Dechlorination Research Articles

Interaction between nitrate and trichloroethene bioreduction in mixed anaerobic cultures

Bioremediation of trichloroethene (TCE)-contaminated sites often leads to groundwater acidification, while nitrate-polluted sites tend to generate alkalization. TCE and nitrate often coexist at contaminated sites; however, the pH variation caused by nitrate self-alkalization and TCE self-acidification and how these processes affect nitrate reduction and reductive dichlorination, have not been studied. This study investigated the interaction between nitrate and TCE, two common groundwater co-contaminants, during bioreduction in serum bottles containing synthetic mineral salt media and microbial consortia. Our results showed that TCE concentrations up to 0.3 mM stimulated nitrate reduction, while the effect of nitrate on TCE reductive dechlorination was more complex. Nitrate primarily inhibited the reduction of TCE to dichloroethene (DCE) but enhanced the reduction of vinyl chloride (VC) to ethene. Mechanistic analysis suggested that this inhibition was due to the thermodynamic favorability of nitrate reduction over TCE reduction, while the promotion of VC reduction was linked to pH stabilization via self-alkalization. As the initial nitrate concentration increased from 0 to 3 mM, the relative abundance of putatively denitrifying genera, such as Petrimonas and Trichlorobacter, increased. However, the abundance of fermentative Clostridium sharply declined from 31.11 to 1.51%, indicating strong nitrate inhibition. Additionally, the relative abundance of Dehalococcoides, a genus capable of reducing TCE to ethene, slightly increased from 23.91 to 24.26% at nitrate concentrations up to 0.3 mM but decreased to 18.65% as the nitrate concentration increased to 3 mM, suggesting that Dehalococcoides exhibits a degree of tolerance to high nitrate concentrations under specific conditions. Overall, our findings highlight the potential for simultaneous reduction of TCE and nitrate, even at elevated concentrations, facilitated by self-regulating pH control in anaerobic mixed dechlorinating consortia. This study provides novel insights into bioremediation strategies for addressing co-contaminated sites.

Monitoring the impact of chlorinated drinking water on the developing gut microbiota of adolescent mice using genetic profiling

ABSTRACT Water chlorination as a method to deter the growth of disease-causing microbes has been standard practice in the United States for over a century. Toxicological studies that originally designated chlorinated water as safe for the human host failed to consider its impact on the developing gut microbiota. Here, this oversight was addressed through comparative assessment of the gut microbiota from post-weaned mice (B6) provided either chlorine-free water or water containing 1–5 mg/L chlorine. Mice provided chlorinated water had a statistically significant decrease in levels of Clostridiaceae 1 and Peptostreptococcaceae, which corresponded to a decrease in virulence factors associated with porphyrin metabolism, which was considered related to a decrease in genes involved in adenosylcobalamin biosynthesis. Taken together, the results demonstrated that the gut microbiota of post-weaned mice were resilient to low levels of chlorine and chlorinated water did not elicit changes to diversity or cause any major community restructuring to occur.

Palladium Nanosheet Enables Synergistic Electrocatalytic Dehalogenation via Direct and Indirect Electron Transfer Mechanisms.

Electrocatalytic dehalogenation is a promising method for the remediation of chlorinated organic pollutants. The dehalogenation performance is controlled by catalytic activity, and the underlying electrocatalytic dehalogenation mechanisms need to be carefully investigated for guiding the design of catalyst. Here we report the preparation of a new Pd-based catalyst with a nanosheet structure (Pd NS) by a simple wet-chemical reduction method. This Pd NS catalyst showed a superior electrocatalytic activity toward the reductive dehalogenation of a chlorinated organic pollutant (e.g., 4-chlorophenol) with the dehalogenation rate of 0.324 h-1. Importantly, the obtained Pd NS catalyst had a good durability that could operate well over 30 h under high concentration of 4-chlorophenol with removal efficiency beyond 82%. Experimental results confirmed the simultaneous occurrence of direct electrocatalytic dehalogenation and H*-mediated indirect electron transfer mechanisms in the dehalogenation process, and their quantitative contributions to the dehalogenation performance were established based on the cyclic voltammetry and quenching experiments. This study provides a promising dehalogenation catalyst and sheds light on the mechanism of electrocatalytic dehalogenation as well as the development of a dual-functional electrocatalyst.

