Page 348 - Wastewater Solids Incineration Systems

Appendix C Determination of Wastewater Solids Incineration Related Costs 309

3.0 STANDARD MULTIPLE-HEARTH FURNACE
SYSTEM EXAMPLE

The following is a summary of the costs incurred by the Northeast Ohio Regional
Sewer District (NEORSD) in 2004 to incinerate wastewater solids at its Westerly
WWTP (Dominak, 2005). Westerly has two multiple-hearth furnaces (MHFs) that
were originally constructed in 1978 and underwent a significant renovation in 1994
to 1995. Wastewater solids are injected to hearth number 4, and the top hearths are
used as an afterburning zone to minimize emissions of potentially toxic organic com-
pounds. Table C.1 contains a summary of some of the differences between waste-
water solids and wastewater solids incineration-related costs at the NEORSD’s
Southerly and Westerly WWTPs.

TABLE C.1 Differences between wastewater solids and wastewater solids incineration-related
costs at the NEORSD’s Southerly and Westerly WWTPs.
Southerly WWTP Westerly WWTP
Biosolids incinerated 75 503 wet tons a 16 444 wet tons
Percent solids 47% 33%
Dewatering device High solids centrifuges High solids centrifuges
Biosolids conditioning Thermal (Zimpro) Chemical
Heat exchangers No Yes
Waste heat boilers Yes No
Steam production natural gas savings 120 702 MCF b 0
Steam production natural gas savings $627,110 0
Ash disposal method Beneficially reused Landfill
Ash disposal costs $115,000 $98,717
Total incineration O&M costs $1,559,747 $902,961
Total incineration O&M unit cost $21.19/wet ton incinerated $54.92/wet ton incinerated
Net incineration O&M costs c $972,637 NA d
Net incineration O&M unit cost $12.88/wet ton incinerated NA
a wet ton 0.907 metric tonne.
3
b MCF 1000 cu ft 28 m .
c Net incineration O&M costs = total incineration O&M costs—natural gas related cost savings attributable
to the steam produced by the waste heat boilers.
d NA not applicable.