Fermenting Animal Manure into Organic Fertilizer Using ePTFE Semi-permeable Membrane
Abstract
With the rapid expansion of intensive livestock and poultry breeding industries globally, massive accumulated animal manure triggers severe environmental pollution, soil degradation and resource waste. Conventional open-air composting and sealed tank fermentation methods suffer from prominent drawbacks including severe odor emission, nutrient loss, unstable fermentation temperature, long curing cycle and low finished fertilizer quality. Expanded Polytetrafluoroethylene (ePTFE) semi-permeable membrane, a novel microporous polymer functional material, has been widely applied in aerobic manure fermentation and organic fertilizer production in recent years. This paper systematically introduces the material properties, working mechanism, standardized fermentation process, core advantages and industrial application prospects of ePTFE semi-permeable membrane technology for animal manure recycling, providing a green, low-carbon and efficient solution for livestock manure harmless treatment and resource utilization.
1. Basic Properties of ePTFE Semi-permeable Membrane
ePTFE semi-permeable membrane is a high-performance porous membrane material manufactured by stretching and sintering pure PTFE raw materials, featuring uniform nano-micron interconnected pore structures with an average pore size of 0.2–0.4 μm and porosity up to 50%–60%. Distinct from ordinary plastic films and common breathable cloths, it possesses selective gas-water permeability and excellent chemical inertness. The membrane allows small molecular gases including oxygen, carbon dioxide and water vapor to pass freely, while intercepting large-molecular odor pollutants, ammonia gas, hydrogen sulfide, dust and pathogenic bacteria efficiently. Besides, ePTFE membrane boasts ultra-high acid and alkali resistance, corrosion resistance, anti-aging performance and tear strength, adapting to high-temperature, high-humidity and corrosive internal environment of manure fermentation piles, with a service life of 5–8 years under outdoor working conditions. It is also waterproof, windproof and ultraviolet-resistant, requiring no extra anti-corrosion and sunshade auxiliary facilities for outdoor fermentation workshops.
2. Core Fermentation Mechanism
The ePTFE membrane-covered aerobic fermentation system relies on the membrane’s selective semi-permeability to build a stable closed micro-ecological fermentation environment for mixed animal manure (cattle, pig, chicken and sheep manure) and auxiliary carbon materials. Firstly, mixed raw materials of crushed animal manure, straw, bran and microbial fermentation agents are piled up uniformly and fully covered with integrated ePTFE membrane to form an independent fermentation unit. During aerobic microbial decomposition, thermophilic flora reproduce rapidly to decompose organic matters such as crude protein, cellulose and hemicellulose in manure, releasing massive heat and maintaining constant high temperature (60–75℃) inside the pile.
Oxygen from external air penetrates the membrane continuously to sustain aerobic microbial activity, avoiding anaerobic fermentation and putrefactive odor generation. Meanwhile, metabolic water vapor and CO₂ produced by fermentation diffuse outward through membrane pores; ammonia, sulfide malodorous molecules and parasitic worm eggs in manure are locked inside the membrane cover. The sealed constant-temperature environment accelerates the inactivation of pathogenic microorganisms, weed seeds and antibiotic residues in raw manure, realizing harmless treatment synchronously. Moreover, intercepted nitrogen-containing substances are retained in the fermentation pile, drastically reducing nitrogen element loss compared with traditional open composting.
3. Standard Production Process
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Raw Material Pretreatment: Collect fresh livestock and poultry manure, adjust moisture content to 55%–60% by mixing dry crop straw, mushroom residue and corn stalks, add compound thermophilic microbial decomposing agents, and crush and stir raw materials evenly to balance carbon-nitrogen ratio.
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Pile Building and Membrane Covering: Stack mixed materials into strip fermentation piles with fixed height and width, lay fixed supporting keels above piles, and cover the whole fermentation area with integrated ePTFE semi-permeable membrane for fully sealed coverage.
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Constant-temperature Aerobic Fermentation: Conduct static high-temperature aerobic fermentation for 18–25 days without frequent turning over. The membrane automatically regulates internal gas and humidity to stabilize fermentation temperature, completing organic matter maturation and harmful substance degradation.
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Post-treatment and Finishing: Uncover the membrane after fermentation maturity, conduct natural air drying, crushing, impurity removal and granulation on decomposed materials, and finally obtain commercial finished organic fertilizer.
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Compared with traditional technology, this process cuts turning-over frequency by over 80% and shortens total fermentation cycle by 30%.
4. Outstanding Technical Advantages
4.1 Environmental Protection and Odor Control
The ePTFE membrane blocks more than 92% of ammonia and hydrogen sulfide odor emissions, eliminating cross-regional odor pollution of breeding farms and solving the environmental complaint problem of manure composting sites. It realizes closed and odor-free whole-process fermentation without additional deodorization equipment.
4.2 High Nutrient Retention Rate
Traditional open composting causes 35%–45% nitrogen loss via ammonia volatilization. The membrane interception structure locks nutrient elements including nitrogen, phosphorus and potassium inside the pile, improving total nutrient content of finished organic fertilizer by 20%–25% and enhancing fertilizer efficiency obviously.
4.3 Low Operation and Construction Cost
This technology requires no closed fermentation tank, heating system or mechanical aeration equipment, adapting to outdoor open workshops with low infrastructure investment. Reduced manual turning-over work cuts labor and energy consumption greatly; the reusable ePTFE membrane lowers long-term production input.
4.4 Superior Harmless Treatment Effect
Stable high-temperature fermentation lasting over 15 days thoroughly kills pathogen bacteria, roundworm eggs and weed seeds in manure, and degrades residual veterinary antibiotics and heavy metal active components, meeting national agricultural organic fertilizer safety standards.
4.5 Climate Adaptability
The membrane resists extreme weather including rainstorm, low temperature and strong wind. It avoids rainwater dilution and nutrient leaching in rainy seasons, and keeps internal fermentation temperature stable in cold winter, applicable for promotion in diverse climatic zones worldwide.
5. Finished Organic Fertilizer Value and Application
The ePTFE membrane fermented animal manure organic fertilizer is rich in humic acid, organic matter, medium and trace elements and active beneficial bacteria. It can improve soil aggregate structure, alleviate soil salinization and hardening, boost soil microbial activity, and reduce chemical fertilizer application dosage. The fertilizer is suitable for grain crops, fruit trees, vegetables and ecological greening planting. Meanwhile, the technology realizes full resource recycling of breeding waste, builds a circular agricultural mode of “livestock breeding-manure fermentation-soil fertilization-crop planting”, and reduces agricultural solid waste disposal pressure.
6. Conclusion and Prospect
ePTFE semi-permeable membrane fermentation technology breaks through multiple bottlenecks of traditional animal manure composting technology, integrating odor control, high-efficiency fermentation, nutrient preservation and low-cost operation. It is an energy-saving, eco-friendly and scalable solid waste recycling technology. At present, this technology has been popularized in large-scale livestock farms and organic fertilizer factories across Asia, Europe and North America. In the future, with optimized membrane pore structure and matched intelligent temperature-gas monitoring system, ePTFE membrane fermentation technology will further improve fermentation efficiency and fertilizer quality, becoming the mainstream technical route for livestock manure resource utilization and green organic fertilizer production in sustainable ecological agriculture.