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On February 19, 1993, the United States Environmental Protection Agency (USEPA) published in the Federal Register its new “Standards for the Use or Disposal of Sewage Sludge (40 CFR Part 503)”.

The new Part 503 Regulation required that the Total Hydrocarbon (THC) concentration in the exit stack gases for all biosolids (sewage sludge) incinerators not exceed 100 ppm, as Propane, corrected to zero percent moisture and seven percent oxygen, on a monthly average basis. EPA noted that the THC limit was a surrogate for the emissions of potentially toxic organic compounds.

In order to demonstrate compliance with the new THC limit, Publicly Owned Treatment Works (POTWs) that practice incineration were required under the Part 503 Regulation to install an instrument that measures and records the THC concentrations in their biosolids incinerator exit stack gases.

In 1994, the Part 503 Regulation was modified to allow the monitoring of Carbon Monoxide (CO) as an alternative to THC monitoring. This action was taken since biosolids incinerators located in the State of New Jersey were already subject to a CO limit of 100 ppm (a more stringent level of control than the 100 ppm THC limit). As a result, USEPA set the alternative limit at 100 ppm CO, corrected to zero percent moisture and seven percent oxygen, on a monthly average basis.

In the mid 1990s THC/CO continuous emissions monitoring systems (CEMS) were purchased and installed by the POTWs that practiced incineration. Over the past few years, a substantial number of these POTWs have reported that they are encountering major operational and maintenance problems with their THC/CO-CEMS, while a limited number have indicated that they are subject to more stringent State or locally-mandated operating requirements than are contained in the Part 503 Regulation.

For example:

A number of POTWs have already replaced some if not all of the components within their existing THC-CEMS, in some cases after less than seven years of service, due to operational and maintenance related problems.

POTWs are encountering higher than anticipated O&M costs with their THC-CEMS.

A number of POTWs are subject to minimum THC/CO capture rate requirements, while the Part 503 Regulation does not establish minimum capture rates.

Given the problems that POTWs are encountering with their THC/CO-CEMS and the differing interpretations of the Part 503 Regulation's requirements concerning THC/COCEMS, the Association of Metropolitan Sewerage Agencies (AMSA) and the Water Environment Research Foundation (WERF) decided to conduct a joint survey to determine the following:

Current THC/CO emissions from biosolids incinerators,

O&M problems being encountered with THC/CO-CEMS,

Cost to purchase, install, operate and maintain the THC/CO-CEMS, an

State and Local THC/CO-CEMS requirements that differ from the requirements contained in the Part 503 Regulation.

The AMSA/WERF THC/CO-CEMS survey, which contains twenty-six (26) questions, was divided into the following sections:

Section 1. Responder/Responding Agency Information

Section 2. Number and type of CEMS and biosolids incinerators, along with CEMS related design, purchase and installation costs.

Section 3. Plant & Process Background Information

Section 4. THC/CO Performance Information

Section 5. THC/CO-CEMS Regulatory Information

Section 6. THC/CO-CEMS Design and Maintenance Information

Section 7. Follow-Up Information and Questions

The AMSA/WERF THC/CO-CEMS survey was issued in May 2004 to all of the known wastewater treatment agencies located within the United States that practice incineration. (A limited number of the agencies that received the survey indicated that they no longer incinerate their biosolids.) Participants were given the option of completing the survey on-line at the AMSA/WERF Clean Water Central website ( or by submitting a paper copy of the survey.

This paper presents detailed information, obtained through the AMSA/WERF THC/COCEMS survey and follow-up interviews with the participants, concerning THC/COCEMS that were installed in the mid 1990s.

Document Type: Research Article


Publication date: 2005-01-01

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