Nitrogen doping turns carbonaceous materials into fast-reacting catalysts for reductive dechlorination.

Nitrogen (N) doping of biomass prior pyrolysis has been identified as an effective approach for enhancing biochar catalytic reactivity. However, high-temperature pyrolysis of N-rich biomass may produce N-devoid biochars with high reactivity, calling for attention to the true causes of the reactivity increases and the role of nitrogen. In this study, N-doped wheat straw biochar (N-BC) materials were produced using urea as N dopant and different pyrolysis conditions, and their catalytic reactivity assessed for the reduction of trichloroethylene (TCE) by green rust (GR), a layered Fe(II)Fe(III) hydroxide. Overall, the extent and rate of TCE reduction increased from ∼8 to ∼90 % and 0.064 to 0.299 h-1, respectively, with increasing urea dosage from 0 to 25 wt%. A similar increase in catalytic activity was also seen with an increase in pyrolysis temperature during N-doping, from 600 to 800 or 1000 oC, while increasing pyrolysis duration had a lower impact. Principal component analysis and Pearson correlation analysis demonstrated some correlation between TCE catalytic reactivity and structural properties of N-BC materials. However, little correlation was seen between catalytic reactivity, and N content and N surface functional groups of N-BC materials; even though N surface functional groups are often described as the key redox active sites in these dechlorination reactions, and also the reason why N-doping is applied. For comparison, N-doping and TCE catalytic reactivity with GR was also performed with a highly conductive graphene (GP) substrate. N-doping of GP led to a similar increase in the rate and extent of TCE as was observed for N-BC, demonstrating the importance of N-doping to create catalytically active sites in these carbonaceous materials. Surprisingly, highly reactive N-GP materials produced at 800 and 1000 °C exhibited no N surface functional groups but instead, N-doping created structural defect sites. Overall, this study demonstrates that N-doping of the bio-substrate may increase catalysis of reductive dechlorination by a factor of ∼5 times but this is not due to the formation of catalytically active N-functional groups, rather we attribute it to changes of the carbonaceous material structure. With this understanding we can then embark on the production of catalytic active biochar materials also from other substrates than wheat straw, forming the basis for optimizing other reductive contaminant degradation systems.

Degradation kinetics, pathways, transformation products, and toxicity assessment of fluorochloridone in agricultural soils.

Flurochloridone (FLC) is a pyrrolidone herbicide used to control broad-leaved weeds in various crop fields. However, there is still a lack of comprehensive research on the environmental fate of the Qinghai-Tibet Plateau (QTP) and the toxicity of its potential transformation products (TPs). In this study, laboratory experiments were conducted to investigate the degradation kinetics, pathways, and toxicity of FLC's TPs. Nine TPs were identified in soil using Ultra-Performance Liquid Chromatography Quadrupole-Orbitrap Mass Spectrometry (UPLC-Q-Exactive Orbitrap MS) and Compound Discoverer software, employing suspect and nontarget screening strategies. The initial report of two TPs, TP204, and TP191 was confirmed through the acquisition or synthesis of their standards. High Performance Liquid Chromatography coupled with Tandem Mass Spectrometry (HPLC-MS/MS) was subsequently used for further quantification of these TPs in all samples under examination. The primary transformation reactions of FLC in the environment include oxidative dechlorination, reductive dechlorination, reductive defluorination, acetylation, and hydrolysis. Predictive assessments via ECOSAR, alongside empirical laboratory experiments, revealed that most novel TPs exhibit significantly lower acute toxicity towards Danio rerio, Daphnia magna Straus, and Algae compared to FLC. However, TP204 demonstrated neutral chronic toxicity towards Daphnia magna Straus and Green algae, potentially posing a latent threat to aquatic ecosystems. These results are crucial for elucidating the environmental fate of FLC, assessing environmental risks, and guiding scientific and reasonable use. This research holds significant importance for the ecological environment protection in the Tibetan Plateau region.

