Showing papers in "Journal of Water Supply Research and Technology-aqua in 2010"

Assessing biological stability of drinking water without disinfectant residuals in a full-scale water supply system

Abstract: Biological stability refers to the inability of drinking water to support microbial growth. This phenomenon was studied in a full-scale drinking water treatment and distribution system of the city of Zurich (Switzerland). The system treats lake water with successive ozonation and biological filtration steps and distributes the water without any disinfectant residuals. Chemical and microbiological parameters, notably dissolved organic carbon (DOC), assimilable organic carbon (AOC), heterotrophic plate counts (HPC) and flow-cytometric total cell concentration (TCC), were measured over an 18-month period. We observed a direct correlation between changes in the TCC, DOC and AOC concentrations during treatment; an increase in cell concentration was always associated with a decrease in organic carbon. This pattern was, however, not discerned with the conventional HPC method. The treated water contained on average a TCC of 8.97 × 10 4 cells ml −1 , a DOC concentration of 0.78 mg l −1 and an AOC concentration of 32 μg l −1 , and these parameters hardly changed in the distribution network, suggesting that the treated water had a high level of biological stability. This study highlights the descriptive value of alternative parameters such as flow-cytometric TCC for drinking water analysis, and pinpoints some of the key aspects regarding biological stability in drinking water without disinfectant residuals.

Rational design of domestic biosand filters

Abstract: A biosand filtration (BSF) unit is an intermittently operated slow sand filter designed for household use. This paper reviews the practical application of B S F , identifies the important design considerations and proposes a systematic design procedure. The media properties, water requirements, filter cycle time and water temperature are identified as the most important design input parameters. The resultant specifications are the water dosage volume, water production rate and media bed dimensions. We propose two parameters for characterising the filtration rate, namely the initial and average clean bed filtration rate. Mathematical expressions for these two parameters and the filtration time are derived. Guideline values for the filtration rate and the ratio of the pore volume to the water dosage volume are established and used as design checks. It is noted that the filtration rate is determined solely by the properties of the water temperature and the media—customary constraints posed by the bed area and the bed depth had been eliminated. Therefore the heart of BSF design lies in the careful and appropriate selection of the filter media. The design procedure proposed is illustrated with an example for a typical rural household in Venda, South Africa.

Comparison of optional process configurations and operating conditions for ceramic membrane MF coupled with coagulation/flocculation pre-treatment for the removal of NOM in drinking water production.

Abstract: The increase of Natural Organic Matter (NOM) in natural water sources, partly caused by progressing climate change issues, is a growing concern for drinking water production. In recent years, membrane technology like Reverse Osmosis (RO) or Nanofiltration (NF) has been successfully applied as a robust solution for NOM removal to produce potable water. However, coagulation/flocculation pre-treatment, combined with Microfiltration (MF) ceramic membrane filtration is nowadays seen as an alternative, less-energy-consuming membrane process for NOM removal. In this study different coagulants have been used under varying coagulation/flocculation conditions to investigate the respective impact on membrane filtration performance. Three alternative coagulation/flocculation configurations were compared. It is shown that NOM was efficiently removed independently on the chosen configuration or coagulant type. Similar and low membrane fouling rates were observed for all tests. Residual metal concentration was found to be the limiting permeate quality parameter, which limits the options of operating conditions. Furthermore, the compact inline pipe flocculator configuration has the potential of designing more compact full-scale units, using less space compared to conventional sand filtration units or even membrane filtration plants using classical tank coagulation/flocculation configurations.

