Low-pressure Lamp Research Articles

The effect of UV/H2O2 treatment on biofilm formation potential

Greater Cincinnati Water Works (GCWW) evaluated the efficacy of ultraviolet light/hydrogen peroxide advanced oxidation (UV/H2O2) for reducing trace organic contaminants in natural water with varying water qualities. A year-long UV/H2O2 pilot study was conducted to examine a variety of seasonal and granular activated carbon (GAC) breakthrough conditions. The UV pilot-scale reactors were set to consistently achieve 80% atrazine degradation, allowing comparison of low pressure (LP) and medium pressure (MP) lamp technologies for by-product formation. Because hydroxyl radicals react non-selectively with organic compounds, unintended by-product formation occurred.Total assimilable organic carbon (AOC) concentration increased through the reactors from 14 to 33% on average, depending on water quality. Natural organic matter (NOM) contains the precursors for AOC production, so when post-GAC water (versus conventionally treated water) served as reactor influent, less AOC was produced. No appreciable difference in AOC concentration was observed between LP and MP UV reactors. The Spirillum strain NOX fraction of the AOC increased from 50 to 65% on average, depending on the quality of the water. The increase in this fraction of AOC occurred because oxidation of NOM yielded smaller more assimilable organic compounds such as organic acids that are necessary for NOX growth. The Pseudomonas fluorescens strain P17 AOC concentration increased only when conventionally treated plant water was used as pilot influent. This organism thrives in waters of differing organic energy sources, but does not thrive well in carboxylic acids alone. The CONV water had more overall TOC that could contribute to higher P17 AOC counts.Biofilm coupon studies indicated that biofilms with greater heterotrophic plate counts were observed in the granular activated carbon (GAC) effluent streams receiving UV/H2O2 pre-treatment. Biofilm coupon studies additionally indicated that the effluent stream of the GAC column proceeded by the MP reactor exhibited more viable biofilm than the other GAC effluent streams based on an ATP-bioluminescence method. The increased viability of the biofilm produced by the MP UV reactor is likely a result of the multiple UV wavelengths and higher energy input characteristic of this technology.

Experimental study on colour removal from textile wastewaters using the H2O2/UV process with low- and medium-pressure lamps

In this paper we present the results of an experimental study aimed at estimating the efficiency and comparing the operating costs of a low pressure lamp and a medium pressure lamp in the H2O2/UV process for colour removal. Trials have been carried out on the secondary effluent of a wastewater treatment plant which treats part of the effluents of one of the largest textile industries district in Italy. Because of the great irregularity of the effluent composition it is very difficult to monitor all the variables and assess their influence on the decolorization process. For this reason the H2O2/UV efficiency in colour removal has been also evaluated using synthetic solutions: demineralized water or groundwater added with five different dyes. In this latter case we determined the single effect of the control parameters on the process. From the experimental results we can assess that the H2O2/UV process guarantees a very high colour removal efficiency (up to 90%), which mainly depends on H2O2 dosages, dye concentration and characteristics, water quality (above all water hardness) and UV intensity. In our experimental conditions, the low pressure lamp showed to be more cost-effective both to remove colour and to reduce TOC and COD.

General method of simulating radiation fields using measured boundary values

A general methodology integrating the Fresnell, Snell, and Beer-Lambert laws for modeling the radiant distribution in a medium is presented. The model considers refraction/reflection through/from the body of the UV lamp and sleeve, as well as the reflections from other sources, such as the reactor body. The measured boundary conditions are applied to realistically simulate the fluence/irradiance rate around the radiant source, in particular, in the zone closest to the radiant source. Different low-pressure UV lamps were tested under different operating conditions using photodiodes and a radiometer. The experimentally measured irradiance rate was in a very good agreement with the simulation results of the presented model.

