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The present study aims at an optimal design of a model water treatment plant comprising of a Rapid mix unit, Clariflocculator and Rapid sand filter. The suspended solids are considered as the basic impurity whose volume is assumed to be reduced to 2 mg/lit in filtered water for different raw water qualities. Various parameters such as velocity gradient, detention time, surface overflow rate, filtration rate, diameter of sand grain, depth of sand bed and time of filter run are considered as design variables for the optimization process. A set of mathematical formulae comprising of the above design variables is used to arrive at optimal values. Algorithms developed based on dynamic programming are used to arrive at the stated optimal design variables. It can be observed from the study that the optimal design differs from conventional design mainly with reference to the two design variables, i.e., surface overflow rate in the clariflocculator and filtration rate of filtration unit. A comparison of the existing treatment plant of capacity 15 MGD locally with that of the optimal design of same capacity plant using the optimal design variables is presented. [ABSTRACT FROM AUTHOR]

The technical performance of a precoat filter was compared with that of a traditional sand filter. Particle concentration and size distribution were measured before and after the filtration of swimming pool water. Both the sand and precoat filters could reduce the particle concentration in the effluent. However, higher particle removal efficiency was generally observed for the precoat filter, especially for particles smaller than 10 µm in diameter. Adding flocculant improved the removal efficiency of the sand filter, resulting in removal efficiencies comparable to those of the precoat filter. Three powders, i.e., two types of perlite (Harbolite® and Aquatec perlite) and cellulose fibers (Arbocel®), were tested for the precoat filter, but no significant difference in particle removal efficiency was observed among them. The maximum efficiency was reached within 30-40 min of filtration. The energy required for the pumps increased by approximately 35% over a period of 14 days. The energy consumption could be reduced by replacing the powder on the filter cloth. The sand filter was backwashed once a week, while the powder on the precoat filter was replaced every two weeks. Under these conditions, it was possible to reduce the water used for cleaning by 88% if the precoat filter was used instead of the sand filter. [ABSTRACT FROM AUTHOR]

Debris flows can be described as rapid gravity-induced mass movements controlled by topography that are usually triggered as a consequence of storm rainfalls. One of the problems when dealing with debris flow recognition is that the eroded surface is usually very shallow and it can be masked by vegetation or fast weathering as early as one-two years after a landslide has occurred. For this reason, even areas that are highly susceptible to debris flow might suffer of a lack of reliable landslide inventories. However, these inventories are necessary for susceptibility assessment. Model transferability, which is based on calibrating a susceptibility model in a training area in order to predict the distribution of debris flows in a target area, might provide an efficient solution to dealing with this limit. However, when applying a transferability procedure, a key point is the optimal selection of the predictors to be included for calibrating the model in the source area. In this paper, the issue of optimal factor selection is analysed by comparing the predictive performances obtained following three different factor selection criteria. The study includes: i) a test of the similarity between the source and the target areas; ii) the calibration of the susceptibility model in the (training) source area, using different criteria for the selection of the predictors; iii) the validation of the models, both at the source (self-validation, through random partition) and at the target (transferring, through spatial partition) areas. The debris flow susceptibility is evaluated here using binary logistic regression through a R-scripted based procedure. Two separate study areas were selected in the Messina province (southern Italy) in its Ionian (Itala catchment) and Tyrrhenian sides (Saponara catchment), each hit by a severe debris flow event (in 2009 and 2011, respectively). The investigation attested that the best fitting model in the calibration areas resulted poorly performing in predicting the landslides of the test target area. At the same time, the susceptibility models calibrated with an optimal set of covariates in the source area allowed us to produce a robust and accurate prediction image for the debris flows activated in the Saponara catchment in 2011, exploiting only the data known after the Itala-2009 event. [ABSTRACT FROM AUTHOR]

