Biofilters based on the action of fungi

Abstract

Traditional biofilters for waste gas treatment are mainly based on the degradation activity of bacteria. The application of fungi in biofilters has several advantages: fungi are more resistant to acidification and drying out, and the aerial mycelia of fungi form a larger surface area in the gas phase than bacterial biofilms, which may facilitate the uptake of hydrophobic volatile compounds. The research described here identifies important conditions for the operation of fungal-based biofilters. Biofilters with perlite packing were operated at different pHs and relative inlet gas humidities. Toluene was used as a model pollutant. It was shown that a low pH is a prerequisite for fungal growth in biofilters. Also, the fungal biofilters were more resistant to drying out and more active than the bacterial biofilters. Fungal biofilters eliminated 80-125 g toluene/m3 filterbed/h. Several measures that could limit the clogging of fungal biofilters with fungal biomass were investigated. The introduction of mites helped to control excessive fungal growth and pressure drop. The pressure drop of a perlite/fungi/mites filter of 1 m height, loaded with 200 m3 gas/m3 filter/h stabilised around 130 Pa. Biofilters based on the action of fungi are cost-effective for the treatment of waste gases containing aromatic compounds, alkenes and other hydrophobic compounds.

Biofilter Treatment of Volatile Organic Compound Emissions from Reformulated Paint: Complex Mixtures, Intermittent Operation, and Startup

“…In spite of the neutral pH of the nutrient solution added to the biofilter on a weekly basis, fungi were observed in all of the biofilm images. Although these SEM images support the hypothesis that aerial mycelia of fungi can be in direct contact with the gas phase and thereby offer faster mass transfer rates than flat aqueous bacterial biofilm surfaces, 24,31 because of the inherent methodological limitations of the biofilm fixation process used before imaging, it is not possible to draw an unequivocal conclusion regarding whether the fungal hyphae were truly in direct contact with the gas phase. It appears, however, that was likely the case.…”

“…24 Because isolates were not identified or characterized with respect to their ability to degrade the VOCs supplied, a general conclusion regarding the relative contributions of the two groups to contaminant removal cannot be drawn. The fact that many fungal species are able to degrade the VOCs present in the waste gas stream, however, raises the distinct possibility that they contributed to VOC removal.…”

“…Because of the considerable difference between the sizes of bacteria relative to fungi (on the order of 1 m for bacteria compared with Ͼ100 m length for some fungi), it is quite possible that bacteria were numerically dominant in the biofilters, while at the same time comprising a lower proportion of total biomass than fungi. Thus, the notion that conventional neutral pH biofilters are primarily bacterial in nature 24,31 may not always be correct.…”

Treatment of hydrophobic VOCs in trickling bed air biofilter: Emphasis on long-term effect of initial alternate use of hydrophilic VOCs and microbial species evolution

“…Many processes were tested for addressing the bioavailability of hydrophobic contaminants. One is the introduction of surfactants (Aly Hassan and Sorial, 2008;Woertz and Kinney, 2004), providing favorable conditions for fungi (Aly Hassan and Sorial, 2008;Arriaga and Revah, 2005a;Hernández-Meléndez et al, 2008;Spigno and De Faveri, 2005;Van Groenestijn et al, 2001); others include mixture of n-hexane with other less hydrophobic compound such as benzene (Aly Hassan and Sorial, 2010a), introduction of more hydrophilic contaminants in mixture with n-hexane, such methanol (Zehraoui et al, 2012(Zehraoui et al, , 2013, and most recently the alternate use of methanol with n-hexane (Zehraoui et al, 2014).…”

Biotechnological removal of H2S and thiols from sour gas streams under haloalkaline conditions

“…Methods for solving these problems were described [81][82][83][84] but they are not necessarily practical. Two-stage reactor systems are proposed to avoid aforementioned…”