Environmental Engineering Reference
In-Depth Information
32.4.2.3 Upflow Velocity .................................................................................... 775
32.4.3 Sequencing Batch Reactor .................................................................................... 776
32.4.3.1 Fill ......................................................................................................... 778
32.4.3.2 React ..................................................................................................... 778
32.4.3.3 Settle ..................................................................................................... 778
32.4.3.4 Decant ................................................................................................... 778
32.4.3.5 Idle ........................................................................................................ 778
32.4.3.6 Sludge Wasting ..................................................................................... 778
32.5 Municipal Sludge Treatment ............................................................................................... 778
32.5.1 Sludge Sources, Characteristics, and Properties .................................................. 779
32.5.2 General Composition ............................................................................................ 779
32.5.2.1 Specific Constituents: Trace Compounds, Nitrogen, Phosphorous,
Potassium, and Heavy Metals ............................................................... 780
32.5.2.2 Sludge Quantities .................................................................................. 780
32.5.2.3 Mass-Volume-Concentration Relationships ........................................ 782
32.5.2.4 Anaerobic Sludge Digestion, Biogas Production, and Use ................... 782
32.5.2.5 Further Treatment and Use of Digested Sludge (Biosolids) and
Supernatant Water ................................................................................ 784
32.5.2.6 Biosolids Composting ........................................................................... 786
References ...................................................................................................................................... 787
32.1 IntroductIon
Like settlements, towns and industries, organic farms also produce polluted wastes and wastewaters.
In some countries, about half of all serious water pollution incidents are due to manure runoff from
farms. Poultry, cows, and pigs are the farm animals most responsible for the pollution. Livestock
production occupies 70% of all land used for agriculture and 30% of the planet's land surface. It is
responsible for 18% of the world's greenhouse gas emissions as measured in CO 2 equivalents. It also
generates 64% of the ammonia, which contributes to acid rain and acidification of ecosystems (FAO
2006; Action 2008; Watson 2008).
When large numbers of animals are farmed intensively in industrial units in an attempt to
maximize financial gain, it is known as “factory farming.” During the second half of the twentieth
century agricultural practices went through massive changes, particularly mechanization, the use of
chemicals, and large-scale intensive farming.
As a result of increasing the density of domestic farm animals, reported farm pollution incidents
have remained high and farm waste remains a major problem (Ritter et al. 1984; FAO 2006).
Another serious problem is sludge from municipal and industrial biological wastewater treatment
plants that can be transformed into biogas at proper conditions because such sludge contains mainly
degradable organic compounds.
Farm waste is a mixture of animal feces and urine, plus milk and chemicals such as antiparasitic
drugs or antibiotics (Boxall et al. 2003; Boxall and Long 2005; Reinoso and Becares 2008). A large
quantity of animal waste is generated by concentrated animal feeding operations, and disposal of
the waste has been a major problem. Factory farms (Wikipedia 2008b) collect the animal waste
and mix it with water to form slurry. Slurry is a type of liquid manure that can be used on fields as
fertilizer (Oleszkiewicz and Koziarski 1981; Schröder 2005; Westerman and Bicudo 2005; Chong
et al. 2008). If the soil or plants are unable to absorb the slurry or if the slurry is spread in too high
a concentration, the run-off can get into water systems.
Slurry is generally more polluting than raw sewage. When slurry tanks are accidentally or
deliberately breached, large amounts of slurry can spill into rivers, streams, or lakes, including
wetlands, causing severe environmental problems. Animal waste is found in soil, surface water,
groundwater, and seawater (Ritter et al. 1984).
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