NDMA and seven other nitrosamines in selected UK drinking water supply systems

Abstract: A survey for N-nitrosodimethylamine (NDMA) and seven other nitrosamines in six UK drinking water supply systems was conducted. At the time of the study, there was no NDMA data for UK drinking waters, and the study remains one of few globally to report concentrations of the other seven nitrosamines in water supply systems. Five of the six water supply systems were selected as probable to have elevated nitrosamine concentrations because of the known source water characteristics and/or treatment practices; the sixth supply system had none of the suspected risk factors and was included as a control case. Sampling was conducted in five intervals and included samples collected from the source water, post-filter, post-disinfection and the distribution system. NDMA was measured barely above the method detection limit (0.9 ng l -1 ) in a few isolated samples in one distribution system; however, otherwise the majority of samples contained no detectable NDMA or other nitrosamines. An exception was that N-nitrosodibutylamine (NDBA) was consistently detected in one distribution system, up to a maximum concentration of 6.4 ng | -1 . There were no identifiable relationships to link source water characteristics, the particular treatment processes or distribution system contact time with the observed nitrosamine concentrations.

Competitive adsorption of micropollutants and NOM onto activated carbon: comparison of different model approaches.

Abstract: Conventional adsorption models are not able to describe exactly the competitive adsorption of natural organic matter (NOM) and micropollutants during drinking water treatment with activated carbon. This problem is a consequence of the complex structure of natural organic matter. In the last years, two user-oriented model approaches, the tracer model (TRM) and the equivalent background compound model (EBCM), were proposed to overcome the difficulties in modelling the competitive adsorption in such multi-component systems. In this paper, these model approaches, as well as a simplified model for batch processes, are compared and opportunities and limitations are pointed out. The different aspects of model application are exemplarily discussed for the adsorption of two pesticides, atrazine and diuron, from Elbe River water onto activated carbon. As can be seen from the examples and from a series of studies, both models are suitable for modelling the micropollutant adsorption in the presence of NOM. The EBCM is somewhat easier to handle whereas the TRM allows for the consistent and parallel description of micropollutant and NOM adsorption.

Perfluorinated compounds contamination in tap water and bottled water in Bangkok, Thailand

Abstract: Perfluorinated compounds (PFCs) such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) have been detected in the environment, in biota and in humans. The exposure pathways of these chemicals to humans are unclear. Tap water and bottled water are two possible pathways of PFCs occurrence in human blood. The major objectives of the study were to identify the occurrences of PFCs in tap and bottled water and to evaluate conventional water treatment processes performance on removal of PFCs. Solid phase extraction coupled with HPLC-ESI-MS/MS were used for the analysis of ten PFCs. PFCs were detected in all tap water samples and bottled water samples. The average PFOS and PFOA concentrations in tap water were 0.17 and 3.58 ng l −1 , respectively. PFOS and PFOA were not similarly distributed in all areas in the city. PFCs concentrations were higher in bottled water than in tap water. Moreover, the current treatment processes were not effective in removing PFCs in aqueous phase. Nevertheless, PFCs in particulate phase were effectively removed by primary sedimentation and rapid sand filtration. Based on the guideline from the New Jersey Department of Environmental Protection, PFOA concentrations in tap water and bottled water found in Bangkok were not expected to cause any health risks.

Flocs and separation processes in drinking water treatment: a review

Abstract: The paper focuses on the properties of flocs that are required to service the needs of solid–liquid separation in conventional treatment units. Beyond the basic requirements of minimum size and surface nature to enable effective trapping on a collecting surface, field data indicate that floc water content affects treatability (as gauged by the hydraulic loading rate or treatment rate). Floc blanket clarifiers, DAF and filter units are examined in terms of implications of floc size, density and strength, insofar as they interact with the process dynamics. It is shown that these features come into play both individually and collectively and are sensitive to the floc fractal structure. It is argued that floc strength often plays a critical role in separation processes through its impact on floc size. Recognising the benefits of densification, the paper provides specific advice on how densification can be achieved. Among the many options considered, it is noted that the most straightforward means of securing greater density or strength, is by use of smaller flocs, this also benefiting dewaterability.

