Ultraviolet Advanced Oxidation Processes Research Articles

UV/Advanced Oxidation Process for Removing Humic Acid from Natural Water: Comparison of Different Methods and Effect of External Factors

Humic acid (HA) is an organic compound naturally present in aquatic environments. It has been found to have detrimental effects on water color, the transport of heavy metals, and the elimination of disinfection by-products (DBPs), thereby exerting an impact on human health. This study introduced four synergistic ultraviolet/advanced oxidation processes (UV/AOPs) systems aimed at eliminating HA from water. The research explored the effect of solution pH, duration of illumination, initial reactant concentration, and oxidant concentration on the degradation of HA. The results indicated that the mineralization rate achieved by individual UV or oxidant systems was less than 15%, which is significantly lower compared to UV/AOPs systems. Among these methods, the UV/peroxymonosulfate (UV/PMS) process demonstrated the highest effectiveness, achieving a mineralization rate of 94.15%. UV/peroxydisulfate (UV/PDS) and UV/sodium percarbonate (SPC) were subsequently implemented, with UV/sulfite (S(IV)) demonstrating the lowest effectiveness at 19.8%. Optimal degradation efficiency was achieved when the initial concentration of HA was 10 mg/L, the concentration of PMS was 3 mmol/L, and the initial pH was set at 5, with an illumination time of 180 min. This experimental setup resulted in high degradation efficiencies for chemical oxygen demand (COD), UV254, and HA, reaching 96.32%, 97.34%, and 92.09%, respectively. The energy efficiency of this process (EE/O) was measured at 0.0149 (kWh)/m3, indicating the capability of the UV/PMS system to efficiently degrade and mineralize HA in water. This offers theoretical guidance for the engineered implementation of a UV/PAM process in the treatment of HA.

Efficacy and Mechanism of Antibiotic Resistance Gene Degradation and Cell Membrane Damage during Ultraviolet Advanced Oxidation Processes.

Combinations of UV with oxidants can initiate advanced oxidation processes (AOPs) and enhance bacterial inactivation. However, the effectiveness and mechanisms of UV-AOPs in damaging nucleic acids (e.g., antibiotic resistance genes (ARGs)) and cell integrity represent a knowledge gap. This study comprehensively compared ARG degradation and cell membrane damage under three different UV-AOPs. The extracellular ARG (eARG) removal efficiency followed the order of UV/chlorine > UV/H2O2 > UV/peracetic acid (PAA). Hydroxyl radical (•OH) and reactive chlorine species (RCS) largely contributed to eARG removal, while organic radicals made a minor contribution. For intracellular ARGs (iARGs), UV/H2O2 did not remove better than UV alone due to the scavenging of •OH by cell components, whereas UV/PAA provided a modest synergism, likely due to diffusion of PAA into cells and intracellular •OH generation. Comparatively, UV/chlorine achieved significant synergistic iARG removal, suggesting the critical role of the RCS in resisting cellular scavenging and inactivating ARGs. Additionally, flow cytometry analysis demonstrated that membrane damage was mainly attributed to chlorine oxidation, while the impacts of radicals, H2O2, and PAA were negligible. These results provide mechanistic insights into bacterial inactivation and fate of ARGs during UV-AOPs, and shed light on the suitability of quantitative polymerase chain reaction (qPCR) and flow cytometry in assessing disinfection performance.

Comparing Hydrogen Peroxide and Sodium Perborate Ultraviolet Advanced Oxidation Processes for 1,4-Dioxane Removal from Tertiary Wastewater Effluent

