bluuebunny/crossref_metadata_2025 huggingface dataset:
Artificial Recharge of Unconfined Aquifer
Authors: Rai S.N. , Singh V.P.
Published: July 2005

Groundwater plays a major role in augmenting water supply to meet the ever‐increasing demands for domestic, agricultural, and industrial usages. Increasing dependence of water supply on groundwater resources leads to more use of aquifers as a source of fresh water supply and subsurface reservoir for storing excess surface water. The advantage of unconfined aquifers over confined aquifers to serve as subsurface reservoir is that the storage of groundwater in large quantity is possible only in unconfined aquifer, which is because the storativity of the unconfined aquifer is linked to the porosity and not to the elastic properties of the water and solid matrix, as in case of the confined aquifer. Also, the vast surface area of the unconfined aquifer above the water table is available to receive the surface applied recharge, whereas in case of the confined aquifer, only a small open area exposed near to the ground surface or leaky portion of the aquifer boundary is available to receive the recharge. This article deals with artificial recharging of the unconfined aquifer and related problems.
Mass Transport in Saturated Media
Authors: Hudak Paul F.
Published: July 2005

Advection and hydrodynamic dispersion affect the movement of solutes in groundwater. Advection is the movement of solutes with flowing groundwater. Hydrodynamic dispersion is the spreading of groundwater and its dissolved constituents by mechanical mixing and chemical diffusion. The aquifer matrix induces mechanical mixing, which causes water to move faster at some locations than at others and forces water to move through different passages. Chemical concentration gradients induce diffusion, which causes solutes to move from areas of high to low concentration. Diffusion may take place in groundwater that is not flowing. Hydrodynamic dispersion takes place in all directions in three‐dimensional space, but to a greater degree parallel to groundwater flow. The longitudinal component of hydrodynamic dispersion parallels the direction of groundwater flow. Transverse components occur in all directions in a plane perpendicular to groundwater flow. Beyond the pore scale, bodies of rock or sediment with different hydraulic conductivity may induce mechanical dispersion within an aquifer. Reactive solutes, which have a tendency to intermittently sorb to the aquifer matrix, move at a slower rate than does groundwater.
Megawatersheds
Authors: Bisson Robert A.
Published: July 2005

The term “megawatershed” describes deep‐seated subsurface aquifer systems that may consist of gravel, fracture‐hosted bedrock, and/or sedimentary structures, which are integrated in terms of recharge, storage, transmissivity, and containment. They may not coincide with surface topographic divides and may receive recharge from parts of several surface watersheds including amounts of mountain block recharge. “Megawatershed” is a conceptual model, or paradigm, that describes this new class of groundwater domain. Megawatersheds are formed over geologic time by a combination of factors, including tectonically induced brittle fracturing and displacement of rock facies and strata and solutioning of parent rock facies and regolith by chemically aggressive meteoric and hydrothermal waters. The history and nature of regional tectonic stress fields and principal bounding faults, interacting with lithology and climate, play a major role in determining the geometry and extent of megawatershed boundaries.
Bacteria Role in the Phytoremediation of Heavy Metals
Authors: Johnson Anthea , Singhal Naresh , Takis Elefsiniotis P.
Published: July 2005

Heavy metals are of particular concern in the environment as they cannot be degraded by natural processes and instead tend to accumulate in ecosystems. At many sites the metals exist in toxic concentrations within the soil, posing a threat to most forms of life, including humans, therefore necessitating their removal. Phytoremediation aims to use plants and bacteria to mediate the removal of heavy metal contaminants from soils. Metals can be mobilized for uptake by plant roots via a number of plant and bacterial processes such as soil acidification, biosurfactant solubilization, chelation, or redox transformation. In addition, other processes immobilize the metals through conversion to insoluble forms. Examples of immobilization processes induced by bacteria and plants are sorption, precipitation, sequestration, and volatilization. Bacteria not only have an influence on the mobility of metals in soils but also have a significant role in the rhizosphere due to their interactions with plants. Bacteria and plants can form synergistic or antagonistic relationships, supplying each other with nutrients or energy sources, or producing toxins to reduce growth and competition for limiting nutritional elements. By utilizing natural biological remedial processes, phytoremediation may present a more sustainable approach for the restoration of contaminated soils.
Fossil Aquifers
Authors: Phoenix Laurel
Published: July 2005

Fossil aquifers are bodies of very deep aquifers that are disconnected from our contemporary hydrologic cycle. Water in these aquifers can be hundreds to thousands of years old and thousands of feet deep. As they are not recharged by today's precipitation, using them as a water supply is not sustainable. Other deep aquifers may still be connected to surface precipitation, but recharge so slowly relative to human time scales that they can practically be considered nonreplenishable fossil aquifers as well. Not only are these supplies finite, but their depth also makes them more expensive, not only for the initial drilling but also for the increased energy required to pump water from these depths.

