Dual Media Filtration Research Articles

Influence of filter backwashing on iron, manganese, and ammonium removal in dual-media rapid sand filters used for drinking water production

Influence of filter backwashing on iron, manganese, and ammonium removal in dual-media rapid sand filters used for drinking water production

Improvement of Removal Rates for Iron and Manganese in Groundwater Using Dual-Media Filters Filled with Manganese-Oxide-Coated Sand and Ceramic in Nepal

Improvement of Removal Rates for Iron and Manganese in Groundwater Using Dual-Media Filters Filled with Manganese-Oxide-Coated Sand and Ceramic in Nepal

Micro plastics removal by Zai water treatment plant, Amman Jordan

Micro-plastics (MPs) concentration, in Zai Water Treatment Plant (WTP) influent, and their removal by the different treatment units have been investigated. Samples were collected from the influent to Zai WTP, and from the effluent of each treatment unit, in December 2022, January, February, May and June of 2023. The samples were sieved at the site using one100 μm, 300 μm and 500 hundred μm sieves. The sieves were rinsed, the rinsed water was collected in 250 ml bottles and brought to the laboratory. The samples were treated and filtered in the Laboratory; two filter papers were prepared for each sample. Filtered samples were tested by Thermo Scientific micro-FTIR spectroscopy, for Microplastic identification, and by fluorescence microscope for MP quantification and morphology. The most frequently identified MPs in the influent were polyester, polyethylene, polypropylene, polystyrene; other MPs were identified at lower frequencies. The results showed that small MPs < 100 μm, in length, were dominant; larger sizes were detected at lower concentrations. The results showed that MPs were removed by the powdered activated carbon unit, coagulation, flocculation followed by sedimentation units, and by the dual media filter. Removal percentages by the different treatment units varied from month to month, which is attributed to the monthly variation in MPs nature and size distribution; variation of MP concentration in the influent; and variation in the operational conditions. Overall MP removal efficiencies were (48, 29, 53, 91, 84) %, for December, January, February, May, and June samples, respectively.

Assessment of up-flow and down-flow dual media filters for secondary treated wastewater

Assessment of up-flow and down-flow dual media filters for secondary treated wastewater

The Pilot Study of a Dual-Media Filter Consisting of Mortar and Modified Zeolite for Removing Heavy Metals from Expressway Stormwater Runoff

Stormwater runoff from expressways generally has high concentrations of heavy metals. However, the heavy metal removal of conventional sand filters is low, so a better alternative is required. In this study, several inexpensive materials were tested for their heavy metal adsorption, and the performances of the selected materials were evaluated via field tests. The results of laboratory experiments showed that the Cu adsorption capacity followed the order of Na-zeolite &gt; zeolite &gt; biochar &gt; granular ferric hydroxide &gt; sand ≥ orchid stone. The performance of a pilot-scale dual-media filter filled with Na-zeolite and mortar granules was monitored for four rainfall events at an expressway site, and was compared to that of a sand filter. Both filters showed similar event mean concentration (EMC) removal for BOD, COD, TOC, and T-N, without a notable decrease in hydraulic conductivity. However, the removal of T-P, Cu, Zn, Cr, Ni, and Fe by the dual-media filter was 37.6–74.8%, 59.1–90.1%, 84.9–99.7%, 100.0%, 100.0%, and 78.7–94.4%, respectively, which was up to 4.5 times of that of the sand filter. In addition, it was stable regardless of the influent EMCs. Overall, we showed that the dual-media filter is excellent in heavy metal removal from stormwater runoff, with negligible clogging.

Nitrogen-sparging assisted anoxic biological drinking water treatment system.