Ultraviolet advanced oxidation processes (UV-AOPs) were compared using sodium perborate (UV/NaBO3 AOP) or hydrogen peroxide (UV/H2O2 AOP) for 1,4-dioxane removal from tertiary wastewater effluent. Both UV-AOPs were also tested with the addition of acetic acid. Results revealed that sodium perborate performed similarly to hydrogen peroxide. The UV/NaBO3 AOP with 6 milligrams per liter (mg/L) as H2O2 resulted in 43.9 percent 1,4-dioxane removal, while an equivalent UV/H2O2 AOP showed 42.8 percent removal. Despite their similar performance, NaBO3 is approximately 3.3 times more expensive than H2O2. However, the solid form of NaBO3 can provide a major benefit to remote and mobile operations. Unlike H2O2 solution, which degrades over time and requires repeated costly shipments, NaBO3 is a convenient source of H2O2, and a long-term supply can be shipped at once and mixed into solution as needed. The addition of acetic acid to a UV/H2O2 AOP was found to enhance 1,4-dioxane removal, increasing treatment effectiveness by 5.7%.

Comparison of Oxidants Used in Advanced Oxidation for Potable Reuse: Non-Target Analysis and Bioassays

Free chlorine (HOCl) and monochloramine (NH2Cl) are less-used oxidants than hydrogen peroxide (H2O2) in ultraviolet advanced oxidation processes (UV-AOPs) but have garnered interest from the water reuse industry and scientific community because they can be more cost-effective than H2O2 and provide a protective disinfectant residual. The destruction of organic compounds, creation of UV-AOP byproducts, and change in toxicity during UV-AOP with H2O2, HOCl, NH2Cl, or ambient residual chloramine were evaluated in recycled wastewater by suspect and non-target screening as well as bioanalytical tests (bioassays). Ten compounds were identified in reverse osmosis (RO) permeate via suspect screening with removal near 100% by UV/H2O2 and UV/HOCl, greater than decomposition by UV/NH2Cl and UV/ambient (∼60%), based on suspect screening mass spectrometry peak area. Non-target analysis based on organic features in mixed-mode cation exchange cartridge extracts indicated that UV/H2O2 destroyed a similar or slightly greater fraction of organic compounds, formed fewer transformation products, and reduced the summed peak area of non-target features to the greatest extent. Fewer chlorinated byproducts were produced from the RO permeate treated by UV/H2O2 than exposure to the chlorine-containing oxidants. Addition of NH2Cl to RO permeate resulted in a slight increase in the bioassay oxidative stress response but dropped below the response limit for all samples after UV-AOP for all oxidants.

Pilot UV-AOP Comparison of UV/Hydrogen Peroxide, UV/Free Chlorine, and UV/Monochloramine for the Removal of N-Nitrosodimethylamine (NDMA) and NDMA Precursors

Three different ultraviolet-advanced oxidation processes (UV-AOPs) (UV/hydrogen peroxide, UV/free chlorine, and UV/supplemental monochloramine) used in full advanced treatment (FAT) for potable reu...

Hydroxyl radical scavenging factor measurement using a fluorescence excitation-emission matrix and parallel factor analysis in ultraviolet advanced oxidation processes

The performance of the UV/H2O2 advanced oxidation process (AOP) is dependent on water quality parameters, including the UV absorbance coefficient at 254 nm and hydroxyl radical (•OH) water background demand (scavenging factor, s−1). The •OH scavenging factor represents the •OH scavenging rate of the background substances in the water matrix, and it is known to be one of the key parameters to predict the performance of the UV/H2O2 process. The •OH scavenging factor has been determined experimentally by using a probe compound such as pCBA and rhodamine B. The experimental method has been validated to accurately predict the micropollutants removal in the UV/H2O2 process, but there is a need for an easier and simple method of determining the OH scavenging factor. We evaluated the alternative method to analyze the •OH scavenging factor using fluorescence excitation-emission matrix and parallel factor analysis (F-EEM/PARAFAC). The correlation between •OH scavenging factor and the spectroscopic characteristics and structure of different organic matter types was evaluated. Organic matter was characterized using a fluorescence excitation-emission matrix, parallel factor analysis, and liquid chromatography-organic carbon detection. Second-order reaction rates of humic acid sodium salt, sodium alginate, Suwannee River humic acid and bovine serum albumin were calculated as 1.30 × 108 M−1 s−1, 1.39 × 108 M−1 s−1, 1.03 × 108 M−1 s−1, and 3.17 × 107 M−1 s−1, respectively. Results of PARAFAC analysis, the ratio of humic and fulvic fluorescence component 2 to terrestrial humic-like fluorescence component 1 (C2/C1), and •OH scavenging factor showed high linearity. A predictive model, which combines with the F-EEM/PARAFAC method, predicted the optimal UV and H2O2 dose to achieve target compound removal.

