Recommended methods for the preconditioning of odourous air prior to treatment in organic biofilters

Recommended methods for the preconditioning of odourous air prior to treatment in organic biofilters

Operation of biofilters for piggery and poultry shed odour control in Korea, and in other parts of the world, has often been problematic for two reasons. Firstly, excessive dust in the incoming air can cause clogging of the organic biofilter material. Secondly, drying out of the organic biofilter can occur if the relative humidity of the incoming air is not close to 100%.

Dust is generated in sheds from the feed and bedding materials, and also dried out manure residue which is disturbed by animal movements. This is worse in hot dry summer conditions but may also be exacerbated in cold winter conditions where shed heating is used. Dust loadings from sheds are typically 1mg/m3 but may exceed 10 mg/m3. Dust particles may vary in size from less than 1µm to more than 100µm, with typically half the volume of the dust is less than 10µm in size.

For bacteria on the biofilm to be healthy and actively reduced odour, the humidity of air spaces inside an organic biofilter material should be as close to 100% as possible. This is achieved if the overall water content of the organic biofilter material is maintained at approximately 25% w/w. If the air entering an organic biofilter has lower than 100% humidity, the effect will be to dry out the organic biofilter material and the biofilm. The drier this air is, the more water is required to be sprayed onto the material and this may lead to poor organic biofilter performance.

The combined effects of dust and water together often leads to clogging causing inhomogeneous flow, preferential flow channelling, poor utilisation of all of the organic biofilter medium and reductions in odour removal efficiency. This can result in a significant decrease in the effective life of the organic biofilter medium. Replacement is expensive and inconvenient to do on a regular basis.

Recommended methods for air preconditioning are therefore :-

1) Cyclone Dust Separation (CDS) for coarse (>10µm) dust removal
2) Trickling Biofiltration (TBF) for fine (<10µm) dust removal, odour pre-treatment and humidification

It may be necessary to use multiple cyclones with a small diameter to remove fine particles (less than 10µm). Multiclones can be manufactured at relatively low cost and there are no moving parts so maintenance costs are minimal. Typical dust loadings are unlikely due cause clogging of the multiclone. Multiclones are therefore appropriate technology for intensive livestock industries.

Trickling biofilters are also easy and cheap to construct, the only component of significant cost being the flow controller units. As the trickling biofilter material is inorganic, water flushing can be relatively heavy and continuous to flushout and remove dust build-up. This should lead to an essentially maintenance free dust elimination process. Relative humidity of the organic biofilter incoming air should also be close to 100%.

NCEA/DPI report on behalf of NRLI, Korea, NCEA / DPI Biofilter Project