Water Softening Process Research Articles

Pilot-scale capacitive deionization for water softening: Performance, energy consumption, and ion selectivity

Capacitive deionization (CDI) has emerged as an efficient process for hardness control than traditional water-softening technologies. However, few systematic studies have been conducted on water softening using pilot-scale CDI systems. For industrial applications, it is essential to investigate deionization performance, energy consumption, and selectivity for divalent cations through pilot-scale studies. In this study, we examined the deionization performance and energy consumption of a pilot-scale CDI process for effective water softening. The key operational variables analyzed were the applied voltage (200–300 V (i.e., 1.0–1.5 V per pair)), feed concentration (550–1250 mg/L), recovery ratio (50–80 %), flow rate (3–5 L/min), and adsorption/desorption time (80–180 s). Within this range, a high voltage, low feed concentration, low recovery ratio, high flow rate, and long adsorption/desorption times are advantageous for the total dissolved solids (TDS) removal ratio. In terms of energy efficiency, expressed as TDS removal per unit energy consumption, a low voltage, low feed concentration, low recovery ratio, fast flow rate, and long adsorption/desorption time are beneficial. Additionally, we investigated the selective removal of Ca2+ over Na+ under various operating conditions, as well as its impact on enhancing energy efficiency. The pilot CDI system achieved a Ca/Na selectivity coefficient of approximately 2.4 and it was analyzed to achieve up to 45 % energy-saving efficiency compared to nonselective systems (i.e., selectivity coefficient = 1). The results of this study are expected to provide valuable data for the application of CDI to water softening and hardness control processes.

Ni-P-PTFE cathode with low surface energy for enhancing electrochemical water softening performance.

Efficient cathode regeneration is a significant challenge in the electrochemical water softening process. This work explores the use of an electroless plating Ni-P-PTFE electrode with low surface energy for this purpose. The Ni-P-PTFE electrode demonstrates improved self-cleaning performance at high current densities. By combining the low surface energy of the electrode with fluid flushing shear force, the precipitation rate on the Ni-P-PTFE electrode remains stable at approximately 18 g/m2·h over extended periods of operation. Additionally, the cleaning efficiency of the Ni-P-PTFE electrode surpasses that of stainless steel by 66.34%. The Ni-P-PTFE electrode can maintain a larger active area and a longer operational lifespan is attributed to its self-cleaning performance derived from low surface energy. Furthermore, the loose scale layers on the electrode surface are easily removed during electrochemical water softening processes, presenting a novel approach to cathode surface design.

Development of the wastewater treatment technology for the mine ‘Ternivska’ of the Kryvyi Rih iron ore plant

ABSTRACT Wastewater treatment in mining and mineral processing technology is a topical problem worldwide. The purpose of this study is to substantiate and develop the technology of complex wastewater treatment for the mine ‘Ternivska’ of the Public Joint Stock Company ‘Kryvyi Rih Iron Ore Plant’ with the production of highly purified water suitable for secondary use or ecologically safe discharge into surface water bodies. The proposed technology is based on the sequential application of the following stages: preliminary treatment of contaminated mine waters by coagulation and soda-lime softening methods to remove hardness, suspended solids, and colloidal substances; desalination via reverse osmosis; evaporation and crystallization of reverse osmosis concentrate in a vacuum evaporation unit; dehydration of salt sludge in a centrifuge with drying of salt crystals in a dryer. The treatment of mine water with an initial salinity of 80 g/L will give an annual effect of 1357 thousand m3 of desalinated water with a mineralization of up to 100 mg/L and 739.6 tons of mineral salt mixture. The purified water can serve as an additional source of fresh water for technological needs in industry or alternative purposes. The obtained solid salt product can be used as an alternative reagent for water-softening processes. In general, the proposed processing of mineralized mine water can be considered a zero-waste technology with clean water production and by-product utilization.

Human health risk assessment framework for new water resource recovery-based bio-composite materials.

