Granular Media Filtration Research Articles

An improved protocol for extracting extracellular polymeric substances from granular filter media

Extracellular polymeric substances (EPS) are an important parameter in drinking-water biofilters, and, to date, this is the first study to compare protocols from the literature for extracting EPS from granular filter media. Five extraction protocols were compared, and one was improved by varying the type of initial physical treatment and the shaking intensity, temperature, and time of incubation. Extracting EPS from granular filter media in triplicate by combining 2 g (wet weight) of filter media with 10 mL of extraction buffer (10 mM Tris, 10 mM EDTA, 2.5% NaCl, pH 8), vortexing for 1 min, and incubating for 4 h at 35 °C with shaking at 200 rpm yielded significantly higher EPS polysaccharide and/or protein concentrations than did protocols from the literature. This improved protocol extracted a significant fraction of the biofilm attached to sand but was less effective on biofilm attached to anthracite or granular activated carbon (GAC). A survey of 11 full-scale biofilters from the U.S. and Canada revealed that EPS polysaccharide and protein concentrations can vary over one order of magnitude, from 0.02 to 0.60 mg glucose/g total solids (TS) and 0.27 to 3.38 mg bovine serum albumin/g TS, respectively. Backwashing significantly lowered the biomass and EPS polysaccharide concentrations, but the majority of the biofilm remained attached to the filter media after backwashing, as expected. The fraction of EPS polysaccharides and proteins removed during backwashing did not differ between anthracite and GAC biofilters. The improved EPS extraction protocol can be utilized to investigate the role of EPS in biofilter performance.

Consequences of pH change on wastewater depth filtration using a multimedia filter

Different media materials in a multimedia filter have the potential to trap particles of different characteristics dependent on the media-suspension particle interactions. However, the removal of particles from wastewater secondary effluent using granular media filtration is relatively poorly understood because of the complexity of the wastewater matrix. Often the wastewater treatment process is liable to undergo pH changes due to removal or addition of chemicals in the treatment chain or from biological instability which in turn may alter the wastewater characteristics. Wastewater contains a mixture of organic and inorganic components, dissolved or particulate which may influence the aggregation and deposition of suspension solids during depth filtration. Changes in wastewater pH has the potential to change the wastewater matrix and media surface properties hence affecting aggregation and deposition in wastewater filtration. This study investigated how pH change affects wastewater filtration by monitoring zeta potential, aggregation and deposition of solids. The wastewater and filter media were also characterised over a range of pH from 1 to 13. Aggregation and deposition of wastewater solids was found to be most efficient near neutral pH. This was not concurrent with the conditions of lowest net charge in the system.

Technology for treatment of groundwater simultaneously containing iron, manganese, ammonium and organic matter

The groundwater used as drinking water often contains unacceptable amounts of iron and manganese compounds and ammonium ions. These substances are efficiently removed using conventional technologies (aeration and filtration through granular media filters). However, the efficiency is drastically reduced for water containing considerable amounts of organic matter, which usually enters the water in wellfields linked with surface water. This paper presents a technology development for treating groundwater with such complex problems. A combination of open and closed aeration and filtering through three filters containing sand, zeolite and sand with oxidizing bacteria are used. Polyaluminium chloride acting as coagulant is the only chemical substance used in the technology. The developed water treatment technology was tested for eight months. The technology ensured the reduction of iron, manganese, ammonium, and organic compounds by 98%, 87%, 99%, and 80%, respectively. The efficiencies are sufficient to meet the requirements of the Council Directive 98/83/EC on the quality of water intended for human consumption for most wellfields fed by both underground and surface water.

