Production of recycled manure solids for bedding in Canadian dairy farms: I. Solid–liquid separation

摘要

Canadian dairy producers have an increasing interestin recycled manure solids (RMS) as bedding materialbecause of reduced availability of traditional beddingresources. Information regarding methods to obtainRMS and composition of RMS is very limited. Hence,a 2-part investigation was developed to compare theperformances of 3 mechanical solid-liquid manureseparators (part I) and 4 composting methods (partII; companion paper in this issue) for the productionof high quality RMS. In this first study, a roller press,a screw press, and a decanter centrifuge were testedfor the separation of slurry manure from a commercialdairy farm. During the experiment, the quantity ofslurry manure processed and the volume and mass ofthe liquid and solid fractions were measured. The energyconsumption of each separator was recorded, andsamples of the slurry, liquid, and solid effluents werecollected for analysis. The type of separator did notsignificantly influence the chemical and bacteriologicalcomposition of RMS produced. The choice of a separatorfor Canadian dairy producers should thus be basedon the equipment cost and its capacity, targeted solidsdry matter (DM) content and structure, and fertilizingquality of the separated liquid. The decanter centrifugeproduced the solid phase with the highest DM and bestseparation efficiencies for DM, N, and P. However, itslow production capacity (1.5 m3/h vs. 9.1–20.3 m3/h)combined with its high acquisition cost (Can$145,000vs. Can$75,000) and energy consumption (4.99 kWh/m3 vs. 0.10–0.35 kWh/m3) reduce its technical andprofitability values. Besides, the centrifuge producedfine structured RMS and a low-quality liquid fraction,not suitable as dairy cow bedding and fertilizer, respectively.Both presses reached acceptable productioncapacity at a minimal operation cost. However, thepoor performance in terms of DM (25%) of the modelof screw press used in this study produced RMS unsuitablefor immediate use without further processing. Themodel of roller press used in this study had the advantagesof almost reaching the recommended DM contentin RMS (>34%), being flexible in terms of inputs, andproducing fluffy RMS. Nevertheless, its compressionprocess seemed to allow greater passage of solids intothe liquid fraction compared with the screw press. PartII of this work explores different composting methodsto reduce the health risks associated with screw-pressedRMS before their use as bedding.