Botanical biofilter for indoor toluene removal and reduction of carbon dioxide emission under low light intensity by using mixed C3 and CAM plants

Botanical biofilters are an interesting technology for indoor air pollution control. However, when growing plants under indoor air conditions with low light intensity (10-50 μmole PAR m−2 s−1), they seem to emit CO2 to the environment. In order to solve this problem, a combination of C3 and CAM plants might be able to decrease the level of CO2 emission and increase pollutant-removal efficiency. Therefore, an effective botanical biofilter with mixed plants was studied. The CO2 emissions from high benzene, toluene, ethylbenzene and xylene (BTEX) removal plants including Zamioculcas zamiifolia (facultative CAM), Dracaena sanderiana (C3), Chlorophytum comosum (C3), Euphorbia milii (CAM cycling), Sansevieria kirkii (CAM), and Sansevieria trifasciata (CAM) were investigated. C. comosum and S. trifasciata emitted very low CO2 under both light (50 μmole PAR m−2 s−1) and dark conditions. These two plant species (total leaf area of 500 cm2) were used in the botanical biofilter. The results showed that the botanical biofilter with a mixture of C. comosum and S. trifasciata plants could rapidly remove 1 m3 of 1 ± 0.2 ppm (3.9-4.7 mg m−3) toluene-contaminated air within only 2-3 h. In addition, the mixed plant system also showed low CO2 emission under both light and dark conditions. The combination of C3 and CAM plants offers an alternative method to limit CO2 emissions from a botanical biofilter under low light-intensity conditions.