Pedro J. CARVALHO1, Luana SARINHO1,2, Maria Isabel NUNE2
1CICECO – Aveiro Institute of Materials, Chemistry Department, University of Aveiro, Portugal
2CESAM - Centre for Environmental and Marine Studies, Department of Environment and Planning, University of Aveiro, Portugal
The increasing worldwide industrialization impact on the environment, and ultimately on quality of life, raised the attention of both the society as the industry to foster the implementation of more sustainable manufacturing practices and shift from linear to circular economy. Salted cod is still considered a highly popular product due to high demand and simplicity of processing. Traditionally, salted cod is obtained by piling up the fish with alternate layers of dry salt (NaCl) and left to mature over period. This salt byproduct will generate a brine with high impact to the environment, regardless of the water body receptor.
Conventional treatment processes are ineffective in reducing the organic load of this brine, given its high salinity. On the other hand, treated cod brines have potential to be used in other industrial activities, such as in the pickling stage in tanneries, which require the use of high amounts of water and salt (~7.5 – 8 % wt. NaCl). In recent years, electrochemical technologies such as electrocoagulation (EC), electrooxidation (EO) and electro-photooxidation have attracted interest in the field of wastewater treatment. In EC process, aluminum or iron electrodes were used as anode for the in-situ generation of coagulant agents that promote the removal of pollutants. The EO process can occur in two ways: (i) direct oxidation, where the pollutants adsorbed on the anode surface are decomposed by the electron transfer between anode surface and pollutants without involvement of oxidizing agent and/or (ii) indirect oxidation, where the pollutants are decomposed in the solution through oxidation reactions with oxidants, such as hypochlorite, chlorine and hydrogen peroxide (H2O2). When iron electrodes and H2O2 oxidant are used, electro-Fenton process (EF) is conducted. EF process is a combination of EC and Fenton process with the use of electricity enhancing the generation of •OH. The EF process can have four different approaches: (i) Fe is externally added to the solution and indirect generation of H2O2 occurs by oxidation reactions with inert electrodes; (ii) H2O2 is externally added to the solution and Fe is provided from sacrificial iron anodes; (iii) Fe2+ and H2O2 are electrogenerated using a sacrificial anode and an inert cathode and (iv) both Fe2+ and H2O2 are externally added to produce •OH in the electrolytic cell and Fe2+ is regenerated at the cathode.
The ability to induce reversible phase transitions between homogeneous solutions and biphasic liquid-liquid systems, at tuned operating conditions, have demonstrated high potential as alternative extraction platform to further push challenging separations.
This work aimed to optimize the application of EF process (with iron electrodes) to treat a real cod brine (reducing the total organic carbon load), enhanced by thermo-responsive ionic liquids based aqueous biphasic systems, as mechanism of achieving the effluent stream specifications required by the pickling stage.