Cradle to Gate
Identity ID
20eadea5-4ced-427c-baed-bdff72233eaf
Waste treatment
Associated ID
03a07153-6990-487e-bee2-6b7636f7a859
Included activities starts
Included activities ends
Description
Raw sludge (95% moisture content) is first thickened and mixed with polyacrylamide (PAM) reagent, followed by centrifugal dewatering to reduce its moisture content to 75%. The dewatered sludge then undergoes hydrothermal carbonization under high temperature and pressure conditions, producing hydrochar with a moisture content of 60%. Subsequently, the hydrochar is fully dried via fluidized bed drying, reducing its moisture content to 10%.
The dried hydrochar can be applied to land as a fertilizer or soil amendment, substituting phosphorus and nitrogen fertilizers to provide nutrients to the soil. However, it may also emit greenhouse gases and release nitrogen, phosphorus, and heavy metal elements, potentially causing environmental pollution. Per ton of dry sludge, the hydrochar produced can replace 13.345 kg of triple superphosphate (TSP) and 9.115568 kg of ammonium nitrate.
The wastewater generated during the process is treated by adding a certain amount of FeCl₃, and then discharged after meeting the required standards.
Activity Description
In the treatment process, sludge first undergoes a concentration stage to reduce its volume and increase its solids content. The concentrated sludge is then dewatered, during which, with the aid of flocculants, its moisture content is further reduced. The dewatered sludge subsequently enters the hydrothermal carbonization stage, where organic matter is converted into char and combustible gases under high-temperature and high-pressure hydrothermal conditions, simultaneously achieving sludge stabilization and volume reduction, while generating a certain amount of hydrothermal carbonization process liquor. The hydrochar is fully dried through fluidized bed drying, reducing its moisture content to 10%. Hydrochar used for land application can improve soil structure and enhance soil fertility due to its organic matter and nutrient elements. However, pollutants present in hydrochar may also enter the environment; therefore, the content of potential contaminants in the hydrochar must be strictly controlled to ensure they remain within safe limits. Wastewater generated during the process is treated with flocculants and discharged only after meeting regulatory standards.
Process Description
"Sewage sludge" is a byproduct generated during the urban wastewater treatment process. 100% sewage sludge, with a moisture content of 97%. 5%, "sludge" consists of the following components: microorganisms, animal and plant residues, inorganic minerals, potential heavy metals, micropollutants, and pathogens. Treatment methods for this by-product include sanitary landfilling, municipal incineration, and use as a raw material for clinker production. Additionally, sludge can be converted into bioenergy through anaerobic digestion or applied to land following stabilization. In the HiQ database, treatment methods for this by-product include incineration, landfilling, aerobic composting, anaerobic digestion, wet oxidation, pyrolysis/hydrothermal carbonization, and land application. Furthermore, this by-product is utilized in the following processes: clinker production, among others.
Time period
2022
2026
Geography
China
Geography comment
National statistics, literature research
Macroeconomic value
Business-as-Usual
Data validation
Yes
Technology
Current Technology
Technology comment
In China's sludge treatment processes, the thickening stage primarily increases the solids content of the sludge through gravity thickeners. Commonly used equipment in the dewatering process includes centrifuges, belt presses, and filter presses. Hydrothermal carbonization is a thermochemical process that converts biomass or organic waste into solid, liquid, and gaseous products under subcritical water conditions. Sludge drying technologies include direct heating, indirect heating, or mixed heating methods. Land application techniques involve using hydrochar produced from hydrothermal carbonization as fertilizer or soil amendment to enhance soil fertility and improve its physical properties. Common application methods include direct application onto the soil surface, incorporation to improve soil structure, band application to directly supply nutrients to crops, surface mulching to reduce water evaporation and suppress weeds, and deep plowing to accelerate organic matter decomposition. These methods aim to ensure the safe and efficient use of sludge or compost while promoting sustainable agricultural development.