Solar still an appropriate technology for potable water need of remote villages of desert state of India — Rajasthan

Rajasthan, the largest state of the India faces a grim scenario in relation to water availability resources. Rajasthan has two-third of its area as desert and it faces scanty rainfall, recurring droughts in 3–4 years in a cycle of 5 years. It would be seen from the present status of drinking water detailed out of 237 blocks in Rajasthan that only 49 are safe in terms of ground water while 101 are critical and semi critical and 86 are over exploited. It is a hard reality that state dependence on ground water is 91% for drinking water. About 21,190 villages/habitations suffer from the problem of excessive salinity, 23,297 villages/habitations suffer from excess fluoride problem and 20,659 villages/habitations suffer from excess nitrate problem. Based on the WHO guidelines for drinking-water quality about 56% of the water sources are un-potable.

But on other hand Rajasthan is blessed with ample amount of solar radiation. The arid parts of Rajasthan receive average maximum solar radiation of about 7.5 kW h/m² in the month of May and minimum of about 4.6 kW h/m² in the month of Dec & Jan. Part of this energy may be utilized to meet out drinking water need of remote area dwellers of Rajasthan.

Solar distillation and desalination unit is most appropriate for remote area dwellers because it is economical, easy to construct and maintain. Most parts of Rajasthan have enough solar radiation available which is the prime input for the system.

A low cost high efficiency solar still with porous evaporating surface is fabricated for the purpose and cost analysis is done to calculate the cost of water in this paper [Bassam et al., Experimental study of a solar still with sponge cubes in the basin, Energy Conserv. Manage., 44 (9) (2003) 1411–1418; Bouchekima et al., Performance study of the capillary film solar distiller, Desalination, 116 (1999) 185–192; Bassam et al., Water film cooling over the glass cover of a solar still including evaporation effect, Energy, 22 (1) (1997) 43–48].

Water samples are collected from a remote village of state and analyzed to find the quality of drinking water. The working habits and medical history of the villagers is also investigated to work out cost analysis more realistically.     

Modeling remineralization of desalinated water by limestone dissolution

Desalted waters or highly soft waters produced by desalination plants cannot be directly used as they are unpalatable, corrosive and unhealthy. Remineralization is necessary in order to overcome these problems. A commonly used operation in the remineralization process is to contact CO₂ acidified desalinated water with a bed of domestic limestone. Limestone dissolution provides two essential ingredients to the water—bicarbonate alkalinity and calcium content: CaCO₃ + CO₂ + H₂O = Ca²⁺ + 2HCO₃^–. Limestone dissolution is a slow rate-controlling step. Prediction of the limestone rate of dissolution as a function of the water composition is essential for reliable design and operation of the limestone contactor. A critical comparison of various kinetic expressions proposed in the literature carried out in this study reveals major differences in results evaluated from different dissolution models. An experimental study was conducted in order to identify the most reliable kinetic dissolution model. Two series of experiments were carried out—one involving remineralization of distilled water containing low initial CO₂ concentrations (0.5–2 mM) and the other, remineralization of soft water, having high initial CO₂ concentrations (1.5–15 mM). The CO₂ acidified water was contacted in a 2 m high vertical column (32 mm I.D.), packed with 2.85 mm calcite particles. The change in water composition along the column was monitored to provide both differential and integral dissolution data. Analysis of the data showed that none of the available models fitted the experimental results. The closest agreement was with the rather complex model of Plummer et al but this agreement was rather mediocre. In the high CO₂ content range, the model predicted dissolution rates higher by a factor of 2–4 in the high CO₂ range and by a factor of 10–20 in the low CO₂ range. Based on the experimental results, two models were developed for the design of limestone dissolution column contactors. When the final composition of the remineralized water has a CO₂ content above 2 mM, the limestone bed can be designed by a very simple integral expression. However, if the dissolution depletes the CO₂ concentration to low values, well below 2 mM, the bed design requires numerical integration of the more general dissolution rate expression derived in this work.     

Reverse osmosis to achieve water control and recycle

A 648,000 GPD reverse osmosis (RO) facility at ERDA's Rocky Flats Plant near Golden, Colorado will convert tertiary sewage plant effluent for recycle as cooling tower makeup to reduce external water demand and achieve “zero discharge” off-site of tertiary sewage effluent.

