Integrating Navajo Pottery Techniques To Improve Silver Nanoparticle-Enabled Ceramic Water Filters for Disinfection

Point-of-use treatment technologies can increase access to safe drinking water in rural areas. Sustained use of these technologies is uncommon due to oversight of community needs, user-perceived risks, long-term maintenance, and conflict with traditional practices. Nanosilver-enabled ceramic water filters are unique due to the use of locally sourced materials available at or near the target community; however, technical limitations persist (e.g., nanosilver's uncontrolled release and passivation from sulfide or chloride). This work aims to overcome these limitations by impregnating nanosilver onto ceramics with a Navajo pottery rosin, collected from pinyon trees with a third-generation artisan. Here, we investigate this sustainable and novel material for drinking water treatment; the study ranges from a proof of concept to testing under realistic conditions. Results show that when embedded in a thin film, the biopolymer controlled ionic silver dissolution and prevented silver passivation from sulfide and chloride. When applied to ceramic filters, the biopolymer effectively immobilized nanosilver in a range of waters. Over a 25 day study to emulate household-use conditions, this coating method sustained disinfection of a coculture of Gram-positive and Gram-negative bacteria while controlling biofouling. Overall, the use of this Navajo pottery material can facilitate adoption while providing the needed technological advancement to these widely used treatment devices.

Protozoan-Priming and Magnesium Conditioning Enhance Legionella pneumophila Dissemination and Monochloramine Resistance

Opportunistic pathogens (OPs) are of concern in drinking water distribution systems because they persist despite disinfectant residuals. While many OPs garner protection from disinfectants via a biofilm lifestyle, Legionella pneumophila (Lp) also gains disinfection resistance by being harbored within free-living amoebae (FLA). It has been long established, but poorly understood, that Lp grown within FLA show increased infectivity toward subsequent FLA or human cells (i.e., macrophage), via a process we previously coined "protozoan-priming". The objectives of this study are (i) to identify in Lp a key genetic determinant of how protozoan-priming increases its infectivity, (ii) to determine the chemical stimulus within FLA to which Lp responds during protozoan-priming, and (iii) to determine if more infectious forms of Lp also exhibit enhanced disinfectant resistance. Using Acanthamoeba castellanii as a FLA host, the priming effect was isolated to Lp's sidGV locus, which is activated upon sensing elevated magnesium concentrations. Supplementing growth medium with 8 mM magnesium is sufficient to produce Lp grown in vitro with an infectivity equivalent to that of Lp grown via the protozoan-primed route. Both Lp forms with increased infectivity (FLA-grown and Mg2+-supplemented) exhibit greater monochloramine resistance than Lp grown in standard media, indicating that passage through FLA not only increases Lp's infectivity but also enhances its monochloramine resistance. Therefore, laboratory-based testing of disinfection strategies should employ conditions that simulate or replicate intracellular growth to accurately assess disinfectant resistance.

A Structural Equation Model to Decipher Relationships among Water, Sanitation, and Health in Colonias-Type Unincorporated Communities

The colonias along the United States-Mexico border are generally self-built neighborhoods of low-income families that lack basic infrastructure. While some government assistance has provided roads and electricity, water and wastewater services are still lacking in many colonias. This research is the first to collect a comprehensive dataset on water, sanitation, health, and living conditions in these unincorporated neighborhoods through collection of water samples and surveys; 114 households in 23 colonias across three geographically diverse Texas counties are studied. Water quality is assessed via traditional microbial indicators, chlorine, and arsenic. This complex dataset requires an advanced statistical tool to disentangle relationships among diverse factors. Structural equation modeling is utilized to identify relationships among surveyed and measured variables. The model reveals that colonias residents with well/hauled water accurately predict their water quality, while those with treated+piped water tend to think that their water is worse than it actually is. Dwelling quality and connection to sanitary sewers influence perceived health risks and household health, respectively. Furthermore, these communities have an overwhelming need and desire for point-of-use water treatment. This model can inform decision making and may be adapted to probe other questions and social dynamics for water and sanitation in unincorporated communities elsewhere.

Designing Solute-Tailored Selectivity in Membranes: Perspectives for Water Reuse and Resource Recovery

Treatment of nontraditional source waters (e.g., produced water, municipal and industrial wastewaters, agricultural runoff) offers exciting opportunities to expand water and energy resources via water reuse and resource recovery. While conventional polymer membranes perform water/ion separations well, they do not provide solute-specific separation, a key component for these treatment opportunities. Herein, we discuss the selectivity limitations plaguing all conventional membranes, which include poor removal of small, neutral solutes and insufficient discrimination between ions of the same valence. Moreover, we present synthetic approaches for solute-tailored selectivity including the incorporation of single-digit nanopores and solute-selective ligands into membranes. Recent progress in these areas highlights the need for fundamental studies to rationally design membranes with selective moieties achieving desired separations.

Seasonal contamination of well-water in flood-prone colonias and other unincorporated U.S. communities

Many of the six million residents of unincorporated communities in the United States depend on well-water to meet their needs. One group of unincorporated communities is the colonias, located primarily in several southwestern U.S. states. Texas is home to the largest number of these self-built communities, of mostly low-income families, lacking basic infrastructure. While some states have regulations that mandate minimum infrastructure for these communities, water and sewage systems are still lacking for many of their residents. Unprotected wells and self-built septic/cesspool systems serve as the primary infrastructure for many such colonias. This research was designed to probe how wells and septic/cesspool systems are influenced by heavy rainfall events. Such events are hypothesized to impact water quality with regard to human health. Inorganic and microbiological water quality of the wells in nine colonias located in Nueces County, Texas, were evaluated during dry and wet periods. Nueces County was selected as an example based on its flooding history and the fact that many colonias there depend entirely on well-water and septic/cesspool systems. The results demonstrate that well-water quality in these communities varies seasonally with respect to arsenic (up to 35 μg/L) and bacterial contamination (Escherichia coli), dependent on the amount of rainfall, which leaves this population vulnerable to health risks during both wet and dry periods. Microbial community analyses were also conducted on selected samples. To explore similar seasonal contamination of well-water, an analysis of unincorporated communities, flooding frequency, and arsenic contamination in wells was conducted by county throughout the United States. This nationwide analysis indicates that unincorporated communities elsewhere in the United States are likely experiencing comparable challenges for potable water access because of a confluence of socioeconomic, infrastructural, and policy realities.