Sequential biofiltration – A novel approach for enhanced biological removal of trace organic chemicals from wastewater treatment plant effluent

Recent studies revealed the benefits of oligotrophic and oxic conditions for the biological removal of many trace organic chemicals (TOrCs) during soil-aquifer treatment. These findings indicate an unused tuning potential that might also be applicable in engineered biofiltration systems with drastically reduced hydraulic retention times for an enhanced mitigation of TOrCs during wastewater treatment. This study introduces the novel approach of sequential biofiltration (SBF) for the advanced treatment of secondary effluent using two granular media filters operated in series with an intermediate aeration step aiming for oxic and oligotrophic conditions in the second filter stage. Results from the experiments conducted at pilot-scale confirm a reduced substrate availability and predominantly oxic conditions in the second filter stage of the SBF setup. An increased removal of several TOrCs was observed in an SBF system as compared to a conventional single-stage biofiltration unit operated at the same overall empty bed contact time (EBCT). Short-term tests with varying EBCTs in the first filter stage revealed a high degree of system robustness of TOrC mitigation when confronted with sudden hydraulic load variations. Higher removal of several TOrCs at increased EBCTs in the second filter stage indicates that EBCT might play a crucial role for the degradation of certain compounds.

Investigation of Algal Biotoxin Removal during SWRO Desalination through a Materials Flow Analysis

The operation of seawater reverse osmosis (SWRO) desalination facilities has become challenged by the increasing frequency and severity of harmful algal blooms (HABs). The efficiency of algal toxins removal during SWRO and pretreatment processes has critical human health implications. Therefore, a probabilistic materials flow analysis (pMFA) was developed to predict the removal of algal toxins in source water by various pretreatment configurations and operations during SWRO desalination. The results demonstrated that an appreciable quantity of toxins exists in the SWRO permeate (ng/L–µg/L levels), the backwash of pretreatment, and final brine rejects (µg/L–mg/L levels). Varying the pretreatment train configuration resulted in statistically significant differences in toxin removals, where higher removal efficiencies were evidenced in systems employing microfiltration/ultrafiltration (MF/UF) over granular media filtration (GMF). However, this performance depended on operational practices including coagulant addition and transmembrane pressures of MF/UF systems. Acute human health risks during lifetime exposure to algal toxins from ingestion of desalinated water were benign, with margins of safety ranging from 100 to 4000. This study highlights the importance of pretreatment steps during SWRO operation in the removal of algal toxins for managing marine HABs.

Modeling pressure drop produced by different filtering media in microirrigation sand filters using the hybrid ABC-MARS-based approach, MLP neural network and M5 model tree

Granular media filters are commonly used to remove suspended solids and prevent emitter clogging in microirrigation systems. Silica sand is the standard filtering media but other granular materials can be used for this purpose. The characterization of the pressure drop produced by the clean filtering media is of practical interest for designing and managing these filters. Different models such as Ergun or Kozeny-Carman equations are usually used to predict pressure drop produced by the filtering media. However, as parameters of the media such as equivalent diameter and sphericity, that are difficult to determine, appear in these equations, the objective of this study was to construct a new model to estimate the pressure drop of different filtering materials of interest in granular filters with limited data of the physical parameters that characterize the filtering media. This paper, taking as starting point the multivariate adaptive regression splines (MARS), develops a new algorithm hybridizing it with the artificial bee colony (ABC) method, to estimate the pressure drop in granular filters broadly used in microirrigation systems for the first time with a data-driven model. Laboratory experiments were used to measure pressure drop across silica sand, crushed glass, modified glass and glass microspheres in a scaled filter at surface velocities ranging from 0.004 to 0.025ms−1. The ABC method allows the tuning of the MARS parameters during the training phase improving significantly the regression accuracy. Additionally, a multilayer perceptron network (MLP) and M5 model tree were fitted to the experimental data for comparison purposes. The results have shown that ABC-MARS-based model was the best estimation of the pressure drop with a coefficient of determination of 0.78. Therefore, ABC-MARS-based model could be easily implemented to predict pressure drop with minimal input parameters for other filtering materials used in microirrigation media filters.

Polymer-Capped Nanoparticle Transport in Granular Media Filtration: Deviation from the Colloidal Filtration Model

AbstractThe single-collector removal efficiency based on the colloidal filtration model is widely used to quantify deposition of nanoparticles in porous media filtration. The validity of this theor...