Why develop an unsustainable and expensive water supply? The world water deficit is straining countries in many ways. Drought, water pollution, and rising populations are making communities drill ever deeper for water. The growing international grain trade is also a trade in water. Examples of mining fossil water are given in China, the Middle East, and the United States.
Modeling Contaminant Transport and Biodegradation in Groundwater
Authors: Oswald Sascha E.
Published: July 2005

Biodegradation is an important factor in the fate of organic contaminants and may reduce the concentration and also the total mass of a contaminant. Although several processes can contribute to the natural attenuation of contaminants, biodegradation is often the main process by which mass may be destroyed; other processes such as sorption merely retain the contaminant mass for later release. Therefore, modeling monitored as well as enhanced natural attenuation, usually has to include biodegradation modeling.

The key processes to be modeled are advection, dispersion, sorption, and degradation by microbes. However, further processes could also be relevant, for example, ion exchange, precipitation and dissolution of minerals, speciation, and surface‐complexation.

The basis for transport modeling is flow modeling; transport modeling is the basis for modeling contaminant itself transport and biodegradation (see Fig. 1). Often in more general terms this is called reactive transport modeling, which includes transport plus biodegradation and/or hydrogeochemical modeling. To model a field scale problem of reactive transport appropriately, one should plan this as a set of modeling tasks building up to this challenging undertaking.
Modeling Non‐Point Source Pollutants in the Vadose Zone UsingGIS
Authors: Corwin Dennis L. , Logue Keith
Published: July 2005

Non‐point source (NPS) pollutants are characteristically diffuse in nature, tend to have a long active presence in the global ecosystem, and result in chronic health effects on humankind. Because of their nature, NPS pollutants are a global concern. Assessing the fate and transport of NPS pollutants both in real time and from model simulations is crucial to understanding cause‐and‐effect relationships and for synthesizing current knowledge into a useable form for policy decisions. However, modeling NPS pollutants is a complex multidisciplinary problem that requires a systems‐based approach within a spatial context with an awareness of scale. It is the objective of this encyclopedia article to provide a general discussion of the three components of an NPS pollutant model: data, geographic information system (GIS), and model. Each component is discussed from a systems‐based perspective to provide an understanding of their interaction and interdependence. Because temporal and spatial scale determines the structure of an NPS pollution model, the theory of hierarchical scales is presented. It is concluded that the future success of landscape‐scale environmental modeling rests not on enhancing the detail of model structure, but rather on characterizing the spatiotemporal variability of model inputs and parameters.
Biofouling in Water Wells
Authors: Smith Stuart A.
Published: July 2005

Biofouling as a term has its origins in pre‐World War II studies of marine fouling and generally refers to coating, encrustation, and corrosion associated with the attachment of organisms to surfaces, including human‐engineered structures. The phenomenon arises from the tendency of life across all known kingdoms to cling to and use surfaces. Biofouling takes many forms, ranging from bacterial‐viral films plaguing urinary tracts to fouling of water intakes and other maritime structures (and even baleen whales) by films that also include macroorganisms such as barnacles and zebra mussels.

Biofouling of water wells and associated downstream systems tends to result from the formation of biofilms by bacteria. It is now widely recognized that biofouling is the first or second most costly deteriorating factor for groundwater systems in North America.
Industrial Mine Use: Mine Waste
Authors: Von Der Heyden Constantin
Published: July 2005

The extraction of minerals and the mining and processing of ores produces a variety of effluents, which, if left untreated and discharged into the environment, can impact the natural and social environment. Various types of mine effluent and the conditions giving rise to their generation are described, with some focus on acid mine drainage (AMD) in particular, both in terms of the chemistry of generation and common methods of AMD remediation. Both active treatment (for example, high density sludge process) and passive remediation (for example, wetlands) treatment of mine effluents are explored and the common processes of remediation are discussed in detail.
Electric Generating Plants—Effects of Contaminants
Authors: Reash Robin J.
Published: July 2005

Coal is an abundant, relatively low‐cost energy source whose extraction and use fostered the rapid industrialization of many countries during the twentieth century. Prior to the enactment of major environmental statutes by the U.S. Congress during the period 1960–1980, the extraction and combustion of coal resulted in pervasive, significant instances of environmental damage in the air, water, and soil. Coal contains a variety of organic and inorganic constituents, and the mobilization of these compounds (typically found in trace levels in geological strata) into concentrated air or water discharges often posed risks to human health and the environment. An enormous amount of coal ash, produced during the combustion process, is disposed onto landfills or in treatment reservoirs. Trace metals that are leached from ash particles can be discharged at levels that may exceed toxic thresholds. Significant improvements in the overall environmental impact of power generating facilities were realized in the United States during the past 30 years, as a result of implementation of more stringent environmental regulations. The development of “clean coal” technologies has allowed continued use of an energy source whose reserves are expected to last at least 200 years.
Observations of Climate and Global Change from Real‐Time Measurements
Authors: Easterling David R. , Karl Thomas R.
Published: July 2005

Is the planet getting warmer?