Existing heterotrophic denitrification reactors rely on microorganisms to consume dissolved oxygen (DO) and create conditions suitable for denitrification, but this practice leads to excessive microbial growth and increased organic carbon doses. An innovative reactor that uses nitrogen gas sparging through a contactor to strip DO was developed and tested in the lab. It reduced influent nitrate from 15 to <1 mg/L as N with nitrite accumulation <1 mg/L as N. It maintained a consistent flow rate and developed minimal headloss, making it easier to operate than the denitrifying dual-media filter that was operated in parallel. Gravel, polyvinyl chloride pieces, and no packing media were assessed as options for the nitrogen-sparged contactor, and gravel was found to support denitrification at the highest loading rate and was resilient to nitrogen-sparging shutoffs and intermittent operation. This innovative reactor appears promising for small drinking water systems.

Evaluation of crushed slates as a suitable capping material for rapid gravity sand filters

In the potable water treatment process, Rapid Gravity Sand Filters (RGSF) are commonly adopted as the last solid-liquid separation stage. Cleaning of the RGSF is done through backwashing. RGSF is widely adopted all over the World due to its ease of operation and high filtration rates. However, these filters suffer from stratification of the sand media, which causes floc removal to occur only at the topmost layer of the filter bed, leaving the remaining depth unutilized. Capping is a technique whereby a thin layer of sand filter media is replaced with a suitable coarse material to overcome the problem of stratification and transform a singlemedia RGSF into a dual-media filter. The objective of this study is to determine the suitability of crushed slates as a capping material. The study evaluated the performance of a crushed expanded slate-capped filter against a conventional single-media RGSF, the effects of its physical and chemical characteristics, and varying the depth of the capping material. Laboratory tests were conducted to assess the physical and chemical characteristics of slates from Maji ya Chumvi (Coast, Kenya). This included specific gravity, acid solubility, water extractable substances, silica content, and friability. A performance comparison was carried out by means of a fabricated model filtration unit set up within an existing community water treatment plant. The model filtration unit was fed with pretreated raw water of varying influent turbidities. Crushed expanded slates met the minimum physical and chemical requirements for use as a capping material for RGSF. The crushed expanded slate-capped RGSF model demonstrated high robustness under high shock turbidity loads (above 150 NTU), which is illustrated by an increased length of filter run of 27% (50–150 NTU) and 45% (150–300 NTU). Increasing the depth of capping material from 25mm to 50mm did not yield any significant improvement or deterioration in the filter run length. At influent turbidities below 150 NTU, the effluent water quality for all three scenarios (uncapped, 25 mm, and 50mm crushed expanded slates capped) is below 5 NTU and therefore meets the Kenyan drinking water standards. Above 150 NTU influent turbidity, the effluent water quality for the uncapped RGSF deteriorates, whereas for the 25mm and 50mm capped RGSF, it remains consistently below 5 NTU. This demonstrates the usefulness of the crushed expanded slates in improving the turbidity removal of RGSF for high (above 150 NTU) turbidity loads. This study recommends a full-scale trial of crushed expanded slates to facilitate a more precise estimation of the overall benefit of full-scale community water filtration systems.

Influence of filter age on Fe, Mn and NH4+ removal in dual media rapid sand filters used for drinking water production