Rapid gravity filters, the final particulate barrier in many water treatment systems, are typically monitored using on-line turbidity, flow and head loss instrumentation. Current metrics for assessing filtration performance from on-line turbidity data were critically assessed and observed not to effectively and consistently summarise the important properties of a turbidity distribution and the associated water quality risk. In the absence of a consistent risk function for turbidity in treated water, using on-line turbidity as an indicative rather than a quantitative variable appears to be more practical. Best practice suggests that filtered water turbidity should be maintained below 0.1 NTU, at higher turbidity we can be less confident of an effective particle and pathogen barrier. Based on this simple distinction filtration performance has been described in terms of reliability and resilience by characterising the likelihood, frequency and duration of turbidity spikes greater than 0.1 NTU. This view of filtration performance is then used to frame operational diagnosis of unsatisfactory performance in terms of a machine learning classification problem. Through calculation of operationally relevant predictor variables and application of the Classification and Regression Tree (CART) algorithm the conditions associated with the greatest risk of poor filtration performance can be effectively modelled and communicated in operational terms. This provides a method for an evidence based decision support which can be used to efficiently manage individual pathogen barriers in a multi-barrier system. [ABSTRACT FROM AUTHOR]

The oxidation process of dissolved iron particles in water changes the iron into red-brown solid particles (particulate), which settle down in the water. Those large particles that settle down in the water can be handled. Nevertheless, iron that does not procedure large enough particles to settle down remains suspended (colloidal iron) and thus leaves the water with red tint. Unfortunately, these particles threat the industry and the municipal of water supplies. This is due to formation of scales as well as blockage of water pipes that lead to economic problems. Numerous studies have been conducted to study the effect of using oxidation processes followed by the filtration process only for the removal of iron from water. This study introduces a comparison of filtration of aerated raw water though a filter of sand bed with and without Alum as a coagulant prior to filter. A synthetic iron dozes are added to tap water to represent a pre-determined different concentrations of iron as 2 and 3 mg/L which result in 14 and 32 NTU, respectively, after aeration of raw water. The effluent of water was taken at regular time intervals to monitor the progressive rate of removal of these elements for different values of filtration rates 120, 180 and 240 m3 /m2 /day. A single layer gravity rapid sand filter was used with sand bed of 70 cm thickness, effective diameter of 0.7 mm and uniformity coefficient of 1.57. During the experiments, the iron concentration and turbidity in the effluent were recorded at all the used filtration rates. The results show that the low limit of the removal efficiency of iron is 89% and the high limit is 97% without coagulation and 78% to 97% with coagulation. Also, the higher the concentration of iron and turbidity, in the influent, the higher the efficiency removal of filter for all filtration rates takes place. For all tested parameters of influent iron concentrations and filtration rates, the effluent iron concentrations and effluent turbidities within the allowable limits of Egyptian drinking water specifications (0.3mg/l for iron and 1.0 NTU for turbidity), except for filtration rates exceeds the 180m3/m2/day the turbidity was above these allowable limits for both cases using coagulant or not. It obvious, also, from experiments that at low concentration of influent iron (below 3 mg/l) and filtration rates up to 180m3/m2/day there is no need to coagulation process. [ABSTRACT FROM AUTHOR]

The article discusses the postcolonial history of Little Falls Water Treatment Plant in Totowa, New Jersey. Topics include the design of Little Falls's first large-scale rapid sand filtration plant by engineer George W. Fuller, doctor John L. Leal, public health officer of Paterson, New Jersey and sanitary advisor to East Jersey Water Co., who recognized the potential of chlorine disinfection for drinking water, and the late Pasaic Valley Water Commission board member Marinus de Nooyer.

Groundwater is an important drinking water resource. Yet, this resource is threatened by pollution from chemicals, such as pesticides and their degradation products. To investigate the potential for remediation of groundwater polluted by trace concentrations of the pesticide residue 2,6-dichlorobenzamide (BAM), we established a pilot waterworks including two sand filters. The waterworks treated groundwater polluted with 0.2 μg/L BAM at flow conditions typical for rapid sand filters. Bioaugmentation of the sand filter with a specific BAM-degrading bacterium ( Aminobacter sp. MSH1) resulted in significant BAM degradation to concentrations below the legal threshold level (0.1 μg/L), and this without adverse effects on other sand filter processes such as ammonium and iron oxidation. However, efficient degradation for more than 2–3 weeks was difficult to maintain due to loss of MSH1-bacteria, especially during backwashing. By limiting backwash procedures, the period of degradation was prolonged, but bacteria (and hence degradation activity) were still lost with time. Protozoa were observed to grow in the filters to a density that contributed significantly to the general loss of bacteria from the filters. Additionally, the concentration of easily assimilable organic carbon (AOC) in the remediated water may have been too low to sustain a sufficient population of degrader bacteria in the filter. This study shows that scaling up is not trivial and shortcomings in transferring degradation rates obtained in batch experiments to a rapid sand filter system are discussed. Further optimization is necessary to obtain and control more temporally stable systems for water purification. However, for the first time outside the laboratory and at realistic conditions a potential for the biodegradation of recalcitrant micropollutants in bioaugmented rapid sand filters is shown. [ABSTRACT FROM AUTHOR]