Modelling the potential for water quality failures in distribution networks: framework (I)

Abstract: The deterioration of water quality can adversely affect consumers' health as well as the aesthetic properties of water (taste, odour, colour). To date, little consideration has been given to the impact of deteriorating (ageing) water mains on water quality as a major decision driver for the renewal/rehabilitation of water mains. The main objective of this research was to identify major deterioration mechanisms in distribution networks that may contribute to water quality failures (WQF) and develop a model to quantify overall potential for WQF as a function of this deterioration. Numerous factors affect water quality in the distribution network and interactions among them are complex and often not well understood. Water quality failures in distribution networks are relatively scarce, which makes it difficult to establish statistically significant generalizations. In such data-sparse circumstances, expert knowledge and judgement can serve as a supplement or even as alternative source(s) of information. This paper discusses major deterioration mechanisms that may contribute to WQFs in distribution networks, and proposes a modelling framework using fuzzy-based methods. The following two papers in this series will provide a mathematical formulation of the proposed model and its application using two case studies, respectively.

Extending membrane longevity by using MIEX as a pre-treatment

Abstract: The use of membrane technology and in particular microfiltration (MF) is becoming more popular as a water treatment technology. The operational lifetime of MF membranes can be reduced by natural organic matter (NOM) which is a known foulant. The MIEX DOC (Magnetic Ion EXchange for Dissolved Organic Carbon removal) process was developed to remove NOM from raw water sources. It was anticipated that a reduction in NOM resulting from the MIEX DOC process would also improve the performance of MF systems. A pilot plant study was undertaken to directly measure the impact of MIEX pre-treatment on MF performance. A long term study with a regular cleaning strategy revealed little benefit in MIEX pre-treatment to improve the lifetime of the MF membrane. However, by applying less frequent cleaning it was immediately apparent that fouling was occurring at a faster rate without MIEX pre-treatment. Further studies showed that irreversible fouling also occurred at a faster rate on the membrane without pre-treatment.

Multicriteria decision analysis for the selection of a small drinking water treatment system

Abstract: The selection of a small drinking water treatment system for a hydro-electrical plant is addressed within a multicriteria and participatory decision analysis process. As a first step, based on problem constraints, we identified and retained three water treatment systems alternatives. In close collaboration with the stakeholders, we then defined and obtained weights for criteria that take into account public health, costs, system impacts and perception issues. The ELECTRE II method was used to aggregate the alternatives evaluations in order to obtain a ranking of the three water treatment systems. The process revealed that the system which combines NF and UV disinfection is ranked first for all the different stakeholder weightings. The sensitivity analysis of the aggregation parameters and evaluations reinforced that conclusion. This study provides useful information for conducting similar analysis on industrial or municipal water treatment systems.

Modelling asset lifetimes and their role in asset management

Abstract: Utilities throughout the world are faced with the challenge of how best to manage their existing asset stock to provide satisfactory customer service with limited funds. Effective asset management helps utilities to meet this challenge; however, this requires the utilization of cost-effective approaches for assessing asset condition, performance and remaining service life. A key component of these approaches requires an understanding of asset lifetimes. This paper discusses the role of asset lifetimes in asset management and the current state of the art for prediction of remaining life using different approaches. It discusses very simple approaches based on assumed lives, as well as sophisticated mathematical approaches using deterministic, statistical, physical/probabilistic and artificial intelligence models. In analysing both asset management strategies and lifetime prediction methodologies, a key factor identified as missing is a standardized technique for the incorporation of lifetime models into the probability side of risk analysis. For asset management to become a valued and readily utilized tool, this issue needs to be urgently addressed.

Ion transport characteristics in nanofiltration membranes: measurements and mechanisms

Abstract: Ion transport characteristics during nanofiltration (NF) were investigated by measuring effective osmotic pressure and diffusivity experimentally. Effective osmotic pressure and diffusivity were measured through lab-scale transport and diffusion tests. First, it was shown that the water flux across NF membranes decreased dramatically with increasing ionic strength because of the noticeable increase in effective osmotic pressure. Second, the results from transport experiments showed that the ion selectivity values, which were derived from the thermodynamic model, decreased with increasing ionic strength. Third, by analysing the data of measured osmotic pressure and diffusivity, it was demonstrated that the former and the latter increased and decreased, respectively, as ionic strength increased. The experimentally determined osmotic pressure across NF membranes was much lower than that calculated theoretically. At best, around 5% or less of the theoretical osmotic pressure was obtained under the experimental conditions investigated. The effective osmotic pressure and ion rejection decreased in the presence of nano-colloids. The influence of nano-colloids on ionic transport was found to be dependent on the concentration and size of the nano-colloids. Therefore, ion transport characteristics across NF membranes can be determined practically by measuring effective osmotic pressure and diffusivity as these reflect both feed water and membrane properties.

