Madjid Mohseni

Application of ultraviolet light-emitting diodes (UV-LEDs) for water disinfection: A review.

Ultraviolet (UV) disinfection is an effective technology for the inactivation of pathogens in water and is of growing interest for industrial application. A new UV source - ultraviolet light-emitting diode (UV-LED) - has emerged in the past decade with a number of advantages compared to traditional UV mercury lamps. This promising alternative raises great interest in the research on application of UV-LEDs for water treatment. Studies on UV-LED water disinfection have increased during the past few years. This article presents a comprehensive review of recent studies on UV-LEDs with various wavelengths for the inactivation of different microorganisms. Many inconsistent and incomparable data were found from published studies, which underscores the importance of establishing a standard protocol for studying UV-LED inactivation of microorganisms. Different UV sensitivities to UV-LEDs and traditional UV lamps were observed in the literature for some microorganisms, which requires further investigation for a better understanding of microorganism response to UV-LEDs. The unique aspects of UV-LEDs improve inactivation effectiveness by applying LED special features, such as multiple wavelengths and pulsed illumination; however, more studies are needed to investigate the influencing factors and mechanisms. The special features of UV-LEDs offer the flexibility of novel reactor designs for a broad application of UV-LED reactors.

Effects of UV/H2O2 advanced oxidation on chemical characteristics and chlorine reactivity of surface water natural organic matter

The advanced oxidation process utilizing ultraviolet and hydrogen peroxide (UV/H(2)O(2)) is currently applied in commercial drinking water applications for the removal of various organic pollutants. Natural organic matter (NOM) present in the source water can also be oxidized and undergo changes at the fluence and H(2)O(2) concentrations applied in commercial drinking water UV/H(2)O(2) applications (fluences less than 2000 mJ cm(-2), initial H(2)O(2) concentrations less than 15 mg L(-1)). In this study, the impact of UV/H(2)O(2) on NOMs aromaticity, hydrophobicity, and potential to form trihalomethanes (THMs) and haloacetic acids (HAAs) was investigated for raw surface water and the same water with the very hydrophobic acid (VHA) fraction of NOM removed. During UV/H(2)O(2) treatments, NOM in the raw surface water was partially oxidized to less aromatic and hydrophobic characteristics, but was not mineralized, confirming findings from past research. Below fluences of 1500 mJ cm(-2) UV/H(2)O(2) treatment of the raw water did not lead to reduction in the formation potential of THMs. The formation potential of HAAs was reduced at a fluence of 500 mJ cm(-2) with only small additional reductions as fluence further increased. For the water from which the VHA fraction was removed, UV/H(2)O(2) treatment led to mineralization of NOM suggesting that, when coupled with a pre-treatment capable of removing the VHA fraction, UV/H(2)O(2) could achieve further reductions in NOM. These subsequent reductions in NOM led to continuous reductions in the formation potentials of THMs and HAAs as fluence increased.

Degradation of natural organic matter in surface water using vacuum-UV irradiation

The use of vacuum-UV (VUV) radiation to degrade natural organic matter (NOM) and the main variables affecting the efficiency of this process were investigated using an annular photoreactor. After 180 min of irradiation with VUV, the total organic carbon (TOC) decreased from 4.95 ppm to 0.3 ppm. Also, decadic absorption coefficients of the water at 185 nm and 254 nm decreased from 3.2 cm(-1) to 2.85 cm(-1), and 0.225 cm(-1) to 0 cm(-1), respectively. The reactor operation was kinetically controlled for Reynolds numbers greater than 600, changes of pH between 5 and 9 had little effect, and increases in alkalinity decreased the process efficacy. Additionally, H(2)O(2)/VUV and VUV processes were compared to H(2)O(2)/UV and UV processes, where the formers showed greater effectiveness with complete mineralization of NOM as opposed to partial oxidation with H(2)O(2)/UV, and no mineralization with UV alone. Modeling and analysis of the photon flux and absorption in the reactor showed that 99% of the 185 nm radiation was absorbed by the water in the reactor. In comparison, only 48% of the 254 nm radiation was absorbed by the water. The overall quantum efficiency of the mineralization for VUV was 0.10 for 50% TOC reduction.

