Exploratory study on modification of sludge-based activated carbon for nutrient removal from stormwater runoff

Nutrients (P, N) in stormwater runoff are a major cause of eutrophication and algal blooms. A promising solution to this problem is to amend the rain garden growing medium (RGGM) with sewage sludge-based activated carbon (SBAC). To optimize the SBAC production process, different metals, pyrolysis conditions (temperature, heating time, carrier gas), and post-treatments were explored. When pyrolyzed at 400 °C for two hours, Zn-activated SBAC removed up to 41% of PO₄-P (initial concentration of 1 mg/L) and 72% of NO₃-N (initial concentration of 2 mg/L), at a dose of 1 g sorbent/L of nutrient-spiked distilled water. When the same dosage was applied to stormwater leachate made from RGGM and spiked with nutrients, the removal efficiencies were reduced to 20% for PO₄-P and 38% for NO₃-N. These reductions were probably caused by competition from other leachate components. Increasing the dosage to 3 g/L leachate improved PO₄-P removal to 31% and NO₃-N to 72%, while also resulting in the removal of 46% of total organic carbon. The major energy cost of producing such sorbents is estimated to be ∼$0.76 CAD/kg SBAC.