Hardness Removal Research Articles

Current Pulsated Electrochemical Precipitation for Water Softening

Electrochemical precipitation has obtained great attentions for water softening in recent years. In order to avoid cathode deactivation, periodical scale detachment is essential. In general, the scale adhered to the cathode is detached by mechanical scraping. Although mechanical scraping is easy operated, elastic scraper must be installed between electrodes, leading to the low softening efficiency and high energy consumption. To overcome such a problem, a new current pulsated electrochemical precipitation process was proposed in this paper. Scale detachment was accomplished by increasing the current density significantly. Experimental results showed that the both high softening and detachment performance were achieved. The precipitation rate was as high as 40.47 g/h/m2. The energy consumption and the total hardness removal efficiency were 8.9–13.2 kWh/kg CaCO3 and 17.8–22.8%, respectively. Repetitive experimental results indicated the current pulsated electrochemical precipitation process could run steadi...

Baker’s yeast wastewater advanced treatment using ozonation and membrane process for irrigation reuse

Abstract This study focused on the advanced treatment of biologically treated baker’s yeast wastewater for the purpose of irrigation reuse. The effects of pH (3, 7.5, 9, 11) and temperature (25 °C, 35 °C, 45 °C) on the removal efficiencies were investigated for ozonation process. Ozone utilization rates were determined at different pH and temperature levels. There were not significant changes in pollutant removal efficiencies at the temperature of 25 °C–45 °C for ozonation process. 96–98% color, 56% COD, 67% UV254, 10% conductivity, 33% chloride, and 29% total hardness removals were obtained with ozonation process at pH 7.5 and 25 °C. NF 90 and BW 30 membranes were used to improve the quality of treated wastewater. Relatively lower flux decline caused from membrane fouling (18%) was occurred for BW 30 membrane. Although higher permeate qualities were achieved with both membranes, the chloride and conductivity values as 35 mg/L and 530 μs/cm were relatively lower for BW 30 permeate. As a result, the treated wastewater using ozonation and membrane process met the quality of class B regarding pH, biological oxygen demand (BOD5), suspended solids (SS) and fecal coliform parameters. Also, II. class irrigation water was obtained considering SAR parameter for degree of restriction on irrigation use.

Electrochemical softening of concentrates from an electrodialysis brackish water desalination plant: Efficiency enhancement using a three-dimensional cathode

Abstract The electrochemical softening method to remove hardness from water has not been applied in desalination practice due to a high cathodic area requirement. In this work, the use of a 3D stainless steel wool cathode is proposed to overcome this technical limitation. An extensive comparison between the 3D cathode and a 2D Ti mesh has been presented, showing higher hardness removal for the 3D one. Experiments have been conducted with waters similar to concentrates derived from a brackish water treatment by electrodialysis. In addition, the method has been proved to be efficient for different water compositions in terms of hardness, alkalinity or the presence of an anti-scalant. The main influencing parameters (flow rate and current density) have been studied and it can be concluded that lower flow rates (below 1.2 L h−1) give rise to a better efficiencies and 100 A m−2 is the optimum current density. Moreover, the precipitate was characterised by SEM, EDX and XRD showing that Ca2+ is removed as calcite and aragonite (CaCO3), whereas Mg2+ is precipitated as brucite (Mg(OH)2). Finally, long-term experiments revealed that the 3D stainless steel cathode has a better performance than the 2D Ti mesh, but only at short times.

Removal of Hardness from Water Samples by a Carbonation Process with a Closed Pressure Reactor

