Electrocoagulation as a tertiary treatment of municipal wastewater: Removal of enteric pathogen indicators and antibiotic-resistant bacteria

Abstract

With the growing population and economic development, there is more stress on natural water resources. Additionally, current and future water shortages, increasing environmental concerns and stringent discharge standards demand high-quality treated water. In this scenario, it is crucial to recover water and wastewater resources for reuse, reducing the dependency on new resources. While aiming for water reclamation, the influence of wastewater quality parameters on human health is given foremost attention in recent times. Enteric pathogens are a major concern when reclaiming municipal wastewater. Electrocoagulation (EC) process that introduces coagulants by electrochemical means has been successfully employed for the treatment of groundwater, industrial and municipal wastewater. EC has been widely accepted over other physicochemical processes due to its process design and lowcost material. In this research, EC has been thoroughly investigated as a tertiary treatment technology for water reclamation from municipal wastewater.
This research is focused on determining the efficiency of low voltage iron EC for the removal of enteric pathogen indicators and antibiotic-resistant bacteria from secondary wastewater effluent. The effect of operational parameters: charge dosage (C/L) and charge dosage rate (C/L/min) on pollutant reduction was evaluated in different water matrices: demineralized water, synthetic wastewater effluent and real wastewater effluent. EC operated at 400 C/L, 7.2 C/L/min and natural pH allowed > 3.5 log units removal for E. coli and Enterococci, > 2.5 log units for ESBL E. coli and VRE and > 2 and 2.7 log units for Somatic coliphages and Clostridium perfringens spores respectively in real wastewater effluent. Furthermore, a significant reduction of phosphorous, COD and the true color was observed at 400 C/L and 36 C/L/min. Pollutant reduction was influenced by sedimentation and floatation mechanisms observed at varying charge dosage rates.
A marginally higher removal rate constant of pathogen indicators as a function of charge dosage at low charge dosage rate showed slow iron dosing to improve microbial adsorption and increase contact time with iron precipitates. The reduction of pathogen indicators was associated with physical removal mechanisms like adsorption, sweep coagulation and entrapment within the flocs, charge neutralization and aggregation based on literature. The effective removal of physical, chemical and microbiological parameters in real wastewater effluent was achieved at 400 C/L and 7.2 C/L/min at an operating cost of 0.17 €/m3 indicating EC to be a cost-effective treatment in comparison to alternative technologies like ozone, UV, activated carbon and reverse osmosis.