Degradation of organics and formation of DBPs in the combined LED-UV and chlorine processes: Effects of water matrix and fluorescence analysis

Innovative microbial water quality management in water distribution systems using in-pipe hydropowered UV disinfection: envisioning futuristic water-energy systems

Hydropower UV disinfection has not been explored as a possible alternative for off-grid disinfection. Hydropowered UV LED technology was developed using off-the-shelf UV-C LEDs and pico - and femto-scale hydro turbine generators and evaluated across point-of-use relevant flow rates. Commercially available UV LED flow through reactors were subjected to microorganism challenge testing with 3 power schemes: wall-plug, hydropower, and hydropower-charged battery. UV LEDs powered by hydropower-charged battery demonstrated similar disinfection as wall-plug powered UV LEDs, achieving 0.5-1.8 MS2 log10 reduction at flow rates 0.5-2.3 L min-1, corresponding to reduction equivalent doses (RED) up to 16 or 30 mJ/cm2 for 254 and 285 nm, respectively. With hydropowered UV LEDs alone, MS2 log10 reduction decreased to <0.3 log10 reduction due to an underperforming and grossly inefficient turbine, with RED of 8 or 18 mJ/cm2 for 254 and 285 nm, respectively. Assessment of existing markets of UV disinfection systems and pico-hydro turbines demonstrated that hydropowered UV systems are already theoretically feasible for scales at point-of-entry (POE) and above. Economic feasibility will improve if turbines and/or UV system efficiencies improve. Prototype hydropower UV LED systems ranged from $145 to 220 depending on the UV LED reactor, and the battery system added $81. This study demonstrates the practicality of sustainable, renewable energy POU UV disinfection technology that can benefit decentralised, off-grid, rural and remote communities. The system may also scale up to provide renewable energy disinfection at larger scales, such as buildings and water distribution systems, for protecting human health in highly populated areas.

Disinfection by-products control in wastewater effluents treated with ozone and biological activated carbon followed by UV/Chlor(am)ine processes

Sequential utilization of ozone (O3) and biological activated carbon (BAC) followed by UV/chlor(am)ine advanced oxidation process (AOP) has drawn attention in water reuse. However, the formation of disinfection by-products (DBPs) in this process is less evaluated. This study investigated the DBP formation and the relevant toxicity during the O3-BAC-UV/chlor(am)ine treatment of sand-filtered municipal secondary effluent. DBP formation in UV/chlorine and UV/dichloramine (NHCl2) processes were compared, where the impact of key operational parameters (e.g., UV wavelength, pH) on DBP formation were comprehensively evaluated. O3-BAC significantly reduced DBP formation potential (DBPFP) (58.2 %). Compared to UV/chlorine AOP, UV/NHCl2 AOP reduced DBP formation by 29.7 % in short-time treatment, while insignificantly impacting on DBPFP (p > 0.05). UV/NHCl2 AOP also led to lower calculated cytotoxicity (67.7 %) and genotoxicity (55.9 %) of DBPs compared to UV/chlorine AOP. Compared to 254 nm UV light, the utilization of 285 nm UV light decreased the formation of DBPs in wastewater treated with the UV/chlorine AOP and UV/NHCl2 AOP by 31.3 % and 19.2 %, respectively. However, the cytotoxicity and genotoxicity in UV/NHCl2 AOP using 285 nm UV light increased by 83.4 % and 58.5 %, respectively, compared to 254 nm. The concentration of DBPs formed in the UV/NHCl2 AOP at pH 8 was 54.3 % lower than that at pH 7, suggesting a better control of DBPs at alkaline condition. In the presence of bromide, UV/NHCl2 AOP tended to generate more brominated DBPs than UV/chlorine AOP. Overall, UV/NHCl2 AOP resulted in lower concentration and toxicity of DBPs compared to UV/chlorine AOP.

