Dissolved Organic Matter Fractions and Their Removal in Full-Scale Drinking Water Treatment Process

Objectives The objective of this study is to investigate characteristics about removal of dissolved organic matter (DOM) and its fraction for improving operation efficiency in an advanced water treatment plant. Methods The monitoring of water quality was conducted at five processes such as raw water, pre-oxidation, after sedimentation, post-ozonation, after biological activated carbon (BAC) from July 2020 to August 2021 in advanced water treatment process (AWTP) supplying 180,000m3/day. The concentration of DOC (dissolved organic carbon) and number of algae were monitored and LC-OCD was used to fractionate DOC to four species, biopolymer (BP), humic substance (HS), building blocks (BB), and low molecular weights (LMWs). Results and Discussion The characteristics of raw water showed that the concentration of DOC and the number of algae increased with an increase in water temperature. The portion of BP and HS significantly increased at low and high water temperature, respectively, while BB and LMWs maintained the similar portion. The removal efficiency of DOC in the AWTP was achieved at 59% with each species of BP, HS, BB, and LMWs obtaining removal efficiency of 87%, 65%, 26%, and 52%, respectively. Coagulation/sedimentation/filtration showed removal efficiency of 84%, 56%, 20%, and 18% for BP, HS, BB, and LMWs, respectively, corresponding to their molecular weight. The effect of post-ozonation would be negligible except for BP. In BAC, removal efficiency of 49% and 12% were obtained for LMWs and BB (low molecular weight, respectively. As a result, the BP portion significantly decreased due to high removal efficiency, while BB portion was increased in the final treated water compared to raw water. Conclusion Most of DOM was removed in coagulation/sedimentation/filtration and BAC, whereas oxidation process such as pre-chlorination, pre-ozonation and post-oxidation did not have an effect on DOM removal. In coagulation/sedimentation/filtration, 84% and 54% of the BP and HS were removed, while BAC removed 49% and 12% of LMWs and BB, respectively. It has been recommended to improve the removal efficiency of BB, which obtained the lowest removal efficiency in AWTP, and to enhance the removal efficiency of LMWs in BAC to inhibit microbial regrowth in the distribution system

Enhancement of Biological Activated Carbon (BAC) Process to Improve Removal Efficiency of Micropollutants

Objectives In this study, the removal efficiency of micropollutants in the biological activated carbon (BAC) process was investigated, and a method for improving the removal efficiency of micropollutants in the BAC process of water treatment plants was proposed. Methods Dibromo-methylparaben (Br2-MP) was selected as the target micropollutant. Batch and lab-scale column experiments were conducted to evaluate the removal efficiencies of Br2-MP in the conventional BAC process and the BAC with enhanced biofilm properties by the addition of phosphorus (P) and hydrogen peroxide (H2O2). Biodegradation kinetics were evaluated using results from batch and lab scale column experiments. Results and Discussion As a result of comparing the removal efficiency of Br2-MP in a batch experiment with the same biomass concentrations (2.0±0.2×107 cells), the biodegradation rate constant (kbio) of the enhanced BAC process was found to be 1.2 times higher than that of the conventional BAC process due to its higher biological activity (enhanced BAC: 3.4±0.3 mg·C/g·hr, conventional BAC: 2.9±0.4 mg·C/g·hr). Comparison of removal efficiencies of Br2-MP in batch experiments with the same wet weight of BAC (1 g) showed that the biodegradation rate constant (kbio) of the enhanced BAC process was 1.9 times higher than that of conventional BAC process due to higher biomass (enhanced BAC: 3.5±0.4 µg·ATP/g·GAC, conventional BAC: 2.3±0.2 µg·ATP/g·GAC). Through the batch experiments, the enhanced BAC process was efficient in removing Br2-MP via increasing both biomass concentrations and activity of attached microorganisms. Lab-scale column experiments conducted under different water temperatures (5 and 25℃) and empty bed contact time (EBCT: 5-40 min) conditions showed higher removal efficiency of Br2-MP in the enhanced BAC process than the conventional BAC process throughout the entire period of operation. In particular, the removal efficiency of Br2-MP between the enhanced and conventional BAC processes showed significant differences at low temperature (5℃) and short EBCT (5 min). At 5℃ and 25℃, the kbio of the conventional BAC process was 0.0229 min-1 and 0.0612 min-1, respectively, and the kbio of the enhanced BAC process was 0.0470 min-1 and 0.1421 min-1, respectively, These results showed that the enhanced BAC process had two times higher biodegradability of Br2-MP than the conventional BAC process. These results showed a similar trend to the results from the batch experiment. In an experiments simulating the impact of frequent EBCT changes during summer, the enhanced BAC process maintained a relatively stable removal efficiency of Br2-MP compared to the conventional BAC process. Conclusion The enhanced BAC process showed superior biodegradation of micropollutant compared to the conventional BAC process. Considering economic costs (e.g., costs of adding phosphate and hydrogen peroxide) and water quality, it appears to be an efficient alternative to operate the enhanced BAC process intermittently, limited to cases where EBCT is shortened, such as summer, or when water temperature is low, such as in winter

