Biological Treatment Processes
Mary Lou Bungay, Henry R. Bungay (auth.), Lawrence K. Wang, Norman C. Pereira (eds.)

I. INTRODUCTION
Breakdown of organic wastes by normal cellular processes is often an ef-
fective and economic treatment. This chapter will introduce certain con-
cepts from biochemistry and biology that are fundamental to biological
waste treatment. Specific treatment processes will be covered in subse-
quent chapters.
Living cells consume organic material and use its energy to sustain
normal activity, to grow, and to reproduce. Some of the cells' wastes-
water, carbon dioxide, and minerals-are environmentally acceptable.
The cellular mass, however, is itself pollutional because its discharge into
streams and lakes would provide nutrients for micoorganisms that
consume oxygen; thus fish could die from suffocation. Biological waste
treatment usually strives to produce cellular material that is easily collect-
ible for disposal.
Operation of treatment processes without regard for basic scientific
principles has little chance of achieving high efficiency. Although under-
standing is incomplete because of the great complexity of bioprocesses
containing ill-defined nutrients and many different organisms, there have
been practical results in terms of design and processes improvements
through considering biochemistry and biology.
II. THE CELL
In a scientific context, life is most adequately described in terms of activ-
ity. An entity that is organized so as to maintain a definite structure, re-
spond to stimuli, grow, reproduce its own kind, and acquire the energy
needed for all of these activities is generally regarded as a living
organism.
The cell is the structural and functional unit of life. In multicellular
organisms, cells are often highly specialized and function in cooperation
with other specialized cells. But many organisms are, in fact, free-living
single cells.
Although cells differ in size, shape, and specialization, all have the
same basic structure. Every cell is composed of cytoplasm: a colloidal
system of large organic molecules and a complex solution of smaller or-
ganic molecules and inorganic salts. The cytoplasm is bounded by a
semielastic, selectively permeable cell membrane that controls the move-
ment of molecules into and out of the cell. Threadlike chromosomes sus-
pended in the cytoplasm bear a linear arrangement of genes. Information
carried on the genes controls every cellular activity, and, as the units of
heredity, genes determine the characteristics of cells from one generation
to the next.
In most cells, the chromosomes are surrounded by a cell membrane,
to form a conspicuous nucleus. A number of other organized intracellular
structures serve as specialized sites for cellular activities. Certain cells of
green plants, for example, contain chloroplasts, which play an essential
role in photosynthesis. Chlorophyll, the photosynthetic pigment is con-
tained within the layered membranous structure of the chloroplast. Cells
that possess organized nuclei are sometimes described as eukaryotic.
In bacteria and blue-green algae the chromosomes are not sur-
rounded by a membrane, and there is little apparent subcellular organiza-
tion. The chlorophyll of blue-gree algae is associated with loosely
arranged membranes within the cytoplasm; bacterial chlorophyll, when
present, is located in vesicular chromatophores. Because they lack a dis-
crete nucleus, these organisms are said to be prokaryotic.
Many cells are surrounded by an outer covering, external to the cell
membrane. Plant cells, bacteria, and blue-green algae are protected by
rigid cell walls. Certain algae and Protozoa are surrounded by siliceous
shells.
The distinctive and sometimes elaborate shape exhibited by many
unicellular organisms is an inherited characteristic. However, evidence
gathered in the culture of isolated cells suggests that in multicellular or-
ganisms, cell shape is environmentally determined.
BIOLOGICAL CONCEPTS FOR ENVIRONMENTAL CONTROL 3
The smallest known cell, pleuropneumonia-like organism (PPLO) is
approximately 0.1 micron (Il-m) in diameter, and the largest, the ostrich
egg, about 150 mm in diameter. Most cells, however, have diameters of
0.5--40 Il-m. Because all of the substances required by the cell must enter
through the surface membrane, one of the most important limitations to
cell size is the ratio of surface to volume. The ease with which a given
substance passes through the membrane, its rate of diffusion through the
cytoplasm, and the rate at which it is used by the cell have a bearing on
cell size. Another important factor in cell size is the proximity of the
genes, which continuously monitor cellular activity; as cell size In-
creases, interaction with remote parts of the cell diminishes.
III. BIOCHEMISTRY
A. Important Compounds
Despite the obvious diversity of living forms, there is a surprising consist-
ency in the chemical nature of all living things. Virtually every living sys-
tem includes the same four kinds of compounds: carbohydrates, lipids,
proteins, and nucleic acids.
Carbohydrates are composed of carbon, hydrogen, and oxygen,
commonly in a ratio of 1: 2: 1 (CnH2nOn ). Carbohydrates that will not
form simpler compounds upon the addition of water (hydrolysis) are
called simple sugars, or monosaccharides. Simple sugars contain from
three to seven carbons; the most common is a six-carbon molecule called
glucose. With the removal of a molecule of water (condensation), two
simple sugars may combine to form a disaccharide. For example, the di-
saccharide maltose contains two molecules of glucose (Fig. 1); the con-
densation of glucose and fructose, another six-carbon sugar, produces su-
crose, or cane sugar.
In the same manner a large number of monosaccharide units may be
joined to form polysaccharides, such as starch, glycogen, or cellulose
(Fig. 2). Starch and glycogen are energy storage compounds. Cellulose is
a major structural material in plants.
Lipids are also made up of carbon, hydrogen, and oxygen. Fats are a
very common form of lipid composed of a molecule of glycerol and usu-
ally three fatty acid molecules. Fatty acids are characterized by a straight
carbon chain and, like all organic acids, by a carboxyl group, -COOH.
Figure 3 shows the general configuration of a triglyceride in which R, R',
and R" represent the carbon chains of three different fatty acids. Palmitic



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