Fluidized-Bed Reactors, thought by many in theindustry to be the cleanest, are one of the newestincineration technologies and one of the least expensivefor large-scale operations. These systems employ a layerof sand, which is “fluidized” by a constant, high-pressure stream of air. The air, essentially, “fans thefire,” which results in a much more intense andcomplete burn and less ash than in an MHF.

Fluidized-bed incinerators are also less mechanicallycomplex than MHF incinerators—making these unitssubstantially easier to operate. With less mechanicalupkeep, equipment, staffing, and repair costs, fluidizedbeds tend to be less expensive to operate and maintainthan MHFs. Most of the region’s newer incinerators usethe fluidized-bed technology.

All sludge incinerators use auxiliary fuel (e.g., oil ornatural gas) to initiate and occasionally maintainburning. Ash is removed from MHF incinerators by

ash-handling systems and then disposed at landfills.Ash from fluidized-bed units is very fine and can beremoved with periodic sand changes and continuousscrubbing of the exhaust. Ash disposal is regulatedunder solid waste disposal regulations. Beneficial useof this ash is actively being investigated.

Air Pollution Control Equipment

In general, air pollution control devices are used toeither remove small particles and metals in the

exhaust gas or to further decompose organics. Devicessuch as wet scrubbers and dry and wet electrostaticprecipitators are used to remove metals. Afterburnersare used to more completely burn organics in exhaustgases. More recently, regenerative thermal oxidizers(RTOs) are being utilized as part of the air pollutioncontrol system in incinerators.

Sludge Incineration

Incineration is a sludge disposal option thatinvolves the firing of sewage sludge at high

temperatures in an enclosed structure. This processreduces the sludge to a mass of ash that is less than20 percent of its original volume. EPA and the statesgenerally support the beneficial use of sludge. Manyurban sewage treatment facilities produce largevolumes of sludge and have limited available spacefor sludge management. They are likely to seeincineration as their most viable option.

Sludge incineration eliminates some environmentaland health problems by destroying pathogens andtoxic organic chemicals. Anyone who fires sludge inan incinerator must meet the sludge incinerationrequirements in Subpart E of the Part 503 rule, whichaddress pollutant limits for seven metals, limits fortotal hydrocarbons, general requirements andmanagement practices, frequency of monitoringrequirements, and recordkeeping and reportingrequirements. In addition, states have their own airquality requirements for incineration.

Incineration Systems

Incineration systems generally consist of anincinerator (furnace) and one or more air

pollution control devices. In New England, the twomost commonly used incineration systems aremultiple hearth furnaces and fluidized-bed reactors.There are also other types of incinerators.

Multiple-Hearth Furnaces (MHFs), which have beenutilized since the mid-1900s, employ a series ofvertically-stacked chambers, or hearths. Air is fedfrom the bottom, and sludge is fed from the top. Thesludge in each chamber is plowed to “drop holes,”where it falls into successive hearths below. The bulkof the burning takes place in the center hearths; theash cools at the bottom levels.

Cost and Technical Feasibility

When considering whether or not to incineratesludge, or which incineration technology to

use, cost is always a major consideration. A sludgeincinerator is a very mechanized and capital-intensiveinvestment that must be managed with a high level ofexpertise and attention to maintenance.

The incineration option is a long-term commitmentthat is most cost-effective for large volume wastewatertreatment systems or as a regional solution. Inevaluating this option, communities must consider ash disposal, economies of scale, and air quality.

How much will it cost to build and operate anincinerator or upgrade and refurbish an existingincinerator? The answer to that question depends onthe site, how much sludge the wastewater treatmentfacility produces, and what other technically feasibleoptions exist. Most sites within approximately a halfmile of a residential neighborhood are not goodcandidates for incineration facilities.

While questions of technical feasibility and cost canbe examined through extensive site-specificengineering studies, a general rule of thumb is thatmost incinerators should handle a sludge input ratebetween 0.25 and 3 dry tons per hour. Anything lessthat 0.25 dry tons would most likely be too expensivefor this technology; over 3 dry tons per hour tends toexceed the limit of the technology and may requiremultiple incinerators.

Beneficial Use/Production of Energy

Energy recovered from the incineration of sludgemay be used to support some of the energy

needs of the Wastewater Treatment Plant. Heat fromthe incinerator may be used to pre-dry the sludge.Incinerators may also be utilized to assist in odorcontrol at a facility. Ash by-products may be used as asubstitute raw matter in the manufacturing of cementand brick and as a landfill cover.

