Abstract
Reed-Phragmites australis (Cav.) Trin. ex Steud, an aquatic plant, commonly used in constructed wetlands for wastewater treatment, supplies oxygen into the subsurface environment. Reed may be used as a ‘green machine’ in the form of a floating vegetation cover with many applications: wastewater lagoons, manure lagoons or sewage sludge lagoons. An important measure of the performance of the plant system is the oxygen transfer capacity (OTC). Accurate prediction of the OTC in relation to reed biomass would be crucial in modelling its influence on organic matter degradation and ammonia–nitrogen oxygenation in such lagoons. Laboratory experiments aiming to determine OTC and its dependence on reed biomass were carried out. Eight plants with a total dry mass ranging from approximately 3 to 7 g were tested. Mean OTC was determined per plant: 0.18 ± 0.21 (g O2·m−3·h−1·plant−1), with respect to leaves-and-stem dry mass (dlsm): 44.91 ± 35.21 (g O2·m−3·h−1·g dlsm−1), and to total dry mass (dtm): 33.25 ± 27.97 (g O2·m−3·h−1·g dtm−1). In relation to the relatively small root dry mass (drm), the OTC value was 136.02 ± 147.19 (g O2·m−3·h−1·g drm−1). Measured OTC values varied widely between the individual plants (variation coefficient 115%), in accordance with their differing size. Oxygenation performance was greatest in the reed plants with larger above ground dry mass (>4 g dlsm), but no influence of the root dry mass on the OTC rate was found.
Highlights
Problematic by-products of wastewater, manure and sewage sludge storage in lagoons are emissions of odour, volatile organic compounds (VOCs), ammonia (NH3 ), hydrogen sulphide (H2 S)
Phragmites australis is generally tolerant of temperature variations, but the optimum temperature for growth is between 12 ◦ C and 25 ◦ C [22,23]
The same trend was apparent with the reed total dry mass (Figure 2C) but not with dry root mass (Figure 2A), because the dry root mass was relatively small in the plants studied and varied little between them. These results indicated that plants with larger above-ground parts, with a greater area for light absorption and assimilation, are more effective in releasing oxygen from the roots into the surrounding water
Summary
Problematic by-products of wastewater, manure and sewage sludge storage in lagoons are emissions of odour, volatile organic compounds (VOCs), ammonia (NH3 ), hydrogen sulphide (H2 S)and greenhouse gases (GHGs) (CH4 , N2 O, and CO2 ). Problematic by-products of wastewater, manure and sewage sludge storage in lagoons are emissions of odour, volatile organic compounds (VOCs), ammonia (NH3 ), hydrogen sulphide (H2 S). Local and regional air quality and potential contribution to climate change [1] due to these emissions require the need for mitigation technologies that target multiple emissions and are cost-efficient to put into practice [2]. Especially in developing countries, where technical infrastructure development is weak, extensive solutions based on natural processes are applicable. One solution is to create floating emergent macrophyte treatment wetlands, a hybrid of ponds and wetlands, that offer potential advantages for the treatment of polluted waters with highly variable flows. A plant commonly used in both rooted and floating systems is reed. Phragmites australis (Cav.) Trin. ex Steud [3].
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