Abstract
Manure characteristics change through processing, including anaerobic digestion (AD). These changes can alter handling of manure during downstream operations. This study analyzed the density, total solids (TS) content, and volatile solids (VS) content of pre-digested and anaerobically digested dairy manure from seven dairy farms in Wisconsin. The density of pre-digested manure increased from 990 to 1065 kg m−3 as the TS level increased from 1.5% to 13.0%. Density and TS for pre-digested manure from facilities using separated solids as bedding were related with a linear model for TS ranging from 1.5% to 13.0% and with a polynomial model for TS ranging from 1.5% to 50%. The model shows that density decreases with an increasing TS content when TS is greater than 8.0%. Manure from dairy facilities that used sand bedding had a VS/TS ratio of 0.87. This ratio was higher than the ratio when manure solids were used as bedding (0.81) and when food waste was incorporated into the digester (0.77). This study also provides a simple methodology to estimate biogas yield by using the density of pre- and post-digested manure.
Highlights
Manure management is a critical activity for the economic and environmental sustainability of dairy farms
The model shows that density decreases with an increasing total solids (TS) content when TS is greater than 8.0%
This study provides a simple methodology to estimate biogas yield by using the density of pre- and post-digested manure
Summary
Manure management is a critical activity for the economic and environmental sustainability of dairy farms. Manure can improve soil health and provide valuable nutrients for crop production when land applied [1]. The handling of manure can be costly and lead to negative environmental impacts [2,3]. The most common utilization method for manure is land application, which costs approximately $306 per cow per year to store, haul, and land apply [4]. Manure is responsible for nearly 7% of both agricultural methane (CH4 ) and nitrous oxide (N2 O) emissions [5]. There has been increased attention to developing and implementing processing technologies that enhance the economic value of manure and reduce the related environmental impacts [6,7]
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