Impact of speciation on removal of manganese and organic matter by nanofiltration

Abstract: The removal of manganese and humic acid (HA) by two nanofiltration membranes, TFC-SR2 and TFC-SR3, was investigated in order to highlight the influence of speciation on manganese and HA retention Manganese speciation and complexation with HA were modelled to understand how speciation could affect NF removal mechanisms The behaviour of the two membranes was dramatically different in terms of manganese retention Manganese retention for TFC-SR3 was higher and dominated by size exclusion Manganese retention for TFC-SR2 varied with pH At pH 7 (ie the pH of most natural waters) manganese retention for TFC-SR2 was about 45% versus 90% for TFC-SR3, with fluxes of about 75 and 25 l m−2 h−1, respectively Both membranes showed very high retention of HA (about 80%); therefore they are suitable for surface waters where no salt removal is required Manganese deposit on both membranes was generally low (<10%), but increased at pH 10 and 12 as manganese deposited as precipitated MnCO3, and the membranes showed a yellow-brownish layer

A pilot-scale study of backwashing ultrafiltration membrane with demineralized water.

Abstract: This study investigates the effectiveness of different backwash waters on ultrafiltration (UF) fouling control on a pilot-scale setup. Surface water and ion exchange (IEX) pretreated surface water were used as feed water. Three backwash waters were tested: demineralized water, UF permeate and nanofiltration (NF) permeate. Results show that backwashing with demineralized water substantially improves fouling control efficiency. It is supposed that both the reduction of charge screening and Ca-bridging effect cause this improvement on fouling control. Furthermore, backwashing with NF permeate also negatively influences the fouling control efficiency, indicating the impact of monovalent ions in backwash water on the ultrafiltration fouling. Findings from such a pilot scale setup also show that it is possible to apply backwashing with demineralized water on the operation of UF plants.

Water supply operation: diagnosis and reliability analysis in a Lisbon pumping system

Abstract: An abnormal accident with no flow in a pumping system occurred with a large displacement of the pipe system. A slow closure of an isolation valve installed in a large suction pipe was the main action. As soon as the valve was closed the 1.6 m diameter pipe moved and the pipe supports were broken, presenting an expansion joint almost fully opened and the main pipe almost broken. This was a critical event that took place in one of the most important pumping stations of the water supply system in Lisbon. In order to avoid future accidents, a detailed analysis was developed as a priority in order to identify the cause of this event. The paper describes the event and the methodology followed in order to fully validate the diagnostic and the proposed chain of events that caused the pipe movement. The process included a careful, in situ observation of the system, hydraulic and structural analyses and some site tests. Ironically, the explanation of abnormal events can give the opportunity to better understand the operation of water supply systems. Weak points in the design and in the operation can then be detected and future accidents can also be avoided.