Transport and abatement of fluorescent silica nanoparticle (SiO2 NP) in granular filtration: effect of porous media and ionic strength

The extensive production and application of engineered silica nanoparticles (SiO2 NPs) will inevitably lead to their release into the environment. Granular media filtration, a widely used process in water and wastewater treatment plants, has the potential for NP abatement. In this work, laboratory-scale column experiments were performed to study the transport and retention of SiO2 NPs on three widely used porous materials, i.e., sand, anthracite, and granular activated carbon (GAC). Synthetic fluorescent core-shell SiO2 NPs (83 nm) were used to facilitate NP detection. Sand showed very low capacity for SiO2 filtration as this material had a surface with limited surface area and a high concentration of negative charge. Also, we found that the stability and transport of SiO2 NP were strongly dependent on the ionic strength of the solution. Increasing ionic strength led to NP agglomeration and facilitated SiO2 NP retention, while low ionic strength resulted in release of captured NPs from the sand bed. Compared to sand, anthracite and GAC showed higher affinity for SiO2 NP capture. The superior capacity of GAC was primarily due to its porous structure and high surface area. A process model was developed to simulate NP capture in the packed bed columns and determine fundamental filtration parameters. This model provided an excellent fit to the experimental data. Taken together, the results obtained indicate that GAC is an interesting material for SiO2 NP filtration.

Application of House of Quality in assessment of seawater pretreatment technologies

Increasing pressure on water resources is leading to a growing reliance on seawater desalination for the provision of freshwater. Pretreatment of seawater is a major step in seawater desalination, which can mitigate problems with reverse osmosis (RO) membranes. No clearly superior pretreatment technology exists, due to the variation in input water quality, and furthermore, the pretreatment must be designed to be functional with input water quality characteristics that vary considerably over time.The objective of this work is to conduct technology assessment by applying a lissome version of HOQ matrix developed in a case study of dissolved air flotation (DAF) system, which is used as water pretreatment for RO desalination systems. The DAF system technology is compared with other pretreatment processes such as ultrafiltration, sedimentation, and granular media filtration. General analysis provides insight to decision makers to help them improve technologies so that they could meet specific demands. HOQ offers a comparative analysis and identifies specific characteristics that must be improved to develop the chosen technology.The HOQ provides a comprehensive analysis for decision making in management, showing that no pretreatment technologies present a superior performance vis-a-vis all customer attributes, however, it identifies the features of the system, to which efforts should be funneled. For DAF system, these are: water quality changes and energy consumption.

Effect of water chemistry and operational conditions on μGAF process performance

Microgranular adsorptive filtration (μGAF) is a water treatment technique in which adsorption and granular media filtration operate simultaneously as water passes through a thin layer of adsorbent pre-deposited on a woven mesh or membrane. Our previous work showed that when heated aluminum oxide particles (HAOPs) are the adsorbent in such systems, substantial natural organic matter (NOM) removal and fouling reduction can be achieved. The present study investigated the effects of feed water chemistry and operational conditions on μGAF performance. Parameters investigated include the pH, ionic strength, and concentration of divalent cations in the feed, the flux through the adsorbent layer, and the pressure drop across both the adsorbent layer and the membrane. In the range from pH 3 to 9, lower pH promoted removal of NOM in general, and transparent exopolymer particles (TEP) in particular, by HAOPs. These enhanced removals led to increased fouling of the HAOPs layer and reduced fouling of a downstream membrane. Higher ionic strength exacerbated fouling of the bare membrane but had little effect on the ability of HAOPs to collect foulants from the feed. Increased concentrations of divalent cations reduced membrane fouling slightly, possibly due to the agglomeration of polysaccharides caused by divalent cations. Increasing the flux through the HAOPs layer had essentially the same effect as lowering the pH of the feed – it enhanced removal of NOM and TEP by, and increased fouling of, the HAOPs layer, thereby reducing fouling of the downstream membrane.The HAOPs layer was incompressible, even when some NOM had accumulated on or in it, suggesting that NOM molecules adsorb on the HAOPs throughout the layer and do not form a continuous gel layer on top of the HAOPs layer. Particulate and colloidal matter were inferred to be the dominant foulants in μGAF units, whereas soluble NOM (including soluble TEP) was the key foulant in the downstream membrane units.