Multifunctional in-situ ferrate treatment and its removal mechanisms of membrane bioreactor residual pollutants

Membrane bioreactors (MBRs) integrate the technique of membrane separation with biologically activated sludge and produce high-quality effluent that can be used for water reclamation. However, removal of residual pollutants, including phosphorus, non-biodegradable organic matter, and microorganisms, is necessary for water reuse in areas with high human exposure to water, necessitating further water treatment. In this study, ferrate (VI) was used to remove various residual pollutants that can be contained in the MBR effluents, and the removal mechanisms were studied by comparing with ferric chloride (FeCl3). Optimal ferrate production using the in situ wet oxidation method in the synthetic MBR effluent occurred at pH 7.0 and Fe3+:OCl- = 5, with a ferrate yield of 1.8 mg L-1. Based on the results of the jar test, the optimised ferrate dosage was 7.5 mg L-1, which removed 90% of total phosphorus, 20% of dissolved organic matter, and 90% of microorganisms in the real MBR effluent. Ferrate was more effective than FeCl3 even at a lower dosage (~25%). The simultaneous oxidising, coagulating, and disinfecting properties of ferrate are expected to reduce the number of post-treatment steps for water reclamation, thus reducing the capital and operational expenses

Hierarchical deep learning model to simulate phytoplankton at phylum/ class and genus levels and zooplankton at the genus level

Harmful algal blooms (HABs) have become a global issue, affecting public health and water industries in numerous countries. Because funds for monitoring HABs are limited, model development may be an alternative approach for understanding and managing HABs. Continuous monitoring based on grab sampling is timeconsuming, costly, and labor-intensive. However, improving simulation performance remains a major challenge in modeling, and current methods are limited to simulating phytoplankton (e.g., Microcystis sp., Anabaena sp., Aulacoseira sp., Cyclotella sp., Pediastrum sp., and Eudorina sp.) and zooplankton (e.g., Cyclotella sp., Pediastrum sp., and Eudorina sp.) at the genus level. The traditional modeling approach is limited for evaluating the interactions between phytoplankton and zooplankton. Recently, deep learning (DL) models have been proposed for solving modeling problems because of their large data handling capabilities and model structure flexibilities. In this study, we evaluated the applicability of DL for simulating phytoplankton at the phylum/class and genus levels and zooplankton at the genus level. Our work was an explicit representation of the taxonomic and ecological hierarchy of the DL model structure. The prerequisite for this model design was the data collection at two taxonomic and hierarchical levels. Our model consisted of hierarchical DL with classification transformer (TF) and regression TF models. These DL models were hierarchically connected; the output of the phylum/class level model was transferred to the genus level simulation model, and the output of the genus level model was fed into the zooplankton simulation model. The classification TF model determined the phytoplankton occurrence initiation date, whereas the regression TF model quantified the cell concentration of plankton. The hierarchical DL showed potential to simulate phytoplankton at the phylum/class and genus levels by producing average R2, and root mean standard error values of 0.42 and 0.83 [log(cells mL-1)], respectively. All simulated plankton results closely matched the measured concentrations. Particularly, the simulated cyanobacteria showed good agreement with the measured cell concentration, with an R2 value of 0.72. In addition, our simulated result showed good agreement in peak concentration compared to observations. However, a limitation remained in following the temporal variation of Tintinnopsis sp. and Bosmia sp. Using an importance map from the TF model, water temperature, total phosphorus, and total nitrogen were identified as significant variables influencing phytoplankton and zooplankton blooms. Overall, our study demonstrated that DL can be used for modeling HABs at the phylum/class and genus levels

Rational Generation of Fe-N-x Active Sites in Fe-N-C Electrocatalysts Facilitated by Fe-N Coordinated Precursors for the Oxygen Reduction Reaction

