General Description of the Plant
Biotricklingfilter
1. Function principle
The biotrickling filter is a 1-stage packed scrubber passed by the waste air from the bottom to the top. This
unit operates under limited aerobic conditions and uses specific bacteria to convert hydrogen sulphide into
water-soluble harmless components.
Biotricklingfilter columns contain a plastic carrier media which provides a large surface area for settlement
and growth of specialised microorganisms. An air blower introduces air to the raw biogas stream at the inlet
of the biotrickling columns in a controlled manner. For provision of an equal air distribution in the biogas
stream an oxygen content of 2 Vol-% in the cleaned biogas stream is targeted.
The oxygen enriched gas stream passes through the carrier material within the bio-trickling column from
the bottom to the top; counter-currently the nutrient-enriched scrubbing liquid will be re-circulated and
irrigated on the top of the carrier material. The scrubbing liquid provides the microorganisms with moisture
and nutrients, and it also washes the metabolic sulphate out of the media. The supply of nutrients is
realised by a time-controlled dosing of a liquid fertilizer solution.
In order to ensure optimum pH conditions and to purge accumulating sulphuric acid, scrubbing liquid has to
be periodically removed from the system and has to be replaced by fresh water or (better) treated effluent.
The frequency of the liquid replacement is controlled by means of a pH measurement in the pump sump.
The waste water is automatically discharged from the recirculation circuit whereas water is automatically
fed into the column sump according to the continuous filling level measurement. The system temperature
is controlled by continuous monitoring of the column sump in order to keep a constant temperature level of
30 to 35°C. The signal from the temperature measurement sensor is used to control the heat supply from
the overall plant heating circuit. In order to reduce the thermal energy consumption the vessel tank is
insulated.
Well adapted biological desulphurisation units are able to achieve a H2S removal efficiency of up to 95 %. It
has to be emphasized that such a biological system can only be designed for an avg. pollutant load. During
and after H2S concentration peaks in the gas stream, the removal efficiency for H2S concentration will
noticeably decrease. The reason is in the nature of biological systems which work best during stable
conditions.

1.1. Gas flow
The waste gas streams upwards through the packing material bed and gets in contact with the washing
liquid sprayed out from the irrigation system placed above the packing bed. This principle using a countercurrent system of gas and liquid circulation leads to the highest distribution of nutrients-enriched scrubbing
liquid.
Biotricklingfilters are mainly uses for waste air or gas streams with only few components of similar physical
quality. One typical application is the desulphurization of biogas streams.
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1.2. Washing liquid circulation / Packing bed
A recirculation pump transfers the washing liquid from the integrated scrubber sump, providing a constant
liquid flow through the duct line, to the spraying nozzles. The spiral full cone nozzles are very widely
opened, nearly plugging-free and able to spray the liquid homogenously on the packing bed. The scrubbing
liquid then trickles through the packing bed, humidifies the biofilm, distributes nutrients to the bacteria and
washes out the generated salts.
1.2.1. Recirculation pump
Very robust and corrosion-free vertical or horizontal chemical recirculation pumps made of thermoplastic
are used for these applications. All parts in contact with the liquid are very resistant and well suited for the
aggressive and abrasive washing medium as well as for the contaminants and chemicals transferred into
the liquid phase.
1.2.2. Packing material
Main function of the packing material is to increase the transfer of the contaminants from the gas phase
into the liquid phase. This is mainly possible due to the very high active surface able to hold up a big
amount of washing liquid.
The used packing material serves with a specific surface of over 100 m2 per m3 of filter bed. Through the
special construction of the packing material (open structure, widely spaced and therefore high free volume)
plenty of washing water droplets are built on the surface. These droplets are segmented and re-shaped
constantly allowing the absorption process of the contaminants in the liquid phase to be renewed
continuously.
1.2.3. Droplet separator
Following the packing bed the air is led through a droplet separator. Its function is the separation of the
washing water droplets from the pre-cleaned gas. These droplet separators are nearly plugging-free with
high efficiency and low pressure loss.
1.3. Measurement and control of the plant
The standard measurement and control of our scrubber includes:
Level control of the scrubber sump with automatic water re-fill
Protection against dry running of the recirculation pump
Pressure gauge to indicate the pressure upstream of the spraying nozzles
pH-value-control when fresh water is added
Temperature monitoring of the scrubbing liquid to control the heat supply
The following options can also be quoted on request:
Analytical measurement of the crude and clean gas
1.4. Dosing station
Nutrients are added by special dimensioned dosing pumps. The pumps are magnetic or motor driven
diaphragm pumps. All materials in contact with the washing liquid are suitable for the chemicals.Each
dosing pump adds nutrients solution discontinuously in a time-controlled manner.
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2. Materials of the plant
The scrubber shell, the recirculation duct line and all other equipment in contact with the washing liquid
(packing material, grids etc.) are built of corrosion-resistant plastic.
The scrubber shell - our scrubber type - G - is manufactured from corrosion-free glass fibre reinforced
plastic (FRP). The shell is produced as a laminate by a filament winding machine. This laminate consists of
high quality polyester resin, woven roving and chop strand mat.
The inner side of the scrubber shell is coated with a special chemical protective layer. The outside is
provided with a pigment layer containing UV-absorbers (colour according to customer’s request). This
method allows a durable protection as well as a long lifetime of the scrubber.
Our scrubber type - P - is built of high quality thermoplastic materials, such as Polypropylene or HDPE
(high molecular polyethylene). There we use plates or winding tubes depending on size and structure.
3. Delivery / Installation
We deliver our scrubbers mostly in one module. Our well practiced installation staff installs the complete
scrubber on site as follows:
Supervision of the positioning of the plant equipment
Installation of the recirculation pump
Filling-in of the packing material and installation of the grids
Installation of the recirculation pipe
Connecting of the supply and disposal lines which are provided by the customer
Installation of the measuring equipment
4. Essentials
Air stream from the bottom to the top
High separation results / high efficiency
Low investments and operation costs
High flexibility against variable waste gas amount
Optimal consumption of fresh water and nutrients
Little space demand / compact size
Low pressure loss
Corrosion resistant
Weather resistant
Low risk of plugging due to the structure of the packing material
Easy overview and easy handling of the display