Cradle to Gate
Identity ID
aa68f51b-9bd1-4e76-bc0f-69b91232d0fa
Waste treatment
Associated ID
2f17abf9-c4b7-41e4-bd6f-eb17707a35bf
Included activities starts
Included activities ends
Description
The initial sludge (95%) first undergoes alkaline thermal hydrolysis to increase the protein content in the sludge. Then, through concentration and the addition of polyacrylamide (PAM) reagents in centrifugal dewatering, the moisture content of the protein solution is reduced to 75%. Subsequently, full drying is achieved via a fluidized bed dryer, producing dried protein with a moisture content of 10%. This dried protein, used as fertilizer or soil amendment on land, can replace phosphate and nitrogen fertilizers by providing nutrients to the soil, but it may also generate greenhouse gases and release nitrogen and phosphorus, causing environmental pollution. The dried protein produced from each ton of dry sludge can replace 33 tons of triple superphosphate (TSP). 1295 kg, ammonium nitrate 51.5872 kg.
Wastewater generated during the process is treated by adding a certain amount of FeCl3, and then discharged after meeting the discharge standards.
Activity Description
The sludge is first subjected to alkaline thermal hydrolysis pretreatment, where it is treated under high temperature and alkaline conditions to reduce the resistance of microbial cells to heat, causing the sludge cells to rupture and release intracellular substances. This process also accelerates the decomposition of organic matter and increases the content of soluble proteins in the sludge. Subsequently, the sludge undergoes a concentration stage to reduce its volume and increase its solids content. The concentrated sludge is then dewatered; under the action of flocculants, its moisture content is further reduced, forming a solution with high protein content. This solution is fully dried via fluidized bed drying to obtain dried protein with a moisture content of 10%. Dried protein is used for land application, where its organic matter and nutrients can improve soil fertility. At the same time, nitrogen and phosphorus in the dried protein may also enter the atmosphere and aquatic environments. The wastewater generated during the process is treated with flocculants and discharged after meeting the required 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, alkaline thermal hydrolysis utilizes the synergistic combination of heat and alkali to rupture sludge cells, release intracellular substances, and accelerate the thermal decomposition of organic matter in sludge. This process also destroys microorganisms and their constituent materials, while producing a high-quality organic fertilizer rich in protein. The concentration stage primarily employs gravity thickeners to increase the solid content of the resulting sludge. Common dewatering equipment includes centrifuges, belt filter presses, and plate-and-frame filter presses. Sludge drying technologies encompass direct heating, indirect heating, or mixed heating methods. Land application techniques involve using dried protein as fertilizer or soil amendment to enhance soil fertility and improve its physical properties. Common implementation methods include surface application directly onto the soil, mixed application to improve soil structure, band application to provide nutrients directly to crops, mulch 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 use of sludge or compost while promoting sustainable agricultural development.