Total Hardness Concentrations Research Articles

High-fluoride groundwater

Fluoride (F(-)) is essential for normal bone growth, but its higher concentration in the drinking water poses great health problems and fluorosis is common in many parts of India. The present paper deals with the aim of establishment of facts of the chemical characteristics responsible for the higher concentration of F(-) in the groundwater, after understanding the chemical behavior of F(-) in relation to pH, total alkalinity (TA), total hardness (TH), carbonate hardness (CH), non-carbonate hardness (NCH), and excess alkalinity (EA) in the groundwater observed from the known areas of endemic fluorosis zones of Andhra Pradesh that have abundant sources of F(-)-bearing minerals of the Precambrians. The chemical data of the groundwater shows that the pH increases with increase F(-); the concentration of TH is more than the concentration of TA at low F(-) groundwater, the resulting water is represented by NCH; the TH has less concentration compared to TA at high F(-) groundwater, causing the water that is characterized by EA; and the water of both low and high concentrations of F(-) has CH. As a result, the F(-) has a positive relation with pH and TA, and a negative relation with TH. The operating mechanism derived from these observations is that the F(-) is released from the source into the groundwater by geochemical reactions and that the groundwater in its flowpath is subjected to evapotranspiration due to the influence of dry climate, which accelerates a precipitation of CaCO(3) and a reduction of TH, and thereby a dissolution of F(-). Furthermore, the EA in the water activates the alkalinity in the areas of alkaline soils, leading to enrichment of F(-). Therefore, the alkaline condition, with high pH and EA, and low TH, is a more conducive environment for the higher concentration of F(-) in the groundwater.

Quality assessment of drinking water in Temeke District (part II): Characterization of chemical parameters

This paper presents a study on drinking water quality in Temeke District (Dar es Salaam), which involved analyses of chemical parameters of drinking water samples from different drinking water sources. The drinking water sources examined included tap water, river water and well water (deep and shallow wells). Water quality studied includes pH, chloride, nitrate and total hardness levels. The concentrations of total hardness in mg CaCO 3 /L and chloride were obtained by titration method while the nitrate concentration levels were determined by spectrophotometer. Tap water was found to be of high quality than other sources in terms of chemical characteristics. The study revealed that the chemical parameters of water sources did not meet the permissible World Health Organization (WHO) and Tanzania Bureau of Standards (TBS) levels. Examining exceedence above the WHO standards, it was revealed that most of the samples contained chloride levels above allowable WHO limits. It was recommended that drinking water sources for domestic use should be protected from pollution sources. Key words: Drinking water quality, pH, chloride, nitrates, total hardness, exceedence.

New desalinated drinking water regulations are met by an innovative post-treatment process for improved public health

The recent supply of large volumes of seawater desalinated water in Israel prompted both the development of new water quality standards and the development of a novel post treatment process, designed to comply with the new standards at a cost effective price. The new process is designed to supply water with alkalinity, Ca2 + and calcium carbonate precipitation potential values as required in the new criteria, along with the addition of a threshold Mg2 + concentration recently recommended by the WHO. The current paper describes the process in general, and focuses in particular on attaining these criteria while maintaining a low total hardness concentration (120 mg/L as CaCO3). The process is based on dissolving calcite using H2SO4 and replacing the excess calcium ions generated in this process by Mg2 + ions (using a specific cation exchange resin—Amberlite) and by Na+ (using a second cation exchange resin—chabazite, from the zeolite group). Once exhausted the resins are re-loaded with Mg2 + and Na+ by the brine generated in the RO process, thus no unwanted brines are generated. A case study is presented for which operational costs were approximated at 0.034 $US/m3 product water.

Treatment Efficiency and Formation of Disinfection By-Products in Advanced Water Treatment Process

This study found that advanced and traditional chlorination water purification processes significantly reduced turbidity and concentrations of ammonia-N (NH3-N), nitrite nitrogen, iron, and manganese. Pellet-softening treatment was effective in reducing alkalinity and total hardness (TH) concentrations. Low TH concentrations are known to reduce cardiovascular death rate. Both total organic compound (TOC) and total dissolved solids (TDS) concentrations are typically considered precursors of trihalomethanes (THMS) and haloacetic acid (HAA5). In this study, advanced and traditional chlorination water purification processes were not effective in reducing TOC and TDS concentrations. In the formation of disinfection byproducts (DBPs), the THMS and HAA5 were efficiently removed by flocculation/sedimentation and the biological activated carbon (BAC) treatment processes. Postchlorination can reproduce THMS and HAA5 levels in a freshwater reservoir. Bromate concentration's lower detection limit were treated by the ozonation process during the study periods. Advanced treatment processes should controlled the doses of ozone and postchlorine to avoid produce DBPs.

