South Korean Researchers Identify Optimized Pyrolysis Thresholds to Neutralize Heavy Metal Risks in Chemical Sewage Sludge

Professor Kitae Baek’s team finds that 550°C is the optimal pyrolysis temperature to stabilize heavy metals in CEPT sewage sludge for safe environmental reuse.

By: AXL Media

Published: Mar 17, 2026, 7:28 AM EDT

Source: Information for this report was sourced from Jeonbuk National University

The Efficiency Shift in Wastewater Management

As global wastewater loads increase, sewage treatment facilities are transitioning toward more advanced and energy-efficient processing methods. Chemical-enhanced primary treatment (CEPT) has emerged as a leading alternative to traditional biological methods, utilizing chemical flocculants rather than microorganisms to treat sewage. While CEPT significantly reduces operational costs and energy consumption, it generates a unique byproduct: chemical sewage sludge (CS). According to Professor Kitae Baek, the environmental impact of this byproduct requires specific management strategies that differ from conventional biological sludge.

The Mechanics of Sludge Pyrolysis

To reduce the volume of sewage waste and degrade organic pollutants, many facilities employ pyrolysis—a high-temperature thermal treatment that transforms sludge into biochar. This process can produce value-added materials, but the behavior of heavy metals within CS-derived biochar has remained a significant research gap. The Jeonbuk National University team sought to clarify how these metals stabilize or migrate during thermal processing, comparing CS-derived biochar against conventional biological treatment sludge (BS) to determine the safest possible disposal or reuse protocols.

Identifying Secondary Pollution Risks

The research team, analyzing samples from treatment plants in Hong Kong, discovered that CS-derived biochar yield is notably lower than that of its biological counterpart. More critically, heavy metals in chemical sludge are less likely to remain trapped within the biochar structure. This finding suggests that improper thermal treatment of chemical sludge can inadvertently lead to secondary heavy metal pollution in the surrounding environment. The data highlights that the chemical composition used in the initial CEPT phase fundamentally alters how metals respond to heat, making standard pyrolysis settings potentially hazardous.