Influence of industrial contamination in municipal secondary effluent disinfection by UV/H2O2

Techno-economic evaluation of UV light technologies in water remediation

Disinfection commonly follows conventional treatments in wastewater treatment and remediation plants aiming at reducing the presence of pathogens. However, the presence of the so called "micropollutants" has emerged as a serious concern, therefore developing tertiary treatments that are not only able to remove pathogens but also to degrade micropollutants is worth investigating. Nowadays, UV-C photo-degradation processes are widely used for disinfection due to their simplicity and easy operation; additionally, they have shown potential for the removal of contaminants of emerging concern. Conventional mercury lamps are being replaced by light-emitting diodes (LEDs) that avoid the use of toxic mercury and can be switched on and off with no effect on the lamp lifetime. This work aims to comparatively evaluate the performance of several photo-degradation technologies for the removal of two targeted micropollutants, the pharmaceutical dexamethasone (DXMT) and the herbicide S-metolachlor (MTLC), using UV irradiation doses typical of disinfection processes. To this end, the technical performance of UV-A/UV-C photolysis, UV-A/UV-C photocatalysis, UV-C/H₂O₂ and UV-C/NaOCl has been compared. The influence of operating conditions such as the initial concentration of the pollutants (3 mg L^-1 - 30 mg L^-1, concentrations found in membrane or adsorption remediation steps), pH (3-10), and water matrix (WWTP secondary effluent, and ultrapure water) on the degradation efficiency has been studied. The economic evaluation in terms of electricity and chemicals consumption and the carbon footprint has been evaluated. UV-C photolysis and UV-C photocatalysis appear as the most suitable technologies for the degradation of DXMT and MTLC, respectively, in terms of kinetics (1.53·10^-1 min^-1 for DXMT and 1.96·10^-2 min^-1 for MTLC), economic evaluation (1 € m^-3 for DXMT and 32 € m^-3 for MTLC) and environmental indicators (0.5 g-CO₂ for DXMT and 223.1 g-CO₂ for MTLC).

Rationale for the Combined Use of Biological Processes and AOPs in Wastewater Treatment Tasks

This paper aims to form a unified concept of the integrated use of different wastewater treatment methods to form a resistant biological treatment stage of technological systems under the influence of such toxic factors as antibiotics and surfactants. The processes of mechanical treatment, ozonation, UV irradiation, and electrolytic anodic oxidation were implemented in an electrotechnological wastewater treatment facility. Wastewater treatment quality was determined by the concentration of nitrogen compounds in aqueous solutions according to the method of Lurie. Biodiagnostics of the investigated activated sludge via surfactant action was carried out at polyethylene oxide concentrations of 10, 30, and 50 mg/dm3. As a result of experiments on wastewater treatment after aquaculture, an improvement in the reduction of pollutants only by the indicator “nitrate concentration” was determined: by 20% after anodic oxidation, and by 15% after photolysis. At almost all surfactant concentrations studied, the activated sludge was not completely recovered, which was expressed in a decrease in its quantity and in the inability to aggregate flakes of activated sludge. The diameter of the growth retardation of the standard disk with antibiotic (amoxiclav) by the accumulative culture of activated sludge was 17.3 ± 2 mm at a concentration of 4 mg/dm3 and 31.3 ± 3 mm at a concentration of 6 mg/dm3. In the process of studying the state of the activated sludge’s biocenosis under the influence of such toxicants, several regularities were revealed. The directions of using combined approaches of water treatment and wastewater treatment were defined. The structural model of treatment facilities using aerobic and anaerobic bioprocesses together with advanced oxidative technologies was substantiated.

Regrowth of bacteria after light-based disinfection - What we know and where we go from here

Regrowth of bacteria after water/wastewater disinfection is a serious risk to public health, particularly when such pathogens carry antibiotic resistance genes. Despite increasing interest in light-based disinfection using ultraviolet or solar radiation, the mechanism of bacterial regrowth and their concentration upon light exposure (i.e., during storage, or after discharge into rivers or lakes) remain poorly understood. Therefore, we present a focused critical review to 1) elucidate regrowth mechanisms, 2) summarize the pros and cons of available experimental designs and detection techniques for regrowth evaluation, and 3) provide an outlook of key research directions for further investigations of post-disinfection bacterial regrowth. Bacterial regrowth can occur through reactivation from a viable but non-culturable state, repair of photo-induced DNA damage, and reproduction of bacteria surviving disinfection. Many studies have underestimated the degree of actual regrowth because of the use of simple experimental designs and plate count methods, which cannot quantify actual abundance of viable bacteria. Further research should investigate the effects of various factors on bacterial regrowth in realistic conditions in regrowth tests and adopt multiplex detection methods that combine culture-based and culture-independent approaches. An accurate understanding of the mechanisms involved in bacterial regrowth following disinfection is critical for safeguarding public health and aquatic environments.