Water Treatment: Are Membranes the Panacea?

Alongside the rising global water demand, continued stress on current water supplies has sparked interest in using nontraditional source waters for energy, agriculture, industry, and domestic needs. Membrane technologies have emerged as one of the most promising approaches to achieve water security, but implementation of membrane processes for increasingly complex waters remains a challenge. The technical feasibility of membrane processes replacing conventional treatment of alternative water supplies (e.g., wastewater, seawater, and produced water) is considered in the context of typical and emerging water quality goals. This review considers the effectiveness of current technologies (both conventional and membrane based), as well as the potential for recent advancements in membrane research to achieve these water quality goals. We envision the future of water treatment to integrate advanced membranes (e.g., mixed-matrix membranes, block copolymers) into smart treatment trains that achieve several goals, including fit-for-purpose water generation, resource recovery, and energy conservation.

Laccase removal of 2-chlorophenol and sulfamethoxazole in municipal wastewater

Laccases were studied for their ability to remove two compounds, 2-chlorophenol and sulfamethoxazole, in batch studies, both in buffered solutions and in wastewater samples from different points in a municipal water resource recovery facility. Two enzymes with and without a mediator (acetosyringone) were investigated: a commercial product derived from Myceliphthora thermophile and a laboratory-generated enzyme mix derived from Tramates versicolor. The chlorophenol was removed rapidly by the commercial enzyme in the presence of acetosyringone, but the primary products were coupling complexes of the reactants. Excellent removal was achieved without acetosyringone by the natural enzyme mix. Sulfamethoxazole was poorly removed in all laboratory-generated chemically buffered solutions, but was very well removed, without the addition of mediators, in secondary effluent suspensions from a municipal water resource recovery facility. Mechanistic studies are still required, but the results suggest that treatment via direct addition of enzymes is feasible to remove recalcitrant compounds in municipal wastewater.

Transformation kinetics of cyclophosphamide and ifosfamide by ozone and hydroxyl radicals using continuous oxidant addition reactors

The detection of pharmaceuticals in water and wastewater has triggered human and ecological health concerns. As highly toxic compounds, chemotherapy agents (CAs), such as the cyclophosphamide (CYP) and ifosfamide (IFO) structural isomers, represent a unique threat. This research elucidated the fate of CYP and IFO during ozonation and advanced oxidation by hydroxyl radicals (HO^•). Novel semi-batch reactors were used to determine the second-order rate constants for CYP and IFO with O₃ and HO^•. These reactors provided independent control of the oxidant exposure through continuous and constant aqueous ozone and peroxone (O₃-H₂O₂) addition. The rate constants for transformation of CYP and IFO by ozone were 2.58 ± 0.40 M^-1s^-1 and 6.95 ± 0.21 M^-1s^-1, respectively, indicating that ozone alone is not suitable for treating CAs. Transformation of CYP and IFO by hydroxyl radicals was fast, with rate constants of 2.69(±0.17)×10⁹ M^-1s^-1 and 2.73(±0.16)×10⁹ M^-1s^-1, respectively. The major transformation products formed by O₃ and HO attack consisted of the 4-hydroxy-, 4-keto-, dechloroethyl-, and imino- derivatives of CYP and IFO. Low yields of the active metabolites of the CAs, namely phosphoramide mustard and isophosphoramide mustard, were detected. These findings suggest that treated water may retain the ability to alkylate DNA and confer toxicity.

Perceived versus actual water quality: Community studies in rural Oaxaca, Mexico

Compromised water quality risks public health, which becomes particularly acute in economically marginalized communities. Although the majority of the clean-water-deprived population resides in Sub-Saharan Africa and Asia, a significant portion (32 million) lives in Meso- and Latin-America. Oaxaca is one of the marginalized southern states of Mexico, which has experienced high morbidity from infectious diseases and also has suffered from a high rate of infant mortality. However, there has been a paucity of reports on the status of water quality of culturally diverse rural Oaxaca. This study follows community-based participatory research methods to address the data gap by reporting on water quality (chemical and microbiological) and by exploring social realities and water use practices within and among communities. Surveys and water quality analyses were conducted on 73 households in three rural communities, which were selected based on the choice of water sources (i.e., river water, groundwater, and spring water). Statistically significant variations among communities were observed including the sanitation infrastructure (p-value 0.001), public perception on water quality (p-value 0.007), and actual microbiological quality of water (p-value 0.001). Results indicate a high prevalence of diarrheal diseases, a desire to improve water quality and reduce the cost of water, and a need for education on water quality and health in all the surveyed communities. The complexities among the three studied communities highlight the need for undertaking appropriate policies and water treatment solutions.

