Impact of active hydroponic biowalls on the indoor air microbiome

Abstract

Fine particles and volatile organic compounds (VOC’s) cause poor indoor air quality. These substances are released by building materials, paints, furniture, printers and human activities and cause discomfort, headache and contribute to chronic diseases. A solution for this problem, sometimes called the ‘sick building syndrome’, is to properly ventilate the building. Due to practical reasons, design choices, maintenance and energy usage, the level of ventilation is often not high enough. Plants can degrade harmful substances and vegetation may therefore be used together with ventilation systems. Enhancing this air cleaning potential, air blowers may be used to generate an airflow through the growth medium of plants. Indoor vertical plant walls that use air blowers are called biowalls. So far, however, the impact of these walls on microbial composition and abundance has hardly been assessed. Therefore, this research seeks to find an answer on what effect indoor vertical plant walls have on the composition of bacteria and fungi in indoor air. Depending on the number and types of bacteria and fungi this answer may be positive, neutral or negative towards the health of humans. In this research air samples were taken in buildings with a large collection of plants (botanical greenhouses) and in a controlled closed environment (i.e. an incubator) before and after introduction of plants or a custom built biowall. The abundance and diversity of the microbes in the indoor air samples was determined. These data were compared to the soil- and leaf samples of the plants in the case of the incubator experiments. It turned out that relative humidity of indoor air significantly increased fungal spore load. Moreover, abundance and diversity of fungi, yeasts and bacteria in the air increased after placing and watering plants in the incubator but this was a short-term effect. In the experiment with the longest duration the conditions at day 35 were similar to the starting conditions. Together, this study suggests that the indoor air microbiome and abundance is not affected by biowalls. This “not harmful” outcome does not hamper the use of biowalls to improve indoor air quality.