Biogas Digestate Processing Line: Dewatering, Fermentation, and Pelleting Solutions

Executive Summary & Engineering Overview

Anaerobic digestion (AD) plants generating renewable natural gas or electricity produce massive quantities of biogas residue and anaerobic digestate. While rich in organic nitrogen, phosphorus, potassium, and beneficial trace minerals, raw digestate presents severe disposal and environmental challenges due to its extremely high water content (85%–95%), pungent odor, and potential pathogen load.

Transforming wet biogas residue into high-value, commercial bio-organic fertilizer requires an automated Biogas Residue Dewatering and Granulation Line. At the core of this modern processing system is the Horizontal In-Vessel Fermentation Tank, which replaces open-air composting yards with a fully enclosed, high-efficiency horizontal biological stabilization process.

Technical Comparison: Horizontal In-Vessel Fermenter vs. Traditional Windrow Composting

For biogas plants and organic fertilizer manufacturers, traditional open-air windrow or groove composting creates odor issues, requires massive land space, and is vulnerable to weather conditions. The horizontal in-vessel fermenter provides a compact, continuous alternative with high structural stability:

Core Equipment Analysis: Horizontal Enclosed Fermentation Tank
The horizontal enclosed fermentation tank serves as the "high-efficiency biological thermal engine" within production lines for fertilizer derived from anaerobic digestion residue.

Key Engineering Features and Structural Components

1. Customizable Heavy-Duty Horizontal Stainless Steel Tank and Insulation System
Structure: Constructed as a U-shaped horizontal vessel, the tank is fabricated from corrosion-resistant SUS304 stainless steel or heavy-duty carbon steel featuring an internal anti-corrosion coating.

Insulation Layer: The space within the tank walls is filled with high-density polyurethane insulation, which effectively retains the heat generated by biological metabolism, ensuring that the core temperature inside the tank is maintained between 55°C and 65°C.

2. Horizontal Multi-Flight Agitator Shaft & Mixing Paddles

Mechanism: A heavy-duty central horizontal shaft fitted with specialized multi-flight paddle blades rotates continuously, lifting, tumbling, and slowly conveying the digestate mass from the inlet to the discharge end.

Uniform Aeration: Ensures thorough oxygen penetration across the entire bed length, preventing anaerobic pockets and ensuring consistent aerobic breakdown.

3. Forced High-Pressure Aeration System & Oxygen Monitoring

Air Injection: Industrial blowers force regulated air streams through lower manifold nozzles into the moving digestate mass.

Self-Sustaining Thermal Action: Thermophilic aerobic microorganisms metabolize volatile components, driving natural heating without external auxiliary burners.

4. Closed-Loop Exhaust Air & Odor Treatment Integration

Negative Pressure Operation: The horizontal chamber maintains a constant negative pressure to eliminate fugitive gas leaks.

Air Scrubbing: Exhaust gases rich in ammonia and moisture are routed through a water spray scrubber and bio-filtration unit before discharge.

Step-by-Step Digestate Processing & Granulation Line Workflow

1. Solid-Liquid Separation (Dewatering): Raw liquid digestate enters a continuous screw press or decanter centrifuge to separate liquid effluent from solid biogas residue, lowering moisture to 60%–65%.

2. Horizontal In-Vessel Biological Stabilization: Dewatered solids are blended with a minor fraction of dry carbon bulking agents (such as straw powder) and fed into the inlet of the Horizontal In-Vessel Fermentation Tank. Over 7 to 10 days of continuous horizontal agitation and aeration, thermophilic bacteria destroy pathogens and weed seeds while reducing moisture to 30%–35%.

3. Milling & Homogenization: Discharged, odorless compost cake is pulverized in a Semi-Wet Material Crusher into fine organic powder (<1 mm). Functional biological inoculants (Bacillus subtilis) or supplementary N-P-K minerals are blended using a horizontal twin-shaft mixer.

4. Pelleting & Granulation: Prepared powder enters a New-Type Organic Fertilizer Granulator, Disc Granulator, or Ring Die Pellet Mill to form uniform spherical granules or high-density pellets.

5. Drying, Cooling & Packaging: Granules pass through rotary drying and cooling drums to drop moisture below 15%. After screening out off-size particles, finished bio-fertilizer is automatically weighed and bagged into commercial packages.

Equipment Maintenance & Operational Checklist
Preventative Maintenance Schedule for Horizontal In-Vessel Fermenters:

Main Drive & Reducer: Check industrial gear oil levels weekly; replace gear lubricant after every 3,000 hours of continuous service.

Agitator Paddle Inspection: Inspect internal mixing paddles and bolts monthly for wear or loosening due to abrasive digestate solids.

Shaft Seal Lubrication: Grease main shaft end seals bi-weekly using high-temperature, moisture-resistant industrial grease.

Request Factory CAD Layouts & Project Quotations
Looking for a complete Biogas Residue Dewatering and Granulation Line or a custom-engineered Horizontal In-Vessel Fermentation Tank tailored to your biogas plant's daily digestate volume? Contact our engineering team today to receive detailed CAD line drawings, fermenter sizing calculations, and direct factory pricing!