Application of UV LEDs to inactivate antibiotic resistant bacteria: Kinetics, efficiencies, and reactivations.

Unregulated antibiotic use has led to the proliferation of antibiotic-resistant bacteria (ARB) in aquatic environments. Ultraviolet light-emitting diodes (UV LEDs) have evolved as an innovative technology for inactivating microorganisms offering several advantages over traditional mercury lamps. This research concentrated on utilizing UV LEDs with three distinct wavelengths (265 nm, 275 nm, and 285 nm) to inactivate E. coli DH10ß encoding the ampicillin-resistant blaTEM-1 gene in its plasmid. Non-linear models, such as Geeraerd's and Weibull, provided more accurate characterization of the inactivation profiles than the traditional log-linear model due to the incorporation of both biological mechanisms and a deterministic approach within non-linear models. The inactivation rates of ARB were higher than antibiotic-sensitive bacteria (ASB) when subjected to UV LEDs. The highest inactivation rates were observed when all microorganisms were exposed to 265 nm. Photoreactivation emerged as the primary mechanism responsible for repairing DNA damage induced by UV LEDs. 285 nm showed the highest reactivation efficiencies for ARB under different fluences. At higher fluences, both 265 and 275 nm displayed similar effectiveness in suppressing reactivation, while at lower fluences, 275 nm exhibited better efficacies in controlling the reactivation. Therefore, the inhibition of reactivation was influenced by the extent of damage incurred to both DNA and enzymes. In nutrient-poor media (0.9 % NaCl), ASB did not exhibit any reactivation potential. However, the addition of Luria-Bertani (LB) broth promoted the reactivation of ASB. Lower fluence rate was more beneficial at 265 nm whereas higher fluence rates were more effective for longer wavelengths. The inactivation of ARB was enhanced by dissolved organic carbon (DOC) at low fluences. However, the removal of ARB was reduced due to the presence of DOC at higher fluences. The highest energy demand for ARB inactivation was reported at 285 nm. ENVIRONMENTAL IMPLICATION: The excessive and unregulated utilization of antibiotics has emerged as a significant issue for public health. This paper presents a comprehensive analysis of the effectiveness of UV LEDs, an emerging technology, in the inactivation of antibiotic-resistant bacteria (ARB). This research paper explores the kinetics of UV LEDs with different wavelengths to inactivate ARB along with the reactivation efficiencies. This research work also explores the impact and relevant mechanisms of the impact of dissolved organic carbon (DOC) on the inactivation of ARB by UV LEDs.

An overview of technologies to recover phosphorus as struvite from wastewater: advantages and shortcomings.

Phosphorus (P) is a significant limiting nutrient which is essential for all forms of lives. However, phosphate rock reserves are depleting rapidly due to population growth. At the same time, several countries have imposed legislative regulations on P-release into surface waters due to eutrophication. Nutrient recovery from wastewater can facilitate a sustainable, cost-effective and environment-friendly source of phosphorus. Although P-recovery as struvite from wastewater has been widely studied for a long time, there still exists a lot of challenges for widespread full-scale implementation. This paper presents a comprehensive analysis of the current state of the technologies for phosphorus recovery in the form of struvite. Fluidized bed reactors (FBRs) are widely used compared to continuously stirred reactors for P-recovery as struvite because of different solid and liquid retention time. Commercially available technologies were reported to accomplish about 80% P-removal efficiencies with a reasonable P-recovery for the most of the cases. The struvite production rate of various technologies varies from 0.89 to 13.7 kg/kg influent P. Nevertheless, these technologies are associated with several shortcomings such as high operational costs, high energy consumption, and large footprint. Increasing efforts focusing on the development of sustainable and commercially feasible technologies are expected in this sector as P-recovery is considered to be the future of wastewater engineering.

Impact of supersaturation ratio on phosphorus recovery from synthetic anaerobic digester supernatant through a struvite crystallization fluidized bed reactor.

Over the past few decades, several technologies have been developed to recover phosphorus (P) as struvite from wastewater. Although these technologies have achieved reasonable P-removal efficiencies, these technologies are associated with several shortcomings such as high capital and operating costs, longer crystallization time and production of low-quality product. This study focussed on the development of an efficient technology by designing a new fluidized bed reactor (FBR) and determining its optimum operating conditions. The supersaturation ratio is the most important process parameter for struvite recovery. This study exerted effort to establish a range of supersaturation ratios in order to achieve optimum P-removal and recovery with a lesser amount of fine crystals produced. Bench-scale FBR used in this study was able to accomplish 90% P-removal with 18% P-recovery. P-removal efficiency was observed to be increasing with an increase in the initial supersaturation ratio up to a value of 6.5. On the other hand, an increase in the supersaturation ratio resulted in a lower P-recovery efficiency with an increase in fines production. The supersaturation ratio from 5.5 to 6.0 was found to be optimum for efficient operation of the reactor.