Rapid sand filtration is a common method for removal of iron (Fe), manganese (Mn) and ammonium (NH4+) from anoxic groundwaters used for drinking water production. In this study, we combine geochemical and microbiological data to assess how filter age influences Fe, Mn and NH4+ removal in dual media filters, consisting of anthracite overlying quartz sand, that have been in operation for between ∼2 months and ∼11 years. We show that the depth where dissolved Fe and Mn removal occurs is reflected in the filter medium coatings, with ferrihydrite forming in the anthracite in the top of the filters (< 1 m), while birnessite-type Mn oxides are mostly formed in the sand (> 1 m). Removal of NH4+ occurs through nitrification in both the anthracite and sand and is the key driver of oxygen loss. Removal of Fe is independent of filter age and is always efficient (> 97% removal). In contrast, for Mn, the removal efficiency varies with filter age, ranging from 9 to 28% at ∼2–3 months after filter replacement to 100% after 8 months. After 11 years, removal reduces to 60–80%. The lack of Mn removal in the youngest filters (at 2–3 months) is likely the result of a relatively low abundance of mineral coatings that adsorb Mn2+ and provide surfaces for the establishment of a microbial community. 16S rRNA gene amplicon sequencing shows that Gallionella, which are known Fe2+ oxidizers, are present after 2 months, yet Fe2+ removal is mostly chemical. Efficient NH4+ removal (> 90%) establishes within 3 months of operation but leakage occurs upon high NH4+loading (> 160 µM). Two-step nitrification by Nitrosomonas and Candidatus Nitrotoga is likely the most important NH4+ removal mechanism in younger filters during ripening (2 months), after which complete ammonia oxidation by Nitrospira and canonical two-step nitrification occur simultaneously in older filters. Our results highlight the strong effect of filter age on especially Mn2+but also NH4+ removal. We show that ageing of filter medium leads to the development of thick coatings, which we hypothesize leads to preferential flow, and breakthrough of Mn2+. Use of age-specific flow rates may increase the contact time with the filter medium in older filters and improve Mn2+ and NH4+ removal.

Exploring the feasibility of dual media filtration at Morton Jaffray Water Works (Harare, Zimbabwe)

Lake Chivero, Harare’s main potable raw water source, is eutrophic. This has complicated water treatment at Morton Jaffray Water Treatment Works (MJWTW) leading to frequent filter backwashing and reduced plant output. This study investigated the use of dual media filters (DMF) as an alternative to single media filters (SMF) currently employed using pilot filters. Key operational parameters (headloss and flow rate) and water quality parameters [electrical conductivity (EC), pH, total dissolved solids (TDS), turbidity and temperature] were monitored hourly. The change in EC, pH, TDS, and turbidity across the SMF and DMF was 6.3% and 6.3%; 0.5%. and 0.2%; 5.5% and 4.5%; 68% and 69%, respectively thus showing no significant difference. However, headloss development for the SMF was significantly higher reaching 247.3 m compared to 134.6 m for the DMF. Use of DMF could increase the filter run and production at MJWTW.

Forecasting and Optimizing Dual Media Filter Performance via Machine Learning

Four different machine learning algorithms, including Decision Tree (DT), Random Forest (RF), Multivariable Linear Regression (MLR), Support Vector Regressions (SVR), and Gaussian Process Regressions (GPR), were applied to predict the performance of a multi-media filter operating as a function of raw water quality and plant operating variables. The models were trained using data collected over a seven year period covering water quality and operating variables, including true colour, turbidity, plant flow, and chemical dose for chlorine, KMnO4, FeCl3, and Cationic Polymer (PolyDADMAC). The machine learning algorithms have shown that the best prediction is at a 1-day time lag between input variables and unit filter run volume (UFRV). Furthermore, the RF algorithm with grid search using the input metrics mentioned above with a 1-day time lag has provided the highest reliability in predicting UFRV with a RMSE and R2 of 31.58 and 0.98, respectively. Similarly, RF with grid search has shown the shortest training time, prediction accuracy, and forecasting events using a ROC-AUC curve analysis (AUC over 0.8) in extreme wet weather events. Therefore, Random Forest with grid search and a 1-day time lag is an effective and robust machine learning algorithm that can predict the filter performance to aid water treatment operators in their decision makings by providing real-time warning of the potential turbidity breakthrough from the filters.

