In the last article on Biobeds we discussed their importance as a simple and effectively environmental contamination method from pesticide point source contamination. In this article on Biobeds Explained we delve a little deeper into Biobeds to explain their differences, how they are constructed and maintained, and their potential cost.

Differences

When it comes to Biobed there are two key differences. The first is lining. Biobeds can be lined or unlined. Unlined Biobeds have no impermeable synthetic layer that isolates them from the ground. Instead the bottom of the Biobed is a layer of clay. Lined Biobeds have a synthetic impermeable layer (plastic, concrete, tarpaulin, etc.) that isolates them from the ground. This design allows for the collection of drainage water that can be sampled or recirculated for further treatment if necessary. While most original Biobeds are unlined, their suitability is limited to small volumes of pesticide rinsate and dry climates. As such, most Biobeds built today are lined.

Biobeds can be built as drive-over or offset systems. A drive-over Biobed, true to its name, is where all pesticide handling, mixing and equipment cleaning is done above the Biobed. All pesticide point source contamination falls onto the Biobed. An offset Biobed, sometime referred to as an indirect Biobed, is where all liquids from pesticide handling, mixing and equipment cleaning are collected and directed to the Biobed.

Size

Biobed size should also be a consideration of several other key variables, including but not limited to local precipitation, working environment, anticipated future use/equipment, and pesticide use. Being able to determine the appropriate size for your Biobed is quite complicated and as such an expert should be consulted. Building a Biobed too small or too large will either be a waste of resources, or will result in an ineffectual Biobed.

Inputs & Maintenance

Biobeds consist of a biomixture in a pit or container. This biomixture consists of soil, lignocellulosic material (most often straw) and organic substrate (most often compost). The exact combination of materials has been well studied to favour microbial activity and maximise pesticide degradation. Again, consulting an expert will ensure that you choose the best mixture for your needs. Beneath the biomixture is a layer of clay, while lined Biobeds also have a drainage layer of gravel, macadam or sand, and a synthetic impermeable layer (as mentioned above).

Once created, a grass layer is used to cover the surface of Biobeds. The grass top-layer helps to regulate moisture, maintain good oxygen levels for microorganisms, and enhance the degradation capacity of the Biobed. A ramp and drive over grid are also required for drive-over Biobeds to support the weight of the equipment and prevent compaction.

During dry hot spells Biobeds require watering, while dead or damaged grass should be replaced. The biomixture in Biobeds should also be replaced every five to eight years. Once removed, the spent biomixture should be stored to allow for degradation of possible pesticide residues before being land applied as topsoil.

Cost

The cost of Biobeds can vary greatly from $7,000 – $50,000 depending on several site-specific factors, include Biobed size and type, site, pesticide use, anticipated use, and labour costs. If you are thinking of installing a Biobed it is always wise to consult a knowledgeable expert.

For more information about Biobeds or if you have any questions regarding pesticide management please contact us, please contact us.