Environmental impact assessment of risk associated with groundwater overdraft remediation in cone of depression, Jining, China

In this paper, a simple scenario and probabilistic approach is used to assess the potential groundwater risk due to proposed overdraft remedial actions in cone of depression, Jining City, China. Focusing on the concentrations of Chloride ions (Cl−) and total hardness (TH), the impact of artificial recharge and reduced pumping on groundwater quality and quantity is analysed by using the three-dimensional finite difference groundwater flow and transport model, Visual MODFLOW, to simulate groundwater flow and transport within the study area based on scenarios, and utilizes SURFER software to map risk levels. Although 5, 10 or 15% reduced pumping with artificial recharge leads to more decrease in Cl− and TH concentrations than the 25%, less volume increase is achieved for the remediation of land subsidence and other environmental problems in the cone of depression. The Cl− concentrations in recovered groundwater are within the desired concentration of 200 mg/l; however, TH in some cases are above the maximum permissible limit of 500 mg/l, with an exceedence probability of about 0.67 for recharge and recharge with reduced pumping at 25%. The presence of fractures and hydrogeological complexity greatly determines impacts of remediation, and the 22% reduced pumping with artificial recharge offers an optimum strategy for overdraft remediation in the Jining cone of depression.

Simulation of the dissolution of weathered versus unweathered limestone in carbonic acid solutions of varying strength

AbstractA simulation was undertaken within a climatic chamber to investigate limestone dissolution under varied carbonic acid (H2CO3) strengths as a possible analogue for future increases in atmospheric CO2 arising from global warming. Twenty‐eight samples cut from a block of Bath (Box Hill) limestone from Somerville College, Oxford, which had been removed during restoration after 150 years in an urban environment, were weighed and placed in closed bottles of thin plastic containing varying concentrations of H2CO3. Half of the stone samples were derived from exposed surfaces of the stone block (weathered) while the others were obtained from the centre of the block on unexposed surfaces (unweathered). The purpose of this was to compare dissolution of previously weathered versus unweathered surfaces in strong (pH 4·73) versus weak (pH 6·43) solutions of H2CO3. A temperature of c. 19 °C was maintained within the chamber representing a plausible future temperature in Oxford for the year 2200 given current warming scenarios. The simulation lasted 25 days with a few stone samples being removed midway. Stone samples show reduced weight in all cases but one. There was greater dissolution of stone samples in a strong H2CO3 solution as conveyed by higher concentrations of total hardness and Ca2+ in the water samples as well as enhanced microscopic dissolution features identified using SEM. The simulation confirms that enhanced atmospheric CO2 under global warming, given adequate moisture, will accelerate dissolution rates particularly of newly replaced limestone building stones. However, previously weathered surfaces, such as those on historical stone exposed for a century or more, appear to be less susceptible to the effects of such increased rainfall acidity. Conservation techniques which remove weathered surfaces, such as stone cleaning, may accelerate future decay of historical limestone structures by increasing their susceptibility to dissolution. Copyright © 2006 John Wiley & Sons, Ltd.

Fouling of reverse osmosis and nanofiltration membranes by diary industry effluents

Fouling experiments of nanofiltration (NF) and reverse osmosis (RO) are reported for treatment of the effluent of chemical-biological treatment plant and the original effluent of dairy industry respectively. In the experiments, a thin film composite type of spiral wound was used and fitted with flowmeters and pressure sensors. The feed water was stored into a feed tank and passed a fine filter and was pumped to membrane. Brine and permeate were recirculated back to the feed tank. Membrane fouling was investigated with 16 and 30% water recovery of a single membrane at different pressures and flowrates for RO and NF membranes respectively. Fouling is evaluated with a relationship between relative flux (J/Jo) which is the ratio of the flux at any time during the fouling test to the initial flux and relative resistance (Rf/Rm) which is the ratio of fouling (cake) layer resistance to clean membrane resistance. Turbidity, conductivity, chemical oxygen demand (COD), total suspended solids (TSS) and total hardness were measured in the feed and permeate side of each membrane. The effluent total hardness concentrations of chemical-biological treatment plant were found greater than the influents. The results are presented in terms of the relative flux as a function of time related to hydrodynamic conditions and pollution characteristics of wastewater. The permeate water flux of RO membrane decreases more rapidly than NF membrane, the relative flux decreases with increasing the fouling layer resistance, Rf onto membrane surface. 50% the drop of permeate flux was observed for RO and NF membranes after 50 h and 80 h of operation, respectively. The fouling rate increases with an increase in the concentration of the wastewater constituents in the dairy industry. The relative flux decreased 10 and 20% with increasing chemical oxygen demand (COD) from 5,000 mgl-1 to 10,000 mgl-1 and from 45 mgl-1 to 450 mgl-1 for RO and NF membranes, respectively after 45 h of time. Fouling of membranes resulted in 100% increase of specific energy consumption as the relative permeate fluxes of NF and RO membranes decreased 30 and 40% respectively. The average of specific energy consumption was obtained at 6 and 10 kWhm-3; consequently, operational costs were estimated at U.S. $0.45 m-3 and U.S. $0.75 m-3 for NF and RO units respectively. Also, operational cost for chemical-biological treatment was found at U.S. $0.30 m-3.

