Fermented sludge-based organic fertilizer is emerging as a new direction for urban solid waste resource utilization. With the advancement of urbanization, the production of municipal sludge continues to grow, and traditional landfill and incineration face constraints related to land availability, cost, and secondary pollution. The core of converting fermented sludge into organic fertilizer lies in achieving the harmlessness, stabilization, and resource utilization of sludge through an organic fertilizer production process, and accelerating composting using fermentation composting turning technology.
- Why Choose Sludge-Based Organic Fertilizer?
Sludge is rich in organic matter, nitrogen, phosphorus, potassium, and trace elements, making it a potential fertilizer resource. However, direct application poses problems such as pathogens, parasite eggs, heavy metals, and foul odors. Aerobic fermentation can kill pathogens, degrade organic matter, and stabilize heavy metal forms, transforming sludge from “waste” into “resource.”
- Core Process: Fermentation Composting Turning Technology
Fermentation composting turning technology is key to aerobic fermentation. Regular turning with a turning machine increases the oxygen content of the compost pile and regulates temperature and moisture. Maintaining a pile temperature of 55–65℃ for 5–7 days effectively kills pathogens and insect eggs. Turning frequency is typically once every 1–2 days, increasing during high-temperature periods. Moisture content is controlled at 50%–60%, and the carbon-to-nitrogen ratio is ideally 25–30:1. The fermentation cycle is approximately 15–20 days; the mature material is brownish-black, odorless, loose, and porous.
- Organic Fertilizer Production Process: The matured sludge enters the organic fertilizer production process through: crushing → batching (adding straw, microbial agents, and trace elements) → mixing → granulation (disc, drum, or extrusion) → drying → cooling → screening → coating → packaging. Strict moisture control is required during granulation; disc granulation typically maintains 25%–35%, while extrusion granulation maintains 2%–4%. The finished product should ideally have a particle size of 2–4 mm, a moisture content below 12%, and meet the NY/T 525-2021 standard.
- Environmental and Agricultural Value
Sludge-based organic fertilizer can replace some chemical fertilizers, increase soil organic matter, improve soil aggregate structure, and reduce non-point source pollution from chemical fertilizers. It also utilizes urban sludge, reducing pressure on landfill and incineration, and achieving carbon emission reduction. However, strict testing for heavy metals, antibiotics, and persistent organic pollutants is essential to ensure compliance with application standards.
- Challenges and Prospects
Sludge sources are complex, requiring separate collection and pretreatment. Policies should establish standards and subsidy mechanisms for sludge-based organic fertilizer. In terms of equipment, high-efficiency compost turners, deodorization systems, and intelligent fermentation monitoring are future directions. With continuous advancements in organic fertilizer production processes and fermentation composting turning technology, sludge-based organic fertilizer is expected to become an important pillar of the urban solid waste circular economy.
In summary, fermented sludge-based organic fertilizer is not only a technological path but also a strategic choice for the resource utilization of urban solid waste. By standardizing fermentation and production processes, sludge can be transformed from waste into valuable resources, providing new impetus for the green transformation of agriculture.