Abstract The objective of this study was to investigate the effects of combined low-pressure ultraviolet (UV)irradiation and chlorination on the formation of disinfection by-products (DBPs) from different dissolved organic matter (DOM) as DBP precursors. Commercially available humic acid (HA), extracellular organic matter (EOM) from green algae, cyanobacteria, and diatom, namely Scenedesmus quadricauda (SQ), Merismopedia sp. (Msp), and Phaedactylum tricornutum (PT), were used as the sources of DOM. The DBP formation increased with increasing total residual chlorine; EOM from PT presented the highest formation potential followed by HA, Msp, and SQ. The low dosage of 40 mJ/cm2 UV irradiation is insignificant to change the DBP formation from HA and SQ; however, it decreased the DBP formation from bromide-containing EOM of PT and promoted the DBP formation from EOM of Msp at various total residual chlorines. The DBP formation of each DOM correlated well with total residual chlorine. The maximum DBP formation potential (DBPFP) reduction of 42.25 and 13.75% for haloacetic acid formation potential (HAAFP) and trihalomethane formation potential (THMFP) was obtained at the UV irradiation dosage of 300 mJ/cm2 for EOM of PT. However, for the EOM derived from Msp, a maximum increase of 58.1 and 51.1% for HAAFP and THMFP was observed after UV-chlorination.
Proving UV reactor performance through validation is becoming a common requirement in wastewater, reuse water and drinking water disinfection applications. However, there is often confusion in understanding the objectives of validation and when choosing an appropriate protocol to follow. This paper will visit the fundamental rationale behind validation. The primary principle behind performance validation is to ensure that public and environmental health is being safeguarded. To do this, regulations must set risk-based disinfection targets, and reactors must be shown to have adequate performance in terms of those targets. Validation must be based on empirical results to eliminate assumptions that are unsafe. Validation must be universal for a given reactor, so that it can be applied to any site where the reactor may be installed. Protocols must not be prescriptive with consequential hindrance to innovation, and they must not be too complex so that they can be accepted and implemented by the industry. This paper will expand on these major points, showing examples of how validation protocols can violate these principles, and also showing alternatives that uphold the principles, ensuring that public and environmental health is safeguarded.
Using UV to Disinfect Low Quality WastwaterThis paper discusses the issues involved in sizing ultraviolet (UV) disinfection systems for low quality water, such as those found in poor quality wastewater (primary effluents) or wet weather flows (combined sewer overflows). Discussions of UV reactor dynamics and the merits of bioassay validation are provided.Author(s)Brian PetriTed MaoBill CairnsMike ShorttSaad AldinSourceProceedings of the Water Environment FederationSubjectSession 16: Disinfection: The Future of Disinfection Is NowDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2006ISSN1938-6478SICI1938-6478(20060101)2006:12L.1190;1-DOI10.2175/193864706783749800Volume / Issue2006 / 12Content sourceWEFTECFirst / last page(s)1190 - 1191Copyright2006Word count53
In this paper, the effect of sonication on the UV disinfection kinetics of primary effluents was investigated. Wastewater samples were collected from local municipal treatment plants and were sonicated with a 20‐kHz ultrasound reactor at constant power but varying sonication times. Sonicated samples were irradiated using low‐pressure UV light to obtain the UV dose‐response curves (DRC). Results showed that sonication improved the UV disinfection of primary effluents by (1) increasing the initial slope of DRC (i.e., k 1 ) and (2) decreasing the tailing level of the UV dose‐response curve (i.e., β). This improvement was confirmed to be caused by the breakage of large particles (>60 μm) that are known to protect coliforms from UV photons. It also was found that the log reduction of the tailing level of DRC was directly proportional to the log reduction of the number of large particles (>60 μm) present in the effluent sample. Although the number of large particles was proportional to the coliform count at high UV dosage, the proportionality constant varied from 0.05 to 0.25, depending on the sample.
Far UV-C, informally defined as electromagnetic radiation with wavelengths between 200 and 230 nm, has characteristics that are well-suited to control of airborne pathogens. Specifically, Far UV-C has been shown to be highly effective for inactivation of airborne pathogens; yet this same radiation has minimal potential to cause damage to human skin and eye tissues. Critically, unlike UV-B, Far UV-C radiation does not substantially penetrate the dead cell layer of skin (stratum corneum) and does not reach germinative cells in the basal layer. Similarly, Far UV-C radiation does not substantially penetrate through corneal epithelium of the eye, thereby preventing exposure of germinative cells within the eye. The most common source of Far UV-C radiation is the krypton chloride excimer (KrCl*) lamp, which has a primary emission centered at 222 nm. Ozone production from KrCl* lamps is modest, such that control of indoor ozone from these systems can be accomplished easily using conventional ventilation systems. This set of characteristics offers the potential for Far UV-C devices to be used in occupied spaces, thereby allowing for improved effectiveness for inactivation of airborne pathogens, including those that are responsible for COVID-19.
The dose–response behavior of pathogens and inactivation mechanisms by UV-LEDs and excimer lamps remains unclear. This study used low-pressure (LP) UV lamps, UV-LEDs with different peak wavelengths, and a 222 nm krypton chlorine (KrCl) excimer lamp to inactivate six microorganisms and to investigate their UV sensitivities and electrical energy efficiencies. The 265 nm UV-LED had the highest inactivation rates (0.47–0.61 cm2/mJ) for all tested bacteria. The bacterial sensitivity strongly fitted the absorption curve of nucleic acids at wavelengths of 200–300 nm; however, indirect damage induced by reactive oxygen species (ROS) was the leading cause of bacterial inactivation under 222 nm UV irradiation. In addition, the guanine and cytosine (GC) content and cell wall constituents of bacteria affect inactivation efficiency. The inactivation rate constant of Phi6 (0.13 ± 0.002 cm2/mJ) at 222 nm due to lipid envelope damage was significantly higher than other UVC (0.006–0.035 cm2/mJ). To achieve 2log reduction, the LP UV lamp had the best electrical energy efficiency (required less energy, average 0.02 kWh/m3) followed by 222 nm KrCl excimer lamp (0.14 kWh/m3) and 285 nm UV-LED (0.49 kWh/m3).
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