Pilot study on arsenic removal from groundwater using a small-scale reverse osmosis system—Towards sustainable drinking water production

Arsenic contamination of groundwater is posing a serious challenge to drinking water supplies on a global scale. In India and Bangladesh, arsenic has caused the most serious public health issue in the world for nearly two decades. The aim of this work was to study an arsenic removal system based on reverse osmosis at pilot scale treating two different water sources from two different locations in the State of Bihar, India. For this purpose two villages, Bind Toli and Ramnagar in the Patna District were selected, both located very close to the river Ganga. The trials were conducted with aerated and non-aerated groundwater. It is the first time that the arsenic removal efficiency for aerated and non-aerated groundwater by reverse osmosis technology in combination with an energy-saving recovery system have been studied. As the principle of reverse osmosis requires a relatively high pressure, its energy demand is naturally high. By using an energy recovery system, this demand can be lowered, leading to an energy demand per liter permeate of 3–4Wh/L only. Due to high iron levels in the groundwater and as a consequence the precipitation of ferric (hydr)oxides, it was necessary to develop a granular media filter for the trials under aeration in order to protect the membrane from clogging. Two different materials, first locally available sand, and second commercially available anthracite were tested in the granular media filter. For the trials with aerated groundwater, total arsenic removal efficiency at both locations was around 99% and the arsenic concentration in permeate was in compliance with the WHO and National Indian Standard of 10μg/L. However, trials under anoxic conditions with non-aerated groundwater could not comply with this standard. Additionally a possible safe discharge of the reverse osmosis concentrate into an abandoned well was studied. It was observed that re-injection of reject water underground may offer a safe disposal option. However, long-term hydrogeological studies need to be conducted for confirmation.

Evaluation of a Point-of-Use Electrocoagulation System for Arsenic Removal

A point-of-use prototype electrocoagulation treatment system was designed and evaluated for its ability to remove arsenic from a synthetic groundwater. The system was comprised of an electrocoagulation reactor providing batch treatment, a rechargeable battery power source, an electrical monitoring and control module, and a granular media filter. The control module and the filter underdrain system were designed to improve user convenience. The system was able to consistently reduce arsenic concentrations to below 20 µg/L. Effluent soluble arsenic concentrations under 10 µg/L were deemed possible with enhanced effluent suspended solids removal techniques. Arsenic removal was found to be a function of the initial arsenic concentration and the cumulative charge dosage as measured in coulombs per liter of water treated. The steel plate size used in the electrocoagulation module influenced the current draw and the overall electrical efficiency of the system. The monitoring and control module allowed the system to produce up to 100 liters of treated water daily on a single battery charge and would automatically control charge and iron dosage. The point-of-use system was capable of meeting household potable demands for water where other treatment options are limited.

Performance comparison of granular media filter beds

Particle capture, head loss development, and efficiency of in-line coagulation in contact filtration were studied using two types of laboratory filters with varying coagulants. One filter consisted of sand and anthracite, whereas the other filter contained crushed glass and anthracite. Effects of in-line coagulation on filter performance were evaluated using a charge measuring device. Performance of filters was monitored in terms of effluent quality as a function of time and development of head loss by anthracite layer and by the entire filter bed. Filterability index was used to provide a measure of effectiveness of filter media and/or operational variables such as coagulant type and dosage. This study found that the crushed glass–anthracite filter was as effective at removal of particles and metals (Fe and Al) as sand–anthracite filters.

Effects of natural organic matter and sulfidation on the flocculation and filtration of silver nanoparticles

Environmental transformations had different effects on self-aggregation and initial deposition in granular media filtration, contrary to traditional theory.

Process Performance of Secondary Effluent Granular Media Filtration with and without Preozonation.

