Sustainable Filter Systems.
Australian designed, engineered and manufactured.
Soil bed biofilter design and construction
The evolution of soil bed biofilters
Soil bed biofilters, also known as soil bed reactors, are a well-established industrial air purification system. This technology was originally developed in Germany in the 1950’s to leverage the power of the diversity in microbial mechanisms to mitigate odourous gases produced by industry and also sewer odours. The naturally occurring microorganisms in the soil bed metabolise the odour causing gases into harmless by-products. If implemented correctly this technology is recognised worldwide as a cost effective and highly efficient odour and emission mitigation and control technology.
Types of odours typically treatable with soil bed biofilters:
- Volatile organic compounds
- Other reduced Sulphur compounds
Typically the contaminated air is collected and extracted from the building or site and ducted to the soil bed. The contaminated air is then humidified and distributed under low pressure through the base of the soil bed in a network of perforated air ducts. The contaminated foul air then rises through a bed biological media such as bark. Critically all the media in the soil bed needs to be kept moist and this is normally achieved through an irrigation system. The pollutant gases and emissions that are contaminating the humidified extracted air are absorbed into the water surrounding the media surface and it is here that the active bacteria that are present destroy the pollutants biologically.
Depending on the size of the media bed and other contributing factors the media will deplete over time and need to be replaced. The media needs to be attended to regularly especially with regards to compaction and degradation of the media so preferential air paths, channeling and venting are prevented. The media replacement for the whole soil bed is typically done every 18 – 24 months. With the specification of higher performance media's, the media life in the soil bed can be extended which reduces maintenance costs.
Typically the weakest point of a soil bed biofilter is the design and structure of the foul air distribution system. Commonly soil bed filters use a network of 100mm perforated PVC pipe laid in an aggregate base to distribute the contaminated air. Unless the pipes are placed in a side-by-side configuration across the base of the soil bed covering the entire surface this will never achieve a perfectly even air distribution. This amount of pipe and infrastructure is obviously impractical and not cost affective to try to achieve perfect air distribution. In addition to this, these pipes are not load rated and this detail becomes critical when it comes time to replace the media in the soil bed. Because certain types of media can be prone to channeling and maldistribution this impacts on the performance of the distribution of the foul air through the media bed over time as the media breaks down reducing the filters effectiveness. The size of many industrial soil bed filters would have a width that is larger than the reach of an excavator; this means a skid loader needs to be used to replace the media. This exercise normally destroys a large proportion of the pipe network in the plenum with the skid loader driving in the soil bed and this incurs extra time and cost to replace the broken pipes. Alternately the bed design would be made so the dimensions of the bed are such that an excavator can be used to service the media in the bed, which necessitates a greater land area being used for roadways for excavator movement and support around the bed.
Bioaction now have new technology to change the design of the plenum base to mitigate these issues. Bioaction are now official distributors of Hanit Grating which is a modular structural industrial flooring system made from recycled plastic which is capable of bearing significant loads and can be driven on by wheel loaders with a gross load weight of 2.0 tons. Because of this load bearing capability it allows the plenum base design to be radically changed. Firstly it removes the necessity to run 100’s of metres of ducted perforated pipe, as you simply need to duct the foul air to one point only in plenum base which is now free of aggregate and this allows the air to disperse evening throughout the plenum base. Secondly as the load bearing capacity is so high, the weight of not only the media but also the skid loader would be easily supported. So the time and cost to replace or service the media is minimised and optionally the media depth could be increased if required to give greater capacity to the bed without increasing surface area. Thirdly as the soil bed is no longer restricted in shape to cope with the requirements for an excavator to get access to the media in the bed, the total area required for the bed is minimised to the surface area of the bed and a thin bund wall. Then lastly one entry point over or through the bund wall is all that is required for the skid loader to enter and exit the bed for media maintenance. With land values at a premium these points are very important especially if the company needs to expand the capacity of the soil bed to cope with additional odour requirements, as they may allow them to achieve this within the existing size of an older style soil bed biofilter.
If you have an existing soil bed biofilter that is due for the media to be replaced or your exhaust air stream gas profile has changed as your business has grown and the soil bed isn’t performing correctly then make contact with Bioaction to discuss your requirements.
The Hanit Grating system has many applications, soil bed biofilters is just one. Industrial flooring for diaries, abattoirs, food processing, roof surfaces, non-conducting double floors for electrical or computer rooms and walkways over environmentally sensitive ground.
The Hanit Grating System.
Review the specifications brochure for the Hanit Grating raised industrial flooring system - Click here to download.
The load testing for the Hanit Grating system is available - Click here to download.
Reference White Papers for Biofiltration technology.
- Biofiltration of Odorous Gas Emissions
- Doctoral Thesis by Anneli Andersson Chan - Click here to download
- Biofiltration - a Primer
- Center for Waste Reduction Technologies by Stephen F. Adler - Click here to download