Case Study of Particle-Related UV Shielding of Microorganisms When Disinfecting Unfiltered Surface Water

Abstract The goal of this case study was to provide pilot-scale information about the ability of ultraviolet (UV) light to disinfect unfiltered surface water. A pilot-scale (0.25 L/s) UV reactor with low-pressure UV lamps was installed on raw water entering an aqueduct from the Pardee Reservoir at the East Bay Municipal District, California. A pilot monitoring system also collected hourly particle count (2 to 100 m), turbidity, and ultraviolet transmittance (UVT) measurements for 14 months. Grab microbial samples were collected and analyzed for indigenous total coliforms and total aerobic spores (TAS) both before and after UV disinfection, to correlate survival of the organisms across the UV reactor to water quality characteristics. Concentrations of indigenous coliforms and TAS ranged up to 163 and 1,383 per 100 mL respectively, before UV exposure. The data showed that the ability of UV to disinfect coliforms was essentially unaffected by the presence of particles (up to 703>10 m per mL and 1.3 nephelometric turbidity unit [NTU]) in the unfiltered surface water. In 13 of 14 samples, no coliforms were detected in the UV treated water. Log-linear inactivation of TAS up to 2.5-log suggests that at least 99.6% of the TAS were not protected from UV disinfection by particles.

Pilot-scale studies of combined clarification, filtration, and ultraviolet radiation systems for disinfection of secondary municipal wastewater effluent

Disinfection of municipal wastewater effluent was evaluated using three alternatives, including: (1) low-pressure (LP) + medium-pressure (MP) UV lamps; (2) clarifier + LP + MP; and (3) pressurized sand filter + LP + MP. Total coliform (TC), fecal coliform (FC), fecal Streptococcus (FS), TSS, several physicochemical parameters, absorbtivity and UV transmittance (UVT; %) were tested. The UVT% for secondary, clarified and filtered effluents were 3.5, 34 and 50, respectively. A 15% photo-reactivation in secondary effluent disinfected by LP lamp was observed, while it was limited to 0.03% by the MP lamp after filtration. Filtration to a surface overflow rate (SOR) of 1050 L/m 2 h, followed by MP irradiation at a dose of 230 mW s/cm 2 was an effective alternative to reduce the TC, FC, and FS in the disinfected secondary effluent. Filtration + MP lamp met the standards of 1000 TC and 400 FC/100 mL for effluent discharge to receiving waters. This process can also inactivate FS, effecting a 6-log reduction. Among the evaluated alternatives, none of the other treatment systems performed as well as the pressurized sand filter + MP lamp, making this the best combination for post-treatment and disinfection of secondary effluent from a well-run wastewater treatment plant.

Kinetic degradation model and estrogenicity changes of EE 2 (17α-ethinylestradiol) in aqueous solution by UV and UV/H 2O 2 technology

The photochemical degradation and estrogenicity removal of 17α-ethinylestradiol in aqueous solutions was investigated via ultraviolet (UV) photolysis and UV/H 2O 2 process with a low-pressure UV lamp. The results indicated that the kinetics of both oxidation processes well fitted the pseudo-first-order kinetics. EE 2 can be partially removed by UV radiation alone with kinetic constants increasing from 0.0054 to 0.2753 min −1 with the UV intensity increase. The EE 2 degradation rate enhanced from 0.0364 to 0.0684 min −1 when H 2O 2 was combined with the photolysis process (UV/H 2O 2), even though EE 2 was not oxidized when same amounts of H 2O 2 existed in the aqueous solutions. The kinetic parameters of pseudo-first-order kinetics showed positive correlation to UV intensity and also H 2O 2 concentration, however negative to the initial EE 2 concentration. A regression model was developed for pseudo-first-order rate constant as a function of the UV intensity, H 2O 2 concentration and initial EE 2 concentration, which could be used to estimate the EE 2 degradation rate at various operational conditions. The yeast estrogen screen (YES) was employed to evaluate the estrogenicity of photolytic water samples. Results showed that more than 95% of the estrogenicity was removed after 40 min irradiation and the parent compound EE 2 was mainly responsible for the observed estrogenicity.

