Abstract
In this paper we analyse the feasibility of low voltage iron electrocoagulation as a means of municipal secondary effluent treatment with a focus on removal of microbial indicators, Antibiotic Resistant Bacteria (ARB) and nutrients. A laboratory scale batch unit equipped with iron electrodes was used on synthetic and real secondary effluent from a municipal wastewater treatment plant. Synthetic secondary effluent was separately assayed with spiked Escherichia coli WR1 and with bacteriophage ΦX174, while real effluent samples were screened before and after treatment for E. coli, Extended Spectrum Betalactamase-producing E. coli, Enterococci, Vancomycin Resistant Enterococci, Clostridium perfringens spores and somatic coliphages. Charge dosage (CD) and charge dosage rate (CDR) were used as the main process control parameters. Experiments with synthetic secondary effluent showed >4log10 and >5log10 removal for phage ΦX174 and for E. coli WR1, respectively. In real effluents, bacterial indicator removal exceeded 3.5log10, ARB were removed below detection limit (≥2.5log10), virus removal reached 2.3log10 and C. perfringens spore removal exceeded 2.5log10. Experiments in both real and synthetic wastewater showed that bacterial removal increased with increasing CD and decreasing CDR. Virus removal increased with increasing CD but was irresponsive to CDR. C. perfringens spore removal increased with increasing CD yet reached a removal plateau, being also irresponsive to CDR. Phosphate removal exceeded 99%, while total nitrogen and chemical oxygen demand removal were below 15% and 58%, respectively. Operational cost estimates were made for power and iron plate consumption, and were found to be in the range of 0.01 to 0.24€/m3 for the different assayed configurations. In conclusion, low voltage Fe-EC is a promising technology for pathogen reduction of secondary municipal effluents, with log10 removals comparable to those achieved by conventional disinfection methods such as chlorination, UV or ozonation.
Highlights
At present, one-third of the world’s population lives in waterstressed countries and by 2025 the figure is expected to rise to two-thirds (Elimelech, 2006)
The main objective of the present research is to evaluate the performance of low voltage Fe-EC during the treatment of municipal secondary effluents in the removal of microbial pathogen indicators (Escherichia coli, enterococci, somatic coliphages and Clostridium perfringens spores) and Antibiotic Resistant Bacteria (Extended Spectrum Beta Lactamase (ESBL) and Carbapenem Resistant (CRE) -E. coli and Vancomycin Resistant Enterococci-VRE)
Concentrations of bacterial indicators (E. coli and enterococci) exceeded that of Extended-Spectrum Betalactamase-producing E. coli (ESBLE) and VRE by 2-3log10 in both influent and effluent, indicating that Antibiotic Resistant Bacteria (ARB) were present in lower numbers (Fig. 2)
Summary
One-third of the world’s population lives in waterstressed countries and by 2025 the figure is expected to rise to two-thirds (Elimelech, 2006). Despite reclamation being an attractive concept, municipal wastewater harbours a wide range of enteric pathogens such as virus, bacteria, protozoa, parasitic worms and eggs, and its (re)use calls for careful management of its associated health risks. Such risks depend on the type of water to be recycled, the type and concentration of pathogens, and in particular, the ability of such pathogens to survive treatment, as well as the type of exposure of susceptible community members to such waters. The required level of pathogen reduction in reclaimed water depends on the nature of reuse application and potential for human exposure to water
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