As a promising technology for wastewater reuse, direct rapid sand filtration has been widely used throughout the world, especially in arid developing and emerging countries. Retention factor describing the equilibrium between retained and mobile total coliform (TC) bacteria plays an important role in the model of TC removal in direct rapid sand filtration. Little attention has been given to the relationship between retention factor and loading rate as well as filter height, two critical parameters impacting retention factor. Therefore, the influence of loading rate as well as filter height on retention factor was discussed. Results showed that retention factor decreased dramatically with loading rate ranging from 9 to 15 m/h, but increased slightly as loading rate ranged from 5 to 9 m/h, which is a little different with the variation of suspended solids and total phosphorus removal efficiency. Retention factor decreased significantly with filter height of 0–30 cm and 120–150 cm, but reduced uniformly with filter height of 30–120 cm. It was deduced that the optimum loading rate and filter height may be 9 m/h and 90–120 cm, respectively. Increasing flocculant could overcome retention factor reduction resulted from higher loading rate or smaller filter height. [ABSTRACT FROM PUBLISHER]

The efficiency of manganese removal in conventional groundwater treatment consisting of aeration followed by rapid sand filtration, strongly depends on the ability of filter media to promote auto-catalytic adsorption of dissolved manganese and its subsequent oxidation. Earlier studies have shown that the compound responsible for the auto-catalytic activity in ripened filters is a manganese oxide called Birnessite. The aim of this study was to determine if the ripening of manganese removal filters and the formation of Birnessite on virgin sand is initiated biologically or physico-chemically. The ripening of virgin filter media in a pilot filter column fed by pre-treated manganese containing groundwater was studied for approximately 600 days. Samples of filter media were taken at regular time intervals, and the manganese oxides formed in the coating were analysed by Raman spectroscopy, Electron Paramagnetic Resonance (EPR) and Scanning Electron Microscopy (SEM). From the EPR analyses, it was established that the formation of Birnessite was most likely initiated via biological activity. With the progress of filter ripening and development of the coating, Birnessite formation became predominantly physico-chemical, although biological manganese oxidation continued to contribute to the overall manganese removal. The knowledge that manganese removal in conventional groundwater treatment is initiated biologically could be of help in reducing typically long ripening times by creating conditions that are favourable for the growth of manganese oxidizing bacteria. [ABSTRACT FROM AUTHOR]

Rapid sand filtration is essential at most waterworks that treat anaerobic groundwater. Often the filtration depends on microbiological processes, but the microbial communities of the filters are largely unknown. We determined the prokaryotic community structures of 11 waterworks receiving groundwater from different geological settings by 16S rRNA gene-based 454 pyrosequencing and explored their relationships to filtration technology and raw water chemistry. Most of the variation in microbial diversity observed between different waterworks sand filters could be explained by the geochemistry of the inlet water. In addition, our findings suggested four features of particular interest: (1) Nitrospira dominated over Nitrobacter at all waterworks, suggesting that Nitrospira is a key nitrifying bacterium in groundwater-treating sand filters. (2) Hyphomicrobiaceae species were abundant at all waterworks, where they may be involved in manganese oxidation. (3) Six of 11 waterworks had significant concentrations of methane in their raw water and very high abundance of the methanotrophic Methylococcaceac. (4) The ironoxidizing bacteria Gallionella was present at all waterworks suggesting that biological iron oxidation is occurring in addition to abiotic iron oxidation. Elucidation of key members of the microbial community in groundwater-treating sand filters has practical potential, for example, when methods are needed to improve filter function. [ABSTRACT FROM AUTHOR]

