/ tech_hwts_chemical_ kanchanarsenicfilter.html

http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5964662

https://engineering.purdue.edu/~frankenb/NU-prowd/sand.htm

Our group in particular used fiberglass and iron shavings, with no nylon

Why is rusted iron used?

The rusted iron provides a slightly positively charged surface which microbes can latch to as the water is filtered, since microbes tend to have a negatively charged surface

How were the filings rusted?

By placing the 5.6 grams of iron shavings in a salt water bath for two days (the solution was composed of 3 tablespoons of salt in 1 cup of unfiltered tap water)

What do you mean by "growing" the filter?

The microbial mat inside the filter grows inside the filter overtime, feeding off of the pathogens in the water

How long does it take for the filter to grow?

The filter is usually considered functional after 2 weeks of growth, however if maintained properly, it will continue to grow

How is the filter "fed" regularly?

The biofilm requires a steady source of nutrients which can be provided by running unfiltered river water through the filter. Because the filter can dry out, killing the biofilm, it is important to keep the water flowing. This can be achieved by adjusting the output hose to arch up along the filter's housing to decrease water pressure and slow the flow rate

What is Turbidity and how is it measured?

Where can I find more information about biosand filters?

Under the archives section of our blog (on the right side of the page) posts titled Literature Study will have links to articles and background research