Dual Media Filtration Research Articles

정수처리장내 급속모래 여과지의 이단복합여과시스템으로의 개량

This study aimed for developing a two stage dual media filtration system. It has a sand and activated carbon layer above the under-drain system, and a sand layer above the middle-drain system for pretreatment. When retrofitting an old sand filter bed or designing a new one, this technology can substitute the existing sand filter bed without requiring a new plant site. The removal rate of total particle is 93, and 3~7 <TEX>${\mu}m$</TEX> and 5~15 <TEX>${\mu}m$</TEX> particles are all 97%. These high removal efficiencies of each pollutant due to adsorption and biological oxidation in activated carbon filter layer. The best backwashing method of two stage dual media filtration system is ascertained by air injection, air + water injection and water injection sequence. In this study, a pilot plant of two stage and dual filtration system was operated for 4 months in water treatment plant. The stability of turbidity was maintained below 1 NTU. The TOC, THMFP and HAAFP were removed about 90% by two stage and dual media filtration system, which is almost 2 times higher than existing water treatment plant.

Optimizing NF/RO Pretreatment at an Integrated Membrane Facility to Treat Challenging Florida Surface Water

Lee County, Fla., owns and operates the 5-mgd Olga Water Treatment Plant. The plant treats Caloosahatchee River water for taste and odor, color, organics, hardness, and turbidity with conventional alum coagulation, flocculation, sedimentation, and granular dual-media filtration followed by granular activated carbon adsorbers. Powdered activated carbon is seasonally added upstream of coagulation to a dedicated contact basin to reduce taste and odor. For many years, seasonal salinity, taste and odor problems, and algal blooms in the river have negatively affected plant operations and caused regulatory concerns. As a result, the plant had to operate at reduced capacity and periodically received consumer complaints. A two-phase bench-scale testing program helped to identify and analyze water supply and treatment alternatives by assessing the benefits of pretreatment to reduce microfiltration (MF) membrane fouling and evaluating a combined pretreatment, MF, and low-pressure reverse osmosis treatment scheme.

Effects of various characteristics of seawater on the performance of dual media filters

In this study, effects of various water quality parameters (TDS, turbidity, DOC) on seawater filtration were evaluated using the laboratory scale dual media fi lter (DMF). For this purpose, DMF was operated with and without in-line coagulation to filter four different types of artificial seawater. The standard seawater (type 1) was used as a control condition. The type 2 feed was used to examine the effect of TDS, type 3 for the effect of turbidity and type 4 for the effect of organic matter. According to this study, high TDS was beneficial in turbidity removal when DMF filtration was performed without coagulation. High ionic strength reduced the electrical repulsion, helping particle capture by the filter media. In-line coagulation diminished the beneficial effect of TDS. Backwash with wash water alone was found insufficient to clean the media effectively when DMF was filtering highly turbid seawater. Coagulation helped backwash of DMF and restored the turbidity removal performance after backwash when fi...

Process evaluation of intermediate chemical demineralization for water recovery enhancement in production-scale brackish water desalting

This study evaluated intermediate chemical demineralization (ICD) as a technique for overcoming mineral salt solubility limits that constrain the water recovery of reverse osmosis (RO) desalting. An empirical approach was developed to determine theoretical cation removal set points for ICD based on predetermined process design and operation guidelines to facilitate increasing the overall water recovery of Colorado River water desalting from 85% (i.e., in the primary RO unit) to 95% via a secondary RO (SRO) unit. Additionally, the study evaluated whether microfiltration (MF) or dual-media filtration (DMF) could serve as the filtration step prior to the secondary reverse osmosis (SRO) unit. The model suggested ranges for ICD influent total-carbonate-to-calcium ratios and ICD effluent pH to simultaneously mitigate barium sulfate, calcium sulfate, and silica scaling. MF was preferred over DMF as the filtration step prior to SRO based on significantly lower filter effluent turbidity and silt density indices. The overall PRO-ICD-SRO system operated for over 550 h at 95% total RO water recovery without evidence of scaling of the terminal RO elements, validating the cation removal set points developed through the ICD model and demonstrating the utility of ICD.

