A novel blue-green infrastructure for providing potential drinking water source from urban stormwater through a sustainable physical-biological treatment

In this research, a sustainable blue-green infrastructure (BGI) was developed to efficiently remove contaminants from stormwater through a combined use of modified porous asphalt (PA) and microalgae cultivation to provide a potential drinking water (DW) source. According to the results, the modified PA with powder activated carbon (PAC) could successfully reduce the level of total suspended solids (TSS), turbidity, polycyclic aromatic hydrocarbons (PAHs), oil and grease to below the DW standards but failed to efficiently remove some heavy metals (HMs) and nutrient pollutants. The results revealed that the treated stormwater was an appropriate medium for microalgae cultivation. Chlorella sorokiniana cultivation in the treated stormwater reduced the concentration of HMs and nutrients to below the DW standard: Cr = 9.45 μg/L, Pb = 0.17 μg/L, Cd = 0.003 μg/L, COD = 1.18 mg/L, total nitrogen (TN) = 0.04 mg/L and total phosphate (TP) = 0.006 mg/L. In addition, microalgae could completely consume CO₂ and increase dissolved oxygen (DO) when different concentrations of CO₂ (natural air, traffic air and tunnel with and without ventilation) were injected into the culture medium. A final biomass concentration of 2.6 mg/L was achieved under the optimal conditions which contained 41%, 35% and 22% of carbohydrate, protein, and lipid, respectively. Based on the results, the PA permeability was reduced by 27.3% after 12 times filtration due to the PA blockage phenomena. However, with defined maintenance, the BGI system could have proper workability for several years (i.e. 80% efficiency after 5 years). Our findings suggested that the BGI system can be implemented in both centralized and decentralized fashions which results in clean water, CO₂ bio-fixation and high-value bioproducts from stormwater.