Meta-omics profiling of full-scale groundwater rapid sand filters explains stratification of iron, ammonium and manganese removals

Rapid sand filters (RSF) are an established and widely applied technology for groundwater treatment. Yet, the underlying interwoven biological and physical-chemical reactions controlling the sequential removal of iron, ammonia and manganese remain poorly understood. To resolve the contribution and interactions between the individual reactions, we studied two full-scale drinking water treatment plant configurations, namely (i) one dual-media (anthracite and quartz sand) filter and (ii) two single-media (quartz sand) filters in series. In situ and ex situ activity tests were combined with mineral coating characterization and metagenome-guided metaproteomics along the depth of each filter. Both plants exhibited comparable performances and process compartmentalization, with most of ammonium and manganese removal occurring only after complete iron depletion. The homogeneity of the media coating and genome-based microbial composition within each compartment highlighted the effect of backwashing, namely the complete vertical mixing of the filter media. In stark contrast to this homogeneity, the removal of the contaminants was strongly stratified within each compartment, and decreased along the filter height. This apparent and longstanding conflict was resolved by quantifying the expressed proteome at different filter heights, revealing a consistent stratification of proteins catalysing ammonia oxidation and protein-based relative abundances of nitrifying genera (up to 2 orders of magnitude difference between top and bottom samples). This implies that microorganisms adapt their protein pool to the available nutrient load at a faster rate than the backwash mixing frequency. Ultimately, these results show the unique and complementary potential of metaproteomics to understand metabolic adaptations and interactions in highly dynamic ecosystems.

Reversible fouling by particulate matter from natural seawater reduces RED performance while limiting biofouling

Reverse Electrodialysis (RED) has shown to be a promising technology for electricity production but membrane fouling can influence the energy yield, thus, it is crucial to gain knowledge on the impact and prevention of fouling. We used a sequence of pre-treatments (dual-media filter, microfilter and activated carbon filter) to fractionate foulants in seawater based on size and investigated its effect on RED. Fouling reversibility was studied by applying a cleaning procedure with reversal and increased flow and air sparging at the end of the experiment. After 63 days of operation, when using only the dual-media filter as pre-treatment, the pressure drop increased by 520 mbar in the seawater compartments without affecting the electrochemical measurements. The application of the cleaning procedure allowed to recover 90 % of the pumping power losses. A membrane autopsy showed the development of a biofilm layer on the membrane of the stacks receiving the most treated water while it was not detected when only the dual-media filter was used, which showed that the presence of particulate matter could help limit biofouling development. Together with the performance recovery, we concluded that the application of the dual media filtration system is a suitable and cost effective pre-treatment for RED.

Pilot-scale evaluation of sulfite-activated ferrate for water reuse applications

Ferrate is a promising, “green” (i.e., iron-based) pre-oxidation technology in water treatment, but there has been limited research on its potential benefits in a water reuse (wastewater recycling) paradigm. Recent studies have shown ferrate treatment processes can be improved by activation, the addition of reductants (i.e., sulfite) to the reaction. Prior bench scale experimentation suggests sulfite-activated ferrate may be a feasible option for water reuse applications; however, extent questions need to be addressed. This study evaluated the viability of sulfite-activated ferrate in water reuse treatment through continuous-flow experiments using synthetic and field-collected secondary wastewater effluents. The effluents were processed through the piloting system which included various physicochemical processes such as ferrate pre-oxidation, coagulation, clarification, and dual-media filtration. In each trial, the system was run continuously for eight hours with data collected via grab samples and online instrumentation with real-time resolution. Results demonstrate that reuse systems using activated ferrate pre-oxidation can produce effluents with water quality meeting most regulatory requirements without major impacts on downstream physicochemical processes. When compared to traditional ferrate pre-oxidation, activation showed several improvements such as lower byproduct yields. Operationally, activated ferrate does increase the development of headloss across the dual-media filter. In general, sulfite-activated ferrate is viable in a water reuse setting, resulting in several improved water quality outcomes. Results from this work create a pathway for adaptation at scale.