Degrading surface-water-based natural organic matter and mitigating haloacetonitrile formation during chlorination: Comparison of UV/persulfate and UV/hydrogen peroxide pre-treatments

Haloacetonitriles (HANs) are unregulated disinfection by-products that are more toxic than regulated species. Therefore, efficient decomposition of HAN precursors prior to disinfection is crucial for allaying the potential HAN-induced health risks. This study investigated the key roles of ultraviolet-activated persulfate (UV/PS) treatment in alleviating HAN formation. The effects of UV/PS treatment were evaluated by correlating with the characteristics of organic matter in surface water and comparing with conventional UV/H2O2 treatment. Upon irradiating raw water samples and a Suwannee River humic acid solution spiked with 10 mM PS or H2O2 with 254 nm UV light, UV/PS treatment was found to be more potent than UV/H2O2 in mitigating the HAN production and degrading organic substances; moreover, UV/PS treatment effectively decreased the dissolved organic nitrogen (DON) content. In contrast, UV/H2O2 treatment did not induce any noticeable reduction in DON level. Furthermore, both UV/PS and UV/H2O2 treatments reduced the dichloroacetonitrile (DCAN) formation potential (FP), leading to strong correlations with the degradation of aromatic and humic-acid-like compounds. Notably, UV/PS treatment efficiently decreased the FP of bromochloroacetonitrile (BCAN) and dramatically reduced that of dibromoacetonitrile (DBAN) after a sharp increase; however, UV/H2O2 treatment gradually increased the DBAN-FP. Bromide was activated by sulfate radicals during UV/PS treatment, negatively correlating with the BCAN-FP and DBAN-FP, indicating that the formation of reactive bromine species increased the DBAN-FP; however, excessive oxidation possibly led to the recovery of inorganic bromine for decreasing the BCAN-FP and DBAN-FP. Additionally, UV/PS treatment effectively suppressed toxicity owing to its high reduction rate for brominated HANs; in contrast, UV/H2O2 treatment resulted in less significant BCAN and DBAN reductions, leading to minimal net reduction in toxicity. Overall, UV/PS treatment was remarkably effective at diminishing the toxicity of brominated HANs, underscoring its potential to mitigate drinking-water-related health risks.

Formation of halonitromethanes from benzylamine during UV/chlorination: Impact factors, toxicity alteration, and pathways

Halonitromethanes (HNMs), a representative nitrogen-containing disinfection byproduct, have gained significant concerns due to their higher cytotoxicity and genotoxicity. UV/chlorination is considered a promising alternative disinfection technology for chlorination. This study aimed to investigate the HNMs formation from benzylamine (BZA) during UV/chlorination. The experimental results revealed that the yields of HNMs initially raised to a peak then dropped over time. Higher chlorine dosage and BZA concentration promoted the formation of HNMs, whereas alkaline pH inhibited their formation. The presence of bromine ion (Br-) not only converted chlorinated-HNMs (Cl-HNMs) to brominated (chlorinated)-HNMs Br (Cl)-HNMs) and brominated-HNMs (Br-HNMs) but also enhanced the total concentration of HNMs. Besides, the calculated cytotoxicity index (CTI) and genotoxicity index (GTI) of HNMs were elevated by 68.97% and 60.66% as Br- concentration raised from 2 to 6 µM. The possible formation pathways of HNMs from BZA were proposed based on the intermediates identified by a gas chromatography/mass spectrometry (GC/MS). In addition, the formation rules of HNMs in actual water verified the results in deionized water during UV/chlorination. The results of this study provide basic data and a theoretical basis for the formation and control of HNMs, which is conducive to applying UV/chlorination.

Leaching of organic matter from microplastics and its role in disinfection by-product formation

Natural organic matter (NOM) is the primary precursor of disinfection by-products (DBPs). However, as emerging environmental contaminants continue to increase in natural waters, there is a possibility of new precursors of DBPs. We investigated the potential of microplastics (MPs), a growing environmental concern, for leaching organic matter (OM) and subsequent DBP formation. Two experimental setups were used, including chlorinated water containing MPs (Cl2-MP), and non-chlorinated water containing MPs (Non-Cl2-MP), using polyethylene (PE), polyethylene tetrahydrate (PET), polypropylene (PP), and polyvinyl chloride (PVC) as MP materials. The UV absorbance spectra of Cl2-PET/PP/PVC showed peaks at 218 nm, which were significantly correlated with dissolved organic carbon (DOC), indicating lower aromaticity of the leached OM. The DOC concentrations in Cl2-MP samples were several times higher than those in Non-Cl2-MP samples. The leached OM from MPs formed trihalomethanes (THMs) and haloacetic acids (HAAs) in Cl2-MP samples. Among the MPs tested, PVC showed the highest total THM formation after 7 days, followed by PET, PE, and PP. Brominated THMs were predominant, while HAAs were highly chlorinated. THM formation increased with contact time for PE, PET, and PVC, and decreased for PP. Compared to THMs, the concentration of HAAs was low (highest total THM = 185.5 μg/L per g-MP and highest total HAA = 120.7 μg/L per g-MP). Further, the total THM concentration decreased and the total HAA concentration increased over the reaction period, indicating the leaching of different types of OM with increasing contact time. Additionally, the differences in the pattern of DOC leaching and DBP formation among different MPs suggested changes in the leached OM.

