Bio washer

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A bio- washer is a biologically working reactor for cleaning exhaust air and exhaust gases. It is the combination of a physical gas scrubber with a biological activation unit in which microorganisms use the absorbed air pollutants as substrates and build up cell mass in this nutrient medium . In contrast to the biofilter on the one hand, in which the microorganisms are bound to a structural material, and on the other hand, the bio- trickle bed reactor , in which a so-called biological lawn forms on the built-in components in the reactor, the microorganisms in the bio-washer are predominantly suspended in the washing liquid.

The first patent application for absorptive exhaust air purification with the help of microorganisms was made in 1934. The use of bio-scrubbers had been tested and carried out on a semi-industrial scale since the early 1940s. The focus was on intensive animal husbandry . The first large-scale industrial application occurred towards the end of the 1970s.

Procedural bases

Process scheme bio washer
(A) absorber
(B) regeneration reactor
(C) settling tank
The exhaust gas to be cleaned (1) flows through the absorber from bottom to top and leaves it as so-called clean gas (2). A large part of the washing liquid (3) is circulated through the regeneration reactor. Fresh water (4) supplements the part of the washing liquid that is discharged as waste water (5). Some of the biomass that collects in the settling basin is also discharged (6).

In the biological gas scrubbing takes place, the first absorption of the dedusted air pollutants , which followed by the reactor are reacted biochemically suspended bacteria, so ideally of the absorbed hydrocarbons , carbon dioxide is produced and water. The biological degradation of the dissolved pollutants prevents the solubility equilibrium from becoming decisive for the cleaning result. The bacteria use the pollutants as a source of carbon. Other nutrients essential for bacterial growth must be added to the washing liquid. In addition, it must be possible to dose acid and lye in order to set an optimal pH value for bacterial growth . The washing liquid is regenerated through the biological degradation of the absorbed ingredients.

A bio-washer is usually made up of the units

  • Absorber,
  • Regeneration reactor and
  • Settling basin

together. In principle, columns or washers are available as apparatus for the absorber . In practice, these are mostly jet , venturi or spray washers . In principle, the same requirements apply to the absorber for bio-washing as for physical washing. By creating the largest possible phase interface and the longest possible residence time , the air pollutants should be given the opportunity to get into the liquid phase. Ideally, the microorganisms are suspended in the washing liquid, but in the case of technical absorbers, a biological turf also forms on the built-in components.

The regeneration reactor is connected downstream of the absorber. It serves to strengthen the washing liquid again and corresponds to the aeration basin in wastewater treatment. Acids or alkalis are usually added in the regeneration reactor in order to maintain an optimal pH value. With a sufficiently large absorber sump and easily degradable substances, a regeneration reactor is not absolutely necessary. If, on the other hand, the absorbed air pollutants are difficult to break down, the necessary longer residence time of these substances in the aqueous phase requires a regeneration reactor.

The sedimentation basin serves to hold back biomass and thus guarantee the efficiency of the bio-scrubber. Excess biomass and part of the washing liquid are discharged from the settling basin and must be disposed of. If there is insufficient oxygen supply in the absorber for the microorganisms, this must be ensured by means of active ventilation in the sedimentation tank.

The construction material of the individual scrubber components must be resistant to chemical stress on both the liquid side and the gas side. Concrete, plastic and steel are suitable for this.

For optimal treatment in the bio-scrubber, the exhaust gas temperature should be between 5 ° C and 60 ° C. Substances that are toxic to the microorganisms must not be present in the exhaust gas. Fluctuations in concentration and temperature in the exhaust gas are to be avoided. Bio washers can be used both continuously and in batches . In the event of longer downtimes, the activity of the microorganisms must be guaranteed by an external supply of substrate.

application areas

The preferred field of application of bio-scrubbers is at air pollutant concentrations of up to a few 100 mg / m 3 with sufficient water solubility of the pollutants. With bio-washers, for example, exhaust air from food processing plants , foundries , sewage treatment plants , paint shops and animal carcass recycling plants can be treated. The substances contained in the exhaust air that can be easily removed by bio-scrubbers include, for example, representatives of the substance groups

Bio washers are also used to desulphurise biogas . In order to feed the biogas into the natural gas network, however, the sulfur contents achieved are usually still too high, so that in such cases fine desulfurization must take place. In a study to reduce bioaerosols , the effectiveness of a combination bio washer / bio filter behind a bio waste treatment plant could be proven.