Hybrid membrane process: Performance evaluation of biological PAC

Abstract: This study investigated the use of biological powdered activated carbon (PAC) for the removal of natural organic matter (NOM) and ammonia from drinking water. The impact of solids retention time (SRT), hydraulic retention time (HRT), PAC diameter and PAC concentration on the process efficiency was evaluated. Five bioreactors were filled with a slurry using two PAC concentrations (5 or 25 g l−1), two PAC mean diameters (25 or 200 μm) and two SRTs (30 or 100–160 days). The bioreactors were operated during 161 days using post-ozonated water as influent. It was determined that the PAC concentration in the bioreactors was a key parameter for the improvement of biological removal. The higher PAC concentration (25 g l−1) was more efficient for the removal of ammonia, dissolved organic carbon (DOC) and biodegradable dissolved organic carbon (BDOC). Full nitrification was observed after 90 days in bioreactors with 25 g l− of PAC. The PAC diameter (25 vs. 200 μm) did not significantly influence BDOC, DOC and N-NH4 removals under stable conditions, although nitrification was initiated faster using a 25-μm diameter PAC. Increasing HRT from 15 to 30 minutes improved NOM and ammonia removals. Reducing SRT from 100–161 to 30 days improved DOC removals but reduced BDOC and ammonia removals. The overall performances observed during this study demonstrate the efficiency of biological PAC. Its combination with ultrafiltration in a hybrid membrane process appears promising but the feasibility from an operational standpoint still has to be demonstrated

Using performance indicators as a water loss management tool in developing countries

Abstract: Water utilities in developing countries are facing the challenges of substantial water losses in their water supply systems. In order to deliver water to their customers more efficiently and effectively, utilities must be able to measure and assess the performance of their water supply systems against set management objectives. However, water loss assessment is still not widely practised in developing countries. The task of measuring and evaluating performance is accomplished by performance assessment systems through well-defined performance indicators (PIs). Most PIs currently used are often not applicable in developing countries. This paper presents an eight-step participatory methodology for the selection of indicators and highlights challenges of integrating a PI culture in developing countries, in total, 25 PIs have been proposed as part of a standardized water balance methodology and so far 16 PIs have been tested successfully. The other nine PIs have not been tested, as the costs of generating and collecting reliable data outweigh the added benefits. In addition an appropriate water loss performance indicator computational tool has been developed to promote use of standardized water balance and performance measures by the utilities of developing countries.

Biological origins and annual variations of earthy-musty off-flavours in the Xionghe Reservoir in China

Abstract: The annual variations in physicochemical parameters, algal abundance and odorous compounds in the Xionghe Reservoir were investigated, in order to identify the possible odorous compounds and their origins. From May 2007 to April 2008, the algal composition, cell number and earthy-musty odorous compounds both in the water and in the flesh of fish at Sites A, B and C were determined monthly. The physicochemical parameters such as total nitrogen (TN), total phosphorus (TP), dissolved oxygen ( DO), pH, transparency, water temperature and chlorophyll a (chl a) were simultaneously determined. A statistical correlation was noted between the chl a and water temperature: 0.678 (P < 0.05) for Site A, 0.831 (P < 0.01) for Site B and 0.659 ( P, 0.05) for Site C. Geosmin and 2-methylisoborneol (2-MIB)-in the reservoir were identified by gas chromatography-mass spectrometry (GC-MS). We observed that a large amount of Anabaena circinalis bloomed in surface water during the off-flavour episodes. In July 2007, we detected the highest concentration of geosmin (2.7 mu g/L in the water, 0.27 mu g/kg in the silver carp and 0.10 mu g/kg in the crucian carp), while no 2-MIB was detected, which indicated that geosmin was mainly responsible for the off-flavour episodes in summer.

Study on failure rate analysis for water distribution pipelines

Abstract: Many of the waterworks facilities in Japan were constructed during the rapid economic growth period. Today, the deterioration and renovation of these aged facilities have become a pressing issue. There are approximately 600,000km worth of water pipelines laid out across Japan, accounting for about 70% of the nation's water-related assets (totalling ¥40 trillion). To provide water that is safe to use, it is necessary to improve and innovate water purification technologies; not only that, it is also vital to properly maintain and manage the pipelines. The current research aims to apply reliability engineering in the waterworks field as one possible approach and to show its viability; it will also obtain vital messages revealed within pipeline incident data. In other words, we collected the information concerning water distribution pipeline incidents through questionnaire surveys and then analysed the cumulative failure distribution (unreliability) by pipeline material, the failure probability density and failure rate, among others.

