Soft Water Research Articles

Mitigation of mineral scaling in membrane capacitive deionization – Understanding the role of pH changes and carbonates

Mineral scaling in water desalination is caused by the precipitation of salts, which is affected by various factors such as the presence of specific ions, solution pH, and temperature. While extensively researched in technologies like reverse osmosis (RO), understanding mineral scaling in membrane capacitive deionization (MCDI) remains limited. During MCDI operation, the pH of the effluent fluctuates, potentially triggering mineral scaling. The present study investigates how the adsorption and desorption of HCO3− ions and the distribution of dissolved inorganic carbon (DIC) species (H2CO3, HCO3−, and CO32−) drive pH changes. We examine mineral scaling formation at various water recoveries during MCDI operation using different thicknesses of the anion exchange membrane (AEM). Our findings indicate that pH changes increase with higher water recoveries and that increasing the AEM thickness provides a pathway to enhance MCDI stability, consequently lowering the need for anti-scaling agents.

Ion migration mechanism of electrochemical water softening in dual-chamber reactors and their performance for real circulating cooling water

Electrochemical water softening studies often use ion exchange membrane (IEM) reactors. However, their practical application is limited because of inevitable cathodic scaling. To overcome this challenge, one necessary approach is to understand the ion migration mechanism in the typical IEM reactor. In this study, we used operando visualization to reveal that the divider such as IEM or nylon nets was essential to confine the neutralization reaction between H+ and OH−. Ca2+ and Mg2+ may transfer from the anode chamber through the divider into the cathode chamber via electromigration. Using mesh electrodes instead of plate electrodes, the total hardness removal in the cathode chamber and anode chamber was 94.2% and 92.5%, respectively. The high removal rate was attributed to H2 microbubbles produced by cathodic water electrolysis, which drove OH− ions diffusion into solution and sequentially strengthened the nucleation of scale crystals in solution rather than on the cathode surface. On the basis of the above ion migration mechanism, the revolutionized reactor with mesh electrode module and nylon-net divider exhibited good performance in softening real circulating cooling water, and the total hardness removal exceeded 93.1% during 30 h running. These results open new horizons for improving the practicability of electrochemical water softening.

From Nature-Sourced Polysaccharide Particles to Advanced Functional Materials.

Polysaccharides constitute over 90% of the carbohydrate mass in nature, which makes them a promising feedstock for manufacturing sustainable materials. Polysaccharide particles (PSPs) are used as effective scavengers, carriers of chemical and biological cargos, and building blocks for the fabrication of macroscopic materials. The biocompatibility and degradability of PSPs are advantageous for their uses as biomaterials with more environmental friendliness. This review highlights the progresses in PSP applications as advanced functional materials, by describing PSP extraction, preparation, and surface functionalization with a variety of functional groups, polymers, nanoparticles, and biologically active species. This review also outlines the fabrication of PSP-derived macroscopic materials, as well as their applications in soft robotics, sensing, scavenging, water harvesting, drug delivery, and bioengineering. The paper is concluded with an outlook providing perspectives in the development and applications of PSP-derived materials.

Syntheses, properties and mechanistic studies of 8-aminooctanoic acid-modified polyaspartic acid polymers for calcium scale inhibition

The anti-scaling agent poly(aspartic acidic) (PASP) polymers had became a hot research topic based on its peptide bond structures with degradation characteristics. However, it was difficult to control the chain length distributions of the synthesized products, which led to difficulty in determining the scaling mechanism for the peptide bond products. In this paper, PASP/8AC graft modified polymers with a narrow dispersity (Ð) and controllable chain lengths was synthesized via a simple two-step method, and 8-aminooctanoic acid (8AC) was introduced into the peptide bond structure of PASP with main chain lengths of 12. The effects of the side-chain lengths and functional groups on the scale inhibition mechanism were determined. The static scale inhibition results showed that the grafted products had significantly improved scale inhibition efficiencies at low concentrations and good temperature and time stabilities. The inhibition rate for CaSO4 scaling was increased by almost 60 % at a concentration of 3 mg/L. At 5 mg/L, the inhibition rate for CaCO3 scaling was increased by 36 %. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) showed that side chain length extensions improved calcium ion chelation by the PASP and increased calcium scale lattice distortion. This study verified the effects of side chains on PASP scale inhibition and its mechanism. This is of great importance in designing new green water treatment agents.

