Handbook of Water and Wastewater Treatment Technology

Paul N. Cheremisinoff

• Editore: Routledge
• Anno: 2019
• ISBN:
  9781351441889
• Edizione: 1
• Argomento: Technologie et ingénierie
• Categoria: Gestion de l'environnement

Offers information on the treatment of water and wastewater for municipal, sanitary and industrial applications, focusing on unit operations and processes that serve the broadest range of users. Wastewater treatement unit operations, including filtration, flotation, chemical coagulation, flocculation and sedimentation, as well as advanced technolog

1

Water Characteristics

Both individuals and industry produce liquid and solid wastes. The liquid portion, wastewater, is essentially water supply after it has been fouled by use. From the standpoint of sources of generation, wastewater may be defined as a combination of the liquid of water-carried wastes removed from residences, institutions, and commercial and industrial establishments together with such groundwater, surface water, and storm water as may be present. The ultimate goal in wastewater management is the protection of the environment commensurate with economic, social, political, and health concerns.

With increasing density of population and industrial expansion, the need for treatment and disposal of waste has grown. The specific reasons for sewage and waste treatment are as follows.

HEALTH CONCERNS

Disease-producing organisms, especially those causing diarrhea, may be present in sewage. Little is known about the presence of toxic substances produced by bacterial decomposition of certain organic substances, although a variety of degradation products are formed. From a health standpoint, the greatest problem of pollution is its effect on public water supplies by overloading the treatment devices so that they pass intestinal organisms, and by producing intestinal irritants in water which are not removed by filtration. Sewage pollution of bathing waters and shellfish areas may result in epidemics such as typhoid or other intestinal diseases as well as contamination of the food chain. Sewage treatment which reduces the pollution and kills intestinal organisms assists in the production of a safe drinking water at a lower cost, prevents contamination of shellfish, and permits bathing, water sports, and recreation.

ESTHETIC CONCERNS

The discharge of sewage into streams and water courses produces odors and discoloration, results in nuisances from sludge, and interferes with bathing facilities and recreation.

PROPERTY DAMAGE

The discharge of sewage affects industrial water supplies by changing the character of the water. Odors and gases in sewage affect real estate by causing paints to discolor as well as damage to boats. Some treatment of wastewaters is usually necessary before disposal. The methods of treatment adopted must be sufficient to ensure the necessary degree of purification required to suit the means of disposal.

Most unit operations and processes used for wastewater treatment are constantly undergoing continual and intensive investigation from the standpoint of implementation and application. As a result, many modifications and new operations and processes have been developed and implemented; more need to be made to meet increasingly stringent requirements for environmental enhancement of water. In addition to the developments taking place with conventional treatment methods, alternative treatment systems and technologies are also being developed and introduced.

AVAILABLE TREATMENT SYSTEMS

The treatment process chosen is a function of several factors:

• Flow rate

• Waste strength and toxicity

• Availability of land

• Esthetics

• Discharge standards

• Climatic conditions

• Degree of permanence desired

• Costs

For example, in remote areas where land is inexpensive and climate is favorable, a percolation/evaporation pond may provide simple zero discharge solution, whereas in a suburban community in which the ultimate discharge enters surface waters, an esthetic and high-performance plant which may include some type of tertiary facility would be more appropriate. Table 1 shows the various wastewater treatment options in use. Materials removed during water/wastewater treatment is called sludge, and Table 2 lists the options for its management.

CHARACTERISTICS OF WASTEWATER

An understanding of the nature of wastewater is essential in the design and operation of collection, treatment, and disposal facilities and in the engineering management for environmental quality.

The physical properties and the chemical and biological constituents of wastewater and their sources are listed in Table 3. The important contaminants of interest in wastewater treatment are listed in Table 4. Wastewater characterization studies are conducted to determine the physical, biological, and chemical characteristics and the concentrations of constituents in the wastewater as the best means of reducing the pollutant concentrations.

