Cradle to Gate
Identity ID
50753ba9-bb6f-4525-8ef9-d4886fcdcd09
Waste treatment
Associated ID
b1008800-3ffd-447f-b1de-a7933dddc1bf
Included activities starts
Included activities ends
Description
The initial sludge (95%) is first concentrated and centrifuged with the addition of polyacrylamide (PAM) to reduce its moisture content to 75%. The removed water is treated with a certain amount of FeCl3 and then discharged after meeting regulatory standards. The dewatered sludge is fully dried via fluidized bed drying, reducing the moisture content to 20%. The dried sludge is then converted via pyrolysis carbonization into biochar, pyrolysis oil, and pyrolysis gas. The biochar is used as a soil amendment, while the pyrolysis oil and gas are utilized for energy recovery. Applying pyrolysis char to land as fertilizer or soil amendment can provide nutrients to the soil by substituting phosphate and nitrogen fertilizers, but it may also produce greenhouse gases and release nitrogen, phosphorus, and heavy metals, causing environmental pollution. The pyrolysis oil and pyrolysis gas generated from each ton of dry sludge can provide 2,936.63 kWh of electricity, substitute 39.25 kg of triple superphosphate (TSP), and 23.6768 kg of ammonium nitrate.
Activity Description
During the treatment process, sludge first undergoes a thickening stage to reduce its volume and increase its solid content. The thickened sludge is then dewatered, where flocculants are used to further reduce its moisture content. The removed water is treated with flocculants, and discharged after meeting regulatory standards. The dewatered sludge proceeds to the drying stage, where thermal energy is applied to reduce moisture, enhancing its stability and facilitating subsequent treatment or utilization. After drying, sludge undergoes pyrolysis carbonization under anaerobic or hypoxic conditions, decomposing its organic matter into biochar, pyrolysis oil, and pyrolysis gas. The pyrolysis oil and gas can be used for energy recovery, while the biochar is utilized as a soil amendment. The organic matter and nutrients in the biochar can improve soil structure and enhance soil fertility. However, contaminants present in the biochar may also enter the environment; therefore, the concentration of potential pollutants in the biochar must be strictly controlled to ensure they remain within safe limits.
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 thickening tanks. Commonly used equipment in the dewatering stage includes centrifugal dewatering machines, belt filter presses, and plate-and-frame filter presses. Sludge drying technologies involve direct heating, indirect heating, or a combination of both. The dried sludge is subsequently subjected to pyrolysis and carbonization, typically employing fixed-bed or fluidized-bed pyrolysis and carbonization processes. Sludge incineration technologies mainly include standalone incineration, co-incineration with municipal solid waste, and co-processing in cement kilns. Land application technology involves using biochar produced through pyrolysis carbonization as fertilizer or soil amendment to enhance soil fertility and improve its physical properties. Common implementation methods include direct surface application, mixed application to improve soil structure, banded application to directly supply nutrients to crops, mulching application to reduce water evaporation and suppress weeds, and deep plowing application to accelerate organic matter decomposition. These methods aim to ensure the safe and efficient utilization of sludge or compost while promoting sustainable agricultural development.