Head Loss Buildup Research Articles

Direct filtration of low-turbidity water by fixed-bed ion exchange treatment

In drinking water treatment, low-turbidity water (e.g., < 5 NTU) is often purified by direct filtration comprising coagulation, flocculation, and rapid sand filtration. This study assessed the potential of replacing the rapid sand filter with a fixed-bed ion exchange column. Two types of anion exchange resins, polyacrylic (Purolite A860) and polystyrene (Purolite A502PS), were used in fixed-bed columns without preceding coagulation and flocculation. After the first use of the new resins (14-h operation), the A860 column showed more significant head loss buildup than the A502PS column (151 and 101 cm, respectively). This can be attributed to the effective size of A860 resins (0.38 mm), which was smaller than that of A502PS resins (0.52 mm). A860 resins were superior to A502PS resins in filtrate quality. The A860 resins achieved filtrate turbidity (0.16–0.26 NTU) lower than the A502PS resins (0.19–0.35 NTU). Similarly, dissolved organic carbon removal by A860 resins (25–37 %) was higher than that by A502PS resin (15–25 %) due to the low hydrophobicity of the feed water. Air scouring and water backwashing were ineffective in regenerating A860 resins. In contrast, cleaning with a NaCl solution (pH = 12) partially recovered the capacity of A860 resins for turbidity removal.

Media selection for anammox-based polishing filters: Balancing anammox enrichment and retention with filtration function.

Retrofitting conventional denitrification filters into partial denitrification-anammox (PdNA)- or anammox (AnAOB)-based filters will reduce the needs for external carbon addition. The success of AnAOB-based filters depends on anammox growth and retention within such filters. Studies have overlooked the importance of media selection and its impact on AnAOB capacity, head loss progression dynamics, and shear conditions applied onto the AnAOB biofilm. The objective of this study was to evaluate viable media types (10 types) that can enhance AnAOB rates for efficient nitrogen removal in filters. Given the higher backwash requirement and lower AnAOB capacity of the conventionally used sand, expanded clay (3-5mm) was recommended for AnAOB-based filters in this study. Owing to its surface characteristics, expanded clay had higher AnAOB activity (304- vs. 104-g NH4 + -N/m2 /day) and higher AnAOB retention (43% more) than sand. Increasing the iron content of expanded clay to 37% resulted in an increase in zeta potential, which led to 56% more anammox capacity compared to expanded clay with 7% iron content. This work provides insight into the importance of media types in the growth and retention of AnAOB in filters, and this knowledge could be used as basis in the development of PdNA filters. PRACTITIONER POINTS: Expanded clay showed the lowest head loss buildup and most likely will result in longer runtime for full-scale PdNA applications The highest AnAOB rates were achieved in expanded clay types and sand compared with smaller media typically used in biofiltration Expanded clay resulted in better AnAOB retention under shear, whereas sand could not withstand shear and required more frequent backwashing Expanded clay iron coating enhanced AnAOB enrichment and retention, most likely due to increased surface roughness and/or positive charge.

Mathematical modeling of biologically active filtration (BAF) for potable water production applications

In this study, a modeling framework was developed to simulate biologically active filtration (BAF) headloss buildup in response to organic removal and nitrification. This model considered not only the biofilm growth on the BAF media but also the particle deposition in the BAF bed. In addition, the model also took temperature effect into consideration. It was calibrated and validated with data collected from a pilot-scale study used for potable water reuse and a full-scale facility used for potable water treatment. The model prediction provided insights that biofilm growth rather than particle deposition primarily contributes to the headloss buildup. Therefore, biofilm control is essential for managing headloss buildup and reducing the backwash frequency. Model simulation indicated that the BAF performance in terms of pollutant removal per unit headloss is insensitive to the BAF bed depth but can be effectively improved by increasing the media size. The partial biofilm coverage of the media is confirmed in this study and was mathematically verified to be a prerequisite for the model fitness.

