Environmental Engineering Reference
In-Depth Information
semi-aquatic plants. It was hypothesised that the very large biomass to building
space ratio utilised would lead to reduced VOCs due to bioremediation from
both the bioscrubber and plants, but may have led to the release of new VOCs and
biological particles, such as mould spores, associated with the biological material.
The bioscrubbers comprised multiple 2.4 m
2
fibreglass supports faced with lava
rock, and colonised with mosses. Indoor air was actively exposed to the bioscrub-
bers with variable speed fans, maintaining a low airflow rate (0.01 ms
-1
) across
the modules. Air was passed through the canopy of a small hydroponic garden
before reaching the bioscrubbers. A substantial non-integrated (i.e. passive) green
wall and hydroponic plantings were also resident in the room. Plants were supplied
with supplementary lighting. The aquarium was integrated in the irrigation system
for both the hydroponics and the green wall. The biofilter appeared to substantially
reduce VOCs including formaldehyde. Unfortunately, the authors (Darlington et al.
2000
) did not record CO
2
levels in their study, as hydroponic plants with supple-
mentary lighting could realistically be expected to remove large amounts of this gas,
based on the findings of Irga et al. (
2013
), who found strong CO
2
removal for small
hydroponic plants in sealed chambers.
Wang and Zhang (
2011
) developed an active biofiltration system combining
both physiochemical and biological bioremediative capabilities, by using activated
carbon as a hydroponic substrate for indoor plants. They tested the system both in a
chamber and fitted to the HVAC system of a 97 m
2
newly built office, thus allowing
a reasonable comparison between closed-system and in situ conditions. They
found that their system was equivalent to a clean air delivery rate of 476 m
3
/h
outdoor air with respect to VOC (formaldehyde and toluene) removal. After
demonstrating the efficacy of their system over a 300 d period, the authors estimated
a 10-15 % reduction in ventilation energy costs in cold climate conditions. The
function of biofilters to reduce building energy consumption will become a major
focus of future research (e.g. Rodgers et al.
2013
).
An active biofiltration system using a column containing inert substrates and
compost, and supporting the growth of spider plant (Chlorophytum comosum), a
species known to be capable of formaldehyde biodegradation (Giese et al.
1994
),
was tested by Xu et al. (
2010
), and found to be very effective at removing high
concentrations of formaldehyde. Active systems thus may have potential to sub-
stantially increase the effectiveness of botanical biofilters, although at the cost of
some energy. The potential for microorganism release when pressurised air is used
may also be a concern (see Sect.
8.12
). The biotrickling filter system used by
Darlington et al. (
2000
), utilised plants as an adjunct to the biologically active
microorganisms is his system, and is thus an alternative active phytoremediation
system.
Active biofiltration is now a widely used air pollution control technology for
industrial waste gases and odours (e.g. Elmrini et al.
2001
; Vergara-Fernández
et al.
2007
; De Visscher and Li
2008
; Mudliar et al.
2010
; Lebrero et al.
2012
).
Systems are now becoming highly developed (e.g. Estrada et al.
2013b
), and due to
low running costs, high removal efficiency for a range of organic and inorganic
gaseous pollutants and lack of secondary pollutant production are now competitive
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