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

Abstract

Canadian dairy producers have an increasing interest in recycled manure solids (RMS) as bedding material because of reduced availability of traditional bedding resources. Information regarding methods to obtain RMS and composition of RMS is very limited. Hence, a 2-part investigation was developed to compare the performances of 3 mechanical solid-liquid manure separators (part I) and 4 composting methods (part II; companion paper in this issue) for the production of high quality RMS. In this first study, a roller press, a screw press, and a decanter centrifuge were tested for the separation of slurry manure from a commercial dairy farm. During the experiment, the quantity of slurry manure processed and the volume and mass of the liquid and solid fractions were measured. The energy consumption of each separator was recorded, and samples of the slurry, liquid, and solid effluents were collected for analysis. The type of separator did not significantly influence the chemical and bacteriological composition of RMS produced. The choice of a separator for Canadian dairy producers should thus be based on the equipment cost and its capacity, targeted solids dry matter (DM) content and structure, and fertilizing quality of the separated liquid. The decanter centrifuge produced the solid phase with the highest DM and best separation efficiencies for DM, N, and P. However, its low production capacity (1.5 m 3 /h vs. 9.1-20.3 m 3 /h) combined with its high acquisition cost (Can$145,000 vs. Can$75,000) and energy consumption (4.99 kWh/ m 3 vs. 0.10-0.35 kWh/m 3 ) reduce its technical and profitability values. Besides, the centrifuge produced fine structured RMS and a low-quality liquid fraction, not suitable as dairy cow bedding and fertilizer, respectively. Both presses reached acceptable production capacity at a minimal operation cost. However, the poor performance in terms of DM (25%) of the model of screw press used in this study produced RMS unsuitable for immediate use without further processing. The model of roller press used in this study had the advantages of almost reaching the recommended DM content in RMS (>34%), being flexible in terms of inputs, and producing fluffy RMS. Nevertheless, its compression process seemed to allow greater passage of solids into the liquid fraction compared with the screw press. Part II of this work explores different composting methods to reduce the health risks associated with screw-pressed RMS before their use as bedding.

Effect of recycled manure solids as bedding on bulk tank milk and implications for cheese microbiological quality

“…Indeed, some studies indicated a high quantity of Streptococcus spp. in RMS [e.g., 9 (Sorter et al, 2014) and 6 log cfu/g of DM (Fournel et al, 2019b)]. Fournel et al (2019b) demonstrated that solid-liquid separation methods and composting time did not affect their number in RMS.…”

“…Anaerobic digestion is used instead of or as well as composting, commonly in the United States (Leach et al, 2015). A lot of potential benefits are associated with RMS, such as cost savings, availability, and cow comfort (Bradley et al, 2014;Fournel et al, 2019b). Also, this type of bedding can be considered as a strategy to mitigate pollution from livestock manure management (Petersen et al, 2007).…”

Addressing Imbalances in Phosphorus Accumulation in Canadian Agricultural Soils

“…Some form of manure treatment to concentrate the nutrients can significantly reduce the transportation costs and creates the opportunity for altering the balance of nutrients in fractions of the treated manure to meet different crop production requirements (Withers et al, 2015). The simplest form of treatment, with the lowest capital cost, is to separate the solid from the liquid portion of the manure (Burton, 2007; Fournel et al, 2019). The majority of the P remains with the solid fraction (Rico et al, 2012), which can then be transported off‐farm to be used in areas that need P. The remaining liquid retains a high proportion of ammonium N, so it can be used for crops with a high N demand that are growing on soils that already have adequate P. Some dairy operations are further composting the solids portion and reusing it as bedding materials for the cows (Fournel et al, 2019; Husfeldt et al, 2012); the use of this composted material has been well documented from the perspective of herd health but not regarding the potential for P concentrations to build up in the bedding material as it is reused over multiple cycles.…”

Production of recycled manure solids for use as bedding in Canadian dairy farms: II. Composting methods

“…The Table 1. Bacterial counts in composted recycled manure solids (RMS) using static windrows (SW), turned windrows (TW), or a drum composter (DC) in original 1 and converted units Item Harrison et al (2008) Timms 2008 Screen-separated RMS composted in windrows outside for 2 wk and turned every few days (30.0% DM and density assumed at 300 kg/m 3 based on part I (Fournel et al, 2019) results at this DM content).…”

“…Physical (bulk density, water absorption, porosity, and particle size distribution), chemical [pH, DM, ash, OM, C, total Kjeldahl N (TKN), NH 4 -N, and organic N], and bacteriological (Escherichia coli, Klebsiella spp., Staphylococcus spp., Streptococcus spp., and Enterococcus spp.) analyses were performed following the methods presented in Table 1 of the companion paper (Fournel et al, 2019).…”