Stormwater and blackwater are two urban wastewater streams with potential as valuable resources. The stormwater quality varies depending on catchment, actual rain pattern, pollutants sources, etc. Blackwater contains nutrients and energy that can be recovered. In addition, it contains organics, metals, micropollutants and microorganisms which might affect the efficiency of downstream processes. Efficient removal of contaminants from both stormwater and blackwater is essential for their reuse and recovery of resources, including water and nutrients. 

Membrane technology offers an advanced solution to improve the quality of stormwater and blackwater. While a number of studies have explored the application of membranes for stormwater treatment, the varying quality of stormwater raises questions about membranes’ efficiency in separating pollutants from different qualities of stormwater. More research is needed to understand the reusability of treated stormwater using membranes as well as the recovery of metals in the concentrate. 

The overall aim of this study is to improve the quality of stormwater and source-separated blackwater, which has a direct impact on the reusability of stormwater as water resource and of struvite as a biofertilizer. Nutrient recovery from blackwater after membrane treatment is a new concept requiring further attention. Membrane cleaning is essential for maintaining membrane efficiency. For stormwater, regular backwashing with different durations and chemical combinations were tested, and the fouling layer on the membrane was analyzed, using a scanning electron microscope. Backwash water was characterised. For blackwater, the membrane cleaning method used included backwashing combined with aeration, raising the question about its adequacy.

The ultrafiltration membrane was able to separate total suspended solids, oil, particulate metals, total phosphorus, turbidity and microorganisms from stormwater and effectively reduced organic compounds. After hygenisation, ultrafiltratered stormwater has a significant potential for non-potable uses, and its quality approaches potable standards, based on Swedish Food Agency. The struvite produced from membrane treated digestate resulted in struvite with more uniform struvite crystals, free of organic substances and metals (As, Ca, Cr, Cu, Pb and Si) stepping towards reusing this struvite as biofertilizer. The optimal backwash duration after stormwater treatment, for these set of experiments was 45 s considering membrane productivity. Chemical cleaning with sodium hydroxide, and with or without sodium hypochlorite followed by hydrochloric acid were compared which indicated that addition of sodium hypochlorite did not improve the efficiency of chemical cleaning. Analyses of the backwash water showed a high metal concentration which might indicate the potential for metal recovery.  Combinations of backwash and aeration was an efficient method to preserve membrane initial flux after digestate blackwater treatment.