Differential diagnosis in archaeology

Diagnosing archaeological bone specimens can be likened to practices used in medical and veterinary medical health care. Increasing the rigor of archaeological diagnosis can be supported by a systematic approach derived from health care settings. The process of information synthesis and diagnosis can be viewed as being very similar among these disciplines. A first diagnostic step is developing an Initial Information Set (sometimes called an Initial Database in health care environments) from descriptive data about the archaeological specimen or the patient, accompanied by recording environmental and ecological observations. The second diagnostic step is to develop an Expanded Information Set that includes structured physical examination, constructing a problem list, and considering potential differential diagnoses for each recorded problem. Subsequently, a Diagnostics Information Set consists of outcomes of carefully selected diagnostic testing, and a Diagnostic Assessment is developed from an orderly mental synthesis of information across Information Sets. Critical aspects of a structured and orderly process are preparing inclusive differential diagnoses, thorough mental synthesis across Information Sets, and recognizing that a short list of the most plausible diagnostic alternatives may represent the furthest possible extent of the evaluation for many archaeological bone specimens.

Multilevel modeling of retention and disinfection efficacy of silver nanoparticles on ceramic water filters

This research examined how variations in synthesis methods of silver nanoparticles affect both the release of silver from ceramic water filters (CWFs) and disinfection efficacy. The silver nanoparticles used were stabilized by four different molecules: citrate, polyvinylpyrrolidone, branched polyethylenimine, and casein. A multilevel statistical model was built to quantify if there was a significant difference in: a) extent of silver lost, b) initial amount of silver lost, c) silver lost for water of different quality, and d) total coliform removal. Experiments were performed on location at Pure Home Water, a CWF factory in Tamale, Ghana using stored rainwater and dugout water (a local surface water). The results indicated that using dugout vs. rainwater significantly affects the initial (p-value 0.0015) and sustained (p-value 0.0124) loss of silver, but that silver type does not have a significant effect. On average, dugout water removed 37.5μg/L more initial silver and had 1.1μg/L more silver in the filtrate than rainwater. Initially, filters achieved 1.9 log reduction values (LRVs) on average, but among different silver and water types this varied by as much as 2.5 LRV units. Overall, bacterial removal effectiveness was more challenging to evaluate, but some data suggest that the branched polyethylenimine silver nanoparticles provided improved initial bacterial removal over filters which were not painted with silver nanoparticles (p-value 0.038).

Incentivizing Decentralized Sanitation: The Role of Discount Rates

In adoption decisions for decentralized sanitation technologies, two decision makers are involved: the public utility and the individual homeowner. Standard life cycle cost is calculated from the perspective of the utility, which uses a market-based discount rate in these calculations. However, both decision-makers must be considered, including their differing perceptions of the time trade-offs inherent in a stream of costs and benefits. This study uses the discount rate as a proxy for these perceptions and decision-maker preferences. The results in two case studies emphasize the dependence on location of such analyses. Falmouth, Massachusetts, appears to be a good candidate for incentivizing decentralized sanitation while the Allegheny County Sanitary Authority service area in Pennsylvania appears to have no need for similar incentives. This method can be applied to any two-party decision in which the parties are expected to have different discount rates.

DLVO Approximation Methods for Predicting the Attachment of Silver Nanoparticles to Ceramic Membranes

This article examines the influence of three common stabilizing agents (citrate, poly(vinylpyrrolidone) (PVP), and branched poly(ethylenimine) (BPEI)) on the attachment affinity of silver nanoparticles to ceramic water filters. Citrate-stabilized silver nanoparticles were found to have the highest attachment affinity (under conditions in which the surface potential was of opposite sign to the filter). This work demonstrates that the interaction between the electrical double layers plays a critical role in the attachment of nanoparticles to flat surfaces and, in particular, that predictions of double-layer interactions are sensitive to boundary condition assumptions (constant charge vs constant potential). The experimental deposition results can be explained when using different boundary condition assumptions for different stabilizing molecules but not when the same assumption was assumed for all three types of particles. The integration of steric interactions can also explain the experimental deposition results. Particle size was demonstrated to have an effect on the predicted deposition for BPEI-stabilized particles but not for PVP.

Comprehensive understanding of nano-sized particle separation processes using nanoparticle tracking analysis

The understanding of nano-sized particle separation processes has been limited by difficulties of nanoparticle characterization. In this study, nanoparticle tracking analysis (NTA) was deployed to evaluate the absolute particle size distributions in laboratory scale flocculation and filtration experiments with silver nanoparticles. The results from NTA were consistent with standard theories of particle destabilization and transport. Direct observations of changes in absolute particle size distributions from NTA enhance both qualitative and quantitative understanding of particle separation processes of nano-sized particles.

Competitive separation of di- vs. mono-valent cations in electrodialysis: effects of the boundary layer properties

In electrodialysis desalination, the boundary layer near ion-exchange membranes is the limiting region for the overall rate of ionic separation due to concentration polarization over tens of micrometers in that layer. Under high current conditions, this sharp concentration gradient, creating substantial ionic diffusion, can drive a preferential separation for certain ions depending on their concentration and diffusivity in the solution. Thus, this study tested a hypothesis that the boundary layer affects the competitive transport between di- and mono-valent cations, which is known to be governed primarily by the partitioning with cation-exchange membranes. A laboratory-scale electrodialyzer was operated at steady state with a mixture of 10mM KCl and 10mM CaCl(2) at various flow rates. Increased flows increased the relative calcium transport. A two-dimensional model was built with analytical solutions of the Nernst-Planck equation. In the model, the boundary layer thickness was considered as a random variable defined with three statistical parameters: mean, standard deviation, and correlation coefficient between the thicknesses of the two boundary layers facing across a spacer. Model simulations with the Monte Carlo method found that a greater calcium separation was achieved with a smaller mean, greater standard deviation, or more negative correlation coefficient. The model and experimental results were compared for the cationic transport number as well as the current and potential relationship. The mean boundary layer thickness was found to decrease from 40 to less than 10 μm as the superficial water velocity increased from 1.06 to 4.24 cm/s. The standard deviation was greater than the mean thickness at slower water velocities and smaller at faster water velocities.

