The sludge is fed through the furnace roof by a screw feeder or a belt and flapgate. The steel shell of the incinerator is either of welded or bolted construction. The burners can handle all common liquid and gaseous fuels, including distillate and residual oils, natural gas, sewage digestion gas, propane, or combinations of these fuels. Exhaust gases at most installations pass from the incinerator furnaces through refractory-lined flues and enter three-stage, impingement-type scrubbers. The operating and exhaust temperature of fluidized-bed incinerators is usually high enough to destroy odorous substances. For advanced waste treatment processes using lime, wastewater treatment facilities can enhance the economics of onsite lime recalcination by using the organic sludge as a partial fuel source for lime and recalcining in a single, multipurpose furnace. The cumulative effect of boron requires further investigation, and monitoring and controlling the toxic material content in all sludge streams is advisable.