This paper proposes the utilization of a nanosecond pulsed (NSP) power supply in the electrocoagulation (EC) system for textile wastewater treatment. Four aluminum plates arranged in a monopolar-parallel configuration are utilized as electrodes in a 200 ml EC reactor. Chemical oxygen demand (COD) and specific energy consumption (SEC) are utilized to characterize the performance of NSP-powered EC. A DC power supply is considered as a benchmark. Field-emission scanning electron microscopy, X-ray diffraction, and energy-dispersive spectroscopy are utilized to characterize flocs. The results reveal that a maximum COD removal efficiency of 77% can be achieved by utilizing NSP power, while a value of only 60% can be achieved by utilizing DC power. Additionally, NSP power consumes at least 24% less energy than DC power at a similar COD removal efficiency. The utilization of NSP power for textile wastewater treatment allows for high COD removal efficiency with a significantly lower SEC compared to traditional DC-powered EC. It is believed that the low SEC exhibited by NSP power could be useful for promoting the utilization of EC for wastewater treatment and could contribute to the reduction of the carbon footprint of this process.
Veterinary antibiotic residues in wastewater discharged from livestock facilities have become an environmental issue. In this study, the removal of veterinary antibiotics by electrocoagulation was investigated for dairy farm wastewater treatment. Three tetracycline antibiotics (TCs) and cefazolin (CEZ), a cephalosporin antibiotic, in synthetic wastewater were electrochemically coagulated using iron electrodes under a constant current. The removal rates of the TCs were higher than 80% after electrocoagulation and gravity settlement. The specific properties of TCs enable them to coordinate to metal ions. In contrast, the electrocoagulation showed a lower removal rate of 2.5% for CEZ which lacks of interaction with metal ions. The results indicated that higher removal of TCs was achieved by this iron–tetracycline interaction. The removal rates of oxytetracycline (OTC) in dairy farm wastewater were increased with increasing electric charge and reached more than 88% at different temperatures. The isothermal data obtained from OTC in the synthetic wastewater showed that the Langmuir model was a better fitting model than the Freundlich model, thus, indicating the applicability of monolayer coverage. The results showed that electrocoagulation is an effective method for the removal of antibiotics that are able to coordinate with the metal ion.
The effect of contact time on the removal of soluble organic matter by the intermittent contact oxidation process was studied. The process describes enhanced in-sewer purification through use of porous media with attached microorganisms which are exposed to sewage and sewer headspace-gas intermittently. Two lab-scale model channels, each installed with a plastic sponge sheet, were fed with a small volume of synthetic sewage for a short period. After feeding, the sponge sheet within each channel was exposed to headspace-gas for various durations ranging between 5–120 min. After exposure, tap water was introduced to wash away the remaining soluble organic matter. The oxygen consumption in the channel was monitored during and after sewage contact to evaluate the oxidation of the organic matter. Results showed that even with a short synthetic sewage contact time of 5–10 min, approximately 150 mgC L-sponge−1 was removed per contact cycle. Soluble organic matter removal was positively influenced by non-flow condition extending up to 24 hrs. Microbial storage was suggested to play the key role in the removal of soluble organic matter. These findings support the effectiveness of the intermittent contact oxidation process for the removal of soluble organic pollutants when applied for in-sewer purification.
Marine microplastics pollution has been an emerging global threat. This study investigated microplastics pollution in the ‘Seto Inland Sea (SIS)’ and ‘Sea of Japan (SJ)’ surrounded Yamaguchi prefecture areas in Japan. The density separation method was applied to extract microplastics from sea surface sediment and water samples. Polymeric compounds were identified through ATR-FTIR analysis. The average microplastic abundances were 112.57 ± 121.30 items/kg in sediment and 57.46 ± 20.82 items/L in water. Abundance comparisons revealed similar level of pollution in both sea areas and medium to high-level pollution than others around the world. Characterization revealed that fragments and small microplastics (< 1,000 µm) predominated sediments. Fragments and films were major shapes in the SIS sediments while only fragments predominated the SJ sediments. Large microplastics (1,000–5,000 µm) fibers predominated water in all the areas. Transparent microplastics predominated both the sediments and water. Polyethylene, polyvinyl alcohol, and polypropylene were major polymers in sediments while polyethylene terephthalate and polyethylene predominated water. No significant correlations of microplastics abundances and characteristics were observed between sediment and water. Anthropogenic activities and environmental factors were speculated to be the main sources of microplastics in these areas. Overall, this study indicated that microplastics pollution in these marine areas could be an alarming environmental problem.