An electrochemical advanced oxidation process for the treatment of urban stormwater

Recharge of urban stormwater has often been limited by the high cost of land and concerns about contamination of groundwater. To provide a possible solution, we developed an electrochemical advanced oxidation system (UV/H2O2) that is compatible with high-capacity stormwater recharge systems (e.g., drywells). The system employed an air-diffusion cathode to generate a H2O2 stock solution (i.e., typically around 600 mM) prior to the storm event. The H2O2 stock solution was then metered into stormwater and converted into hydroxyl radical (center dot OH) by an ultraviolet lamp. The energy consumption for H2O2 generation was optimized by adjusting the applied current density and adding an inert salt (e.g., Na2SO4) to stormwater. H2O2 in the stock solution was unstable. By mixing the basic H2O2 containing catholyte and the acidic anolyte, the stability increased, enabling generation of the H2O2 stock solution up to three days prior the storm event with loss of less than 20% of the H2O2. Lab-scale experiments and a kinetic model were used to assess the feasibility of the full-scale advanced oxidation system. System performance decreased at elevated concentrations of dissolved organic carbon in stormwater, due to enhanced light reflection and backscattering at the water-air interface in the UV reactor, competition for UV light absorption with H2O2 and the tendency of organic matter to act as a center dot OH scavenger. The proposed system can be incorporated into drywells to remove greater than 90% of trace organic contaminants under typical operating conditions. The electrical energy per order of the system is estimated to range from 0.5 to 2 kWh/m(3), depending on the dissolved organic carbon concentration.

Automated summary

The study developed an electrochemical advanced oxidation system as a solution for urban stormwater recharge. By optimizing H2O2 generation through adjusting current density and adding salt, up to three days advance generation of H2O2 stock solution is possible.