Due to increasing water consumption and stress on natural water resources, enhanced treatment of wastewater and reuse of water are becoming more important. Treated municipal wastewater has potential to be used for irrigation purposes, but pathogens are a major concern to protect environmental and human health. Therefore, an advanced treatment step is required to reduce the levels of microorganisms, nutrients and suspended solids. This literature review focusses on electroflotation (EF) as disinfection method of secondary municipal wastewater treatment. EF is a combination of electrocoagulation (EC) and dissolved air flotation (DAF). In EC treatment, a sacrificial metallic anode releases metal ions (usually iron or aluminium) into the solution while hydroxyl ions and hydrogen gas are produced at the cathode. Coagulants are created in situ by the hydrolysis of these metal ions to hydroxides that can destabilize pollutants. DAF is an adsorptive bubble separation process where generated gas bubbles (of 10-100 µm) separate the impurities by flotation. This paper outlines the processes involved in EF technology and its applications in (waste)water treatment. Therefore, the processes of EC and DAF are discussed first. Influencing parameters such as electrode material, pH, retention time, charge dosage, charge dosage rate, bubble formation and size are discussed, as well as pollutant removal mechanisms. The main mechanisms responsible are charge neutralization, adsorption, sweep coagulation, microbial destruction by the electric field and deactivation by free radicals. The conclusion is drawn that the hybrid EF technique, which has been implemented in different water treatment processes, promises to increase removal efficiencies compared to single EC and DAF treatment, but the full potential of EF as a tertiary treatment step for secondary municipal wastewater effluent is yet to be fully realized. The process needs to be empirically optimized, a challenging task due to the involvement of complex chemical and physical processes.

With the rapid population growth and industrialization, water bodies are being infiltrated by a rising number of contaminants like metals, pharmaceuticals, pesticides and detergents, which requires the need for novel treatment technologies. Electrocoagulation (EC) is a water treatment technology where the coagulant is dosed electrochemically from a pure metal electrode. The performance of Fe-EC in a full water column using a continuous flow setup has had little to no attention yet. The aim of this proof of principle study is to determine the feasibility and the practical potential of Fe-EC during a continuous flow implementation, and to give insight to the general performance of the system in terms of water quality improvement. Experiments were conducted in a continuous flow Fe-EC unit with descending flow. Two pairs of electrodes were used, evenly distributed along the length of the unit, and at the bottom an air diffuser was used to provide aeration. Operational configuration of the unit was needed as no prior experiments had been performed with this unit and the exact behavior of the electrodes, flow and aeration within the continuous flow system were unknown. Furthermore, experiments were conducted to evaluate the removal efficiency of Fe-EC on nutrients, organic micropollutants (OMPs), microbes and (heavy) metals, operating at a pH of 8 and 7. The operational parameters were set to deliver an Fe dosage of 50 mg/L, flow rate of 7.5 L/h, and a current density of 15 mA/cm2. It was found that the system was able to achieve high removal of phosphorus up to 99% during all experiment sets. Highest removal of E. coli and coliphages was found when operating at a pH of 7, reaching 1.56 and 0.65 log removal respectively. Removal of OMPs was found to vary greatly among the compounds and measurements. More stable results were found when using increased OMP concentrations (around 50 µg/L), reaching removals varying from 7% to 25% at a pH of 8, and slightly lower removals from 1% to 15% at a pH of 7. No correlation was found between the observed removal and the acid dissociation constant (pKa) or the η–octanol–water partition ratio (Kow) of measured OMPs. Lastly, various heavy metals show affinity for removal during Fe-EC, such as arsenic, copper, zinc, manganese, chromium and vanadium. Using increased influent concentrations of the heavy metals (around 80 µg/L) resulted in removals above 85% for arsenic, zinc, chromium and vanadium. The system has shown to have high removal potential on secondary effluent, even when contaminant concentrations reach high levels. Nevertheless, uncertainties and were found for the practical implementation of Fe-EC, and design and operational parameters first have to be optimized in order to fully utilize the potential that Fe-EC has.

Due to the quick growth in human population and subsequently a high rate of urbanization, fresh water sources are under pressure. Estimated 1.8 billion people drink water from potentially sewage-contaminated sources and also the presence of antibiotic resistant bacteria in sewage has made the improper treatment of wastewater effluent an emerging problem. Iron electrocoagulation (Fe-EC) has shown to be successful in reducing pathogen concentration, although to different extent for types of pathogens. Besides, the water quality was found to be of influence on the effectiveness. This study therefore aimed to determine the removal mechanism for both bacteria and virus as well as assess the effect of wastewater components on the Fe-EC treatment process. EC experiments were conducted in an aerated beaker with a volume of 1L, continuously stirred. pH and current were kept stable at 7.5 and 200mA, respectively. The total charge dosage was 180 C/L. After electrolysis the samples were left to settle. Blank measurements were conducted in a 230 mg/L NaCl solution. Wastewater components were added in concentration of 4.0 mg/L for phosphate, 60 mg/L calcium, and 10 mg/L humic acids. E. coli WR1 and 휙X174 were used as indicator organisms. Contributing disinfection mechanisms for E. coli were inactivation and physical removal. During electrolysis a log removal of 3.8 log units was found, ascribed to inactivation. Further increase in removal to 6.0 log units was observed after settling. In the presence of TEMPOL only 0.3 log units removal were observed during electrolysis, but removal after settling still amounted 5.5 log units. For 휙X174 removal reactive species were not effective. Disinfection after settling equaled 4 log units, when settling was complete. Settling was found to be dependent on mixing conditions, and removal was correlated as well. Extended mixing promoted the formation of larger flocs and thereby enabled sweep flocculation for phage removal. Phosphate decreased attenuation of E. coli either for inactivation, 2.0 log units as for physical removal, 4.7 log units. Phosphate has high affinity for iron and competes with bacteria for iron surface. Calcium as well inhibited abatement of E. coli. Inactivation only amounted for 1.4 log units and removal after settling equaled 2.1 log units. Calcium is expected to complex bacteria surface, increasing repulsive forces between E. coli and iron. The effect of carbonate was only seen during electrolysis, 1.3 log units. The formation of the carbonate radical is suggested as explanation for the decrease in effectiveness. The effect of NOM on E. coli attenuation was unclear. Inactivation was inhibited to only 1.4 log units, but no effect was found on the total removal. Therefore, it can be concluded that NOM does not successfully compete with bacteria for iron surface. 휙X174 attenuation was not effected by addition of phosphate, calcium, or carbonate. On the other hand, the addition of NOM inhibited phage removal, only 0.6 log units in comparison to 4.0 log units for the blank. Adsorption of NOM onto iron surface is expected to negatively change the surface charge, inhibiting association between iron and virus.

