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

摘要

Recent technological advances in the dairy industryhave enabled Canadian farms with liquid manure systemsto use mechanical solid-liquid separation pairedwith composting of the separated solids for on-farmproduction of low-cost bedding material. However, becauseseveral approaches are available, it is difficult forfarmers to select the appropriate one to achieve highquality recycled manure solids (RMS). Whereas 3 solidliquidmanure separators were compared in part I ofthe series (companion paper in this issue), the presentstudy (part Ⅱ) aims to assess the performance of 4 compostingmethods (static or turned windrow and drumcomposter for 24 or 72 h) under laboratory conditions.Parameters evaluated included temperature, physicochemicalcharacteristics, and bacterial composition ofRMS, as well as airborne microorganisms, dust, andgases associated with composting RMS. Because eachtreatment attained the desired composting temperaturerange of 40 to 65°C (either in heaps or in the drumcomposter), reductions in bacteria were a better indicatorof the sanitation efficiency. The treatment offresh RMS in a drum composter for 24 h showed decreasedbacterial counts, especially for Escherichia coli(from 1.0 × 105 to 2.0 × 101 cfu/g of dry matter) andKlebsiella spp. (from 3.2 × 104 to 4.0 × 102 cfu/g ofdry matter). Increasing the time spent in the rotatingvessel to 72 h did not result in further decreasesof these pathogens. Composting in a static or turnedwindrow achieved similar E. coli and Klebsiella spp.reductions as the 24-h drum composting but in 5 or10 d, and generally showed the lowest occupationalexposure risk for dairy farmers regarding concentrationsof airborne mesophilic bacteria, mesophilic andthermotolerant fungi, and total dust. Drum-compostedRMS stored in piles exhibited intermediate to high risk.Composting approaches did not have a major influenceon the physico-chemical characteristics of RMS andgas emissions. Drum composting for 24 h was the bestcompromise in terms of product quality, temperaturereached, decreased bacterial numbers, and emitted airbornecontaminants. However, because levels of pathogenicagents rapidly increase once composted RMS arespread in stalls, bacteriological characteristics of RMSalong with milk quality and animal health and welfarefeatures should be monitored in Canadian dairy barnsapplying recommended separation (part Ⅰ) and composting(part Ⅱ) systems to evaluate health risk andoptimize management practices.