Electrodialytic treatment of sewage sludge: current intensity influence on phosphorus recovery and organic contaminants removal

There is a need to develop viable techniques for removal and/or recovery of organic and inorganic compounds from environmental matrices, due to their eco-toxicity, regulatory obligations or potential supplies as secondary materials. Simultaneous phosphorus (P) recovery and removal of emerging organic contaminants (caffeine, bisphenol A, 17α-ethinylestradiol and oxybenzone) from sewage sludge (SS) was assessed using the electrodialytic (ED) process. The SS samples were collected at the secondary settling tank between May and July, 2015. Different current intensities were tested continuously or sequentially (between 50, 75 and 100 mA), in a 2 compartment cell, placing the SS in the cathode end, separated from the anode end through an anion exchange membrane. After 24 h, between 45 and 55% of P electromigrated to the anode end in all experiments and the application of higher current intensities did not promote significant improvements in its recovery. After 72 h, the best results were obtained when 100 mA (0.21 mA/cm²) were applied: 70% of P were recovered in the anolyte and between 79 and 96% of organic compounds were degraded. Still, the obtained anolyte enriched in P was not completely free of organic contaminants.