On the Aging Effects of 4H-SiC Schottky Photodiodes Under High Intensity Mercury Lamp Irradiation

Ultraviolet (UV) germicidal irradiation uses high-power 254-nm radiation from low-pressure mercury discharge lamps to kill or inactivate viral, bacterial, and fungal species. Since UV germicidal irradiation effectiveness depends primarily on the UV dose delivered to the microorganisms, it is essential to monitor the power emitted from the source by using appropriate UV-light detectors. We report on preliminary aging tests performed on high signal-to-noise ratio 4H-SiC Schottky photodiodes under high intensity mercury lamp irradiation (10 mW/cm2).

Optical and electrostatic potential investigations of electrical breakdown phenomena in a low-pressure gas discharge lamp

The ignition phase is a critical stage in the operation of gas discharge lamps where the neutral gas enclosed between the electrodes undergoes a transformation from the dielectric state to a conducting phase, eventually enabling the production of light. The phenomena occurring during this phase transition are not fully understood and the related experimental studies are often limited to local optical measurements in environments prone to influencing these transient phenomena. In this work unipolar ignition phenomena at sub-kilovolt levels are investigated in a 3 Torr argon discharge tube. The lamp is placed in a highly controlled environment so as to prevent any bias on the measurements. A fast intensified CCD camera and a specially designed novel electrostatic probe are used simultaneously so as to provide a broad array of measured and computed parameters which are displayed in space–time diagrams for cross comparisons. Experiments show that three distinct phases exist during successful ignitions: upon the application of voltage a first ionization wave starts from the active electrode and propagates in the neutral gas towards the opposite electrode. A local front of high axial E field strength is associated with this process and causes a local ionization to occur, leading to the electrostatic charging of the lamp. Next, a second wave propagates from the ground electrode back towards the active electrode with a higher velocity, and in this process leads to a partial discharging of the lamp. This return stroke draws a homogeneous plasma column which eventually bridges both electrodes at the end of the wave propagation. At this point both electrode sheaths are formed and the common features of a glow discharge are observed. The third phase is an increase in the light intensity of the plasma column until the lamp reaches a steady-state operation. Failed ignitions present only the first phase where the first wave starts its propagation but extinguishes in the lamp, leading to a charge memory effect. It is found that the full propagation of this first wave is a requirement for successful lamp ignition. Differences in the properties of the waves were observed depending on the voltage polarity, and it was estimated that a photoelectric effect at the wall is the most likely source of electrons for the ionization wave of positive polarity. Finally, a simple model of the first ionization wave is developed and used to analyse the fundamental differences between processes occurring at negative and at positive polarity. From this study three conditions are developed for the successful unipolar ignition of lamps and the relations between them are derived.

Versatile Thin-Film Reactor for Photochemical Vapor Generation

A novel thin-film reactor is described and evaluated for its analytical performance with photochemical vapor generation (TF-PVG). The device, comprising both the generator and a gas-liquid separator, utilizes a vertical central quartz rod onto which the sample is pumped to yield a thin liquid film conducive to the rapid escape of generated hydrophobic species. The rod is housed within a concentric quartz tube through which a flow of argon carrier/stripping gas is passed to remove and transport the generated species to a detector, which in this study is an inductively coupled argon plasma optical emission spectrometer (ICP-OES). The concentric quartz tube is itself surrounded by a 78-turn 0.5 m long quartz coil low-pressure mercury discharge lamp operating at 20 W. The performance of this thin-film photoreactor was evaluated through comparison of analytical figures of merit for detection of a number of elements undergoing PVG in the presence of formic or acetic acid with those arising from conventional solution nebulization under optimized conditions. The TF-PVG reactor provided sensitivity enhancements, of 110-, 120-, 130-, 250-, 120-, 230-, 78-, 1.3-, 16-, and 32-fold for As, Sb, Bi, Se, Te, Hg, Ni, Co, Fe, and I, respectively, and detection limit enhancements of 110-, 140-, 170-, 270-, 200-, 300-, 160-, 2.7-, 50-, and 44-fold for these same elements. Vapor generation efficiencies ranged from 20-100% for this suite of analytes. The utility of this technique was demonstrated by the determination of Fe and Ni in Certified Reference Materials DORM-3 (fish protein) and DOLT-4 (dogfish liver tissue).