A mineral coating develops on the filter grain surface when groundwater is treated via rapid sand filtration in drinking water production. The coating changes the physical and chemical properties of the filter material, but little is known about its effect on the activity, colonization, diversity, and abundance of microbiota. This study reveals that a mineral coating can positively affect the colonization and activity of microbial communities in rapid sand filters. To understand this effect, we investigated the abundance, spatial distribution, colonization, and diversity of all and of nitrifying prokaryotes in filter material with various degrees of mineral coating. We also examined the physical and chemical characteristics of the mineral coating. The amount of mineral coating correlated positively with the internal porosity, the packed bulk density, and the biologically available surface area of the filter material. The volumetric NH4+ removal rate also increased with the degree of mineral coating. Consistently, bacterial 16S rRNA and amoA abundances positively correlated with increased mineral coating levels. Microbial colonization could be visualized mainly within the outer periphery (60.6 ± 35.6 μm) of the mineral coating, which had a thickness of up to 600 ± 5 1 μm. Environmental scanning electron microscopic (E-SEM) observations suggested an extracellular polymeric substance-rich matrix and submicron-sized bacterial cells. Nitrifier diversity profiles were similar irrespective of the degree of mineral coating, as indicated by pyrosequencing analysis. Overall, our results demonstrate that mineral coating positively affects microbial colonization and activity in rapid sand filters, most likely due to increased volumetric cell abundances facilitated by the large surface area of internal mineral porosity accessible for microbial colonization. [ABSTRACT FROM AUTHOR]

Abstract: The removal of dissolved organic carbon (DOC) during potable water treatment is important for maintaining aesthetic water quality standards, minimising concentrations of micro-pollutants, controlling bacterial regrowth within distribution systems and, crucially, because it contains a sub-component that can act as trihalomethane (THM) precursors. In this study, the concentration and characteristics of raw water DOC and THM formation potential (THMFP) entering an upland potable water treatment works were analysed over twelve months. Correlations between raw water DOC characteristics, standardised THMFP (STHMFP) and % DOC removal were also investigated. DOC and THM precursor removal during a series of treatment stages was examined over this period, as well as potential selectivity in the removal of DOC fractions, to assess the importance of different treatment stages for DOC removal and THM amelioration. Though THMFP removal remained high and fairly stable throughout the study period (83–89%), the data suggest that this was mostly the result of high DOC removal rates rather than the selective removal of THM precursors. Whilst this chemical agnosticism makes DOC removal more robust, it may make the overall process more vulnerable to exceeding permissible THM concentrations under changing climatic conditions. The kinetics of the reaction between DOC and chlorine appeared to vary seasonally, indicating temporal changes in the proportions of fast- and slow-reacting precursors with implications for THM concentrations at the point of delivery to the consumer. The initial treatment stages, comprising coagulation–flocculation and dissolved air floatation (DAF) were by far the most important in terms of bulk DOC removal and the preferential removal of THM precursors, though, surprisingly, DOC quality was also modified following chlorination and secondary rapid gravity filtration (RGF). Though net THM concentration decreased following initial treatment stages, a doubling in the proportion of brominated THMs (BrTHMs), which are reported to be more carcinogenic, was also observed. [Copyright &y& Elsevier]

