Performance of a green wall in treating organics, nutrients and pathogens in greywater in a cool climate

This study investigated the performance of the vertECO® green wall system with lightweight expanded clay aggregate (LECA) and biochar-pumice media in treating greywater from an urban city district (1000 residents) under Scandinavian climate conditions. Over one year, the system effectively removed organic matter, achieving 90–97 % of biological oxygen demand (BOD) reduction and 56–94 % for total suspended solids (TSS). However, nitrogen and phosphorus removal were inconsistent and low. Significant reductions of up to 5.1 Log₁₀ of Escherichia coli ( E. coli ), 4.0 Log 10 of enterococci, 4.5 Log 10 of Pseudomonas aeruginosa , and 2.7 Log 10 of Clostridium perfringens were observed, while Legionella and Campylobacter were not detected. Cold temperatures (<5 °C) and vegetation had a minimal impact on the treatment performance. Among 17 plant species, Carex nigra , Armeria maritima , Lythrum salicaria , and Menyanthes trifoliata, Comarum palustre, Caltha palustris, and Iris sibirica showed high resilience. Despite the effective treatment of organic matter and pathogenic microorganisms, the average effluent quality did not meet the European Commission's Class A requirement (≤10 mg/L for BOD and TSS, ≤5 NTU for turbidity, and ≤ 10 CFU/100 mL for E. coli) for the reuse of reclaimed water in agriculture. Moreover, the microbial quality of the effluent indicated the necessity of a hygienisation step and protective measures to reduce infection risks if such a green wall system is placed in a public setting. • A modular green wall system was evaluated for greywater treatment under Scandinavian climate conditions over one year. • High removal efficiencies were achieved for BOD (90–97 %), with effluent concentrations ranging from 5 to 47 mg/L. • Nitrogen and phosphorus removal was limited, with some evidence of nutrient leaching. • Significant removals, up to 5.1 log₁₀, were achieved for E. coli , enterococci, P. aeruginosa , and C. perfringens . • Seasonal temperature and vegetation growth had minimal impact on treatment performance.