Calcite precipitation from aqueous solutions with different calcium and hydrogen carbonate concentrations

Abstract: This paper describes the influence of different Ca 2 + and HCO 3 − concentrations on the precipitation of calcite in aqueous solutions. Mixtures of CaCl 2 and NaHCO 3 solutions with different concentrations were stirred, covering a wide range of supersaturation and precipitation of calcite. The resulting reduction of the Ca 2 + concentration was recorded as a function of time by measuring the electric conductivity and the pH value. The nucleation rate increased with increasing supersaturation and can be described with the classical theory of nucleation. For different solutions with similar values of supersaturation, the hydrogen carbonate/calcium ratio had no significant influence on the rate of nucleation. At a given calcium concentration the precipitation rate increased with increasing supersaturation. This effect was more pronounced at higher supersaturations. Measurements at similar values of supersaturation showed that the calcite precipitation rate increased with increasing hydrogen carbonate/calcium ratio. These results can be explained by applying a surface complexation model. The crystal surface concentrations of the two species > CaCO 3 − and > CO 3 − and the adsorption of CaCO 3 0 ion pairs are responsible for catalysing calcite precipitation.

Seawater desalination — a green technology?

Abstract: The need for resource-saving, low-impact “green” desalination technologies is evident as the use of desalination accelerates in many parts of the world. The concept of “best available techniques” (BAT) aims at the identification of state of the art technologies, processes, or methods of operation which indicate the practical suitability for preventing or reducing pollution of the atmosphere, water and soil, as well as the quantities of waste, and for reducing the impact on the environment as a whole. This paper describes a general BAT approach for seawater desalination plants, focusing on the resource consumption of the different processes and methods of operation and their likely environmental impacts. The results may be a useful reference in the determination of individual BAT solutions on a case by case basis, taking site- and project-specific considerations into account, such as environmental regulations and local environmental conditions.

Parameters affecting steady-state floc blanket performance

Abstract: A laboratory-scale reactor was used to simulate a water treatment process sequence of rapid mix, hydraulic flocculation, upflow clarification with a floc blanket, and lamellar sedimentation to accomplish removal of colloidal particles. This study focused on variables affecting performance of the floc blanket including: provision of hydraulic flocculation, raw water turbidity, coagulant dose, upflow velocity through the floc blanket, and bulk density and solids concentrations of the floc blanket. An upflow clarifier velocity between 1.0 and 1.3 mm s -1 produced the best floc blanket performance for turbidities studied between 10 and 200 NTU while an upflow velocity between 0.6 and 0.8 mm s -1 produced the best floc blanket performance at 500 NTU. The results show that overall particle removal efficiency improved with increasing hydraulic flocculator residence time and energy dissipation rate. Particle removal efficiency improved with increasing floc blanket depth for floc blanket depths between 15 and 75 cm. Lamellar sedimentation with a capture velocity of 0.12 mm s -1 is a key component in improving clarifier performance when utilizing a floc blanket.

Feasibility of in-line coagulation as a pretreatment for ceramic microfiltration to remove viruses

Abstract: The feasibility of in-line coagulation as a pretreatment for ceramic microfiltration (MF) was verified by comparing its efficiency in the removal of viruses with that of the traditional mechanical mixing approach for coagulation, and by examining the effect of coagulant dose and coagulation time on virus removal. The in-line coagulation–ceramic MF system efficiently removed bacteriophage Qβ and MS2: removal ratios were >8.2 log for infectious viruses and >5.4 log for total (infectious + inactivated) virus particles. These values were similar to those of the mechanical coagulation–ceramic MF system. The in-line coagulation system has potential as a useful pretreatment for the removal of viruses as an alternative to the mechanical mixing system, because the former efficiently removes viruses and has a smaller footprint in treatment plants. For the in-line coagulation–ceramic MF system, a coagulant dose of 1.08 mg-Al/L and a coagulation time of 1 min were required to achieve a high level of virus removal. Infectious Qβ and MS2 were removed to similar levels by the two precoagulation methods tested, but the removal of total MS2 particles was higher than that of Qβ particles, possibly because of the selective interaction with the cake layer.