Abstract: Rapid sand filtration (RSF), proceeded by chemical coagulation and flocculation, is a commonly used, effective pretreatment in the desalination industry. We designed and tested a novel, large pilot-scale, two-stage granular Rapid Bioflocculation Filter (RBF) based on a first-stage Bioflocculator (BF) unit followed by a mixed-media bed filter (MBF). The BF filter bed consisted of an extremely porous volcanic Tuff granular medium which provided an enlarged surface area for microbial development and biofilm proliferation. We compared the efficiency of the pilot RBF to that of a full-scale RSF, operating with upstream chemical coagulation, by measuring the removal from the same untreated seawater feed of key factors related to membrane clogging: SDI, turbidity, chlorophyll a (Chl a) and transparent exopolymer particles (TEP). After 2 weeks of operation, the Tuff grains were colonized extensively by coccoid bacteria that formed biofilm along the entire BF. With bacterial colonization and biofilm development, numerous aggregates of bacteria and some algal cells embedded in an amorphous organic matrix were formed on and within the Tuff grains. By 1–3 months, the biotic diversity within the Tuff filter bed had increased to include filamentous bacteria, cyanobacteria, fungi, protista and even crustaceans and marine worms. During and for ∼24 h after each cleaning cycle (carried out every5 to 7 days by upward flushing with air and water), large numbers of floc-like particles, from ∼15 μm to ∼ 2 mm in size were observed in the filtrate of the BF unit. Microscopic examination of these flocs (stained with Alcian Blue and SYTOR 9) showed that they were aggregates of many smaller particles with associated bacteria and algae within a polysaccharide gel-like matrix. These biogenic flocs (bioflocs) were observed to form during normal operation of the RBF, accumulating as aggregates of inorganic and organic material on the Tuff surfaces. With each flush cleaning cycle, these bioflocs were released into the BF effluent but were retained by the second phase MBF unit. No flocs were seen in the MBF filtrate. Over a year-long study, both the pilot RBF and the full-scale RSF showed similar filtration efficiencies, measured as the percentage removal of Chl a, TEP, turbidity and SDI from the same seawater feed. These results indicate the potential of the bioflocculation approach with no chemical additives as an alternative to conventional RSF pretreatment for large SWRO facilities. [Copyright &y& Elsevier]

Experiments were conducted to determine ammonium removal kinetics in an operating biologically active sand filter at a waterworks treating anaerobic groundwater. The ammonium load varied between (concentration ranged from ), and the inlet water flux varied between . Ammonium profiles and salt breakthrough curves were obtained in four different locations of the filter six times during two filter runs. The experiments show that the nitrification in the rapid sand filter was heterogeneous. The ammonium profiles exhibited variation in time and in space, vertically and laterally within the filter. The nitrification rate constants were calculated by using the ammonium profiles and the local pore velocity data obtained from the breakthrough curves. The local pore velocities were estimated to vary from . The nitrification rate constants varied randomly in time, and it was not possible to determine a clear order of the nitrification reaction. The average zero-order nitrification rate constant was , and the average first-order nitrification rate constant was with an average ammonium load. The first-order nitrification rate constant was closely related to the water pore velocity, which implies that the rate is strongly determined by the resistance to mass transport in the diffusion boundary layer around the sand grains. [ABSTRACT FROM AUTHOR]

Sand has been the main filter media used in rapid gravity filtration since its introduction. The dominance of sand has been due to its low cost and availability. Extensive experience has led to sand filters with a dependable and predictable performance. Sand remains the preferred filter medium but usually with a larger sized anthracite capping to reduce the onset of head loss. Other approved filter media are now commercially available and this paper compares sand with recycled glass, Filtralite® and slate at pilot scale. The results have reaffirmed the basic importance of p.article size on head loss and turbidity performance rather than surface activity or specific surface area. The results did suggest, however, that particle shape and packing exerted a stronger influence on performance than previously acknowledged. These could be used to improve the design and the contribution to sustainability made by rapid gravity filters. [ABSTRACT FROM AUTHOR]

Rapid sand filters are a familiar and mature technology, but the mechanical sophistication they incorporate in industrialized nations limits their sustainable application in developing countries. Conventional rapid sand filters require pumps, elevated tanks, or multiple filter units to generate high flow rates for backwashing. Stacked rapid sand filtration is introduced here as a more robust and sustainable alternative. A stacked rapid sand filter can backwash itself with no additional flow, which eliminates the need for pumps or other expensive equipment. This study presents laboratory and field proof-of-concept demonstrations of this novel technology. The multilayer configuration of stacked rapid sand filters allowed a laboratory unit to be loaded at () per layer and backwashed at () with the same or similar total flow rate. The filtered effluent met U.S. Environmental Protection Agency drinking water standards. The backwash cycle was also demonstrated, and flushing of contaminants from the sand bed was effective even with 5-10 NTU backwash water. A test stacked filter unit also demonstrated satisfactory filtration performance and effective backwashing at several water treatment plants in Honduras. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the influence of the global velocity gradient G (in the range of 28–307s−1) on properties of suspension (size and structure) formed during water treatment. Furthermore, it describes the influence of these properties on separation using depth filtration (filtration velocities of 3 and 6mh−1). The methods of image and fractal analysis were used to determine the aggregate size and structure, respectively. The experiments were conducted in a pilot plant (a mixing tank and a rapid gravity sand filter) with ferric sulphate used as coagulant. The experiments confirmed that with an increasing velocity gradient the aggregate size decreased; the aggregate size distribution narrowed (suspension was more homogenous); the fractal dimension D 2 increased (aggregates were more compact) and the fractal dimension Dpf diminished (aggregates were more regular). The smallest and most compact aggregates (d ∼60μm and D 2 =1.9) formed at G >200s−1 displayed the best filterability with the time of filtration up to 78h. On the contrary, the filtration of large and porous aggregates formed at G ∼30s−1 lasted only about 30h. [Copyright &y& Elsevier]