A 10-month pilot study compared the performance of conventional granular media filtration (CGMF) with granular media filtration with preozonation (OGMF) to determine the effects of preozonation on filter performance. Filtration recoveries were lower for OGMF compared to CMGF when operated at a loading rate of 18.3 m/h. Operation at 18.3 m/h met turbidity requirements for California Department of Public Health Title 22 unrestricted reclaimed water requirements for both OGMF and CGMF. Preozonated secondary effluent at a transferred dose of 3 mg/L resulted in an increase in ultraviolet transmissivity (UVT) of approximately 6% and greater than 5-log inactivation of male-specific bacteriophage MS2. Wet weather flow events resulted in UVT decrease and a decline in MS2 inactivation to less than 3 log attributed to higher ozone demand in the secondary effluent. Preozonation increased N-nitrosodimethlyamine (NDMA) concentration approximately 10 times, but subsequent filtration reduced levels to secondary effluent values. A net increase in NDMA was observed at times.

Surface Roughness Impacts on Granular Media Filtration at Favorable Deposition Conditions: Experiments and Modeling.

Column tests were conducted to investigate media roughness impacts on particle deposition in absence of an energy barrier (i.e., high ionic strength). Media/collector surface roughness consistently influenced colloid deposition in a nonlinear, nonmonotonic manner such that a critical roughness size associated with minimum particle deposition could be identified; this was confirmed using a convection-diffusion model. The results demonstrate that media surface roughness size alone is inadequate for predicting media roughness impacts on particle deposition; rather, the relative size relationship between the particles and media/collectors must also be considered. A model that quantitatively considers media surface roughness was developed that described experimental outcomes well and consistently with classic colloid filtration theory (CFT) for smooth surfaces. Dimensionless-scaling factors froughness and fPCIF were introduced and used to develop a model describing particle deposition rate (kd) and colloid attachment efficiency (α). The model includes fitting parameters that reflect the impact of critical system characteristics such as ionic strength, loading rate, hydrophobicity. Excellent agreement was found not only between the modeled outcomes for colloid attachment efficiency (α) and experimental results from the column tests, but also with experimental outcomes reported elsewhere. The model developed herein provides a framework for describing media surface roughness impacts on colloid deposition.

English

The paper making industry is characterized by high rate of water consumption and hence high rate of wastewater generation. The purpose of this research was to assess and optimize the existing complete mix activate sludge treatment plant that is used to treat the high strength paper mill effluent with the highest possible efficiency at a reasonable cost. The collected paper mill wastewater is equalized in an equalization tank before being pumped to the treatment plant. The treatment plant includes chemical treatment unit, complete mix activated sludge and granular media filtration unit. The results showed that effluent of a chemical treatment unit was found to be relatively similar to the laboratory simulated plain sedimentation unit. It can be concluded that addition of chemical coagulant can be eliminated with an overall saving of chemical addition costs. The complete mixing activated sludge achieved good removal of biochemical oxygen demand (BOD) and chemical oxygen demand (COD). Furthermore, the results showed that the plant is operated under low BOD:P ratio. The treatment efficiency of the plant can be improved by increasing the phosphorous dose to the plant to have BOD:P ratio of 100:0.5 to 100:1. It was found that 50% of the treated effluent is recycled to the manufacturing process, however this percentage can be increased through proper plant optimization and control of nutrient addition to the activated sludge unit.

