Environmental Engineering Reference
In-Depth Information
Diffuse pollution is originated through agriculture (fertilizing, sprinkling, watering, and
irrigation). Pollutants such as nitrates, phosphates, pesticides, and heavy metals are mainly spread
out over larger surfaces and have mainly two ways to reach water bodies (Núńez-Delgado et al.
2002; Centner et al. 2008; Drolc and Zagorc Koncan 2008; Ribbe et al. 2008). First, during the rain
they rinse into surface water and, second, they trickle through land into groundwater.
32.3
Waste treatment
32.3.1 w
aStE
t
rEatmEnt
When we talk about waste treatment we have generally in mind detoxification of pollutants and
organic mineralization. Most agriculture waste contains organic compounds that are mainly
well biodegradable. That is why we can mineralize them either through wastewater treatment,
composting, or through digestion in special reactors called digesters. All systems either run under
aerobic or anaerobic conditions.
32.3.1.1 composting
Composting (Wikipedia 2008a) is the aerobic decomposition of biodegradable organic matter,
producing compost. Or in a simpler form: composting is the decaying of food, mostly vegetables
or manure. The decomposition is performed primarily by facultative and obligate aerobic bacteria,
yeasts and fungi, helped in the cooler initial and ending phases by a number of larger organisms,
such as springtails, ants, nematodes, and oligochaete worms.
Composting can be divided into home composting and industrial composting. Essentially, the
same biological processes are involved in both scales of composting; however, techniques and
different factors must be taken into account.
Compost also known as brown manure, is the aerobically decomposed remnants of organic matter.
It is used in landscaping, horticulture, and agriculture as a soil conditioner and fertilizer. It is also
useful for erosion control, land and stream reclamation, wetland construction, and as landfill cover.
Composting recycles or “downcycles” organic household and yard waste and manures into an
extremely useful humus-like, soil end product called compost. Examples are fruits, vegetables, and
yard clippings. Ultimately this permits the return of needed organic matter and nutrients into the
food chain and reduces the amount of “green” waste going into landfills. Composting is widely
believed to considerably speed up the natural process of decomposition as a result of the higher
temperatures generated. The elevated heat results from exothermic processes, and the heat in turn
reduces the generational time of microorganisms, and thereby speeds up the energy and nutrient
exchanges taking place. It is a popular misconception that composting is a “controlled” process;
if the right environmental circumstances are present the process virtually runs itself. Hence, the
popular expression: “compost happens.” It is, however, important to engineer the best possible
circumstances for large amounts of organic waste to break down properly. This is especially so
when it is accompanied by heating, because at elevated temperatures oxygen within the piles is
consumed more rapidly, and if not controlled, will lead to malodor.
Decomposition similar to composting occurs throughout nature as garbage dissolves in the
absence of all of the conditions and weather patterns, that modern composters talk about; however,
the process can be slow. For example, in the forest, bark, wood and leaves break down into humus
over 3-7 years. In restricted environments, for example, vegetables in a plastic trash container,
decomposition with a lack of air encourages growth of anaerobic microbes, which produce
disagreeable odors. Another form of degradation practiced deliberately in the absence of oxygen is
called anaerobic digestion—an increasingly popular companion to composting as it enables capture
of residual energy in the form of biogas, whereas composting releases the majority of bound carbon-
energy as excess heat (which helps sanitize the material) as well as copious amounts of biogenic
CO
2
to the atmosphere.
