Page 168 - Wastewater Solids Incineration Systems

Emission Control and Monitoring 135

certified opacity observer or electronically by an opacity monitor. Condensed water
vapor (i.e., steam plume) will have high opacity but because condensed water vapor
is not a pollutant, it is excluded from opacity measurements. Most incinerators use
wet scrubbers, which means that stack gases are wet and contain condensed water
vapor. An opacity monitor cannot be used on these sources. If the wet flue gas is
reheated, use of an opacity monitor is possible.
Particulate matter from inorganic ash as well as smoke particles from incomplete
combustion can contribute to opacity. It is important to note that particulate matter
and opacity are not synonymous. A plume with a low, acceptable level of fine partic-
ulate can exhibit high light-scattering properties, hence have high opacity.

1.1.2 Metals
High levels of metals in liquid and solids of a wastewater treatment plant (WWTP)
are attributable to a number of factors, namely

• Industrial wastewater discharges (particularly from metal finishing and elec-
troplating industries).
• Infiltration of ground water with high metals concentrations into sewer
systems.
• Leaching of metals from old piping systems
• Chemicals added at the WWTP.
• Urban runoff entering the sewer system.

Concentration of metals in solids can vary widely (as great as 100- to 1000-fold)
from plant to plant. As a result of this extreme variability, there are no typical metal
emission rates for incinerators. Even at a given plant, daily metals concentrations can
vary by two- to threefold. Primary metals of interest because of their detrimental
health effects are: arsenic, beryllium, cadmium, chromium, copper, lead, mercury,
nickel, selenium, and zinc.
The vapor pressure of a metal or the compound in which it is contained will
determine the fate of a metal during the incineration process. In simple terms, the
vapor pressure of a metal is a measure of how easily it can be volatilized into a
gaseous state. Several metals and compounds containing these metals (particularly
metallic chlorides) are considered volatile, including arsenic, cadmium, mercury,
selenium, and zinc. Lead is primarily a nonvolatile metal but it can be converted to a
volatile compound, namely lead chloride. Arsenic, cadmium, selenium, zinc, and, to