Lake water chemistry and local adaptation shape NaCl toxicity in Daphnia ambigua.

The increasing application of road deicing agents (e.g., NaCl) has caused widespread salinization of freshwater environments. Chronic exposure to toxic NaCl levels can impact freshwater biota at genome to ecosystem scales, yet the degree of harm caused by road salt pollution is likely to vary among habitats and populations. The background ion chemistry of freshwater environments may strongly impact NaCl toxicity, with greater harm occurring in ion-poor, soft water conditions. In addition, populations exposed to salinization may evolve increased NaCl tolerance. Notably, if organisms are adapted to the water chemistry of their natal environment, toxicity responses may also vary among populations in a given test medium. We examined the potential for this evolutionary and environmental context to interact in shaping NaCl toxicity with a pair of laboratory reciprocal transplant toxicity experiments, using natural populations of the water flea Daphnia ambigua collected from three lakes that vary in ion availability and composition. We observed a strong effect of the lake water environment on NaCl toxicity in both trials. NaCl caused a much greater decline in reproduction and r in lake water from a low-ion/calcium-poor environment (20 μS/cm specific conductance; 1.7 mg/L Ca2+) compared with water from both a Ca2+-rich lake (55 μS/cm; 7.2 mg/L Ca2+) and an ion-rich coastal lake (420 μS/cm; 3.4 mg/L Ca2+). Daphnia from this coastal lake were most robust to the effects of NaCl on reproduction and r. A significant interaction between the population and lake water environment shaped survival in both trials, suggesting that local adaptation to the test waters used may have contributed to toxicity responses. Our findings that the lake water environment, adaptation to that environment, and adaptation to a contaminant of interest may shape toxicity demonstrate the importance of considering environmental and biological complexity in mitigating pollution impacts.

Investigation on Disaster Mechanism of Diversion Tunnel Induced by Gripper TBM in Hydrokarst Erosion Stratum and Engineering Measures

In gripper tunnel boring machine (TBM) tunneling through complex geological formations, the safe and efficient recovery from large-scale collapses remains a formidable challenge. In this study, we investigate the causes of a 1246 m3 collapse that occurred during the gripper TBM tunneling in the diversion tunnel in Xinjiang, China. Various techniques including TSP seismic waves, CFC advanced water exploration, laboratory point load tests and packer permeability tests were employed for thorough research. The examination discloses that the water softening in biotite-quartz schist in fractured zones contributes significantly to the loosening and dislocation of rock layers along joints. The gripper TBM’s cutterhead exacerbates this process through cutting action and vibrations, causing large-scale instability and eventual rock mass collapse. To tackle this engineering problem, we propose a three-step treatment scheme comprising “Reinforcement-Backfill-Re-excavation”. Furthermore, we propose a technique to handle TBM collapses by creating a “protective shell” within the cavity. The safety and feasibility of these proposed solutions were thoroughly validated through numerical simulations. Also, we utilized the Hoek-Brown theory and Rostami prediction formula to establish recommended values for the total thrust and total torque of the TBM during the collapsed section. The proposed treatment scheme and estimated parameters were successfully applied, resulting in a comprehensive solution from collapse handling to tunneling. This study offers valuable details on effectively managing large-scale collapses in gripper TBM tunneling, which can be useful for similar tunnel engineering and improve safety and efficiency.

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.

Animal Feedlots and Domestic Wastewater Discharges are Likely Sources of N-Nitrosodimethylamine (NDMA) Precursors in Midwestern Watersheds.