NOM-removal by the SIX®-process

Abstract Some waters can have elevated concentrations of dissolved organic carbon (DOC), especially sources like surface waters that are under the influence of secondary effluent, recreation, heavy population, farming and industry. In a number of locations in north-west Europe, for example the United Kingdom and Scandinavia, DOC levels are increasing over time, most likely due to climate change effects and changes in land use. For these types of water, ion exchange (IX) is of interest as a pre-treatment option because the removal of colour and DOC by IX will increase the efficiency of all downstream processes, including: coagulation, membrane filtration, advanced oxidation processes (AOP) and granular activated carbon filtration (GAC). It will also lead to improved water quality (i.e., less by-product formation) and most likely improvements in biostability within the distribution network. Surface waters also contain suspended and colloidal matter, making it nearly impossible to use standard state-of-the-art, fixed bed IX columns. This is because these beds will foul quickly (i.e., head loss build-up) with suspended matter. When this happens, the IX bed starts to function as a filtration bed rather than as an adsorption media. The newly developed suspended ion exchange process SIX® (suspended ion exchange, PWN Technologies, Netherlands) presents an advanced solution for a world-wide challenge: how to remove natural organic matter (NOM/DOC) as a first step in surface water treatment to improve the efficiency of downstream processes and water quality. In addition to the possibility to treat water that contains suspended matter, another advantage is that the process has advanced to an economically and technically feasible process, requiring low contact times and small resin inventories, with a large tolerance for flow fluctuations. Depending on the water source, adding a relatively low concentration of coagulant after IX removes even greater quantities of DOC, especially in the fraction of the high molecular weight organic carbon (whilst the IX primarily removed the humic and fulvic organic fractions). The most important advancement is that almost any commercially available resin can be used, creating the desired flexibility in resin suppliers for water supply companies. This paper describes the process and its advantages and disadvantages compared to conventional technologies. NOM-characterisation with size exclusion chromatography, liquid chromatography – organic carbon detection (SEC/LC-OCD) before and after this process showed the outstanding performance of the process, especially on water types which contain high colour/DOC-concentrations and low total dissolved solids, which are typical of the majority of the surface waters in the north-west of Europe.

Initial and hourly headloss modelling on a tertiary nitrifying wastewater biofiltration plant

ABSTRACTThe headloss prediction capability of a wastewater biofiltration model is evaluated on data from a full-scale tertiary nitrifying biofilter unit located in the Paris conurbation (Achères, France; 6,000,000 population equivalent). The model has been previously calibrated on nutrient conversion and TSS filtration observations. In this paper the mass of extracted biofilm during biofilter backwash and the headloss value at the start of an operation cycle are first calibrated on sludge production estimations and relative pressure measurements over the year 2009. The calibrated model is then used on two one-month periods in 2012 for which hourly headloss measurements were acquired. The observed trends are correctly predicted for 2009 but the model exhibits some heavy daily variation that is not found in measurements. Hourly predictions stay close to observations, although the model error rises slightly when the headloss does not vary much. The global model shows that both nutrient conversion and headloss build-up can be reasonably well predicted at the same time on a full-scale plant.

Small City Tackles Radium in Well Water

This article discusses a pilot study by the city of Goodview, Minnesota, for the removal of radium with hydrous manganese oxide (HMO) and coprecipitation with iron from its well water. Dual media, sand, and manganese greensand media were tested in the pilot plant, and results showed that the manganese greensand media had the lowest filter headloss buildup and would produce the longest filter runs. The media also produced the best quality water with the highest removal rate of radium and iron.