High-Yield UV-Photochemical Vapor Generation of Iron for Sample Introduction with Inductively Coupled Plasma Optical Emission Spectrometry

A novel approach to the generation of volatile iron compounds (likely the pentacarbonyl) with high efficiency is described, wherein solutions containing either Fe(2+) or Fe(3+) and low molecular weight organic acids such as formic, acetic or propionic are exposed to a UV source. An optimum generation efficiency of 60 +/- 2% was achieved in 50% formic acid at pH 2.5 with an irradiation time of 250 s by use of a 17 W low-pressure mercury grid lamp. Compared to conventional solution nebulization, sensitivity and limit of detection were improved 80- and 100-fold, respectively, at the 238.204 nm Fe II emission line. A precision of 0.75% RSD was achieved at a concentration of 100 ng/mL. Photochemical vapor generation sample introduction was used for the determination of trace iron in several environmental Certified Reference Materials, including National Research Council Canada DORM-3 fish muscle tissue, DOLT-3 and DOLT-4 fish liver tissues, and SLRS-5 river water, providing analytical results in excellent agreement with certified values based on a simple external calibration.

Demonstration and evaluation of germicidal UV-LEDs for point-of-use water disinfection

Ultraviolet (UV) irradiation is a common disinfection option for water treatment in the developed world. There are a few systems installed in developing countries for point-of-use treatment, but the low-pressure mercury lamps currently used as the UV irradiation source have a number of sustainability issues including a fragile envelope, a lifetime of approximately one year, and they contain mercury. UV light emitting diodes (LEDs) may offer solutions to many of the sustainability issues presented by current UV systems. LEDs are small, efficient, have long lifetimes, and do not contain mercury. Germicidal UV LEDs emitting at 265 nm were evaluated for inactivation of E. coli in water and compared to conventional low-pressure UV lamps. Both systems provided an equivalent level of treatment. A UV-LED prototype was developed and evaluated as a proof-of-concept of this technology for a point-of-use disinfection option, and the economics of UV-LEDs were evaluated.

Halonitromethanes formation in wastewater treatment plant effluents

Halonitromethanes (HNMs) constitute one class of emerging disinfection by-products with high potential health risks. This study investigated the formation and occurrence of HNMs under different disinfection scenarios and the presence of their precursors in municipal wastewater treatment plant (WWTPs) effluents. Formation potential tests performed on WWTP effluents revealed that HNM formation occurred in the order of ozonation–chlorination ≫ ozonation–chloramination > chlorination > chloramination. Ozonation alone did not produce any HNM. Municipal WWTP effluents contained some reactive HNM precursors, possibly the by-products of biological treatment processes and/or some moiety of industry or household origin. No effects of nitrate on the formation of HNMs were observed in this study, and nitrification in WWTPs appears to remove appreciable portion of HNM precursors, especially those reactive to chlorine. UV disinfection using low pressure lamps in municipal WWTPs had negligible impact on HNM formation potential. HNM concentrations in the effluents of selected WWTPs were either non-detectable or less than minimum reporting level, except for one WWTP that gave trichloronitromethane concentrations in the range of 0.9–1.5 μg L −1. No HNMs were observed in the effluents disinfected with UV radiation. Therefore, it appears the typical wastewater disinfection processes involving chlorination or UV treatment in WWTPs do not produce significant amounts of HNMs.