Is the hydrologic cycle changing?

Is the atmospheric/oceanic circulation changing?

Is the weather and climate becoming more extreme or variable?

Is the radiative forcing of the climate changing?

These are the fundamental questions that must be answered to determine if climate change is occurring. However, providing answers is difficult due to an inadequate or nonexistent worldwide climate observing system. Each of these apparently simple questions are quite complex because of the multivariate aspects of each question and because the spatial and temporally sampling required to address adequately each question must be considered on a global scale. A brief review of our ability to answer these questions reveals many successes, but points to some glaring inadequacies that must be addressed in any attempt to understand, predict, or assess issues related to climate and global change.
Overview of Weather Systems
Authors: Nielsen‐Gammon John W.
Published: July 2005

The attempt to understand the weather is driven largely by the desire to be able to forecast the weather. However, the atmosphere is a complicated dynamical system, and an understanding of even the basic physical principles came only recently. Before that, scientists either attempted to understand the physical causes of weather events or recorded “weather signs,” rules for weather forecasting. Because the physical understanding was incorrect, and most weather signs had no physical basis, neither approach was very successful. True progress in the study of the atmosphere that would lead to success in weather forecasting required a complete understanding of physical principles and a comprehensive set of observations of the atmosphere.
Basic Research for Military Applications
Authors: Bach W. D.
Published: July 2005

The military must understand the atmosphere in which it operates. That understanding will ultimately depend on scientific understanding of the atmospheric processes, an ability to use all of the information available, and an ability to synthesize and display that information in a quickly understandable fashion.

The military's needs for understanding the atmosphere's behavior has changed as a result of geopolitics and advancing technology. On the battlefield, future enemies are more apt to resort to chemical or biological attacks as a preferred method of mass destruction. The atmospheric boundary layer is the pathway of the attack. Increased reliance on “smart” weapons means that turbulent and turbid atmospheric effects will influence electromagnetic and acoustic signals propagating through the boundary layer. Intelligence preparation of the battlespace, a key to successful strategies, depends on full knowledge of the enemy, weather, and terrain. It requires an ability to estimate atmospheric details at specific locations and future times to maximize strategic advantages that weather presents a commander. It also avoids hazards and strategic disadvantages.
Rain and Rocks: The Recipe for River Water Chemistry
Authors: Islam Mohammed Riajul
Published: July 2005

Aerosols are the primary source of chemical elements transported by rainwater, which are removed from the atmosphere by rainout or by washout. Atmospheric aerosols (sea salt, crustal dust, and biogenic aerosols) have been found as the major sources of dissolved species in river water. Dissolved components from rainwater come from those originating from sea salt aerosols; from those originating from terrestrial aerosols (soil dust, biological emissions); and from those originating from anthropogenic sources (industry, agriculture, burning of fossil fuels, etc.).

Along with the geological characterization of the watershed, meteorological parameters are critically important in evaluating rainfall effects.
Uncertainties in Rainfall–Runoff Modeling
Authors: Willems Patrick
Published: July 2005

Errors and uncertainties in the prediction of rainfall–runoff are often substantial. Consideration of these errors is therefore crucially important. When water decision‐making is based on the rainfall–runoff prediction, for instance, by means of rainfall–runoff, uncertainties affect model outcomes and, consequently, the decisions. Hence, good modeling practice provides not only the results of model predictions but also the accuracy of these results. It supplies decision makers with important additional information on the uncertainty in the data and information that they use as a basis for their decisions. After quantification of the runoff prediction errors, water policies can be set up for which the efficiency can be guaranteed up to specified acceptable risk levels. Combined with the uncertainty analysis, a sensitivity analysis provides the modeler and decision maker with information about the importance of various types of model limitations and sources of uncertainty.
Cosmic Water
Authors: Marrin D. L.
Published: July 2005

Water is present throughout the cosmos in solid and vapor phases; occurrence in the liquid phase appears to be more limited. The origins of water may be traced back to hydrogen atoms that were created following the Big Bang and oxygen atoms that continue to be created in the interior of dying stars. Water resides on everything from interstellar dust and gas clouds to the surface of planets and stars, where it performs a myriad of roles in creating and sustaining the physical universe. Moreover, cosmic water molecules themselves are continuously created, destroyed, and transported in the vast interstellar realms. Easily recognized by the wavelengths of light that it adsorbs and emits, cosmic water also exists as a flowing icy phase that may have been instrumental in combining the simple organic molecules that are required for biological life. Even the much sought‐after liquid water is more common on planetoids within our galaxy than astronomers originally suspected.
Sublimation
Authors: Adelaide Boss Edinara
Published: July 2005

Sublimation occurs when the matter passes directly from the solid phase to the vapor phase. Examples include dry ice, how a frost‐free refrigerator works, and naphthalene. Sublimation is an endothermic process:urn:x-wiley:9780471478447:media:me391:xm1

The heat required to change the phase of a pure substance is given byurn:x-wiley:9780471478447:media:me391:xm2where m is the mass of the pure substance and L is the latent heat.