Impact of UV/H2O2 advanced oxidation treatment on molecular weight distribution of NOM and biostability of water

The presence of natural organic matter (NOM) poses several challenges to the commercial practice of UV/H(2)O(2) process for micropollutant removal. During the commercial application of UV/H(2)O(2) advanced oxidation treatment, NOM is broken down into smaller species potentially affecting biostability by increasing Assimilable Organic Carbon (AOC) and Biodegradable Organic Carbon (BDOC) of water. This work investigated the potential impact of UV/H(2)O(2) treatment on the molecular weight distribution of NOM and biostability of different water sources. A recently developed flow cytometric method for enumeration of bacteria was utilized to assess biological stability of the treated water at various stages through measurement of AOC. BDOC was also assessed for comparison and to better study the biostability of water. Both AOC and BDOC increased by about 3-4 times over the course of treatment, indicating the reduction of biological stability. Initial TOC and the source of NOM were found to be influencing the biostability profile of the treated water. Using high performance size exclusion chromatography, a wide range of organic molecule weights were found responsible for AOC increase; however, low molecular weight organics seemed to contribute more. Positive and meaningful correlations were observed between BDOC and AOC of different waters that underwent different treatments.

In-situ identification of iron electrocoagulation speciation and application for natural organic matter (NOM) removal.

In this work, iron speciation in electrocoagulation (EC) was studied to determine the impact of operating parameters on natural organic matter (NOM) removal from natural water. Two electrochemical EC parameters, current density (i) and charge loading rate (CLR), were investigated. Variation of these parameters led to a near unity current efficiency (φ = 0.957 ± 0.03), at any combination of i in a range of 1-25 mA/cm(2) and CLR in a range of 12-300 C/L/min. Higher i and CLR led to a higher bulk pH and limited the amount of dissolved oxygen (DO) reduced at the cathode surface due to mass transfer limitations. A low i (1 mA/cm(2)) and intermediate CLR (60 C/L/min) resulted in low bulk DO (<2.5 mg/L), where green rust (GR) was identified by in-situ Raman spectroscopy as the primary crystalline electrochemical product. Longer electrolysis times at higher i led to magnetite (Fe3O4) formation. Both higher (300 C/L/min) and lower (12 C/L/min) CLR values led to increased DO and/or increased pH, with lepidocrocite (γ-FeOOH) as the only crystalline species observed. The NOM removal of the three identified species was compared, with conditions leading to GR formation showing the greatest dissolved organic carbon removal, and highest removal of the low apparent molecular weight (<550 Da) chromophoric NOM fraction, determined by high performance size exclusion chromatography.

The treatment of waste air containing phenol vapors in biotrickling filter

This research aimed at investigating the biodegradation of phenol contaminated-air streams in biotrickling filter. The effect of inlet concentration (200-1000 ppmv) and empty bed contact time (EBCT) (15-60 s) were investigated under steady state, transient and shock loading, and shutdown periods. Upon rapid start up operation, inlet phenol concentrations of up to 1000 ppmv did not significantly affect the performance of the biotrickling filter at EBCT of 60 s, so that removal efficiency was well greater than 99%. In addition, the EBCT as low as 30 s did not have detrimental effects on the efficiency of the bioreactor and phenol removal was greater than 99%. Decreasing the EBCT to 15s reduced the removal efficiency to around 92%. The maximum elimination capacity obtained in the biotrickling filter was 642 g(phenol) m(-3) h(-1), where the removal efficiency was only 57%. Results from the transient loading experiments revealed that the biotrickling filter could effectively handle the variations of the inlet loads without the phenol removal capacity being significantly affected.

Production and transformation of mixed-valent nanoparticles generated by Fe(0) electrocoagulation.