Comparison of UV/H2O2 and UV/PS processes for the treatment of reverse osmosis concentrate from municipal wastewater reclamation

Reverse osmosis concentrate (ROC) from municipal wastewater treatment contains high concentrations of complex toxic biorefractory pollutants. We studied the mechanisms by which two ultraviolet advanced oxidation processes, UV/H2O2 and UV/PS, degraded pollutants in ROC from municipal wastewater reclamation processes. Both technologies had similar removal efficiencies of bulk dissolved organic matter based on the observed reduction in COD, chromophores, and fluorophores. However, UV/PS decomposed both high and medium molecular weight (MW) fractions (57 and 67.7%), while UV/H2O2 preferentially decomposed only the high MW fraction (60 and 39.1%), suggesting that the two methods operate by different reaction mechanisms. The changes in electron donating capacity resulting from treatment by UV/H2O2 (42.3%) and UV/PS (75.2%) were different. SO4•− primarily decomposed compounds containing electron-donating groups better than •OH. The removal of dissolved organic matter by UV/PS resulted in decreases in both relative electron-donating capacity and relative specific ultraviolet absorbance. The distinct reaction mechanisms were observed between UV/PS and UV/H2O2, being that UV/PS preferentially decomposed the contaminants via electrophilic addition and hydroquinone generation, while UV/H2O2 preferentially decomposed the contaminants via phenolic-ring cleavage reactions. Changes in the UV absorbance (UVA254) and the fluorescence index (FI) were used to monitor the rate of elimination of toxic biocides in the ROC.

Life-cycle assessment of two potable water reuse technologies: MF/RO/UV–AOP treatment and hybrid osmotic membrane bioreactors

A life cycle assessment tool and methodology were used to study two potable reuse treatment schemes: a full-advanced treatment (FAT) approach and a hybrid ultrafiltration osmotic membrane bioreactor (UFO-MBR). FAT combines conventional wastewater treatment followed by low-pressure membrane filtration, reverse osmosis (RO), and ultraviolet advanced oxidation processes (UV–AOP). The UFO-MBR couples biological treatment processes with forward osmosis (FO) membranes and ultrafiltration (UF) membranes in one integrated system. RO is coupled with FO in the UFO-MBR process to produce ultra-pure water and a reconcentrated draw solution (DS) for reuse in the FO process. Construction material, energy demand, and chemical use data were collected and calculated to determine the energy use and a subset of environmental impacts of each system. Results from the LCA illustrate that the energy use and environmental impacts of FAT are lower than those of UFO-MBR treatment. The higher impacts of UFO-MBR treatment were associated with the required large area of the FO membrane and high RO energy use. UFO-MBR treatment was further assessed using higher permeability FO membranes and RO energy recovery. Following simulation of process optimization, the environmental impacts of UFO-MBR were brought much closer to those of FAT.

Fundamentals and applications of the photocatalytic treatment for the removal of industrial organic pollutants and effects of operational parameters: A review

Photocatalysis process, as an environmental application, is a relatively novel subject with tremendous potential in the near future. A number of studies determine the economic viability of applying various ultraviolet advanced oxidation processes for the purpose of degradation and destroying of various pollutant solutions. The present paper reviews the treatment of hazardous wastewater bearing organic compounds and the effects of various parameters such as pH, initial concentration, mass of catalyst, wavelength, light intensity, electron acceptor, temperature, etc., with the treatment cost for different reactor type. This study investigates the effect of various types of waste-water treatment parameters and the treatment cost for various designs of photocatalytic reactors, using both solar and artificial light, have been proposed for their different types of pollutants.