Homogeneous, heterogeneous and biological oxidation may precipitate iron (II) as iron (III) hydroxides. In this paper we evaluate the conditions under which each of these processes is dominant in rapid sand filtration (RSF). It is demonstrated that in the presence of iron (III) hydroxide precipitates homogeneous oxidation is negligible compared with heterogeneous oxidation. As soon as iron oxidizing bacteria (I0B) are present, biological oxidation may contribute substantially, in particular under conditions of slight acidity and low oxygen concentration. As the oxidation step is preceded by an adsorption/uptake step, the competition between heterogeneous and biological oxidation is not determined by the oxidation rate, but by the adsorption or uptake rate. Extracellular polymeric substance (EPS), excreted by all kinds of bacteria, may serve as an initial adsorbent for dissolved iron (II) and iron (III) hydroxides. Because adsorption and oxidation of iron (II) either on biofilms (or EPS) or on mineral surfaces, are chemical processes, 'EPS iron oxidation' is not considered as a biological process. The so-called 'biological iron oxidation' actually refers to a treatment method characterized by high filtration rates and limited oxygen supply, where iron (II) is removed mainly by heterogeneous oxidation. The contribution of oxidation of iron (II) by 10B in this method is variable and may even be absent. [ABSTRACT FROM AUTHOR]

To ascertain the quality of drinking water being supplied and maintained, it is necessary to conduct water quality surveillance for evolving suitable strategy for future planning. In the present investigation, water quality was monitored in treatment plants, service reservoirs, and at consumer ends in three seasons to assess the baseline water quality status at Shillong in Meghalaya. There are three water treatment plants at Shillong namely Umkhen, Mawlai and GSWS with design capacities of 1.5, 3.4 and 34 Million liter per day (MLD) respectively. Each treatment plant is having rapid sand filtration followed by disinfection. The study reveals that the physico-chemical parameters of water quality at consumer end meets Indian drinking water quality standards (BIS ) after conventional treatment followed by disinfection, whereas the bacteriological parameters for raw water sources exceed the permissible limit indicating the treatment need for drinking purposes. Throughout year the average feacal coliform contamination at service reservoir and to consumer end were found as 44 to 156 CFU/100 ml which may be attributed to the general management practices for maintenance of service reservoirs and the possibility of en route contamination. [ABSTRACT FROM AUTHOR]

Laboratory and full-scale experiments were conducted to investigate the development and effect of heterogeneity caused by filter media nonuniformity, biofilm, particles, precipitates, and gas bubbles in rapid sand filters used for drinking-water treatment. Salt tracer experiments were conducted in laboratory columns and in a waterworks, where a new tracer method for rapid sand filters was developed. Pore-water velocities and dispersivities were estimated by fitting an analytical solution to the measured breakthrough curves. Results of the column experiments showed an increase in average longitudinal dispersivity of more than 33% in the 116 h after the start of filtration with a constant pore-water velocity and a zero-order nitrification rate of 9 mg N/L/h. The full-scale experiments showed that the rapid sand filter was heterogeneous with pore-water velocities ranging from 2.2 to 3.3 m/h for the same inlet flow. A first-order nitrification reaction with spatially variable pore-water velocity could be interpreted as a zero-order reaction with a constant pore-water velocity. A model demonstrated that filter heterogeneity could result in higher filter outlet ammonium concentrations. [ABSTRACT FROM AUTHOR]

