A review of technologies for the removal of sulfate from drinking water

Because of the current water crisis worldwide, it is of great importance to find alternative sources of drinking water, such as sulfur water. This review analyses laboratory, pilot and industrial-scale technologies available for sulfate removal from water produced for human consumption, from naturally occurring sulfur water and that resulting from human activities. Most of them exceed 90% removal efficiencies. However, the concentrations treated in each study were different; some technologies evaluate concentrations below recommended limits (250 mg L⁻¹), while others evaluate much higher concentrations but require previous treatments. The technologies with higher energy requirements such as reverse osmosis and ion exchange have better removal efficiencies but require larger initial investments and have higher operational costs. Biological treatments, on the other hand, with lower energy and material requirements, are less expensive but require long retention times and depend on the season of the year and/or environmental conditions. Lastly, adsorption removal technologies fall in the middle, especially for energy requirements and operational costs and retention times. This review shows that although there are a variety of sulfate removal technologies suitable for use, there is still room for a novel methodology that removes sulfates from a wider range of concentrations more economically, more effectively and in less time than what is currently available.     

Nitrate removal from ground water

A new technique is described for nitrate removal from ground water. This technique is a combination of ion exchange and biological denitrification. Nitrate is removed by ion exchange. Regeneration of the resin in a closed circuit is achieved with a denitrification reactor. In contrast with traditional denitrification procedures there is no direct contact between ground water and denitrifying bacteria. Also brine production and regeneration salt requirements are minimal as compared with conventional regeneration of ion exchange resins. The basic design criteria and the first pilot plant results are presented. The pilot plant results show that the process is very attractive when compared with ion exchange and biological denitrification as separate techniques. Ground water with a relatively high sulfate concentration can be treated when a nitrate selective resin is used.     

Investigation of phosphorus removal from water

The removal of different phosphate compounds from water and waste water by precipitant was investigated. Calcium hydroxide precipitated orthophosphate with greater efficiency than aluminium sulphate, while aluminium sulphate gave better efficiency in the removal of polyphosphates. Calcium hydroxide was not able to precipitate the phosphate in glucose phosphate—and aluminium sulphate effects only a slight precipitation. Bentonite and polyelectrolyte (partly anionic type), in conjunction with aluminium sulphate, gave an increased phosphate reduction, settling velocity, a decreased turbidity of the liquid and a decreased sludge volume.

In the case of waste water, considerably better results were achieved due to the high content of suspended matter, which helped to bind the phosphate compounds into flocs. The use of bentonite and polyelectrolyte in treating waste water gave better results and better results were also obtained when calcium hydroxide was used alone for precipitation.     

Organic arsenic removal from drinking water

Arsenic occurs in both inorganic and organic forms in water. Although various methods have been adopted to remove inorganic species of arsenic from drinking water, not much emphasis has been given to the removal of organic species of arsenic. In the present study column studies were conducted using manganese greensand (MGS), iron oxide-coated sand (IOCS-1 and IOCS-2) and ion exchange resin in Fe³⁺ form, to examine the removal of organic arsenic (dimethylarsinate) spiked to required concentrations in tap water. Batch studies were conducted with IOCS-2, and the results showed that the organic arsenic adsorption capacity was 8 μg/g IOCS-2. Higher bed volumes (585 BV) and high arsenic removal capacity (5.7 μg/cm³) were achieved by the ion exchange resin among all the media studied. Poor performance was observed with MGS and IOCS-1.     

Occurrence and removal of pharmaceuticals and hormones through drinking water treatment

The occurrence of fifty-five pharmaceuticals, hormones and metabolites in raw waters used for drinking water production and their removal through a drinking water treatment were studied. Thirty-five out of fifty-five drugs were detected in the raw water at the facility intake with concentrations up to 1200 ng/L. The behavior of the compounds was studied at each step: prechlorination, coagulation, sand filtration, ozonation, granular activated carbon filtration and post-chlorination; showing that the complete treatment accounted for the complete removal of all the compounds detected in raw waters except for five of them. Phenytoin, atenolol and hydrochlorothiazide were the three pharmaceuticals most frequently found in finished waters at concentrations about 10 ng/L. Sotalol and carbamazepine epoxide were found in less than a half of the samples at lower concentrations, above 2 ng/L. However despite their persistence, the removals of these five pharmaceuticals were higher than 95%.     

Phosphorus removal from water by means of electrolysis

P removal from water by electrolysis was examined by an experimental laboratory system. Two types of electrodes, Al and Fe, were investigated with respect to the relationship between P removal and energy consumption. The Al electrodes were most efficient in this respect. Alternating current gave the best “self-cleansing” of the electrodes, but the period should exceed 2–3 min to give maximum P-removal efficiency.     

