Reducing Indoor Air Pollutants Through Biotechnology - Biotechnologies and Biomimetics for Civil Engineering - page 191

systems. Whilst fungi have been shown to have very high removal capacity for
some VOCs due to the large surface area created by aerial growth (Kennes and
Veiga 2004 ; Vergara-Fernández et al. 2008 ), the resistance to air flow created by
fungal mycelia restricts their utility in microbial biofiltration systems, although
biofilter packing material technology (e.g. Gutiérrez-Acosta et al. 2012 ) may
effectively address this problem in future developments. The ability of individual
fungal species to degrade specific VOCs also appears to be variable (see García-
Peña et al. 2008 ). Resistance to low pH, water and nutrient availability are key
advantages of fungal systems over bacteria-based biofilters, and these may emerge
as key constraints in future bacterial biofiltration systems (Estrada et al. 2013a ).
Microbial air cleaning systems have been classified into three general types
(Guiyesse et al. 2008 ): bioscrubbers, where pollutants are collected in a mobile
aqueous phase and exposed to microorganisms in a bioreactor (Fig. 8.3 );
Biotrickling filters where microorganisms are grown on an inert support such as
activated carbon or geological materials such as vermiculite, supplied with
nutrients from a gravity fed solution and exposed to the air either passively or
actively (Fig. 8.4 );
Biofilters where air is passed through a porous support on which microorgan-
isms are growing, and which may or may not receive an exogenous nutrient supply
(Fig. 8.5 ). However, systems that utilise natural microbial communities such as
those found in potted plant substrates (Fig. 8.6 ), obviate the need for a continually
provided nutrient supply and are self-supporting over a period of months to years
(e.g. Wood et al. 2002 ), thus having substantial maintenance advantages.
It seems that virtually all organic pollutants are biodegradable by bacteria,
although the rates at which they are degraded vary widely based on a number of
factors, notably their polarity (which determines their diffusion coefficient in
aqueous environments, and thus their accessibility to microorganisms) and toxicity
effects, which could be expected to be minimal at the low concentrations found in
Fig. 8.3 Simplified
representation of a
bioscrubber system (Mudliar
et al. 2010 )