In-line flocculation–filtration as pre-treatment to reverse osmosis desalination

In this paper the performance of single and dual media filters with in-line flocculation have been examined as pretreatment to seawater reverse osmosis (SWRO). A comparison of filter performance was made between single medium filter (80 cm) consisting of sand or anthracite, and dual media filter consisting of sand (40 cm at the bottom) and anthracite (40 cm on top). Short term (6 hours) experiments were conducted with in-line coagulation followed by direct filtration. Filtration velocities of 5 m/h and 10 m/h were used. The performances of these filters were assessed in terms of turbidity removal, head loss build-up, and organic compound removal in terms of molecular weight distribution (MWD). The efficiency of the filter as pretreatment was evaluated in terms of silt density index (SDI) and modified fouling index (MFI). It was found that the turbidity removal was high and all the filters produced more or less same quality water. There was a slower buildup of head loss for coarser filter medium. A post treatment of reverse osmosis after an inline-flocculation-dual media filtration showed lower normalized flux decline ( J/ J 0) (0.35 to 0.22 during the first 20 hours operation) while, seawater without any pretreatment showed steeper flux decline (0.18 to 0.11 at first 20 hours operation) in RO.

Comparison of single and dual media filtration in a full-scale drinking water treatment plant

In this paper, the operation of mono and dual media filter beds was examined in a large-scale drinking watertreatment plant, located in Thessaloniki (N. Greece). The efficiency of filtration process was improved, regardingthe removal of undesirable constituents, which mainly include organic matter and suspended solids (turbidity). Acomparison was attempted between a sand filter bed (of 1 m depth) and a dual media filter bed, consisting of sand(60 cm-bottom) and anthracite (40 cm-top) layers. Two alternative treatment schemes were examined: theconventional coagulation–flocculation/sedimentation, followed by gravity filtration and the direct filtration (i.e.coagulation–flocculation and filtration, but without sedimentation). All these experiments were conducted at fullscalefilter beds, presenting an effective surface area of 40 m 2 and with a volume loading rate over 375 m 3 h –1 (i.e.large-scale experiments); therefore, the respective velocity was around 10 m h –1. The performance of filter bedswas assessed in terms of removal capacity, regarding mainly the turbidity, as well as the head-loss build-up. Itwas found that the dual media filter bed produced water of the same (high) quality as the single bed, but with theadvantage of operating at greater filtration cycles (around 3 times higher), which resulted to a 10% higher waterproduction.

Air Binding of Granular Media Filters

Air bubbles that form in water treatment filters create headloss and can form whenever the total dissolved gas pressure exceeds the local solution pressure. The location of potential bubble formation in filters can be predicted based on measurements of the clean bed headloss with depth, flow rate, and the influent total dissolved gas concentration. Bubble formation within filters can be reduced by increasing the pressure within the filter via greater submergence (water head above the media), lower hydraulic flow rate, or using a more porous media. Bubbles trapped in the bed can be released by “burping,” which can reduce the extent of headloss buildup. Burping is more significant at lower flow rates and within a lower density, higher porosity, hydrophobic anthracite layer.

Pilot-Plant Study of the Tertiary Filtration of Wastewater Using Local Sand

Local sand with E.S. of 2.4 mm, U.C. of 1.21, and size range of 2.0 to 3.36 mm was studied using a field-scale pilot-filter, which has a cross-section of 30 cm x 30 cm. Three filter runs were performed using filtration rates of 4, 8 and 18 m3/m2/hr. The three runs were continued up to 40,100 and 53 hours, respectively. In Run # 1, the headloss build-up was minimum (about 25 cm), while in Runs 2 and 3, the maximum available headloss (about 2.25 m) was reached. The effluent turbidity, TSS, COD and BOD were all found to be within the acceptable limits. Neither turbidity nor solids breakthrough were reached using a filtration rate as high as 18 m3/m2/hr. Being more economical and suitable for the use in the tertiary filtration of wastewater treatment, local sand is recommended for utilization in the Wastewater Treatment Plants.

