Friday, August 29, 2014

Coal and Drinking Water

Coal has been a bit of a topic in Washington State and Oregon as well with several coal export terminal schemes proposed. Coal has been portrayed as a toxic substance by some opponents to coal export terminals. But there is a lot of variability in coal toxicity and quality. Powder River coal, the primary coal that is being railroaded across Washington State is low in sulfur relative to most other coal, but is not particularly high in energy content. That low sulfur content makes it an attractive coal relative to more polluting coal with higher sulfur.

High quality anthracite coal is very carbon rich, has a very high energy content and burns very cleanly (excepting CO2 emissions). Very high quality anthracite is more typically used for steel production and for water filtration. Yes, you might be drinking water that passed through a sand filter full of anthracite coal.

Anthracite is almost glass-like and when crushed it makes a fine sand that combined with the carbon content makes an excellent filter media for purifying drinking water.

I was doing some source area work for a water district and got a tour of the treatment plant and had the fortune of getting to see the backwash cleaning of the anthracite and garnet sand filter media.

Backwashing of filter media

Periodically the water flow is reversed with a surge of water to break up the sand column and
knock out the trapped fine sediment.

The muddy water is then routed to a waste discharge out of the system. The backwash is timed to last long enough for the water to clarify. All that brown fine sediment coloring the water had been trapped by the anthracite coal. Good clean water thanks to coal!


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