I. Core Process and Key Technologies

1. Raw Material Pretreatment

• Classification and Collection
  • Carbon Sources: Crop straw (wheat, corn, rice), sawdust, rice husks, fruit shells (high carbon, low nitrogen).
  • Nitrogen Sources: Livestock manure (pig, cattle, poultry), urea, or septic tank waste (high nitrogen).
  • Exclusions: Avoid diseased animal waste, plant residues contaminated with pesticides/heavy metals.
• Crushing and Adjustment
  • Carbon Sources: Straw crushed to ≤8 cm (wheat: 1–3 cm; corn: 5 cm; sawdust: 0.5–1 cm).
  • Nitrogen Sources: Livestock manure dewatered to ≤60% moisture using screw press dewaterers.
  • Mixing Ratio: Carbon-to-nitrogen (C/N) ratio of 25–35:1, supplemented with microbial agents (e.g., EM bacteria, Bacillus), ensuring initial microbial count ≥10⁶ CFU/g.

2. Fermentation and Maturation

• Compost Pile Construction

  • Dimensions: Width 1.5–3 m, height 1–1.5 m (avoid >2 m to prevent anaerobic conditions).
  • Aeration: Bottom ventilation pipes or wooden sticks; surface covered with film for insulation.
  • Initial Conditions: Moisture 55–60%, pH ~8.

• Temperature-Controlled Stages

   

  Stage	Temperature Range	Duration	Key Operations
  Heating	<55℃ → ≥55℃	1–3 days	No turning; natural temperature rise.
  Thermophilic	55–65℃	7–14 days	Turn pile every 3–5 days; immediate turning if temp >65℃ to kill pathogens.
  Cooling	<55℃	7–12 days	Turn pile every 7–12 days; rehydrate if moisture <40%.
  Stabilization	≤35℃	Until end	End when temp difference <2℃ for 2 days; moisture 20–30%; dark brown, odorless.

• Environmental Control

  • Moisture: Initial 55–60%; adjust via spraying (low) or drying (high).
  • Aeration: Regulate via turning or aeration systems; test with wooden stick insertion.
  • pH: Adjust to ≥5 using lime if pH <5.

3. Post-Treatment and Processing

• Crushing and Screening
  • Equipment: Semi-wet material crusher for clumps; rotary/vibrating screens to remove impurities (plastics, stones).
  • Target: Particle size ≤5 mm.
• Blending
  • Additives: NPK fertilizers (urea, superphosphate), microbial agents.
  • Uniformity: Mixing variation coefficient ≤5% (dual-axis mixer).
• Granulation
  • Equipment:
    • Disc Granulator: Small-scale; 2–5 mm particles.
    • Rotary Drum Granulator: Large-scale; high strength.
    • Extrusion Granulator: No drying; suitable for heat-sensitive materials.
  • Binders: Humic acid, bentonite, or starch (≥90% granulation rate).
• Drying and Cooling
  • Drying: Rotary dryer (hot air 80–120℃); moisture ≤15%.
  • Cooling: Counterflow cooler to prevent caking.
  • Heat Recovery: Use dryer exhaust heat for fermentation heating.
• Screening and Coating
  • Grading Sieve: Separate qualified particles (2–4 mm ≥90%) from recycled materials.
  • Coating: Spray anti-caking agents (mineral oil, resin).
• Packaging and Storage
  • Packaging: Automatic weighers (accuracy ±0.2%); bagged or bulk.
  • Storage: Cool, dry warehouse; stack height ≤5 layers.

4. Quality Control

• Sanitary Standards
  • Maintain ≥50℃ for 10 days or ≥60℃ for 5 days.
  • Ascaris egg mortality ≥95%; fecal coliform value ≥0.1; Salmonella not detected.
• Nutrient Standards
  • Organic matter >30%; total nutrients (N+P₂O₅+K₂O) ≥4%.
• Safety
  • Heavy metals (As, Pb, Cd) comply with Organic Fertilizer (NY/T 525-2021).
  • Seed germination index >80% (no phytotoxicity).

5. Equipment Selection and Capacity

6. Environmental and Safety Measures

• Air Emissions
  • Reduce NH₃ emissions by ≥35% (add zeolite, bentonite).
  • Negative-pressure ventilation + biofilter for exhaust.
• Wastewater
  • Dewatering effluent treated in biogas digesters; reused for irrigation.
• Safety
  • PPE (masks, gloves) for operators.
  • Temp/O₂ sensors in fermentation zones.

This solution enables efficient conversion of agricultural waste into compliant organic fertilizer, achieving dual goals of resource recycling and environmental protection.