Supplier
Language
Biofilter
What are biofilters
Biofilters are not filters in an original sense but complex bio-catalysators resp. bio-reactors. The metabolism of microorganism in biofilters transform contaminants and odorous compounds of waste air or waste gas into non-toxic, odorless and mainly low-molecular substances as carbondioxid (CO2) and water.
Filters in a classical sense separate a mixture of substances by different methods and criteria without changing them substantially. The separated substances keep conserved and must be disposed. In contrast biofilters change the contaminants of the waste air by biochemical degradation.
The biofilter material (for example peat, coconut fibre, bark or preferably root wood) adsorbs odorous compounds resp. contaminants out of the waste air stream. Natural microorganism in and on the filter material reduce these substances more or less free of residues. Biofilters are suitable for elimination of gaseous or volatile contaminants out of waste air streams or waste gases. More detailed data about the applications of biofilters and the demands to biofilter plants are written in the VDI Richtlinien 3477 "Biofilter".
Why you need biofilter
Everyone can remember a situation when he has been annoyed shortly or longer by unpleasant or even nauseating odors. But waste air doesn't contain only odors which affect the well-being but also chemical substances such as hydrogensulfide (H2S) which in high concentrations or at long-term effect might result in health issues.
The source of odors could be in most but not all cases located. Many times manholes, waste water treatment plants (WWTP) or industry are responsible.With suitable biofilter plants all these problems can be solved.
Biofilters are used successfully since long times on waste water treatment plants, sewage sludge drying plants, in the food industry (breweries, malthouses, coffee or cocoa roasting facilities), in the animal feedstuff industry, in the chemical industry, in paint shops, in animal husbandry or composting facilities.
How do biofilters work
When microorganism in biofilters transform contaminants of waste air into low-molecular substances by their metabolism they cover their demand on feed and energy by this.
The indispensible precondition for the good function of a biofilter or a biofilter plant is the presence of physical and chemical environmental conditions such as temperature, moisture, nutrient supply and pH-value, which allow the microorganism in the biofilter to keep their metabolism on a high level and thus to clean the waste air with high efficiency.
In order to achieve this you need good microbiological, technical and physical knowledge for projecting, planning and building a biofilter plant. A simple compost pile which is lying on a grid is the most easy way of biofiltration but very sure not the best way. Such a "biofilter" will cause problems within a very short time or show disfunctions from the beginning on.
What you should know about biofilters
Before the microorganism could start working the biofilter material (preferably root wood) needs to adsorb odorous compounds resp. contaminants out of the waste air stream. With its surface it serves as a growth matrix for micros at the same time. These natural microorganism on the filter matrix metabolize the organic compounds and also hydrogensulfide (H2S) or ammonia (NH3) to non-toxic and uncomplicated substances.
As a precondition that microorganism (mainly natural bacteria and funghi) could metabolize the annoying or even toxic substances which are of great value for them the environmental conditions in the biofilter bed must be at least adequate.
moisture content
As well as all other creatures microorganism need water in a sufficient amount. This could be provided best way with a humidifier (cross-flow humidifier or counter-flow humidifier). An irrigation system on top of the biofilter bed can't subsitute a good working humidifier but it can be a senseful addition. Dry biofilters could at least work short time as an adsorber, wetted biofilters will suffer from low oxygen and may start with anaerobic processes which causes remarkable odors by themselves.
temperature
Microorganism are able to metabolize at temperatures below zero as well as at temperatures above 100 ˚C. Extreme temperature regimes are only occupied by strongly specialized types. The best temperature regime for biofilter plants is between appr. 15 ˚C and 40 ˚C. Below and above this regime the efficiency of the micros decreases. The temperature in the biofilter bed is determined by the temperature of the waste air stream as well as the environmental temperature. At waste air streams above 45 ˚C a cooling of the waste air should be considered. At waste air streams below 0 ˚C a warming of the waste air should be considered.
pH-value
In consequence of the waste air composition and the according metabolism in the biofilter bed a relative constant pH-value will establish within two to three weeks. This pH-value could be between pH 2,0 (for example in consequence of a high H2S-concentration in the waste air) up to pH 8,5. Only at extreme cases an adjustment of the pH-value is necessary, because in most cases a microorganism population will establish which is adapted to this surrounding condition.
Very high contaminated waste air streams could be treated with an air conditioner with pH-control (dosing station with acid resp. caustic).
Biofilter material
The choice of a biofilter material should be orientated according to the above given requirements. A good biofilter material has a great surface with an additional so called "inner surface" which is used by micros as well as by contaminants and nutrients. Beside fine structures there should be also coarse structures to allow exchange of air and water. Ideally a biofilter material is able to supply those nutrients by itself (without fertilizing) which the microorganism can't find in the waste air stream. As most profitable material under this aspects proved to be torn root wood whose capacity could be even enhanced by manufacturer's treatments.
Life-time of biofilter material
An important economic issue is the life-time of a biofilter material. Basically each organic biofilter material will be consumed at a certain time because it suffers from the work of the microorganism and those substances are decomposed which give the material its structure. Root wood grants a good long-term stability. The incorporated tanning agents which the living plant uses to defend its roots against attacks of microorganism prohibit or prolongate a quick decomposition of the root wood in biofilters. In dependence to the waste air contamination the life-time could last on average between three and seven years.
Back pressure of the biofilter material
A good biofilter material shows beside a high cleaning efficiency also a low back pressure. A high back pressure, which is stated for example for compost materials or peat as biofilter material, causes high operational cost. In order to push the same amount of waste air through the filter bed you need a multiple of electric energy compared with low back pressure materials like torn root wood.
Flow direction through the biofilter material
The flow direction through the biofilter bed should always be from the bottom up to the top in order to avoid any recontamination of the cleaned air with odors which maybe exist above a drain sump below the filter bed. Metabolized contaminants of the waste air which exist in the filter matrix are washed down by irrigation or by rain and accumulate in the drain sump below the filter bed where they could be part of ongoing biochemical processes and maybe produce new odors again. It is most questionable first to clean the waste air with high effort and then allow it to contact the atmosphere above the drain sump again and collect some odors before entering the atmosphere.
Simple biofilter
There are many applications where a simple biofilter is sufficient for solving an odor problem. These biofilters consist mainly of a corpus with biofilter material. These simple solutions are for example biofilter cartridges, manhole biofilters, vent pipe biofilters, roof gutter biofilters or ventilation shaft biofilters.
Layout of biofilter plants
The layout of a biofilter plant needs a lot of experience. The cleaning efficiency is not described in the best way by the area load of the biofilter (m3/h waste air per m2 filter area) but by the volume load of the biofilter (m3/h waste air per m3 filter volume). Only this value can fix a minimum residence time of the waste air in the filter matrix (max 100 m3/h per m3 according to the German VDI-guideline 3477).
The layout can include various components of a biofilter plant:
- ventilator
- humidifier
- automatic refill of the humidifier
- automatic drain of the humidifier
- pump, y-strainer, nozzles, manometer for internal water circle
- freeze protection
- dosing station for extraordinary cleaning efficiencies
- explosion protection for waste air of explosive atmosphere
- control panel with or without display.
Certified manufacturers of biofilters and biofilter plants
Imprint | Data Privacy Statement | © 1995-2021 bioteg Biofilter Systems GmbH