Digital Image Analysis to Determine Pore Opening Size Distribution of Nonwoven Geotextiles

The filtration performance of a geotextile is controlled by its pore opening size distribution (PSD). Current methods for determining PSD are mostly indirect and contain inherent disadvantages. Recent technological advancements in image analysis offer great potential for a more accurate and direct way of determining the PSD of nonwoven geotextiles. A new and accurate method of image analysis for PSD determination of nonwoven geotextiles is presented in this paper. The image analysis method was developed using various mathematical morphology algorithms to provide a complete PSD curve for each geotextile. The two characteristic pore opening sizes, O95 and O50, were determined from image analysis and were compared to the results from laboratory tests, analytical equations, as well as manufacturer’s reported apparent opening sizes (AOS). The image-based O95 pore opening size of various geotextiles was comparable to the manufacturer’s reported AOS as well as to those determined from the laboratory dry sieving test. However, the measured O50 pore opening size was lower than the one determined using the analytical equations developed by two previous researchers. Overall, the image analysis method presented provides a unique and accurate method that can measure fiber thickness and pore opening sizes in a cross-sectional image of a woven geotextile.     

Ceramic Filter for Small System Drinking Water Treatment: Evaluation of Membrane Pore Size and Importance of Integrity Monitoring

Ceramic filtration has recently been identified as a promising technology for drinking water treatment in households and small communities. This paper summarizes the results of a pilot-scale study conducted at the U.S. Environmental Protection Agency’s (EPA) Test & Evaluation (T&E) Facility in Cincinnati on two ceramic filtration cartridges with pore sizes of 0.05 and 0.01?μm to evaluate their ability to remove turbidity and microbiological contaminants such as bacteria [Bacillus subtilis ( ≈ 1.0?μm) and Escherichia coli ( ≈ 1.4?μm)], Cryptosporidium oocysts (4–6?μm), polystyrene latex (PSL) beads (2.85?μm) (a surrogate for Cryptosporidium), and MS2 bacteriophage ( ≈ 0.02?μm) (a surrogate for enteric viruses). The results demonstrated that the relatively tighter 0.01-μm cartridge performed better than the 0.05-μm cartridge in removing all the biological contaminants and surrogates. For turbidity removal, the 0.01-μm cartridge performed slightly better than the 0.05-μm cartridge; however, the permeate rate in the 0.01-μm cartridge reduced rapidly at higher feed water turbidity levels indicating that a tighter membrane should only be used with adequate pretreatment or at a low feed water turbidity to prolong membrane life. Microbiological monitoring was identified as a more sensitive indirect integrity monitoring method than turbidity and particle count monitoring to ensure effective treatment of water by ceramic filtration. Both PSL beads and B. subtilis showed potential as effective surrogates for Cryptosporidium, with B. subtilis showing higher degree of conservatism. Any opinions expressed in this article are those of the writer(s) and do not necessarily reflect the official positions and policies of the EPA. Any mention of products or trade names does not constitute recommendation for use by EPA. This document has been reviewed in accordance with EPA’s peer and administrative review policies and approved for publication.     

Analytic Solution on Critical Suspended Particle Size and Minimum Collection Efficiency in Deep Bed Filtration

Deep bed filtration is one of the most frequently employed water treatment techniques, and is routinely applied in the clarification of dilute particle suspensions. The prediction of critical suspended particle size is important due to the fact that the corresponding minimum collection efficiency is one of the primary considerations in the design of facilities based on filtration mechanisms. In this study, critical suspended particle size was studied analytically for the case of the Rajagopalan and Tien (RT) filtration model using a harmonic mean type of approximation, as well as a calculation of minimum collection efficiency. The obtained analytic solutions were then compared with the experimental and numerically calculated results, showing good agreement. This analytic solution for critical suspended particle size appears to be applicable to the determination of optimal conditions in deep-bed filtration protocols.     

