The influence of nanostructure and electrolyte concentration on the performance of nickel sulfide (Ni3S2) catalyst for electrochemical overall water splitting.

Developing non-precious nanostructured electrocatalysts, exhibiting high catalytic activity in combination with excellent stability, has an enormous potential to replace noble-metal-based catalysts for Hydrogen production through electrochemical water splitting. In this study, a facile method is used for the synthesis of three different hierarchical nanostructures of nickel sulfide (Ni3S2) including nanosheets, nanorods, and multiconnected nanorods that are directly grown on 3D nickel foam (NF). These nanostructured electrocatalysts are evaluated for electrochemical water splitting in alkaline media using four different concentrations to understand the effect of nanostructure and ion concentration on the efficiency. Among different combinations of structure and electrolyte concentration, the Ni3S2 in the form of nanosheets exhibited the best electrocatalytic performance for hydrogen evolution reaction (HER) as well as oxygen evolution reaction (OER) in 3.0 M alkaline solution. The hierarchical Ni3S2 nanosheets exhibited a high electrochemically active surface area, which facilitated the charge transport phenomenon along the electrode-electrolyte interface in a higher electrolyte concentration that improved the reaction kinetics so as overall water splitting. The developed Ni3S2 nanosheets required an overpotential of 110 mV (@10 mA cm-2) and 211 mV (@100 mA cm-2) for HER and OER, respectively in 3.0 M electrolyte concentration. This work provides insight into how the materials' nanostructures and electrolyte concentration could be utilized to improve the electrocatalytic performance for an overall water-splitting process, and the concept could be applied for material designing and conditions optimization for other catalytic applications.

Mechanism Analysis of Discharge Energy in the Electrostatic-Field-Induced Electrolyte Jet Micro-EDM.

The discharge energy determines the machining resolution, minimum processable feature size, and surface roughness, which makes it a hot research topic in the microelectrical discharge machining (EDM) field. In this paper, a kind of novel discharge-energy-generation method in micro-EDM is investigated. In this method, the opposite induced charges on the electrolyte jet and workpiece serve as the source of the discharge energy. The operating mechanism of this discharge energy is revealed by analyzing the equivalent discharge circuit. The unique discharge current and voltage between the electrolyte jet and the workpiece are sampled and investigated. In contrast with the pulsating energy in conventional EDM, this study shows that the direct current (DC) voltage source can automatically generate a continuously periodical pulsating discharge in the electrostatic-field-induced electrolyte jet (E-Jet) EDM process. After further analyzing the electric signals in a single discharge process, it can be found that the interelectrode voltage experienced a continuous sharp electric breakdown, a nearly unchanging process, and a fast exponential recharging process. The discharge frequency increases as the electrolyte concentration and interelectrode voltage increase but decreases as the interelectrode distance increases. The discharge energy per pulse increases with the increasing interelectrode distance and electrolyte concentration but with the decreasing interelectrode voltage. Finally, the electrostatic-field-induced discharge-energy generation and change mechanisms are revealed, which provides a feasible method for micro-EDM with continuous tiny pulsed energy only using the DC power supply.

How does calcium and sodium in saline water affect the potential of different rates and size of sugarcane biochar to soil water repellency remediation?

Soil water repellency (SWR) is a growing problem in arid and semiarid regions with non-saline water limitations. The objective of this study was to investigate the potential of different rates and sizes of sugarcane biochar on reducing soil water hydrophobicity when using saline and non-saline water. Eleven sugarcane biochar application rates from 0 to 10% with two different sizes including <0.25 and 0.25-1 mm were studied. The experiment was conducted in two strongly and extremely water-repellent soil. In addition, to investigate the effect of electrolyte concentration on biochar potential for SWR reduction, calcium chloride and sodium chloride electrolyte solutions with 5 concentrations including 0, 0.15, 0.3, 0.45 and 0.6 mol L-1 were considered. The results showed that both sizes of biochar reduced the soil water repellency. While in strongly repellent soil the 4% biochar was enough to change the soil from strongly repellent to hydrophilic, in extremely water-repellent soil, the use of 8% of fine biochar and 6% of coarse biochar changed the extremely water-repellent soil to slightly hydrophobic and strongly hydrophobic respectively. Increasing the electrolyte concentration caused the expansion of soil hydrophobicity and reduced the positive effect of biochar to water repellency management. Increasing the electrolyte concentration in sodium chloride solution has a greater effect on increasing hydrophobicity than in calcium chloride solution. In conclusion, biochar could suggest as a soil-wetting agent in these two hydrophobic soils. However, the salinity of water and the its dominant ion could increase the amount of biochar for soil repellency reduction.

