Environmental Engineering Reference
In-Depth Information
VOCs in indoor air have targeted means to expose active, contained microbial
communities or populations to large volumes of air. With the high airflow rates
required with such systems, the release of microorganisms back into the air has
been recognised as a potential concern for microbial air remediation processes (see
Sect.
8.12
).
8.4.2 Carbon Dioxide
Indoors, excess CO
2
is produced mainly by human respiration. It is not normally
considered to be a toxic air contaminant, but with increasing levels above the
current outdoor ambient concentration (currently *397 ppmv; Tans
2014
) it can
act as a simple narcotic, and has been associated with adverse symptoms related to
the mucous membranes (dry eyes, sore throat, nose congestion, sneezing) and to the
lower respiratory tract (tight chest, short breath, cough and wheezing) (Erdmann
and Apte
2004
). At concentrations between 2,500 and 5,000 ppmv, CO
2
can cause
headache, with serious health consequences arising at concentrations greater than
50,000 ppmv (Milton et al.
2000
; Harris and Moore
2009
; Gurjar et al.
2010
). It is
well known that elevated CO
2
concentrations in office buildings are associated with
increased illness symptoms among occupants (Milton et al.
2000
; Erdmann and
Apte
2004
; Seppänen and Fisk
2004
), and student academic performance and
workplace productivity have both been shown to decline with increased CO
2
levels
(Bakó-Biró et al.
2004
; Seppänen et al.
2006
; Shaughnessy et al.
2006
). In most
cases, inadequate building ventilation system is found to be the cause of CO
2
accumulation indoors (Redlich et al.
1997
). The American Society of Heating,
Refrigeration and Air-Conditioning Engineers (ASHRAE) recommends that the
maximum concentration of CO
2
should not exceed 1,000 ppm (ASHRAE
2011
), but
even at this level some reductions in workplace performance can be expected.
The bioremediation of indoor CO
2
has received limited research attention,
although several studies have tested the potential of indoor plants for mitigating
excess CO
2
. Oh et al. (
2011
) demonstrated chamber CO
2
reduction capacity for
three indoor plant species. Pennisi and van Iersel (
2012
) examined the CO
2
draw-
down capacity of common indoor plants and concluded that the limited photo-
synthetic rate of indoor plants would lead to the necessity for an impractical
volume of indoor plants to make a substantial difference to indoor CO
2
levels.
Contrasting with these results, Tarran et al. (
2007
) performed a study using city
offices and found that three or more potted plants were associated with a 10 %
reduction in CO
2
concentrations in an air-conditioned building, and a 25 %
reduction in a non-air-conditioned building. The greatest potential use of phyto-
technology for CO
2
mitigation thus possibly lies in replacing a proportion of a
building's ventilation system, and thus saving energy. It has been estimated that
the use of appropriate green plant design could reduce HVAC energy loads by
10 % (Afrin
2009
), whilst Rodgers et al. (
2012
) estimated an 86 % energy saving
from an active 'Biowall' system.
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