Characterization of the Flocculation Process from the Evolution of Particle Size Distributions

A flocculator-imaging system was developed to characterize the dynamics of particle size distribution (PSD) during flocculation. The system consisted of a flocculator coupled with an external flow-through cell for observation and photography, a microscopic charge-coupled device video recorder with backlighting, and an image analyzer. This nonintrusive side-stream setup was used to record the evolution of the PSD to determine the flocculation dynamics of three types of particle systems: Clean kaolin, kaolin coated with natural organic matter (NOM), and the kaolin/NOM system after ozonation. In addition to the PSD measurement, the ζ potential, NOM reduction, and turbidity removal after the jar test of flocculation and sedimentation were determined for the particle systems at various alum dosages. The results of the ζ-potential analysis and the PSD measurement indicated that flocculation takes place rapidly to form highly porous aggregates when the particle surface charge is fully neutralized. The adsorption of NOM on the particle surface stabilized the particles considerably, and thus hindered the flocculation process. Sweep flocculation using a much higher alum dosage was an effective means of process enhancement for the removal of particulates and associated organic matter. Ozonation of the kaolin/NOM solution, however, did not appear to have any positive effect on particle destabilization and flocculation. It is argued that ozonation produced more acidic functional groups in the NOM on kaolin, which increased the surface charge density and hence the stability of the particles in softer water.     

Effective Diameter for Shear-Induced Diffusion for Characterizing Cake Formation in Crossflow Microfiltration at Polydisperse Conditions

During crossflow microfiltration, formation of cake layer on the membrane inhibits the filter performance. Previous studies on cake formation have focused on the monodisperse conditions, although most field applications are under the polydisperse conditions. In this study, microfiltration experiments were conducted to investigate the effect of particle size on cake formation, especially, at polydisperse conditions. Kaolin and two kinds of CaCO3 were used as polydisperse particles and a polysulfon hollow fiber microfilter was used as the membrane for the experiment. To describe the effect of particle size on cake formation at polydisperse conditions, effective diameter for shear-induced diffusion (EDSD) was introduced as a representative particle size. Statistical analyses of the experimental results showed that EDSD can be used in quantifying the potential of cake formation at polydisperse conditions, and the larger the EDSD, the thinner the cake layer. EDSD was an imperative indicator which showed the potential of cake formation at polydisperse conditions quantitatively and can be applied to find efficient strategies for reducing the cake layer.     

Modeling Uncoupled Solute Transport in Natural Organic Matter Size Fractionation by Ultrafiltration

Physicochemical separation of organic macrosolutes and colloidal particles is routinely required during the analysis of natural, waste, and process waters derived from aquatic and terrestrial environmental samples. This study was conducted to demonstrate the utility of a two-parameter nonlinear permeation coefficient model (PCM) in describing the uncoupled transport of solutes in dilute heterogeneous solutions subjected to batch ultrafiltration (UF). The PCM was used in conjunction with natural organic matter (NOM) permeate data for a natural water and six hydrophobic and hydrophilic subfractions to determine permeation coefficients p and NOM concentrations Cr0 with apparent molecular weight less than membrane specific cutoff values of moderately hydrophilic YC/YM series Amicon? UF membranes. Experimentally measured permeation coefficients p determined for the whole water were found to correlate well with composite permeation coefficients p? calculated using a mass-fraction weighted average of individual NOM subfraction permeation coefficient values. Correlation of experimentally measured and calculated permeation coefficient values (p and p?) indicated that the PCM can adequately describe uncoupled transport of chemically distinct solute fractions during batch UF of heterogeneous dilute solutions.     

Determination of Perchlorate Rejection and Associated Inorganic Fouling (Scaling) for Reverse Osmosis and Nanofiltration Membranes under Various Operating Conditions

This study focused on perchlorate (ClO4?) rejection and flux-decline in bench-scale cross-flow flat-sheet filtration for two reverse osmosis (RO) and two nanofiltration (NF) membranes with a natural water, and addressed estimation of precipitative fouling/scaling with inorganic salts and characterizations of inorganic fouling and antiscalants. Thus the study considered tradeoffs between productivity (increased recovery and flux) versus ClO4? rejection versus membrane fouling/scaling. In this study, the rejection of water quality parameters (cations, anions, dissolved organic carbon, UVA254, total dissolved solids) and flux-decline trends for four different membranes were investigated over a various range of operating conditions (i.e., J0/k ratio and recovery). Inorganic foulants on the membrane surface were analyzed by various methods (i.e., x-ray diffraction and scanning electron microscopy), and demonstrated inhibition effects of antiscalant. With increasing recovery and J0/k ratio, high productivity (flux) was achieved, however, the rejections of perchlorate and other water quality parameters decreased and the precipitative fouling/scaling potential of membranes increased. At the same operating conditions in the presence of an antiscalant, embodying phosphonate functional groups, flux decline trends for the four membranes indicated lower scale formation supported by the results of the fouled membrane characterizations.     