Effect of Electrolyte Concentration on the Electrochemical Performance of Spray Deposited LiFePO4.

LiFePO4 is a common electrode cathode material that still needs some improvements regarding its electronic conductivity and the synthesis process in order to be easily scalable. In this work, a simple, multiple-pass deposition technique was utilized in which the spray-gun was moved across the substrate creating a "wet film", in which-after thermal annealing at very mild temperatures (i.e., 65 °C)-a LiFePO4 cathode was formed on graphite. The growth of the LiFePO4 layer was confirmed via X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. The layer was thick, consisting of agglomerated non-uniform flake-like particles with an average diameter of 1.5 to 3 µm. The cathode was tested in different LiOH concentrations of 0.5 M, 1 M, and 2 M, indicating an quasi-rectangular and nearly symmetric shape ascribed to non-faradaic charging processes, with the highest ion transfer for 2 M LiOH (i.e., 6.2 × 10-9 cm2/cm). Nevertheless, the 1 M aqueous LiOH electrolyte presented both satisfactory ion storage and stability. In particular, the diffusion coefficient was estimated to be 5.46 × 10-9 cm2/s, with 12 mAh/g and a 99% capacity retention rate after 100 cycles.

A Nano Refractive Index Sensing Structure for Monitoring Hemoglobin Concentration in Human Body.

This paper proposes a nanosensor structure consisting of a metal-insulator-metal (MIM) waveguide with a rectangular root and a double-ring (SRRDR) with a rectangular cavity. In this paper, the cause and internal mechanism of Fano resonance are investigated by the finite element method (FEM), and the transport characteristics are optimized by changing various parameters of the structure. The results show that the structure can achieve double Fano resonance. Due to the destructive disturbance between the wideband mode of the inverted rectangle on the bus waveguide and the narrowband mode of the SRRDR, the output spectrum of the system shows an obvious asymmetric Fano diagram, and the structural parameters of the sensor have a great influence on the Fano resonance. By changing the sensitive parameters, the optimal sensitivity of the refractive index nanosensor is 2280 nm/RIU, and the coefficient of excellence (FOM) is 76.7. In addition, the proposed high-sensitivity nanosensor will be used to detect hemoglobin concentration in blood, which has positive applications for biosensors and has great potential for future nanosensing and optical integration systems.

Lactation mastitis: Promising alternative indicators for early diagnosis.

Although lactation mastitis (LM) has been extensively researched, the incidence rate of LM remains a salient clinical problem. To reduce this incidence rate and achieve a better prognosis, early and specific quantitative indicators are particularly important. It has been found that milk electrolyte concentrations (chloride, potassium, and sodium) and electrical conductivity (EC) significantly change in the early stages of LM in an animal model. Several studies have evaluated EC for the detection of subclinical mastitis in cows. EC, chloride, and sodium content of milk were more accurate for predicting infection status than were other variables. In the early stages of LM, lactic sodium, chloride, and EC increase, but potassium decreases. However, these indicators have not been reported in the diagnosis of LM in humans. This review summarizes the pathogenesis and the mechanism of LM in terms of milk electrolyte concentration and EC, and aim to provide new ideas for the detection of sub-clinical mastitis in humans.

Ultra-Low Concentration Electrolyte Enabling LiF-Rich SEI and Dense Plating/Stripping Processes for Lithium Metal Batteries.

The interface structure of the electrode is closely related to the electrochemical performance of lithium-metal batteries (LMBs). In particular, a high-quality solid electrode interface (SEI) and uniform, dense lithium plating/stripping processes play a key role in achieving stable LMBs. Herein, a LiF-rich SEI and a uniform and dense plating/stripping process of the electrolyte by reducing the electrolyte concentration without changing the solvation structure, thereby avoiding the high cost and poor wetting properties of high-concentration electrolytes are achieved. The ultra-low concentration electrolyte with an unchanged Li+ solvation structure can restrain the inhomogeneous diffusion flux of Li+ , thereby achieving more uniform lithium deposition and stripping processes while maintaining a LiF-rich SEI. The LiIICu battery with this electrolyte exhibits enhanced cycling stability for 1000 cycles with a coulombic efficiency of 99% at 1 mA cm-2 and 1 mAh cm-2 . For the LiIILiFePO4 pouch cell, the capacity retention values at 0.5 and 1 C are 98.6% and 91.4%, respectively. This study offers a new perspective for the commercial application of low-cost electrolytes with ultra-low concentrations and high concentration effects.