The influence of hydraulic loads on depth filtration

The influence of hydraulic loads on the detachment of particles from the collector surface or from previously retained particles was observed in a packed glass beads column. A hydraulic shock load (i.e., 20% increase of flow rate) was applied after 4 h of particle attachment at a constant flow rate. A single type of particle suspension (Min-U-Sil 5, nearly pure SiO(2)) and three different chemical conditions (pH control, alum and polymer destabilization) were utilized. The magnitude of particle detachment increased with increasing particle size for non-Brownian particles because more shear force was applied to large particles due to their large surface area. More favorable particles (i.e., particles with small surface charge) were detached to a lesser extent than unfavorable particles during the hydraulic shock loads application. This phenomenon can be caused by floc strength. In some cases, when the zeta potential of influent particles was relatively high, the magnitude of detachment of bigger particles (e.g., 4.0-5.0 μm) was less than that of smaller particles (e.g., 3.0-4.0 μm). This can be attributable to the breakup of detached flocs as an individual particle. It was also found that the shape of the curve relating the magnitude of particle detachment and particle size can be concave, linear, or convex depending on physicochemical conditions such as floc strength.

Laccase-catalyzed oxidation of oxybenzone in municipal wastewater primary effluent

Pharmaceuticals and personal care products (PPCPs) are now routinely detected in raw and treated municipal wastewater. Since conventional wastewater treatment processes are not particularly effective for PPCP removal, treated wastewater discharges are the main entry points for PPCPs into the environment, and eventually into our drinking water. This study investigates the use of laccase-catalyzed oxidation for removing low concentrations of PPCPs from municipal wastewater primary effluent. Oxybenzone was selected as a representative PPCP. Like many other PPCPs, it is not recognized directly by the laccase enzyme. Therefore, mediators were used to expand the oxidative range of laccase, and the efficacy of this laccase-mediator system in primary effluent was evaluated. Eight potential mediators were investigated, and 2,2'-Azino-bis(3-ethylbenzthiazoline-6sulphonic acid) diammonium salt (ABTS), a synthetic mediator, and acetosyringone (ACE), a natural mediator, provided the greatest oxybenzone removal efficiencies. An environmentally relevant concentration of oxybenzone (43.8 nM, 10 μg/L) in primary effluent was completely removed (below the detection limit) after two hours of treatment with ABTS, and 95% was removed after two hours of treatment with ACE. Several mediator/oxybenzone molar ratios were investigated at two different initial oxybenzone concentrations. Higher mediator/oxybenzone molar ratios were required at the lower (environmentally relevant) oxybenzone concentration, and ACE required higher molar ratios than ABTS to achieve comparable oxybenzone removal. Oxybenzone oxidation byproducts generated by the laccase-mediator system were characterized and compared to those generated during ozonation. Enzymatic treatment generated byproducts with higher mass to charge (m/z) ratios, likely due to oxidative coupling reactions. The results of this study suggest that, with further development, the laccase-mediator system has the potential to extend the treatment range of laccase to PPCPs not directly recognized by the enzyme, even in a primary effluent matrix.

The effect of antiscalant addition on calcium carbonate precipitation for a simplified synthetic brackish water reverse osmosis concentrate

The primary limitations to inland brackish water reverse osmosis (RO) desalination are the cost and technical feasibility of concentrate disposal. To decrease concentrate volume, a side-stream process can be used to precipitate problematic scaling salts and remove the precipitate with a solid/liquid separation step. The treated concentrate can then be purified through a secondary reverse osmosis stage to increase overall recovery and decrease the volume of waste requiring disposal. Antiscalants are used in an RO system to prevent salt precipitation but might affect side-stream concentrate treatment. Precipitation experiments were performed on a synthetic RO concentrate with and without antiscalant; of particular interest was the precipitation of calcium carbonate. Particle size distributions, calcium precipitation, microfiltration flux, and scanning electron microscopy were used to evaluate the effects of antiscalant type, antiscalant concentration, and precipitation pH on calcium carbonate precipitation and filtration. Results show that antiscalants can decrease precipitate particle size and change the shape of the particles; smaller particles can cause an increase in microfiltration flux decline during the solid/liquid separation step. The presence of antiscalant during precipitation can also decrease the mass of precipitated calcium carbonate.

Effect of antiscalants on precipitation of an RO concentrate: metals precipitated and particle characteristics for several water compositions

Inland brackish water reverse osmosis (RO) is economically and technically limited by the large volume of salty waste (concentrate) produced. The use of a controlled precipitation step, followed by solid/liquid separation (filtration), has emerged as a promising side-stream treatment process to treat reverse osmosis concentrate and increase overall system recovery. The addition of antiscalants to the RO feed prevents precipitation within the membrane system but might have a deleterious effect on a concentrate treatment process that uses precipitation to remove problematic precipitates. The effects of antiscalant type and concentration on salt precipitation and precipitate particle morphology were evaluated for several water compositions. The primary precipitate for the synthetic brackish waters tested was calcium carbonate; the presence of magnesium, sulfate, minor ions, and antiscalant compounds affected the amount of calcium precipitated, as well as the phases of calcium carbonate formed during precipitation. Addition of antiscalant decreased calcium precipitation but increased incorporation of magnesium and sulfate into precipitating calcium carbonate. Antiscalants prevented the growth of nucleated precipitates, resulting in the formation of small (100-200 nm diameter) particles, as well as larger (6-10 microm) particles. Elemental analysis revealed changes in composition and calcium carbonate polymorph with antiscalant addition and antiscalant type. Results indicate that the presence of antiscalants does reduce the extent of calcium precipitation and can worsen subsequent filtration performance.