Edema disease in two gold-spotted pond frogs (Pelophylax chosenicus) raised in captivity: two case reports

Two gold-spotted pond frogs (Pelophylax chosenicus) experienced anorexia, buoyancy without diving, and systemic swelling for 1 month and died several days later. On necropsy, the liver had protruding dark gray nodules scattered on its surface, and the kidneys were fat-like beige. Bacteriology showed the presence of Citrobacter braakii, Delftia acidovorans, Elizabethkingia spp., and Chryseobacterium indologenes. On microscopy, the liver showed melanomacrophagic aggregates, inflammatory cell infiltration, and fibrosis. In the case of these frogs, the edema disease is suspected to have been caused by long-term exposure to chlorine and chloramines in tap water rather than infection.

Amplicon sequences of sourdough starter cultures treated with varying levels of water chlorination.

Here, we present amplicon sequences from sourdough starter cultures that have been treated with a chlorine concentration gradient mirroring public water distribution systems. Data derived present insights into the effect of important environmental factors that may influence the formation of microbial communities in food biomes.

Modeling Water Age and Chlorine Reduction Effects on Water Quality in the Distribution Network of the Lower Usuma Dam Using EPANET

Modeling Water Age and Chlorine Reduction Effects on Water Quality in the Distribution Network of the Lower Usuma Dam Using EPANET

Dehalogenimonas Strain W from Estuarine Sediments Dechlorinates 1,2-Dichloroethane under Elevated Salinity.

Organohalide-respiring bacteria (OHRB) have been found in various environments and play an indispensable role in the biogeochemical cycling and detoxification of halogenated organic compounds (HOCs). Currently, few ORHB have been reported to perform reductive dechlorination under high salinity conditions, indicating a knowledge gap on the diversity of OHRB and the survival strategy of OHRB in saline environments (e.g., estuarine, marine). This study reports the characterization of an enrichment culture dominated by a new Dehalogenimonas population strain W derived from estuarine sediments, which demonstrates the capability to dechlorinate 1,2-dichloroethane (1,2-DCA) to ethene under elevated salinity (≥5.1% NaCl, w/v). Metagenomic and proteomic analyses revealed that the distinctive high-salinity dechlorination of strain W is primarily attributed to a putative reductive dehalogenase (RDase) DdeA, which shares >91.4% amino acid identity with the dihaloeliminating RDase DcpA from other Dehalogenimonas strains. Additionally, ectoine biosynthesis enzymes (EctABC) contribute to the strain's salt tolerance. These findings underscore the potential of OHRB, particularly Dehalogenimonas, to detoxify HOCs in high-salinity environments, such as estuarine and marine ecosystems, by employing compatible solutes as an adaptive mechanism.

Assessing the factors affecting the use of chlorine dispensers for household water treatment in rural Kenya, Malawi, and Uganda

ABSTRACT Although chlorination is widely accepted as a safe and cost-effective water treatment method, its adoption by the rural populations remains low. This leaves about 26% of the world's population – including 70% in Sub-Saharan Africa – with a lack of access to safely managed drinking water and exposure to hazards of drinking unsafe water. This work used data collected in a repeated cross-sectional study conducted between 2021 and 2022 in Kenya, Uganda, and Malawi to assess factors that influence a community's adoption of chlorine to treat water. The results indicate that households that observed good water storage and handling practices, had knowledge on the benefits of chlorine, understood the correct procedure of using chlorine dispensers, received promotional messages, and used functional chlorine dispensers were more likely to have chlorine residual in their drinking water. Conversely, households where children collected the drinking water were less likely to have chlorine residual in their drinking water. Community promoters who themselves used chlorinated water were associated with a higher chlorine adoption by the communities they serve. The study recommends continuous community education on chlorine water treatment; training on water collection, storage, and handling practices; extending water treatment education to children; and ensuring robust chlorine supply chains.

