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The past few years have seen the emergence of a growing, widespread desire in this country, and indeed everywhere, that positive actions be taken to restore the quality of our environment, and to protect it from the degrading effects of all forms of pollution-air, noise, solid waste, and water. Since pollution is a direct or indirect consequence of waste, if there is no waste, there can be no pollution, and the seemingly idealistic demand for "zero discharge" can be construed as a demand for zero waste. However, as long as there is waste, we can only attempt to abate the consequent pollution by converting it to a less noxious form. In those instances in which a particular type of pollution has been recognized, three major questions usually arise: (1) How serious is the pollution? (2) Is the technology to abate it available? and (3) Do the costs of abatement justify the degree of abatement achieved? The principal intention of this series of books on environmental engineering is to help the reader formu­ late useful answers to the second and third of these questions, i. e. , to outline the best currently available engineering solutions, and to examine their costs in the light of the real level of benefits afforded. The traditional approach of applying tried-and-true solutions to specific pollution problems has been a major factor contributing to the success of environmental engineering, and in large measure has ac­ counted for the establishment of a "methodology of pollution control.



1. Biological Concepts for Environmental Control

Breakdown of organic wastes by normal cellular processes is often an effective and economic treatment. This chapter will introduce certain concepts from biochemistry and biology that are fundamental to biological waste treatment. Specific treatment processes will be covered in subsequent chapters.
Mary Lou Bungay, Henry R. Bungay

2. Treatment by Application onto Land

This chapter considers the use of various land application techniques as means for treatment and disposal of wastewater. Considerations include the disposal of the water, removal of pollutants in the wastewater, the impact upon the soil through which the liquid is passed, and potential groundwater contamination. Means discussed for the disposal of wastewater include (a) surface spreading or overland flow, (b) slow rate or crop irrigation, and (c) rapid infiltration-percolation. There are variations of these techniques, but in general they can be considered in terms of these three mechanisms. Application in wetlands and subsurface disposal are not considered here. The advantages and disadvantages of applying the liquid onto ground that has a plant cover as opposed to application onto bare ground are considered. No one method is recommended over and above all the others, since certain methods may be more adapted to a specific situation than others. All factors, including economics, must be considered before a final decision is made to use any method of land application of wastewaters.
Donald B. Aulenbach, Nicholas L. Clesceri

3. Treatment by Subsurface Application

Public health considerations demand proper treatment of domestic wastes. A number of diseases such as typhoid fever, dysentery, and diarrhea are transmitted by fecal contamination of food and water.
Nicholas L. Clesceri, Donald B. Aulenbach, James F. Roetzer

4. Submerged Aeration

Aeration is a mass transfer process by which oxygen molecules are exchanged between a water and an oxygen molecule at a gas/liquid interface. Aeration plays an important role in the purification of wastewater; the aerator transfers oxygen to the wastewater and mixes the liquid contents such that the prevailing environment in the aeration basin permits microorganisms to use the organic material as a substrate for growth and a source of energy.
Jerry Y. C. Huang

5. Surface and Spray Aeration

Gas transfer in water and wastewater treatment is a process whereby water is brought into contact with air or a gas and, because of the presence of a concentration gradient, the transfer of gases to and/or from the water occurs. In water treatment, for example, aeration is used to remove carbon dioxide, hydrogen sulfide, methane, and various volatile organic compounds, and to oxidize iron and manganese in the water. In wastewater treatment, the gas transfer is used primarily in the activated sludge and trickling filtration processes and in aerated lagoons and aerobic digesters. Air or oxygen gas is supplied to the wastewater by air compressors and by mechanical aerators to induce a higher concentration gradient in the wastewater and thereby to accelerate oxygen transfer. The spray of wastewater by nozzles over trickling filter beds also results in an accelerated oxygen transfer. In polluted streams and lakes, oxygen transfer from the limitless atmosphere to the water occurs, also because of the existence of dissolved oxygen concentration (or deficit) gradient. This reaeration process is an important and essential element of the stream self-purification process.
Chin-Shu Liu, Shu-Hong Shieh

