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38612 results in Cambridge Textbooks

Page 946 of 1931

  • 1 - Water Resources

  • from Part I - Concepts Related to Water
  • Sudha Goel
  • Book:
    Water and Wastewater Engineering
    Published online:
    11 August 2021
    Print publication:
    21 November 2019, pp 3-34

  • Summary

    Learning Objectives

  • • Identify and classify water resources

  • • Describe the hydrologic cycle

  • • Differentiate between surface water and groundwater resources

  • • Describe confined and unconfined aquifers

  • • Derive Darcy's law and apply it to relevant groundwater scenarios

  • • Determine yields, permeabilities, hydraulic conductivities and flow velocities of groundwater through confined and unconfined aquifers

  • • Describe different types of wells, their methods of construction and conditions for their use

  • • Identify sources of groundwater contamination and their transport in the subsurface

  • • Identify potential sources of contamination for surface water bodies

  • • Classify surface water bodies based on CPCB standards

  • • Calculate pollutant or nutrient loading to a water body

  • • Design and describe different types of surface water intakes and wells

  • • Identify sources of contamination, their constituents and concentrations in surface water bodies

  • • Describe and design infiltration wells and galleries and the conditions under which they can be used

    • Freshwater is only 3 percent of the total water on the planet, and includes groundwater which is almost 30 percent of this, while surface water is a meager 0.3 percent. Glaciers and icecaps comprise the remaining, at slightly less than 70 percent of the total, freshwater resources of the planet.

    The movement of water in any of its three states (solid, liquid, or gaseous) through different parts of the planetary environment is termed the hydrologic cycle and is shown in Figure 1.1

    It can be broadly defined in terms of six major processes:

    Precipitation is the sum total of all water that falls over land and surface water bodies including rivers, seas, and oceans and includes rain, ice, snow, hail, and sleet.

    Condensation is that part of water vapor in the atmosphere that condenses on particles to form clouds. When these clouds are supersaturated, the water vapor is released in the form of precipitation.

    Evapotranspiration is the release of water to the atmosphere from various water bodies by evaporation and from plants during the process of transpiration or respiration.

    Surface runoff is defined as the amount of water that flows over land towards any surface water body. Any and all surface water bodies from small ponds and lakes to seas and oceans can serve as sinks for surface runoff. Some of these water bodies are transient (seasonal) while others are permanent.

  • 5 - Physico-Chemical Processes for Water and Wastewater Treatment

  • from Part II - Water and Wastewater Treatment Processes
  • Sudha Goel
  • Book:
    Water and Wastewater Engineering
    Published online:
    11 August 2021
    Print publication:
    21 November 2019, pp 177-262

  • Summary

    Learning Objectives

  • • Use water supply and demand data to design balancing storage reservoirs or equalization tanks

  • • Describe the 2-film theory of gas transfer

  • • Evaluate different aeration strategies and design an appropriate aeration process for water or wastewater treatment

  • • Describe different types of screens and their applications in water and wastewater treatment

  • • Design screens and determine head loss through different types of screens

  • • Define different types of settling and the conditions under which they occur

  • • Design different types of settling tanks for primary and secondary clarification

  • • Describe the double layer model for particles and its application in coagulation processes

  • • Describe the mechanisms of coagulation and flocculation

  • • Determine hardness in water and design processes for softening water

  • • Identify types of filtration processes, evaluate their use for different water samples and design appropriate units

  • • Describe different types of membrane filters and conditions for their use

  • • Design membrane filtration processes for drinking water treatment

    • BALANCING STORAGE OR FLOW EQUALIZATION

    A major design unit in water and wastewater treatment is a balancing storage reservoir (water treatment) or a flow equalization tank (wastewater treatment). Since flow is never constant and is subject to seasonal and diurnal variations, fluctuations in water demand and generation of wastewater have to be accounted for in the design of these reservoirs or tanks.

    Distribution reservoirs are used in water treatment plants to store treated water for balancing hourly variations in water demand and for emergencies like fires, break-downs, and repairs. These reservoirs are also called service reservoirs. The main functions of a distribution reservoir are:

  • To balance hourly variations in water demand thus allowing water treatment units and pumps to be operated at a constant rate. This in turn reduces costs and improves efficiency,

  • To maintain constant heads in the distribution mains. In the absence of storage reservoirs, pressure would fall as demand increases. Use of distribution reservoirs dampens pressure fluctuations,

  • To allow pumping of water in shifts to meet the whole day's demand without affecting water supply,

  • To supply water during emergencies like fires, breakdowns or repairs, and

  • To reduce the size of pumps, pipelines and treatment units, thereby leading to overall economy in design of water supply systems.