N-nitrosodimethylamine (NDMA) precursor concentrations along four major rivers in Minnesota, USA were quantified and correlated with watershed land cover types, anthropogenic activity, and organic matter characteristics. River water samples (36 in total) were chloraminated under uniform formation conditions (UFC) before and after lime-softening treatment, and the resulting NDMA concentrations were quantified (NDMAUFC). Regarding land cover, NDMAUFC in raw river water exhibited weak positive correlations with urban land (ρ = 0.33, p = 0.05) and cropland coverage (ρ = 0.35, p = 0.04). For anthropogenic activity, NDMAUFC in raw river water positively correlated with the number of feedlots (ρ = 0.57), total weight of animals (ρ = 0.68), and total number of domestic wastewater treatment plants (WWTPs; ρ = 0.63) with p < 0.01. NDMAUFC positively correlated with region IV fluorescence intensity from fluorescence excitation-emission spectra (ρ = 0.70, p < 0.01). Lime softening of river water typically increased NDMAUFC and preferentially removed organic matter that fluoresces in region V, suggesting that the organic matter in this region decreases NDMAUFC by competing for available chloramines. Overall, animal feedlots, along with domestic WWTPs, are predominant sources of NDMA precursors in the studied watersheds, while croplands and urban runoff are of lesser importance.

Nonlinearities in phytoplankton groups across temperate high mountain lakes

Abstract High mountain lakes are increasingly recognized as sentinel ecosystems of global change. Monitoring phytoplankton changes or reconstructing their composition from sedimentary records can help identify systemic changes in these lakes and their catchments. This study aimed to evaluate the distribution of the major phytoplankton groups in high mountain lakes across environmental gradients and identify tipping points in relative dominance. The phytoplankton groups were estimated using pigment‐based chemotaxonomy in 79 lakes in the Pyrenees selected to cover the bedrock and elevation gradients. Fifty‐four environment variables were considered, including in‐lake and catchment descriptors. Redundancy analyses showed that in‐lake descriptors override the explicative capacity of landscape variables. Generalized additive models and multivariate regression trees showed that water hardness, trophic state and food‐web descriptors were, in this order, the most influential factors determining phytoplankton group dominance. Calcium concentration of about 200 μeq L−1 defined the threshold between soft waters—with chrysophytes and chlorophytes showing a higher affinity for them—and harder waters that favour diatoms and cyanobacteria. Across the trophic gradient, there was a threshold at ~5 μg L−1 of total phosphorus (TP), chrysophytes being dominant below that TP value and cryptophytes above. The dominance of chlorophytes and cryptophytes increased with the density of macrozooplankton. Chrysophytes were significantly lower and diatoms higher in lakes with fish. Synthesis. The relative abundance of phytoplankton groups in temperate high mountain lakes responds in a nonlinear way to the hardness of the water in the range 20–1195 Ca2+ μeq L−1 and the trophic state in the range 0.94–19 TP μg L −1. The thresholds across water hardness and trophic state gradients coincide with studies based on other organisms, pointing to a robust typology for mountain lakes that should be considered when selecting global change sentinel lakes and anticipating abrupt transitions across these thresholds.

Simultaneous water softening and selective ammonia nitrogen recovery from coal gasification gray water using an innovative four-chamber flow-electrode electrochemistry system

Capacitive deionization-based technologies such as flow electrode capacitive deionization (FCDI) have shown great promise for desalination and resource recovery, but simultaneous desalination and resource recovery using one FCDI device has thus far received minimal attention. In this study, a novel four-chamber FCDI coupled with a monovalent cation exchange membrane (MCEM) was proposed to realize simultaneous desalination (including water softening) and ammonia-rich solution production from coal gasification gray water (CGGW). The results showed that under optimal conditions, up to 91.2 ± 0.1 % ammonia nitrogen, 88.9 ± 1.0 % Ca2+, and 92.6 ± 5.5 % total organic carbon of real CGGW were removed by the desalination chamber. Furthermore, NH4+ passed through the MCEM and entered the recovery chamber, while Ca2+ was effectively blocked from entering the recovery chamber by MCEM. Thus, a multipurpose ammonia-rich solution with purity of 98.0 % was obtained. The process was superior since two typical FCDI cells are needed to realize water softening and recover ammonia-rich solutions. The mechanistic insights into the proposed four-chamber FCDI coupled with MCEM can be expanded to other simultaneous desalination, ion separation and recovery processes. Thus, the four-chamber FCDI is a promising technology for simultaneous desalination and resource recovery with the advantages of being chemical-free, capital efficient and operable.