Catalytic Promiscuity of Fatty Acid Photodecarboxylase Enables Stereoselective Synthesis of Chiral α-Tetralones.

In the field of biocatalysis, discovering novel reactivity from known enzymes has been a longstanding challenge. Fatty acid photo-decarboxylase from Chlorella variabilis (CvFAP) has drawn considerable attention as a promising photoenzyme with potential green chemistry applications; however, its non-natural reactivity has rarely been exploited to date. Herein we report a non-natural reductive dehalogenation (deacetoxylation) reactivity of CvFAP inspired by its natural oxidative decarboxylation process, enabling the stereoselective synthesis of a series of chiral α-substituted tetralones with high yields (up to 99 %) and e.r. values (up to 99 : 1). Mechanistic studies demonstrated that the native photoenzyme catalyzed the reductive dehalogenation via a novel mechanism involving oxidized state (FADox)/semiquinone state (FADsq) redox pair and an electron transfer (ET)/proton transfer (PT) process of radical termination, distinct from the previous reports. To our knowledge, this study represents a new example of CvFAP promiscuity, and thus expands the reactivity repertoire of CvFAP and highlights the versatility of CvFAP in asymmetric synthesis.

INTENSITY OF CHEMICAL NEUTRALISATION OF CHLORINE DURING PRECIPITATION BY A FINELY DISPERSED LIQUID STREAM

One of the main tasks of the unified state system of civil protection is to forecast and assess the socio-economic consequences of emergencies, determine the need for forces, means, material and financial resources based on the forecast; carry out rescue and other urgent work to eliminate the consequences of emergencies, and organise life support for the affected population. The paper modifies the model of chlorine sorption by a fine liquid flow. The developed mathematical model allows to take into account the following basic parameters of sorption, environmental parameters, parameters of the liquid flow supplied for deposition and physical and chemical properties of the liquid in this flow. The developed model allows minimising the number of input parameters and the forecasting time, which is critical for emergency response. The results of numerical modelling have shown that the deposition of chlorine, which is a low-valent gas in water, is determined by the Henry's constant, and not by the intensity of the liquid flow, as previously thought. The poor solubility of chlorine in water does not provide significant efficiency (6% compared to ammonia) of its deposition by dispersed streams even at maximum intensity, which confirms the need for rescue units to use water-soluble additives that are chemically active to react with chlorine. It is also worth noting the logarithmic nature of the dependence of gas deposition intensity on the intensity of the dispersed flow. This can be explained by the fact that the intensity of sorption decreases due to a decrease in gas concentration, which in turn decreases due to the absorption process. Therefore, it is possible to determine the critical intensity of the liquid dispersion flow at which the sorption intensity almost stabilises. This confirms the urgent need for rescue units to use chemical neutralisers in the elimination of accidents involving chlorine emissions into the atmosphere.

WQI Improvement Based on XG-BOOST Algorithm and Exploration of Optimal Indicator Set

This paper takes a portion of the Manas River Basin in Xinjiang Province, China, as an example and proposes an improved traditional comprehensive water quality index (WQI) method using Extreme Gradient Boosting (XG-BOOST) to analyze the groundwater quality levels in the region. Additionally, XG-BOOST is used to screen the existing dataset of ten water quality indicators, including fluoride (F), chlorine (Cl), nitrate (NO), sulfate (SO), silver (Ag), aluminum (Al), iron (Fe), lead (Pb), selenium (Se), and zinc (Zn), from 246 monitoring points, in order to find the dataset that optimizes model training performance. The results show that, in the selected study area, water quality categorized as “GOOD” and “POOR” accounts for the majority, with “GOOD” covering 48.7% of the area and “POOR” covering 31.6%. Regions with water quality classified as “UNFIT” are mainly distributed in the central–eastern parts of the study area, located in parts of the Changji Hui Autonomous Prefecture. Comparatively, water quality in the western part of the study area is better than that in the eastern part, while areas with “EXCELLENT” water quality are primarily distributed in the southern parts of the study area. The optimal water quality indicator dataset consists of five indicators: Cl, NO, Pb, Se, and Zn, achieving an accuracy of 98%, RMSE = 0.1414, and R2 = 0.9081.