  • 3 - Water Quality

  • from Part I - Concepts Related to Water
  • Sudha Goel
  • Book:
    Water and Wastewater Engineering
    Published online:
    11 August 2021
    Print publication:
    21 November 2019, pp 67-134

  • Summary

    Learning Objectives

  • • Identify pollutants present in water and evaluate their impact on the water quality of surface and groundwater resources

  • • Analyze water samples for basic water quality parameters and describe their significance for public health or the environment

  • • Describe the importance of pH and the factors affecting it

  • • Define ionic strength and calculate it

  • • Define activity coefficients and describe their importance in quantifying chemical equilibrium relationships

  • • Define electrical conductivity and why it can serve as a surrogate for total dissolved solids

  • • Differentiate between different categories of solids in water or wastewater samples based on their measurement methods

  • • Describe the importance of temperature in evaluating the health of an aquatic system, the factors affecting it and water quality parameters affected by it.

  • • Describe the importance of dissolved oxygen levels in water with respect to public health and aquatic systems

  • • Describe the importance of turbidity in evaluating the health of an aquatic system and the factors affecting turbidity

  • • Describe sources of alkalinity in water sources, and their importance in determining water quality

  • • Describe problems associated with hardness, its impact on water quality and water uses.

  • • Describe the importance of color as a water quality parameter

  • • Define and describe different methods for estimating oxygen demand in water, their importance and applications

  • • Calculate ThOD for specific compounds or for a wastewater with known chemical composition

  • • Describe the COD test and its relation to ThOD

  • • Describe the BOD test and its relation to ThOD and COD and to the health of aquatic systems

  • • Describe the use and importance of TOC measurements for aquatic samples

  • • Describe the processes by which synthetic organic compounds enter natural aquatic systems

  • • Evaluate the presence of different elements in water and their importance

  • • Evaluate concentrations of major macronutrients in water and their importance

  • • Define the limiting nutrient in any aquatic system

  • • Evaluate the concentrations of micronutrients in water and their impact on the growth of organisms

  • • Evaluate the presence of toxic heavy metals in water and their impact on public health or environment

  • • List microbiological constituents in natural waters and their importance from a water quality perspective

  • • Differentiate between prokaryotes and eukaryotes

  • • Describe viruses and list some examples of diseases associated with viruses

  • • List common pathogenic bacteria and diseases associated with bacteria in water

  • 7 - Strategies for Water and Wastewater Treatment

  • from Part II - Water and Wastewater Treatment Processes
  • Sudha Goel
  • Book:
    Water and Wastewater Engineering
    Published online:
    11 August 2021
    Print publication:
    21 November 2019, pp 343-381

  • Summary

    Learning Objectives

  • • Estimate the quantity and quality of wastewater generated in a community

  • • Analyze water quality data and determine treatment needs for different water uses

  • • Identify contaminants in untreated water or wastewater and the extent of removal required based on prevalent standards

  • • Describe the objective of each treatment unit to be used in water or wastewater treatment

    • The first step in the design of water and wastewater treatment plants is identification of appropriate treatment processes for meeting the required standards or treatment objectives. This requires identification of contaminants in water or wastewater based on regulatory standards that are applicable and an understanding of the extent to which treatment objectives can be achieved by a given treatment process. In many cases, treatment objectives cannot be fulfilled by one treatment process and a combination of two or more processes becomes necessary. All sections in this chapter address the issue of treatment objectives and the choice of treatment processes that can be used to achieve these objectives. Conventional drinking water treatment processes for surface and groundwater are addressed first, followed by non-conventional water treatment. Specific treatment methods (combinations of unit processes) for removal of specific pollutants like arsenic, fluoride, and nitrate are discussed in this section. The last section deals with conventional and higher levels of municipal wastewater treatment.

