Application of HACCP principles in drinking water treatment

One of the most important tasks at any water treatment plant is safeguarding the quality of drinking water. Worldwide, the drinking-water sector is increasingly aware of the limitations of end-product testing for ensuring safety. One limitation is the steady increase in the number of potentially occurring pathogens and chemicals that need to be monitored. A further limitation is the delayed availability of results in relation to the timing of interventions needed to maintain the safety of a supply. Ensuring the safety of a supply requires monitoring not only of the finished drinking-water, but particularly of parameters which indicate whether the key control measures in a given process are functioning correctly. Preventative measures have therefore become very important. The Hazard Analysis Critical Control Points system (HACCP) is a food safety management system which uses the approach of controlling critical points in food and drink production, and the framework of its concept consists of 7 principles. According to the Council Directive 93/43/EEC and the recent Regulation (EC) No 852/2004 on the hygiene of foodstuffs, the application of HACCP in food production is obligatory. In the present work, the HACCP principles were applied to the Aspropyrgos Water Treatment Plant. The critical control points identified include filtration and chemical disinfection.     

Fouling characteristics of an ultrafiltration membrane used in drinking water treatment

The fouling characteristics of ultrafiltration membranes used in drinking water were investigated when used alone and when used in an integrated biofilter-membrane system to treat a humic-acid laden solution. Membrane strands from sacrificial modules operating in parallel with bench-scale modules were analysed from both systems (with and without pretreatment). Chemical and microbiological analyses were performed on these strands together with different process streams along the treatment train. Microscopic observations performed on the sacrificial membrane strands revealed that most of the fouling material was organic in nature with high numbers of viable microorganisms. When comparing their fouling characteristics, a positive effect from the biofilter was observed on the performance of the membrane with pretreatment, decreasing in general the amount of material deposited and reducing the fouling rate. Membranes were tested at two different permeate fluxes; this variable did not have an effect on the overall amount of material deposited, but it significantly impacted the membrane fouling rate.     

Treatment of perchlorate in drinking water: A critical review

Because of its extremely low concentrations and strong resistance to most treatment technologies, perchlorate has become one of the biggest challenges currently being faced by the drinking water industry. Although significant research has been performed to evaluate different treatment technologies for perchlorate removal from drinking water, there has not been a holistic review performed recently. A complete and critical review on the intriguing contaminant ‘perchlorate’ is presented. The sources of perchlorate along with the degree of contamination are discussed. The policy aspects including the regulation and toxicity in addition to the most recent developments in perchlorate analysis are also considered. The applicable treatment technologies including their feasibility are discussed in detail. Although some technologies such as microbial reduction and ion-exchange have become more established than the others, there is still not a single technology that can be directly applied to a drinking water treatment system for compete removal of perchlorate. Although significant research is still being conducted to come up with a novel technology for perchlorate remediation, it is highly likely that it would not be a single novice or conventional technology but a combination of these technologies that would have to be employed to overcome this challenge.     

Study of drinking water treatment by ultrafiltration of surface water and its application to China

In China, many water supplies depend on conventional water treatment. Due to unfit soil and water conservationin some regions of China, conventional water treatment has showed some defects for the poor quality of water resource. In addition, advances in membrane technology and increasing requirements on water quality have stimulated ultrafiltration (UF) for water treatment. In this research, OF test apparatus was set up to produce drinking water from raw water of the Binxian Reservoir (China). The performance of UF membranes was investigated. There was a linear relationship between membrane resistance and accumulated permeate water. Using coagulation before OF increased permeate flux and retarded membrane flux decline. Surprisingly, membrane permeate flux in a coagulation/UF process was higher than that in coagulation-sand filtration-UF process with raw water of medium turbidity. OF treatment provided effective turbidity removal. Iron, manganese and aluminum were removed completely. The UF membrane also perfectly removed all coliform bacteria. The reduction of total organic carbon was satisfactory. The treated water quality complied with China's drinking water guidelines. The Ames test showed that the mutagenic activities of membrane permeate water was negative.     

Pilot study of the removal of THMs, HAAs and DOC from drinking water by GAC adsorption

The objective of this pilot study was to evaluate the performance of a GAC postfilter-adsorber for the removal from the drinking water of Athens, Greece, of the two main groups of chlorination by-products, trihalomethanes (THMs) and haloacetic acids (HAAs), as well as of dissolved organic carbon (DOC). The analyses performed during the whole operation period (638 days) showed that the GAC breakthrough capacity for DOC was much higher than the capacity for total HAAs, which was higher than that for total THMs. The removal of THMs and the most part of the removal of HAAs and DOC should be attributed to adsorption by GAC, while that of a smaller part of HAAs and DOC may be attributed to biodegradation in the adsorber bed, where dechlorination, caused catalytically by the carbon surface, favoured microbial growth. Additionally, the GAC postfilter-adsorber showed a much higher adsorption efficiency than a GAC filter-adsorber, due to the smaller size of the carbon and the lower hydraulic loading rate. Also, observed desorption incidents of THMs (mainly) and HAAs, especially during the postfilteradsorber operation, were favoured by the same factors. Formation of THMs within the GAC bed was also indicated by the mass balance of total THMs during the whole cycle.     