Evaluation of Apparatus for Membrane Cleaning Tests

Membrane cleaning is critical to the operation of membrane processes. This paper studies the impact of using four different types of bench-scale membrane systems to assess the effectiveness of different cleaning steps after the filtration of colored river water. The systems are a stirred ultrafiltration (UF) cell, a SEPA cell, a small cross-flow (CF) cell, and a six-CF-cell-in-parallel system. The effect of cleaning frequency was also investigated. The comparison was implemented in terms of flux recovery, solute removal, solute resistance removal, and changes of contact angles. The stirred UF cell was only reliable and comparable in terms of flux and flux recovery results. The six-cell-in-parallel system requires further development due to their much lower flux. For cleaning at 30-min intervals, the cleaning efficiency of membranes was similar for the three CF systems. For cleaning intervals of 2 and 4 h did not statistically affect the flux recovery for the stirred UF cell and SEPA cell. There was some irreversible fouling that could not be restored completely by clean-in-place method even with rigorous chemical treatment.     

Mechanistic Model for CaSO4 Fouling on Nanofiltration Membrane

One of the major limitations of nanofiltration (NF) in drinking water treatment is inorganic scaling. In this study, a mechanistic model has been proposed to describe the permeate flux decline process during CaSO4 scaling in NF. It has been observed that the permeate flux decline follows four distinct stages. At first stage, 22–30% flux is reduced due to concentration polarization. At the second stage, flux is not reduced, instead, nucleation of CaSO4 occurs. The major permeate flux decline (60–70%) occurred at the third stage due to CaSO4 cake formation. At the final stage, the system reached the steady state, where rate of CaSO4 deposition on the membrane is balanced by shearing caused by the increase of concentrate flow rate. Beyond this stage, the flux does not decrease significantly. At each stage, the concentration of the salt at the membrane surface was estimated. The maximum salt concentration was found at the initial stage of permeate flux reduction, which gradually decreases as the filtration proceeds.     

Radial Pore Diffusion with Nonuniform Intraparticle Porosities

Effects of radially dependent intraparticle pore sizes on solute fate and transport are examined for batch systems with spherical particles using a recently developed numerical model. The model can accommodate multiple particles distributed in size, mass transfer resistance at particle boundaries, intraparticle reversible sorption kinetics, and first-order decays. Two applications are examined. In the first application, random or deterministic intraparticle porosities across a spherical particle are considered. In the second application, multiple particles distributed in sizes with particle size-dependent intraparticle porosities are studied. Results from these applications indicate that concentration profiles are largely determined by interplays between B, η, and ε that incorporate the effects of intraparticle pore structures. Steady-state concentration values in both applications are determined by the volume-averaged intraparticle porosities. These results could be useful for understanding solute tailing behavior in natural porous media and the design of synthetic sorbents for treatment of contaminated waters.     

Impact of Membrane Surface Modification on the Treatment of Surface Water

New polyethersulfone (PES) based membranes for ultrafiltration (UF) were developed by blending a surface-modifying macromolecule (SMM) in the casting solution, in an attempt to minimize the impact of fouling. Fouling was evaluated using concentrated Ottawa River water (CORW), either unfractionated or fractionated via UF. These membranes also included some polyvinylpyrrolidone (PVP), a pore forming additive. A statistical analysis was conducted to evaluate the impact of some variables on the treatment of the surface water. The independent variables included PVP/PES ratio in the casting solution, with and without SMM, and the nature of the feed CORW [low molecular weight (LMW) fraction, unfractionated, high molecular weight (HMW) fraction]. The performance variables studied were total organic carbon (TOC) removal, the foulant accumulation at the membrane surface after filtration, the flux reduction, and the final permeate flux. The most important variable was the feed water. Filtration of LMW had a higher final flux, less fouling, but slightly lower TOC removal. The SMM did not significantly impact the membrane performance. TOC removal was high, compared with results reported in the literature for UF membranes.     

用激光粒度分析仪测定二氧化锆粒度

介绍以六偏磷酸钠作为分散剂，采用激光粒度分析仪测量二氧化锆粒度的一种新方法。该方法的测量范围为0．05～300μm。     

Evaluation of Membrane Processes for Reducing Total Dissolved Solids Discharged to the Truckee River

Truckee Meadows Water Reclamation Facility (TMWRF) is a 150,000?m3/day (40?mgd) tertiary wastewater treatment facility that serves the cities of Reno and Sparks, Nev. The effluent from TMWRF is discharged into the Truckee River which flows to Pyramid Lake—a very sensitive ecosystem and habitat for endangered species. Reverse osmosis (RO) and nanofiltration (NF), in conjunction with ultrafiltration (UF) pretreatment, were evaluated for total dissolved solids (TDS) and nutrient removal from the effluent of TMWRF at bench and pilot scale. Results from short-term pilot-scale tests showed that RO and NF membrane processes can successfully remove both TDS and nutrients from the effluent when paired with coagulation-enhanced UF pretreatment. NF membranes were able to achieve the necessary removal while maintaining higher fluxes and lower specific power consumption.     

