biological waste air decontamination: microbial

Biological waste airdecontamination:Microbial decompositionof formaldehyde

Formaldehyde is one of the most impor-tant basic chemicals. It is required,among other things, for the productionof synthetic resins, synthetic varnishes orglue resins, chipboard and laminates. Inthe textiles industry, formaldehyde isused, for example, in the production ofnon-crease fabrics. Because of its volatili-ty, formaldehyde is mainly released viathe waste air and as a result it harms theenvironment. Inhaling formaldehydevapors can seriously damage the health.

Purification of waste air containing formaldehyde

Biological waste air decontaminationutilizes the metabolic activities ofmicro-organisms to remove harmful orfoul-smelling substances from waste air

streams. Fraunhofer IGB has developeda bio-trickling filter reactor. A textilesupport material that is itself not at-tacked biologically serves as the growthsupport for the biofilm formation. Itoffers a large specific surface area, ahigh affinity for micro-organisms andboasts very low flow resistance, a lowweight and high mechanical stability.The support material is rinsed with aliquid flow that is pumped continuous-ly in the circuit. The area-related liquidflow rate can be varied. With a higherarea-related liquid flow rate, the reac-tor serves as a bio-washer, whichassists the decomposition of substancesthat are well soluble in water. With alow liquid volumetric flow, the reactorassumes more of a filter characteristic,which permits the decomposition ofsubstances that are poorly soluble inwater.

Fraunhofer Institute forInterfacial Engineering andBiotechnology IGBManaging Director:Prof. Herwig BrunnerNobelstrasse 1270569 Stuttgart, GermanyPhone: +49 (0) 7 11/9 70-40 01Fax: +49 (0) 7 11/9 70-42 00E-Mail: info@igb.fraunhofer.deInternet: www.igb.fraunhofer.de

Contact:Dr. Dieter BryniokPhone: +49 (0) 7 11/9 70-42 11E-Mail: bryniok@igb.fraunhofer.de

BioSolutionsIngenieurgesellschaft mbHGrasweg 250769 Köln, GermanyPhone: +49 (0) 2 21/29 79 08-0Fax: +49 (0) 2 21/29 79 08-76E-Mail: info@biosolutions-engineering.deInternet: www.biosolutions-engineering.de

PB_D3_FA-Abbau_e_030725

Fig. 1: Experimental bio-trickling filter plant for the bio-treatment of waste air containing formaldehyde.

Technical experiments

The experiments for decontaminatingwaste air containing formaldehydewere carried out with an area-relatedliquid flow rate of 0.3 m3/(m2*h). Thewaste air flow was carried in the coun-ter-flow. The crude gas was mixed inaccordance with the specifications ofthe industrial partners. To achieve this,formaldehyde was continuously strip-ped in a vessel filled with formalin andcarried in the air stream into the bio-trickling filter.

The reactor was inoculated with a star-ter culture of Pseudomonas putida J3,a bacterial strain that is characterizedby extremely high tolerance to formal-dehyde (Figure 2) and high decomposi-tion rates. The system was continuous-ly operated over a period of more thanone year. The crude gas concentrationswere between 76 and over 1000 ppm(95 to >1250 µg/l) formaldehyde, andthe contaminant loads were between3.4 and 30.9 mmol/h (102 to 927mg/h). At a reactor volume of 30 litersand a filter volume of nine liters, thespecific filter load in the experimentswas 18.7 to 220 g/(m3*h) formaldehy-de. In these experiments, we did notreach the biological capacity limit ofthe filter. The formaldehyde concentra-tions in the crude gas were below 15ppm (12.5 µg/l). The efficiency η of thefilter was normally at least 0.99.

Further development

Biological waste air decontamination inthe bio-trickling filter reactor is beingextended to other substances, such asstyrene and methyl ethyl ketone, andalso mixtures of harmful substancessuch as formaldehyde / methanol anddichloromethane / ethanol.Thermophilic micro-organisms shouldalso be used for hot, water-saturatedwaste air flows.In collaboration with its Cologne part-ner company BioSolutions, theFraunhofer IGB is planning to constructa mobile experimentation plant withwhich the biological decontaminationof authentic waste air flows can betested on site on a scale that is relevantto practical conditions. Several produ-cer companies have already announcedtheir interest in a pilot trial.

FA co

ncen

trat

ion

[mM

]

Strain J3

0 15

24Time [h]

80

80*40

2010

51

0

100

103

106

109

CFU

109

Strain H

106

800 1

524

Time [h]

80*40

2010

51

0

FA c

once

ntra

tion

[mM

]

100

103

CFU

Fig 2: Formaldehyde Tolerance of Pseudomonas putida J3 compared with Pseudomonas putida H.Colony-forming units (CFU) were determined after incubation with formaldehyde in various con-centrations. Pseudomonas putida J3 is a strain containing formaldehyde dismutase, whereasPseudomonas putida H contains a formaldehyde dehydrogenase only.

Table 1: Performance data of the bio-tricklingreactor; FA: formaldehyde

Reactor volume 0,03 m3

Filter volume 0,009 m3

Area-related liquid flow rate 0,3 m3/m2*hCrude gas concentrations FA 76 to 1000 ppm

(95 to >1250 µg/l)Pollutant loads 3,4 to 30,9 mmol/h

(102 to 927 mg/h)Specific filter load min. 18,7 g/m3*h FA

max. 220 g/m3*h FAEfficiency η 0,99