Risk assessment study for water supply network using GIS

Abstract: In recent years, contamination of water in water distribution systems (WDS) has been recognized as a major cause of waterborne diseases. Owing to old and deteriorated pipes, and the presence of pollution sources in contact with the supply line, water boards often decide to replace the network in the interests of public health. This being a cost-intensive and time-consuming programme, decision makers need a basis for phase-wise investment planning. In view of this, Integrated Risk Assessment of Water Distribution System (IRA-WDS) for the supply network of Adikmet Subzone-I in Hyderabad, India, was undertaken. GIS maps were prepared for the water supply network, sewer network, open drains, soil and groundwater table at 1:2,200 scale and ‘pipe condition assessment’ and identification of ‘contaminant ingress’ locations were performed using IRA-WDS. Findings indicated 18 pipes in ‘very bad’ and ‘bad’ condition in the entire network. ‘High risk’ of contamination was exhibited in 20 locations, suggesting the need for rehabilitation of only 2 to 3% of pipes in the initial phase.

Influence of permeation on air/water cleaning of spiral wound membrane NF/RO elements

Abstract: To improve hydraulic conditions, periodic air/water cleaning (AWC) is applied to a nanofiltration (NF) spiral wound membrane (SWM) element under permeation conditions to control biofouling and particulate fouling. A pilot study was carried out for 212 days with a vertically positioned SWM element fed by tap water enriched with a biodegradable compound (60 mu g acetate-C l(-1)). Operational parameters were daily recorded, rinse water was collected and analysed and a membrane autopsy was performed at the end of the experimental run. Normalized pressure drop (NPD) increased as a result of biofouling and particulate fouling, and could be controlled by periodic AWC, while the membrane transport coefficient (MTC) and retention based on the conductivity remained constant. Rinsing water from AWC contained biomass and particulate matter (iron), predominantly during the first few minutes of AWC. Membrane autopsy revealed active biomass and inorganic deposits (mainly iron and copper) at the inlet and outlet of the membrane element. The use of AWC in (vertically positioned) NF/RO SWM elements under permeation conditions improved the control of membrane fouling (especially biofouling and particulate fouling) and did not compromise the integrity of the membrane element (until day 60).

Los Angeles water supply impacts from a M7.8 San Andreas Fault earthquake scenario

Abstract: The City of Los Angeles, as well as the entire Southern California population of over 22 million people, is highly dependent on water imported through the Los Angeles, California and Colorado River Aqueducts. The San Andreas Fault poses one of the greatest risks to these critical water supply lines; all three aqueducts cross the San Andreas Fault. A preliminary review of potential damage to these three major aqueducts in response to a magnitude 7.8 earthquake scenario on the San Andreas Fault was performed. The results indicate repairs to restore flow into each aqueduct may take a year or more. Local storage is estimated to last approximately 6 months with significant rationing. As a result, there may be inadequate storage to supply the local population during the length of time it takes to repair the aqueducts. Inadequate water storage has significant health, safety and economic impacts on the Southern California region. This investigation identifies the need for a more thorough evaluation of aqueduct restoration times. In addition, mitigation measures for additional local storage and more rapid aqueduct restoration must be implemented.

Application of the membrane fouling simulator to determine biofouling potential of antiscalants in membrane filtration

Abstract: In treatment of groundwater with reverse osmosis, the applied antiscalant can significantly contribute to the formation of biofouling, especially when legislation enforces the use of biodegradable, phosphorous-free products. As an alternative to extensive piloting, the use of the membrane fouling simulator (MFS) is proposed here to assess the biomass growth potential of different antiscalants. The biomass growth potential of two newly developed, phosphorous-free antiscalants was compared to a blank (no antiscalant) and a phosphorous-based antiscalant. The difference in biomass growth potential in the four experiments was significant, with the phosphorous-based antiscalant showing little biomass accumulation and strong and moderate biomass accumulation for the two newly developed phosphorous-free antiscalants. The results of visual observation and pressure measurements of the MFS were compared to the results of autopsy of the membrane sheets. Visual and pressure measurements were found to be a more reliable method to judge the biomass accumulation than membrane autopsy. In a comparison study of MFSs and test rigs with 4″ spiral-wound membrane modules, similar results were found, validating MFS use for simulating membrane modules.

