I. Turning equipment: Chain turner, large disc turner, and fermentation turner each have their applicable scenarios
Aerobic fermentation is the first step in the production of bio-organic fertilizer. The choice of turning equipment directly impacts pile temperature, oxygen distribution, and microbial activity. Chain-type turners utilize a chain-plate structure; they offer relatively shallow turning depths, making them ideal for windrow fermentation. They disturb the material gently, minimizing the risk of bringing undecomposed material to the surface. Large rotary-disc turners feature large-diameter wheels capable of turning depths exceeding 1.5 meters; they are suitable for large-scale in-vessel (trench) fermentation, with a single unit capable of processing hundreds of tons daily. “Fermentation turner” is a general term encompassing the aforementioned models. Key control points include turning frequency and pile temperature: the high-temperature phase (55–65°C) kills pathogens, but exceeding 70°C inhibits thermophilic microbial activity, thereby impairing the decomposition process. Insufficient turning depth leads to oxygen depletion at the pile core and the generation of foul odors, while excessive turning causes rapid heat loss and prolongs the fermentation cycle.
II. Mixing Equipment: Horizontal and twin-shaft mixers must operate “gently”
Horizontal mixers and twin-shaft organic fertilizer mixers are the primary equipment used for mixing prior to granulation. Horizontal mixers employ ribbon or paddle structures; while they offer short mixing times and high uniformity, their strong shear forces can cause mechanical damage to the microbial strains. Twin-shaft mixers utilize two symmetrically rotating spiral shafts, creating three-dimensional convection within the mixing chamber. This achieves mixing uniformity exceeding 95% while operating at lower speeds with gentler shear forces. For bio-organic fertilizers, the mixing time should be controlled at 3–5 minutes with a loading factor of 60%–70% to prevent temperature rises caused by excessive agitation. If microbial agents are to be added, it is recommended to spray them in during the final stages of mixing to minimize friction between the microbes and the raw materials.
III. Production Line Integration: Temperature and moisture are critical limits
Bio-organic fertilizer granulation typically employs either disc granulation or extrusion granulation. Disc granulation operates entirely at ambient temperature, keeping material temperatures below 55°C, which is favorable for microbial strains. Extrusion granulation can also avoid high temperatures if a dry, ambient-temperature process is used. Key integration points for the entire bio-organic fertilizer production line include: fully cooling the fermented material before it enters the mixer; controlling the moisture content to between 25% and 35% after mixing; and, if drying follows granulation, ensuring the inlet air temperature does not exceed 60°C and the discharge temperature remains below 45°C. Packaging materials must balance breathability with moisture resistance to prevent microorganisms from becoming inactive due to oxygen deprivation or moisture absorption.