A new type of bio-composite material is being produced from water-recovered resources such as cellulose fibres from wastewater, calcite from the drinking water softening process, and grass and reed from waterboard sites. These raw materials may be contaminated with pathogens and chemicals such as Escherichia coli, heavy metals, and resin compounds. A novel risk assessment framework is proposed here, addressing human health risks during the production of new bio-composite materials. The developed framework consists of a combination of existing risk assessment methods and is based on three main steps: hazard identification, qualitative risk mapping, and quantitative risk assessment. The HAZOP and Event Tree Analysis methodologies were used for hazard identification and risk mapping stages. Then, human health risks were quantitatively assessed using quantitative chemical risk assessment, evaluating cancer and non-cancer risk, and quantitative microbial risk assessment. The deterministic and the stochastic approaches were performed for this purpose. The contamination of raw materials may pose human health concerns, resulting in cancer risk above the threshold. Microbial risk is also above the safety threshold. Additional analysis would be significant as future research to better assess the microbial risk in biocomposite production. The framework has been effectively used for chemical and microbial risk assessment.

Sodium benzyl sulfonate functionalized-bentonite as a novel adsorbent for water softening process

In this work, novel Sodium benzyl sulfonate functionalized-bentonite (SBSB) adsorbent was synthesized through the reaction of bentonite with benzyl alcohol and chlorosulfonic acid. The prepared adsorbent was characterized using Low-angle XRD, FT-IR and TGA methods, and applied for the removal of calcium and magnesium ions from water solutions. The effect of contact time and initial hardness concentration on the hardness removal efficiency of the prepared adsorbents were studied. It was found that the adsorption was reached the equilibrium condition within about 60 min, and the maximum adsorption capacity (52.5 mg g−1) was achieved in the hardness of 150 mg L−1. Compared to pristine bentonite, the adsorption efficiency of SBSB was significantly enhanced, which is ascribed to the presence of benzyl sulfonate functional groups on its surface. The adsorption isotherm of calcium and magnesium ions on SBSB was described by Langmuir and its adsorption kinetic behavior followed pseudo-second-order model.

Unraveling the Ion Uptake Capacitive Deionization of Sea- and Highly Saline-Water by Sulfur and Nitrogen Co-Doped Porous Carbon Modified with Molybdenum Sulfide.

In parallel to the depletion of potable water reservoirs, novel technologies have been developed for seawater softening, as it is the most abundant source for generating deionized water. Although salt removal at subosmotic pressures and ambient temperatures by applying low-operating potentials with high energy efficiency made capacitive deionization (CDI) an advantageous water-softening process, its practical application is limited by insufficient ion removal capacity and low concentration influent. The performance of a CDI system is in progress with engineering the electrode active materials, also facilitating the advance design in highly saline- and seawater study. Herein, an innovative strategy was developed to provide high-performance CDI systems based on efficient and electrochemical ion-uptake active materials with a simple initial preparation. Nitrogen-doped porous carbons (N-pCs) received benefits from a high specific surface area and good surface wettability. The N-pCs were modified with molybdenum oxide/sulfide intercalative array and developed as CDI electrode active materials for desalination of both low/medium saline- and seawater. The MoS2/S,N-pC electrode materials exhibited perfect optimized salt adsorption capacity (SACs) of 47.9 mg g-1 when compared to N-pC (37.9 mg g-1) and MoO3/N-pC (39.6 mg g-1) counterparts at 1.4 V in a 750 ppm NaCl solution. In addition, the assembled CDI cells exhibited reasonable cycle stability and retained 96.7% of their initial SAC in continuous CDI cycles for 128,000 s. The fabricated CDI cell rendered an excellent salt removal efficiency (SRE, %) of 13.34% from the real seawater sample at 1.2 V. In detail, the SRE % of the NaCl, KCl, MgCl2, and CaCl2 soluble salts with respect to seawater sample exhibited a remarkable SRE % of 30.8%, 36%, 32.6%, and 19.3%, respectively. These SRE % values (>13.34%) provide convincing evidence on the reasonable ion uptake capability of the fabricated CDI cells for removing Na+, K+, Mg2+, and Ca2+ ions compared to other soluble component. The advanced cell design parallel to the promising outcomes provided herein makes these CDI systems immensely propitious for efficient water softening.

