Biohavens – the only truly bio-mimicking floating wetland – Case Study #2 – propylene glycol removal

24 October 2015

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The BioHaven range of floating wetlands, also known as floating islands, provides a wide range of wetland aesthetic, habitat and treatment options designed from nature.  DH Environmental Consulting (Pty) Ltd (South Africa) has been partnered with Floating Island International, the designers of the BioHaven range, since 2008.  Over the next while our blog will document some Biohaven case studies.

2. BioHavens Remove Propylene Glycol from Airport Stormwater

Project Location: Bangor International Airport, Maine USA

A BioHaven® floating treatment wetland (FTW) installed to remove propylene glycol from airport stormwater has thrived during harsh conditions but its efficacy has not been measurable due to its small size and low glycol concentrations. However, glycol concentrations were reduced from greater than 500 mg/L to less than 1 mg/L in subsequent lab-scale BioHaven tests.

Overview

In early 2008, Bangor International Airport personnel began evaluating BioHavens to enhance water quality discharged from the airport property, with three objectives:

  1. Reduce trace amounts of propylene glycol, which is added as a deicing agent in the winter;
  2. Reduce levels of nutrients such as nitrogen and phosphorus; and
  3. Reduce the water temperature.

Results from other sites using BioHavens supplied by Floating Island International (FII) had already shown that Objective #2 could be achieved. Shade provided by BioHavens would achieve Objective #3. Thus, testing focused on the efficacy of glycol removal with BioHavens.

Installation Data

Screen Shot 2015-10-23 at 10.01.20Operational Data

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Results

The BioHaven was installed in 2008 but because of its small size (0.2% of the pond surface area) and the pond’s low glycol concentration (consistently below the detection limit of 5 mg/L before FTW treatment), its effect could not be measured. To better determine the efficacy of this technology, a pilot-scale BioHaven with an area of 0.88 ft2 was used in a series of lab tests. These tests were run in batch mode and outstanding glycol removal was measured, with results shown in the table below.

Screen Shot 2015-10-23 at 10.03.30

Conclusions:

Glycol concentrations were reduced from greater than 500 mg/L to less than 1 mg/L in lab-scale BioHaven tests. It is believed that glycol is converted to carbon dioxide by aerobic bacteria attached to roots and other underwater surfaces of the FTW.

The full-scale BioHaven vegetation has survived three Maine winters and thrived each summer. To better determine its efficacy, this FTW may be moved to a smaller pond farther upstream in the process where glycol concentrations are 5-10 mg/L or higher. In the current location, a series of larger BioHavens may be required to measurably improve water quality.

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