In Situ Partial Exfiltration of Rainfall Runoff. II: Particle Separation

Metal elements or other constituents transported in urban and transportation land use rainfall runoff are often adsorbed on or incorporated with entrained particles that are ubiquitous in such runoff. Infiltration–exfiltration can be an effective in situ particle separation and quantity control structural best management practices or low impact development practices allowing runoff to return to soil after passive physical-chemical treatment. The in situ partial exfiltration reactor (PER), which combined the surface straining of the cementitious porous pavement (CPP) layer with filtration of oxide coated sand media beneath, provided control of water quantity and quality. Particle analyses were carried out for both influent and effluent to examine filter efficiency as a function of particle size and hydrology. Influent dm/dp ratios suggest that the dominant PER particle separation mechanisms were unsaturated physical–chemical filtration with the CPP layer functioning as a straining surface. Particle size distributions were modeled based on a two-parameter cumulative power-law function. The performance of the PER as a filter is shown to be a function of the unsteady site hydrology. Temporal variation in the filter coefficient and the volumetric particle fraction remaining were directly related to the unsteady influent loading rate. Particle removal efficiency by the PER based on concentration ranged from 71 to 96% on a mass-based concentration and 92–99% on a number based concentration. Results suggest that a properly designed PER can provide effective in situ control for particles and could be combined with or function separately from source control (i.e., pavement cleaning or a mass trading framework).     

Hydrophobicity and Molecular Size Distribution of Unknown TOX in Drinking Water

The analysis of total organic halogen (TOX) in drinking water indicates that a substantial amount of the halogenated compounds cannot be accounted for by known specific disinfection by-products (DBPs). The primary aim of this research was to characterize the hydrophobicity and molecular size distribution of the unknown halogenated DBPs using XAD resins and ultrafiltration membranes. The impact of membrane rejection on the size analysis of unknown TOX was also investigated using chlorinated fulvic acid. Six finished waters from different locations and treatment processes were collected and fractionated into various hydrophobicity and molecular size groups. The results showed that most unknown TOX was in the size range between 0.5?kDa and 10?kDa, but it could have a wide spectrum of hydrophobicities. Simple ultrafiltration was not always reliable as a characterization tool, as it was shown to reject a significant fraction of DBPs with molecular weight (MW) lower than the membrane cutoffs. Flushing with deionized water was effective in removing these low MW compounds from the ultrafiltration cell. A significant reduction in the apparent size of unknown TOX resulted when low MW DBPs were flushed out of the cell (comparing with classic parallel ultrafiltration). Coagulation of fulvic acid also significantly reduced the apparent size of unknown TOX formed by chlorine.     

Use of Membrane Bioreactor for Biodegradation of MTBE in Contaminated Water

An ultrafiltation membrane bioreactor was evaluated for biodegradation of methyl tert-butyl ether (MTBE) in contaminated water. The system was fed 5 mg/L MTBE in granular activated carbon (GAC) treated Cincinnati tap water containing ample buffer and nutrients. Within 120 days the culture had adapted to membrane operational conditions and was consistently achieving greater than 99.95% biological removal of both MTBE and tert-butyl alcohol. This condition was steadily maintained for the next 200 days of study. Effluent dissolved organic carbon values remained at or below concentrations of the feed GAC treated tap water alone. An increase in biomass concentration as measured by volatile suspended solids was observed to correlate with an increase in MTBE removal efficiency. Some operational observations, including fouling, recovery from an accident, and overall performance, are described.     