Successfully Operating a Seawater UF Pretreatment System

To overcome problems of high silt density index (SDI) and reverse osmosis (RO) feedwater turbidity in its Phase A plant, Kindasa Water Services, Jeddah, Saudi Arabia, introduced ultrafiltration (UF) in the pretreatment system of its Phase B1 expansion. Based on pilot trials of the UF plant, it was decided to include high-rate dual-media filters upstream of UF to make the pretreatment system more reliable. Commissioned in August 2006, the plant's pretreatment system was able to achieve SDI of less than 1.0 and turbidity of less than 0.2 ntu. Raw seawater SDI was not measurable, and turbidity was greater than 10 ntu. Although the UF system's performance was satisfactory, the plant experienced UF fiber damage, lower UF recovery because of high consumption of flushing water, biofouling in RO membranes, and mechanical damage of UF components. Remedial measures were adopted to overcome those problems.

Hybrid filtration method for pre-treatment of stormwater

In this study the hybrid filtration process (combining fibre filter with deep bed dual media filtration) was investigated as pre-treatment to stormwater. This process was investigated in-terms of reduction in turbidity, dissolved organic carbon (DOC), colour, headloss development across the filters, suspended solids removal, organic matter removal, nutrients and heavy matter (such as iron, copper, lead, zinc) removal efficiency. A comparison was made between the hybrid filter with single media (sand) deep bed filter and fibre filter. It was found that the hybrid filtration system successfully removed turbidity (98%), colour (99%), suspended solids (99%), and DOC (55%). The removal efficiency of heavy metal was relatively low as the concentration of heavy metals present in stormwater was low. The removal efficiency of nitrate, nitrite and phosphorous (as orthophosphate) was 27, 35 and 72% respectively. Hybrid filtration processes showed a better reduction of Modified Fouling Index (MFI) value (from 15.500 s/l(2) to 9 s/l(2)) compared with single media sand, anthracite and fibre filter which were 35 s/l(2), 13 s/l(2)and 14 s/l(2) respectively when operated at FeCl(3) dose of 15 mg/l.

Reverse osmosis pretreatment alternatives: Demonstration plant in the seawater desalination plant in Carboneras, Spain

This paper presents the results of a demonstration study for the RO pretreatment that was performed on an AcuaMed open intake desalination plant in Carboneras (Almería, Spain). The main goal was to test different configurations of conventional pretreatments in order to establish the limit of each process as well as their reliability. The pretreatment processes tested were Actiflo® (a process that consists of coagulation, polymer and microsand injection, maturation and settling of microsand ballasted flocs), multimedia filtration at atmospheric pressure, pressurized dual-media filtration and pressurized three-layer filtration. During the tests, the silt density index (SDI) of the filtered water was regularly measured and then evaluated in probability graphs. The raw seawater SDI ranged from 4.5 to 25. The results from this study showed that the Actiflo® system followed by two pressurized multimedia filters (dual-media and three-layer filters) in series, provided effluent SDI values lower than 3 with a reliability of 95% under the optimized operating conditions. These results were obtained when the Actiflo® system included coagulation, flocculation (with flocculant and microsand addition) and maturation stages or just working as a coagulation stage.

Comparison of fouling indices in assessing pre-treatment for seawater reverse osmosis

In this study, different processes such as fl occulation with ferric chloride (FeCl3) and deep bed filtration (sand filtration and dual media filtration) as a pre-treatment were used for seawater desalination. The performance of these pre-treatments was determined in terms of silt density index (SDI) and modified fouling index by using microfilter (MF-MFI), ultrafilter (UF-MFI), and nanofi lter (NF-MFI) membrane. MFI and SDI indicated that deep bed filtration with in-line flocculation was better pre-treatment than flocculation alone as colloidal particles are removed after this pretreatment. UF-MFI and NF-MFI indicated that these pretreatment cannot remove dissolved organic matter as the fouling reduction was smaller. Detailed molecular weight distribution (MWD) of seawater organic matter was examined after different pretreatments. MWD of the initial seawater mainly ranged from 1510 Da to 130 Da. Deep bed filtration with in-line flocculation removed relatively large molecular weight of organic matter (151...

Metal oxide/hydroxide-coated dual-media filter for simultaneous removal of bacteria and heavy metals from natural waters