EFFECTS OF POLLUTION

Effects of pollution can be manifested by many characteristics and variations in degree when pollution enters the aquatic environment. Specific environmental and ecological responses to a pollutant will depend largely on the volume and strength of the waste and the volume of water receiving it. Within each response there can be many changes in magnitude and degree. A classic response that has often been described is the effects of organic wastes that may be discharged from sewage-treatment plants and certain industries. As these wastes enter the receiving water, they create turbidity, decrease light penetration, and may settle to the bottom in substantial quantity to form sludge beds. Wastes are attacked by bacteria and this process of decomposition consumes oxygen from the water and liberates essential nutrients that in turn stimulate the production of some forms of aquatic life.

Upstream from the introduction of organic wastes is a clean water zone or one that is not affected by pollutants. At the point of waste discharge and for a short distance downstream there is formed a zone of degradation where wastes become mixed with the receiving waters and where the initial attack is made on the waste by bacteria and other organisms in the process of decomposition.

Following the zone of degradation there is a zone of active decomposition that may extend for miles or days of stream flow, which depends in large measure on the volume of the waste by the stream and the temperature of the water. Biological processes that occur within this zone are similar in many respects to those that occur in a typical sewage treatment plant. Within this zone, waste products are decomposed and those products that are not settled as sludge are assimilated by organisms in life processes.

Table 1 Wastewater Treatment Options

Table 2 Options for Sludge Management

Disposal	Sludge treatment	Sludge disposal
	Aerobic Digestion
Chlorination Ozonation	Anaerobic Digestion	Incineration
Receiving Waters or Reuse	Wet Combustion	Land Fill
Controlled or Transported Discharge	Centrifugation	Soil Conditioning
Ocean Disposal	Thickening	Ocean Disposal
Surface Application or Ground Water Seepage	Vacuum Filtration Lagooning, or Drying Beds
Evaporation + Incineration

A recovery zone follows the zone of active decomposition. The recovery zone is essentially a stream reached in which water quality is gradually returned to that which existed prior to the entrance of pollutants. Water quality recovery is accomplished through physical, chemical, and biological interactions within the aquatic environment. The zone of recovery may also extend for many miles, and its extent will depend principally on morphometric features of the waterways. The zone of recovery will terminate in another zone of clean water or area unaffected by pollution that is similar in physical, chemical, and biological features to that which existed upstream from the pollution source.

Organic Wastes

The effects of organic wastes on the receiving stream often become confused with a specific stream because additional sources of pollution may enter the environment before the receiving water has been able to assimilate the entire effects of an initial source. When this occurs, the effects of subsequent introductions become superimposed on the initial source and the total effect may confine large reaches of stream to a particular zonal classification.

Effects of organic wastes in the static water environment, as opposed to the flowing water environment, are modified by the features of the receiving water. Zonal changes for flowing water do exist but may be compressed in great measure either laterally or vertically when the discharge is to a lake or estuary. Such compression may tend to decrease the severity of pollution that is often observed in the flowing water environment and, on the other hand, may increase substantially the development of biotic nuisances such as algae or rooted aquatic plants that may develop from the nutrients released with and decomposed from the introduced organic materials.

Table 3 Physical, Chemical, and Biological Characteristics of Wastewater and Their Sources

...

Characteristic	Sources
Physical Properties
Color	Domestic and industrial wastes, natural decay of organic materials
Odor	Decomposing wastewater, industrial wastes
Solids	Domestic water supply, domestic and industrial wastes, soil erosion, inflow-infiltration
Temperature	Domestic and industrial wastes
Chemical Constituents Organics
Carbohydrates	Domestic, commercial, industrial wastes
Fats, oils and grease	Domestic, commercial, industrial wastes
Pesticides	Agricultural wastes
Phenols	Industrial wastes
Proteins	Domestic and commercial wastes
Surfactants	Domestic and industrial wastes
Others	Natural decay of organic materials
Inorganics
Alkalinity	Domestic wastes, domestic water supply, ground water infiltration
Chlorides	Domestic water supply, domestic wastes, ground water infiltration, water softeners
Heavy metals	Industrial wastes
Nitrogen	Domestic and agricultural wastes
pH	Industrial wastes
Phosphorus	Domestic and industrial wastes, natural runoff
Sulfur	Domestic water supply, domestic and industrial wastes
Toxic compounds	Industrial wastes
Gases
Hydrogen sulfide	Decomposition of domestic wastes
Methane	Decomposition of domestic wastes
Oxygen	Domestic water supply, surface water infiltration