Wearable Microfluidic Sensor for the Simultaneous and Continuous Monitoring of Local Sweat Rates and Electrolyte Concentrations.

Temperature elevation due to global warming increases the risks of dehydration, which can induce heat-related illness. Proper rehydration with appropriate amounts of water and electrolytes is essential to aid body fluid homeostasis. Wearable sweat sensors which can monitor both the sweat rate and sweat electrolyte concentration may be an effective tool for determining appropriate rehydration. Here, we developed a novel potentially wearable sensor that can monitor both the local sweat rate and sweat electrolyte concentration continuously. The new device includes a system with a short microfluidic pathway that guides the sweat appearing on the skin to a small space in the device to form a quantifiable droplet. The sweat rate is assessed from the time for the droplet to appear and droplet volume, while an integrated electric sensor detects the sodium chloride concentration in each sweat droplet. We demonstrated that this new device could record both the flow rates of artificial sweat and its sodium chloride concentration in ranges of human sweating with an accuracy within ±10%. This is equivalent to the accuracy of commercially available sweat rate meters and sweat ion sensors. The present study provides a new perspective for the design of wearable sensors that can continuously monitor sweat rates and sweat electrolyte concentrations for potential application to a healthcare device.

Stabilizing the Nanosurface of LiNiO2 Electrodes by Varying the Electrolyte Concentration: Correlation with Initial Electrochemical Behaviors for Use in Aqueous Li-Ion Batteries.

This study attempted to stabilize the nanosurface of LiNiO2 (LNO) electrodes by varying the electrolyte concentration, significantly influencing its initial electrochemical behaviors for use in aqueous lithium-ion batteries. The charge/discharge capacities, reversibility, and cyclability of LNO were improved during initial cycles with an increase in the concentration of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). As determined by the galvanostatic intermittent titration technique, the superior diffusivity of Li+ ions in the LNO electrode is also obtained in the concentrated electrolyte. Nanoscale observation of the LNO surface revealed that its morphology is maintained relatively well in the concentrated electrolyte while it is destroyed in dilute electrolytes after the initial electrochemical cycles. These results are considered to be attributable to the variation of the interface condition in the electrical double layer with an increase in the electrolyte concentration, thus stabilizing the nanosurface of LNO by suppressing the dissolution of Ni ions from the surface. Additionally, in situ X-ray diffraction analysis demonstrated that LNO shows more stable phase transitions and volume changes as the electrolyte concentration increases, indicating that its structural changes in bulk can be directly related to the state of the nanosurface, which has a positive impact on the initial electrochemical behaviors in this system.

Influence of Electrolyte Concentration on Single-Molecule Sensing of Perfluorocarboxylic Acids.

Perfluorocarboxylic acids (PFCAs) are an emerging class of persistent organic pollutants. During the fabrication process, it is unavoidable to form PFCA homologs or isomers which exhibit distinct occurrence, bioaccumulation, and toxicity. The precision measurement of PFCAs is therefore of significant importance. However, the existing characterization techniques, such as LC-MS/MS, cannot fully meet the requirement of isomer-specific analysis, largely due to the lack of authentic standards. Single-molecule sensors (SMSs) based on nanopore electrochemistry may be a feasible solution for PFCAs determination, thanks to their ultra-high spatiotemporal resolutions. Hence, as a first step, this work was to elucidate the influence of electrolyte concentration on the four most critical indicators of nanopore measurements, and furthermore, performance of nanopore SMSs. More specifically, three of the most representative short-chain PFCAs, perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA) and perfluoroheptanoic acid (PFHpA), were adopted as the target analytes, aerolysin nanopore was employed as the sensing interface, and 2, 3 and 4 M KCl solutions were used as electrolytes. It was found that, when the concentration of KCl solution increased from 2 to 4 M, the conductance of aerolysin nanopore increased almost linearly at a rate of 0.5 nS per molar KCl within the whole voltage range, the current blockade of PFPeA at -50 mV increased from 61.74 to 66.57% owing to the enhanced steric exclusion effect, the maximum dwell time was more than doubled from 14.5 to 31.5 ms, and the barrier limited capture rate increased by 8.3 times from 0.46 to 3.85 Hz. As a result, when using 4 M KCl as the electrolyte, over 90% of the PFPeA, PFHxA and PFHpA were accurately identified from a mixed sample, and the calculated limit of detection of PFPeA reached 320 nM, more than 24 times lower than in 2 M KCl. It was thus clear that tuning the electrolyte concentration was a simple but very effective approach to improve the performance of nanopore SMSs for PFCAs determination.