Arsenate removal from water using sand--red mud columns

This study describes experiments in which sorption filters, filled with chemically modified red mud (Bauxsol) or activated Bauxsol (AB) coated sand, are used to remove As(V) (arsenate) from water. Bauxsol-coated sand (BCS) and AB-coated sand (ABCS) are prepared by mixing Bauxsol or AB with wet sand and drying. Samples of the BCS and ABCS are also used in batch experiments to obtain isotherm data. The observed adsorption data fit the Langmuir model well, with adsorption maxima of 3.32 and 1.64 mgg(-1) at pH values of 4.5 and 7.1, respectively for BCS; and of 2.14 mgg(-1) for ABCS at a pH of 7.1. Test results show that higher arsenate adsorption capacities can be achieved for both BCS and ABCS when using the columns compared to results for batch experiments; the difference is greater for BCS. Additional batch tests, carried out for 21 days using BCS to explain the observed discrepancy, show that the equilibrium time previously used in batch experiments was too short because adsorption continued for at least 21 days and reached 87% after 21 days compared to only 35% obtained after 4h. Fixed bed column tests, used to investigate the effects of flow rate and initial arsenate concentration indicate that the process is sensitive to both parameters, with lower flow rates (longer effective residence times in the columns) and initial arsenate concentrations providing better column performance. An examination of the combined effect of potential competing anions (i.e. silicate, phosphate, sulphate and bicarbonate) on the column performance showed that the presence of these anions in tap water slightly decreases arsenate removal. Each breakthrough curve is compared to the Thomas model, and it is found that the model may be applied to estimate the arsenate sorption capacity in columns filled with BCS and ABCS. The data obtained from both batch and column studies indicate that BCS and ABCS filtration could be effectively used to remove arsenate from water, with the latter being more efficient.     

Experimental assessment of an innovative process for simultaneous PAHs and Pb removal from polluted soils

This paper tests a soil washing process using flotation in its effectiveness for the removal of both polycyclic aromatic hydrocarbons (PAHs) and Pb from three polluted soils (soils A, B and C). The optimal flotation conditions were defined as: pulp density = 10%, Cocamidopropylhydroxysultaine (CAS) = 0.2% ww^− 1, [NaCl] = 5.5 M, pH = 3, flotation time = 15 min, air flow rate = 3 l min^− 1, stirring speed = 1800 rpm and temperature = 20 °C. Under these conditions, successive flotation stages (n), decreased the contaminant content to below permitted levels (up to 90% PAHs and Pb removal). Thus, a more contaminated matrix required the addition of a growing number of successive flotation stages to lower contamination levels below legal thresholds. While PAHs were distributed within the solid fractions of the process, Pb was mainly present in the liquid fractions. Electrodeposition allowed a total recovery of Pb after 60 min using a 2A electrical current.     

污水资源化探讨

通过了解国内、国外污水资源化的利用现状情况,阐述了污水资源化的必要性及解决对策,指出全民应重视污水资源化问题,将节水与治污相结合,以使污水再生利用得以顺利进行,从而构建完善的污水资源化利用体系。     

Effects of water chemistry on arsenic removal from drinking water by electrocoagulation

Exposure to arsenic through drinking water poses a threat to human health. Electrocoagulation is a water treatment technology that involves electrolytic oxidation of anode materials and in-situ generation of coagulant. The electrochemical generation of coagulant is an alternative to using chemical coagulants, and the process can also oxidize As(III) to As(V). Batch electrocoagulation experiments were performed in the laboratory using iron electrodes. The experiments quantified the effects of pH, initial arsenic concentration and oxidation state, and concentrations of dissolved phosphate, silica and sulfate on the rate and extent of arsenic removal. The iron generated during electrocoagulation precipitated as lepidocrocite (γ-FeOOH), except when dissolved silica was present, and arsenic was removed by adsorption to the lepidocrocite. Arsenic removal was slower at higher pH. When solutions initially contained As(III), a portion of the As(III) was oxidized to As(V) during electrocoagulation. As(V) removal was faster than As(III) removal. The presence of 1 and 4 mg/L phosphate inhibited arsenic removal, while the presence of 5 and 20 mg/L silica or 10 and 50 mg/L sulfate had no significant effect on arsenic removal. For most conditions examined in this study, over 99.9% arsenic removal efficiency was achieved. Electrocoagulation was also highly effective at removing arsenic from drinking water in field trials conducted in a village in Eastern India. By using operation times long enough to produce sufficient iron oxide for removal of both phosphate and arsenate, the performance of the systems in field trials was not inhibited by high phosphate concentrations.     