Compared to biofilters, bio-scrubbers have greater degradation rates per reactor volume, but are more prone to failure when the amount of exhaust air changes.

literature

  • VDI 3478 Part 1: 2011-03 Biological exhaust gas cleaning; Biological waste gas purification (bioscrubbers) . Beuth Verlag, Berlin. ( Table of contents , abstract )
  • Klaus Fischer: Biological exhaust air purification: application examples, possibilities and limits for bio filters and bio washers . Expert, Ehningen bei Böblingen 1990, ISBN 3-8169-0428-9 .

Individual evidence

  1. ↑ a b Klaus Fischer, Franjo Sabo: Separation of gaseous pollutants through biological reactions. In: Heinz Brauer (Ed.): Handbook of environmental protection and environmental protection technology. Volume 3: Additive environmental protection: treatment of exhaust air and exhaust gases. Springer-Verlag, Berlin / Heidelberg / New York 1996, ISBN 3-540-58060-3 , pp. 594-645.
  2. ↑ a b H. Kohler: Biowasher to minimize organic gaseous emissions - state of development work using the example of the foundry industry, paint shops, fat melting and fiberglass production. In: Odor substances: sources, spread, effects, olfactometry, technical and administrative measures. VDI-Verlag, Düsseldorf 1985, ISBN 3-18-090561-1 , pp. 169-190.
  3. ↑ a b E. Schippert: Air pollution control through absorption with biological regeneration of the washing liquid - theoretical principles and practical application in can painting, animal carcass recycling, grinding wheel manufacture. In: Odor substances: sources, spread, effects, olfactometry, technical and administrative measures. VDI-Verlag, Düsseldorf 1985, ISBN 3-18-090561-1 , pp. 147-168.
  4. ↑ Herwig Hulpke, Herbert A. Koch, Rudolf Wagner (eds.): Römpp Lexikon Umwelt . Thieme Verlag, Stuttgart 1993, ISBN 3-13-736501-5 , p. 114.
  5. ^ A b Gabi Förtsch, Heinz Meinholz: Manual of operational pollution control . Springer Spectrum, 2013, ISBN 978-3-658-00005-9 , pp. 253-254.
  6. ↑ Michael Schultes: Exhaust gas cleaning . Springer-Verlag, 1996, ISBN 3-540-60621-1 , p. 218.
  7. ^ Günter Baumbach: Air pollution control. 3. Edition. Springer-Verlag, Berlin / Heidelberg / New York 1993, ISBN 3-540-56823-9 , p. 417.
  8. ↑ St. Schirz: Biological exhaust air purification. In: Ammonia in the Environment. KTBL , 1990, pp. 31.8-31.9.
  9. ↑ VDI 3896: 2014-06 (draft) emission reduction; Upgrading biogas to natural gas quality. Beuth Verlag, Berlin, p. 15.
  10. ^ Siegfried Bajohr, Frank Graf: Biogas processing. In: Siegfried Bajohr, Frank Graf (Hrsg.): Biogas: Generation - Processing - Feeding . Oldenbourg Industrieverlag, Munich 2011, ISBN 978-3-8356-3197-7 , pp. 158–159.
  11. ↑ Volker Kummer, Renate Haumacher, Werner Philipp, Reinhard Böhm: Investigations into the separation behavior of exhaust air purification systems with regard to bioaerosols . Hazardous substances - keeping the air clean , Volume 63 (2003) 9, pp. 368–372.
  12. ^ Walter Reineke, Michael Schlömann: Umweltmikrobiologie . Springer-Verlag, Berlin and Heidelberg 2015, ISBN 978-3-642-41764-1 , p. 413.