The water latent heat for sublimation is 2.83 × 106 J/Kg.
Tornado
Authors: Meaden Terence
Published: July 2005

The strong naturally‐formed vortices in the atmosphere known as tornadoes are of great research importance for the risk they pose to life and property. They are made visible by the condensation of water vapor in the outer sheath of spinning funnels that develop at the time of severe storms, usually over land but occasionally over expanses of water, more especially near coastal shores when they have the appearance of strong waterspouts.
Vapor Pressure
Authors: Persaud Naraine
Published: July 2005

Vapor pressure is the partial pressure exerted by the vapor of a substance in the gaseous phase of a closed heterogeneous system at equilibrium with condensed phases (i.e., solid or liquid) of the substance present in the system. It is the macroscopic measure of the tendency of the molecules of a given species in the condensed phases of the system to escape into the gaseous phase. A heterogeneous system means a mixture of two or more distinct, physically or chemically homogeneous phases. Mixture implies the phases are mechanically separable; distinct implies presence of unequivocally defined physical boundaries (interfaces) between phases; and homogeneous implies each phase is uniform throughout chemically and physically. The simplest possible conceptualization for a heterogeneous system is any closed two‐phase system consisting of the solid or liquid of a pure substance in equilibrium with its vapor at a given temperature. In more complex heterogeneous systems, the condensed phases may be completely miscible or immiscible liquids, aqueous solutions, discontinuous liquid aerosols, or solid/liquid emulsions, and the vapors may be mixed with other vapors and gases present in the gaseous phase. Although the entire system is closed (permitting only energy transfer) with respect to its surroundings, the subsystems (phases) are open, permitting both energy and mass transfer between phases.
Condensation
Authors: Conti Aldo
Published: July 2005

Condensation is the physical process by which a vapor changes to its liquid state. Condensation happens when the temperature of the vapor decreases below the so‐called dew point. In physics, this sort of process is called a phase change because the matter involved changes its state (i.e., from gaseous to liquid, in this case). Water condensation is evident in our atmosphere; it produces fog, mist, dew, clouds, and rain, depending on the conditions. It can be seen on a cold sheet of glass, where condensed water forms a maze of droplets.
Dew
Authors: Conti Aldo
Published: July 2005

Dew forms when water condenses on objects on the surface near the ground and forms a thin layer or many droplets. Dew forms normally during the night when the air temperature decreases and approaches the dew point. Objects on the surface cool down, too, by radiative cooling, facilitating the condensation of small droplets of water. Dew formation is helped by the high humidity of the bottom layer of air, close to the surface. This layer can supply the needed water and prevent the evaporation of the dew already deposited. Strong winds can inhibit the formation of dew. Turbulence mixes a larger layer of air and creates a more homogeneous distribution of humidity and heat, thus preventing the formation of the right conditions near the ground. Dew forms more easily on surfaces that cool efficiently, like metals, which is the reason that cars are often covered with dew in the morning. But dew is often seen on grass or plants because their transpiration creates a thin layer of very humid air.
Dew Point
Authors: Conti Aldo
Published: July 2005

The dew point is the temperature to which air must be cooled at constant pressure until it reaches saturation and the water, or any other vapor, begins condensing. The result is the formation of fog. When the dew point falls below freezing, it is called the frost point. In this case, water forms ice crystals directly. The dew point is also a good indicator of the amount of water contained in the air. The more humid the air, the higher the dew temperature. The dew point is often reached in the evening, when the air cools down, which is why fog is more common in the evening, or why one normally finds that dew or frost are common in the morning but disappear as soon as the temperature increases.
Flocculation
Authors: Ahmad Rasheed
Published: July 2005

The flocculation process aggregates destabilized particles into larger and more easily settleable flocs. The coagulation process destabilizes particles through chemical reactions between the coagulant and the suspended colloids, but flocculation is the transport step that causes the necessary collision between destabilized particles. The purpose of the flocculation process is to promote the interaction of particles and to form aggregates that can be efficiently removed in the subsequent separation processes such as sedimentation, flotation, and coarse bed filtration. In practice, flocculation is accomplished by providing a gentle mixing phase that follows the rapid dispersion of coagulants.
Giardiasis
Authors: Bean Christine L.
Published: July 2005