Abstract: A new concept for household and large-scale safe drinking water production is presented. Raw water is successively filtered through a series of sand and iron filters. Sand filters mostly remove suspended particles (media filtration) and iron filters remove anions, cations, micro-pollutants, natural organic matter, and micro-organisms including pathogens (reactive filtration). Accordingly, treatment steps conventionally achieved with flocculation, sedimentation, rapid sand filtration, activated carbon filtration, and disinfection are achieved in the new concept in only two steps. To prevent bed clogging, Fe0 is mixed with inert materials, yielding Fe0/sand filters. Efficient water treatment in Fe0/sand filters has been extensively investigated during the past two decades. Two different contexts are particularly important in this regard: (i) underground permeable reactive barriers and (ii) household water filters. In these studies, the process of aqueous iron corrosion in a packed bed was proven very efficient for unspecific aqueous contaminant removal. Been based on a chemical process (iron corrosion), efficient water treatment in Fe0 beds is necessarily coupled with a slow flow rate. Therefore, for large communities several filters should work in parallel to produce enough water for storage and distribution. It appears that water filtration through Fe0/sand filters is an efficient, affordable, a flexible technology for the whole world. [ABSTRACT FROM AUTHOR]

The article presents a research study to evaluate crushed recycled glass as a medium for rapid filtration by studying the physical and hydraulic characteristics of the glass medium and carrying out pilot scale inline filtration experiments using raw waters from three different sources. The decision regarding the sources of raw waters is explained with the Ikitelli and Omerli waters and the Haci Osman. Results are discussed involving experiments without coagulant, and with alum and iron.

Abstract: A finite element model was set-up to determine degradation rate constants for p-TSA during rapid sand filtration (RSF). Data used for the model originated from a column experiment carried out in the filter hall of a drinking water treatment plant in Berlin (Germany). Aerated abstracted groundwater was passed through a 1.6m long column-shaped experimental sand filter applying infiltration rates from 2 to 6mh−1. Model results were fitted to measured profiles and breakthrough curves of p-TSA for different infiltration rates using both first-order reaction kinetics and Michaelis–Menten kinetics. Both approaches showed that degradation rates varied both in space and time. Higher degradation rates were observed in the upper part of the column, probably related to higher microbial activity in this zone. Measured and simulated breakthrough curves revealed an adaption phase with lower degradation rates after infiltration rates were changed, followed by an adapted phase with more elevated degradation rates. Irrespective of the mathematical approach and the infiltration rate, degradation rates were very high, probably owing to the fact that filter sands have been in operation for decades, receiving high p-TSA concentrations with the raw water. [Copyright &y& Elsevier]

Abstract: The abundance of Transparent Exopolymer Particles (TEP) in surface waters has been unnoticed for many years until recently as a potential foulant in reverse osmosis systems. Recent studies indicate that TEP may cause organic and biological fouling and may enhance particulate/colloidal fouling in reverse osmosis membranes. The presence of TEP was measured in the raw water, the pre-treatment processes and reverse osmosis (RO) systems of 6 integrated membrane installations. A spectrophotometric method was used to measure TEP in the particulate size range (>0.40μm) and was extended to measure TEP in the colloidal size range (0.05–0.40μm). Ultrafiltration pre-treatment applied in 4 plants, totally removed particulate TEP while microfiltration systems (2 plants) and coagulation/sedimentation/rapid sand filtration systems (3 plants) partially removed this fraction. None of the pre-treatment systems investigated totally removed colloidal TEP. Biopolymer analysis using LC–OCD showed consistency between colloidal TEP and polysaccharide removal by UF pre-treatment and further verified the presence of TEP in the RO feedwater. TEP deposition in the RO system was determined after measuring total TEP concentrations in the RO feed and concentrate. The TEP deposition factors and specific deposition rates indicate that TEP accumulation had occurred in all plants investigated. This observation was verified by an autopsy of RO modules from two RO plants. Further improvement and verification of the (modified) TEP method, in particular the calibration, is necessary so that it can be employed to investigate the role of TEP in the fouling of RO systems. [Copyright &y& Elsevier]

Combined rapid gravity filtration and backwash models have been applied to simulate filtration and backwash cycles. The simulated results from the backwash model suggest that an optimum air flow rate exists to maximise particle removal efficiency in the backwash operation for a certain backwash system. The simulation of combined rapid gravity filtration and backwash models suggests that the filter shouldn't be completely cleaned up in the backwash and a certain amount of particles retained on filter grains after backwash can be beneficial for subsequent filtration runs. This is consistent with the experimental results in the literature. [ABSTRACT FROM AUTHOR]