改性滤料用于净水处理的研究进展

本文介绍了改性滤料的过滤机理及改性滤料用于净水处理的研究状况。     

Response surface methodological approach to optimize the coagulation-flocculation process in drinking water treatment

Performing jar tests often requires carrying out a time consuming iteration procedure to find out the right amount of chemical for coagulation-flocculation process in water treatment plants. Applying the response surface method (RSM) in jar tests as an alternative to the conventional methods was investigated in this study. The purpose is finding out the optimum combination of coagulant dose and pH with respect to the highest removal efficiency of turbidity and dissolved organic carbon (DOC). The results achieved using poly-aluminum chloride (PACl) were compared to those achieved using conventional coagulant such as alum. The quadratic models developed for the two responses (turbidity removal and DOC removal) indicated that the optimum conditions to be PACl concentration of 0.11 mM at pH 7.4 and alum concentration of 0.15 mM at pH 6.6. Compromising to simultaneously optimize the two responses resulted in 91.4% turbidity removal and 31.2% DOC removal using PACl whereas 86.3% turbidity and 34.3% DOC were removed using alum. Confirmation of experimental results was found to be close to the prediction derived from the models. This demonstrates the benefits of the approach based on the RSM in achieving good predictions while minimizing the number of required experiments.     

Development of solid-phase microextraction for the determination of trihalomethanes in drinking water from Bizerte, Tunisia

Headspace-solid-phase microextraction (HS-SPME) combined with gas chromatography-electron capture detector (GC-ECD) has been developed and studied for the determination of trihalomethanes (THMs) in treated water samples. Experimental parameters such as the selection of thickness of the polymer coating, addition of salt, magnetic stirring, extraction temperature, and extraction time were studied. Extraction of the analytes was performed using HS-SPME with a 100 µm poly(dimethylsiloxane) coating followed by thermal desorption at 250 °C and GC analysis. The optimized conditions were 20 min extraction time at 35 °C with 25 w/v% NaCl. Analytical parameters such as linearity and limit of detection were also evaluated. The linear range of 1-100 µg/l was established with relative standard deviations (%RSD) within the range, 1.3-11.7%. The limits of detection (LODs) were ranged from 1.4 ng/l to 6.1 ng/l. The average THM concentration was 88.16 µg/l which was well within the proposed European Union directive of 100 µg/l.     

Desalination in the gaza strip: drinking water supply and environmental impact

More than 90% of the population of the Gaza Strip depends on desalinated water for drinking purposes. About 90% of the groundwater is unacceptable for drinking as a result of contamination by nitrate and chloride. One of the major options for resolving the water problems is the utilization of desalination technology for both sea and brackish water. The objective of this article is to address desalination water management in its embryonic stage in the Gaza Strip. The sources of drinking water supply, distribution system and the environmental impact of brine water will be fingered in detail. Desalination facilities range from large seawater plants to small brackish desalination units on a home scale. Governmental, non-governmental and private desalination plants are common. The distribution system of desalinated water is a responsibility of governmental, non-governmental, private small community bodies and even individuals. Disposal of brine water is made either directly or indirectly into the sea, sewage system, poor land, channels, wadies, etc. Brine constituents have an adverse impacton the surrounding environment, e.g., sea life, soil, wastewater treatment plants and the groundwateraquifer. The lack of real environmental impact assessments, especially for mid- and home-scale units may lead to a deterioration of the environment. The fragmentation of the responsibilities of water desalination, distribution of desalinated water and the disposal of brine water suggest that urgent action should be taken (e.g., legislation or establishment of a supervisory body). In other words, strict policies and management actions are to be taken in order to alleviate the health and environmental impact of an important and uncontrolled new system.     