The present study was conducted to compare the performance of a dual-media filter consisting of manganese oxide-coated (MOCS) and iron hydroxide-coated sand (IOCS) with that of IOCS filter and uncoated sand filter in treating water contaminated by microorganisms, heavy metals and turbidity with a view to its use in simple household water purification devices in developing countries. Long-duration column tests were conducted using two natural waters namely, roof-harvested rainwater and canal water. Performance of the filters showed that dual-media filter was more efficient in removing bacteria and heavy metals compared to IOCS filter, while uncoated sand filter showed very poor performance. The average effluent levels for dual-media filter when tested with rainwater were: turbidity 1.0 ± 0.1 NTU; total coliforms 3 ± 2 MPN/100 mL; heterotrophic plate count 170 ± 20 CFU/mL; zinc 0.06 ± 0.01 mg/L, while that for IOCS filter were: turbidity 1.0 ± 0.1 NTU; total coliforms 4 ± 2 MPN/100 mL; heterotrophic plate count 181 ± 37 CFU/mL; zinc 0.20 ± 0.07 mg/L. Similar results were obtained for canal water also. Up to 900 bed volumes (BV) could be treated without affecting the efficiency in the case of rainwater, while the filter operation had to be terminated after 500 BV due to excessive headloss in the case of canal water. The study thus showed the potential of the dual-media for use in low-cost household water filters for purification of natural waters.

Deep bed filter as pre-treatment to stormwater

This paper presents the results of experiments on the application of dual media and single media deep bed filters as pre-treatments to stormwater. In-line flocculation-filtration experiments were conducted with dual and single media filter. The single filter media (80 cm) consisted of either anthracite or sand, and the dual media filter consisted of sand (40 cm at the bottom) and anthracite (40 cm on top). Filtration velocities of 5 m/h, 10 m/h and 15 m/h were examined. The removal efficiency for turbidity, suspended solids and TOC was found to be 95%, 99% and 30–45% respectively at a flocculant dose of FeCl3 of 15 mg/L. The anthracite filter media showed a lower headloss development (26 cm, operated at 5 m/h filtration velocity with FeCl3 dose of 5 mg/L). The removal efficiency for nitrogen was lower than phosphorus which was relatively good (up to 50%). The removal efficiency for heavy metals such as Cd, Pb, Cr and Ni was found to be very low for all tested filtration systems because concentrations of these metals in the influent were also low. This filter can be used as a pretreatment to a membrane filter as the modified fouling index was reduced from 750 s/L2 (for stormwater) to 15 s/L2 (for filtered effluent). Detailed submerged membrane filter experiments conducted with pre-treated water showed that the membrane filter can be successfully be used as post-treatment to in-line flocculant-filter at a sustainable flux of 10 L/m2.h to remove the remaining solids and pathogens. An increase of air scouring in the membrane unit decreased the pressure development although it did not have any effect on increasing the critical flux beyond 10 L/m2.h.

Estimating progress of specific deposit in a dual-media BOPS-sand water filter using a matrix approach

A new matrix approach which incorporated Rajagopalan and Tien model was developed to simulate the progress of sediment deposition in sublayers of filtration media for mono-media sand and BOPS filters as well as dual-media BOPS-sand filters, at different time until the end of filtration process. The results of specific deposit in the matrix form can be used later to predict the operational head loss in the sublayers of filter at different time. The experiment on filtration process using a filter column was carried out to treat raw water at typical rapid filtration flow rate of 3 to 7.5 m/h. The influent and effluent water turbidity, total suspended solids and the operational head loss at specific thickness and time were monitored and recorded during filtration process. A dual-media filter of BOPS-sand with ES of 0.8:0.5mm to 1.0:0.5mm are effective in treating raw water and produce high quality effluent turbidity as good as the conventional mono-media sand filter.

Phosphorus and nitrogen profile measurements to locate phosphorus limitation in a fixed bed filter

The European Union presented in 2000 the European Water Framework Directive (WFD). Within the WFD approach the focus is more and more on ultra low nitrogen (<2.2 mg N-total/L) and phosphorus concentrations (<0.15 mg P-total/L) in waste water treatment plant (WWTP) effluent. Nitrogen concentrations of 2.2 mg N-total/L can be reached with denitrifying filters as a tertiary treatment step. When combining nitrogen and chemical phosphorus removal in a filter, phosphorus limitation may occur. After nitrite accumulation, caused by phosphorus limitation, was measured in the filtrate water of the dual media filter, research was started to locate, to understand and to solve the problem. Profile measurements for nitrate, nitrite and orthophosphorus (PO(4)-P) combined with COD and O(2) were conducted. Results show that the minimal required PO(4)-P/NO(x)-N ratio is 0.006 mg/mg after coagulation and flocculation. Profile measurements have proven to be a useful tool. It showed how nitrate and orthophosphorus are removed through the filter bed and it showed the consequences for the PO(4)-P/NO(x)-N ratio. When orthophosphorus is removed more rapidly compared to nitrate the PO(4)-P/NO(x)-N ratio decreases. When the PO(4)-P/NO(x)-N ratio becomes below 0.006 mg/mg for a certain period of time, orthophosphorus limitation occurs. The solution can be either changing the filter bed configuration or decreasing the coagulant dosage.