    CONVENTIONAL DRINKING WATER TREATMENT SCHEMES

    The main objective of any water supply scheme is to provide safe and adequate amount of potable water to all residents in the service area. This requires ‘sourcing’ of water so that it is of good quality to begin with. Protection of raw water quality for maintaining its quality in the future and ensuring that it remains a sustainable source is the next important aspect of a water supply scheme. The source water then has to be treated to the level of the prevailing drinking water standards. Water treatment has two major outputs: finished water which is provided to the consumer through the distribution system and wastewater including sludge which requires further management. Wastewater generated at the drinking water treatment plant, includes backwash water, wastewater generated from housekeeping in the treatment plant, and supernatant from the sludge drying beds.

  • Part II - Water and Wastewater Treatment Processes

  • Sudha Goel
  • Book:
    Water and Wastewater Engineering
    Published online:
    11 August 2021
    Print publication:
    21 November 2019, pp 175-176

  • Summary

    Part II of the book deals with the treatment processes that are used in water or wastewater treatment plants. Water for domestic or municipal use is drawn from surface or groundwater sources and depending on the quality desired for drinking purposes, it is treated in a water treatment plant. After treatment, the treated water is supplied to consumers through a distribution network. Wastewater is generated by consumers after use and is collected in sewer systems from where it is transported to a wastewater treatment plant. The treated wastewater is then discharged on land, into a surface water body or into the sea. However, due to water scarcity and costs of wastewater treatment, water is now increasingly reused for irrigation or industrial purposes or recycled for other purposes. In some cases, wastewater that has been treated to tertiary or even higher levels can be used for drinking purposes. Two examples of such complete recycling of water are the public water supply systems in Singapore since 1998 and Namibia since 1968 (Pruden 2014).

    Water treatment processes were mainly physico-chemical processes until a few decades ago. This was done based on an intuitive understanding that one of the major objectives of water treatment was elimination of microbes, especially pathogens, and therefore, all biological processes were kept out. However, increase in water quality requirements (removal of TOC was not necessary until regulations for disinfection by-products became effective), and the recognition that processes like filtration (porous media and membrane) and disinfection are inherently a mix of physical, chemical and biological processes has led to an understanding that any categorization is necessarily arbitrary. A specific example is the use of biofiltration for enhanced removal of TOC along with turbidity in water treatment and the recognition that biological growth occurs naturally in porous media filters and can be controlled and used to advantage. It should also be noted that physico-chemical processes are generally considered to be either primary or tertiary levels of treatment for wastewater. A list of the treatment processes, included in Chapters 5 and 6, is provided in the following table along with their points of application in water and wastewater treatment.

  • 9 - Municipal Wastewater Collection and Disposal

  • from Part II - Water and Wastewater Treatment Processes
  • Sudha Goel
  • Book:
    Water and Wastewater Engineering
    Published online:
    11 August 2021
    Print publication:
    21 November 2019, pp 397-410

  • Summary

    Learning Objectives

  • • Compare and contrast separate versus combined wastewater collection systems

  • • Describe different methods for disposal of wastewater and conditions for doing so

  • • Describe options for reusing municipal wastewater and treatment requirements for reuse

    • Sewage or municipal wastewater includes human and household wastes, street washing, wastewater from industrial and commercial activities in the municipal area, groundwater and stormwater. There are two major types of sewage collection systems: dry or conservancy systems in unsewered areas and wet carriage systems in sewered areas (Duggal 2007).

    The dry or conservancy system is common in rural and semi-urban areas where there are no sewer systems. Night soil (feces and urine, i.e., human excreta) is collected in latrines, privies, septic tanks, cesspits, or twin-pit latrine systems. Anaerobic conditions develop and reduce the solid concentrations in the sewage in these systems, which are removed manually or mechanically at relatively long intervals of 1–5 years.

    Wet carriage systems are common in urban centers where sewerage systems have been provided. Wastewater is collected from individual buildings (toilets, sinks, bathrooms, any other water using facilities) and taken for treatment to a sewage treatment plant. The wet carriage system is popular in urban centers all over the world since it does not require manual transport of excreta, it results in better hygiene and reduced risk of waterborne diseases, has less odor and is aesthetically better than the dry systems. The only disadvantages are the high capital and maintenance costs, and excessive water consumption. Only wet carriage systems are addressed in this textbook.

    Conventional and advanced wastewater treatment schemes were discussed in Chapter 7, Section 7.3. After treatment, municipal wastewater can be reused or disposed in various ways and are discussed in this chapter.