Removal of 17β Estradiol and Fluoranthene by Nanofiltration and Ultrafiltration

With the recent emergence of endocrine disrupting compounds as an important potable drinking water and reclaimed wastewater quality issue, the removal of two estrogenic compounds (17β-estradiol and fluoranthene) by nanofiltration and ultrafiltration membranes was investigated. A less hydrophobic organic compound model species [parachlorobenzoic acid (PCBA)] was tested. 17β-estradiol (E2), fluoranthene, and PCBA were applied to the membrane in the presence and absence of natural organic matter (NOM). Both batch adsorption and dead-end stirred-cell filtration experiments indicated that adsorption is an important mechanism for transport/removal of relatively hydrophobic compounds, and is related to the octanol-water partition coefficient (KOW) values. All filtration measurements were performed approximately the same permeate flow rate in order to minimize artifacts from concentration polarization varied with different hydrodynamic operating conditions at the membrane interface. The percent removal by dead-end stirred-cell filtration ranged from 10 to >95% depending upon membrane pore size/hydrophobicity and presence/absence of NOM at an initial concentration ranging from 0.1 to 0.5 μM. Additional batch adsorption experiments with radio-label (3H) E2 at lower concentrations ranging 0.025 to 5 nM showed that E2 removal due to adsorption was independent of its initial concentration. Adsorption occurs both on the membrane surface and interior membrane pore surfaces. However, adsorption was insignificant for PCBA (log?KOW = 2.7), but removal presumably occurred due to electrostatic exclusion. Partition coefficients (log?K) of 0.44 to 4.86 measured in this study increased with log?KOW and membrane pore size.     

Application of Cross-Flow Microfiltration for the Treatment of Combined Sewer Overflow Wastewater

Application of cross-flow microfiltration with and without backpulsing is evaluated for the treatment of dilute primary sewage effluent simulating combined sewer overflow wastewater. Four alpha alumina ceramic membranes of various pores sizes (0.2–5.0?μm) were tested to understand the impact of cross-flow velocity and transmembrane pressure on the permeate water quality and flux rate. The 0.2 and 0.8?μm membranes produced a permeate water quality that is likely to be suitable for surface water discharge. The combination of permeate chemical and biological water quality and long-term flux rates suggest that a 0.2?μm membrane would be the most appropriate membrane for the treatment of combined sewer overflow wastewater within sewersheds.     

Biological Kinetic Data Evaluation of an Activated Sludge System Coupled with an Ultrafiltration Membrane

A membrane bioreactor (MBR) system treating wastewater containing high molecular weight compounds was operated at solids retention times (SRTs) ranging from 30 to 2 days. Chemical oxygen demand removal efficiencies exceeded 99% and effective nitrification was obtained at SRTs between 30 and 5 days. A significant shift in the biological population structure was observed at the 2 days SRT as the content of gram-negative microorganisms increased and nitrifying bacteria were washed out. At this low SRT, limitations in the biological reaction kinetics resulted in incomplete degradation of the feed protein increasing the presence of soluble organic matter in the effluent. Furthermore, the diluted mixed liquor prevented the formation of a filtration cake on the membrane surface, further deteriorating effluent quality. Biological kinetic data parameters were analyzed using three different representations for biomass: volatile suspended solids, lipid phosphates, and total enzymatic activity. All three indicators exhibited similar trends resulting in very comparable estimates for endogenous decay coefficients, thus demonstrating the reliability of volatile suspended solids as a measure for biological activity in activated sludge. Lower than typical endogenous decay rates in the MBR suggested favorable environmental conditions for respiration and a lower potential for self oxidation and predation. The true yield coefficient was in the range of conventional activated sludge systems, refuting previous suggestions of lower yields in MBRs.     

Particle Characterization and Settling Velocities for a Water Supply Reservoir during a Turbidity Event

Characterization of the particle population for a location in a water supply reservoir, Kensico Reservoir, N.Y., is documented for a high turbidity event, from its onset, through alum treatment and its waning. Supporting in situ measurements included the beam attenuation coefficient at 670?nm (c670) and 660?nm (c660) [surrogates of turbidity (Tn)], particle concentrations (N) and size distributions (PSDs), and size class specific settling velocities (SVs). Laboratory measurements included chemical and morphometric analyses of individual particles, and routine measurements of Tn. The turbidity is shown to be primarily derived from clay minerals, mostly in the size range of 1.5–6?μm. An initial high c670 level (40?m?1;Tn ～ 100?NTU) decreased sevenfold in less than 1?week in response to alum treatment that largely eliminated the particle size classes responsible for the elevated turbidity. Successful SV experiments, made using a laser in situ scattering and transmissometry (LISST) instrument, for seven particle size classes in the range of 1.25–129?μm yielded SV values of 0.17–69.4?m?day?1. Size classes larger than ～ 5?μm settled much slower than Stokes law predictions, before alum treatment, indicating that these classes existed as porous flocs or aggregates. Decreases in SVs following treatment suggest changes in floc character consistent with increased porosity. In situ measurements of c670, N, PSDs, and SVs can contribute to the development and testing of a multiple particle size class model to simulate fate, transport, and impacts of suspended particles.