Fundamentals of Wastewater Treatment and Engineering

Rumana Riffat, Taqsim Husnain

• Publisher: CRC Press
• Year: 2022
• ISBN:
  9781000575163
• Edition: 2
• Topic: Tecnología e ingeniería
• Subtopic: Gestión medioambiental

The 2nd edition of Fundamentals of Wastewater Treatment and Design introduces readers to the fundamental concepts of wastewater treatment, followed by engineering design of unit processes for sustainable treatment of municipal wastewater and resource recovery. It has been completely updated with new chapters to reflect current advances in design, resource recovery practices and research. Another highlight is the addition of the last chapter, which provides a culminating design experience of both urban and rural wastewater treatment systems.

Filling the need for a textbook focused on wastewater, it covers history, current practices, emerging concerns, future directions and pertinent regulations that have shaped the objectives of this important area of engineering. Basic principles of reaction kinetics, reactor design and environmental microbiology are introduced along with natural purification processes. It also details the design of unit processes for primary, secondary and advanced treatment, as well as solids processing and removal. Recovery of water, energy and nutrients are explained with the help of process concepts and design applications.

This textbook is designed for undergraduate and graduate students who have some knowledge of environmental chemistry and fluid mechanics. Professionals in the wastewater industry will also find this a handy reference.

Chapter 1 Sustainable wastewater treatment and engineering

DOI: 10.1201/9781003134374-1

1.1 Introduction and history

The science and engineering of wastewater treatment has evolved significantly over the last century. As the population of the world has increased, our sources of clean water have decreased. This has shifted our focus towards pollution reduction and resource recovery. Disposal of wastes and wastewater without treatment in lands and water bodies is no longer an option. An increasing body of scientific knowledge relating waterborne microorganisms and constituents to the health of the population and the environment have spurred the development of new engineered technologies for the treatment of wastewater and potential reuse.

The term wastewater includes liquid wastes and wastes transported in water from households, commercial establishments, and industries, as well as storm water and other surface runoff. Wastewater may contain high concentrations of organic and inorganic pollutants, pathogenic microorganisms, as well as toxic chemicals. If the wastewater is discharged without treatment to a stream or river, it will result in severe pollution of the aquatic environment. The decline in water quality will render the stream water unusable for future drinking water purposes. Sustainable wastewater engineering involves the application of the principles of science and engineering for the treatment of wastewater, to remove and/or reduce the pollutants to an acceptable level prior to discharge to a water body or other environment, without compromising the self-purification capacity of that environment. The treatment, disposal, and beneficial reuse of the generated solids and other by-products are an integral part of the total process.

If we look back in time, wastewater engineering has progressed from collection and open dumping, to collection and disposal without treatment, to collection and treatment before disposal, all the way to collection and treatment prior to reuse. Evidence of waste collection in the streets, and then use of water to wash them through open sewers have been found in the ancient Roman Empire. In the early 1800s, the construction of sewers was started in London, in Great Britain. In 1843, the first sewer system of Hamburg, Germany, was officially designed by a British engineer Lindley (Anon, 2011). In the United States (US), in seventeenth-century Colonial America, household wastewater management consisted of a privy (toilet) with an outlet constructed at ground level that discharged outside to a cesspool or a sewer. With low population densities, privies and cesspools constructed in this way did not cause many problems (Duffy, 1968). But as the population increased, the need for an engineered system for wastewater management in large cities became more evident. Scientists and public health officials started to understand the relationship between disease outbreaks and contamination of drinking water from wastewater. Nuisance caused by odors, outbreaks of diseases, e.g. cholera, and other public health concerns prompted the design of a comprehensive sewer system for the city of Chicago in the 1850s. At that time, the sewer system was used to transport the untreated wastewater outside of the residential community to a stream or river. Dilution of the wastewater with the stream water was the primary means of pollutant reduction. These were called water-carriage sewer systems.