Fluidized Bed Reactor

Multiple Hearth Furnace

Cooling Air Discharge

SewageSludgeInlet

SewageSludgeInlet Fluidized

Sand Bed

FluidizedAir Intake

Burner

Exhaustand Ash

GasExhaust

Ash Discharge

Cooling Air Intake

A Residual of Worth

Sludge is an organic solid, semi-solid, or liquidby-product of the wastewater treatment process.

Sludge characteristics vary depending on eachtreatment facility’s wastestream and the processes thatare used. Sludges that meet EPA standards for landapplication, which include reduction or elimination ofpathogens and very low limits for heavy metals, arereferred to as Biosolids.

Although there has been significant research on thebeneficial use of biosolids, and history has demon-strated, in the U.S. and other regions of the world, thathigh quality biosolids can be beneficial soil additivesand plant nutrients when applied properly, concernsstill exist. These concerns relate primarily to the qualityof the biosolid material and its impact on soilproductivity, water resources, and adjacent land uses.

To ensure that sludges that are used as biosolids aretreated and managed in a manner that protects bothhuman health and the environment, Congress directedEPA to develop a comprehensive national SewageSludge Program aimed at reducing risks andmaximizing the beneficial uses of sludge. In Februaryof 1993, EPA issued its sewage sludge use or disposalregulation, 40 CFR Part 503, commonly referred to asthe “503s.” The 503s set minimum quality standardsand dictate proper management practices for allsewage sludge that is used or disposed of through landapplication, surface disposal, and incineration. Manystates have more stringent rules.

The Northeast States, NEIWPCC, and the EPA believethat, when managed and applied properly, biosolidscan be valuable resources. With the phaseout ofunlined landfills, the federal ban on ocean dumping,and growing public awareness of environmental issues,communities have begun to recognize that biosolidscan be a resource and not a waste. Many communitieshave discovered viable, safe, and environmentallysound options for the beneficial use of their biosolids.Some communities have implemented a singlebeneficial use method, some employ a combination of different sludge use and/or disposal methods, othershave entered into regional solutions or contracted withprivately-owned facilities. In choosing an option,communities must consider cost, odor control, andsiting issues.

CT: Bob NorwoodCT DEP – Water Compliance Unit79 Elm Street, Hartford, CT 06106(860) 424-3746robert.norwood@po.state.ct.us

ME: David WrightME DEP – Sludge Residuals Unit17 State House StationAugusta, ME 04333-0017(207) 287-2651david.w.wright@state.me.us

MA: Larry PoleseMA DEP Training Center, Residuals Section50 Route 20, Millbury, MA 01527(508) 368-5606larry.polese@state.ma.us

NH: Richard FlandersNH DESP.O. Box 956 Hazen Drive, Concord, NH 03302(603) 271-3571rflanders@des.state.nh.us

NJ: Mary Jo AielloNJ DEP – Bureau of Pretreatment and ResidualsP.O. Box 029, Trenton, NJ 08625(609) 633-3823maiello@dep.state.nj.us

NY: Sally RowlandNYS DEC – Division of Solid & Hazardous Materials625 Broadway, Albany, NY 12233(518) 402-8704sjrowlan@gw.dec.state.ny.us

RI: Alexandre Pinto P.E.RI DEM – Office of Water Resources235 Promenade St, Providence, RI 02908(401) 222-4700apinto@dem.state.ri.us

VT: Cathy JamiesonVT DEC – Residuals Management Section103 So. Main St, Sewing BuildingWaterbury, VT 05671(802) 241-3831cathyj@dec.anr.state.vt.us

EPA: Thelma MurphyUS EPA – New England1 Congress Street, Suite 1100 (CMU)Boston, MA 02114(617) 918-1615murphy.thelma@epa.gov

NEIWPCC:Boott Mills South – 100 Foot of John StreetLowell, MA 01852(978) 323-7929mail@neiwpcc.org

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For more information...

This fact sheet was funded through a grant from EPA-New England to the

New England Interstate Water Pollution Control Commission (NEIWPCC).

The fact sheet was prepared by NEIWPCC’sResiduals Workgroup, which is comprised of

the state sludge coordinators from the Northeast States.

Printed on recycled paper

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