MATHEMATICAL DESCRIPTION AND ALGORITHM FOR SOLVING THE MODEL OF THE IONITE REGENERATION PROCESS IN THE ION EXCHANGE METHOD OF WATER SOFTENING

Based on the modern representation of the water softening process by the ion exchange method, modeling was carried out, an algorithm was developed and the ionite regeneration process was calculated in a water softening plant with a fixed ionite layer. To solve the system of equations of the model, special, but simple enough for use in engineering calculations, techniques and methods have been developed and applied. The constructed model and its solution algorithm can be used to predict the process of ionite regeneration in an ion exchange apparatus. It can also be used to calculate the time of the ionite regeneration process.

New insights into hydration-induced creep behavior of shale: A comparison study of brittle black shale and clayey oil shale at micro-scale

During hydraulic fracturing for shale gas development, water softening and creep deformation of shale rock are two common engineering problems that severely impair production performance. In order to understand the mineralogical and microstructural control on this mechanism from microscale, a brittle black shale from Lower Silurian Longmaxi Formation (named as LMX shale) and a clayey oil shale from Paleogene Youganwo Formation (YGW shale), which represent two members of shale family with different mineral constitutes and microstructures, were selected for hydration process under various durations (0.5 h–96 h) and temperatures (25 °C and 50 °C). The accompanied changes of microstructural and mechanical properties during hydration at microscale were investigated via nuclear magnetic resonance (NMR) and nanoindentation, respectively. Based on NMR T2 spectra, peak T2 time and water-infiltrated pore increment for both LMX and YGW shales rise sharply within the first 12 h, whereas remain invariable hereafter. And the values increase at higher temperature. For YGW shale, the maximum peak T2 time is lower but the incremental porosity is higher than LMX shale, respectively. Such difference indicates an occurrence of gradually enlarged and connected pores inside LMX shale after hydration, while a greater number of disconnected pores have been developed in YGW shale, comparatively. For both shales, great strength deterioration and creep enhancement are monitored within the first 12 h of hydration. The modulus reduction could be as high as 26.27% and 80.16% after 96 h soaking at 50 °C for LMX and YGW shales, respectively. Creep strain rate sensitivity increases from 0.026 to 0.234 for LMX shale, and 0.011 to 0.099 for YGW shale with intensified softening degree. The softening mechanism for LMX brittle shale is dominated by secondary pores and cavities generated as a result of dissolution of carbonate cementation and grain detachment after water infiltration, while microstructural integrity of YGW oil shale is degraded by clay swelling. Due to different mineral constitutes and microstructures, creep deformation for clayey YGW shale is mainly mediated by dislocation movement of fine clay grains, whereas diffusion creep plays the key role in coarse-grained LMX shale. This comparative study with two distinct shale samples provides the mineralogy- and microstructure-based framework for interpreting water softening process and creep mechanism of shale, which benefits hydraulic fracture design in different shale formations so as to enhance shale oil/gas production.

