Green wall for domestic wastewater treatment

Landscape architecture is increasingly introducing green walls in urban regions. Most of the scientific research on green walls has been focused on the benefits they provide to the urban surrounding and to the building itself; energy savings due to insulation properties being the main benefit. Wastewater treatment has not yet been exploited as a function of green walls, and only a few studies have been conducted in that topic. If this function can be attributed to green walls, vertical built urban areas could be intended for onsite sanitation system for households and office buildings. Therefore the overall aim of this study is to design a green wall system and assess the efficiency for onsite treatment of domestic wastewater. 3 green wall modules where constructed, using vermiculite as substratum. One was left unplanted, another was planted with Juncus effusus and the third one was planted with Spathiphyllum wallisii. They were irrigated daily with 3 litres of wastewater (primary settled) from Harnaschpolder WWTP. Water Quality parameters from the green walls effluents were analyzed every week. After 2 weeks of adaptation period the modules showed to be at steady state for organic matter removal, during 6 weeks monitoring the removal efficiencies were more than 80% for TSS, BOD and COD. For Faecal Coliforms the modules showed more than 95% removal. For nutrient removal the modules showed efficiencies of 40% removal for TP and 50% for TN. There was no significant difference between the performances of the 3 modules; therefore no additional contribution of plants could be attributed to the overall efficiency of the modules. Vermiculite showed to have almost none adsorption capacity for phosphorus and very low potential for nitrification, denitrification and microbial activity. Nevertheless it occupied almost 100% of the module's volume and was responsible for the overall performance of the modules. The effluents meet the EU standard only for the organic matter parameters but not for TN and TP; further treatment would be needed to discharge the effluents in natural water bodies