Efficiency and toxicity: comparison between the Fenton and electrochemical processes

Assessment of phytotoxic potential and pathogenic bacteria removal from secondary effluents during ozonation and UV/H2O2

Wastewater reuse is an important strategy for water resource management. For this reason, the disinfection process must be appropriated, eliminating pathogenic microorganisms. Ozonation (O₃) and UV/H₂O₂ treatments can be used for effluent disinfection, but few studies just address the Escherichia coli quantification. In this study, secondary effluents from two wastewater treatment plants with different characteristics were exposed to O₃ (5 and 10 mg L^-1) or UV/H₂O₂ (H₂O₂: 90 mg L^-1) treatments and evaluated by BD Phoenix ™ 100 (Becton Dickinson, USA) and MALDI-TOF for the characterization of the indigenous microorganisms in the effluents, before and after treatments. Additionally, all the samples were tested for phytotoxicity by Lactuca sativa bioassay. The results showed that the highest ozone dose and the UV/H₂O₂ treatment were effective in removing E. coli. UV/H₂O₂ was more efficient as it eliminated most of the microorganisms. Acinetobacter sp., Aeromonas and Pseudomonas were still found after O₃ treatment. Bacillus sp. was found after O₃ and UV/H₂O₂ treatments. The results with L. sativa showed inhibition of root growth for all dry period (low rainfall) samples of one of the WWTP, due to the high concentration of the phytotoxicity compounds. For environmental and human health safety, treated effluents should be evaluated for their toxic and pathogenic potential before being released into the environment. Pathogens evaluation on treated effluents should cover a wider range of pathogenic microorganisms than those routinely required by legislation.

Combination of electroflotation process and down-flow granular filtration to treat wastewater contaminated with oil

One of the main problems faced by the oil industry is related to the amount of produced water generated during the oil extraction process. For proper disposal of this effluent, treatment processes should be applied to meet the requirements established by environmental agencies. Thus, the present study aimed to evaluate the efficiency of the combination of electroflotation process and down-flow granular filtration in the treatment of wastewater contaminated with oil. To this end, they were studied in a pilot system, to optimize the electroflotation process and combination of processes. The performance of the pilot system was determined by removal of oil and grease content (OG) in the treated effluent. According to the results, the electroflotation process had the best performance with an effluent input rate of 62 m³ m^-2 d^-1, current density of 80 A m^-2 and NaCl concentration of 7900 mg L^-1. Under these conditions, the mean removal of OG from synthesized solution after 720 minutes of treatment was 86.64% (59.51 mg L^-1) for the electroflotation process and 61.52% (12.91 mg L^-1) after down-flow granular filtration. By combining the processes studied, we obtained an initial OG removal (470.55 mg L^-1) of over 98% (6.42 mg L^-1) in 720 minutes of treatment, with an energy consumption of the electrochemical reactor of 1.47 kWh m^-3.

ABBREVIATIONS

ANOVA: analysis of variance; CCRD: Central Composite Rotational Delineation; DOC: dissolved organic carbon; DSA: dimensionally stable anodes; LAPOA: Laboratory of Water Potabilization; OG: oil and grease; OPER: operating parameters of the electrochemical reactor; TDS: total dissolved solids; UFSC: Federal University of Santa Catarina.