Removal of natural organic matter (NOM) using different coagulants and lightweight expanded clay aggregate filters

Chitosan and lightweight expanded clay aggregates were investigated as alternatives to traditional metal coagulants and anthracite in pilot scale coagulation-filtration experiments for the removal of natural organic matter (NOM) from drinking water. The raw water tested covered a range of colour and organic carbon of 15–50 mg Pt/L and 2–5 mg NPOC, respectively. Aluminium sulphate, poly aluminium chlorides with different calcium content, iron chloride sulphate, and chitosan coagulants were tested. The dual media filter bed was built with 0.6 m of 0.8–1.6 mm lightweight expanded clay aggregates (Filtralite) above 0.35 m of 0.4–0.8 mm sand. A conventional anthracite-sand filter with the same layer depths and grain sizes was used as a reference. In general, the maximum permissible concentration level of 0.1-mg Me/L controlled the minimum coagulant dose requirements when metal-based coagulants were used (Norwegian water quality standard). Typical NOM removal efficiencies obtained with metal coagulantswere in the range of 75–90% and 40–70% with respect to colour and organic carbon, respectively. Chitosan was able to remove colour quite effectively, but this coagulant was less effective with respect to organic carbon removal. Lightweight expanded clay aggregate was a good alternative to anthracite, with lower rates of head loss build-up, and increased filter run length and filter storage capacity. Only small differences in effluent water quality were detected with the two filters.

Iron oxide–coated media for NOM sorption and particulate filtration

Newly developed iron oxide–coated media offers several advantages over conventional sand media for NOM removal and particulate filtration.This study applied newly developed iron oxide–coated media (IOCM) to the removal of natural organic matter (NOM) and particulate filtration in drinking water treatment. The sorption capacity of IOCM for NOM directly depends on the amount of iron retained on the media surfaces and generally increases with the decrease of solution pH, the increase of empty bed contact time, and the concentration of Ca2+. Using olivine as the supporting medium significantly improved the performance of IOCM at neutral pH. Although the sorption capacity of IOCM is limited by the amount of oxides that can be coated on the media surfaces (about 5 percent by weight), results from the pilot studies indicated that frequent regeneration of the media (twice a week) can effectively maintain system performance at the desired level. The NOM‐laden IOCM was nearly completely regenerated using 3 bed volumes of 0.5 N sodium hydroxide solution, and NOM concentration in the regenerant was as high as 4,300 mg/L DOC. The sorption capacity of IOCM deteriorated mildly in a long‐term test, possibly because of loss of iron during the backwash cycles. Results from both bench tests and pilot studies also showed that IOCM outperformed regular sand in particulate filtration in terms of head loss buildup and turbidity breakthrough.

Effects of ozonation on coagulation of NOM using polymer alone and polymer/metal salt mixtures

The possible benefits of reduced coagulant demand and head loss resulting from preozonation must be weighed against increased organic matter in the finished water.Prior investigations have identified many of the mechanisms by which natural organic matter (NOM), coagulant, and particles interact in ozonated systems. This study investigated the effects of ozonation on coagulation with cationic polymer and with polymer‐metal salt mixtures. Preozonation decreased the concentration of NOM that reacts with polymer, reducing organic carbon removal, polymer coagulant demand, and the rate of head loss buildup during direct filtration. The effects of ozonation in systems using dual coagulants (alum‐polymer or ferric chloride‐polymer) were a blend of the effects observed for the coagulants individually.

Investigating Filter Performance as a Function of the Ratio of Filter Size to Media Size

The size of the filters used in a water treatment pilot study has a big impact on the cost of the pilot facility itself. It has been shown that errors can be avoided by maintaining an adequate ratio between filter column diameter and media diameter (D/d). The purpose of this study was to investigate the effect of this same scaleup parameter on the filtration process itself. Five pilot‐filter columns were operated in parallel with a full‐scale filter. In these tests, (D/d) ranged from 26:1 for the smallest column to 6,000:1 for the full‐scale filter. No significant differences were observed in the mean rate of head loss buildup, the effluent turbidity, or the effluent particle count for any of the filters, although the variance in the estimate of rate of head buildup was much greater for the smallest filter. A D/d ratio of 50 or greater is recommended for most pilot‐filter operations.

ELECTROKINETIC PHENOMENA IN THE FILTRATION OF ALGAL SUSPENSIONS

Modification of sand and suspended particle surface properties, the authors assert, is an effective means of increasing filter removal efficiencies beyond those possible with normal doses of coagulants and with minimal head loss buildup.