Page 355 - Wastewater Solids Incineration Systems

316 Wastewater Solids Incineration Systems

• Electricity; fuel oil; natural gas; and potable water unit costs; and incinerator
ash hauling, tipping, and solid waste fees can vary greatly, depending on the
area in the country in which the WWTP is located.
• The amount of fuel required to combust the wastewater solids depends on the
kilojoule (British thermal unit) content and the moisture content of the waste-
water solids, which are determined by the WWTP’s influent, the solids condi-
tioning system (e.g., digestion, chemical, thermal), and the dewatering devices
used (e.g., belt filter press, plate and frame press, low solids centrifuge, high
solids centrifuge).
• The type of incinerator being used (e.g., fluid bed, multiple hearth, electric
arc).
• Whether a waste heat recovery or a waste heat steam generation system is
used.
• Wage rates, benefits, and other miscellaneous costs.
• The quantity of wastewater solids being incinerated.

For example, in 2004, the NEORSD’s Southerly WWTP incurred an incineration-
related O&M unit disposal cost of $21.19 per wet ton, whereas its Westerly WWTP
incurred costs of $54.92 per wet ton (see Table C.1 for a comparison of cost differ-
ences). The greatest benefit of knowing incineration costs is the ability to track them
over time and to use this information to reduce costs.
Figure C.2 is a graph of Westerly WWTP’s total incineration-related O&M costs
from 1996 to 2004. Figure C.3 is a graph of Westerly WWTP’s wastewater solids incin-
eration costs on a unit weight basis.
Given the dearth of information concerning actual costs associated with the oper-
ation of wastewater solids incinerators, it is recommended that WWTPs enact a
process by which their incineration-related total and unit O&M costs are calculated
on a regular basis.
The approach to developing amortized capital costs described above is similar to
how accountants might depreciate an incineration “asset” over its useful life. That is,
an asset (e.g., pump, reactor, electrical control panel) is typically depreciated, or
amortized, by dividing its original installed cost by the number of years assigned as
its useful life. This approach ignores the method used to finance the asset and any
related interest costs.