Development of a Novel Water Jet Polisher Using Soft Abrasives for Small Complex-Structure Heat Pipes of Aluminum Alloy Produced Using Additive Manufacturing.

It is a challenge to polish the interior surface of a small bent pipe with complex structures and sizes less than 0.5 mm. This is because of the fact that traditional polishing methods could destroy, block, or break the small complex structures. For a small bent pipe made of aluminum alloy produced using additive manufacturing, the defects, such as adhered powders and spatters, are easy to jam the pipe without polishing, possibly resulting in catastrophic failure for aerospace applications. To overcome this challenge, a novel water jet polisher was developed using soft polymethyl methacrylate (PMMA) abrasives. After polishing a specific area, the adhered powders on the interior surface were reduced from over 140 to 2, 3, and 6 by the soft abrasives with mesh sizes of 200, 400, and 600, respectively. The surface roughness Sa was decreased from 3.41 to 0.92 μm after polishing using PMMA abrasives with a mesh size of 200. In comparison, silica abrasives were also employed to polish the small bent pipes, leading to the bent part of pipes breaking. However, this kind of failure was absent when using soft abrasives. Computational fluid dynamics calculations elucidate that a peak erosion rate of silica abrasives for a bent pipe with a turn angle of 30° is 2.18 kg/(m2·s), which is 17 times that of soft abrasives. This is why the small bent pipe was broken using silica abrasives, whereas it remained intact when polished with soft abrasives. In addition, water jet polishing has a lower erosion rate, a relatively smooth erosion curve, and less erosion energy, leaving the bent parts intact. The developed soft abrasive water jet polisher and the findings of this study suggest new possibilities for cleaning the adhered powders and spatters and polishing the interior surface of small bent pipes with complex structures.

Failure investigation of the tunnel lining in expansive mudstone – A case study

When studying the deformation characteristic of tunnel lining in the expansive surrounding rock, most research focuses on the expansion effect of surrounding rock after water absorption, while seldom considers the softening effect caused by water absorption at the same time. Therefore, based on a failure case of a tunnel in expansive mudstone in northern China, this paper investigates the expansion characteristics of the mudstone and the deformation as well as the failure law of tunnel lining through laboratory tests, field monitoring and numerical simulations. The results show that the mudstone exhibits significant water disintegration and softening characteristics, with a noticeable deterioration in strength. The clay mineral content of the mudstone is 68.8 %, and evaluations of various indicators indicate moderate expansion potential. The failure modes at the crown of the preliminary lining are compressive failure, which are coincident with that of field monitoring. The expansion of the surrounding rock leads to a sharp increase in the internal forces of the preliminary lining, significantly weakening its safety and causing large deformation even damage. The maximum deformation of lining reached 449 mm, necessitating the dismantling and rebuilding of the damaged preliminary lining. Therefore, in the design and construction of tunnels in mudstone, considering the expansive potential is essential to ensure the safety of the project.

Methodology for assessing the food attractiveness of feeding objects on the example of juvenile Australian red claw crayfish