Removal of arsenic from drinking water by the electrocoagulation using Fe and Al electrodes

A novel technique of electrocoagulation (EC) was attempted in the present investigation to remove arsenic from drinking waters. Experiments were carried out in a batch electrochemical reactor using Al and Fe electrodes with monopolar parallel electrode connection mode to assess their efficiency. The effects of several operating parameters on arsenic removal such as pH (4–9), current density (2.5–7.5 A m⁻²), initial concentration (75–500 μg L⁻¹) and operating time (0–15 min) were examined. Optimum operating conditions were determined as an operating time of 12.5 min and pH 6.5 for Fe electrode (93.5%) and 15 min and pH 7 for Al electrode (95.7%) at 2.5 A m⁻², respectively. Arsenic removal obtained was highest with Al electrodes. Operating costs at the optimum conditions were calculated as 0.020 € m⁻³ for Fe and 0.017 € m⁻³ for Al electrodes. EC was able to bring down aqueous phase arsenic concentration to less than 10 μg L⁻¹ with Fe and Al electrodes. The adsorption of arsenic over electrochemically produced hydroxides and metal oxide complexes was found to follow pseudo second-order adsorption model. Scanning electron microscopy was also used to analyze surface topography of the solid particles at Fe/Al electrodes during the EC process.     

Comparative investigation of stainless steels used in drinking water distribution systems

Five stainless steel alloys were tested and compared to find a test method for the qualification of stainless steel used in drinking water systems. Determination of the pitting/critical potentials from the conventional cyclic polarization results was shown to be difficult when stainless steels have high Mo and Cr content. The electrochemical impedance data indicated that results received with the conventional methods do not necessarily reflect the steady state. The low frequency time constant determined from the impedance measurements showed that the anodic polarization should be conducted with very slow scan rate to get information about the mechanism. The steady state investigations were compared with the conventional electrochemical results to propose an electrochemical-based route as a standard qualification method. The qualification method was tested to be valid by a European round-robin-test.     

Design and installation of a decentralized drinking water system based on ultrafiltration in Mozambique

Access to drinking water is a human right that has turned into an international aim included in the Millennium Development Goals. However, at present, more than 1 billion people live with no access to drinking water, especially in developing countries. Particularly, in Mozambique, where this work has been performed, 43% of the population can only access to improved water sources and 32% of the population live with access to improved sanitation. Main reasons that explain lack of drinking water in developing countries are: absence of proper infrastructures and chemicals, deteriorated distribution network or interrupted service that encourages stagnancy of water and growth of pathogens.The AQUAPOT project was developed in Polytechnic University of Valencia (Spain), and it is intended for the installation of decentralized drinking water systems based on membrane technologies as an alternative of the current water management in developing areas. At present, this project is being satisfactorily applied in rural areas of Ecuador (South America) and Mozambique (Africa). This work describes the evaluation of drinking water system, main characteristics of the UF-purification plant placed at Ressano Garcia (Mozambique), and assesses the main results obtained since the plant is working from the point of view of membrane performance and drinking water quality.     

Removal of total dissolved solids, nitrates and ammonium ions from drinking water using charge-barrier capacitive deionisation

A charge-barrier capacitive deionisation system was tested for electrochemical removal of Total Dissolved Solids (TDS), nitrates and ammonium ions. Several experiments were conducted with inorganic species spiked in tap water. The system efficiency was first evaluated using experimental statistical designs with different concentrations of NaCl (150 to 3000 mg/L). The raw water conductivity and the targeted residual TDS in treated water were the key process variables. Power consumption increased linearly as the difference between these two values increased. Water recovery rate and electrical consumption, which varied respectively from 63.9% to 95.8% and from 0.45 to 5.35 kWh/m³, were adequately described by a simple linear regression model (R²: 0.98 and 0.99, respectively). Additional experiments performed on nitrates (100 mg N-NO₃/L) and ammonium ions (1000 mg N-NH₄/L) showed high levels of removal. A rise in TDS concentration led to a decrease in their removal due to the competition for electrodes carbon adsorption sites. It was concluded from this study that this technology offers an innovative alternative for demineralising water. However, assays should be conducted in natural waters and in a steady-state manner to confirm data obtained and get long-term performance.     

Integration of immersed membrane ultrafiltration with the reuse of PAC and alum sludge (RPAS) process for drinking water treatment

Effects of PAC and alum sludge generated from water treatment process on the effluent quality and fouling of immersed UF membrane were systematically investigated with representative source of natural water and the efficiency of coagulation, PAC adsorption and RPAS to treat natural surface water prior to UF were compared. It was found that the average turbidity removal by RPAS could reach up to 80.2%, and the turbidity removal of immersed membrane UF was independent of the influent, which could be kept at 99%. Particulates were reduced after being pre-treated by different processes, and particles with sizes ranging from 0.5 to 3.5 μm and larger than 13.5 μm were effectively removed by RPAS. UF coupled with RPAS pre-treatment got the best removal for DOM compared to other processes with average DOC and UV₂₅₄ removal 54.1% and 47.2% due to the high removal in the influent of UF. The residual alum content in the effluent of RPAS with UF was less than coagulation and bacteria were almost all removed by membrane. The membrane-fouling was mitigated by pre-treatment processes at different degrees, TMP of UF coupled with RPAS process was relatively stable in 15 d of run, the adsorption of PAC and large number of Al(OH)₃ complexes and precipitates for the foulant molecules might be an important mechanism.     