Giardia lamblia
is an intestinal flagellated protozoan, which infects the intestinal tract of a wide range of mammals, including humans. Two forms of this protozoan exist, a highly resistant cyst and a motile, feeding trophozoite. Cysts may be found in freshwater surface water supplies as a result of contamination from sewage and animal waste runoff. Trophozoites of this obligate parasite do not typically survive outside the host and are therefore not the major mode of transmission. The cyst form is capable of surviving for long periods of time in cool water supplies and has been responsible for major waterborne outbreaks in the United States.
Granular Activated Carbon
Authors: Mohan Dinesh , Singh Kunwar P.
Published: July 2005

Activated carbon is the generic term used to describe a family of carbonaceous adsorbents with a highly crystalline form and extensively developed internal pore structure. Activated carbon is distinguished from elemental carbon by the removal of all noncarbon impurities and the oxidation of the carbon surface. Activated carbon has the highest volume of adsorbing porosity of any substance known to humans (5 grams of activated carbon can have the surface area of a football field). It can be defined as:

Activated carbon is a crude form of graphite, with a random or amorphous structure, which is highly porous, over a broad range of pore sizes, from visible cracks and crevices, to cracks and crevices of molecular dimensions.

The use of activated carbon is not new. The Egyptians used carbonized wood around 1500B.C.as an adsorbent for medicinal purposes as well as a purifying agent. The ancient Hindus in India used charcoal for filtration of drinking water. However, the basis for industrial production of active carbons was established in 1900–1901 in order to replace bone char in the sugar refining process.

Active carbons can be prepared from a wide range of carbonaceous materials, which include coconut shells, wood char, lignin, petroleum coke, bone char, peat, saw dust, carbon black, rice hulls, sugar, peach pits, fish, fertilizer waste, and waste rubber tire. The range of raw materials is diverse and widespread and greatly influenced by the need to produce low‐cost carbon. Among the most commonly used raw materials, precursors for the production of commercially activated carbons are wood (130,000 tons/year), coal (100,000 tons/year), lignite (50,000 tons/year), coconut shell (35,000 tons/year), and peat (35,000 tons/year).
Threat Agents and Water Biosecurity
Authors: Higgins James
Published: July 2005

In the aftermath of the anthrax bioterror outbreak in the eastern United States in the fall of 2001, the security of the potable water distribution network assumed new importance. Both source and finished waters may represent possible targets for the introduction of biological threat agents. These agents may consist of viruses such as smallpox or hemorrhagic fever viruses; bacteria, such as
Bacillus anthracis
and
Francisella tularensis
; and toxins, such as staphylococcal enterotoxin or ricin. Little is known about the stability of threat agents in source and finished waters and the effects of conventional disinfection regimens on pathogen survival and infectivity. Methods currently in use for the recovery of waterborne pathogens such as
Escherichia coli, Cryptosporidium
, and enteric viruses, may be readily adapted for use in detecting threat agents in water samples. Newer diagnostic technologies, based on immunologic and molecular biology approaches, may be able to provide the water industry with more sensitive and accurate testing methods for threat agents. Recently, a number of research and development programs dealing with water biosecurity were implemented by federal and industry organizations. These initiatives should assist water resource managers as they confront this new challenge to water quality and public health.
Selective Coagulant Recovery from Water Treatment Plant Residuals Using the Domain Membrane Process
Authors: Prakash Prakhar , SenGupta Arup K.
Published: July 2005

Let us consider solutions of aluminum sulfate (feed) and sulfuric acid (recovery) in a Donnan membrane cell divided into two chambers by a cation‐exchange membrane that allows only cations to migrate from one side to the other but rejects any passage of anions according to Donnan's co‐ion exclusion principle (9). At equilibrium, the electrochemical potential of aluminum ion Al3+ion () in the feed solution will be the same as that in the recovery solution for both aluminum and hydrogen ions, which corresponds to the following Donnan equilibrium condition:urn:x-wiley:9780471478447:media:mw1760:xm2If the ratiois 10, it meansis 1000 times greater than. Thus, by maintaining high hydrogen ion concentration in the recovery solution, aluminum ions can be driven from the feed to the recovery side even against a positive concentration gradient, i.e., from a lower concentration region to a higher concentration one.
Disinfection
Authors:   National Drinking Water Clearinghouse
Published: July 2005

Disinfection is an important step in ensuring that water is safe to drink. Water systems add disinfectants to destroy microorganisms that can cause disease in humans. The Surface Water Treatment Rule requires public water systems to disinfect water obtained from surface water supplies or groundwater sources under the influence of surface water.

