Pig manure, with a moisture content of 70%–85%, is prone to anaerobic fermentation, foul odors, and nutrient loss if composted directly. Scientific treatment can transform it into high-quality organic fertilizer. Below are detailed steps and key techniques:

I. Pretreatment: Reduce Moisture and Adjust C/N Ratio

1. Solid-Liquid Separation
   • Method: Use screw extrusion or centrifugal separators to divide pig manure into solid (60%–70% moisture) and liquid (over 90% moisture) fractions.
   • Purpose: The solid fraction can be directly composted, while the liquid fraction can be further processed into biogas slurry or liquid fertilizer.
2. Add Dry Bulking Agents
   • Common materials: Crushed straw, sawdust, rice husks, mushroom residue, or garden waste.
   • Ratio: Mix pig manure with bulking agents at a volume ratio of 1:1–1:2 to reduce initial moisture to 55%–65% (optimal: squeezable into a ball that crumbles when dropped).
   • C/N ratio adjustment: Pig manure has a C/N ratio of ~10:1; add high-carbon materials (e.g., straw) to reach 25–30:1 for efficient microbial decomposition.

II. Composting Fermentation: Control Conditions to Kill Pathogens

1. Choose a Composting Method
   • Windrow composting: Pile materials into long strips (1.5–2 m wide, 1–1.5 m high) and turn every 3–5 days.
   • Trench composting: Use mechanical turners in enclosed trenches for large-scale production.
   • Reactor composting: Employ sealed fermentation tanks with forced aeration and temperature control, reducing the cycle to 7–10 days.
2. Key Parameter Control
   • Temperature:
     • Heating phase (Days 0–3): Microbes activate, raising temperature to 50–60°C.
     • Thermophilic phase (Days 5–15): Maintain 60–70°C for 5–7 days to kill pathogens, weed seeds, and insect eggs.
     • Cooling phase (After Day 15): Temperature drops below 40°C, indicating compost maturity.
   • Oxygen: Maintain >5% oxygen via turning or forced aeration to prevent anaerobic odors.
   • pH: Adjust initial pH to 6.5–7.5 with lime if acidic.
3. Add Composting Inoculants
   • Purpose: Accelerate decomposition, raise temperatures, and shorten fermentation time.
   • Common strains: EM bacteria, Bacillus subtilis, or actinomycete composites.
   • Application: Mix 0.1%–0.2% (by weight) with water and spray evenly.

III. Post-Treatment: Enhance Fertilzer Efficiency and Storage

1. Secondary Maturation
   • Let composted material rest for 1–2 weeks to stabilize undecomposed organic matter.
2. Crushing and Screening
   • Use crushers to break large particles into <5 mm sizes, then screen out impurities (e.g., plastic, stones).
3. Granulation and Drying (Optional)
   • Granulation: Add binders (e.g., bentonite) and use a pan granulator to form pellets for better marketability.
   • Drying: Reduce moisture to <20% at 60–70°C for long-term storage and transport.

IV. Treatment of Liquid Fraction (If Not Separated)

If solid-liquid separation is skipped, process high-moisture manure via:

1. Biogas Fermentation
   • Add inoculum (e.g., digestate) and seal for anaerobic digestion, producing biogas (methane) and slurry.
   • Use biogas slurry diluted as liquid fertilizer; mix digestate with solid compost.
2. Direct Land Application (Cautious)
   • Only for low-pollution farmland, limited to ≤5 tons/acre/year to avoid root burn and heavy metal accumulation.

V. Key Considerations

1. Environmental Protection
   • Locate composting sites away from residential areas; install impermeable liners and leachate collection ponds to prevent groundwater contamination.
   • Use deodorization systems (e.g., biofilters) or sprays (e.g., hydrogen peroxide) to reduce ammonia and hydrogen sulfide emissions.
2. Safety Protocols
   • Avoid open flames during early fermentation to prevent methane explosions.
   • Require operators to wear masks and gloves to avoid pathogen exposure from uncomposted material.
3. Quality Testing
   • Final organic fertilizer must meet NY/T 525-2021 standards:
     • Organic matter ≥30%
     • Total nutrients (N+P₂O₅+K₂O) ≥4%
     • Heavy metals (e.g., As, Cd, Pb) and Ascaris egg mortality within limits.

VI. Case Study (Large-Scale Process)

1. Raw Material Mixing: Pig manure (80% moisture) + straw (15% moisture) at 1:1.5 ratio → 62% moisture.
2. Windrow Composting: Pile dimensions 2 m × 1.5 m × 1 m; add 0.2% EM inoculant.
3. Turning Schedule: Turn every 3 days; maintain thermophilic phase for 8 days; total cycle 25 days.
4. Product Testing: Organic matter 45%, total nutrients 5.2% → compliant with organic fertilizer standards.

By following these steps, high-moisture pig manure can be efficiently converted into safe, nutrient-rich organic fertilizer, achieving dual goals of resource recycling and environmental protection.