Effect of softening precipitate composition and surface characteristics on natural organic matter adsorption

Natural organic matter (NOM) removal during water softening is thought to occur through adsorption onto or coprecipitation with calcium and magnesium solids. However, details of precipitate composition and surface chemistry and subsequent interactions with NOM are relatively unknown. In this study, zeta potentiometry analyses of precipitates formed from inorganic solutions under varying conditions (e.g., Ca-only, Mg-only, Ca + Mg, increasing lime or NaOH dose) indicated that both CaCO3 and Mg(OH)2 were positively charged at higher lime (Ca(OH)2) and NaOH doses (associated with pH values above 11.5), potentially yielding a greater affinity for adsorbing negatively charged organic molecules. Environmental scanning electron microscopy (ESEM) images of CaCO3 solids illustrated the rhombohedral shape characteristic of calcite. In the presence of increasing concentrations of magnesium, the CaCO3 rhombs shifted to more elongated crystals. The CaCO3 solids also exhibited increasingly positive surface charge from Mg incorporation into the crystal lattice, potentially creating more favorable conditions for adsorption of organic matter. NOM adsorption experiments using humic substances extracted from Lake Austin and Missouri River water elucidated the role of surface charge and surface area on adsorption.

Reverse osmosis desalination: water sources, technology, and today's challenges

Reverse osmosis membrane technology has developed over the past 40 years to a 44% share in world desalting production capacity, and an 80% share in the total number of desalination plants installed worldwide. The use of membrane desalination has increased as materials have improved and costs have decreased. Today, reverse osmosis membranes are the leading technology for new desalination installations, and they are applied to a variety of salt water resources using tailored pretreatment and membrane system design. Two distinct branches of reverse osmosis desalination have emerged: seawater reverse osmosis and brackish water reverse osmosis. Differences between the two water sources, including foulants, salinity, waste brine (concentrate) disposal options, and plant location, have created significant differences in process development, implementation, and key technical problems. Pretreatment options are similar for both types of reverse osmosis and depend on the specific components of the water source. Both brackish water and seawater reverse osmosis (RO) will continue to be used worldwide; new technology in energy recovery and renewable energy, as well as innovative plant design, will allow greater use of desalination for inland and rural communities, while providing more affordable water for large coastal cities. A wide variety of research and general information on RO desalination is available; however, a direct comparison of seawater and brackish water RO systems is necessary to highlight similarities and differences in process development. This article brings to light key parameters of an RO process and process modifications due to feed water characteristics.

Particle size distribution dynamics during precipitative softening: constant solution composition

In the treatment of surface water for potable use, precipitative coagulation (e.g., lime softening, alum or iron sweep coagulation) is widely utilized prior to particle removal processes. The particle size distribution (PSD) formed during such processes is a prime determinant of the removal efficiency for suspended and dissolved contaminants, but little is known quantitatively about how PSDs change by simultaneous precipitation and flocculation. Using precipitative softening as an example, detailed measurements of the PSD (using electronic particle counting) were made during precipitation of CaCO(3) under conditions of constant solution composition. Examination of the time-varying PSDs revealed dramatic changes resulting from nucleation, crystal growth, and flocculation. The influence of the saturation ratio, seed concentration, and mixing intensity on those processes was quantified. Implications with respect to the design and operation of water treatment facilities are discussed.

Neonatal and pediatric care of the puppy and kitten

Although the interval from birth to weaning is brief for dogs and cats, it is a very intensive period of adjustment to the extrauterine environment and preparation for the relatively greater independence of post-weaning. This rapid progression of events is preceded by critical developmental transitions, including organogenesis and parturition, and it is characterized by postparturient transitions that include the 3-4d neonatal period, the 21-28 maturation, and weaning itself. The purpose of this discussion is to characterize the primary events of these five transitional zones and to describe practical methods for evaluating progression through each transition, for establishing differential diagnoses, and for supportive actions and responses.

Influence of surface charge distributions and particle size distributions on particle attachment in granular media filtration

Filtration experiments were performed with a laboratory-scale filter using spherical glass beads with 0.55 mm diameter as collectors. Suspensions were made with Min-U-Sil 5 particles, and two different methods (pH control and polymer dosing) were used for destabilization. In the pH control experiments, all particles had negative surface charge, and those with lower (absolute value) charge were selectively attached to the collectors, especially during the early stage of filtration. This selective attachment of the lower charged particles caused the zeta potential distribution (ZPD) of the effluent to move to a more negative range. However, the ZPD of the effluent did not continue moving to more negative values during the later stages of filtration, and this result was attributed to two reasons: ripening effects and detachment of flocs. In the polymer experiments, substantial differences were found between experiments performed with negatively charged particles (underdosing) and those with positively charged particles (overdosing). With under-dosing, the results were similar to the pH control experiments (which also had negatively charged particles), but with overdosing, the effluent's ZPDs in the early stages did not overlap with those of the influent and more highly charged particles were removed more efficiently than lesser-charged particles. It is hypothesized that, despite a substantial period of pre-equilibration of media and coagulant, this equilibrium shifted when particles were also added. It was assumed that coagulant molecules previously adsorbed to the particles desorbed and subsequently attached to the filter media because of surface area differences in the particle and filter media.

Particle detachment during hydraulic shock loads in granular media filtration

Particle breakthrough can occur by either the breakoff of previously captured particles (or flocs) or the direct passage of some influent particles through the filter. Filtration experiments were performed in a laboratory-scale filter using spherical glass beads with a diameter of 0.55 mm as collectors. A single type of particle suspension (Min-U-Sil 5) and three different destabilisation methods (pH control, alum and polymer destabilisation) were used to destabilise particles. The filtration velocity of 5 m/h was similar to that used in standard media filtration practice. To assess the possibility of particle detachment during normal filtration, a hydraulic shock load (20% increase of flow rate) was applied after 4 h of normal filtration. The magnitude of particle detachment was proportional to the particle size for non-Brownian particles. At the same time, less favourable particles, i.e. particles with larger surface charge, were easily detached during the hydraulic shock load. Therefore, proper particle destabilisation before filtration is crucial for maximum particle removal, as well as minimum particle breakthrough.