As antibiotics now save millions of human and animal lives annually, the World Health Organisation (WHO, 2019) declared Antibiotic Resistance (AR) as the number five most dangerous risk to global health. Several researchers mention WWTPs to be an important source for AR as the growth of bacteria is stimulated in an environment with a selective pressure facilitated by a relatively high concentration of antibiotics. Tertiary treatment steps are implemented primary to polish the effluent and reduce the OMP load of the effluent. The O3-STEP filter is an innovative example of such a tertiary treatment combining the oxidative effects of ozone with the adsorption effects of a Granular Activated Carbon (GAC) filter. In addition to these effects, a coagulant is dosed for the removal of Phosphorus (P). The implications for AR are still unknown. In literature varying results are found on the disinfecting effects of ozone, GAC and coagulation and nothing is found on the combination of these treatment steps yet. The purpose of this document is to present how effective the treatment with ozone and coagulation is in the removal of antibiotic resistant bacteria (ARB) in comparison with antibiotic sensitive bacteria (ASB). Agar growth media are used to test four different microorganisms: two faecal indicators (E. coli and Enterococci) and a resistant strain of each of these bacteria (ESBL E. coli and Vancomycin Resistant Enterococci (VRE)). Several experiments are conducted in the laboratory to test disinfection of ozone and coagulation on these microorganisms. In confirmation of the hypothesis, ozonation and coagulation disinfect ARB as well as ASB. However, as both treatment steps are not aiming at the removal of microorganisms but at the removal of OMPs and phosphorus respectively, the microorganism removal is limited (with 0.7 log on average). Increasing the coagulant and ozone dosage showed promising results in the laboratory. Dosing the coagulant above the optimum sweep coagulation dosage is not favourable because the increase in removal stagnated above this concentration whilst the residual coagulant concentration in the supernatant water increased. In the GAC of the O3-STEP filter and its backwash water, an increase of VRE is found relative to Enterococci in comparison with the ozonated water but not over the complete O3-STEP filter. This was different for the 1-STEP filter which showed the worrying result that VRE increased in the same amounts as Enterococci decreased. As the 1-STEP filter is a filter with a matured biology, where O3-STEP was recently started, the O3-STEP filter might increase the absolute and relative amount of ARB in long term as well. In case the aim for the O3-STEP filter is to remove AR as well, several suggestions are made. As ozone and coagulation both potentially remove ARB, an increase in these concentrations is a no-regret possibility. Furthermore, ultrafiltration (UF) and the combination of ultraviolet (UV) and O3 are proposed as possible alternatives. Using a multicriteria analysis (MCA), increasing the ozone dosage with the existing bypass is recommended.

Limitless usage of antibiotics has led antibiotic resistance to be one of the largest threats to world health and development. In this study, the concentrations of Extended spectrum betalactamase Escherichia coli and carbapenem resistant Escherichia Coli was assessed in a major drain in New Delhi, India. The performance of Anaerobic membrane bioreactor, photobioreactor and constructed wetlands in treating ESBL-E.coli and CRE-E.coli was evaluated. The results showed ESBL-E.coli and CRE-E.coli removal efficiencies of 99.82% and 99.69% for AnMBR, 99.62% and 99.86% for PBR and 98.1-99.3% for constructed wetlands respectively. Log10 reduction values of 2.7-3 for AnMBR, 2.8-3.2 for PBR and 1.82.3 for CWs was achieved in this study. Coupling micro-aeration with AnMBR improved the removal efficiency by 36-46%. A quantitative microbial risk assessment showed probability of infection by Enterotoxigenic E.coli (ETEC O55) post treatment to be reduced below 10-18% for AnMBR and PBR and below 20-35% for CWs. Treated effluents accounted for a high reduction in the total DALYs pppy by 63% for PBR, followed by 41.6% for AnMBR and 12.5% for CWS. ESBL-E. coli and CRE-E.coli counts decreased below the monitoring level of 103-105 for unrestricted irrigation and 104-105 for restricted irrigation as declared by WHO. Treated water was not recommended for direct consumption due to higher risk above 10%. This study exhibits the potential of these efficient and sustainable technologies in treating antibiotic resistant bacteria.