Page 33 - Wastewater Solids Incineration Systems

2 Wastewater Solids Incineration Systems

• Review of toxic substances such as dioxins and furans in incinerator emis-
sions. As a result of the review, the U.S. Environmental Protection Agency
(U.S. EPA) said that the amount of dioxins and furans in emissions from incin-
erators were so small they posed no threat to public health and need not be
regulated (U.S. EPA, 2000).
• Review of solid waste regulations. The U.S. EPA decided not to include incin-
erators under the solid waste regulations (U.S. EPA, 2007).

Great strides have been made in dewatering and cake conveyance technologies.
The ability to produce and convey cake with a solids concentration of 27 to 30% has
made it possible to achieve autogenous combustion without thermal pretreatment,
which has greatly simplified solids processing and increased reliability or the incin-
eration system.

1.0 THE CARBON CYCLE
The carbon cycle, an important but often misunderstood process, is the natural
pathway of carbon through our ecosystem. The carbon cycle includes the following
basic steps:

• People eat carbon-containing food.
• People excrete waste carbon as carbon dioxide through exhalation and as
body wastes.
• Body wastes are collected and treated in wastewater treatment plants where
microorganisms consume carbon-bearing wastes in the aeration and digestion
processes and release carbon dioxide and waste.

• Carbon-bearing solids are generated. During incineration, the high heat,
oxygen- rich environment of an incinerator allows for oxidation of carbon in
the solids to carbon dioxide.
• Plants convert carbon dioxide from air and sunlight (photosynthesis) and the
cycle begins again.

Figure 1.1 illustrates the carbon cycle and demonstrates that it is not related to
any wastewater processing or solids management process.
Most public discussion about the carbon cycle deals with greenhouse gas emis-
sions and carbon produced from fossil fuels. The carbon produced by burning fossil