Design parameters for the facility, determined by three years of pilot plant testing, include 98% feedwater recovery, 100 ppm T.D.S. product water, and minimum brine production for evaporation to dryness.

Pretreatment consists of RO feed attenuation in a large pond, chlorination, sand filtration, softening, diatomaceous earth filtration, feed-water heating and pH adjustment. The RO plant will have three 150 GPM trains, each with a combination of HFF modules producing about 90% of the permeate, followed by SW modules producing the final 10%. Permeate from the SW modules can be combined with permeate from the HFF modules or returned to the RO feed stream.

Unique design considerations include heating the 40–70°F fee to 77°F by means of heat recovery from the permeate and supplemental steam heating, recycling of pretreatment backwash streams wherever possible to reduce the volume of brine, and precautions to avoid silica scaling of the modules.     

Removal of manganese from water supplies intended for human consumption: a case study

In the Volcano Etna area (Sicily) a substantial part of groundwater, used for potable purpose, has concentrations of metals (vanadium, iron and manganese) higher than the maximum contaminant levels (MCLs) set by European and National regulations (European Directive 98/83 and D.Lgs. 31/2001). Specifically, high levels of manganese, up to 1810 μg/l, significantly exceeding the maximum contaminant level (MCL = 50 μg/l), were detected in groundwaters currently used as drinking water supply upwelled from the Etna Volcano aquifer. The paper presents the results of the manganese removal process by potassium permanganate oxidation followed by flocculation, settling and filtration. Batch tests were carried out varying pH, oxidant doses and polyelectrolytes. Two different filters (35 μm and 0.45 μm mesh) were tested as a final step of the treatment. Significant removal (up to 95%) was achieved by addition of polyelectrolytes at pH 8.5, with a 0.5 stoichiometric dose of oxidant and final filtration through 35 μm mesh filter.     

Effect of electro-chemical properties of sodium salts of various anions on their diffusional parameters in symmetrical cellulose acetate membranes

A relation was obtained between electro-chemical properties of sodium salts (NaCl, NaBr, and Na₂SO₄), and the thermodynamic property of permeability in symmetrical cellulose acetate membranes, the distribution coefficient K and the kinetic property, the overall diffusion coefficients D. K and D were obtained by the method we proposed using measured unsteady- and steady-state dialysis data. The K values increase with the increase of water content and are in the range of 10⁻² for sodium halides and 10⁻³ for Na₂SO₄. D is found to increase with the increase of the solute concentration, and the extrapolated values of D to zero concentration D⁽⁰⁾ are obtained as 0.015–0.03 μm²/s and increase with the increase of water content in the membrane. D can be divided into the concentration independent diffusion coefficients in the dense part of the membrane D_d and in the porous D_p, applying a two-part (perfect or dense and imperfect or porous) model of the membrane. Contrary to D_d, D_p increases with the increase of W_w and can be correlated as D_p,c = _d exp (γ × W_w). It is shown that the averaged D_d, _D increases with the increase of the quantity of the ionic mobility u of the solutes at infinite dilution divided by valence, and that the parameter γ increases with the increase of the ionic mobility u. The value of K increases slightly with the increase of water content and decreases with the increase of the Flory—Huggins parameter χ. The Flory—Huggins parameter χ is calculated from the measured values of distribution coefficients and data obtained from the literature. And it was found that the gradient of linear decrease of χ (λ_cation) depends on equivalent ionic conductivity of anion of salt, λ_an.     

Research and Development Needs in Filtration and Dewatering

The first part o f this paper deals with technology issues. These ye megorised as ( i) fundamental aspects. specifically susoension characteristics and dewatcrinn mechanisms along with process modelling and control; ( ii) pre-treatment procedures, both physical and chemicd, that optimise the dewatering characteristics, ( iii) types of dewatering devices based on centrifuges, vacuum and pressure filters with particular reference to various combined field approaches using two or more complentary. driving forces to achieve better performance. The second part of the paper ( attributed principally to the fim-named author) deals with related R & D issues. namely economic assessments and justification for particular R & D strategies, including benchmarking and operational factors that apply in industrid environments Dewaterine operation and R & D needs are also analysed from the perspective of matching and integration into overall proccss flowsheets, and in the context of alternative processing or utilisation strategies which avoid the dewaering step. The analysis concludes with a discussion on effective identification and utilisation of existing knowledge, and the R & D management process. Although the paper draws heavily on experiences relating to the coal industry, much of the material is relevant to fine suspensions in general.     

