Biotrickling filter

Synonyms, abbreviations and/or process names

• BTF
• Lava filter
• Biodenox

 

Removed components

• Hydrocarbons: alcohols, aldehydes and ketons, fatty acids and their esters, phenols, styrene, naphthalene
• Odour
• Nitrogen components: NH₃, amines, heterocyclical nitrogen components
• Sulphur-laden components: H₂S, mercaptans, heterocyclical sulphur compounds, carbon disulphide
• Chlorine-laden components: dichloromethane, 1,2-dichloroethane, chlorophenol, trichloroethene, monovinylchloride
• NO_x

Not suitable for aliphatic hydrocarbons, perchloroethene and 1,1,1-trichloroethane

 

Diagram

 

Process description

A biotrickling filter is a combination of a biofilter and a bioscrubber. The bacteria responsible for decomposition are immobilised on a carrier or filter material. The filter material consists of synthetic foam, lava or a structured plastic packing. The surface must have a structure that allows biomass to bond to it effectively.

The carrier material is constantly covered with water. This mean that water must be uniformly sprayed over the packing. The polluted components absorb in the liquid film and are decomposed by the bacteria.

In order to feed the biomass, the required nutrients are added to the water. This water also carries away excess sludge/biofilm, as well as decomposition products which may hinder the biomass.

The scrubbing liquid which is circulated over the packing must be checked for pH, nutrients and salt concentration. The pH can be continuously measured and corrected. The nutrients are constantly dosed and dosage is periodically checked via analyses. In order to keep salt concentrations within acceptable limits, one section must be discharged and filled with fresh water. This can take place on the basis of conductivity.

To safeguard the process, a temperature measurement can be taken for flue gases, if there is a likelihood of temperatures exceeding required limits. This will help to spare the biotrickling filter. 

In the biotrickling filter, the packing may become blocked due to strong growth in the biofilm. This will lead to prefered flows, which will in-turn reduce efficiency and increase pressure drop. If the blockage is too severe, the packing will have to be replaced. During dimensioning it is important to set the load at a modest level in order to avoid such blockages.

 

Variants 

H₂S removal:

For the removal of H₂S, one can acidify the biotrickling filter to a pH of 1 – 2 , without negatively effecting removal efficiency. This will allow alkaline usage to be limited. If the company has a use for low concentrations of impure sulphuric acid, for neutralisation of waste water for example, this acid could be considered.

 

Efficiency

Component	Efficiency (%) [1]	Comments
Hydrocarbons	80 – 95
Ammonia	80 – 95
Odour	70 – 90
H2S	80 – 95
Mercaptans	70 – 90
Carbon disulphide	98 – 99	For an entry concentration of 100 mg/Nm³
Styrene	80	For an entry concentration of 160 mg/Nm³
Monovinylchloride	99	For an entry concentration of < 100 mg/Nm³

 

Odour reduction in pig-stalls of 200 – 800 ou_E/m³ to below detection limit [8].

 

Boundary conditions

• Temperature: 15 – 40 °C, optimum 30 – 35 °C [1]
• Atmospheric pressure
• VOC concentration: 400 -2 000 mg/Nm³
• NH₃-conc: 100 - 400 mg/Nm³
• Odour: > 20 000 ou/Nm³
• H₂S: 50 -200 mg/Nm³
• Mercaptan: 5 -100 mg/Nm³
• There must be a relatively consistent emission supply. Biological techniques are not suited, or are less suited, to work schedules less than 8 hours per day, 5 days per week.

 

Auxiliary materials

Nutrients to feed bacteria

Suppletion water to compensate for discharge and vapour losses.

Chemicals for pH correction.

 

Environmental aspects

The discharged sludge must be carried away. Quantity is determined by the load and composition of flue gases.

In addition to sludge, discharge water is also formed and must be treated or released into sewers.

One must be careful when buffering spray water. When storage is low, anaerobic circumstances may arise and cause odour. It is important to pass odour-laden gases from the storage place through the biotrickling filter or another air purification device. Because water storage normally takes place under the trickling filter, this does not normally pose any problems.

 

Energy use

The filter itself uses little energy (< 1 kWh/1 000 Nm³ [2]). Only a small recirculation pump is need for vaporisation water. Most usage can be attributed to the ventilator. The pressure drop over the filter is 1 – 10 mbar.

 

Cost aspects

Investment

• 5 000 -20 000 EUR for 1 000 Nm³/h [1]
• 9 – 13 EUR/ m³/h [4]

Operating costs

• Personnel costs:    ca. 0.5 days per week [1]
• Total operating cost: 0.77 EUR/1 000 m³ [4]

Case studies:

• Case study 1: Tobacco industry [3]
  • Flow 160 000 m³/h
  • Investment costs: 2.2 million EUR (1995) including channels, cooling towers and heat exchangers
  • Total operating cost: 82 000 EUR per year = 500 EUR/year per 1 000 m³/h
• Case study 2: Glue-spreading booths [6]
  • Flow: 50 000 m³/h
  • VOC: Acetone 80 % and ethylacetate 20 %, small quantity styrene.
  • Concentration: average 300 mg/Nm³ and max. 600 mg/Nm³
  • Investment costs: 410 000 EUR excl. VAT
• Case study 3: H₂S and CS₂ removal [6]
  • Flow: 250 000 m³/h
  • CS₂ and H₂S, conc. of 450 and 50 mg/Nm³ respectively
  • removal 70 % CS₂ and 85 % for H₂S
  • Investment costs: 5.2 million EUR excl. VAT.
  • Operating costs: 500 000 – 800 000 EUR

 

Advantages and disadvantages

Advantages

• Biological decomposition of components; no VOC residual products
• Suitable for decomposition of acid-forming components
• pH checking and correction is possible under certain conditions
• Low pressure drop
• Average investment and operation costs

Disadvantages

• Fluctuations in composition and load of incoming air have serious consequences for the yield
• Components with poor solubility are difficult to treat
• Toxic and high concentrations of acidic components must be avoided
• Packing can become blocked by biomass
• More difficult to construct than a biofilter.
• More expensive than a biofilter
• Waste water flow created

 

Applications

Biotrickling filters are primarily used to remove gases with acidic components.

Application areas are:

• Removal of H₂S and NH₃ from gases at water purification plants. The filter will be divided into two parts. The first part ensures removal of H₂S and NH₃ via autotrophic bacteria. This phase may become acidic. The second phase is for heterotrophic bacteria which decompose organic odour components. This phase must have a pH of 7 – 8 in order to function effectively.
• Removal of CS₂ and H₂S from waste gases in the textile industry
• Treatment of odour-laden gases in the tobacco industry
• NH₃ and odour removal in stalls

 

References

1. Common waste water and waste gas treatment and management systems in the chemical sector, BREF document, European IPPC Bureau, http://eippcb.jrc.es, 2002
2. Factsheets on Air-emission reduction techniques, www.infomil.nl, Infomil
3. J.S. Devinny et Al.:"Biofiltration for air pollution control"Lewis publishers, 1999
4. VDI Seminar 434802 am 25 November 2003: Optimieren der biologischen abluftreinigung
5. VDI 3478: “biological waste gas purification: bioscrubbers and trickle bed reactors” July 1996
6. Supplier information
7. T Feyaerts, D. Huybrechts and R. Dijkmans., “Best Available techniques for manure processing, edition 2”, October 2002
8. A. Derden, J. Schrijvers, M. Suijkerbuijk, A. Van de Meulebroecke1, P. Vercaemst and R. Dijkmans., “Best Available Techniques for the slaughterhouse sector”, June 2003

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