Electrocoagulation Coupled to Electro-Oxidation for the Electrochemical Treatment of Hemodialysis Wastewater

Abstract

Hemodialysis is an extracorporeal kidney replacement procedure to remove impurities or waste products from the blood used to treat kidney failure. During this process, large amounts of water are used, which, lacking control, end up in sewage systems, potentially flushing high levels of organic and inorganic contaminants into the receiver’s aqua biota. In recent years, a hybrid electrocoagulation (EC) and electro-oxidation (EO) process in sequential or simultaneous coupling has been used for the treatment of wastewater.This research considered synthetic water from hemodialysis under acid and basic conditions. To better simulate the presence of organic compounds, 10 mg L-1 of amoxicillin (AMX), an antibiotic commonly present in wastewater from clinics and hospitals, was added. Laboratory and pilot tests were performed using coupled EC and EO. They used stainless-steel (SS-304) and aluminum (Al-6061) as sacrificial anodes that were compared in acidic and basic pH during EC. The SS-304 rod anode and a titanium (Ti) mesh cathode were used during EC in acidic conditions at a field strength of 3.0 V, which was applied for 60 min. After EC, the solution obtained was filtered to separate precipitates. The supernatant was then treated with EO using an IrO2-Ta2O5|Ti (70:30) anode and the Ti mesh cathode while applying 10 mA for 120 min. The wear of the SS-304 anode was identified by scanning electron microscopy (SEM) and microanalysis (EDS). Removal of organic compounds, including AMX, was significant. This result was confirmed by decreased concentration found by diode coupled chromatography (UPLC-UV-Vis) detection.In conclusion, combining EC and EO in a sequential arrangement for the treatment of hemodialysis wastewater was carried out. EC was performed using a cylindrical SS-304 bar electrode (f = 0.8 cm) as an anode and a concentric Ti mesh as the counter electrode. A 3.0 V cell potential was maintained over one hour of electrolysis in acidic pH (pH = 5.06, s = 227 mS cm-1). This treatment yielded a removal efficiency of 86 ± 1.25 % of AMX contaminate (pH = 8.21, s = 217.26 mS cm-1, i = 11.36 mA, E = 0.568 kWh m-3). After EC, it was necessary to include a filtration or separation process to remove the Fe(OH)3 and [AMX-cation-AMX] sludge generated (2.3 g). This separation employed a settler. Subsequently, the supernatant was placed in an EO cell to remove residual organic compounds as AMX. It used a similar cell arrangement as in EC but changed the anode to IrO2-Ta2O5|Ti (70:30) (f = 0.5 cm) to perform the EO of the pharmaceutical product. During this step, the team achieved an overall removal efficiency of AMX of 100 % (pH = 8.14, s = 179.83 mS cm-1, E = 500 kWh m-3). EO was performed using a continuous 10 mA cell current for 2 h. EO generated reaction products ADP 1, ADP 2, and ADP 3. Additionally, this process decreased the content of ‘salty’ cations: Na+, K+, Ca2+, and Mg2+, while generating Cl2 gas at the electrode.