One of the undesirable characteristics of some ground and natural water sources is hardness. Hard water can cause many problems around the world, including increased scaling on water pipes, boilers, atopic eczema and odd-tasting drinking water. Hardness in natural water is caused by dissolved minerals, mainly calcium and magnesium compounds. According to the Water Quality Association (WQA) and the United States Geological Survey (USGS), hard water is classified based on the Ca2+ and Mg2+ ion concentration in waters, as follows: 0–60 ppm as soft; 61–120 ppm as moderately hard; 121–180 ppm as hard and more than 180 ppm as very hard water. Most water utilities consider a hardness level between 50 and 150 ppm of CaCO3 as publicly acceptable. The present study investigated the effects of a carbonation process on the removal of hardness in different water samples. Currently, a wide variety of hardness removal technologies are available. Among those conventional methods, carbonation is an inexpensive process which can be used for the removal of Ca2+ and Mg2+ ions from hard water. This study measured the hardness levels of 17 different water samples using the ethylene diamine tetra acetic acid (EDTA) method. Among these, Seoul outdoor swimming pool water (140 ppm) samples showed high concentrations of Ca2+ and Mg2+ ions. The hardness of the different water samples was reduced by 40–85% by a carbonation process with a closed pressure reactor for a 5 min reaction time.

A Novel Technique for Water Hardness Removal by Using Polystyrene

A Novel Technique for Water Hardness Removal by Using Polystyrene

Effectiveness of Domestic Reverse Osmosis Units for Removal of Fluoride and Hardness for Drinking Purposes in Chronic Kidney Disease of Unknown Etiology (CKDu) Affected Areas in Anuradhapura

The hypothesis having excessive fluoride and hardness levels in ground water in combination is said to have been associated with the onset of CKDu. Provision of good quality drinking water devoid of fluoride and hardness to levels less than nephrotoxic levels would be considered of paramount importance. In this respect, several types of water filters have been introduced to CKDu affected areas of which RO units are the most popular filters. Hence, this research aims at investigating the effectiveness of domestic RO units in removing fluoride and hardness levels reported in CKDu affected areas under different climatic conditions for a period covering dry and wet seasons. Two monsoons and the 2nd inter monsoon were simulated in the laboratory and the removal of fluoride and hardness by the RO unit were evaluated according to the drinking water guidelines. Northeast monsoon was subdivided into extreme wet and wet to dry periods. Hardness and fluoride concentrations in the raw water during above periods were 110 ppm and 578 ppm and fluoride concentrations were 0.52 ppm and 2.93 ppm respectively. In the above periods hardness values obtained in the permeate were 12 ppm and 24 ppm and the fluoride was completely removed during extreme wet period and 0.15 ppm fluoride was observed in wet to dry period. In the 2nd inter monsoon, hardness and fluoride concentrations in raw water were 1032 ppm and 7 ppm respectively and in the permeate 40 ppm hardness and 0.39 ppm of fluoride were observed. All the above fluoride and hardness values in the permeate do not comply with the required drinking water guidelines. Southwest monsoon was subdivided in to three periods namely extreme dry, dry and dry to wet. In extreme dry period hardness and fluoride in raw water were 1230 ppm and 15.5 ppm respectively. In the permeate hardness concentration varied from 48 ppm-184 ppm and fluoride concentrations varied from 0.19 ppm-1.67 ppm. At the latter stage both the fluoride and hardness values have exceeded the required drinking water guideline values. This happen when all the adsorption sites of the filter unit get saturated with the increase of the raw water concentration and then excess amount of water constituents will pass through the RO membrane. Flow rate was dropped from 0.24 litres/min to 0.03 liters/min during these periods implying that the membrane of the unit has started to get clogged. As the performance of the RO unit depends on the initial constituent’s concentration in the raw water, according to this study people can use RO unit for a period of 6 months without getting clogged. Keywords: Chronic kidney disease of unknown etiology, Fluoride, Hardness, Reverse osmosis

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.

Avaliação do abrandamento de água calcária utilizando hidróxido de cálcio e carbonatação