Electrolyte Concentration Regulation Boosting Zinc Storage Stability of High-Capacity K0.486V2O5 Cathode for Bendable Quasi-Solid-State Zinc Ion Batteries.

Vanadium-based cathodes have attracted great interest in aqueous zinc ion batteries (AZIBs) due to their large capacities, good rate performance and facile synthesis in large scale. However, their practical application is greatly hampered by vanadium dissolution issue in conventional dilute electrolytes. Herein, taking a new potassium vanadate K0.486V2O5 (KVO) cathode with large interlayer spacing (~ 0.95 nm) and high capacity as an example, we propose that the cycle life of vanadates can be greatly upgraded in AZIBs by regulating the concentration of ZnCl2 electrolyte, but with no need to approach "water-in-salt" threshold. With the optimized moderate concentration of 15 m ZnCl2 electrolyte, the KVO exhibits the best cycling stability with ~ 95.02% capacity retention after 1400 cycles. We further design a novel sodium carboxymethyl cellulose (CMC)-moderate concentration ZnCl2 gel electrolyte with high ionic conductivity of 10.08 mS cm-1 for the first time and assemble a quasi-solid-state AZIB. This device is bendable with remarkable energy density (268.2 Wh kg-1), excellent stability (97.35% after 2800 cycles), low self-discharge rate, and good environmental (temperature, pressure) suitability, and is capable of powering small electronics. The device also exhibits good electrochemical performance with high KVO mass loading (5 and 10 mg cm-2). Our work sheds light on the feasibility of using moderately concentrated electrolyte to address the stability issue of aqueous soluble electrode materials.

Controlled Adhesion of HUVEC on Polyelectrolyte Multilayers by Regulation of Coating Conditions.

Adhesion of host cells on the surface of implants is necessary for a healthy ingrowth of the implanted material. One possibility of surface modification is the coating of the implant with a second material with advantageous physical-chemical surface properties for the biological system. The coverage with blood proteins takes place immediately after implantation. It is followed by host-cell interaction on the surface. In this work, the effect of polyelectrolyte multilayer coatings (PEMs) on adhesion and activity of human umbilical vein endothelial cells (HUVECs) was studied. The PEMs were formed from poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) from solutions with different concentrations of NaCl varying between 0 and 1.0 M. The adhesion of HUVEC and their viability on the PEM is related to the amount of adsorbed proteins from the applied cell growth medium. The amount of adsorbed proteins is controlled not only by the surface charge but also by the internal excess charge of the PEM. The internal excess charge of the PEM was controlled by changing the electrolyte concentration in the deposition solutions.

Poorly Soluble 2,6-Dimethoxy-9,10-anthraquinone Cathode for Lithium-Ion Batteries: The Role of Electrolyte Concentration.

In this work, a 9,10-anthraquinone (AQ) derivative functionalized by two methoxy groups, 2,6-dimethoxy-9,10-anthraquinone (DMAQ), was synthesized and its electrochemical performance was comprehensively studied with different electrolyte concentrations. Density functional theory (DFT) calculations demonstrate that there exists a conjugation effect between oxygen atoms of methoxy groups and the AQ skeleton, which could extend the conjugate plane and increase intermolecular interaction. As a result, DMAQ shows considerably reduced solubility in ether solvent/electrolyte and greatly enhanced cycling performance compared with those of AQ. Interestingly, it is found that the electrolyte concentration plays an important role in determining the electrochemical performance. Cycling under a relatively low (2 M) or high (6 M) concentration electrolyte of lithium bis(trifluoromethanesulfonyl)imide in a mixture solvent of 1,3-dioxolane and 1,2-dimethoxyethane (1/1, v/v) displays unsatisfied cell performance. While a moderate electrolyte concentration of 4 M delivers the highest initial capacity and the best cycling stability. The work would shed light on the rational molecular structure design and electrolyte concentration optimization for achieving the high electrochemical performance of organic electrode materials.

Relationships between Electrolyte Concentration and the Supercapacitive Swing Adsorption of CO2.