Granular media filtration: old process, new thoughts

The design of granular media filters has evolved over many years so that modern filters have larger media sizes and higher filtration velocities than in earlier times. The fundamental understanding of filtration has also improved over time, with current models that account reasonably for all characteristics of the media, the suspension and the filter operation. The methodology for design, however, has not kept pace with these improvements; current designs are based on pilot plants, past experience, or a simple guideline (the ratio of the bed depth to media grain size). We propose that design should be based universally on a characteristic removal length, with the provision of a bed depth that is some multiple of that characteristic length. This characteristic removal length is calculated using the most recent (and most complete) fundamental model and is based on the particle size with the minimum removal efficiency in a filter. The multiple of the characteristic length that yields the required bed depth has been calibrated to existing, successful filters.

Integral water treatment plant modeling: improvements for particle processes

An update of research on particle behavior in water treatment plants first performed 25 years ago under the direction of Charles O'Melia is provided. The earlier work involved mathematical modeling of the changes in particle size distributions in the flocculation and sedimentation processes in water treatment plants. The current model includes corrections for short-range interactions between particles as they approach one another. These corrections severely reduce the expected collision frequency between particles that are very different in size and, therefore, substantially change the model predictions. Both experimental and field measurements of particle size distributions are provided; such measurements were unavailable in the earlier work and represent a touchstone to reality for the modeling efforts. The short-range model successfully fits experimental results for flocculation when the mechanism of particle destabilization is charge neutralization. However, the model does not account for the creation of new solids by precipitation either when hydrolyzing salts of aluminum or iron are added for particle destabilization by "sweep floc" destabilization or lime is added to remove calcium and magnesium as calcium carbonate and magnesium hydroxide in softening. The flocculent sedimentation model yields results that are in strong qualitative agreement with typical field measurements.

Investigation of membrane fouling in ultrafiltration using model organic compounds

Natural organic matter (NOM) is known to be the worst foulant in the membrane processes, but the complexities of NOM make it difficult to determine its effects on membrane fouling. Therefore, simple organic compounds (surrogates for NOM) were used in this research to investigate the fouling mechanisms in ultrafiltration. Previous research on NOM components in membrane processes indicated that polysaccharides formed an important part of the fouling cake. Three polysaccharides (dextran, alginic acid, and polygalacturonic acid) and a smaller carbohydrate (tannic acid) were evaluated for their removal in softening (the treatment process in the City of Austin). Two polysaccharides (dextran and alginic acid) were selected and further investigated for their effects on membrane fouling. The two raw organic waters (4 mg/L C) showed quite different patterns of flux decline indicating different fouling mechanisms. Softening pretreatment was effective to reduce flux decline of both waters. The SEM images of the fouled membrane clearly showed the shapes of deposited foulants. The high resolution results of the XPS spectra showed substantially different spectra of carbon, C(1s), in the membrane fouled by two raw organic waters. The XPS was beneficial in determining the relative composition of each fouling material on the membrane surface.

Fouling mechanisms in the integrated system with softening and ultrafiltration

Softening is designed to remove hardness ions, but it can also remove NOM and particles, yielding the possibility to use the process as a pretreatment for ultrafiltration. The objectives of this research were to understand the nature of the fouling mechanisms for ultrafiltration when used for waters that either require softening or have been softened, and to use that understanding to determine promising options for the use of softening as a pretreatment before ultrafiltration. To understand fouling mechanisms in the integrated system with softening and ultrafiltration, three different levels of softening performance in terms of removal of inorganics and organic matter were selected. Experiments were performed with both natural waters and synthetic waters with similar (but separable) inorganic, organic, and particulate characteristics. The synthetic waters were used to distinguish among inorganic fouling by precipitates, organic fouling, particulate fouling, and combined fouling by particles and organic matter. The results showed that organic matter played a major role in fouling, either by itself or by adsorption onto particles, and that softening pretreatment effectively reduced the foulants prior to ultrafiltration.

Investigation of membrane fouling by synthetic and natural particles

The biggest impediment for applying membrane processes is fouling that comes from mass flux better (such as particle and organic matter) to the membrane surface and its pores. Numerous research articles have indicated that either particles or natural organic matter (NOM) has been the most detrimental foulant. Therefore, the role of particles in membrane fouling was investigated with two synthetic waters (having either particles alone or particles with simple organic matter) and a natural water. Membrane fouling was evaluated with flux decline behavior and direct images from scanning electron microscopy. The results showed that the combined fouling by kaolin and dextran (a simple organic compound selected as a surrogate for NOM) showed no difference from the fouling with only the organic matter. The similarity might stem from the fact that dextran (i.e., polysaccharide) has no ability to be adsorbed on the clay material, so that the polysaccharide behaves the same with respect to the membrane with or without clay material being present. In contrast to kaolin, the natural particles showed a dramatic effect on membrane fouling.

The scientific basis of flocculator design

A new guideline for the design of flocculators is proposed. This guideline is to design continuous flow flocculators on the basis of the characteristic reaction time for the loss of one micrometre particles in the suspension. The most commonly used guideline at the present time is that of Camp, but later proposals by Ives and O'Melia expanded the Camp guideline and incorporated more complete knowledge of flocculation. The suggestion here continues that process, by accounting explicitly for the heterodisperse nature of typical suspensions and the multiple collision mechanisms for particles in determining a characteristic reaction time. While the historical guidelines have served the water treatment industry well for reasonably similar size distributions in waters destabilized by precipitating metal hydroxides, the proposed guideline should be more robust in considering other suspensions. In particular, the new guideline can account explicitly for the effects of nanoparticles on flocculation.

