In-situ Electrochemical Generation of the Fenton Reagent for Treatment of Human Wastewater
Luis A. Godínez was born in Mexico city on November 10, 1967. After getting a B.S. degree in Chemical Engineering and a M.Sc. in Science in Physical Chemistry at the National Autonomous University of Mexico (UNAM), he moved to the University of Miami in the USA where he got a M.Sc. and a Ph.D. degree in Physical Chemistry under Prof. Angel E. Kaifer.
In 1997 he got an appointment as a post-doctoral fellow at the Center for Molecular Design and Recognition at the University of South Florida under Prof. George Newkome and in 1998 he returned to Mexico to join the Center for Electrochemical Science and Technology in Querétaro, where he currently works as Researcher and General Director.
In 2009 he also completed a Master in Science and Technology commercialization degree (MSTC) from CIMAV-UT. Luis A. Godinez has co-authored over 110 papers and his research focuses in modified electrodes and electrochemical advanced oxidation processes for water treatment.
Midterm Update | May, 2015
Luis A. Godínez, Principal Investigator
Francisco J. Rodríguez-Valadez, Jennifer Bañuelos, Dennys Fernández, Ana I. Zarate
The aim of this project is to design, build, characterize and optimize a small Electro-Fenton reactor for human wastewater treatment. A fast and effective approach for water disinfection without expensive wastewater infrastructure is electrochemical treatment, in which an electrochemically produced oxidant species eliminates the biologically hazardous pollutants. Traditionally, hypochlorite has been used for disinfection; however, due to its limited oxidation potential, it cannot eliminate all biologically hazardous elements in human waste-contaminated water. The hydroxyl radical (OH) species, on the other hand, has a substantially larger oxidation potential, which makes its effectiveness for disinfecting this type of contaminated water promising.
To that end, the research team has been working to develop approaches to electrochemically prepare the OH radical in-situ, so that it may be used for the oxidation of organic pollutants in wastewater. The team has based their approach on the cathodic generation of H2O2 from oxygen reduction in a carbonaceous electrode. The combination of H2O2 with Fe2+ ions gives rise to the Fenton reagent, which generates the OH radical species.
An electrochemical reactor using this Electro-Fenton process can produce a powerful oxidant species that may disinfect water contaminated with parasites that cannot be effectively eliminated using chlorine-based technology. The proposed reactor will be comprised of a packed activated carbon (AC) electrode flanked by two compartments containing a cation exchange resin, one of which will be previously loaded so that it can release Fe2+, Fe3+ and H+ cations as the aqueous effluent flows through it.
Testing the Disinfecting Power of the Fenton Reagant
Before working on the design of the resin chamber and the electrochemical AC compartment, the team conducted some preliminary experiments to test the disinfection potential of the Fenton reagent as compared to the commonly employed chlorine approach. They first tested the ability of the Fenton reagent to eliminate Helminth eggs of the parasite Ascaris lumbricoides from wastewater. Helminth eggs (HE) are highly resistant to the disinfection process due to their robust external layers. The team treated a sample of contaminated water containing an average amount of 110,000 eggs/L with both a Fenton mixture and with a hypochlorite solution at concentrations employed in standard disinfection processes (8ppm). Over time, both solutions reduced the amount of HE; however, the disinfection power of the two solutions is different. After 120 minutes, for instance, while the hypochlorite solution reduced the amount of HE by 60%, the Fenton reagent had reduced the HE by 92%.
Observing the treated water under a microscope revealed that the OH radical not only reduced the density of HE present in the sample, it also significantly changed the shape and size of the HE, suggesting their membranes had been destroyed. Further inspection showed that a spherical egg began to leak intracellular material after 30 minutes and finally lost its shape and integrity after 120 minutes. It is important to note that these experiments were performed with Fenton reagent concentrations that may not necessarily be present at the cathodic interface of the electrochemical reactor to be constructed. However, considering the proposed design of the reactor, it is reasonable to expect a similar and efficient disinfection performance.
Designing the Middle AC Compartment
The first step in designing the middle AC compartment was defining a treatment protocol to be applied to the commercial activated carbon purchased. The team needed to have a standardized structure and average population of surface chemical groups on the AC surface that will enable reproducible results for a future study of the performance of the packed electrode as a function of its density. Based on the previous findings of Shi and co-workers (2011), the team selected a treatment in which the as-received AC was washed with 0.01 M HCl followed by a 15 hour treatment with 10% HNO3 at room temperature. The team observed that the pre-treatment method resulted in both a material with a zero point charge (pHpzc) of 2.5 and an increase in the total number of acidic groups that changed from 0.99 to 1.33 mmol/g upon HNO3 treatment.
The team next determined the density of the AC to be used in the reactor. If the density is too high, the conductivity of the AC packed compartment will be maximized, but the aqueous effluent flow will be inhibited and O2 will probably not be able to reach a high fraction of the cathodic polarized AC surface. If, on the other hand, the density is too low, the conductivity of the AC electrode could be lost, and the potential distribution across the compartment will be difficult to control, causing the anticipated electrochemical reactions to behave erratically.
To determine the optimum AC density conditions, the team is currently constructing a constant volume reactor in which they will introduce different amounts of AC. The reactor will have several electric contacts along its length to enable the study of AC conductivity values as a function of the density of AC. In a later stage of the study, the team will introduce O2 bubbling to determine the potential distribution under complete Electro-Fenton operation conditions.
Next Steps: Designing the System for H+ and Ionic Fe Administration and Collection
For this part of the project, the team must prepare and characterize the loaded resin for the reactor with a proper ratio of ionic Fe and H+ and then measure the time needed to wash away these species from the resin chamber at the working water flow rate. They will also need to confirm that the collection time is equivalent to the release time and, if possible, model the behavior so that they may make predictions about the amount of resin and the time it will take to collect or release ionic iron and protons as a function of different flow rates and ionic compositions of contaminated water.
Since they are interested in optimizing the amount of resin to be used in the chambers, they will study the iron and proton release from the loaded resin using different flow rates of water and different amounts of resin, rather than trying different concentrations of iron in the resin.