Introducing sand filter capping for turbidity removal for potable water treatment plants of Mosul/Iraq

Sand filter capping had been tried as an alternative for the currently practiced rapid sand filters. A 1000 m3/day capacity pilot plant constructed similarly to full scale water treatment plants was used for this purpose. Four levels of sand material with respect to grain size and thickness were used. Capping filter was represented by one level of anthracite coal with one thickness. In order to optimize the most efficient combination(s) of the two materials for maximum filter performance in terms of quality and quantity, four filtration rates were tried. A series of forty test runs and experiments exceeding 120 using different filter configurations were tried. Filters were operated in pairs and subjected to the same conditions. Filters consisting of 20 cm anthracite coal (0.91 mm E.S.) over 40 cm of sand (0.69 mm E.S.) appeared to be the best fit configuration among tried filters. Considerable economical consequences could be achieved using sand filter capping. This was reflected in reducing filter numbers or increasing the plant capacity by two folds in the minimum. Economic revenue was gained through reduction of disinfection doses as well as reduction in filter sand material. Runtimes of filters were increased by 2 - 3 folds indicating capability of more furnished water productivity and less amount for backwash need. Above all the water produced was of very good quality that met the most stringent specifications and promoted health. Capping sand filters were proven to suitably operate under varying conditions of influent turbidity and filtration rates. Key words: Drinking water filtration, rapid sand filtration, dual-media filtration, multi-media filters, water treatment, filter media, gravity filtration.

Assessment of pretreatment to microfiltration for desalination in terms of fouling index and molecular weight distribution

In this study, different processes such as flocculation with ferric chloride (FeCl 3) and deep bed filtration (sand filtration and dual media filtration) as a pre-treatment to microfiltration (MF) were used for seawater desalination. The performance of these pre-treatments was determined in terms of silt density index (SDI) and modified fouling index (MFI) and flux decline in MF. Flux decline of MF with seawater was 45% without any pre-treatment, 42% after pre-treatment of FeCl 3 flocculation, 24% after pre-treatment of sand filtration with in-line coagulation and 22% after pre-treatment of dual media filtration (sand and anthracite), respectively. MFI and SDI also indicated that deep bed filtration with in-line flocculation was better pre-treatment than flocculation alone. Detailed molecular weight distribution (MWD) of seawater organic matter was examined after different pretreatments. MWD of the initial seawater mainly ranged from 1510 Da to 130 Da. Deep bed filtration with in-line flocculation removed relatively large molecular weight of organic matter (1510–1180 Da), while the small molecular weights (less than 530 Da) were not removed.

IMS SWRO Kindasa — Two years of operational experience

Kindasa Water Services (KWS) derived its name “Kindasa” from the first seawater desalination plant built in Jeddah in the early 19th century. KWS is a limited liability company January 2000. KWS owns and operates desalination plants for supply of water to various industries, compounds etc. Recently KWS has built and is operating sea water reverse osmosis (SWRO) desalination plant in Jeddah Islamic Port with Hydranautics’s integrated membranes system (IMS®). KWS has selected hybrid pretreatment system consisting of conventional dual media filtration in conjunction with the latest state-of-the-art ultrafiltration (UF) process to produce stable RO feed water quality that remains unaffected by the seasonal changes of the seawater quality. KWS’s SWRO plant is the largest IMS operating already for two years in very difficult water. A pretreatment system was successfully commissioned in June 2006, and reverse osmosis section was commissioned in August-September 2006. There are different views in desalination industry on the use of membrane pretreatment utilizing or upstream of seawater reverse osmosis systems. Up to date unbiased information about real long term operational experience is not available. On the contrary, there are quite a few papers presenting membrane pretreatment as a “magic solution” to reverse osmosis performance problems. Two years of successful operational experience of this large SWRO IMS® working in very difficult raw water conditions has shown that this technology is viable, but it has also shown that this technology still needs proper attention and tuning and can create disappointment on end-user’s side if certain design aspects and operational aspects are not properly addressed at the early stage of operation. Information will be provided which shows that close cooperation between technology supplier and user can solve these operational issues. Kindasa SWRO IMS® is designed for product capacity of 25,500 m³/d at 95% availability. The present plant production is 26,840 m³/d. The seawater is treated by 8 ultrafiltration racks equipped with Hydranautics HydraCap 60 and downstream by seawater reverse osmosis trains equipped with Hydranautics SWC3 seawater reverse osmosis membranes operating at 50% recovery. Product water is further treated in partial second pass trains utilizing Hydranautics low energy ESPA 2 membranes. The paper presents long term experience, operational data as well as normalized data and discusses all aspects of the plant operation and performance in detail. The plant is a key reference for future development of SWRO plants for difficult waters in the Middle East area as well as for global view of SWRO desalination and serves as “model plant” to demonstrate viability of MF/UF as pretreatment upstream of SWRO.