Criteria for the existence of self-sustaining water softening and desalination processes for a basic two-component system

Criteria for the existence of self-sustaining water softening and desalination processes for a basic two-component system

Flexible structural engineering of PPy-NiCo-LDH@Mxene for improved capacitive deionization and efficient hard water softening process

Capacitive deionization (CDI), as a potential desalination technology, shows the prominent advantage in processing low-concentration brackish water. However, the traditional CDI electrodes suffer from the problems like the limited salt adsorption capacity and inferior practical application in selective ion separation process. Herein, the effective-designed three-dimensional Mxene-based composite PPy-NiCo-LDH@Mxene is constructed by integrating PPy, NiCo-LDH, and Mxene together through the hydrothermal method. Particularly, the excellent conductive PPy network can greatly alleviate the restacking of Mxene and NiCo-LDH flakes and provide effective charge diffusion and transfer channels. Moreover, the Mxene substrate can strengthen the structure stability of the composite and further reinforce the total electrical conductivity of the composite material. Meanwhile, the NiCo-LDH and Mxene provide rich ion intercalation sites, contributing to the high ion storage capacity and fast electrosorption kinetics. Consequently, the PPy-NiCo-LDH@Mxene achieves the significant specific capacitance (174 F g−1), superior charging and discharging property, and enhanced electrochemical cyclic stability. The asymmetric CDI cell (AC//PPy-NiCo-LDH@Mxene) displays the prominent salt adsorption capacity (31.5 mg g−1), rapid salt removal rate (4.7 mg g−1 min−1), fast electrosorption kinetics, and stable adsorption/desorption process. Furthermore, in the multi-salt solutions with different salt solution concentrations, the PPy-NiCo-LDH@Mxene electrode displays the superb adsorption selectivity to the Ca2+ and Mg2+ than Na+, which indicates its suitable application for hard water softening process. The effective structural design exhibits huge potential for applying effective electrode materials for fast CDI process and hard water softening.

ZEÓLITA NaA SINTETIZADA SOBRE FIBRA DE VIDRO COMO ESTRATÉGIA PARA OTIMIZAÇÃO DO ABRANDAMENTO DE ÁGUAS DURAS

NaA ZEOLITE SYNTHESIZED OVER FIBERGLASS AS A STRATEGY FOR OPTIMIZING HARD WATER SOFTENING. Zeolite NaA has been successfully synthesized over glass fiber surface previously activated by alkaline treatment. By varying the time of the treatment and the amount of silica and alumina precursors used in the reaction mixture, a sample with higher zeolite concentration could be obtained. This material was evaluated for water softening process as an alternative substitute for the use of the zeolite in its powder form, in which several drawbacks related to recovery and reuse limit its application. Water softening experiments, carried out in a continuous flow system, with a column containing the glass fiber-zeolite NaA, showed high performance in decreasing the Ca2+ ions, with complete removal achieved for 20 mL of simulated hard water (Ca2+ 100.0 mg L– ¹) by using 200 mg of the sample in form of column (10 mm diameter × 300 mm high). The sample maintained this performance in a wide range of pH (3.0-9.0), and also presented a feasible regenerability, with no decrease in its performance during the first four cycles of use, reaching 87.3% of efficiency over the tenth cycle.

Calcium carbonate nanoparticles fabricated by a facile method based on the colloidal gas aphrons for removal of fluoride ions from aqueous solutions

In this study, calcium carbonate nanoparticles were proposed as a potential material for fluoride ion removal from aqueous solution. For this purpose, a new method based on the colloidal gas aphrons was applied for the preparation of the calcium carbonate nanoparticles. The synthesized nanoparticles were characterized by SEM, XRD, and FTIR analyses. Factors affecting the sedimentary reaction including the initial concentration of fluoride ion, pH, time, and temperature were individually investigated. The morphology of the successfully synthesized nanoparticles was quasi-spherical vaterite structure without important aggregation. The maximum fluoride ion removal capacity was obtained about 460 mg/g at 298 K. Also, the effect of temperature displayed that temperature change has a significant effect on the removal rate. The removal rate was highly dependent on the pH and by decreasing the pH, the removal rate decreased. Kinetic results indicated that the removal kinetics is in perfect agreement with the first-order model. The experiments showed that although the synthesized sample has a better performance than the industrial one, the purity and the low cost of calcium carbonate particles produced in the water softening process make them a great candidate for the removal of fluoride from aqueous solutions.