Mixed-valent iron nanoparticles (NP) generated electrochemically by Fe(0) electrocoagulation (EC) show promise for on-demand industrial and drinking water treatment in engineered systems. This work applies multiple characterization techniques (in situ Raman spectroscopy, XRD, SEM, and cryo-TEM) to investigate the formation and persistence of magnetite and green rust (GR) NP phases produced via the Fe(0) EC process. Current density and background electrolyte composition were examined in a controlled anaerobic system to determine the initial Fe phases generated as well as transformation products with aging. Fe phases were characterized in an aerobic EC system with both simple model electrolytes and real groundwater to investigate the formation and aging of Fe phases produced in a system representing treatment of arsenic-contaminated ground waters in South Asia. Two central pathways for magnetite production via Fe(0) EC were identified: (i) as a primary product (formation within seconds when DO absent, no intermediates detected) and (ii) as a transformation product of GR (from minutes to days depending on pH, electrolyte composition, and aging conditions). This study provides a better understanding of the formation conditions of magnetite, GR, and ferric (oxyhydr)oxides in Fe EC, which is essential for process optimization for varying source waters.

Metal type and natural organic matter source for direct filtration electrocoagulation of drinking water.

Electrocoagulation (EC) was combined with immediate microfiltration as direct filtration electrocoagulation (DFEC) for dissolved organic carbon (DOC) removal in drinking water from synthetic and natural highly natural organic matter (NOM) impacted waters from three different sources: Suwannee River (Georgia, USA DOC(0)=13.79 mg/L), Nordic Reservoir (Vallsjøen, Norway DOC(0)=9.03 mg/L), and a natural source (Lost Lagoon, Vancouver, Canada DOC(0)=13.31 mg/L). Three anode materials were investigated: iron, aluminum, and zinc, in a batch EC process without rapid mixing, flocculation, or settling. Fifteen seconds of process time with the iron electrode (36 mg Fe/L) led to DOC removal of 44%. After 1 min of process time, DOC reduction was 65% (zinc)-73 (iron)%, with ~ 85% reduction (all metals) in UV-abs-254 (UV-abs-254 final=0.06 cm(-1)) for Suwannee NOM. Specific UV absorbance (SUVA-L/mgm) values decreased from 3.1 to 4.2 to under 2.0, indicating removal of high MW fractions of NOM. High performance size exclusion chromatography (HPSEC) fractionation supported SUVA results, showing reductions from 76% of DOC>1450 Da to approximately 40% after EC for all metals and Suwannee NOM. EC performed equally well for two different initial DOC concentrations of 13.79 and 21.59 mg/L DOC, showing 75% DOC and 89% UV-abs-254 reductions.

Parameter estimation and characterization of a single-chamber microbial fuel cell for dairy wastewater treatment.

In this study, for the first time, the conduction-based model is extended, and then combined with Genetic Algorithm to estimate the design parameters of a MFC treating dairy wastewater. The optimized parameters are, then, validated. The estimated half-saturation potential of -0.13 V (vs. SHE) is in good agreement while the biofilm conductivity of 8.76×10(-4) mS cm(-1) is three orders of magnitude lower than that previously-reported for pure-culture biofilm. Simulations show that the ohmic and concentration overpotentials contribute almost equally in dropping cell voltage in which the concentration film and biofilm conductivity comprise the main resistances, respectively. Thus, polarization analysis and determining the controlling steps will be possible through that developed extension. This study introduces a reliable method to estimate the design parameters of a particular MFC and to characterize it.

A study of enhanced performance of VUV/UV process for the degradation of micropollutants from contaminated water

VUV/UV is a chemical-free and straightforward solution for the degradation of emerging contaminants from water sources. The objective of this work was to investigate the feasibility of VUV/UV advanced oxidation process for the effective degradation of a target micropollutant, atrazine, under continuous flow operation of 0.5-6.5L/min. To provide an in-depth understanding of process, a comprehensive computational fluid dynamics (CFD) model, incorporating flow hydrodynamics, 185nm VUV and 254nm UV radiation propagation along with a complete kinetic scheme, was developed and validated experimentally. The experimental degradation rates and CFD predicted values showed great consistency with less than 2.9% average absolute relative deviation (AARD). Utilizing the verified model, energy-efficiency of the VUV/UV process under a wide range of reactor configurations was assessed in terms of electrical energy-per-order (EEO), OH concentration as well as delivered UV and VUV dose distributions. Thereby, the extent of mixing and circulation zones was found as key parameter controlling the treatment economy and energy-efficiency of the VUV/UV process. Utilizing a CFD-driven baffle design strategy, an improved VUV/UV process with up to 72% reduction in the total electrical energy requirement of atrazine degradation was introduced and verified experimentally.