Transition-Metal Free Amination and Hydrodefluorination of Aryl Fluorides Promoted by Solvated Electrons.

Cross-coupling reactions for constructing C-N bonds represent a pivotal advancement in chemical science. Traditional methodologies, including nucleophilic aromatic substitution (SNAr) and transition metal-catalyzed cross-couplings, have limitations concerning aryl scope, reliance on toxic and costly transition-metal catalysts, and issues related to atom economy and waste generation from ligands and additives. In this work, we introduce a novel method for aminating neutral, electron-rich, and electron-deficient aryl halides, eliminating the need for transition metals. Our approach involves the activation of aryl halides using solvated electrons generated from granulated lithium and sonication. This serves as a sustainable source of reducing power, facilitating the efficient formation of C-N bonds under near ambient conditions. Competitive selectivity studies between halide and ester functionalities were explored. Reaction scope and conducted mechanistic studies which supported the proposed radical-nucleophilic substitution (SRN1) mechanism for the reaction. Notably, the developed reaction has a highly competitive reductive dehalogenation pathway during the C-N coupling reaction, and this mechanistic divergency was thoroughly explored. This work not only broadens the scope of C-N coupling reactions which typically employs aryl bromides and iodides and rarely aryl fluorides which is also equally abundant, but also introduces a new way to do C-N coupling reactions using solvated electrons.

Ultrafast Synthesis of IrB1.15 Nanocrystals for Efficient Chlorine and Hydrogen Evolution Reactions in Saline Water.

The production of storable hydrogen fuel through water electrolysis powered by renewable energy sources such as solar, marine, geothermal, and wind energy presents a promising pathway toward achieving energy sustainability. Nevertheless, state-of-the-art electrolysis requires support from ancillary processes which often incur financial and energy costs. Developing electrolysers capable of directly operating with water that contains impurities can circumvent these processes. Herein, we demonstrate the efficient and durable electrolysis of saline water to produce chlorine gas (Cl2) and hydrogen using structurally ordered IrB1.15, synthesized through ultrafast joule heating. IrB1.15 exhibits remarkable performance, achieving overpotentials of 75 mV for the chlorine evolution reaction (CER) and 12 mV for hydrogen evolution reactions (HER) at current densities of 10 mA cm-2. Moreover, IrB1.15 displays a durability of over 90 h towards both CER and HER. Density functional theory reveals that IrB1.15 has adsorption energies significantly closer to 0 eV for Cl and H, compared to IrO2 and Pt/C. Furthermore, in situ Raman investigations reveal that Ir in IrB1.15 serves as the active center for CER, while the introduction of B atoms to Ir lattices mitigates the formation of absorbed hydrogen species on the Ir surface, thereby enhancing the performance of IrB1.15 in HER.

Ultrafast Synthesis of IrB1.15 Nanocrystals for Efficient Chlorine and Hydrogen Evolution Reactions in Saline Water