Absorption spectroscopy measurements of resonant and metastable atom densities in atmospheric-pressure discharges using a low-pressure lamp as a spectral-line source and comparison with a collisional-radiative model

The well-known absorption method for measuring metastable and resonant atom densities in reduced-pressure discharges using a low-pressure lamp as a spectral-line source is extended to plasmas sustained at atmospheric pressure where the line profiles are of the Voigt type rather than Gaussian. This technique is further applied to determine the axial distribution of metastable and resonant atom densities in a tubular argon surface-wave (microwave) discharge. At atmospheric pressure, the discharge is radially contracted and determination of the absorption length through lateral probing of the tube becomes a critical issue. Good agreement of the metastable and resonant atom densities calculated from a collisional-radiative model with the measured values supports the validity of the method developed. The model underlines the influence of the molecular ion kinetics on the Ar I 4s level population and reveals an efficient 3-step ionization process involving the 4s and 4p levels for atomic ion formation.

Relationship between Ba atom emission and electrode temperature in a low-pressure fluorescent lamp

A relationship between emission characteristics of Ba atom as an emitter material and temperature distributions of an electrode in a fluorescent lamp is described, which is measured by using laser-induced fluorescence and black-body radiation method, respectively. In a virgin lamp, a hot spot observed at the electrode edge connected to the power supply is the main source of Ba atom emission. In a long-term-used lamp, it is shown that Ba atom emission, thermionic electron emission in cathode half-cycle and electron collection in anode half-cycle are most active on the hot spot appearing on the center of the electrode.

Microbiological effluent control by UV-disinfection of a small-scale SBR system

Abstract Decentralized wastewater management systems, with the wastewater treated close to where it is generated, are considered by various researchers as an alternative to the traditional centralized system. The wastewater treatment facility should produce an effluent which is hygienically safe and can subsequently be utilized for watering lawns and irrigation. This article presents the operational data of such a small system and also presents disinfection efficiency data using a low-pressure UV lamp. To evaluate the SBR performance, several effluent parameters, such as BOD 5 , COD t and SS eff were measured and compared with the influent. The removal efficiencies were 90.9% for BOD 5 , 86.9% for COD t and 93.9% for SS eff (average values). Disinfection efficiency was evaluated through measurement of the controlled encountering coliform bacteria (total coliforms (TC) and faecal coliforms (FC) before and after the UV lamp), because of the central role they play in discharge permits. To overcome disinfection problems that result from the influence of particle-associated organisms, a Mean Cell Retention Time (MCRT) of 20 d was used, in combination with a well-designed clarification phase. A clear reduction of the coliform bacteria concentration was observed, which followed a similar pattern of the reduction of the SS eff . The Pearson correlation coefficient was used to express the degree of linear relationship between the TC and SS eff and FC and SS eff parameters.

A Physically Based Fluorescent Lamp Model for a SPICE or a Simulink Environment

This paper describes a method of modeling fluorescent lamps. The lamp model can be implemented in all major circuit simulation software packages, an example has been given for SPICE and Simulink. The model is based upon a simplified set of physical equations that gives the model validity over a wider range of operating conditions than current fluorescent lamp SPICE models allow for. The model can be used to model any low-pressure mercury-buffer gas fluorescent lamps by entering key lamp parameters, length, radius, cold-spot temperature, and buffer gas fill pressure. If fill pressure is not known, a default value dependent on lamp radius is used. The model shows good agreement over a wide range of operating frequencies and lamp powers.

Photocatalytic decolourization of the X3B textile dye in aqueous solutions using iron-rich montmorilloniteA paper submitted to the Journal of Environmental Engineering and Science.

Photocatalytic decolourization of textile dye X3B in aqueous solutions was investigated, using iron-rich montmorillonite (MMt, 2.24%Fe2O3) under a 15 W low-pressure UV lamp (λ = 254 nm, I = 48.4 μW/cm2). Hydroxyl radicals (•OH) were detected by tert-butyl alcohol (TBA) in aqueous MMt suspensions under UV irradiation and were found to be responsible for the degradation of X3B. Free iron ions dissolved in MMt suspensions, structural iron in the MMt solid, and the charged surface of nano clay are responsible for hydroxyl radical (•OH) production. Low pH values are favorable for the decolourization of X3B. The •OH concentration increased with increasing aqueous MMt concentrations in the range of 0 – 2.0 g/L; higher concentrations, for example, 5.0 g/L MMt, inhibited the •OH production. The addition of oxalate was favorable for X3B photodegradation in acid-washed MMt suspensions. This study shows that iron-rich MMt is a potential photocatalyst for the treatment of dye wastewater.

