Treatment Process
Sewage sludge is produced from the treatment of wastewater and consists of two basic forms — raw primary sludge (basically fecal material) and secondary sludge (a living ‘culture’ of organisms that help remove contaminants from wastewater before it is returned to rivers or the sea). The sludge is transformed into biosolids using a number of complex treatments such as digestion, thickening, dewatering, drying, and lime/alkaline stabilization. Some treatment processes, such as composting and alkaline stabilization, that involve significant amendments may affect contaminant strength and concentration: depending on the process and the contaminant in question, treatment may decrease or in some cases increase the bioavailability and/or solubility of contaminants. In general, the more effectively a wastewater stream is treated, the greater the resulting concentration of contaminants (to broad - define contaminants) into the product sludge. See also List of waste water treatment technologies.
Bacteria in Class A sludge products such as "Milorganite" can actually "rebloom" under the right environmental conditions.
Sewage treatment systems can have an "upset", meaning the bacteria that break the wastes down either all died or are unbalanced. Typically in these types of events the sludge will have a profuse odor, due to lack of active bacterial processes. Solvents, gasoline, paint thinner, high strength bleach, or other organic solvents can all cause significant upset to a sewage treatment plant. Upset is typically noticed very easiy as the treatment plant will have a pungent and detectable odor near the facility for potentially weeks at a time.
Read more about this topic: Sludge
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