Aerosol growth studies — IV. Phase transformation of mixed salt aerosols in a moist atmosphere

The phase transformation and subsequent droplet growth of the mixed salt aerosols NaCl—KCl and (NH₄)₂SO₄—H₂SO₄ were investigated in a continuous-flow apparatus at 25 and 30°C as a function of relative humidity. Monodisperse salt aerosols (d = ≈ 0.5 μm, OG = 1.07–1.13) were prepared and mixed with N₂ carrier gas at controlled humidities. The particle-size distribution of the aerosol before and after growth by water vapor condensation was continuously monitored with an optical particle counter. It was found that mixed salt aerosols were characterized by stage-wise growth when the relative humidity in the atmosphere was increased. The onset of growth took place at a specific deliquescence humidity determined by the water activity at the eutonic composition. Thus, mixed NaCl—KCl aerosols deliquesce at 73.8 ± 0.5% r.h. regardless of initial compositions. For sulfate aerosols containing 0.75 to 0.95 mole fraction (NH₄)₂SO₄ (the balance being H₂SO₄), the onset of growth occurs at 69.0 ± 0.5% r.h.. In the composition range of 0.5 to 0.75, a deliquescence humidity of 39.0 ± 0.5% is noted. Below 0.5 mole fraction, however, the mixed-sulfate aerosols are expected to exhibit hygroscopic properties on the basis of thermodynamic considerations.     

Hydrogen production from catalytic gasification of cellulose in supercritical water

Interests in large-scale use of biomass for energy and in hydrogen are motivated largely by global environmental issues. Cellulose and sawdust were gasified in supercritical water to produce hydrogen-rich gas in this paper, and Ru/C, Pd/C, CeO₂ paticles, nano-CeO₂ and nano-(CeZr)_xO₂ were selected as catalysts. The experimental results showed that the catalytic activities were Ru/C > Pd/C > nano-(CeZr)_xO₂ > nano-CeO₂ > CeO₂ particle in turn. Low-concentration sodium carboxymethylcellulose (CMC) (2–3 wt.%) was mixed with particulate biomass and water to form a uniform and stable viscous paste which can be efficiently gasified. The 10 wt.% cellulose or sawdust with CMC can be gasified near completely with Ru/C catalyst to produce 2–4 g hydrogen yield and 11–15 g potential hydrogen yield per 100 g feedstock at the condition of 500 °C, 27 MPa, 20 min residence time in supercritical water.     

Synthesis, structure and thermal properties of a novel 3D aluminophosphate UiO-26

The synthesis of a novel 3D aluminophosphate is described. The thermal properties of the material were investigated, and the existence of three high-temperature variants was revealed. The crystal structures of the as-synthesized material (UiO-26-as) and the material existing around 250°C (UiO-26-250) were solved from powder X-ray diffraction data. UiO-26-as with the composition [Al₄O(PO₄)₄(H₂O)]²⁻[NH₃(CH₂)₃NH₃]²⁺ crystallizes in the monoclinic space group P2₁/c (no. 14) with a=19.1912(5), b=9.3470(2), c=9.6375(2) Å and β=92.709(2)°. It exhibits a 3D open framework consisting of connections by PO₄ tetrahedra with AlO₄ tetrahedra, AlO₅ trigonal bipyramids and AlO₅(H₂O) octahedra forming two types of layers stacked along [1 0 0] and connected by Al–O–P bondings. The structure possesses a 1D 10-ring channel system running along [0 0 1], in which doubly protonated 1,3-diaminopropane molecules are located. UiO-26-250 with the composition [Al₄O(PO₄)₄]²⁻[NH₃(CH₂)₃NH₃]²⁺ crystallizes in the monoclinic space group P2₁/c with a=19.2491(4), b=9.27497(20), c=9.70189(20) Å and β=93.7929(17)°. The transformation to UiO-26-250 involves removal of the water molecule which originally is coordinated to aluminum. The rest of the structure remains virtually unchanged. The crystal structures of the two other variants existing around 400 (UiO-26-400) and 600°C (UiO-26-600) remain unknown.     

