Environmental Engineering Reference
In-Depth Information
reliance in modern buildings on heating, ventilation and air conditioning systems
(HVACs) for the maintenance of thermal comfort, and a growing dependence on
reducing ventilation rates to save energy. Since the 1970s, building designers have
increasingly sealed buildings to reduce energy expenditure from having to adjust
the temperature of outdoor air used for ventilation (Darlington et al.
2000
). To
maintain IAQ, building designers have come to rely on HVAC systems to recir-
culate indoor air (Fadzli Haniff et al.
2013
) with a greatly reduced outdoor air
dilution level, leading to the accumulation of VOCs and CO
2
. Noise, security and
declining outdoor air quality are other reasons that increased outdoor ventilation
is declining as a means of regulating IAQ (Guieyesse et al.
2008
). If these
low external ventilation rates are to be maintained, air cleaning technology
will become essential for maintaining adequate IAQ whilst reducing energy
expenditure.
8.3 The History of Bioremediation of Indoor Air
The early impetus for developing biological systems to mitigate the deterioration
of IAQ came from space research, in particular the move to develop long-term
habitations outside of the earth's atmosphere. 'Biological life support systems'
(BLSS) have been proposed over a number of decades as a means for supporting
sustainable human habitation in the vacuum of space (e.g. Myers
1954
).
Early studies on potted plants and air-pollution reduction were carried out by
Wolverton and colleagues for NASA and, subsequently, for the US Interior Plant
Growers Association (Wolverton et al.
1984
,
1989
). These studies investigated
potential uses of potted plants in space stations. It was found that these plants
could absorb substantial concentrations of the VOCs formaldehyde, trichloroeth-
ylene and benzene from chamber air (Wolverton et al.
1984
,
1989
). Wolverton
(
1997
) subsequently conducted screening chamber studies of the VOC removal
ability of 50 indoor plant species, and found they all showed some capacity to
reduce VOC concentrations. This early work was developed by Wood et al. (
2002
)
and Orwell et al. (
2004
,
2006
), who established that it was the microflora asso-
ciated with the growth substrate, rather than the potted plant itself that was the
active component of the system for removing VOCs. These studies demonstrated
VOC (benzene) removal by potted plants at very high rates for initial VOC con-
centrations of up to 163,000 lg.m
-3
, and also at more indoor air realistic levels
of *800 lg.m
-3
for n-hexane, toluene and xylene.
Numerous further laboratory test-chamber studies demonstrated the potential for
significant improvement in IAQ through the passive use of potted plants, and, to
date, approximately 200 species have been tested for VOC removal capacity, all
with positive results (e.g. Liu et al.
2007
; Yang et al.
2009
; Kim et al.
2008
).
However a number of criticisms have appeared in the literature, in particular chal-
lenging the validity of extrapolating static chamber data to real-world environments,
most notably regarding the capacity of passive potted plants to quantitatively
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