Primary methods of disinfection are chlorination, chloramines, ozone, and ultraviolet light. Other disinfection methods include chlorine dioxide, potassium permanganate, and nanofiltration. Since certain forms of chlorine react with organic material naturally present in many water sources to form harmful chemical byproducts, the U.S. Environmental Protection Agency has proposed maximum levels for these contaminants.
Corrosion Control
Authors:   National Drinking Water Clearinghouse
Published: July 2005

Corrosion occurs because metals tend to oxidize when they come in contact with water, resulting in the formation of stable solids. Corrosion in water distribution systems can impact consumers' health, water treatment costs, and the aesthetics of finished water.

Various methods can be used to diagnose, evaluate, and control corrosion problems. Techniques for controlling it include distribution and plumbing system design considerations, water quality modifications, corrosion inhibitors, cathodic protection, and coatings and linings.
Ion Exchange and Demineralization
Authors:   National Drinking Water Clearinghouse
Published: July 2005

Ion exchange and membrane processes are becoming used extensively in water and wastewater treatment. Ion exchange is primarily used for the removal of hardness ions, such as magnesium and calcium, and for water demineralization. Reverse osmosis (RO) and electrodialysis, both membrane processes, remove dissolved solids from water using membranes.
Organic Removal
Authors:   National Drinking Water Clearinghouse
Published: July 2005

Some small drinking water systems face contamination of raw water by natural or synthetic organic chemicals (SOCs). Natural organic materials might be present in water supplies, especially from surface water sources. Dissolved organics may cause taste, odor, or color problems in a community's drinking water, resulting in consumer complaints. Sources of SOCs include leaking underground gasoline/storage tanks, agricultural runoff containing herbicides or pesticides, solid waste or hazardous waste landfills, and improperly disposed chemical waste. The technologies most suitable for organic contaminant removal in drinking water systems are granular activated carbon (GAC) and aeration.

GAC has been designated by the U.S. Environmental Protection Agency (EPA) as the best available technology (BAT) for synthetic organic chemical removal. Various kinds of GAC are available for removing organics from drinking water. The most frequently used carbon in U.S. treatment plants is coal‐based carbon because of its hardness, adsorption capacity, and availability. Some peat and lignite carbons have been used also.

Aeration systems that might be suitable for small drinking water systems include packed column aeration, diffused aeration, and multiple‐tray aeration. Recent technologies that use aeration for organics removal include mechanical aeration, catenary grid, and Higee aeration.

Table 1 presents operational conditions for the organics treatment technologies most suitable for small systems.
Gravity Separation/Sedimentation
Authors: Ahmad Rasheed
Published: July 2005

Gravity separation or sedimentation is the step in conventional water treatment systems that follows flocculation and precedes filtration. Its purpose is to enhance the filtration process by removing particulate matter. Sedimentation requires that the water flow through a basin at a slow enough velocity to permit the particulate matter to settle to the bottom of the basin before the water exits the basin. The equipment required for this process includes a settling basin of rectangular, square, or circular configuration. The basin includes provisions for inlet and outlet structures and a sludge collection system. In addition, sedimentation systems are optionally equipped with tube or plate settlers to improve performance.
Water Conservation Measures
Authors:   National Drinking Water Clearinghouse
Published: July 2005

Water is a finite resource, and in many areas, future water supplies are uncertain. Individuals are usually aware when there is a drought; however, because water is inexpensive, there are often few incentives to reduce water loss. Water has no viable substitutes, and its depletion bodes profound economic and social impacts. Citizens and utilities need to consider water conservation programs.

This fact sheet considers the role of water conservation as an integral part of long‐term resource planning. It might be more appropriate to use the term “water demand management.” Traditional water supply management seeks to provide all the water the public wants, which, in some sections of the country, translates to a constant search for untapped sources.
Ozone
Authors:   National Drinking Water Clearinghouse
Published: July 2005

New water treatment goals for disinfection byproducts (DBP) and for microbial inactivation will increase the need to consider new disinfection technologies. Ozone is an attractive alternative. This technology has evolved and improved in recent years, thereby increasing its potential for successful application. It is important to note that ozone, like other technologies, has its own set of advantages and disadvantages that show up in differing degrees from one location to the next.
Radionuclides
Authors:   National Drinking Water Clearinghouse
Published: July 2005

Radionuclide contamination of drinking water is a significant, emerging issue. Until now, manmade radioactivity in drinking water has not been a major problem. Natural sources have been the primary cause of contamination. However, the potential for contamination exists throughout the country as releases from medical facilities or nuclear power plants may wind up in drinking water. Because of their potential health effects and widespread occurrence, natural radionuclides—including radon, radium, and uranium—cause much concern.
Slow Sand Filtration
Authors:   National Drinking Water Clearinghouse
Published: July 2005

First used in the U.S. in 1872, slow sand filters are the oldest type of municipal water filtration. Today, they remain a promising filtration method for small systems with low turbidity or algae‐containing source waters. Slow sand filtration does not require pretreatment or extensive operator control—which can be important for a small system operator with several responsibilities.
Ultraviolet Disinfection
Authors:   National Drinking Water Clearinghouse
Published: July 2005