Chemoattractant properties of conditioned medium from equine corpora lutea collected at various stages of the oestrous cycle

This study investigated the chemotactic activity of equine CL at different stages of the oestrous cycle. The purpose of this was to ascertain whether luteal tissue itself contributes to the massive influx of leucocytes around the time of natural and induced luteal regression. Corpora lutea were collected at different stages of dioestrus and after treatment with PGF2alpha. Culture medium harvested after incubation of luteal tissue for 20 h was chemotactic for both polymorphonuclear and mononuclear cells in late dioestrus (before functional regression) as well as after natural and induced luteal regression. By contrast, midluteal tissue showed no chemotactic activity. This is the first report of the ability of equine luteal tissue actively to recruit inflammatory cells in vitro and supports our earlier findings that this infiltration starts prior to functional luteolysis. We hypothesise that this early influx of inflammatory cells may play an active role in luteal regression. Further research is needed to identify the specific chemotactic factor(s).

The influence of age and gender on the immune system: a longitudinal study in Labrador Retriever dogs

While aging studies employing a cross-sectional design have been informative in documenting many age-related alterations in immune function between different age cohorts within a population, longitudinal studies are invaluable for verifying changes at the level of the individual and for defining the precise periods of life during which particular changes occur. In the present study, a battery of immunological parameters were evaluated in a group of Labrador Retrievers as part of a comprehensive longitudinal aging study. Twenty-three dogs (14 females, 9 males; from 4 to 11 years of age) were evaluated annually for total WBC counts, lymphocyte subset distributions, natural killer cell activity and neutrophil phagocytic activity, and biannually for lymphoproliferative activity. An age-related decline in absolute numbers of lymphocytes, T-cells, CD4-cells and CD8-cells was observed in both genders. The distribution of lymphocyte subsets shifted with age, most dramatically in the females; percentages of B-cells declined while those of T-cells increased. Changes in percentages of CD4- and CD8-cells over the 8-year period were not dramatic; in females, percentages of CD8-cells increased significantly in early- to mid-life and then stabilized. Lymphoproliferative responses to mitogens declined over time in both genders. Males demonstrated higher levels of NK cytolytic activity than females; a marginal decline in activity with age was observed. No significant age-related changes in the phagocytic capacity of PMN were observed. These longitudinal findings help to discriminate between those immune parameters which change most dramatically in early-life versus those which either change more dramatically later in life or change gradually over the entire span of life. In addition they identify significant gender differences in several parameters and corroborate our previously published cross-sectional aging data in the same species.

Evaluation of the effect of limited food consumption on radiographic evidence of osteoarthritis in dogs

OBJECTIVE

To determine prevalence of radiographic evidence of osteoarthritis in 4 diarthrodial joints of dogs with restricted feed intake, compared with dogs without restricted feed intake.

DESIGN

Paired feeding study.

ANIMALS

48 Labrador Retrievers.

PROCEDURE

Dogs in litters from 7 dams and 2 sires were paired by sex and weight within litters and randomly assigned to a control-fed group or a limit-fed group that received 25% less food than the control-fed group. Radiographic evaluation of prevalence and severity of osteoarthritis in the hip, shoulder, elbow, and stifle joints was performed when dogs were 8 years of age.

RESULTS

Radiographic evidence of osteoarthritis that affected multiple joints was significantly more common in the control-fed group than in the limit-fed group. Prevalence of lesions in the hip joint was 15/22 in the control-fed group and 3/21 in the limit-fed group. Prevalence of lesions in the shoulder joint was 19/22 in the control-fed group and 12/21 in the limit-fed group; lesions in this joint were generally mild. Severity, but not prevalence, of osteoarthritis in the elbow joint was greater in the control-fed group than in the limit-fed group.

CONCLUSIONS AND CLINICAL RELEVANCE

Prevalence and severity of osteoarthritis in several joints was less in dogs with long-term reduced food intake, compared with control dogs. Food intake is an environmental factor that may have a profound effect on development of osteoarthritis in dogs.

Immune cell populations in the equine corpus luteum throughout the oestrous cycle and early pregnancy: an immunohistochemical and flow cytometric study

Recent evidence indicates that the cells of the immune system and their large network of secretory products, or cytokines, play an active role in the ovary throughout the oestrous cycle. In the present study, immune cell populations (T and B lymphocytes, macrophages, granulocytes and eosinophils) and expression of major histocompatibility complex (MHC) class II were investigated in corpora lutea from mares in early (days 2-4), mid- (days 7-10) and late (days 12-14) dioestrus, the post-luteolytic phase (days 16-17) and early pregnancy. The number of T lymphocytes within the corpus luteum increased in the late luteal phase. CD4+ cells did not increase until day 16, whereas the number of CD8+ cells increased before functional luteolysis; an apparently selective luteal infiltration of CD8+ cells was observed. MHC class II expression by non-steroidogenic cells was increased in samples from days 16-17, as was the number of infiltrating macrophages. Flow cytometry revealed very low expression of MHC class II by large luteal cells at all stages of the oestrous cycle. In early pregnancy, the number of CD4+ and CD8+ cells and macrophages decreased, as did MHC class II expression, compared with mid-dioestrous samples. B cells were present in very small numbers in all samples examined. Eosinophils were similarly sparsely distributed and numbers decreased further in pregnancy. After exogenous PGF2 alpha administration, populations of CD4+ cells and non-specific esterase staining cells were significantly smaller than after natural luteolysis, whereas eosinophil numbers were increased compared with samples from days 16-17. However, the number of CD8+ and CD5+ cells and MHC class II expression were not significantly different from those observed after natural luteolysis. These findings indicate that populations of immune cells in the equine corpus luteum vary during its lifespan. The selective increase in CD8+ cells before functional luteolysis indicates that they have a physiological role in the regression of the corpus luteum.