GC-MS测定饮用水中挥发性有机物

建立了吹扫捕集与气相色谱/质谱(GC-MS)联用测定饮用水中13种挥发性有机物的测定方法.该方法的加标回收率在90%～110%,相对标准偏差小于5.0%,灵敏度高,准确度好,已成功地用于饮用水中挥发性有机污染物的测定,且结果令人满意.     

超滤在饮用水处理中的应用和研究进展

介绍了超滤在饮用水处理中的应用和研究进展;研讨微絮凝+超滤组合工艺、粉末活性炭(PAC)+超滤组合工艺,以及膜污染及其防治技术;从处理效果、经济性能上对超滤工艺与常规过滤工艺进行对比。认为超滤工艺必将成为未来饮用水最重要最有效的处理技术之一;而混凝+超滤工艺比较适合我国国情,具有很好的发展前景。     

饮用水中污染物的检测及处理工艺

综述了近些年来国内外饮用水处理过程中污染物质的检测方法和处理工艺。现有的检测方法主要有分光光度法、气相色谱法、液相色谱法、质谱法以及各种方法的改进和联合使用,主要采用的去除污染物的手段有臭氧氧化、活性炭吸附、树脂吸附和一些传统工艺的改进等,并对现有的检测方法和去除手段进行了评价,同时提出了未来饮用水处理领域的发展方向。     

The role of membrane technologies in supplying drinking and industrial water in Tunisia: Conventional process and new trends

Tunisia has utilized a large portion of its moderate water potential. Needs increase exponentially as a result of population growth and socio-economic development. Since the 80's, Tunisia has resorted to desalination of brackish water and particularly via membrane techniques to supply the traditionally deficient regions with good quality water and come up with a solution for industrial water utilities. The choice and the management of desalination technologies must be studied. With this aim, a national research program has been established to dealing with the optimal management of existing units with a view to propose technological schemes more adapted to the quality of the raw water. In the present work, three plants are studied. The first one is an RO fed by water drawn from a subsoil aquifer. The operating parameters show that partial iron oxidation and chlorine are responsible for the short life of modules. The second deals with the water from a deep geothermal layer. Membrane autopsies show that the fouling is essentially biological and that the shock treatment has led to a significant improvement. The third one is an EDR plant fed by dam water. The main difficulty is the turbidity fluctuation, the instantaneous adjustment of the dose injected into flocculant and coagulant which has led to a substantial improvement of the plant performances. The follow up and diagnosis are presented and discussed in the light of new trends in material.     

Catalytic processes for the purification of drinking water and industrial effluents

Catalytic liquid-phase hydrogenation of aqueous nitrate solutions is presented as a potential, advanced treatment technology for the removal of excessive quantities of nitrate ions from polluted drinking water streams. Catalysts are briefly reviewed first, followed by mechanistic speculations and kinetics that have been proposed for the liquid-phase nitrate reduction. Subsequently, a novel process scheme consisting of integrated ion-exchange and catalytic denitrification steps is discussed.

This paper reviews also the developments in the field of catalytic wet-air oxidation (CWAO). Particular attention was given to the heterogeneously catalyzed wet-air oxidation of real industrial wastewaters (such as Kraft bleach plant effluents) in batch and continuous-flow oxidation reactors. Finally, considerable potential of the CWAO process to ultimately destroy organic pollutants in industrial effluents and detoxify them by using novel titania-supported Ru catalysts is reported.     

饮用水中隐孢子虫与贾第虫的危害及其去除灭活研究

本文在介绍"两虫"即贾第虫和隐孢子虫的生态、危害及传播的基础上,综述了常规水处理工艺、膜法及组合工艺对"两虫"去除效果;分析了各种消毒剂和消毒方法灭活的优缺点,提出多种方法协同灭活将成为水消毒技术研究和开发的一个发展方向。预处理、絮凝、沉淀、澄清和过滤等常规水处理单元不能有效去除两虫,难以保证饮用水安全;膜过滤法两虫去除效率高,但大规模应用困难较大。而常规的氯消毒剂灭活两虫的效果不佳,臭氧对两虫的灭活效果优于氯和二氧化氯;UV能有效灭活两虫,但穿透力弱,UV灯管寿命短,运行费用高;US灭活两虫,能耗比较高。单一的消毒剂灭活两虫效果欠佳,采用多种消毒剂(方法)联合使用,通过协同作用,可达到较高的灭活率。