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December, 1994 

Municipal Waste Combustion and MACT

Ronald Gossman

Maximum Achievable Control Technology (MACT) has been discussed for some time. The USEPA has issued a proposed standard of interest to the Cement Kiln industry which uses MACT as its basis. This proposed standard was published in the Federal Register on September 20, 1994, and is applicable to Municipal Waste Combustors (MWC). The proposed standard gives us a great deal of insight into how we can expect MACT to be applied in the future to the rest of the industries that use waste in one form or another as a fuel or supplemental fuel.

This review of the proposed standard will be in three parts. The first part will describe the ground rules for application of the new standard and the possibilities for cement kiln involvement. The second will cover the proposed standards for new or modified MWCs. The third will cover the proposed guidelines for existing MWCs.

First, the new proposed standards (Subpart Eb of 40 CFR part 60) which we will outline here apply to new MWCs where construction, modification, or reconstruction began after September 20, 1994. Modification is defined, but in summary any changes costing, over the life of the unit, more than 50% of the original unit at current costs (excluding land) or which increase the amount of any air pollutant which is regulated would cause this proposed standard to be applicable. For existing units, appropriate management planning would prevent these new standards from becoming applicable.

The new standard applies to any setting or equipment that combusts municipal solid waste (MSW). MSW is generally well defined, but it includes refuse-derived fuel (RDF) which is solid waste that is shredded (or pelletized) and classified by size before combustion. A single item waste stream of tires is excluded from this definition. Further, the standard applies to those units whose capacity exceeds 35 megagrams per day (approximately 39 short tons). In addition, units with capacities between 25 and 35 Mg/day would be required to submit an initial report of capacities and location. Co-fired combustors that combust a fuel feed stream comprised, in aggregate, of equal to or less than 30% MSW or RDF (by weight, based on a 24-hour average) would not be subject to these proposed standards. They would be required to submit an initial notification of construction and reports of the amount of MSW and other fuels combusted. Cement kilns, unless they burn more than 30% of their fuel by weight using MSW would not be covered by this standard. Note, however, that the use of MSW does entail an obligation to file a report on amounts used.

Second, the USEPA established standards (right or wrong) using a rational train of thought. As each pollutant was considered, the USEPA did not try to mix control technologies, which may have been incompatible, in order to achieve the lowest possible standard. Since this new standard applies to new MWCs, or where major modifications occur, it is a moot question whether it is compatible with all MWC designs. The baseline standards are as tabulated in Table I, and are based on:

1. good combustion practices

2. spray dryer/fabric filter/activated carbon injection

3. selective noncatalytic reduction

4. wet ash or enclosed ash handling

Table I

Dioxins/furans 13 ng/dscm total mass or 

0.20 ng/dscm dioxin/furan TEQ

PM 15 mg/dscm
Opacity 10 %
Cd 0.010 mg/dscm
Pb 0.10 mg/dscm
Hg 0.080 mg/dscm
SO2 30 ppmv or 80% reduction
HCl 25 ppmv or 95% reduction
NOX 180 ppmv
Fly ash/bottom ash no visible emissions


These standards that are applicable to new MWCs reduced dioxins and PM by over 50%, and also added the metals and ash emission requirements. There is no definition regarding "no visible emissions" for fly ash. Additional requirements are included for new MWCs regarding siting, operator certification, and materials separation. Monitoring of CO and flue gas temperature is a requirement. The CO monitoring is over a 4-hour or 24-hour arithmetic average depending upon the MWC unit type. The flue gas temperature is established during the dioxin/furan stack test as the maximum 4-hour block average. The MWC must then be operated so that the temperature at the final PM control device inlet does not exceed this level by more than 17C on a 4-hour block average basis. MWCs are allowed to operate up to 110% of the maximum capacity, as achieved during the dioxin/furan compliance test. These standards are based upon MACT, but there is absolutely no indication that the standards are related to the best 12%. To the contrary, there is every indication that the proposed standard may be based on data from a single unit or, in the case of mercury, on the basis of experimental data.

Third, the USEPA did not completely ignore the older MWCs. They are proposing to replace Subpart Ca with Subpart Cb. This subpart establishes guidelines for states to accomplish over a period of time, but never-the-less will require all existing MWCs to comply eventually. After the guidelines are promulgated, a State Plan must be submitted within one year. The MWC must be fully compliant with the State Plan within three years with a compliance schedule beginning within one year. These guidelines are listed in Table II and are applicable to existing MWC plants with a capacity of greater than 225 Mg/day. For existing plants with a capacity between 35 and 225 Mg/day, the guidelines are significantly less stringent except for opacity and mercury, and no guideline for NOX.

Table II

Dioxins/furans 30 ng/dscm total mass or 

0.50 ng/dscm dioxin/furan TEQ

PM 27 mg/dscm
Opacity 10 %
Cd 0.040 mg/dscm
Pb 0.50 mg/dscm
Hg 0.080 mg/dscm
SO2 35 ppmv or 75% reduction
HCl 35 ppmv or 95% reduction
NOX 180 ppmv
Fly ash/bottom ash No visible emissions

These are significant reductions and additions to the old guidelines which undoubtably will require the older MWCs to undergo major modifications,which in turn may trigger the new Eb standard which is even more stringent. In establishing these guideline values the EPA began with a MACT floor. The floor values were determined by averaging the 12% best plants on the basis of their permits. The population of this size MCW was 235. Therefore,the average is based upon 29 units. If the data were basically a straight line, then only 14 to 15 units could meet the individual levels established, but not necessarily all the levels. From the MACT floor,only PM, SO2, and HCl remained the same in the guidelines. The MACT floor for Dioxins/Furans was 100 ng/dscm. The floor for cadmium was 0.25 mg/dscm. For lead, the floor was 0.53 mg/dscm. The floor for mercury was 0.36 mg/dscm. The MACT floor for NOX was 215. All of the reductions from the MACT floor were explained by, "it is possible through improved controls and modifications such as activated carbon injection."

The USEPA established these new standards and guidelines based upon their alleged study of the best 12% of existing MWCs and experimental work. The experimental work was done both in the United States and Europe. As a part of the proposal for change, the USEPA included cost information. This part of the justification can not be validated by GCI, but it is quite evident that all citizens in the U.S. whose garbage goes to a MWC plant can expect to see higher taxes/fees for their garbage disposal in the future. The EPA has said so.

For purposes of comparison, Table III is a listing of the Table I standards and Table II guidelines, plus the minimum, maximum, and average composite cement kiln compliance testing data for cadmium, lead and mercury.

As is very apparent, the proposed standards and guidelines for MWCs go far beyond the MACT floor. A new MWC will cost more than a comparable existing unit in order to meet the new standards. Existing MWCs will have to be modified to meet the new guidelines. No matter what, the average consumer/taxpayer is going to pay more to get rid of their garbage. The EPA in these proposed changes discussed a number of the impacts, but at no time did they discuss any potential benefits the people will get (if any) from the expenditure of their money.

These proposed changes, based (?) on MACT, for MWCs are only the beginning. We can fully expect that standards/guidelines for other combusters that use waste for fuel (incinerators, boilers, and industrial furnaces) will be upgraded. If these proposed changes are any indication, then a MACT floor is only a starting point for the thumb screws. All concerned parties need to be on the alert and keep on top of what is happening.

Table III


Cement Kiln Compliance Testing 

Table I Table II Minimum Maximum Average
Cadmium 0.010 0.040 0.00104 0.185 0.0332
Lead 0.10 0.50 0.0027 2.31 0.43
Mercury 0.08 0.08 0.000207 3.01 0.187

Note: All above values in mg/dscm @ 7% O2