Influence of restricted food intake on estrous cycles and pseudopregnancies in dogs

OBJECTIVE

To examine effects of restricted food intake on estrous cycle frequency, interestrus interval, and pseudopregnancy prevalence in dogs.

ANIMALS

28 female Labrador Retrievers.

PROCEDURE

Dogs were paired by body weight when they were 6 weeks old and fed so that the limit-fed pair-mate received 75% of the amount of food offered to its maintenance-fed counterpart. Estrous cycle, interestrus interval, and pseudopregnancy data were recorded.

RESULTS

Mean annual frequency of estrous cycles and duration of interestrus intervals did not differ between feeding groups. Prevalence of clinically evident pseudopregnancy was significantly greater among females that were maintenance fed, although results of endocrinologic testing did not identify a mechanism for this observation.

CONCLUSIONS AND CLINICAL RELEVANCE

Pseudopregnancy in dogs can be influenced by physiologic factors related to nutrition. Clinicians should consider a variety of physiologic and environmental factors when evaluating reproductive function in dogs.

Within- and between-examiner repeatability of distraction indices of the hip joints in dogs

OBJECTIVE

To evaluate in vivo repeatability of the distraction index method of evaluating hip joint laxity in dogs.

ANIMALS

31 two-year-old Labrador Retrievers.

PROCEDURE

Each dog was anesthetized and radiographically evaluated for hip joint laxity 4 times: twice by an experienced examiner and twice by an examiner who had no previous knowledge of or training in the technique prior to the first day of testing. Distraction indices (DI) were determined from the radiographs and intraclass correlation coefficients were calculated to evaluate the repeatability of DI measurements between and within examiners.

RESULTS

Intraclass correlation coefficients were high (range, 0.85 to 0.94). Lower limits of the 95% confidence intervals for the intraclass correlation coefficients ranged from 0.75 to 0.89.

CONCLUSIONS

Between- and within-examiner repeatabilities of DI measurements were high, suggesting that the technique is clinically reliable.

CLINICAL RELEVANCE

Distraction index is a reliable measure of hip joint laxity and a good predictor of the risk of development of degenerative joint disease associated with hip dysplasia in dogs. Establishment of high repeatability of DI measurements suggests that the stress-radiographic method may be used by multiple examiners with the expectation of comparable and consistent results.

Evaluation of weight loss protocols for dogs

Several canine weight loss protocols were evaluated to determine their relative safety and efficacy. Dogs were fed 100%, 75%, 60%, or 50% of maintenance energy requirements (MERs) using the dogs' target body weights. No indications of adverse health effects were observed with any weight loss protocol. Triiodothyronine (T3) levels and apparent MERs decreased in dogs restricted to 50% to 60% of their MERs. The rate of weight loss was correlated linearly with degree of calorie restriction, although there was considerable individual variation. Percent overweight by the end of the test was not different between protocol groups for dogs fed 50%, 60%, or 75% of MERs. Therefore, any of the protocols tested in this study may be used in the management of overweight dogs; however, individual responses will be expected to vary, and severe calorie restriction may predispose dogs to weight rebound.

Five-year longitudinal study on limited food consumption and development of osteoarthritis in coxofemoral joints of dogs

OBJECTIVE

To examine the effects of limited food intake on frequency and severity of osteoarthritis in coxofemoral joints of labrador Retrievers.

DESIGN

Dogs were paired according to gender and body weight, within each litter at 8 weeks of age. One dog of each pair was fed ad libitum. The limit-fed pairmate was fed 75% of the amount eaten the previous day by the ad libitum-fed counterpart.

ANIMALS

48 Labrador Retrievers.

PROCEDURE

All dogs received the same diet. Radiographic evaluation of coxofemoral joints for frequency and severity of osteoarthritis were made when dogs were 4 and 6 months and 1, 2, 3, and 5 years old.

RESULTS

Radiographic evaluation for osteoarthritis indicated greater frequency and more severity of osteoarthritis in the ad libitum-fed group of dogs.

CLINICAL IMPLICATIONS

Analysis of data suggested that limit feeding of dogs over a 5-year period minimizes development of osteoarthritis in the coxofemoral joints.

The influence of age on the canine immune system

Immune function was assessed in a group of 47 Labrador Retrievers, ranging in age from 0.8 to 11.5 years, in order to establish baseline data on canine immunosenescence. Natural killer cell activity, lymphocyte subset distributions, antibody production, and mitogen-induced lymphoproliferative responses, all of which have been demonstrated to undergo age-related changes in humans and mice, were chosen as indicators of immune function. Dogs were categorized by age as young (mean 2.4 years), middle-aged (mean 5.8 years), and old (mean 9.1 years). Natural killer cell activity was not affected significantly by age. Lymphocyte subset analysis revealed a significant age-related increase in the percentage of cells staining with a pan T-cell reagent, accompanied by a corresponding increase in the percentage of CD8 cells from youth to middle age. An age-related decrease in the percentage of B-cells was observed concomitant with the increases in T-cell percentages. A gender-related difference in pan T-cell distribution was also observed, with females having a higher percentage than males. Lymphoproliferative responses of both young and middle-aged dogs to the mitogens concanavalin A, phytohemagglutinin, pokeweed mitogen, and staphylococcal enterotoxin B were significantly higher than those of old dogs. In general, the mitogen responses of male dogs were affected more dramatically by age than those of females. A significant age-related decline in in vivo antibody responses to the protein antigen, keyhole limpet hemocyanin, was not observed, although the mean titers of the young dogs were higher than those of the old.