A água é um recurso fundamental para a vida na terra e a sua qualidade define seus diversos usos. A qualidade da água é entendida como resultado das ações antrópicas e da sua interação com o meio físico. Assim a água possui características físicas, químicas e biológicas em virtude de suas propriedades de solvente e de sua capacidade de transportar partículas. Dentre as características químicas está a dureza de carbonatos que representa a concentração de íons como o cálcio e o magnésio em solução. Esses íons estão presentes na água subterrânea através de processos de intemperismo químico que dependem do tempo de contato entre a água e a rocha, temperatura, CO2 disponível e da presença de ácidos orgânicos e inorgânicos. Em níveis elevados de dureza total a água apresenta um sabor diferenciado o que pode ser desagradável ao paladar das pessoas. O objetivo desse trabalho é verificar o abrandamento da concentração dos carbonatos de cálcio e magnésio, pela dissolução de gás carbônico e hidróxido de cálcio, alterando o equilíbrio do sistema carbonato. Foram testadas a água carbonatada, água carbonatada e aerada e a água natural com cinco concentrações de hidróxido de cálcio (0, 25, 50, 75 e 150 mg L-1). O parâmetro avaliado foi a dureza de carbonatos. Os experimentos foram configurados em fatorial com dois fatores, aplicou-se o teste Tukey a um nível de 1% de significância. Os resultados mostraram que o fator água e o fator concentração de hidróxido foram significativos a 1% de significância, já a interação dos dois fatores não. Contudo o melhor resultado na remoção da dureza foi na concentração de 150 mg L-1 de hidróxido de cálcio em água carbonatada e aerada.

Removal of calcium hardness from solution by fluidized-bed homogeneous crystallization (FBHC) process

Calcium is one of the divalent ions contributing to the hardness level of the water. This work describes the removal of calcium ions from aqueous solution using carbonate salts as precipitants and the recovery of homogeneous calcium carbonate crystals via a fluidized-bed homogeneous crystallization (FBHC) process without a heterogeneous seed material. The considered parameters were effluent pH, initial molar ratio of carbonate salt to Ca, up-flow velocity, and cross-section loading. The removal efficiency of Ca hardness reached 95% at the optimal pH of 10–11 and the corresponding crystallization ratio was 88% for initial concentrations of Ca of 50–330 ppm. The FBHC process was effective with a cross-section loading of calcium in the water of up to 4.5 kg/m2/h. The efficiency of Ca immobilization as the crystal grew on the fluidized pellets was greatly improved by adjusting the degree of supersaturation in the range 2–3, resulting in the crystallization ratio (CR) and total removal of Ca (TR) of 88% and 92%, respectively. XRD analysis revealed that the formed crystals comprised two calcium carbonate (CaCO3) phases—calcite and aragonite. SEM images of the surface morphology revealed that calcium carbonate particles (around 1–2 mm) were formed by the aggregation of fine crystals (around 5 µm).

Technologies for the Removal of Water Hardness and Scaling Prevention

Technologies for the Removal of Water Hardness and Scaling Prevention

Integrated approach of chemical and electrodialysis process in textile effluent contaminated groundwater for irrigation

The quality of the agricultural water and soil is worst in the situation due to the rapid growth of industrialisation and uncontrolled discharge of effluent.Though soil is treated by electrokinetic (EK) to remove contaminants, this technology cannot take the lead without treatment of groundwater. In the present study, the groundwater sample was collected from Kathanganni Village, Tirupur(Textile Valley) and treated with a chemical process for removal of hardness and followed by the electrodialysis process. Two different current densities viz., 10mA/cm2(system I) and 20mA/cm2(system II)were used. Mixed metal oxide (IrO2-RuO2-TiO2/Ti) was used as anode and Titanium used as cathode. The anionic exchange (AMI − 7001) and cationic exchange (CMI − 7000) membranes were placed between anodic and cathodic compartments respectively. The anolyte and catholyte reservoirs were filled with distilled water and the middle compartment filled with chemically treated contaminated water. The optimization of alkali and soda ash for efficient removal of hardness in the groundwater was examined. The efficient removal of salinity such as chloride (90%), sulfate (98%), and TDS (96%) were achieved within 12h of electrodialysis process.This treated water quality was compared with standard irrigation water quality parameters.The electrical conductivity of the groundwater effectively reduced from 19.3±1 dS/m to 0.538±0.5 dS/m for the system I and 0.795±0.6 dS/m for system II with energy consumption of 53.85 and 149.68kWh/m3 for the system I and system II respectively.

