What’s Class A? What’s Class B?
The EPA provides A Plain English Guide to the EPA Part 503 Biosolids Rule, which is broken into ten chapters. Table 2-5 in Chapter 2 (PDF) summarizes the differences between the pathogen reduction requirements for Class A and Class B biosolids:
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Class A |
Class B |
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In addition to meting the requirements in one of the six alternatives listed below, fecal coliform or Salmonella sp. Bacteria levels must meet specific density requirements at the time of biosolids use or disposal or when prepared for sale or give-away (see Chapter Five [PDF] of this guidance). |
The requirements in one of the three alternatives below must be met. |
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Alternative 1: Thermally Treated Biosolids |
Alternative 1: Monitoring of Indicator Organisms |
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Alternative 2: Biosolids Treated in a High pH-High Temperature Process |
Alternative 2: Use of PSRP |
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Alternative 3: For Biosolids Treated in Other Processes |
Alternative 3: Use of Processes Equivalent to PSRP |
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Alternative 4: Biosolids Treated in Unknown Process |
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Alternative 5: Use of PFRP |
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Alternative 6: Use of a Process Equivalent to PFRP |
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Tags: Class 'A' Biosolids, Biosolids Process, EPA, Biosolids Handling
Wastewater is not considered sludge until it has been de-watered to at least 7% solids content, according to the EPA. To create an end product that is considered Class A grade acceptable, sludge must be used. Acceptable sludge must be free of pollutants, shown below is the EPA specified amount of pollutants allowed:
| Pollutant | Must not exceed concentration [Milligrams / kilogram] |
| Arsenic | 41 |
| Cadmium | 39 |
| Chromium | 1,200 |
| Copper | 1,500 |
| Lead | 300 |
| Mercury | 17 |
| Nickel | 420 |
| Selenium | 36 |
| Zinc |
If any of these pollutants are found to be above the ceiling set by the EPA, the sludge is not safe and must be land filled or incinerated. Providing the sludge is acceptable, a range of processes (drying, alkaline stabilization, etc.) can be used to create Class A product. Although no specific process is outlined and approved by the EPA over another, the restrictions for the end product are what sets the bar and defines a Class A product.
Class A product must have "less than 1000 Most Probable Number per gram of total solids on a dry weight basis" (EPA regulation 503) of fecal coliform & salmonella sp. bacteria. These pathogens can only be tested for in the lab environment where a sample is put into a Petri dish and the bacteria is allowed to grow so it can be accounted for. Then the amount of organisms per gram of material must be below 1000. Meeting this level of pathogen kill is accomplished in most class cases by keeping the sludge in an elevated temperature environment for an extended period of time.
In addition to acceptable levels of pathogen kill the end product must also have "sufficiently reduced vector attraction of the material" (EPA regulation 503). Vectors are bugs such as flies or mosquitoes that carry diseases. Vector reduction can be accomplished in several ways. By increasing material PH or drying the material to greater than 90% the attractiveness of the material to sustain or breed for the bugs is eliminated. At a minimum, each batch needs to be tested and pass these standards before they can be considered Class A biosolids and land applied.
Tags: Biosolids Process, Bisolids Handling, EPA, Sewage Sludge, Biosolids Drying