A study of the mechanical properties and appearance of efflorescence in paving bricks under different curing environments

Taiwan has witnessed rapid economic development in recent years, and with urban development, the planning and design of compressed paving units and pervious ground tile structures are focused on the demand for esthetic appearance in addition to practical functioning and legal requirements for strength and water permeability. In this study, the efflorescence appearance of structures was effectively reduced using calcium carbonate crystallization from the water purification and softening process to fill the pores in generic high-pressure bricks. The same water-to-binder ratio of 0.35 was used for three different mix proportions, and 20 cm × 20 cm × 6 cm general high-pressure bricks, calcium carbonate high-pressure bricks, and pervious bricks were made under a 50 kg/cm2 molding pressure at a concrete-brick-making plant. The samples were cured in five different environments with curing times of 2, 7, 28, 56 and 91 days. The effect of the curing age, the curing environment and the brick type on the hardness, solidity and appearance of efflorescence of the bricks were analyzed in terms of the compressive strength, the ultrasonic pulse velocity, and the coefficient of permeability, using Paint.net image analysis, scraping rate tests, SEM analysis and EDS analysis.The test results showed that the compressive strengths of the general high-pressure bricks, the calcium carbonate high-pressure bricks and the pervious bricks were 46.78 MPa–84.97 MPa, 56.89 MPa–100.23 MPa and 35.38 MPa–59.20 MPa, respectively. The ultrasonic pulse velocities were 3296 m/s–4524 m/s, 3567 m/s–5703 m/s and 2623 m/s–4319 m/s, respectively. The coefficient of permeability of the pervious bricks was larger than 1 × 10–2 cm/sec. Quantitative analysis of efflorescence using Painet.net image analysis and scraping rate tests showed that the ratio of the efflorescence to the total area at the surface or bottom of the bricks and the scraping rate were larger for curing on hardened concrete than under other curing conditions. The efflorescence that was generated on the bottom layer of the bricks was higher than that on the surface layer by 5.31%–19.82%. Microscopic analysis of the specimens (SEM) showed the existence of many crystalloid Ca (OH)2 colloids that accounted for 20–25% of the cement volume. EDS analysis showed that Ca was the main element in efflorescence, at 6.64%, which was much higher than the percentage of other elements. To summarize the results, curing in a cling film seal can inhibit efflorescence crystallization.

Investigating the Effect of a New Industrial Waste on Strengthening the Soft Clayey Soil

The use of waste materials of industries to protect the environment and save the economy has always been significant to humankind. In this research, in order to stabilize and improve soft clay soils, we tried to investigate the possibility of replacing a part of conventional additives in the improvement of soft clay soils (lime) with the waste resulting from the water softening process. In addition, sodium silicate as a facilitating agent of the reactions in soil stabilization process was studied. Firstly, the optimum percentage of lime was obtained by performing the relevant experiments; afterwards, different percentages of waste and sodium silicate were added to this optimum percentage of lime to achieve the best result. Compaction, unconfined compressive strength and consolidation tests were conducted on the specimens, and it was specified that the best function of the stabilized soil will be achieved when there is 6% lime, 6% industrial waste and 1.5% sodium silicate. Then, in order to find the causes of the changes in the results, the specimens were examined using scanning electron microscopy and X-ray diffraction. The pH changes were studied, as well. The results showed that the strength of the treated soil improved with the addition of additives which reduced its porosity by forming the C–S–H gel.