Electrochemical treatment of pentachlorophenol in water and pulp bleaching effluent

Adsorbable organic halides (AOX) compounds produced during bleaching of pulp are recalcitrant and known to have eco-toxic effect. We have studied the removal of pentachlorophenol (PCP) as a model AOX compound in water as well as in pulp bleaching effluent of a bamboo based mill by electrochemical treatment in batch mode. It was found that 10 mg L⁻¹ of PCP in water was removed almost completely in <10 min at a current density of 6 mA cm⁻² in the presence of 1000 mg L⁻¹ NaCl serving as an electrolyte and source of chloride ions. The initial rate of PCP removal was found to decrease at alkaline pH (9.3) as compared to that at acidic pH (5.5). PCP removal in neutralized raw pulp bleach effluent (containing 1830 mg L⁻¹ of chloride) was very slow and incomplete even after 2 h of electrochemical treatment at a current density of 15 mA cm⁻². Various pretreatments of raw bleach effluent such as, alkaline sulfide using sodium sulfide, alkaline reduction using ferrous sulfate and coagulation using potash alum were evaluated. Electrochemical treatment of potash alum pretreated effluent (spiked with PCP) could achieve >90% removal of initial colour, COD and PCP in <1 h. The treatment scheme presented here may be a promising technology for removal of AOX, COD and colour from pulp bleaching effluent. The estimated cost of combined treatment (potash alum coagulation + electrochemical) is US$ 0.7–0.9 per cubic meter of the raw pulp bleach effluent.     

Dielectric relaxation due to absorbed water in various thermosets

The dielectric relaxation due to absorbed water has been studied with a number of epoxies and other thermosets. In all cases, the absorbed water relaxation strength, as measured by both the dielectric-constant increase and the increase in area under the ″ versus 1/T curve, seems to be attributable to the relaxation of water dipoles and not to Maxwell-Wagner-Silars effects. The activation energies obtained are in the 11–16 kcal mol⁻¹ range. The relaxation strengths observed show that the water molecules manifest roughly 70–100% of their free-state polarizability. In general, the dielectric constant increase per 1 wt% of water absorbed is given to a good approximation by 4.0[(dry) + 2]² pf/T where f is the fractional polarizability of water in the polymer to its free-state value, found to be 0.7 to 1.0 for most thermosets, and and T are the density and temperature.     

Environmentally benign chemical additives in the treatment and chemical cleaning of process water systems: Implications for green chemical technology

Supersaturated process waters high in silicates frequently result in deposition of colloidal silica or metal silicate salts. Silica cannot be inhibited by conventional phosphonate mineral scale inhibitors. Chemical cleaning poses hazards and requires operational shut-downs. This paper is focused on a dual approach for silica scale control, inhibition of colloidal silica formation and colloidal silica dissolution in water technology applications by use of designed chemical approaches. The additives used for silica inhibition were polyaminoamide dendrimers (PAMAM) and polyethyleneimine (PEI), in combination with carboxymethyl inulin (CMI) and polyacrylate (PAA) polymers. In principle, silica inhibition is a function of time and inhibitor dosage. Amine-terminated PAMAM-1 and 2 dendrimers as well as PEI combined with anionic polymers, such as CMI and PAA, seem to have a significant inhibitory effect on silica formation, most likely at its earlier stages where the reaction products are oligomeric silicates. CMI and PAA assist the inhibitory action of PAMAM-1 and 2 and PEI by alleviating formation of insoluble SiO₂-PAMAM precipitates. This most likely occurs by partial neutralization of the positive charge that exists in –NH⁺₃ surface groups. Increase of anionic polymer dosage above a certain threshold has a detrimental effect on the activity of the cationic inhibitors. In that case the polymer’s negative charge “overwhelms” the cationic charge of the inhibitor and poisons its inhibition ability. For silica dissolution, acetic, oxalic, citric acids, histidine and phenylalanine were used as potential replacements of ammonium bifluoride (NH₄F·HF). Silica dissolution is dependent in a rather unpredictable fashion on the structure of the dissolver, time and dosage. This paper continues our research efforts in the discovery, design and application of antiscalant additives that have mild environmental impact. These chemicals are also known as “green additives”.     

