Sludge carbonization is an advanced sewage sludge treatment technology with significant potential and significance in environmental protection and resource utilization. In an oxygen-deficient or oxygen-free environment, it converts organic matter in sludge into stable biochar, tar, and syngas at high temperatures (350-700°C). As a new type of thermochemical conversion technology, sludge carbonization technology has the advantages of reduction, stabilization, harmlessness and resource utilization.
This pyrolysis carbonization technology is gaining increasing attention and application worldwide. It offers numerous advantages, including volume reduction, product resource utilization, effective heavy metal fixation, and reduced greenhouse gas emissions. The combustible gas produced by sewage sludge pyrolysis carbonization is used for energy production, while the solid char is used in building materials, soil conditioners, and adsorbents.
What is Pyrolysis Carbonization?
Pyrolysis carbonization involves heating biomass at high temperatures in an oxygen-deficient environment. During this process, organic carbon compounds are converted into synthesis gas and solid elemental carbon.
Although organic carbon compounds are biodegradable and release greenhouse gases into the atmosphere during their natural decomposition. But elemental carbon can remain stable for thousands of years. As long as this carbon is not burned, it does not react with any other elements. Instead, it remains in a stable form of carbon called biochar.
Therefore, when biochar is applied to soil, it can be considered a permanent carbon sink.
Sludge Pyrolysis Carbonization Projects
Sludge pyrolysis carbonization projects typically have been operating for several years, with large treatment scales and a high level of technological maturity.
Japan is one of the countries with the most successful commercialization of sludge pyrolysis carbonization technology. Many wastewater treatment plants use biomass carbonization plant to process hundreds of tons of dry solids daily.
The pyrolysis gas and oil produced by sludge carbonization are typically burned to provide heat for the pyrolysis process itself. Excess heat can also be used to dry the sludge, reducing external energy consumption. Biochar is primarily used as a fuel and raw material replacement in cement plants, for green space and farmland soil improvement, and as a landfill cover material.
European sewage sludge carbonization projects place a strong emphasis on phosphorus recovery. Sludge biochar is a significant source of phosphorus, and European countries have policies promoting phosphorus recovery from sewage sludge ash or biochar. The pyrolysis process effectively concentrates phosphorus and destroys organic pollutants, creating conditions for subsequent phosphorus extraction.
Sludge pyrolysis carbonization projects are growing rapidly in the United States, particularly in regions with strict environmental regulations, such as California and Florida. Policies prohibiting ocean dumping and restricting landfills are driving the development of pyrolysis carbonization technology. Concurrently, concerns about carbon sequestration and soil health are driving market demand for biochar production.