Investigating the fouling layer of polyamide nanofiltration membranes treating two different natural waters: internal heterogeneity yet converging surface properties

Abstract: This study investigated the fouling of four polyamide nanofiltration membranes by two surface waters that differed substantially in major properties. The emphasis was on determining the characteristics of the fouling layer on the membranes. The rates of fouling for the two waters differed considerably, with a more rapid flux decline being observed for the water having higher biopolymer and major ion concentrations. Measurements of membrane roughness, contact angle and zeta potential in general showed considerable differences for each of these properties among the virgin membranes. However, values of each of these parameters tended to converge for all membranes after fouling, regardless of which water had been used. This result is very significant (for example for the removal of trace contaminants, which in many cases may depend on membrane properties) because in practice a membrane spends virtually all of its operating life fouled to some degree. Several techniques including transmission electron microscopy (TEM) were used to conduct detailed investigations of the fouling layer. These results demonstrated the great heterogeneity within that layer, despite the similar overall properties mentioned above. This heterogeneity is significant for quantitative understanding of the relationship between fouling and flux and for strategies to reduce or remove fouling.

Behaviour of pyrene and its decomposition by-products in chlorination

Abstract: The behaviour of pyrene and its decomposition by-products in chlorination and their aryl hydrocarbon receptor (AhR) ligand activities were investigated. In the study on pyrene behaviour in chlorination, the pyrene and chlorine concentrations and the pH range were 0.82–21 μg l −1 , 2.0–2.1 mg l −1 and 3.2–10, respectively. In the pH range of 3.2–5.1, pyrene was decomposed faster in the order of pH 3.2, 3.7 and 5.1. However, when the pH ranged from 5.1 to 10, pyrene was decomposed faster in a pH range of approximately 7.8–8.8. When the effects of the initial pyrene concentration were investigated, a lower pyrene concentration was decomposed faster. Pyrene decomposition in chlorination was inhibited by the presence of 30 mM ethanol, but was enhanced by the presence of 3.0 and 6.0 mgC l −1 humic acid. Pyrene decomposition by-products in chlorination were also characterized (pyrene, 92 μg l −1 ; chlorine, 7.9 mg l −1 ; pH, 7.1). 1-Chloropyrene, 1,6- and 1,8-dichloropyrenes, and pyrene-4,5-dione were identified as pyrene decomposition by-products. 1-Chloropyrene and pyrene-4,5-dione in chlorination were found to be major by-products at pH 3.2, but minor by-products at pH 7.1 (pyrene, 56–67 μg l −1 ; chlorine, 3.9–4.0 mg l −1 ). The yeast assay revealed that pyrene-4,5-dione was an AhR agonist.

Air/water cleaning for the control of particulate fouling

Abstract: Fouling of feed spacers in spiral wound membrane elements due to particulate fouling and biofouling is one of the main operational problems of nanofiltration or reverse osmosis membrane plants. Removal of particulate fouling from spiral wound membrane elements is investigated using frequent air/water cleaning (AWC). In a pilot setup two spiral wound elements were operated in parallel and were fed by tap water containing suspended solids. The reference membrane (REF) was fed with tap water pre-filtered with a 1.0-μm cartridge filter and fouled within 50 days indicated by a 55% increase in the pressure drop. The second membrane element (AWC) was fed with unfiltered tap water (with an average turbidity of 0.3 NTU) resulting in a 73% increase in the pressure drop within a few days of operation. By using air/water cleaning, the pressure drop decreased to initial pressure drop values, indicating complete removal of particulate fouling. It was concluded that periodical air/water cleaning proved to be effective in controlling membrane spacer channel fouling as a result of particles in the feed water.