Dehydration of water/1-1-dimethylhydrazine mixtures by zeolite membranes

In this research, dehydration of water/1-1-dimethylhydrazine (UDMH) mixtures by zeolite NaA and hydroxy sodalite membranes has been investigated. Support of these membranes has been tubular mullites that have been made by extruding a mixture of about 67–75% kaolin clay and 33–25% distilled water using an extruder. Zeolite NaA and hydroxy sodalite membranes have been coated on the external surface of the porous supports by the hydrothermal synthesis.

UDMH/water mixtures have been separated at ambient temperature and pressure by pervaporation (PV) using these zeolite membranes. These membranes showed very high selectivity of water for all UDMH mixtures. For the UDMH/water mixtures, separation factor as high as 10 000 has been obtained for UDMH feed concentration of 2%. Total mass fluxes of 1.05–0.2 kg/(m² h) have been also obtained.     

Riyadh''s reverse osmosis water treatment plants - the largest demineralization complex in the world

The water demand in Riyadh has increased very rapidly during recent years owing to the rapid expansion of the city with a population growth of about 50,000 per year. The water from the main source, an aquifer of Minjur sandstone at a depth of 1,200–1,500 m reached, by drilling, has high hardness, sulphate and TDS. The existing water works with raw water cooling, lime-soda softening, sedimentation, filtration and disinfection have been in operation at Malez, Shemessy and Manfouha since 1969. VBB, a member of Swedish Consulting Group (SWECO), is consultant to the Ministry of Agriculture and Water (MAW) regarding the water supply in Riyadh.

In 1973, VBB made an investigatory study on additional water treatment. The aims were to consider the possible need for further improvement of the actual water quality, to point out how such improvements could be achieved and finally, to discuss alternative treatment methods suitable for the purification of water taken from the new well fields.

The purpose of this paper is to give an overview of the technical design and construction of the new water treatment plants in Riyadh, with a total capacity of about 254,000 m³ /d. The treatment of Minjur deep-well water includes not only chemical softening but also demineralization with reverse osmosis (RO) as a final purification stage. The Salbukh plant (50,700 m³/d) should come onstream in autumn 1979.     

ABSORPTION OF CARBON DIOXIDE WITH A FREELY FALLING AQUEOUS SODIUM HYDROXIDE SOLUTION DROP

Measurements for the rates of absorption of carbon dioxide from carbon dioxide-air mixtures with a water and an aqueous sodium hydroxide solution drop falling freely were made for Fourier number Fo = 1.53 · 10^-5 — 9.83 × 10^-5, initial concentration of aqueous sodium hydroxide solution C_BO — 0.05 — 0,4 mol/1 and feed gas concentration of carbon dioxide y = 0.05 — 1.0. Observed dimensionless rates of absorption were compared with the theoretical values by the present model and gave a good agreement with theory. The effect of drop diameter on the enhancement factor, which is a measure of the effect of chemical reaction on the rates of absorption of carbon dioxide with a freely falling alkaline solution drop, were also discussed by using numerical simulation     

基于二氧化碳、水、太阳能的绿色化工精炼

化石资源为人类提供了不可或缺的化学品、材料以及燃料,但也造成了大量二氧化碳排放。生物质是可以生产低碳化工产品的可再生资源,但要占用有限的可耕地资源。提出了直接以二氧化碳、水和太阳能为原料的绿色化工精炼。采用光电板收集太阳能并转化为电能,电能通过膜式水电解池产生氢气,氢气通入新型生物反应器并在自养菌的作用下把二氧化碳还原为聚三羟基丁酸酯(PHB)。此新型生物反应器解决了因气体溶解性低而影响传质速度的关键技术,微生物干重产出达0.18 g·L^-1·h^-1,其中PHB质量分数约50%。PHB不仅是优良的可生物降解塑料,也是可用于生产C₃～C₄有机低分子和芳香烃的平台化合物。在磷酸催化作用下,PHB可转化为与汽油相当热值和元素组成的C₄～C₁₆燃料油。分离PHB后的细菌生物质残渣可水热分解获得生物油和富氮水相产物。此生物油具有比植物生物油更高的热值,而水相产物可作为营养物用于培养微生物。     