The production of storable hydrogen fuel through water electrolysis powered by renewable energy sources such as solar, marine, geothermal, and wind energy presents a promising pathway toward achieving energy sustainability. Nevertheless, state‐of‐the‐art electrolysis requires support from ancillary processes which often incur financial and energy costs. Developing electrolysers capable of directly operating with water that contains impurities can circumvent these processes. Herein, we demonstrate the efficient and durable electrolysis of saline water to produce chlorine gas (Cl2) and hydrogen using structurally ordered IrB1.15, synthesized through ultrafast joule heating. IrB1.15 exhibits remarkable performance, achieving overpotentials of 75 mV for the chlorine evolution reaction (CER) and 12 mV for hydrogen evolution reactions (HER) at current densities of 10 mA cm−2. Moreover, IrB1.15 displays a durability of over 90 h towards both CER and HER. Density functional theory reveals that IrB1.15 has adsorption energies significantly closer to 0 eV for Cl and H, compared to IrO2 and Pt/C. Furthermore, in‐situ Raman investigations reveal that Ir in IrB1.15 serves as the active center for CER, while the introduction of B atoms to Ir lattices mitigates the formation of absorbed hydrogen species on the Ir surface, thereby enhancing the performance of IrB1.15 in HER.

A Novel Process for Extracting Lead and Zinc from Low-Grade Lead–Zinc Ore Via Low-Temperature Chlorination Roasting and Water Leaching

A Novel Process for Extracting Lead and Zinc from Low-Grade Lead–Zinc Ore Via Low-Temperature Chlorination Roasting and Water Leaching

Protecting the Safe Water Chain in Refugee Camps: An Exploratory Study of Water Handling Practices, Chlorine Decay, and Household Water Safety in South Sudan, Jordan, and Rwanda.

In refugee and internally displaced person settlements, hygienic water handling and free residual chlorine (FRC) are crucial for protecting water against recontamination after distribution up to the household point-of-consumption. We conducted a secondary analysis of water quality and water handling data collected in refugee camps in South Sudan, Jordan, and Rwanda using statistical and process-based modeling to explore how water handling practices affect FRC decay and household FRC outcomes. The two practices that consistently produced a significant effect on FRC decay and household FRC were storing water in direct sunlight and transferring water between containers during household storage. Samples stored in direct sunlight had 0.22-0.31 mg/L lower household FRC and had FRC decay rates between 2 and 3.7 times higher than samples stored in the shade, and samples that were transferred between containers had 0.031-0.51 mg/L lower household FRC and decay rates 1.65-3 times higher than non-transferred samples in sites in which the effect was significant, suggesting that humanitarian responders should aim to provide additional water storage containers to prevent water transferring in households and encourage water-users not to store water in direct sunlight. By contrast, the effect of the three recommended hygienic water handling behaviors (clean, covered containers and drawing by tap or pouring) was mixed or inconclusive. These inconclusive results were likely due to imbalanced or unreliable approaches to gathering the data, and we recommend that hygienic water handling practices that mechanistically provide a physical barrier against recontamination should always be promoted in humanitarian settings.

Reductive dechlorination of trichloroethene at concentrations approaching saturation by a Desulfitobacterium-containing community.

In dense nonaqueous phase liquid (DNAPL) contaminant source zones, aqueous concentrations of trichloroethene (TCE) in groundwater may approach saturation levels (8.4 mM). It is generally believed that such saturation concentrations are toxic to organohalide-respiring bacteria (OHRB), thus limiting the effectiveness of bioremediation. Here, we describe a Desulfitobacterium-containing culture capable of dechlorinating TCE to cis-dichloroethene (cis-DCE) at aqueous concentrations as high as 8.0 mM. A novel Desulfitobacterium population, designated as strain THU1, was identified by the 16S rRNA gene-targeted polymerase chain reaction and Illumina MiSeq sequencing. Microbial community analysis revealed that TCE concentrations above 4.6 mM significantly affected the composition of the microbial community but had little effect on the Shannon index. The genome of strain THU1 revealed two reductive dehalogenases (RdhA), and the RdhA2 is a putative pceA. Additionally, its genome encodes proteins involved in stress response and regulatory pathways, enabling tolerance to near-saturation TCE concentrations. Our findings provide insights into the metabolic flexibility of Desulfitobacterium, suggesting its potential use as a candidate for source zone bioremediation to enhance the dissolution of TCE DNAPL by increasing the concentration gradient at the DNAPL-water interface.

