Experimental study of greywater treatment through green walls

Among nature- based solutions (NBSs), green walls represent a key technology in the urban context because of the low energy demand and of the many ecological and social outcomes. This work presents the results of the experimental study at laboratory scale of the treatment of greywater (e.g. domestic wastewater excluding toilet flushes) through a green wall. It is made of two modular panels (1-set up for this study and 2-in use for 15 months), made of twelve pots arranged on four columns and three rows, and filled with a mix of coconut and perlite and different ornamental plant species. The green wall was fed discontinuously with 96 L/d of synthetic greywater for two months during the winter season. The treatment performances of the two panels were very high about total suspended solids (>87%), biological oxygen demand (>98%) and chemical oxygen demand (∼80%), in agreement with literature. Panel 1 exceeded the performances of panel 2 only about total suspended solids (96% vs 87%), probably because of a clogging phenomenon. This study proved the efficiency of green walls towards greywater treatment in challenging experimental conditions, as winter temperature and high hydraulic loading rate.