Mass flow distribution of stormwater pollutants in ultrafiltration treatment system and permeate reuse

Stormwater can have environmental impacts because it causes various pollutants to be released into the environment during precipitation events. This study quantifies the flow of different metals through an ultrafiltration membrane unit during stormwater treatment and investigates the possibility of reusing treated stormwater both as non-potable and potable purposes and of metal recovery from the backwash water obtained from membrane cleaning. The stormwater used for the ultrafiltration experiments was sampled in three catchments during different rain events. The results indicate that the permeate quality complied with most of the parameters for potable water as stipulated by the Swedish Food Agency, except in respect of manganese, nitrate and ammonia concentrations from permeate from stormwater samples originating from road runoff. The backwash water from the membrane cleaning contained metals in high concentrations, e.g. average copper concentrations were 5.2 times higher in the backwash than in the feed. Recovering metals like Cu, Ni, and Zn from backwash water could be a sustainable process, as stormwater transports 0.03%, 0.01%, and 0.04% of their annual production in high-extraction countries, provided operational costs and logistics are feasible.