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Heavy metals in sewage sludge

Heavy metals in sewage sludge
A backgrounder on Saratoga Biochar, Feb 2024

”Domestic sewage sludge, also known as biosolids, can contain various heavy metals, which are often present as a result of human activities, industrial discharges, and household waste. Some of the common heavy metals that can be found in domestic sewage sludge include
• Lead (Pb)
• Cadmium (Cd)
• Mercury (Hg)
• Chromium (Cr)
• Arsenic (As)
• Nickel (Ni)
• Copper (Cu)
• Zinc (Zn)

These heavy metals can accumulate in sewage sludge due to their presence in wastewater from various sources, including industrial processes, stormwater runoff, and household sewage. The concentrations of these heavy metals in sewage sludge varies. Proper treatment and management of sewage sludge are essential to minimize the potential environmental and human health risks associated with heavy metal contamination.”

In addition, EPA documents in its Rule 503 how it calculates "pollutant limits" for 5 of these
heavy metals when sludge is incinerated. We have not located an EPA rule that states pollutant limits in products of pyrolysis.

Sewage sludge also may contain, at last count, at least 726 chemicals, according to EPA. The
attached article describes how federal regulations require EPA to review sewage sludge
regulations every 2 years to identify any additional pollutants. The results of the last 8 studies
have shown an increase in new chemical pollutants during each review period.


A 2022 study concludes with this statement:“The long-term environmental implications of
various co-pyrolysis models is still needed to demonstrate that co-pyrolysis should be
considered as a viable solution to current technologies.”


"Emerging Contaminants" is the title of a Canadian study identifying the vast number of
pollutants that end up in our wastewater. Whatever is removed from the wastewater during
sewage treatment ends up in the sludge.

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