Public health concerns in the 1850s also resulted in the planning and development of a water-carriage sewer system for the city of London. A cholera epidemic struck London in 1848 and again in 1854, causing a total of more than 25,000 deaths (Burian et al., 2000). Dr. John Snow was the first doctor at that time who established a connection between the cholera outbreak and a contaminated water supply at the Broad Street public well. In addition, he showed statistically that cholera victims had drawn their drinking water from a sewage-contaminated part of the river Thames, while those who remained healthy drew water from an uncontaminated part of the river. These findings together with the discoveries by Pasteur and Koch prompted the British parliament to pass an act in 1855, to improve the waste management system of the city of London. This led to the development of a comprehensive water-carriage sewer system for London, designed by Joseph Bazalgette (Hey and Waggy, 1979).

Toward the beginning of the twentieth century, sewage treatment plants mainly used settling tanks (primary treatment) to remove suspended particles from the wastewater before discharge to streams and rivers. In the early 1900s, about one million people in the US were served by 60 such treatment plants. During that time, the first trickling filter was constructed in Wisconsin, Madison to provide biological (secondary) treatment to wastewater. The Imhoff tank was developed by German engineer Karl Imhoff in 1906 for solids separation and further treatment. The first activated sludge process was constructed in San Marcos, Texas, in 1916 (Burian et al., 2000). Advances in sludge digestion and gas production were also being accomplished by researchers and utilities. From the mid-1900s to the present time, we have seen the development of various types of biological and biochemical processes for the removal of pollutants from wastewater. The earlier objectives were mainly to reduce the total suspended solids (TSS), biochemical oxygen demand (BOD), and pathogens. Primary and secondary biological treatment was considered sufficient for the production of treated wastewater of acceptable standards. With industrialization and scientific advances, chemical and toxic compounds have been detected in municipal wastewater. This has resulted in the need for additional treatment beyond the secondary, giving rise to tertiary treatment. Tertiary or advanced treatment can be physical, chemical or biological, or a combination of these processes.

1.2 Current practice

The primary treatment in most municipal wastewater treatment plants consists of preliminary and primary stages. It typically includes screens, grit chambers, comminutors, and primary clarifiers, depending on the flow rates. Larger plants use chemically enhanced primary clarification for higher solids removal efficiency. The primary treatment is followed by a secondary treatment. The secondary treatment consists of a biological process followed by a secondary clarifier. If the secondary effluent meets the regulatory standards for BOD and TSS, it is discharged to receiving waters following disinfection. The solids and sludge collected from the various units undergo further processing and treatment before disposal. Various options are available for sludge processing. A conventional wastewater treatment plant is illustrated in Figure 1.1.

Figure 1.1 Flow diagram of a conventional wastewater treatment plant.

More than half of the municipal wastewater treatment plants in the US are capable of providing at least secondary treatment. About 92% of the total flow is treated by plants with a capacity of 0.044 m³/s (1 million gallons per day or MGD) or larger (Metcalf and Eddy et al., 2013). In the last two decades, nutrient removal has become increasingly more important in parts of the US, as well as in Europe and Asia. Eutrophication caused by excessive nitrogen and phosphorus in wastewater discharges has disrupted the aquatic life in receiving water bodies with a subsequent decline in water quality. Wastewater treatment plants in affected areas and watersheds have to provide additional nutrient removal prior to discharge. Biological nutrient removal is incorporated as part of the secondary treatment, or as tertiary treatment. Nutrient removal is no longer considered an advanced treatment option. An example of this is the Chesapeake Bay watershed in the eastern US, and the municipal wastewater treatment plants within the watershed. Most of the plants use biological nitrification–denitrification together with BOD removal, and/or chemical precipitation for removal of phosphorus. The use of granular media filtration as a tertiary treatment for the reduction of TSS is also quite common. Table 1.1 presents the pollutants commonly found in municipal wastewater and the physical, chemical, and biological processes used to remove or reduce their concentrations.

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Table 1.1 Common wastewater pollutants and the processes used to reduce/remove them

Pollutants	Unit processes
Suspended solids	Coarse screens, fine screens Grit chamber Clarification Filtration Chemically enhanced clarification
Colloidal and dissolved solids	Chemical precipitation Membrane filtration Ion exchange Activated carbon adsorption
Biodegradable organics	Suspended growth processes (aerobic and anaerobic) Attached growth processes (aerobic and anaerobic) Ponds and lagoons Membrane bioreactors
Pathogens	Chlorination Ozonation Ultraviolet disinfection
Nutrients