The aim of the work: to identify behavioral responses that make it possible to characterize the food attractiveness of potential feeding objects for juveniles of the crayfish Cherax quadricarinatus.Used methods: the study was conducted on the juvenile Australian red-clawed crayfish C. quadricarinatus, in the aquarium room of aquaculture invertebrate department at VNIRO. 11 types of feeding objects of plant and 4 types of animal origin were studied, as well as TetraWaferMix compound feed as a control. A total of 616 experiments were performed.Newness: on the juveniles of the Australian red-clawed crayfish C. quadricarinatus, the methodology for assessing the nutritional attractiveness of feeding objects by the nature of behavior during feed consumption was tested.Result: the experiments conducted showed that a large proportion of individuals who threw, crumbled, held food with their oral limbs for a long time without attempting to mechanical processing it or did not eat the food, indicates its unsatisfactory nutritional qualities. The time spent by crayfish on eating food depends on the hardness of the proposed components, the rate of their softening in water, the size of individuals and therefore cannot directly characterize the nutritional attractiveness of the feed. Most of the proposed forage objects (11 out of 15) had attractive nutritional characteristics for juveniles of C. quadricarinatus crayfish. The most active juveniles consumed animal feed (larvae of Chironomus sp. and Hermetia illucens, squid meat, Gammarus sp.), and among the feeds of plant origin, the seeds of oats, wheat and fried buckwheat, as well as beets and potatoes had the greatest attractiveness.

Medicinal plants for gallstones: A cross-sectional survey of Moroccan patients

BackgroundGallstone is an expensive and very common gastrointestinal disorder affecting 10–20 % of the adult population. The traditional use of medicinal plants in Morocco is an ancestral and common practice to solve health problems, including gallstone disease. Our study aimed to identify the medicinal plants used by patients suffering from gallstones. MethodsA cross-sectional survey was conducted on the use of medicinal plants for the treatment of gallstones in the visceral surgery department, University Hospital Center Ibn Rochd of Casablanca, Morocco. Face to face interviews were carried out with 128 hospitalized patients using a closed-ended questionnaire. ResultsPatients with gallstones underlined the use of 35 species belonging to 21 botanical families. The most frequently used plant was Citrus limon, followed by Petroselinum sativum, Herniaria hirsuta and Olea Europea, belonging respectively to Rutaceae, Apiaceae, Caryophyllaceae and Oleaceae. The respondents used different parts of plants; seeds, aerial parts, fruits and leaves. The most commonly preparations were decoction, infusion and powder form. More than two-thirds of the patients were overweight or obese, regularly consume soft drinks and drink little water a day. ConclusionThe pharmacological effect of the inventoried plants and their active ingredients are consistent with their use in the traditional Moroccan pharmacopoeia to treat and to prevent gallstones. These plant species could be a potential avenue for the discovery of an alternative treatment; however, further chemical and pharmacological investigations are needed.

Electrodialysis Technology for Water Softening Regarding Water Equilibrium

Electrodialysis Technology for Water Softening Regarding Water Equilibrium

A novel in-situ hydrolysis approach to prepare ultra-selective and ultrasmooth nanofiltration membrane for efficient and sustainable ion separation

Nanofiltration (NF) membranes are increasingly recognized for their proficiency in monovalent/divalent ion separation, making them highly suitable for application such as water softening and resource recovery. This study introduces an innovative in-situ hydrolysis method to enhance the ion selectivity of thin-film composite nanofiltration (TFC-PA NF) membranes. In this method, the reactive monomer in the oil phase was pre-hydrolyzed by contacting with water, producing a partially hydrolyzed monomer that remained soluble in the oil phase. This in-situ hydrolysis process introduced more carboxylic groups to the membrane. That could lead to a proper enlargement of the pore size, subsequently facilitating the separation of Cl−/SO42−. Additionally, the hydrolysis altered the polarity of the acyl chloride molecule, prompting its accumulation at the oil/water interface and accelerating the polymerization reaction rate. This resulted in a thin and exceptionally smooth PA layer. The resulting membrane exhibited a remarkable Cl−/SO42−separation factor of ∼316 under moderate feed concentration and ∼478 under high feed concentration, while maintaining decent water permeance (14.4 L m−2 h−1 bar−1). Moreover, its maintained surface carboxylic group density, combined with ultra-low surface roughness, offered drastically enhanced fouling resistance. Our study illuminates the pathway for a straightforward and scalable method to fabricate highly selective membranes with superior fouling resistance.

Interaction and Stability of Nanobubbles and Prenucleation Calcium Clusters during Ultrasonic Treatment of Hard Water.