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.

Hybrid filtration method for pre-treatment of seawater reverse osmosis (SWRO)

Hybrid processes combining fibre filter with deep bed filtration process such as (i) fibre filter and sand filter, (ii) fibre filter and anthracite and (iii) fibre filter and dual media filter were investigated as pre- treatments to SWRO. Seawater was drawn from Chowder Bay, Sydney. The effect of different pretreatment hybrid systems was investigated in terms of silt density index (SDI 10), modified fouling index (MFI), headloss across the filters and reduction in turbidity and dissolved organic carbon (DOC). The in-line flocculation in fibre filter improved the performance of the pretreatment hybrid system as measured by the MFI, SDI 10, headloss, turbidity and DOC removal. The lowest SDI 10 and MFIwere found with a fibre filter operated at a filtration velocity of 40 m/h followed by dual media filter operated at a filtration velocity of 5 m/h. The lowest headloss and turbidity was found with a fibre filter operated at a filtration velocity of 40 m/hr followed by anthracite operated at a filtration velocity of 5 m/h. This system also gave an effluent with the lowest DOC of 0.64 mg/L corresponding to a removal efficiency of about 70%.

Influence of iron on nitrification in full-scale drinking water trickling filters

In the production of drinking water from groundwater, iron removal in filters may interfere with nitrification. Microbial nitrification might decline because of irreversible accumulation of iron deposits in pores and on filter material. This paper shows the successful application of two experimental techniques applied at a full-scale water treatment plant in the Netherlands to maintain sustainable nitrification. Filter performances were evaluated by measurements of ammonium in the filter effluent, accumulation of deposits and their removal during backwash, development of the mainly inorganic filter coating and media expansion curves. The application of dual-media drinking water trickling filters, in combination with filter backwash with media expansion, minimizes the irreversible accumulation of iron deposits in the filter. Subsurface aeration results in a lower iron content of the filter coating.

Bioassay evaluation of toxicity reduction in common effluent treatment plant

This paper investigates the utility and validity of bioassay toxicity testing using Daphnia magna straus as test organism for monitoring the common effluent treatment plant (CETP) receiving both industrial as well as domestic effluent. The average daphnia toxicity (Gd) at inlet, after primary settling tank (PST), secondary settling tank (SST) and tertiary treatment unit were reported as Gd-16, Gd-12, Gd-4 and Gd-1 respectively. However, a cumulative percentage removal in toxicity after PST, SST and tertiary treatment units was observed as 25%, 75% and 100%, respectively, during entire study period. It showed that a complete removal in daphnia toxicity (Gd) i.e.100% had been achieved only after tertiary treatment unit involving Dual Media Filters followed by activated carbon filters. Further attempts have been made to establish the relationship between key wastewater constituents i.e. Chemical Oxygen Demand (COD) and Suspended Solids (SS) with respects to daphnia toxicity (Gd). It was observed that COD and SS show a statistically significant correlation (r2) with daphnia toxicity (Gd) i.e. 0.89 and 0.81, respectively. Thus COD and SS can serve as a regulatory tool in lieu of an explicit toxicity standard (to check and improve the operational status of wastewatertreatment plants in time).

Pre-treatment optimisation of SWRO membrane desalination under tropical conditions

Seawater quality and temperature under tropical conditions require particular attention to optimise the pre-treatment process and to minimise reverse osmosis (RO) membrane fouling in order to maximise plant performance. A skid-mounted pilot plant of 50 m3d-1 was constructed to examine the impact of various pre-treatments on RO feed quality and to optimise the operation conditions for continuous seawater RO (SWRO) membrane desalination. The pilot plant consisted of five main subsystems: (1) open seawater intake, (2) conventional pre-treatment, (3) one-stage RO membrane, (4) effluent discharge and (5) supervised control and data acquisition (SCADA). Such set-up allows pre-treatments of varying coagulants and their doses, hydraulic retention time, with and without chlorination, different filtration schemes of the dual-media filter, several methods of clean-in-place of the RO membrane and its service and flushing arrangement. The sub-systems were tested and the operation conditions optimised. The optimal oper...