Consumption of Ion Exchange Resin Waste in Concrete

This project deals with the investigation of strength property of concrete made by partial replacement of cement using ion exchange resin waste. Ion exchange resin waste is readily available at free of cost in various industries. We are using the cation exchange resin waste from water softening process. This waste material is collected from a local place in Chennai In recent years, ion exchange resin is used in concrete for corrosion resistant purpose. The percentage replacements of cement by using ion exchange resin waste are 10%, 20% and 30% by weight. The results indicate The selected concrete grade is M30 and water cement ratio is 0.45. Cubes and cylinders are casted with the specified replacement of cement by using ion exchange resin waste. The strength has been checked at 7 days, 14 days and 28 days curing for the specimens made with specified partial replacement of cement by using ion exchange resin waste. Cubes are subjected to compressive strength test and cylinders are subjected to split tensile strength test. It has been concluded that the reasonable strength of 31.76 N/mm2 (Target strength of M20 grade concrete) may be attained in M30 grade mix ratio while adding ion exchange resin waste as 10% replacement of cement. So the optimum percentage of replacement of cement is 10% for both cubes and cylinders.

Development of Copper-Aluminum Layered Double Hydroxide in Thin Film Nanocomposite Nanofiltration Membrane for Water Purification Process.

This study aims to fabricate a thin film composite (TFC) membrane, modified with copper-aluminium layered double hydroxide (LDH) nanofillers via interfacial polymerization technique for nanofiltration (NF) processes. It was found that Cu-Al LDH nanofillers possessed layered structured materials with typical hexagonal plate-like shape and positive surface charge. The study revealed that TFN membrane exhibits a relatively smooth surface and a less nodular structure compared to pristine TFC membrane. The contact angle of TFN progressively decreased from 54.1° to 37.25°, indicating enhancement in surface hydrophilicity. Moreover, the incorporation of LDH nanofillers resulted in a less negative membrane as compared to the pristine TFC membrane. The best NF performance was achieved by TFN2 membrane with 0.1° of Cu-Al LDH loading and a water flux of 7.01 Lm-2h-1.bar. The addition of Cu-Al LDH resulted in excellent single salt rejections of Na2SO4 (96.8%), MgCl2 (95.6%), MgSO4 (95.4%), and NaCl (60.8%). The improvement in anti-fouling properties of resultant TFN membranes can be observed from the increments of pure water flux recovery and normalized water flux by 14% and 25% respectively. The findings indicated that Cu-Al LDH is a promising material in tailoring membrane surface properties and fouling resistance. The modification of the LDH-filled TFN membrane shows another alternative to fabricating a high-performance composite membrane, especially for water softening and partial desalination process.

Incorporation of layered double hydroxide nanofillers in polyamide nanofiltration membrane for high performance of salts rejections

Abstract In this work, thin film composite (TFC) membrane embedded with self-synthesized layered double hydroxide (LDH) nanofillers was prepared via interfacial polymerization technique for nanofiltration (NF) process. Prior to filtration experiments, the morphologies and physicochemical properties of the prepared LDH nanofillers and TFC membranes were characterized using TEM, XRD, FESEM, FTIR, AFM, zeta potential analyzer and contact angle goniometer. The results revealed that the self-synthesized LDH nanofillers possessed layered structured materials with typical hexagonal plate-like shape. Meanwhile, it was found that the membrane contact angle decreased remarkably from 53° to 33.96° upon addition of 0.1 wt% LDH nanofillers in the active polyamide layer. TFN membrane of 0.1 wt% LDH loading possessed the highest water flux of 54.62 Lm−2 h−1 at 7 bar. The highest rejections of Na2SO4 (97.3%), MgSO4 (95.5%), MgCl2 (95.2%) and NaCl (63.7%) were also achieved by the TFN embedded with 0.1 wt% LDH in polyamide layer. In addition to the excellent water flux and rejection, incorporation of LDH also enhanced the fouling resistance, proven by the improvement of pure water flux recovery by 52% after BSA filtration. The findings indicated the potential of the newly developed TFN membrane incorporated with LDH nanofillers for efficient NF membrane in water softening and pre-desalination process.