Application of a new baffled horizontal flow constructed wetland-filter unit (BHFCW-FU) for treatment and reuse of petrochemical industry wastewater

The shortage of water resources and generation of large quantum of wastewater has posed a significant concern to the environment and public health. Recent research on wastewater treatment has started to focus on reusing wastewater for different activities to reduce the stress on natural water resources. Constructed wetland (CWs) is a low-cost wastewater treatment option. However, some drawbacks include large areal requirements and the need for tertiary treatment units for reusable effluent. In this study, a novel composite baffled horizontal flow CW filter unit (BHFCW-FU) was developed to overcome the drawbacks of the conventional CW. The BHFCW-FU planted with Chrysopogon zizanioides provided a nine times longer flow path, and the adjoined variable depth dual media filter reduced the total area requirement and served as a polishing unit. On average, the BHFCW-FU with horizontal sub-surface flow regime could efficiently remove around 93.93%, 87.20%, and 66.25% of turbidity, phenol, and COD, respectively, from real petrochemical wastewater (initial turbidity: 29.6 NTU, phenol: 4.52 mg/L, and COD: 381 mg/L) and rendered the effluent quality reusable for irrigation, industrial, and other environmental purposes. In synthetic wastewater (initial turbidity: 754 NTU, phenol: 10.87 mg/L, and COD: 1691 mg/L), the removal efficiency of turbidity, phenol, and COD were 99.50%, 93.73%, and 87.05%, respectively. In-depth substrate characterization was done to study the removal mechanism. The developed BHFCW-FU required less space and maintenance, provided reusable effluent, and overcame the drawbacks of conventional CWs. Hence, it may show immense potential as an effective wastewater treatment.

Evaluation of water consumption in rapid sand filters backwashed under varied physical conditions

Egypt suffers from water scarcity. In water treatment plants using sand filters, a significant amount of treated water is consumed, estimated at 10%–15% of the filtered water during backwashing. The objective of this study is to determine the most effective way to reduce the amount of treated water used for backwashing. The methodology of this study was to evaluate the effects of air and water rates, treated water turbidity of 1.6 NTU or slightly higher synthetic turbidity of 4.0 NTU, and media type with single or dual media on reducing treated water consumption during rapid sand filter backwashing procedures. The experimental set up was a bench-scale filter operated at a filtration rate of 189 m3/m2/day. Backwashing with the right water and air rates reduce water usage by 18%, enhanced process performance, and reduced the ripening period. Backwashing using synthetic turbid water recovered 100% of the treated water and improved the ripening duration without affecting backwashing efficiency. This study concluded that backwashing the dual media filter with silica sand and activated carbon achieved the highest treated backwash water consumption by approximately 60%. While anthracite coal was utilized as a dual-media filter, the least reduction in treated water consumption was discovered.

Particle-scale modelling of rapid granular filtration in a dual-media filter

Multi-media filters are widely applied in water treatment, yet the understanding of powder transportation mechanisms at particle-scale and clogging prediction is still lacking. In this work, a dual-media (anthracite and sand) rapid granular filtration is numerically studied at particle-scale by a smoothed computational fluid dynamics-discrete element method (CFD-DEM) model. In this model, a multi-sphere model and a modified Johnson-Kendall-Roberts (JKR) model are integrated to describe anthracite shapes and material cohesion, respectively. The model is validated in terms of pressure drop across a packed bed and powders migration through another packed bed. The powder transportation in the filtration through a dual-media filter is studied. The results show that the motion of powders in the anthracite layer are governed by deposition, penetration, and connection, while the motion of powders in the sand layer experience core formation, core growth, and cluster connection. The evolution of solid volume fraction Φ indicates a saturation value (0.67) exists in the entries of layers. The small powders tend to be clogged in the anthracite layer and the large powders prefer to be clogged in the sand layer. The density evolution of the clogged powders nv shows that the sand layer has a saturation nvs=0.21 in the entry, and that of the anthracite layer nva=0.252 is obtained by extrapolation. Finally, a probabilistic model is originally derived for quantifying the clogging by clogging probability. After verification, the sand layer has the clogging probability of 0.47 while the anthracite layer has the clogging probability of 0.10.