We quantitatively investigate the influence of the NaCl electrolyte concentration on the adsorptive and energetic characteristics of supercapacitive swing adsorption (SSA) for the separation of CO2 from a simulated flue gas mixture containing 15% CO2 and 85% N2. The investigated concentrations were that of deionized water, 0.010, 0.10, 1.0, 3.0, and 5.0 M NaCl. We find that the energetic metrics strongly improve with the increasing NaCl concentration, whereas the adsorptive metrics improve by a comparatively small degree. The CO2 adsorption capacity increases up to 1.0 M NaCl and then remains constant. The adsorption rate remains near constant for all concentrations, except that it is somewhat smaller for deionized water. The charge efficiency also remains near constant for all experiments with 30 min potentiostatic holding steps but near doubles for pure water when the potential holding step is doubled, because the chemical adsorption equilibrium is reached only after 60 min. The results can be most satisfactorily explained by assuming that both ionic and nonionic adsorption mechanisms contribute to the SSA effect.

Toluidine blue staining for cell and tissue biology applications.

Toluidine blue (TB) staining either alone or in association with other methodologies has the potential to answer a variety of biological questions regarding the human, animal and plant tissues or cells. In this brief review, we not only report the primary use of TB to detect the anionic substrates and availability of their binding sites, but also unveil the resulting applications of TB staining in biological research. Among these applications, the uses of TB staining to identify the changes in chromatin DNA-protein complexes, nucleolus location, and extracellular matrix proteoglycan complexes associated with different physiological and pathological events are described. The usefulness of TB staining to monitor the effects elicited by environmental insults on chromatin and intercalation of drugs into the DNA is also included.

Towards a better understanding of the aggregation mechanisms of iron (hydr)oxide nanoparticles interacting with extracellular polymeric substances: Role of pH and electrolyte solution.

Extracellular polymeric substances (EPS) are ubiquitous in the soil and water environment and interact strongly with mineral surfaces. However, these interactions and their impacts on the behavior and fate of minerals remain poorly understood. Here, for a better understanding of the colloidal stability of minerals in the environment, we investigated the aggregation of goethite (α-FeOOH) nanoparticles (NPs) in the presence of EPS from Bacillus subtilis under different environmental conditions (pH, ionic strength and ionic valence). Results showed that the aggregation processes of goethite NPs are determined by the solution chemistry, and the colloidal stability of goethite NPs is strongly influenced by the addition of EPS. In the absence of ionic strength, the addition of EPS promotes the aggregation of goethite NPs only when the pH (pH = 6) is less than the point of zero charge for the goethite nanoparticles (pHpzc ≈ 8). In the presence of ionic strength, the aggregation rate of goethite NPs increases with increasing concentration of NaCl, NaNO3 and Na2SO4 solutions, and after the addition of EPS solution, the critical coagulation concentrations (CCC) of goethite NPs are increased from 43.0, 56.7 and 0.39 mM to 168.0, 304.9 and 126.2 mM in the three electrolyte solutions, indicating that the addition of EPS inhibits the aggregation of goethite NPs. While in Na3PO4 solution, when the concentration of Na3PO4 solution ranged from 0 to 1 mM, the aggregation rate of goethite NPs increases first, followed by a decrease, and with the concentration of Na3PO4 solution exceeding 1 mM, the aggregation rate of goethite NPs increases again, due to the charge screening by sodium counter ions. This study provides a fundamental understanding of the behavior of goethite NPs in natural soil and water environments.

Effects of Functional Group Density in Stylene-Divinylbenzene Copolymer Phase and of Supporting Electrolyte Concentration in Aqueous Phase on Performance of Iminodiacetate-type Chelating Resin in Terms of Contribution of Ion-Exchange Mechanism.

The effects of the functional group density in the stylene-divinylbenzene copoymer phase and of the supporting electrolyte concentration in the aqueous phase on the perfomance of the iminodiacetate (IDA)-type chelating resin were studied in terms of contribution of an ion-exchange mechanism. High hydrophobicity of the resin having a low functional group density interfered with penetration of aqueous solutions into the resin phase to slow the acid-base reaction and the adsorption reaction. Uptake of the cation in the supporting electrolyte into the resin phase was clearly indicated in each of two acid dissociation reactions. The high concentration of the supporting electrolyte enhanced acid dissociation of the IDA group, and a singly deprotonated species interacting with the supporting electrolyte cation strongly interfered with adsorption by the ion-exchange mechanism, while only slightly interfering with adsorption by the complexation. Both the complexed and ion-exchanged species respectively involving two or more IDA groups were destabilized to reduce the adsorption capacity of the resin having the low functional group density.

