Potential of the electrodialytic process for emerging organic contaminants remediation and phosphorus separation from sewage sludge

The present work discusses the efficiency of the electrodialytic process (ED) applied to sewage sludge aiming phosphorus recovery and organic contaminants removal. Six emerging organic contaminants were studied: caffeine (CAF), ibuprofen (Ibu), 17β-oestradiol (E2), 17α-ethinyloestradiol (EE2), bisphenol A (BPA), and oxybenzone (MBPh). Three different ED experimental cell designs were tested, in a 2-compartment cell set-up, using sewage sludge spiked with 8 mg/L of each compound. In total, five ED experiments were carried out during 5 days. Two control experiments without current were also carried out. At the end of the experiments, changes in the sewage sludge pH and in the microbial communities were observed and these changes affected contaminants degradation. Still, independently of the cell design used, the application of a low level direct current, improved the degradation of Ibu between 46 and 97%, as well as Caf between 20 and 47% (except in Exp-4), comparing against the control experiments. A contrary effect was observed for MBPh which degradation was less effective when the sewage sludge was subjected to ED, being the only exception the results obtained for Exp-5. This cell design, sewage sludge in the cathode compartment separated from the anode by an anion exchange membrane, also promoted higher contaminants degradation and in the final sludge all contaminants, except MBPh, were below limit of quantification and limit of detection. In terms of P, the highest recovery was achieved when the pH increased to 12.5 in Exp-5, 78 ± 2% of total P was recovered in the electrolyte. Independently of the experiments, the recovered P was still mixed with the studied organic contaminants.