Can tree bark filters be used to clean urban stormwater?

I had a pretty exciting Earth Day. I spent the morning on assignment for the US Forest Service Northern Research Station documenting installation of a treatment device that uses filters filled with tree bark to clean urban stormwater.

The filter boxes were installed by the Parks and People Foundation under the guidance of their Green Infrastructure Manager Christina Bradley, ASLA, LEED AP BD+C. The crew was already on the job when I arrived, preparing the pre-treatment box for installation.

P&P prepping for first filter box

The filters are designed by the US Forest Service Forest Products Lab and use ponderosa pine bark pellets, as demonstrated here by USFS FPL’s David Eustice:

2014-04-23 09.46.56 pellets

The pellets fill cages that the water flows through for treatment. There are three cages of pellets in each treatment box:

2014-04-23 09.31.12 box with three filters

The water flows into the pre-treatment box and then into dual, side-by-side treatment boxes and to an outflow at the rear. The set up installed looks like this (L to R): Inflow, pre-treatment, dual treatment boxes, outflow.

2014-04-23 10.58.32 three boxes with connnection

USFS NRS will assist with the monitoring plan so we can see if we’re making a difference. But don’t worry – this is not a shot in the dark. USFS FPL has a history of using these devices for over a decade. They have been used in agricultural and coal mine applications. However, this is the very first time they have been used in an urban stormwater application. Being part of that made this a very memorable Earth Day!

Many thanks to Baltimore City, Parks and People, USFS FPL and USFS NRS for helping people in cities use trees to improve water quality.


4 thoughts on “Can tree bark filters be used to clean urban stormwater?

  1. That looks fairly easily retrofitable….what drainage area is being treated by this? How long does the mulch last before it has to be changed out?

    • I would have to check with Christina at Parks and People for the drainage area. For the mulch…we don’t know. You change a filter in your home HVAC when it is dirty. In this setup, we will not see it in the mulch. We will see it in a change in the water quality monitoring data. When quality begins to decrease, we’ll know it’s time for a change but service life of filter material is one of the things we hope to figure out here.

  2. Reblogged this on BDG Blog and commented:
    Interesting project in Baltimore, Maryland. The treatment and control of stormwater in our urban settings is moving into the fore front of modern design and thinking. It is great to see sustainable alternatives in action for the treatment of stormwater that will provide monitoring and data to test their success. Should be interesting to follow.

  3. Jeff – I’m just seeing your question now. The drainage area served by the boxes is 8600 sf. That drainage area is 100% impervious surfaces, including roadway, curb, and sidewalks. Thank you for your question! And a big thank you to Mike for the post and all of his hard work!

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