UV Disinfection of Wastewater and Combined Sewer Overflows

Abstract

Municipal wastewater contains bacteria, viruses, and other pathogens that adversely affect the environment, human health, and economic activity. One way to mitigate these effects is a final disinfection step using ultraviolet light (UVL). The advantages of UVL disinfection, when compared to the more traditional chlorine, include no chlorinated by-products, no chemical residual, and relatively compact size. The design of most UV reactors is complex. It involves lamp selection, power supply design, optics, and hydraulics. In general, medium pressure lamps are more compact, powerful, and emit over a wider range of light than the more traditional low pressure lamps. Low pressure lamps, however, may be electrically more efficient. In UV disinfection, the fraction of surviving organisms (e.g. E. coli) will decrease exponentially with increasing UV dose. However, the level of disinfection that can be achieved is often limited by particle-associated organisms. Efforts to remove or reduce the effects of wastewater particles will often improve UV disinfection effectiveness. Regrowth, photoreactivation, or dark repair after UV exposure are sometimes cited as disadvantages of UV disinfection. Research is continuing in this area, however there is little evidence that human pathogens can photoreactivate in environmental conditions, at doses used in wastewater treatment. The UV disinfection of combined sewer overflows, a form of wet weather pollution, is challenging and remains largely at the research phase. Pre-treatment of combined sewer overflows (CSOs) with a cationic polymer to induce fast settling, and a low dose of alum to increase UV transmittance, has shown promise at the bench scale.

Catchment-wide validated assessment of combined sewer overflows (CSOs) in a mediterranean coastal area and possible disinfection methods to mitigate microbial contamination

“…The advantages of UV disinfection compared to the chemical agents, include no by-products, no chemical residual, and relatively compact size. However, the level of disinfection that can be achieved is often limited by particle-associated organisms in CSO water and the UV transmittance of CSOs can be as low as 30% and the TSS can reach 200 mg/l (Gibson et al, 2017); hence, the use of a pretreatment unit is utmost important to increase disinfection efficiency. Two pilot-scale disinfection units comprised of ozone and UV were tested by (Tondera et al, 2015) on CSOs; where the ozone was found to be more effective than UV (ozone: 3.1-3.4 log, UV: 1.7-2.2 log) on the reduction of E. coli, coliform bacteria and intestinal enterococci.…”

“…In fact, the bathing water quality can be maintained by instant disinfection of inflowing CSO water (Chhetri et al, 2016). To date, various disinfection methods at lab-and/or pilot-scale were proposed for the removal of pathogens from CSOs, such as peracetic acid (Chhetri et al, 2016), performic acid (Chhetri et al, 2014;Tondera et al, 2016), hypochlorite (McFadden et al, 2017), ozone (Tondera et al, 2015) and UV (Gibson et al, 2017(Gibson et al, , 2016. However, the applicability and frequency of a disinfection method applied for CSOs are often site-specific due to high variability of the pollution load in CSOs and therefore need optimization to assess the effectiveness of the chosen disinfectant agent.…”

Uso de aguas residuales de porcicultura y faenamiento para el crecimiento y obtención de biomasa algal de Chlorella vulgaris

“…Sin embargo, para que la luz UV pueda ejercer efectos desinfectantes es necesario que la longitud de onda sea absorbida con la finalidad de generar alteraciones en los ácidos nucleicos, como la formación de dímeros de pirimidina, para la interrupción de procesos como la replicación celular en los microorganismos contaminantes. Con base en lo anterior, es necesaria la implementación de reactores de pre tratamiento de luz UV que permitan maximizar la exposición del agua a la radiación y evitar problemas asociados con compuestos que absorban la luz y disminuyan su capacidad de desinfección 23 . Con respecto a los tratamientos químicos, las máximas concentraciones empleadas en este estudio no lograron eliminar por completo la carga bacteriana, a pesar de presentar disminuciones de UFC significativas, en comparación con el agua sin pre tratar.…”

“…Otro tipo de tratamientos químicos, como el uso de 5 M NaOH junto con 5 M HCl son capaces de disminuir una elevada carga bacteriana hasta valores de 100 UFC/mL 27 . A pesar de esto, en general, los métodos de desinfección químicos suelen tener como una mayor desventaja frente a la luz UV la presencia de cloro o sustancias químicas residuales o la necesidad de aplicar tratamientos posteriores a la desinfección del agua empleada 23,28 . En el caso del CH₃CO₃H, no se presentan compuestos tóxicos o mutagénicos residuales en el agua pretratada, lo cual constituye una ventaja sobre los procesos de cloración.…”

Challenges to detect SARS-CoV-2 on environmental media, the need and strategies to implement the detection methodologies in wastewaters

“…Aerosol containing HCoV under different UV wavelengths showed that doses required to inactivate the virus ranged between 1.2 - 1.7 J/m 2 [18] . Even though particular studies have not been done directly with wastewater, known technologies can generate dosages between 1-200 J/m 2 and could be easily modified to dose sufficient UV especially at 254 nm as long as the transmission of UV to the wastewater considered the turbidity and UV transmittance for succesfull virus elimination [45] . The advantage of employing UV for wastewater treatment for SARS-CoV-2 is the absence of residues resulting in toxic byproducts.…”