UV LED wastewater disinfection: The future is upon us

Advanced oxidation processes for the degradation of tralomethrin: Impacts on zebrafish embryonic development

Tralomethrin (TRA), a synthetic pyrethroid insecticide, has long-term adverse effects on aquatic organisms, highlighting the necessity for effective methods to mitigate its toxicity. This study investigated the degradation efficiency of TRA using ultraviolet (UV) irradiation, ozone (O3) oxidation, and a combined O3/UV process. Unlike previous studies that primarily focused on degradation efficiency, this research not only compares the performance of UV, O3, and O3/UV processes but also evaluates the detoxification effects of their degradation products using zebrafish embryos. The results showed that the UV irradiation alone exhibited a low UV254 removal rate (20.69 %) but achieved the highest debromination efficiency (40.51 %), leading to the formation of less toxic degradation products. In contrast, both O3 and the combined O3/UV processes attained higher removal rates but exhibited lower debromination efficiencies compared to UV irradiation alone. Acute toxicity assessment demonstrated a significant decrease in the toxicity of TRA to zebrafish post-treatment. Specifically, the UV irradiation and O3/UV treatments resulted in enhanced detoxification compared to the parent compound TRA, as evidenced by normal hatching rates and lower rates of malformation, as well as improved gene expression profiles and normal movement patterns in zebrafish embryos. The zebrafish toxicity assay further revealed that UV irradiation and the combined O3/UV process fully restored the normal expression of neural markers (slc6a3 and th), suggesting its superior safety as a detoxification strategy. The optimal processing time for UV irradiation to achieve efficient TRA degradation was identified as 10 min, and the photodegradation pathways were identified. These findings underscore the practical applicability of UV-based processes in wastewater treatment, providing a promising strategy for reducing TRA contamination risks to aquatic ecosystems.

Inactivating facultative pathogen bacteria and antibiotic resistance genes in wastewater using blue light irradiation combined with a photosensitizer and hydrogen peroxide

The effectiveness of antimicrobial blue light (aBL) irradiation in eliminating ten clinically significant antibiotic resistance genes (ARGs) and four taxonomic marker genes of the WHO-priority ESKAPE bacteria group from wastewater treatment plant (WWTP) effluent was examined. Experiments were conducted using an LED-driven continuous-flow photoreactor operating at wavelengths of 405 nm, 420 nm, and 460 nm. Irradiation with aBL alone was insufficient for effectively inactivating or eliminating ESKAPE bacteria and clinically relevant ARGs. The addition of the porphyrin-based photosensitizer TMPyP (10-6 M) or the oxidative agent H₂O₂ (1 mM) resulted in several log10 unit reductions of facultative pathogenic bacteria (FPB), their taxonomic gene markers, and target ARGs. However, the additional effects of TMPyP and H2O2 were only noticeable in conjunction with aBL irradiation, as they were ineffective without it. The reduction of the different FPB and ARGs in WWTP effluents was analyzed using culturing and qPCR together with living/dead discrimination. Different FPB and ARGs showed varying susceptibility to aBL-mediated irradiation. Among the FPB, enterococci were the most sensitive, while among the ARGs bacteria carrying ermB, tetM, sul1, and blaVIM genes exhibited the strongest removal. This sensitivity may be due to the gene-carrying microorganism's response to aBL irradiation combined with TMPyP or H2O2. Additionally, molecular biology results revealed that aBL irradiation induced up to 13 lesions per 10 kb DNA, which is hypothesized to contribute to the acute inactivation effect and prevent regrowth by inhibiting DNA repair activities.

A critical review of ultra-violet light emitting diodes as a one water disinfection technology

UV light emitting diode (LED) disinfection technologies have advanced over the last decade and expanded the design space for applications in point of use, industrial, and now full-scale water treatment. This literature review examines the progression of UV LED technologies from 2007 to 2023 using key features such as total optical power, price, and wall-plug efficiency. The review found that optical power is increasing while the price per Watt is decreasing; however, the wall plug energy (WPE) is slowly improving over the last decade. These factors govern the feasibility of many UV LEDs applications and establish the current state of the art for these technologies. An analysis of inactivation rate constants for low-pressure, medium-pressure, and UV LED sources was undertaken and provides a comprehensive view of how current UV LED technologies compare to traditional technologies. This comparison found that UV LEDs perform comparably vs conventional UV technologies when disinfecting bacteria and viruses. Furthermore, comparison of reported reduction equivalent fluences for UV LED flow-through reactors at the bench-, pilot-, and full-scale were explored in this review, and it was found that LED treatment is becoming more effective at handling increased flowrates and has been proven to work at full-scale. UV LEDs do however require additional research into the impacts of water matrices at different wavelengths and the impact that each available LED wavelength has on disinfection. Overall, this work provides a broad assessment of UV disinfection technologies and serves as a state-of-the-art reference document for those who are interested in understanding this rapidly developing technology.

UV LED disinfection as a novel treatment for common salmonid pathogens

Aeromonas salmonicida and Yersinia ruckeri are common pathogenic bacteria that impact salmonid aquaculture. Although vaccinations are available against both organisms, large-scale vaccination efforts can be expensive, cumbersome, and are not always reliable. Alternatively, these pathogens have been effectively inactivated using UV radiation from mercury-based systems. These systems are energy intensive and fragile which currently limits their use to closed and semi-closed production systems. UV light emitting diodes (UV LEDs) have recently emerged as a novel alternative to traditional mercury-based treatment. UV LEDs have durable housing, a relatively low energy draw, can be powered by a battery source and are adaptable to challenging environments. This study examined the effectiveness of three UV LED wavelengths for disinfection of A. salmonicida and Y. ruckeri in pure culture and resuspended in a wastewater matrix. All tested UV LEDs were effective in disinfecting both organisms. 267 and 279 nm wavelengths outperformed 255 nm disinfection in both test matrices. Particulate matter from wastewater reduced the upper limit of treatment for A. salmonicida but results still indicated that all wavelengths were effective for disinfection in a challenging matrix. This study represents the first use of UV LEDs for disinfection of A. salmonicida and Y. ruckeri and provides impact to aquaculture producers looking to implement novel technologies for disease control.