Using ultraviolet (UV) light for drinking water disinfection dates back to 1916 in the U.S. Over the years, UV costs have declined as researchers develop and use new UV methods to disinfect water and wastewater. Currently, several states have developed regulations that allow systems to disinfect their drinking water supplies with UV light. Running a UV light system requires a basic level of operator skill and relatively clean source water. On the down side, however, UV offers no residual disinfection within the distribution system.
System Control and Data Acquisition (
SCADA
)
Authors: Lahlou Zacharia Michael
Published: July 2005

As small water systems continue to struggle to become more efficient, technology provides good ways to improve operations. Nowhere is this more apparent than in the application of control and communications systems—namely SCADA [System Control and Data Acquisition]—and their ability to provide system and information management that can help utilities meet regulatory requirements, reduce operating costs, and improve customer service. A water distribution system transports water from the treatment facility to the user. The distribtion system should supply water, without impairing its quality, in adequate quantities and at sufficient pressures to meet system requirements.
Valves
Authors: Lahlou Zacharia Michael
Published: July 2005

Valves direct, start, stop, mix, or regulate the flow, pressure, or temperature of a fluid. Valves range from simple water faucets to control valves equipped with microprocessors. Many different valve types exist; however, the most common types include gate, plug, ball, butterfly, check, pressure relief, and globe valves.
Water Hammer
Authors: Lahlou Zacharia Michael
Published: July 2005

Water hammer refers to fluctuations caused by a sudden increase or decrease in flow velocity. These pressure fluctuations can be severe enough to rupture a water main. Potential water hammer problems should be considered when pipeline design is evaluated, and a thorough surge analysis should be undertaken, in many instances, to avoid costly malfunctions in a distribution system. Every major system design change or operation change—such as the demand for higher flow rates—should include consideration of potential water hammer problems. This phenomenon and its significance to both the design and operation of water systems is not widely understood, as evidenced by the number and frequency of failures caused by water hammer.
Pumps
Authors: Bhardwaj Vipin , Reed Bethany
Published: July 2005

From start to finish, pumps play an important role in all water distribution systems. They are used to transfer raw water to the treatment plant; they supply water to sections of a distribution system where it is not possible to supply it by gravity; they add appropriate chemical doses during treatment; and they transfer sludge from settling chambers for further treatment and disposal. Pumps will provide long‐term efficient service if they are properly operated and maintained.
Assessing the Bactericidal Efficiency of Polydex for the Disinfection of Drinking Water in Rural Areas ofSouthAfrica
Authors: Momba M. N. B. , Makala N. , Okeyo A.
Published: July 2005

To evaluate the effectiveness of polydex for the removal of total coliforms (TC), fecal coliforms (FC), and presumptiveSalmonella(PS), three types of water sources were considered, which included raw water from a river, filtered surface water, and groundwater. The water samples were treated with two different doses of polydex: 3.9 mg/l and 5.4 mg/l. The dose of 3.9 mg/l appeared to be suitable for the disinfection of filtered surface water and groundwater samples with turbidity values ranging between 0.59 and 8.18 NTU. In these water samples, no coliforms were detected 5 h after disinfection, and the copper residuals ranged between 1.01 and 2.96 mg/l 7 h after disinfection. The results revealed that the dose of 3.9 mg/l was not sufficient for the disinfection of highly turbid waters (>9 NTU). A dose of 5.4 mg/l used for the disinfection of these waters completely removed coliform bacteria 7 h after disinfection, and the copper residual in the finished water ranged between 2.52–3.06 mg/l. Although this study has revealed the effectiveness of polydex as a disinfectant, its efficiency may vary with the turbidity of water source. For turbid water, it is recommended that the dose of polydex be higher than the one recommended by the manufacturer.
Chlorine and Chlorine Residuals
Authors: Rajagopal S. , Van Der Velde G. , Venugopalan V. P. , Jenner H. A.
Published: July 2005

Chlorine is a very commonly used biocide, widely employed for drinking water disinfection and cooling water treatment in industries. Being a strong oxidant, it involves itself in several reactions with a number of oxidizable substances present in water. Consequently, chemistry of chlorination in water is very complex and involves many reaction products. This chapter gives a brief account of the various reactions, their products (compounds as well as ionic species), and mentions about the analytical methods used for their measurement.
Anaerobic Sewage Treatment
Authors: Seghezzo Lucas , Zeeman Grietje , Lettinga Gatze
Published: July 2005