Influence of manganese oxide‐coated granular media on disinfection byproduct formation

AbstractThe objective of this study was to determine the influence of manganese oxide (MnOx) coated granular media on disinfection byproduct (DBP) formation for dissolved manganese (Mn(II)) and natural organic matter (NOM) concentrations typical in drinking water treatment (DWT). Instantaneous and 24‐h haloacetic acid and total trihalomethane concentrations of influent and effluent samples from two DWT plants, one using MnOx‐coated dual media (DM) filters and the other using second‐stage contactors for Mn(II) sorption by coarse MnOx‐coated ceramic media after DM filtration, were examined. Results showed that interaction with MnOx‐coated surfaces did not increase measured DBP concentrations. Observed increases in 24‐h DBP concentrations for the surface water plant were attributed to filter‐associated NOM, and not the MnOx coating. The findings of this study indicate that a second‐stage contactor – with MnOx‐coated media utilized for Mn(II) removal after a particle removal filter – does not increase DBP formation under typical treatment conditions.

Jellyfish swarm impair the pretreatment efficiency and membrane performance of seawater reverse osmosis desalination

Circumstantial evidence has suggested that jellyfish swarms impair the operation of seawater reverse osmosis desalination facilities. However, only limited information is currently available on the pretreatment efficiency of jellyfish and their effects on reverse osmosis (RO) membrane performance. Here, we have comprehensively tested the pretreatment efficiency of a dual-media gravity filter and cartridge micro-filtration following the addition of jellyfish into the feedwater. Concurrently, the fouling propensity and performance of the RO membranes were examined. We show that jellyfish demise resulted in seawater eutrophication that triggered a significant increase in bacterial biomass (∼50-fold), activity (∼7-fold), and release of transparent exopolymer particles (∼5-fold), peaking three days after the addition of jellyfish into the feedwater. In parallel, a significant reduction in permeate water flux was recorded (∼10%) while trans-membrane pressure sharply increased (15%), reaching the operation pressure limit of our system (75 bar) after five days. At the conclusion of the experiments, the membrane surface was heavily covered by large chunks of organic-rich material and multilayered biofilms. Our results provide a holistic view on the operational challenges of seawater reverse osmosis (SWRO) desalination triggered by jellyfish swarms in coastal areas. Following the above, it can be inferred that freshwater production will likely be halted three days after drawing the jellyfish into the pretreatment system. Outcomes from these results may lead to the development of science-based operational protocols to cope with growing occurrence of jellyfish swarms around the intake of SWRO desalination facilities worldwide.

Efficient removal of iron from groundwater by dual-media filter

Efficient removal of iron from groundwater by dual-media filter

Impacts of sewage outbursts on seawater reverse osmosis desalination

Sewage outbursts affect coastal environments as seawater is enriched with nutrients, organic matter and microbes, thus can potentially impair seawater reverse osmosis (SWRO) desalination. In this study, we evaluated how municipal sewage outbursts affect SWRO desalination in a pilot-scale system. To this end, feedwater characteristics (i.e., coastal water), the removal efficiency of organic foulants by a dual-media gravity filter, and cartridge micro-filtration were determined daily for 12 days. Permeate water flux was maintained constant during the study, while trans-membrane pressure (TMP) was automatically adjusted and continuously monitored. The results indicate that sewage outbursts caused an immediate (∼1 d) buildup of phyto/bacterioplankton biomass (up to 10-fold), and enhanced activity (maximal 30-fold) followed by an increase in transparent exopolymer particle (TEP) concentrations. After sewage addition, algal biomass was significantly removed by the pretreatment system (72–90%), while a considerable fraction of the bacterial biomass (42–65%) and TEP (53–65%) passed these procedures. The result was a negative impact on the desalination performance reflected by a significant increase (> 10%) in RO-TMP 7.5 d after the sewage addition. Our results indicate on a direct link between sewage outbursts, pretreatment efficiency, and SWRO desalination. Nevertheless, these findings can lead to new avenues for the development of science-based operational protocols to minimize the deleterious effects of abrupt sewage outbursts on SWRO desalination.