Managing land application of coal seam water: A field study of land amendment irrigation using saline-sodic and alkaline water on a Red Vertisol.

Coal seam (CS) gas operations coproduce water with gas from confined CS aquifers. This CS water represents a potential agricultural resource if the water is able to be chemically amended to comply with management guidelines. Stoichiometric quantities of sulphur and gypsum amendments can be used to neutralise the alkalinity and reduce the sodicity of CS water respectively. These amendments can either be mixed in-line at a water treatment plant or applied directly to land prior to the application of CS water (a practice termed land amendment irrigation - LAI). This study compared the efficacy of LAI with in-line chemical amendment of CS water and irrigation with non-saline, non-sodic and non-alkaline (good quality) water under field conditions in southern Queensland. Soil chemical properties, soluble Ca, Mg, K, Na, electrical conductivity (EC), pH, chloride and alkalinity, as well as saturated hydraulic conductivity were measured to determine the impact of the irrigation treatments on soil chemical and physical conditions. Irrigation of lucerne pasture using solid-set sprinklers applied a total of 6.7 ML/ha of each treatment irrigation water to the experimental plots over a 10-month period. Alkalinity was neutralised using LAI, with no increase in soil alkalinity observed. Soil sodicity did not exceed threshold electrolyte concentration values under either CS water irrigation treatment. Soil chemical and physical properties were comparable for both LAI and in-line chemical amendment of CS water. Soil saturated hydraulic conductivity was maintained under all irrigation treatments. Results showed that the constrained capacity of the irrigation system was unable to meet crop evapotranspiration demand. This resulted in accumulation of salt within the root-zone under the CS water treatments compared to the good quality water treatment. LAI successfully chemically amended Bowen Basin CS water facilitating its beneficial use for agricultural irrigation.

Electrokinetic Properties of the Pristine and Oxidized MWCNT Depending on the Electrolyte Type and Concentration.

Electrostatic stabilization is reduced in its efficiency in an electrolyte-containing environment. The effect of electrolyte concentration is mostly described as negative factor for dispersion stabilization. Usually, zeta potential and physical stability decrease at increasing electrolyte concentration. The purpose of the present study was to measure the surface properties of nanotubes in aqueous solution of monovalent electrolytes at different concentration. Characteristics such as size distribution, surface chemistry, surface charge, and dispersability in aqueous phase have been identified. Hydrodynamic size and zeta potential in aqueous multiwalled carbon nanotube (MWCNT) suspensions were determined at different pH with the desired concentrations of electrolyte of the cationic group (NaCl, KCl, CsCl) and the anionic group (NaClO4). The correlations between the response of the surface functionality of pristine and oxidized multiwalled carbon nanotubes and electrical double layer (EDL) forming at different ionic environments in the vicinity of a nanotube surface were determined. The nanotube dispersion stabilization was found to be more affected by ion size and pH medium then electrolyte concentration. The data obtained confirms the predominant role of surface reactions. The most stable dispersion of nanotubes was achieved in KCl electrolyte solution at less negative charge of the surface.

Optimization of electrochemical reaction for nitrogen removal from biological secondary-treated milking centre wastewater.

In order to remove the residual nitrogen from the secondary-treated milking centre wastewater, the electrochemical reaction including NH4-N oxidation and NOx-N reduction has been known as a relatively simple technique. Through the present study, the electrochemical reactor using the Ti-coated IrO2 anode and stainless steel cathode was optimized for practical use on farm. The key operational parameters [electrode area (EA) (cm(2)/L), current density (CD) (A/cm(2)), electrolyte concentration (EC) (mg/L as NaCl), and reaction time (RT) (min)] were selected and their effects were evaluated using response surface methodology for the responses of nitrogen and colour removal efficiencies, and power consumption. The experimental design was followed for the central composite design as a fractional factorial design. As a result of the analysis of variance, the p-values of the second-order polynomial models for three responses were significantly fit to the empirical values. The nitrogen removal was significantly influenced by CD, EC, and RT (p < .05), whereas colour removal was significantly governed by EA, CD, RT, the interaction of EA and EC (p < .05). For higher efficiency of nitrogen removal over 90%, the combination of [EA, 20 cm(2)/L; CD, 0.044 A/cm(2); EC, 3.87 g/L as NaCl; RT, 240 min] was revealed as an optimal operational condition. The investigation on cathodic reduction of NOx-N may be required with respect to nitrite and nitrate separately as a future work.