Repeated detection of polystyrene microbeads in the Lower Rhine River

Microplastics are emerging pollutants in water bodies worldwide. The environmental entry areas must be studied to localise their sources and develop preventative and remedial solutions. Rivers are major contributors to the marine microplastics load. Here, we focus on a specific type of plastic microbead (diameter 286–954 μm, predominantly opaque, white–beige) that was repeatedly identified in substantial numbers between kilometres 677 and 944 of the Rhine River, one of Europe's main waterways. Specifically, we aimed (i) to confirm the reported abrupt increase in microbead concentrations between the cities of Leverkusen and Duisburg and (ii) to assess the concentration gradient of these particles along this stretch at higher resolution. Furthermore, we set out (iii) to narrow down the putative entry stretch from 81.3 km, as reported in an earlier study, to less than 20 km according to our research design, and (iv) to identify the chemical composition of the particles and possibly reveal their original purpose. Surface water filtration (mesh: 300 μm, n = 9) at regular intervals along the focal river stretch indicated the concentration of these spherules increased from 0.05 to 8.3 particles m−3 over 20 km. This spot sampling approach was supported by nine suspended solid samples taken between 2014 and 2017, encompassing the river stretch between Leverkusen and Duisburg. Ninety-five percent of microbeads analysed (202/212) were chemically identified as crosslinked polystyrene-divinylbenzene (PS-DVB, 146/212) or polystyrene (PS, 56/212) via Raman or Fourier-transform infrared spectroscopy. Based on interpretation of polymer composition, surface structure, shape, size and colour, the PS(-DVB) microbeads are likely to be used ion-exchange resins, which are commonly applied in water softening and various industrial purification processes. The reported beads contribute considerably to the surface microplastic load of the Rhine River and their potential riverine entry area was geographically narrowed down.

Polarity reversal electrochemical process for water softening

• Polarity reversal has been tested for scale detachment in the electrochemical water softening process. • Effective scale detachment was achieved. • High softening efficiency and low energy consumption could be obtained stably. • The DSA used could keep active steadily in polarity reversal condition. Electrochemical precipitation has attracted widespread attention in the treatment of recirculating cooling water in recent years. In order to guarantee continuous water softening efficiency, periodic scale detachment of cathode is indispensable. Nevertheless, periodic mechanical scrapping, prevalent scale detachment technique currently, increases the interelectrode gap, resulting in the decline of water softening efficiency and the rise of energy consumption. In this paper, polarity reversal was applied in the electrochemical precipitation process for removing scale deposits. The results showed that scale deposits were removed effectively and high water softening efficiency were accomplished steadily. The precipitation rate obtained was 53.9–73.4 g/h/m 2 . The reactor still could remove hardness ions efficiently after the scale detachment by polarity reversal. The energy consumption maintained in the range of 17.3–23.6 kWh/kg CaCO 3 . The total hardness removal efficiency was 16.4–21.4%. Repeated experimental results demonstrated that the electrochemical precipitation process adopting polarity reversal for scale detachment could operate steadily without any performance degradation detected. Cyclic voltammetric investigation showed good electrochemical stability of dimensionally stable anode (DSA) used. Accelerated life test indicated that it could keep active steadily in polarity reversal condition.

Electrochemical water softening using air-scoured washing for scale detachment

Treatment of recirculate cooling water using electrochemical method has obtained great attentions in recent years due to its environmental friendliness and easy operation. In order to ensure persistent hardness removal efficiency, periodical cleaning of cathode surface is essential. However, currently available electrode cleaning techniques are either inefficient or laborious. In this work, air-scoured washing was proposed to replace conventional scale detachment methods in the electrochemical water softening process. Mirror stainless steel was found to be the most suitable cathode material because it could enhance scale detachment significantly. Effective water softening and scale detachment were achieved. The precipitation rate was as high as 25.5–34.3 g/h/m2. After the air-scoured washing scale detachment, the cathode could resume their ability to soften. The energy consumption and the total removal efficiency were 17.6–22.3 kWh/kg CaCO3 and 12.2–15.2%, respectively. Repetitive experimental results indicated the electrochemical water softening process using air-scoured washing could run steadily without any performance decay detected after repetitive operation.