A review of water recovery by vapour permeation through membranes

In vapour permeation the feed is a vapour, not a liquid as in pervaporation. The process employs a polymeric membrane as a semi-permeable barrier between the feed side under high pressure and the permeate side under low pressure. Separation is achieved by the different degrees to which components are dissolved in and diffuse through the membrane, the system working according to a solution-diffusion mechanism. The materials used in the membrane depend upon the types of compounds being separated, so water transport is favoured by hydrophilic material, whether organic or inorganic. The process is used for the dehydration of natural gas and various organic solvents, notably alcohol as biofuel, as well as the removal of water from air and its recovery from waste steam. Waste steam can be found in almost every plant/factory where steam is used. It is frequently contaminated and cannot be reused. Discharging the spent steam to the atmosphere is a serious energy loss and environmental issue. Recycling the steam can significantly improve the overall energy efficiency of an industry, which is responsible for massive CO₂ emissions. Steam separation at high fluxes and temperatures has been accomplished with a composite poly(vinyl alcohol) membrane containing silica nanoparticles, and also, less efficiently, with an inorganic zeolite membrane.     

Naproxen removal from water by chlorination and biofilm processes

Naproxen is an anti-inflammatory pharmaceutical that has been detected in natural and engineered aquatic environments. The primary aim of this research was to study chemical transformations of naproxen following chlorine oxidation, which is common in water and wastewater treatment systems. Synthetic waters containing elevated concentrations of naproxen were oxidized by free chlorine at naproxen:chlorine molar ratios of 0.02-3:1 and pH values of 5-9. The formation of naproxen products was dependent on pH, chlorine dosage and contact time. This study demonstrates that naproxen readily reacts with free chlorine and forms disinfection products. The formation of specific reaction products can vary depending on the characteristics of the water or wastewater and treatment operating conditions. More research is needed to identify intermediate and chemical reaction end products and to understand the reaction kinetics of naproxen chlorination for a range of water and wastewater treatment conditions. A secondary aim of this research was to study effects of naproxen and its chlorination products on biofilm processes, which are common in water and wastewater treatment systems and natural aquatic environments. A bioreactor was fed a naproxen solution and then fed a solution at the same naproxen concentration following contact with free chlorine. Results indicate that naproxen was not degraded biologically for the conditions of this study. In contrast, the naproxen solution containing products of chlorination caused an adverse response by discharging biomass from the bioreactor. Results therefore demonstrate that naproxen products of chlorination can adversely affect a biofilm process, which potentially can impact the performance of biofilm processes in natural and engineered aquatic environments. More research is needed to study naproxen chlorination reactions at low concentrations and in complex matrices, and to understand the toxicological relevance of naproxen and its products of chlorination in natural and engineered aquatic environments.     

氢自养反硝化去除饮用水中硝酸盐的研究

基于氢自养反硝化脱氮原理,构建了生物陶粒反应器和生物电化学反应器模型去除水中硝酸盐,通过对两个反应器脱氮性能的研究,探讨了氢自养反硝化生物脱氮的实现过程,为氢自养反硝化技术去除水中的硝酸盐提供了依据。     

Adsorptive selenite removal from water using iron-coated GAC adsorbents

Removal of selenite from aqueous phase using iron-coated granular activated carbons (GAC) was investigated in this study. Five different types of GAC were used for iron coating by oxidizing ferrous chloride with sodium hypochlorite and the iron-coated GAC (Fe-GAC) were tested for selenite removal. Nitrogen adsorption-desorption analyses indicated that Brunauer-Emmett-Teller (BET) specific surface area, pore size, and pore volume decreased with the iron coating. The Darco 12x20 GAC was shown to be the most effective adsorbent among the five tested GACs after iron coating. Among the different concentrations used for iron coating, the Darco 12x20 GAC coated with 0.1M ferrous chloride achieved the highest selenite removal (97.3%). High removal efficiency of selenite occurred in a wide range of pH (i.e., 2-8), but the efficiency decreased when pH was higher than 8. Adsorption kinetics showed that selenite removal efficiency reached more than 90% after 6-h adsorption for initial selenium concentration of 2mg/L and equilibrium was obtained after 48h. A pseudo-second-order kinetic model was found to characterize the adsorption kinetics well for all the initial selenium concentrations and temperatures tested (R(2)>/=0.9969). Three temperatures (25, 35, 45 degrees C) were used to examine temperature effect on the adsorption behavior of the Fe-GAC with initial selenium concentration of 1mg/L. Activation energy was calculated to be 30.42kJ/mol. Adsorption isotherms for initial selenium concentration of 2mg/L at various temperatures and ionic strengths were developed and the data generally fit the Langmuir model well (R(2)>/=0.994). The adsorption capacity reached as high as 2.50mg-Se/g-adsorbent at equilibrium for initial concentration of 2mg/L at 25 degrees C. The Gibbs free energy was determined to be negative, indicating the spontaneous nature of the adsorption reaction. Oxyanion competitive adsorption showed that sulfate (0.1-5mM) barely affected selenite adsorption. Other anions (phosphate, silicate and carbonate) impact selenite adsorption to various degrees with phosphate completely excluded selenite adsorption at 5mM. The possible adsorption mechanisms were discussed.     

