Reducing Indoor Air Pollutants Through Biotechnology - Biotechnologies and Biomimetics for Civil Engineering - page 197

the rapid growth of aquatic bacterial pathogens. If such systems also have the potential
for these bacterial suspensions to be aerosolized, such systems may be of concern and
should be further researched. Legionnaires disease caused by L. longbeachae has on
rare occasions been implicated in potting-mix handling scenarios (Patten et al. 2010 );
however, poor hand washing procedures and long-term smoking were found to be
better determinants of the disease than exposure to the potting-mix itself (O'Conner
et al. 2007 ), so major concerns over this disease may not be warranted.
Few studies to date on indoor biofiltration have included any assessment of
bacterial emissions from the tested systems. Lu et al. ( 2012b ) addressed concerns
over bacterial emission from an active biofiltration system by using a calcium
alginate gel to immobilise the active bacterial strain in their system (Pseudomonas
putida). The study detected no bacterial release, whilst effectively biodegrading
formaldehyde. Whilst the system required a constant supply of liquid nutrients, the
amount required was relatively low and no loss of biodegradation efficiency was
detected over 10 days. The pressure drop across the filtration matrix was higher
than optimal, leading to a relatively high energy usage for this system. If the
economics of energy use and nutrient supply can be effectively addressed, this
technology may have some potential for preventing bacterial release from active
biofilters, which may find use in buildings that have demanding microbial stan-
dards, such as hospitals. The system, however, would be unlikely to control fungal
spore release due to the aerial growth and sporulation of mould fungi.
Thus there appears to be some potential that biological air cleaning systems can
lead to increased microbial density in the treated air. Whilst no reliable research
has indicated the potential for danger to health, there is nonetheless a need for both
the assessment of existing systems and a consideration of microbial safety when
developing new systems. It is probable that the greatest potential for microbial
material release from any biofiltration system will occur when the medium
becomes excessively dry (Pasanen et al. 1991 ). With increased airflow rates across
media with uncontrolled microbiological communities, and the use of supports that
have the potential for rapid desiccation if irrigation fails, some of the active
systems thus have the potential for major microbial release. It is thus suggested
that future research assess these systems in both their functional state and at
reduced moisture levels to assess the potential for health (and thus legal) problems
that may arise in failure situations. The integration of HEPA into both active
microbial and botanical IAQ cleaning systems would solve the problems of bio-
pollutant emission, although at the cost of further increasing pressure drop.
8.11 Commercial Systems
A small number of biological indoor air cleaning systems are currently available
on the market (Table 8.1 ); however, it is clear that this industry is expanding. Of
the available systems, all use plants, and most have an interior design component
to increase their acceptability to purchasers.