Environmental Engineering Reference
In-Depth Information
organic Chemicals
Natural organics contain carbon and consist of biodegradable organic mat-
ter such as wastes from biological material processing, human sewage, and
animal feces. Microbes aerobically break down the complex organic mol-
ecules into simpler, more stable end products. Microbial degradation yields
end products such as carbon dioxide, water, phosphate, and nitrate. Organic
particles in water may harbor harmful bacteria and pathogens. Infection by
microorganisms may occur if the water is used for primary contact or as
a raw drinking water source. Treated drinking water will not present the
same health risks. In a potable drinking water plant, all organics should be
removed from the water before disinfection (see
Chapter 11
).
Organic chemicals also contain carbon; they are substances that come
directly from, or are manufactured from, plant or animal matter. Plastics pro-
vide a good example of organic chemicals obtained from petroleum, which
is derived from plant and animal matter. Some organic chemicals released
by decaying vegetation occur naturally and by themselves tend not to pose
health problems when they get into our drinking water; however, more seri-
ous problems are caused by the more than 100,000 different manufactured or
synthetic organic chemicals in commercial use today. These include paints,
herbicides, synthetic fertilizers, pesticides, fuels, plastics, dyes, preserva-
tives, flavorings, and pharmaceuticals, to name a few.
Many organic materials are soluble in water and are toxic, and many can
be found in public water supplies. The presence of organic matter in water
is troublesome. Organic matter causes: “(1) color formation, (2) taste and
odor problems, (3) oxygen depletion in streams, (4) interference with water
treatment process, and (5) the formation of halogenated compounds when
chlorine is added to disinfect water” (Tchobanoglous and Schroeder, 1987, p.
94). Remember that organics in natural water systems may come from natu-
ral sources or may result from human activities. Generally, organic matter
in water comes primarily from natural sources, including decaying leaves,
weeds, and trees; the amount of these materials present in natural waters
is usually low. Anthropogenic (manmade) sources of organic substances
include pesticides and other synthetic organic compounds.
Again, many organic compounds are soluble in water, and surface waters
are more prone to contamination by natural organic compounds than are
groundwaters. In water, dissolved organics are usually divided into two cat-
egories: biodegradable and nonbiodegradable.
Biodegradable (able to break down) material consists of organics that can
be used for food by naturally occurring microorganisms within a reasonable
length of time. Alcohols, acids, starches, fats, proteins, esters, and aldehydes
are the main constituents of biodegradable materials. They may result from
domestic or industrial wastewater discharges, or they may be end products of
the initial microbial decomposition of plant or animal tissue. Biodegradable
