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 Biofiltration of indoor air, as an alternative to ventilation with outside air, is a truly novel application of conventional biofiltration. In conventional biofilters, the waste gas streams are generally well defined in terms of contaminant composition and concentrations. These provide design parameters for optimum biofilter configuration. In contrast, the indoor air stream comprises a complex mixture of VOCs at variable concentrations. Over three hundred different compounds have been reported to occur indoors. And the range and concentrations of these compounds change dependent on the transient activities that can occur within the space. Thus, an indoor biofilter must be capable of degrading a broad range of VOCs and adapting to a dynamic air stream. Microbial species diversity is a key parameter. To maximize diversity, an indoor biofilter must provide many different microbial ecological niches. Conventional biofilters generally treat contaminant concentrations in the order of 10-3 to 10 g m-3. This range enables adequate biofilm concentrations for efficient degradation. Concentrations below this range are typically too dilute to affect an adequate biodegradation response. However, an indoor air biofilter must be able to treat trace levels of VOCs. In fact, single component concentrations are typically 10-7 to 10-4 g m-3 while total VOCs (tVOC) range from 10-5 to 10-3 g m-3. With the low solubility of many of the common indoor VOCs, concentrations in the aqueous phase of the biofilter may be below threshold levels for microbial degradation.
The extremely low concentrations further complicated by the extremely large volumes of air that must be treated indoors. Considering that standard ventilation rates range from 2 to 15 air changes per hour, an indoor air biofilter has to handle large air volumes. To understand why green plants are included in the Naturaire® Systems, click here. |
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