Machine Learning-Assisted High-Throughput Experiments for Selective Seawater Electrolysis

Global warming is an urgent issue for our planet thereby many countries has declared to achieve zero emission of carbon dioxide in 2050s. In the next generation industry, electricity produced from renewable energy becomes major energy while heat is a major in the current industry. Therefore, electrochemical process should play a critical role. For example, water electrolysis and seawater electrolysis combined with solar energy or wind energy to produce hydrogen must be developed. However, developing non-precious electrocatalysts with high catalytic activity is still a big challenge in material science.Among various electrochemical processes, seawater electrolysis is recently paid much attention as an attractive process for cost effective hydrogen production. In sea water electrolysis, oxygen, chlorine, or hypochlorous acid (HClO) is evolved at anodic side as well as hydrogen in cathodic reaction. In this reaction, HClO is usually regarded as undesired byproduct in mass production. On the other hand, HClO can be high-value-added oxidative material than oxygen, contributing to a cost-effective system, especially in the case of rather small distributed system. Therefore, it is important to selectively generate both oxidative products.Recently, many papers investigated the potential research scheme which is supported by machine learning and/or robots. Here, the authors developed the high-throughput automatic robot for electrochemistry (namely HARfE) as shown in Fig. 1. High-throughput screening of 4-element system was performed for salted water (NaCl solution) electrolysis that is a model reaction for sea water electrolysis.This robot is able to perform fully automatically from preparing samples to measuring electrochemistry. Mainly, this robot is consisted of two parts; sample preparation part, and sample measuring part. HARfE can prepare 88 separated samples in a single run and subsequently measure electrochemistry. One notable advantage of this robot is that the robot can perform almost the same procedure as human researchers do using almost the same sizes of facilities as human researchers use, intending that this robot system can replace human labor force. The size of electrodes (≈0.5 cm2), an electrochemical cell (21 mL of solution), and measurement conditions are very similar to those of human researchers. In addition, a relatively long-term measurement such as stability test which requires a certain amount of solution is also able to be done. Hence, the robot can cover a wide range of electrochemical measurements.The typical procedures are the following. First, the pipetting arm dispenses and mixes up to ten kinds of solution that include metal ion. Second, the robot drops the mixed solution onto the substrates such as F-doped tin oxide (FTO) with a size of 5 mm by 30 mm and dry them on a hotplate. Third, the transfer arm transports the sample holders to an electrical furnace to calcine. Then, the picking-up arm transfers each obtained electrode to a H-type cell to perform electrochemical measurements. Finally, the pipetting arm dispenses a small amount of solution from the cell, mixes with color reagent, subsequently measures absorption to quantitate the products. After each measurement, solution was changed automatically from a tank behind the robot.In this study, the composition effect of Co-Mn-Fe-Ni-Cr electrocatalysts was investigated. Current density at 2.0 V vs. Ag|AgCl reference electrode, Faraday efficiency for hypochlorous acid/oxygen when 1 mA of current flew for 200 s (0.2 C), and the ratio of current density at 2.0 V vs. Ag|AgCl after 1000 s and 100 s were calculated. It was revealed that the obtained color maps clearly showed the composition dependence, and that The optimal composition varied depending on each evaluation criterion. For example, Co-rich composition provides high current densities and Mn-rich electrodes produced little HClO. It is notable that NiO x exhibited poor stability while stability was drastically improved by combining with FeO x .In addition, we demonstrated the composition optimization using Bayesian optimization (BO) algorithm. In this case, we used the dataset of Co-Mn-Fe-Ni four elements system with 286 data points. Composition is explanatory variables and current density at 2.0 V vs. Ag|AgCl is the target variable. Usually, BO-assisted experiment was performed one sample by one sample. Contrary, HARfE can deal with multiple samples in a single run. Therefore, multi-sample Gaussian process regression was performed to effectively search superior compositions. The detailed results will be shown in the presentation. Figure 1