Needed seawater reverse osmosis pilot plant in Qatar

Seawater reverse osmosis (SWRO) is the most cost-effective, practical, and widely used desalting system. Its energy consumption, for Arabian Gulf seawater conditions is in the range of 5–6 kWh/m3. These are less than 1/3 of the equivalent mechanical energy of the thermal desalination systems presently used in Qatar. Besides, these thermal systems consume 2–4 kWh/m3 for pumping. Therefore, using SWRO system in Qatar can save up to 75% of the desalination energy cost. For Qatar, current desalting water production using thermal methods is 480 Mm3/year at $0.1–1.2/kWh energy price; the energy cost is at least one Billion US dollars per annum. A SWRO pilot plant is to be built in Qatar prior to building a full size desalting plant (DP) in order to determine site-specific treatment guidelines and to provide a full range of performance information to be used in the design of a full-scale plant. The pilot plant will be tested when the feedwater quality is good, and when there are major storm events or algae blooms exist. Red tide events in 2008–2009 forced many DPs in Gulf Co-operation Countries area to shut down. This paper reviews the SWRO pretreatment process, which depends on local conditions and is the main factor affecting the SWRO reliability. These include the extensively used conventional pretreatment of coagulation–flocculation and granular media filtration (GMF). This is almost necessary for open sea intake. Sever red tide blooms, when occur, cause clogging of GMF, resulted in biological and organic foulants on SWRO membranes, and even DP shut down. So, low-pressure membranes such as ultrafiltration (UF) or microfiltration (MF) can replace or integrated with GMF. Since flotation is more robust than sedimentation (used in GMF) in dealing with high concentration of suspended matter, dissolved air flotation is started to be used as pretreatment. Since it is a new method that met success in several plants, it thoroughly reviewed in this paper when integrated with GMF or membrane treatment. Additionally, the expensive pretreatment with UF and MF is discussed with given examples. Preliminary experimentation with SWRO pretreatment in Qatar was presented. Moreover, energy recovery devices to be used with the pilot SWRO are discussed. Membranes configuration and the equipment to be included are also outlined.

Holistic Assessment of Trace Organic Compounds (TOrC) in Wastewater Treatment

A study of trace organic compound (TOrC) reactivity to selected, advanced wastewater treatment processes was conducted as part of a demonstration-scale pilot study. The pilot facilities consisted of a biological nitrogen removal (BNR) activated sludge treatment process, parallel membrane and granular media filtration processes and a biologically active filter preceded by ozone treatment, and three parallel disinfection processes: free chlorine, ozone, and UV irradiation. Twelve trace organic indicator compounds were selected to represent the treatability of a breadth of compounds. Measurements of TOrC concentrations entering and exiting each unit process were made over a period of nine months, under a range of operating conditions to assess the treatability of each compound by each process. Comparisons were made to TOrC treatability through the existing full scale plant, a high purity oxygen activated sludge (HPOAS) secondary treatment plant using chloramination for disinfection. Eight of the twelve studied indicator TOrCs were reduced through the BNR process. Removals through the BNR process were more effective than removals through the HPOAS process, likely owing to longer solids retention time (SRT) and higher mixed liquor suspended solids (MLSS) concentration in the BNR process providing more bio-oxidation capacity than in the HPOAS process. Neither membrane nor granular media filtration was effective in reducing TOrCs, implying TOrCs are not particle associated. Many of the TOrCs were reduced by ozone treatment preceding biologically active filtration. The biologically active filter was not effective at reducing TOrCs, with the exception of NDMA, which was formed during ozonation, but then reduced through the bio-filter. Post-filtration disinfection processes had varying degrees of effectiveness reducing TOrCs, with ozone being most effective, followed by chlorine and UV. This title belongs to WERF Research Report Series . ISBN: 9781780405179 (eBook)

Characterization of polystyrene granules as granular media filters

The need for water production is increasing in urban populations. In conventional water treatment plants, the filters are backwashed by treated water, which represents high long-term costs. In order to obtain a highly effective production of water with a subsequent reduction in production costs, it was proposed to feature a granular filter element with low density and its potential to provide a down-flow rapid filter, which can represent a reduction in the volume of water used for backwash. The polymer used for this purpose appears to be favorable; in addition, there are possibilities of recycling this material. A velocity of 6.08 m/h for a 50% expansion was demonstrated, which is very low compared to conventional filter elements (i.e. sand and anthracite). So, this element has shown great potential in reducing the volume of water during the backwash process, as observed using mathematical models. The final quality of the filtered water still needs to be analyzed. However, the permeability coefficient was determinate at 1.79 × 10−5 ± 2.87 × 10−6 m/s being satisfactory as filtration. The outlook is that it may become an option for element filtration in down-flow rapid filters for water treatment.