Water Filter Fabrication from a Mixture of KMnO<sub>4</sub> Modified Kapok Carbon Fiber, Zeolite, Bentonite and Clay for Fe<sup>3+</sup>Removal and Water Hardness Treatment

A water filter was fabricated from a mixture of KMnO4 modified kapok carbon fiber, zeolite, bentonite and kaolinite clay for Fe3+ removal and water hardness treatment. The effects of amount of KMnO4 modified kapok carbon fiber (30-60 wt%), zeolite (20-40 wt%) and sintering temperature (500-700°C) on the properties of sintered products were evaluated. The best of sintered products were tested for treatment of solutions with 5 mg L-1 Fe3+ and 40-200 mg L-1 total water hardness. The results show that the physical properties of the sintered products were affected by the contents of KMnO4 modified kapok carbon fiber and sintering temperature. The linear drying shrinkages of the mixture of raw materials increase with increasing content of modified kapok carbon fiber amounts due to the effect of water amount used for mixing process. Furthermore, firing shrinkages of sintered products increased with increasing sintering temperature for the same ratio of raw materials. Finally, the firing shrinkages and density of sintered products decrease with increasing content of the modified kapok carbon fiber at constant sintering temperature. It was shown that the sintered product made with 40 wt% of KMnO4 modified kapok carbon fiber and sintered at 600°C is suitable for filter fabrication. The KMnO4 modified kapok carbon fiber filter could adsorb 5-6% more Fe3+ at equilibrium than filter made with kapok carbon fiber. The Fe3+ was removed by adsorption and precipitation processes. The Fe3+ adsorption process of modified kapok carbon fiber filter was fitted to the Langmuir model with maximum adsorption capacity of 53.76 mg g-1. For hardness removal, the Ca2+, Mg2+ and HCO3ˉ ions removal capacities from solutions of total hardness in the range 40-200 mg L-1 by modified kapok carbon fiber filter are 4.49-19.21 mg g-1 for Ca2+, 1.55- 5.31 mg g-1 for Mg2+ and 28.1-123.5 mg g-1 for HCO3ˉ, respectively.

Treatment and operation cost analysis of greywater by electrocoagulation and comparison with coagulation process in mining areas

ABSTRACTElectrocoagulation process is a new and developing method that has been employed significantly to remove pollutants from wastewater. In this research the electrocoagulation process has been examined for the removal of chemical oxygen demand (COD), turbidity, hardness, and organic matter from greywater. An economical comparison has been implemented between electrocoagulation and coagulation processes near the mining areas. The results demonstrate that the electrode type and operation time have a significant impact on the removal of COD, turbidity, and hardness. The least operating cost to remove organic matters is ~US$ 0.04 m−3 for the iron electrode. Since the least operating cost was US$ 0.09 m−3 in coagulation process, economically, the electrocoagulation process in comparison with the coagulation process is a more effective process.

Sulfate removal from wastewater using ettringite precipitation: Magnesium ion inhibition and process optimization

One of the main challenges in industrial wastewater treatment and recovery is the removal of sulfate, which usually coexists with Ca2+ and Mg2+. The effect of Mg2+ on sulfate removal by ettringite precipitation was investigated, and the process was optimized in the absence and presence of Mg2+. In the absence of Mg2+, the optimum conditions with sulfate removal of 99.7% were obtained at calcium-to-sulfate ratio of 3.20, aluminum-to-sulfate ratio of 1.25 and pH of 11.3 using response surface methodology. In the presence of Mg2+, sulfate removal efficiency decreased with increasing Mg2+ concentration, and the inhibitory effect of Mg2+ matched the competitive inhibition Monod model with half maximum inhibition concentration of 57.4 mmol/L. X-ray diffraction and Fourier transform infrared spectroscopy analyses of precipitates revealed that ettringite was converted to hydrotalcite-type (HT) compound in the presence of Mg2+. The morphology of precipitates was transformed from prismatic crystals to stacked layered crystals, which confirmed that Mg2+ competes with Ca2+ for Al3+ to form HT compound. A two-stage process was designed with Mg2+ removal before ettringite precipitation to eliminate the inhibitory effect, and is potential to realize sludge recovery at the same time of effective removal of sulfate and hardness.