Evolutions of dissolved organic matter and disinfection by-products formation in source water during UV-LED (275 nm)/chlorine process

Ultraviolet light-emitting diode (UV-LED) is a promising option for the traditional low-pressure UV lamp, but the evolutions of DOM composition, the formation of disinfection by-products (DBPs) and their toxicity need further study in raw water during UV-LED/chlorine process. In UV-LED (275 nm)/chlorine process, two-dimensional correlation spectroscopy (2DCOS) analysis on synchronous fluorescence and UV-vis spectra indicated the protein-like fractions responded faster than the humic-like components, the reactive sequence of peaks for DOM followed the order: 340 nm→240 nm→410 nm→205 nm→290 nm. Compared to chlorination for 30 mins, the UV-LED/chlorine process enhanced the degradation efficiency of three fluorescent components (humic-like, tryptophan-like, tyrosine-like) by 5.1%-46.1%, and the formation of carbonaceous DBPs (C-DBPs) significantly reduced by 43.8% while the formation of nitrogenous DBPs (N-DBPs) increased by 27.3%. The concentrations of C-DBPs increased by 17.8% whereas that of N-DBPs reduced by 30.4% in 24 h post-chlorination. The concentrations of brominated DBPs increased by 17.2% during UV-LED/chlorine process, and further increased by 18.5% in 24 h post-chlorination. According to the results of principal component analysis, the non-fluorescent components of DOM might be important precursors in the formation of haloketones, haloacetonitriles and halonitromethanes during UV-LED/chlorine process. Unlike chlorine treatment, the reaction of DOM in UV-LED/chlorine treatment generated fewer unknown DBPs. Compared with chlorination, the cytotoxicity of C-DBPs reduced but the cytotoxicity of both N-DBPs and Br-DBPs increased during UV-LED/chlorine process. Dichloroacetonitrile had the highest cytotoxicity, followed by monobromoacetic acid, bromochloroacetonitrile and trichloroacetic acid during 30 mins of UV-LED/chlorine process. Therefore, besides N-DBPs, the more toxic Br-DBPs formation in bromide-containing water is also not negligible in the practical applications of UV-LED (275 nm)/chlorine process.

Chlorination disinfection by-products in Southeast Asia: A review on potential precursor, formation, toxicity assessment, and removal technologies

This review discusses disinfection by-products' (DBPs) potential precursors, formation, and toxicity, alongside available research on the treatment of DBPs in Southeast Asian countries' water sources. Although natural organic matter (NOM) in the form of humic and fulvic acids is the major precursor of DBPs formation, the presence of anthropogenic organic matter (AOM) also plays essential roles during disinfection using chlorine. NOM has been observed in water sources in Southeast Asian countries, with a relatively high concentration in peat-influenced water sources and a relatively low concentration in non-peat-influenced water sources. Similarly, AOMs, such as microplastics, pharmaceuticals, pesticides, and endocrine-disrupting chemicals (EDCs), have also been detected in water sources in Southeast Asian countries. Although studies regarding DBPs in Southeast Asian countries are available, they focus on regulated DBPs. Here, the formation potential of unregulated DBPs is also discussed. In addition, the toxicity associated with extreme DBPs' formation potential, as well as the effectiveness of treatments such as conventional coagulation, filtration, adsorption, and ozonation in reducing DBPs' formation potential in Southeast Asian sources of water, is also analyzed.