Fe-N-C catalysts synthesized by pyrolysis of Fe and N precursors have been intensively studied due to their remarkable activities for the electrochemical oxygen reduction reaction (ORR). Although Fe-N-4 coordinated structures have been suggested as active sites by recent spectroscopic studies, the influence of precursor coordination on the generation of the active sites during high-temperature pyrolysis is not well understood. In this work, phenanthroline isomers were used as systematic model precursors to reveal the correlation between precursor coordination and active site formation in Fe-N-C catalysts. Coordination between Fe and each phenanthroline isomer was effectively controlled by the molecular structure: monodentate (1,7- and 4,7-phenanthroline) and bidentate coordination (1,10-phenanthroline). Through X-ray absorption spectroscopy and X-ray photoelectron spectroscopy study, large difference in atomic distribution of both Fe and N was revealed; the preferential formation of Fe-N-x active sites was featured only in Fe(1,10-phenanthroline)/KB with homogeneously distributed Fe and highly retained pyridinic N. With Fe-N-x active site moieties, Fe(1,10-phenanthroline)/KB exhibited superior ORR activity and stability in alkaline half-cell and full-cell tests. These results highlight the importance of the use of precursors with multiple coordination (i. e. bidentate) for the effective derivation of Fe-N-x active sites for highly active and stable ORR electrocatalysts. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim11sciescopu

Electrochemically Synthesized Nanoporous Molybdenum Carbide as a Durable Electrocatalyst for Hydrogen Evolution Reaction

Demands for sustainable production of hydrogen are rapidly increasing because of environmental considerations for fossil fuel consumption and development of fuel cell technologies. Thus, the development of high-performance and economical catalysts has been extensively investigated. In this study, a nanoporous Mo carbide electrode is prepared using a top-down electrochemical process and it is applied as an electrocatalyst for the hydrogen evolution reaction (HER). Anodic oxidation of Mo foil followed by heat treatment in a carbon monoxide (CO) atmosphere forms a nanostructured Mo carbide with excellent interconnections, and these structural characteristics lead to high activity and durability when applied to the HER. Additionally, characteristic behavior of Mo is observed; metallic Mo nanosheets form during electrochemical anodization by exfoliation along the (110) planes. These nanosheets are viable for chemical modification, indicating their feasibility in various applications. Moreover, the role of carbon shells is investigated on the surface of the electrocatalysts, whereby it is suggested that carbon shells serve as a mechanical barrier against the oxidative degradation of catalysts that accompanies unavoidable volume expansion © 2017 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Lithium manganese phosphate-carbon composite as a highly active and durable electrocatalyst for oxygen reduction reaction

Development of Pt-free electrocatalysts for oxygen reduction reaction (ORR) is one of the most important tasks for fuel cell commercialization. Various Mn compounds have been proposed as catalysts for ORR, but poor activity and stability necessitate further advances for their practical utilization. In this study, we demonstrate a lithium manganese phosphate-carbon composite (LMP-C) as a highly active and durable electrocatalyst for ORR in alkaline medium. LMP-C, synthesized by the solid-state method, exhibited significantly enhanced electrical conductivity and electrochemical properties, which led to a substantial increase in ORR performance. Comparison between LMP-C and the manganese phosphate-carbon composite, based on various physicochemical characterizations, revealed a high preference for the formation of the Mn3+ state on the surface of LMP-C that resulted in effective charge transfer during oxygen reduction. Moreover, the excellent stability of LMP-C was confirmed by carrying out 3000 cycles of the accelerated durability test, in which no drop in ORR performance was observed. © 2017 Elsevier Lt1

Tailoring the porosity of MOF-derived N-doped carbon electrocatalysts for highly efficient solar energy conversion

Metal-organic framework (MOF)-derived carbon materials have been widely used as catalysts for a variety of electrochemical energy applications, and thermally carbonized zinc-2-methylimidazole (ZIF-8) has shown particularly high performance owing to its microporous structure with a large surface area. However, in the presence of bulky chemical species, such as triiodide, in mesoscopic dye-sensitized solar cells (DSCs), the small pore size of carbonized ZIF-8 causes a significant limitation in mass transfer and consequentially results in a poor performance. To resolve this problem, we herein report a simple strategy to enlarge the pore sizes of ZIF-8-derived carbon by increasing the dwelling time of Zn in ZIF-8 during the thermal carbonization process. A thin and uniform polydopamine shell introduced on the surface of ZIF-8, with the aim of retarding the escape of vaporized Zn species, leads to a dramatic increase in pore sizes, from the micropore to mesopore range. The porosity-tailored carbonized ZIF-8 manifests an excellent electrocatalytic performance in triiodide reduction, and when it was applied as the counter electrode of DSCs, an energy conversion efficiency of up to 9.03% is achievable, which is not only superior to that of the Pt-based counterpart but also among the highest performances of DSCs employing carbonaceous electrocatalysts. (c) 2018 The Royal Society of Chemistr