Biofilters – the next generation

Biofilters have long been established as an odour control technology within the wastewater sector. The technology, however, has a mixed reputation for system efficiency and operational maintenance.

So, the industry has seen a shift toward wet chemical scrubbing technology, despite the attendant risks of chemical storage and handling.

Traditionally biofilters have consisted of an organic media, such as, peat,

seaweed, bark or shells. The media provides a substrate that supports bacteria that neutralises the odours.

And other odours, such as methyl mercaptans and amines, are also present and cannot be removed by traditional biofilters with the same degree of efficiency as hydrogen sulphide. The same of course is true in respect of chemical scrubbers that generally require a polishing filter such as activated carbon to remove other odorous compounds.

Operationally traditional biofilters present two principle problems:

· Media degradation, leading to short-circuiting

· Poor maintenance, leading to calcified media beds

All organic media will degrade after time losing its compressive strength and consequently the media compacts. As the media depth reduces as a result of compaction, the residence time falls and the pressure drop increases.

Media compaction is rarely achieved uniformly and channels appear, generally around the edge of the biofilter walls leading to short-circuiting and untreated odour release.

One of the biggest operational problems with organic media biofilters is the requirement for an efficient water distribution system to maintain the required moisture level for the media to remain effective.

All too often, the system, be it manual or automatic, fails leaving the media to dry and eventually calcify to the texture of concrete. This requires a costly reinstatement process and leads to odour complaints in the meantime.

Eliminating problems

There are two potential ways of eliminating the problems with traditional biofilters:

· Option 1 – Use organic media but at very shallow depths to eliminate compaction and use a fully automated humidifying section to maintain moisture levels throughout the media bed

· Option 2 – Use a non-organic manufactured media

with extremely high compressive strength to avoid compaction and again use a fully automated humidifying section to maintain moisture levels throughout the media bed

CSO Technik has recently introduced new generation Biofilters into the UK from North America. Biorem the manufacturer has over 700 Biofilter installations worldwide.

The Biocube system uses a compost-based organic media with additional nutrients, adsorbents and PH buffers for effective removal of hydrogen sulphide and other reduced sulphur compounds. The media is contained within a series of fully insulated trays with in-built air plenums; this restricts the unsupported media depth to around 300mm eliminating compaction and channelling. The foul air stream is humidified prior to passing through the media to ensure that the media does not dry out.

Media life is between three and five years dependent on load and can deal with hydrogen sulphide odour loads up to 300ppm with removal rates greater than 99%. The Biocube system is suitable for smaller airflows up to 3,000m3/h.

A mobile Biocube pilot plant will soon be available in the UK for product proving and emergency hire.

Where odour loads exceed 300ppm hydrogen sulphide or air flows exceed 3,000m3/h, CSO recommends the use of the inorganic media Biosorbens. The

media is an engineered mineral that is light but incredibly strong with a very high compressive strength.

The media is coated with nutrients, adsorbents and PH buffers to support a thriving microbiological population. All systems are again installed with a pre-humidifier section to ensure moisture levels within the media.

The Biosorbens media can be supplied in either a prefabricated GRP or stainless steel modular container or for large contracts can be supplied bulk packed for installation into a site-fabricated tank.

The largest operational permanent media biofilter in North America (424,000m3/hr) was supplied by Biorem and utilises the Biosorbens media. Media life is typically ten years and total odour removal rates are 98%, even at low residence times.

CSO and Biorem offer three levels of after sales care, the basic level media analysis is included within the cost of the system; the highest level of service includes remote web hosted monitoring and parameter adjustment.

CSO Technik is now offering a range of odour control technologies, including: Terminodour (ionisation process), dry scrubbing systems, wet chemical scrubbers, biofilters, CIFs and tailored combinations of the above technologies.

Tel: 01732 867892

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