6. Activated Sludge Processes

Current practice in the secondary treatment of wastewater calls for the use of biological oxidation to remove organic substances. When it comes to selecting the method of biological oxidation, the pollution control engi¬neer has at his or her disposal a variety of treatment processes, among which activated sludge is currently the most popular. In this section, the function and limitations of the activated sludge processes are reviewed. The principles of biological oxidation and of the energy flow concept are described, and the relationship of synthesis and respiration are discussed in relation to the importance of activated sludge process control.
Calvin P. C. Poon, Lawrence K. Wang, Mu Hao Sung Wang

7. Waste Stabilization Ponds and Lagoons

One of the simplest forms of biological treatment process is the stabiliza¬tion pond or stabilization lagoon. It is also the most common industrial wastewater treatment facility. This versatile installation serves many ba¬sic purposes, including: (a) storage or impoundment of wastewater; (b) settling and removal of suspended solids; (c) storage or impoundment of settled solids; (d) equalization; (e) aeration; (0 biological treatment; and (g) evaporation. The relative simplicity and low operating costs of a stabi¬lization pond make it the preferred technology for handling, treatment, and disposal of industrial wastewater as well as municipal wastewater for small communities in most instances. Based on a recent survey by the US EPA [1], treatment systems in the general category of 44stabilization ponds’ constituted 34.7% of the 9951 secondary treatment systems operating in the United States in 1968. Stabilization ponds served 7.1% of the 85,600,000 people served by secondary treatment plants. These ponds usually small communities, and 90% were in communities with 10,00 pesons or fewer.
Calvin P. C. Poon, Lawrence K. Wang, Mu Hao Sung Wang

8. Trickling Filters

A contact bed, contact aerator, trickling filter, rotating disc, or other attached growth system consists of a bed of coarse contact media such as crushed traprock, granite, limestone, clinkers, wood slats, plastic tubes, corrugated plastic sections, hard coal, or other material over which wastewater is distributed or contacted [1–7]. Wastewater flows over the contact media on which a biological slime layer (i.e., zoogleal slime) develops. Dissolved organic pollutants in the wastewater are transported into the slime layer, where biological oxidation takes place. Organic pollutants are removed by the biological slime film, which consists of various microorganisms, as shown in Fig. 1. In the outer portions of the film, organic pollutants (CaHbOcNdPeSf/) are degraded by aerobic and facultative bacteria under aerobic conditions according to a biochemical reaction approximately expressed by Eq. (1):
Lawrence K. Wang, Mu Hao Sung Wang, Calvin P. C. Poon

9. Rotating Biological Contactors

Rotating biological contactors (RBCs) were originally developed in Europe and recently accepted by America and Asia. The process system, as shown in Fig. 1 is primarily a fixed-film biological reactor consisting of a synthetic medium mounted on a horizontal shaft and placed in a contour-bottomed tank. The general concept of rotating biological contactors is to let wastewater flow through the tank, and to rotate the medium in the wastewater to be treated, alternatively exposing the medium (and the attached biological growth) to air and the wastewater. The slowly rotated media are about 40% immersed in the wastewater for aerobic removal of organic waste by the biological film developing on the media. The lattice-structured medium, and to a lesser extent the disc structure, is fragile and should be protected from direct exposure to wind, sun, and weather fluctuation. Therefore, the media are usually enclosed in a superstructure or individual shaft covers.
Mu Hao Sung Wang, Lawrence K. Wang, Calvin P. C. Poon

10. Anaerobic Sludge Digestion

Conversion of the organic material in solid wastes to methane-containing gases can be accomplished in a number of ways, including hydrogasification, pyrolysis, and anaerobic digestion. Hydrogasification is usually associated with the conversion of petrochemical raw materials. Although the process has been tried with solid wastes, it is not well defined and therefore is not considered in this book. The production of methane from solid wastes by pyrolysis has been considered previously. The production of methane from solid wastes by anaerobic digestion, or anaerobic fermentation as it is often called, is described in the following discussion.
David A. Long


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