A review on semi-aromatic polyamide TFC membranes prepared by interfacial polymerization: Potential for water treatment and desalination

Abstract This review centers on the reverse osmosis (RO) and nanofiltration (NF) membranes for water treatment and desalination. Specifically the RO and NF membranes, whose rejection layer is being formed using semi-aromatic polyamide in various configuration and structure, have found prominent space in membrane arena. An interfacial polymerization (IP) is a distinctive technique for producing in - situ polyamide membrane in the form of films or composites using wide variety of amines and acid chloride monomers of various compositions. In this context, thin film composite membranes prepared by IP techniques are reviewed with their history in the present review. Emphasis is given on systematic development of membranes with its structural composition and separation characteristics. The functions of various additives and effect of IP reaction parameters on performance of membranes have been briefly discussed. Types of composite polyamide (PA) membranes prepared from comonomers, their derivatives and oligomers are reviewed. Commercial PA membranes are also discussed in details with their niches in the separation of monovalent and divalent ions and organics from water. Poly(piperazine amide) and polyethyleneimine based PA membranes show promising applications for water softening (hardness removal) in the form of flat sheet and hollow fiber configuration. This review may guide the researchers and separation scientists to develop novel approach for further development and modification of membranes for removal the toxic and harmful ions from water.

Hardness Removal from Water by Modified Starch

This is a preliminary study for hardness removal via modified starch combined with an ultrafiltration process that provides on high effluence quality and low cost, footprint and environmental impact treatment. This studied on potential of chemisorption process using modified starch as absorbents for hardness removal. Four modified tapioca starches were selected for evaluation that includes of oxidize starch, di-starch phosphate, hydroxyphophyl starch and phosphate monoester as well as non-modified tapioca starch too. Phosphate monoester starch achieved the highest efficiency about 98.2% of hardness removal within the adsorption capacity about 18 mg-hardness removed/g-starch. The modified starch had capable to reduced total hardness from 350.5 mg/L as CaCO3 to 6.3 mg/L as CaCO3 from water. However, the modified starch is an organic matter its can be contaminates in water. Then, a coagulation-flocculation processes were applied for starch colloidal destabilization and flocs by aluminum chloride (PAC) and cationic polymer for starch separation. After that process, turbidity was less than 1 NTU in the effluents. However, the total dissolved solids were increased that may be cause of some starch was solutes. These should be having a future treatment for particulate removal and cutoff the soluble starch in water likes an ultrafiltration process.

Treatment and reuse of shale gas wastewater: Electrocoagulation system for enhanced removal of organic contamination and scale causing divalent cations

The present study explores the feasibility of using the electrocoagulation (EC) process for the treatment and reuse of wastewater produced during shale gas recovery by hydraulic fracturing. The electrocoagulation process has been evaluated for the removal of suspended solids, total organic carbon (TOC) and scale (hardness) causing divalent cations, which, if untreated, can clog the gas well. Experiments were performed with actual shale gas wastewater (ASWW), synthetic shale gas wastewater prepared with low concentration of dissolved salts (SSWW – LDS) and synthetic shale gas wastewater prepared with a high concentration of dissolved salts (SSWW – HDS).EC is found to be effective for removing TOC and hardness from both the actual and synthetic shale gas wastewaters. The electric energy required per unit mass (EEM) for removal of TOC for ASWW, SSWW – LDS and SSWW – HDS are 243, 102 and 70kWh/kg respectively. The EEM for removal of hardness for ASWW, SSWW – LDS and SSWW – HDS are 303, 104 and 25kWh/kg respectively. The high conductivity of SSWW – HDS helps in achieving higher currents and hence the lower reported EEM values for SSWW – HDS. Also, under alkaline conditions, the performance of EC increases significantly. Combination of aeration with EC is also found to increase the performance of EC, especially for wastewater containing high concentrations of chloride ions.

Removal of hardness from groundwater using two nanofiltration membranes: experimental study and modeling

Removal of hardness from groundwater using two nanofiltration membranes: experimental study and modeling

Removal of hardness from RO concentrate of paper mill effluents with NF membrane for water reuse

Removal of hardness from RO concentrate of paper mill effluents with NF membrane for water reuse

Hardness removal in membrane capacitive deionization with a selective cation exchange membrane

Hardness removal in membrane capacitive deionization with a selective cation exchange membrane