Relative importance of calcium and magnesium in hardness‐based modification of copper toxicity

AbstractWe cause of the relationship between water hardness and the toxicity of many metals, total hardness is used as a model parameter to calculate ambient water quality criteria for copper and other metals. However, the relative contribution of the Ca and Mg components of total hardness as modifiers of metals toxicity is not considered in the water quality criteria. Acute Cu toxicity was measured in rainbow trout (Oncorhynchus mykiss) and chinook salmon (O. tshawytscha) swim‐up fry in laboratory waters that were formulated to have similar total hardness and alkalinity but different Ca and Mg concentrations. Experiments were performed at nominal total hardness values of 40 and 90 mg/L (as CaCO3). In four paired toxicity tests, acute Cu toxicity was significantly lower, i.e., 96‐h LC50s were higher, in laboratory waters containing proportionately more Ca (Ca:Mg molar ratios of 1.5–5.2) than in waters containing less Ca (Ca:Mg molar ratios of 0.2–0.8). The relative increase in the 96‐h Cu LC50 at higher Ca concentrations, but similar total hardness concentrations, was between 28 and 86% when the low Ca treatment was similar to American Society for Testing and Materials laboratory water (Ca:Mg molar ratio = 0.7). Failure to account for differences in Ca when matching or adjusting for total hardness thus exerts an important influence on the prediction of metal toxicity. These differences must be addressed in water‐effect ratio testing in which paired tests with laboratory and site waters are conducted.

Quality of Water Wells in an Agricultural Area in the City of La Plata, Argentina

The quality of the water from 62 home wells in a section (with no sewerage system) of the agricultural-industrial area of La Plata, was analyzed. The measurement of the studied parameters concentrations were compared with those obtained in seventeen water wells located in another area of town, with commercial characteristics. The pH, total dissolved salts (TDS), nitrates, chlorides, total hardness (TH) and coliform bacteria, these being differentiated between colifaecals and IAC group bacteria, were studied. The average concentration of TDS was 619 and 497 mg L-1 respectively. 34% of the samples exceeded the limit of 45 mg L-1 established by the World Health Organization (WHO). The nitrate levels varied widely from 6 to 216 mg L-1, with an average value of 56 mg L-1 in the agricultural area, and between 5 and 61 mg L-1 in the commercial area, with an average of 19 mg L-1. The average concentrations of chlorides and TH were 89 mg L-1 and 177 mg L-1, respectively in the agricultural area; while in the other area, the average levels were 38 mg L-1 chloride and 107 mg L-1 TH. Significant differences were observed between the chemical parameters evaluated in the two areas analyzed. E. Coli bacterium was detected in 49% of the well water samples analyzed. IAC group bacteria were confirmed in 28% of the samples. The average depth of the water wells within 10 m from the cesspits was 28.2 m, and those situated farther than 10 m. had an average of 39.9 m depth. Results indicated a remarkable quality degradation of the well waters as regards their contents of E. Coli bacteria and nitrate. This could be due to the deficient construction of the absorption wells, to their closeness with cesspits and the inexistence of septic chambers within every dwelling.

Elemental and Geochemical Analysis of the Umm-Khurisan Spring Water (Al-Hasa Area, Eastern Province, Saudi Arabia)

Abstract The Umm-Khurisan spring is a small spring, located in the Al-Hasa area in the Eastern Province of Saudi Arabia. The high concentrations of total hardness, total disolved solids, Cl−, NO− 3 and F−, and the high value of the electrical conductivity of the spring water are above the limits recommended by the World Health Organization standards with regard to potability. Concentrations, of other minor constituents are around these limits. Therefore, it is recommended that the Umm-Khurisan spring water should not be used for drinking purposes. The Umm-Kurisan water is a saline water with medium sodium hazard. Such water should be used only on soils of moderate to good permeability. The Umm-Kurisan spring water probably is of meteoric origin of deep percolating water.

Regional Geology and the Chemical and Trophic State Characteristics of Florida Lakes

ABSTRACT A limnological survey of 165 Florida lakes was conducted between September 1979 and August 1980 to determine their chemical and trophic state characteristics. A wide range of limnological conditions was documented. Average lake pH values ranged from 4.1 to 9.2 and average total alkalinity concentrations ranged from 0 to 204 mg/L as calcium carbonate (CaCO3). Average specific conductance values ranged from 11 to over 5600 μS/cm at 25° C. Mean total nitrogen concentrations ranged from 0.063 to 4.6 mg/L and mean total phosphorus concentrations ranged from 3 to 834 mg/m3. Although lake trophic states ranged from oligotrophic to hypereutrophic, Florida lakes as a group can be characterized as productive, softwater lakes. Over 75 percent of the sampled lakes had total alkalinity concentrations below 40 mg/L as calcium carbonate and total hardness concentrations below 75 mg/L as calcium carbonate. Most of the sampled lakes were either mesotrophic (52 percent) or eutrophic (35 percent) because total phos...