    MUNICIPAL WASTEWATER COLLECTION SYSTEMS

    Wastewater collection systems are generally designed as combined sewer overflow (CSO) especially in old cities with sewerage systems where wet and dry weather flows are collected and treated together. However, a relatively recent trend which started in the twentieth century (Mannina and Viviani 2009) is to design separate sewage collection systems for dry and wet weather flows, respectively. Separate collection systems have two drainage networks, one for stormwater flows and the other for sewage flows, which result in higher capital costs. However, cost-benefit analysis and comparison of the two systems remains a difficult and debatable issue with no clear answers.

  • Part I - Concepts Related to Water

  • Sudha Goel
  • Book:
    Water and Wastewater Engineering
    Published online:
    11 August 2021
    Print publication:
    21 November 2019, pp 1-2

  • Summary

    ‘Clean water and sanitation’ is one of the seventeen Sustainable Development Goals set by the United Nations General Assembly in 2015 and is to be achieved globally by 2030. Access to safe drinking water is considered a basic human right and more than 1 billion people in the world continue to suffer due to water-related diseases, resulting in many deaths.

    Achieving this goal will require designing appropriate water supply and wastewater treatment systems. The first part of this book provides background information that is essential for understanding and designing these systems. The first step in the design of water supply systems is to identify a sustainable water source for the community. These water sources can be surface water or groundwater and are described in the first chapter. Methods for withdrawal of water from these sources are included. The extent to which these sources are contaminated will determine the degree of treatment that is necessary.

    The next important step in the design of water supply systems is to determine the quantity and quality of the water that is needed. Water demand varies both temporally and spatially. Temporal variations on a daily and seasonal basis need to be accounted for in design. Spatial variations in water demand are mainly due to the size of the population that is to be served. Accurate forecasting of future populations is an extremely important step in determining the size and design of both water supply and wastewater systems. Factors that influence water demand are addressed in Chapter 2. Water quality requirements have become more stringent over time necessitating higher levels of treatment. Major water quality parameters of importance in water supply and wastewater systems are described with examples in Chapter 3.

    Finally, basic principles of reaction kinetics and reactor design are described in Chapter 4. These principles are necessary for understanding the transport and transformation of contaminants within water and wastewater treatment systems and are applied to the design of treatment processes which are covered in the second part of the book.

  • 2 - Water Demand

  • from Part I - Concepts Related to Water
  • Sudha Goel
  • Book:
    Water and Wastewater Engineering
    Published online:
    11 August 2021
    Print publication:
    21 November 2019, pp 35-66

  • Summary

    Learning Objectives

  • • Determine water requirements for different uses, communities, and future populations

  • • Define consumptive and non-consumptive uses of water

  • • Cite appropriate standards for different uses of water and determine minimum water requirements

  • • Describe how scale affects quantification of water use

  • • Describe differences in water use and supply in rural and urban communities in India

  • • Model available population data to forecast future populations in different communities

  • • Justify the use of different population forecasting methods for different conditions

  • • Quantify seasonal and daily variations in water demand for design of water supply systems

    • Water is the most important requirement for sustaining life. Design of water supply systems requires that the water source be adequate in terms of quantity, quality and sustainability. Design of wastewater systems requires knowledge of water quantities used and treatment standards to be achieved. This chapter deals with the different uses of water and how much needs to be supplied at a minimum.

    Figure 2.1 shows the flow of water through water supply and wastewater systems for any given location, e.g., a city, town, or small community. Water is extracted from a groundwater or surface water resource and is taken for treatment to a water treatment plant. The degree of treatment provided depends on the quality of the raw water. After treatment, the water is sent into the distribution system from where it reaches individual consumers. These consumers may be single households, apartment buildings, offices, industries or factories, commercial or business establishments, or any other place where clean water is required.

    After use, the discarded water is termed ‘wastewater’ and in general, it goes into drains in sewered communities. The wastewater in sewerage systems is taken for treatment to a wastewater treatment plant. After treatment, the wastewater is discharged on land or in the sea, or it can be reused for horticulture, irrigation, industrial uses, and cleaning activities depending on the degree of treatment provided. Where drainage or sewerage systems are not present, the wastewater may be drained into cess pits, septic tanks, or reused after providing some treatment.

    DESIGN OF WATER SUPPLY SYSTEMS

    The most important task in the design of water supply systems is identification of an appropriate source of water.

Page 946 of 1931