Eco-friendly bricks manufactured from municipal sewage sludge before and after electrodialytic recovery of phosphorus

This study evaluates electrodialytic (ED) treatment as a dual‑function route to recover phosphorus (P) and remove heavy metals from digested sewage sludge and then reuse untreated and ED‑treated sludge in bricks. Two digested municipal sludges (Sludge‑A, Sludge‑L) were treated under varied ED conditions (10 and 50 mA, corresponding to ∼ 0.20 and ∼ 0.99 mA/cm²; 1-5 days). Sludge‑A released P faster (40% after 5 days at ∼ 0.20 mA/cm²) than Sludge‑L (36%), and both reached ∼ 70% P recovery at ∼ 0.99 mA/cm² in 4 days. Zn and Cd were efficiently removed (60-80%), whereas Cu and Pb showed limited mobilization. Bricks with 10-30% sludge fired at 1020-1040 °C exhibited the expected trade‑off: higher sludge content increased open porosity and lowered dry density due to gas evolution and flux‑controlled vitrification; higher firing temperature enhanced densification. Bricks made with ED‑treated sludge were slightly more porous and less dense-consistent with ED‑altered chemistry-yet up to 10% treated‑sludge mixtures retained acceptable physical properties. Overall, direct ED on digested sludge enables meaningful P recovery and heavy metal removal while supporting partial sludge reuse in bricks. The results define operating windows for balancing resource recovery and material performance and motivate further optimization of ED settings and sintering schedules.