Windrow compost turner

The windrow compost turner is the most versatile core piece of equipment in aerobic composting processes. Designed specifically for ground-based windrow composting, it features a self-propelled structure that straddles long piles of material to perform turning operations, reforming the material into a new windrow as it passes. Integrating the functions of mixing, crushing, oxygenation, and displacement, this machine serves as a critical link between raw material pre-treatment and the post-processing discharge stage.

These turners process viscous materials—such as livestock manure, sewage sludge, and distillery grains—to produce organic fertilizer using the windrow composting method. The equipment not only turns and piles the material uniformly but also breaks up compacted clumps within the fermenting feedstock. Compared to in-vessel or channel-based turning systems, the windrow method eliminates the need for permanent fermentation channels; it offers lower investment costs and greater site adaptability, making it particularly suitable for small-to-medium-scale organic fertilizer production and the on-site treatment of manure at livestock farms.

Component Composition and Functional Zoning

From the perspective of the composting process, the windrow turner can be categorized into the following functional units:

(I) Turning Unit: Composed of a turning drum and turning blades. The rotating spiral drum gathers the windrow material toward the center while simultaneously throwing it backward, thereby achieving mixing, pulverization, and aeration (loosening) of the material.

(II) Propulsion and Displacement Unit: Consists of a crawler track or tire-based drive mechanism. It propels the equipment along the length of the windrow to perform continuous turning operations.

(III) Oxygen Supply and Aeration Unit: Facilitates natural oxygen supply through thorough contact between the material and the air during the turning process. The material is lifted and thrown backward by the high-speed rotating drum; its suspension in the air enables heat and mass exchange.

(IV) Depth Adjustment Unit: Controls the operating depth of the turning drum via a hydraulic lifting system.

(V) Control Unit: Comprises the operator's cab and a hydraulic control valve assembly.

Production Line Roles and Process Flow

The windrow compost turner plays a central role in the fermentation stage of an organic fertilizer production line. The complete windrow composting process involves: raw material pretreatment (proportioning and mixing) → windrow formation and turning/fermentation → discharge of matured compost → crushing → granulation → drying → cooling → screening → packaging.

During the windrow fermentation phase, the compost turner performs several critical tasks: it arranges materials into windrows of specific height and width, laid out in parallel on a flat composting site (either outdoors or indoors); the machine straddles the windrow to carry out continuous turning operations; it mixes, breaks up, and blends the materials during the turning process; and it ensures thorough contact between the materials and the air, thereby regulating oxygen levels, temperature, and moisture content within the compost. The windrow composting process offers a short fermentation cycle, typically allowing materials to fully ferment and mature within 15 days.

Detailed Explanation of the Aerobic Fermentation Process

The aerobic fermentation process facilitated by windrow turners constitutes the core technical stage of organic fertilizer production. This process generally comprises the following phases:

Heating-up phase: The temperature of the compost pile gradually rises from ambient levels to approximately 45°C. Mesophilic microorganisms (fungi, bacteria, and actinomycetes) are the dominant agents during this stage, primarily decomposing substrates such as sugars and starches.

High-temperature phase: The process enters this phase once the pile temperature exceeds 45°C. Mesophilic microorganisms are inhibited or die off, while thermophilic microorganisms become dominant. Residual and newly formed soluble organic matter undergoes continued oxidative decomposition, and complex organic compounds—such as hemicellulose, cellulose, and proteins—begin to break down rapidly. Thermophilic fungi and actinomycetes are typically most active around 50°C; as the temperature rises to 60°C, fungal activity virtually ceases, leaving only thermophilic bacteria and actinomycetes active. Windrow turners maintain the pile temperature within the 55–70°C range for 3–4 days through the turning process.

Cooling phase: As the high-temperature phase leads to microbial mortality and reduced activity, the pile gradually enters the cooling phase. Mesophilic microorganisms regain dominance, further decomposing the remaining, more recalcitrant organic matter.

Maturation phase: Organic matter stabilizes and oxygen demand drops significantly, marking the compost's entry into the maturation phase.

Process parameters for windrow stacking

The operational performance of a windrow turner is closely linked to the parameters of the windrow itself:

Windrow width: The width must be determined based on the turner's operating span; it generally should not exceed the machine's rated turning width and typically ranges from 2 to 3 meters.

Windrow height: The height generally does not exceed 1.2 meters, with a typical range of 0.8 to 1.4 meters.

Windrow shape: The cross-section of the pile is roughly semi-circular or triangular.

Windrow spacing: Windrows are arranged in parallel with a spacing of generally 0.6 to 1 meter to ensure sufficient maneuvering space for the equipment between them.

Site requirements: The operating site must be level and firm; operation on slopes is strictly prohibited, and the work area must be free of surface irregularities exceeding 5 centimeters.

Operational Guidelines and Key Control Points

Proper operation of the windrow compost turner is crucial for ensuring effective fermentation and extending the equipment's service life:

Break-in period requirements: As specialized site-based machinery, the turner requires operating procedures that differ from those of standard vehicles. Before commencing actual turning operations, the equipment must undergo a 40–56 hour break-in period (involving driving, reversing, turning, etc.); actual turning operations are strictly prohibited during this time.

Pre-start inspection: Check for any damage sustained during transport and ensure all components are securely fastened. Inspect drive belts for proper tension and check for signs of severe wear or breakage.

Starting procedure: Disengage the turning shaft before starting. Limit the starter engagement time to no more than 10 seconds per attempt; do not attempt to start the engine more than three times consecutively, and allow an interval of at least 2 minutes between attempts. After starting, let the engine idle for 10 minutes.

Operational procedure: Increase the throttle to the rated speed during operation and slowly release the clutch to engage the turning shaft. If the diesel engine exhaust emits black smoke, it indicates material overload; in this case, depress the clutch, wait for the engine speed to return to normal, then release the clutch to resume forward movement and turning.

Turning Frequency and Process Control

The turning frequency of windrow compost turners should be flexibly adjusted based on the fermentation stage:

Initial stage: Generally turn once a day to promote rapid temperature rise and ensure uniform mixing.

Middle and late stages: Turn once every 2–3 days to maintain aerobic fermentation conditions.

Temperature control: Increase turning frequency if the temperature exceeds 65°C to prevent excessive heat from inhibiting microbial activity.

Moisture management: Closely monitor material moisture during turning; add water if moisture is too low, or enhance aeration through turning if moisture is too high.