EVALUATING RUNOFF WATER QUALITY FROM GREEN ROOFS COMPARED TO CONVENTIONAL ROOFS

Código

XXVI-SBRH0358

Autores

Thiago Masaharu Osawa, Brenda Coelho Chaves Leite, José Rodolfo Scarati Martins

Tema

C - Águas Urbanas e Cidades Sustentáveis

Resumo

Green roofs (GRs) are increasingly adopted in urban areas to manage stormwater and promote sustainable water reuse. This study evaluated the hydrological and water quality performance of an aged extensive GR under a humid subtropical climate, focusing on its potential for non-potable rainwater reuse. Runoff from the GR and a conventional roof (CR) was monitored during three rainfall events, and key water quality parameters were compared against Brazilian and international reuse standards. GR runoff consistently showed low concentrations of total suspended solids (<5 mg/L) and stable pH, indicating effective filtration and buffering. However, biochemical oxygen demand (BOD) and total organic carbon (TOC) levels occasionally exceeded conservative thresholds, and high total phosphorus and total nitrogen concentrations were observed in GR runoff, likely resulting from substrate leaching and organic matter mineralization. Despite these exceedances, the low BOD/TOC ratios (<0.5) suggest that the exported organic matter is predominantly refractory, reducing the risk of microbial regrowth. Although untreated GR runoff does not fully comply with the strictest reuse criteria, it shows strong potential for non-potable applications such as irrigation and toilet flushing when combined with low-cost treatment technologies like filtration, biochar, or constructed wetlands. These findings highlight the dual role of GRs as both mitigators and potential sources of pollutants, particularly nutrients. Study limitations include the restricted number of monitored events and focus on a single system. Future research should explore optimized substrate compositions and compact treatment solutions to enhance water quality and support broader implementation of rooftop rainwater reuse in urban areas.