Oil removal from water in parallel plate gravity-type separators

Aspects of oil removal by gravity separation in parallel plate separators have been investigated both theoretically and experimentally. Attention has been paid to the possible influence of retention time distribution, co- or countercurrent flow (in tilted plate separators) and to the effect of perforation of the plates. Perforation enables an easy removal of separated oil in horizontal plate separators. It appears that the overflow rate-related to the horizontal projection of the real plate area-determines the performance of a plate separator in all these cases. A residence time distribution will lower the separation efficiency only when it is caused by a velocity profile over the width of the tank or by an extremely unequal distribution of the influent over the plates. A tilted full plate separator and a horizontal perforated plate separator with the same overflow rate perform equally well as to separation efficiency; only secondary, practical reasons will determine the choice between either construction.     

Investigation on the river water polluted with acidic hot spring water

Tamagawa hot spring in Akita Prefecture gushes hot water of 1 pH hydrochloric acid at some 140 1 s⁻¹. This quantity flows into the River Tama with the result that the river has been denied use for any significant hydropower development thus far. For the purpose of mitigating the acidity of the river water, the hot spring water is carried away through channels and infiltrated into the soil of a mountainside for chemical neutralizing through seepage before flowing into the river.The following facts have been obtained by field geochemical investigation (1951–1963). The neutralization effect following the injection of hot-spring water into the soil is about 80 per cent, the larger part of which effect is due to the function of dissolution of Al³⁺; the pH values of the water in the reservoir of Yoroibata dam to be constructed downstream of the river do not exceed 5; and even in the absence of hot-spring water injection treatment there is acidity reduction due to the alkalinity of the tributary waters as well as due to the dissolution of river-bed components by the acid during seepage.     

复合湿地系统处理小城镇污水

采用地埋式生化处理系统与复合湿地——塘系统的组合工艺,结合生态及景现园林建设进行了小城镇污水生态处理工程设计,结果表明：组合工艺对小城镇生活污水具有良好的处理效果,且出水水质达到《城镇污水处理厂污染物排放标准》（GB18918—2002）中的一级A标准。进水负荷的变化对去除效率影响较小,出水水质能稳定达到国家一级排放标准。该工程既处理了生活污水,又改善了生态环境,体现了污水处理与生态环境建设的相结合。     

The analysis of ammonia in polluted sea water

Measurement of ammonia in polluted sea water or fresh water is important, especially in fish rearing, but existing methods for its determination are subject to serious suppression interference by many substances, including all types of amines, nitrite and amino acids, which may participate in the chain of reactions employed diverting it: some methods suffer from breakdown of amino acids to ammonia. Hydrogen sulphide, often present in anoxic waters also interferes and must be removed. The present method overcomes these difficulties by internal standard calibration, and by specific u.v. photo-activation of the required ammonia → indophenol blue reaction at low temperature.     

水厂突发毒死蜱污染的应急处理工艺研究

针对受毒死蜱污染的原水,通过小试研究了粉末活性炭(PAC)吸附强化聚合氯化铝混凝工艺对毒死蜱的去除效果。结果表明,单独投加8mg/L聚合氯化铝和0.05mg/LPAM难以将毒死蜱浓度降低至《生活饮用水卫生标准》的限值(0.03mg/L)要求,需要采用PAC吸附与混凝沉淀联用工艺。当原水毒死蜱浓度超标5,10,20,30,40和50倍时,所对应的粉末活性炭最佳投加量分别为20,30,30,40,40和50mg/L,出水浓度均小于0.03mg/L。PAC吸附强化工艺聚合氯化铝混凝工艺可有效应对原水的毒死蜱污染,保障供水安全。