An FTIR/ATR in situ study of sorption and transport in corrosion protective organic coatings: Paper 2. The effects of temperature and isotopic dilution

A detailed temperature variation (18–50 °C) FTIR/ATR study of sorption and desorption of water into a series of cured epoxy resins has been reported. For higher temperatures (35–50 °C) the data were modelled with a single Fickian diffusion equation, giving an increased D as the temperature increased and an activation energy (E_A) in the 55–60 kJ mol⁻¹ region. At lower temperatures (18–35 °C)—well-below the T_g—a two-stage sorption equation was needed and the apparent E_A was negative. This is probably associated with changes in water clustering among the distributed ‘voids’ in the glassy polymer associated with chain relaxation at extended times. The use of D₂O as a penetrant allowed diffusion coefficient measurements for highly dense epoxy matrices, where FTIR/ATR cannot detect the ν(OH) band of water over and above the residual polymer–OH groups (in the dry state). The data for the D₂O studies were notably influenced by isotopic exchange; which was found to be a diffusion controlled process, even in a polymer matrix.     

Catalytic oxidation of phenol in aqueous solutions

The objective of this work is to investigate catalyst systems for the oxidation of phenol in water in a batch autoclave. The main experimental variables are the type and the composition of the catalyst, the catalyst loading, temperature, oxygen partial pressure, initial phenol concentration and the stirrer speed. Commercial catalysts were used. Experimental work was conducted in two different laboratories. In one laboratory, the catalysts tested were 35% CuO+65% ZnO; 5–15% CuO+85–95% Al₂O₃; 26% CuO+74% Cu Chromite. In the other laboratory, the catalysts tested included 35% CuO+65% ZnO; 5–10% Ba₂CO₃+<5% C+30–40% CuO+60–70% ZnO; and 8–15% Al₂O₃+1–5% C+35–45% CuO+40–50% ZnO. With some of these catalysts depending on the operating conditions, complete phenol conversion could be obtained within 90 min. Under certain experimental conditions, the reaction underwent an induction period after which there was a transition to a much higher activity regime. The induction period may be due to an autocatalytic reaction system or to a very slow rate of formation of hydroquinone and catechol which then readily oxidize to o- and p-benzoquinone. An increase in the temperature and the oxygen partial pressure decreased the induction period, which increased as the catalyst to phenol ratio increased. 26% CuO+74% Cu Chromite and 8–15% Al₂O₃+1–5% C+35–45% CuO+40–50% ZnO were found to be the most active catalysts.     

Soft modes and proton tunneling in PbHPO4, squaric acid and KH2PO4, type ferroelectrics

It is pointed out that the huge observed differences in the soft mode frequencies of KH₂PO₄, PbHPO₄, CsH₂PO₄ and squaric acid do not necessarily reflect a large difference in the proton 0—H———O tunneling frequencies but rather result from a difference in the short range correlations renormalizing the single proton O——H—O tunneling frequency.     

Quantitative studies on the coal—oil agglomeration process

This paper summarises the work carried out at the Indian School of Mines on the quantification of the coal—oil agglomeration process for the purpose of modelling. The growth of agglomerates in the coal—oil agglomeration process follows a self-preserving behaviour. Using this, a characteristic curve, which is independent of the levels of the process variables, has been developed. It has also been found that the growth of agglomerates follows a second-order kinetics. The kinetic equation can be used for predicting the size (d₅₀) which passes 50% of the agglomertes. The prediction of the size distribution of the agglomerates needs the estimation of d₅₀ and the shape of the characteristic curve. The characteristic curve has been quantified using the equation Y = 1 — exp (—0.693x^m) and the d₅₀ values of the agglomerates have been evaluated through the kinetic equation and also through direct correlation of d₅₀ with the process variables. The percentage yield of agglomerates has been found to follow a relationship of the form Y = k₃{1 — exp[;—k₄(d₅₀ — x₀)^m]} with d₅₀.

The significance of these equations in modelling the process is outlined.