To investigate the stability of nanobubbles in natural hard water, a series of eight samples ranging in hardness from 0 to 332 mg/L CaCO3 were sonicated for periods of 5-45 min with an ultrasonic horn. Conductivity, temperature, ζ-potential, composition, and pH of the water were analyzed, together with the crystal structure of any calcium carbonate precipitate. Quasi-stable populations of bulk nanobubbles in Millipore and soft water are characterized by a ζ-potential of -35 to -20 mV, decaying over 60 h or more. After sonicating the hardest waters for about 10 min, they turn cloudy due to precipitation of amorphous calcium carbonate when the water temperature reaches 40 °C; the ζ-potential then jumps from -10 to +20 mV and remains positive for several days. From an analysis of the change of conductivity of the hard water before and after sonication, it is estimated that 37 ± 5% of calcium was not originally in solution but existed in nanoscale prenucleation clusters, which decorate the nanobubbles formed in the early stages of sonication. Heating and charge screening in the nanobubble colloid cause the decorated bubbles to collapse or disperse, leaving an amorphous precursor of aragonite. Sonicating the soft supernatant increases its conductivity and pH and restores the negative ζ-potential associated with bulk nanobubbles, but there is no further precipitation. Our study of the correlation between nanobubble production and calcium agglomeration spanning the hardness and composition ranges of natural waters shows that the sonication method for introducing nanobubbles is viable only for hard water if it is kept cold; the stability of the nanobubble colloid will be reduced in any case by the presence of dissolved calcium and magnesium.

Hydrothermal synthesis of zeolites from residual waste generated via indirect carbonation of coal fly ash

Indirect carbonation, a technology to store CO2 and produce stable CaCO3 and MgCO3, involves elution of Ca and Mg from industrial waste and subsequent carbonation. Although substantial residual waste is generated after the elution of Ca and Mg, its recycling attributes have not been adequately scrutinized. The residual waste has lower Ca and Mg contents and higher Si and Al contents than those of the raw material (i.e., industrial waste). This study involves the hydrothermal synthesis of zeolite-P using residual waste from indirect carbonation, conducted at both 100 and 180 ℃. The properties of these zeolites are compared with those synthesized from coal fly ash (CFA). The synthesized zeolites were characterized by X-ray diffraction, field emission scanning electron microscope, thermogravimetric analyzer, and Brunauer–Emmett–Teller (BET). A high zeolite conversion efficiency was achieved through a hydrothermal reaction (up to 87%), even though Si and Al were not added to the residual waste. Additionally, the cation exchange capacity and BET specific surface area of the synthesized zeolites were high (200 cmol kg−1 and 73 m2 g−1, respectively). These findings highlight the possibility of synthesizing zeolites using the residual waste from indirect carbonation as an alternative to conventional zeolite synthesis using industrial waste such as CFA. The synthesized zeolite-P is expected to be effective in wastewater treatment, detergent manufacturing, and water softening.

Application of capacitive deionization technology in water treatment and coupling technology: a review

CDI plays an important role in water desalination, water softening, removal of heavy metals, purification of industrial wastewater, and removal of nutrients, and CDI coupling technology is emphasized.

Magnetic Modification of Ion Exchange Processes

Today, the ion exchange method is widely used in water treatment systems. Ion exchange systems are used to correct the mineral composition of water to the required standards; wastewater treatment; desalination and softening of natural waters. To present day, there are technical solutions to improve the process of water purification, treatment, softening and demineralization. They include: improvement of physical and chemical conditions; intensification of the ion exchange process; use of new ion exchange materials; modification of ion exchange resins; combination with other water treatment methods; modernization of equipment and designs of ion exchange devices. In order to improve the flow conditions and reduce the burden on the environment, it is promising to implement technologies aimed at intensifying the ion exchange process by activating the components of the process. The paper investigates the effect of magnetic modification on the intensification of ion exchange processes during the adjustment of the mineral composition of natural waters. The obtained results demonstrate the influence of the magnetic field on the ion exchange process.