The state‐of‐the art of the anaerobic treatment of sewage, or domestic wastewater, is presented. The chapter begins with a brief definition of sewage and a description of the main pollutants contained in it. Negative consequences of the uncontrolled discharge of raw or badly treated sewage into the environment are summarized, with emphasis on health aspects. The technologies available to treat sewage are presented, focusing on the upflow anaerobic sludge bed (UASB) reactor. Some examples of the use of UASB reactors for sewage treatment are discussed. The chapter ends with an indication of the potential of UASB reactors to contribute to the achievement of more sustainable sanitation in developing countries.
Application of Risk Assessments in Crafting Drinking Water Regulations
Authors: Macler Bruce A.
Published: July 2005

Assessments of adverse health outcomes and estimations of health risks from contaminants of drinking water are used at several points in the overall development of U.S. drinking water regulations. They are applied during the extensive discussions surrounding consideration of a contaminant's risk and approaches to risk mitigation, and in the required elements of National Primary Drinking Water Regulation (NPDWR) proposals, support documents, and final rules. Risk assessments are of several types with substantially different intents and characteristics. No one approach fits all applications. The type of assessment chosen depends on the application and the nature and availability of relevant data.

The regulatory process starts with the identification of a constituent as either a possible contaminant of drinking water or as having some adverse toxicological or pathogenic properties. Available health data are then collected and analyzed, leading to the possible development of a toxicological profile of adverse health outcomes and dose–response characteristics. This is then coupled with occurrence data and exposure estimates to provide an estimate of national public health impact.
Multistage Drinking Water Filtration
Authors: Rooklidge Stephen J.
Published: July 2005

Multistage drinking water filtration is a combination of roughing filter and slow sand filter unit processes that broadens the use of these passive treatment methods to include source water whose turbidity is higher than that normally suitable for biological filtration. Slow sand filtration is one of the oldest surface water treatment techniques, but it is easily compromised by source water with high turbidity caused by erosional or meteorologic events in the upstream watershed. By providing roughing filter pretreatment, suspended solids are decreased and the biological integrity of the slow sand filter is maintained with a concomitant extension of the filtration period. Slow sand filtration is still a viable method of water treatment most suitable for raw water sources low in turbidity and suspended solids. Multistage filtration has been shown to be an efficient and effective drinking water treatment technique for source water with high turbidity, organic matter, and suspended solids.
Approaches for Securing a Water Distribution System
Authors: Hosner Marsha A.
Published: July 2005

The world focus on water security has been extremely heightened since the attack on the World Trade Center on September 11, 2001. The thinking behind the new focus is in response to terrorist threats on our drinking water and infrastructure in general. This heightened focus is generally a public response—citizens wanting something to be done to make them safer than they are currently. But water related security issues are not new.

The possibilities of things that could go wrong are impossible to list—a fact that points to a reality that has to be faced. There is no way to stop things from happening to your water systems. And though there are a number of things you can do to reduce the risk, the most important step to take is preparing in advance for the time when something does happen.
Nitrification of Potable Water Using Trickling Filters
Authors: Vayenas D.V. , Lyberatos Gerasimos
Published: July 2005

Due to the nitrogenous oxygen demand and the carcinogenic chloramines that are formed, ammonia needs to be removed from potable water before it can be consumed. Ammonia may be removed chemically or biologically. Biological ammonia removal (nitrification) is carried out by two different nitrifying bacteria,
Nitrosomonas
and
Nitrobacter
. Due to the low specific growth rates of these bacteria, high nitrification rates can be secured only in attached growth systems such as trickling filters. This allows retaining the slow‐growing nitrifiers even at high hydraulic loadings. The choice of filter medium is of great importance because it provides the surface for bacterial growth and determines the air and water flow characteristics of the filter. Recirculation may enhance nitrification in trickling filters for high hydraulic and ammonia loads, whereas iron and manganese inhibit nitrification. Modeling of nitrification in trickling filters allows proper design of the filters and prediction of their performance. Such mathematical models have been used to develop operating diagrams that may be used to ensure safe and complete nitrification of potable water for a wide range of flow rates and ammonia feed concentrations.
Design of Water Distribution Systems
Authors: Lingireddy Srinivasa , Ormsbee Lindell E. , Wood Don J. , Ramalingam D.
Published: July 2005

The ultimate goal of drinking water utilities is to provide adequate quantities of water to its consumers while maintaining satisfactory pressures throughout the distribution system. Efficient design of water distribution system components is an important step that allows not only achieving this goal but also enabling the utilities to provide water at affordable costs. Design of water distribution systems is a complex and tedious process. Several optimization techniques have been reported in literature to automate and reduce the complexity of the design process. However, lack of robust optimization platforms that allow specification of preferred objective functions and desired combinations of constraints and decision variables have seriously limited the use of available optimization technology for water distribution systems design. This article presents a comprehensive iterative method that makes use of a hydraulic network model for design of water distribution systems. The article describes various components of a water distribution system that would affect the design process along with a list of constraints that should be considered for efficient design. Although the procedure presented is for design of new water distribution systems, the method can be easily adapted for sizing enhancements to existing systems.