Oxidation of iron particles occurring as a result of oxidation of ferrous iron Fe(II) result in undesirable effects in water quality. These iron particles can be removed from water through physical treatment processes of filtration, adsorption, and membrane systems. Iron removal with a rapid sand filtration method was investigated. Effects of iron concentrations, filter hydraulic loading rates, and porosities were studied for the effluent iron concentration, turbidity, and head loss parameters. Plexiglas filter column system with an inner diameter of 30 mm and an equivalent diameter of silica sand with 0.59 mm was used. Four iron concentrations and four hydraulic loading rates were applied. Effects of filter hydraulic loading rates depend on the influent iron concentrations. Low iron concentrations could be removed by rapid sand filtration without high head loss occurrences. Moreover, effluent iron concentrations obtained for this situation were found to be lower than 0.2 mg/L, which is the legislative limit of Turkish Drinking Water Regulation (TDWR). Filter operation time increased with increasing the porosity. Filter operation time was about 2.4 times higher at the porosity of 0.40 than that at the porosity value of 0.36. Low effluent iron concentrations were obtained at the porosity value of 0.36. [ABSTRACT FROM AUTHOR]

Slow and rapid sand filtration methods were tested for their ability to remove triactinomyxon actinospores (Tams), the waterborne infective stage of the salmonid parasite Myxobolus cerebralis, from contaminated water. Within the rapid sand filtration treatments, two backflush protocols were tested. The first consisted of extended backflush duration, and the second consisted of diverted flow past the aquaria with fish for 5 min after backflushing. A slow sand filter treatment served as a nonbackflushed control to the two rapid sand filters and also as its own unique filtration technique. Negative and positive controls were run simultaneously and served both slow and rapid sand filters. The sand used consisted only of particles greater than 180 µm (diameter). Triactinomyxon actinospores were regularly introduced to the fish-rearing systems above the sand filters. After 60 d, clinical signs of whirling behavior and black tails were seen among the positive controls. A polymerase chain reaction (PCR) assay for M. cerebralis conducted at the study's conclusion indicated no infection among the negative controls and both of the rapid sand filter treatments. In the slow sand filter treatment 1.6% of all fish were infected, whereas 98% of the positive controls were infected. Portions of the same tissue samples used for the PCR analysis were also assayed according to the pepsin-trypsin digest (PTD) test. Within the rapid sand filters, 2.9% of fish within the long back flush treatment were infected, as were 100% of the positive controls. The diverted backflush, slow sand filter, and negative controls were all negative according to the PTD test. These results demonstrate that the backflush technique is important in the proper function of rapid sand filters used to remove Tares and that both rapid and slow sand filtration could be viable options in treating hatchery water supplies that are contaminated with whirling disease. [ABSTRACT FROM AUTHOR]

The elimination of wastewater microbes is often necessary when effluent receiving waters are reused for different purposes e.g. for irrigation or as a raw water source of drinking water. In the present study, rapid sand filtration (SF) combined with the use of polyaluminium chloride coagulation was used as a pre-treatment to improve the quality of wastewater effluent before further treatment with UV irradiation. Pilot-scale experiments were run in four treatment plants in Finland. Treatment performance was followed by measuring physical and microbial parameters. Rapid sand filtration reduced suspended solids, turbidity and colour of effluents by about 90%, 70-80% and 20-50% respectively. It also improved the UV transmittance of water by up to 20%. Microbes and phosphorus were reduced by 90-99% and to 0.05 mg/L respectively. UV irradiation further reduced the number of microbes up to 99.9%. The efficiency of UV doses in pilot UV reactors was confirmed with collimated-beam device determinations and with added FRNA phages. More than 99.9% reduction of MS2 was achieved with the dose of 140mWs/cm2 in pilot UV reactors. Rapid sand filtration and the subsequent UV irradiation reduced the number of all the tested microbes to a low level, often below the detection limit. Suspended solids and the water turbidity were reduced to 1-2 mg/L and ~1 NTU respectively. [ABSTRACT FROM AUTHOR]