High-resolution spectrometer for atmospheric studies

A high-resolution spectrometer (0.0014 nm at 313 nm) has been developed at the University of L’Aquila (Italy) for atmospheric spectroscopic studies. The layout, optics and software for the instrument control are described. Measurements of the mercury low-pressure lamp lines from 200 to 600 nm show the high performances of the spectrometer. Laboratory measurements of OH and NO 2 spectrums demonstrate that the system could be used for cross-section measurements and to detect these species in the atmosphere. The first atmospheric application of the system was the observation of direct solar and sky spectrums that shows a filling-in of the sky lines due to rotational Raman scattering. The measurements have been done with clear and cloudy sky and in both there was a strong dependence of the filling-in from the solar zenith angle whereas no dependence from the wavelengths was evident at low solar zenith angles (less than 85°).

Photocatalytic Degradation of Orange II in Aqueous Iron-Rich Montmorillonite Solutions

In this work the photodegradation of orange II was carried out in the presence of iron-rich montmorillonite (MMt) (2.24% Fe2O3) using a 15-W low-pressure ultraviolet lamp (λ=254 nm, I=48.4 μW/cm2). The effects of pH, MMt dose, and dye concentration were studied. A low pH value is favorable for the decolorization of orange II. The hydroxyl radical (O•H) concentration increased with increasing concentration of MMt in aqueous solutions in the range of 0–1.5 g/L. Concentrations higher than 5.0 g/L MMt inhibited the O•H production. There was no significant decrease in photocatalytic activity when the catalyst was reused. Hydroxyl radicals were detected by tert-butyl alcohol in aqueous MMt suspensions under ultraviolet irradiation and were responsible for the degradation of orange II. Free iron ions dissolved in MMt suspensions, structural iron in the MMt structural and the charged surface of nanoclay are responsible for the hydroxyl radical (O•H) production. Free iron ions dissolved in solution plays a predominant role in the degradation of orange II. This study shows that iron-rich MMt is a potential photocatalyst for dye wastewater treatment.

H2O2/UV-Coxidation of potential endocrine disrupting compounds: a case study with dimethyl phthalate

This paper discusses the feasibility of the ultraviolet radiation-hydrogen peroxide (H(2)O(2)/UV-C) process as an advanced oxidation process (AOP) in the treatment of endocrine disrupting compounds (EDC). Dimethyl phthalate (DMP) was chosen as the model compound owing to its classification as an EDC. Experiments have been conducted at various pH values (3.5, 6.0 and 9.0) and initial H(2)O(2) concentrations (0-60 mM) in a batch reactor equipped with a low-pressure mercury UV-C lamp in order to evaluate the optimal operation conditions of the H(2)O(2)/UV-C process. The most effective pH value for the degradation of DMP by H(2)O(2)/UV-C treatment was found as 6.0. DMP abatement increased with increasing H(2)O(2) concentrations from 5 to 30 mM. Further increase in initial H(2)O(2) concentration, however, reduced both the rate and extent of DMP removal as well as chemical oxygen demand (COD) and total organic carbon (TOC) removals. A simple kinetic model was proposed for DMP, COD and TOC abatements confirmed pseudo-first-order reaction. The electrical energy per order (EE/O) values for DMP oxidation and TOC mineralization were calculated as 3.3 and 19 kWh m(-3) order(-1) respectively for the optimum treatment conditions (H(2)O(2,o) = 30 mM, pH(o) = 6.0, DMP(o)= 100 mg L(-1)). Inhibition of oxygen uptake rate by activated sludge (ISO 8192) was evaluated as a tool for assessing the acute toxicity of untreated and H(2)O(2)/UV-C treated DMP. According to the results obtained in this work, the use of the H(2)O(2)/UV-C process is recommended to achieve a complete DMP oxidation and high mineralization degree of aqueous solution of DMP.