The power of plants
Although the microbes in active Living Walls do the majority of contaminant breakdown, there are many reasons why NEDLAW includes plants in our systems:

• Based on their physical characteristics, plant materials make excellent ‘packing material’ for a biofilter. High porosity allows for easy air flow, while high surface area provides for good bio-film contact, even with very shallow bed depths.

• Living plants are a bio-regenerative packing medium, constantly replacing themselves. As well, plant material provides alternative carbon sources to maintain biological activity. Alternative packing mediums, such as bark, have a limited life-span as they degrade.

• A plant can alter the composition of its associated microbial population. Careful selection of plant species can promote desirable VOC degraders.

• Plants can quickly adapt to growth on vertical surfaces.

• The rhizosphere surrounding the roots of the plants contains higher microbial populations than bare soil. Hence, plants are able to enhance degrader populations.

• Plants can break down some indoor pollutants directly. Plants grown in cell culture could metabolize formaldehyde into cellular components. However, house-plants have limited impact on indoor VOCs, due to boundary-layer resistance. The incorporation of a biofilter into the air-handling system greatly reduces this resistance and maximizes any ability of the plant to break down pollutants.

• Through photosynthesis, green plants are able to convert CO₂ — which is considered an indoor pollutant — into oxygen. The true impact of this on indoor air quality is minor. To be a true CO₂ scrubber would require over 10m² of wall per occupant instead of the typical 0.2m² required to provide clean air.

• Plants reduce the amount of dust in an enclosed space.

• Green plants have aesthetic value. Maintaining an indoor green space increases worker productivity and lowers absenteeism.