Inactivation of microbiota from urban wastewater by single and sequential electrocoagulation and electro-Fenton treatments

Abstract

This work aims at comparing the ability of two kinds of electrochemical technologies, namely electrocoagulation (EC) and electro-Fenton (EF), to disinfect primary and secondary effluents from municipal wastewater treatment plants. Heterotrophic bacteria, Escherichia coli, enterococci, Clostridium perfringens spores, somatic coliphages and eukaryotes (amoebae, flagellates, ciliates and metazoa) were tested as indicator microorganisms. EC with an Fe/Fe cell at 200 A m and natural pH allowed >5 log unit removal of E. coli and final concentration below 1 bacteria mL of coliphages and eukaryotes from both effluents in ca. 60 min, whereas heterotrophic bacteria, enterococci and spores were more resistant. A larger removal was obtained for the primary effluent, probably because the flocs remove higher amount of total organic carbon (TOC), entrapping more easily the microbiota. EF with a boron-doped diamond (BDD) anode and an air-diffusion cathode that produces HO on site was first performed at pH 3.0, with large or even total inactivation of microorganisms within 30 min. A more effective microorganism removal was attained as compared to EC thanks to OH formed from Fenton's reaction. A quicker disinfection was observed for the secondary effluent owing to its lower TOC content, allowing the attack of greater quantities of electrogenerated oxidants on microorganisms. Wastewater disinfection by EF was also feasible at natural pH (∼7), showing similar abatement of active microorganisms as a result of the synergistic action of generated oxidants like active chlorine and coagulation with iron hydroxides. A sequential EC/EF treatment (30 min each) was more effective for a combined decontamination and disinfection of urban wastewater.

Electrocoagulation as a Pretreatment for Electroxidation of E. coli

“…The model shallow aquifer was not included in these tests as substantial E. coli mitigation was observed at lower current densities ( Figure 2). Similar to other investigations [25,45], the increased current led to higher free chlorine production and greater E. coli mitigation. Table 1).…”

Highly efficient bacterial removal and disinfection by magnetic barium phosphate nanoflakes with embedded iron oxide nanoparticles

“…4 Recently, a number of new materials or methods have been proposed to remove bacteria from water, for example, polyoxometalate supported ionic liquid phases, 5 single cell imprinting on Ag-ZnO bimetallic nanoparticle modified graphene oxide sheets, 6 silvermodified zeolite, 7 cellulose nanofibers and activated carbon membranes, 8 pompon-like ZnO-PANI heterostructures, 9 electrocoagulation and electro-Fenton. 10 These materials showed removal and/or bactericidal properties. However, developing more sustainable materials for bacterial disinfection is still of great urgency and significance, especially with low cost and easy separation.…”

Advantages of electro-Fenton over electrocoagulation for disinfection of dairy wastewater

“…The inactivation of HT and LA bacteria in EF can then be associated to the action of strong oxidizing agents generated, including • OH from Fenton's reaction (4), BDD( • OH) from reaction (7) and active chlorine (Cl2/HClO) from reactions (8) and (9), as established elsewhere [50,51]. These strong oxidants are expected to attack the molecules of the cell walls causing the lysis and death of bacteria [24,52]. In contrast, the weaker oxidant H2O2 is expected to contribute to the disinfection to a much smaller extent [48,49], being rather inactive for LA bacteria, as stated above.…”

“…Several authors used EC for disinfection in urban wastewater treatment facilities (WWTFs), describing total inactivation (> 99.99%) of Escherichia coli [14][15][16], total coliforms [17,18] or Staphylococcus aureus [19]. EC has also been applied to minimize the organic load of dye and textile wastewater [13,[20][21][22][23], urban wastewater [24], olive oil mill wastewater [25] and cheese whey or dairy wastewater [3,[26][27][28][29]. For a synthetic whey solution, Un et al [3] described a maximum COD removal of 86.4% using a reactor in continuous with Fe electrodes…”