Abstract
AbstractBiogas production on dairy farms is promoted as a climate change measure since it captures methane, a greenhouse gas emitted by manure, and produces renewable energy. Digestate is a by‐product of biogas production and is often used for nutrient recycling in a similar way as traditional manure. Despite having similar functions, manure and digestate have different behaviors related to nitrogen recycling and nitrogen emissions which are significant agricultural and environmental concerns of manure. This paper provides an insight into the impact of biogas production on nitrogen emissions and nitrogen recycling issues of the current dairy farming practice. Using the Substance Flow Analysis (SFA) approach, we analyzed the changes on three levels: manure handling, dairy farm, and the whole chain. Four biogas production options on a Dutch dairy farm related to types and sources of feedstocks were considered. We quantified biogas output, nitrogen fertilizer replacement percentage (%) and consequential nitrogen emissions (kgN/year; kgN/m3 biogas produced) of these productions in comparison with the baseline of current dairy farming without biogas. We conclude that biogas production options with additional feedstocks will cause profound changes in the nitrogen recycling on dairy farms and the nitrogen emissions at the chain level. Besides, the results show that determining the optimal biogas production option can be challenging as the evaluation is highly dependent on the used nitrogen indicator and the included level of analysis. Our findings show how SFA and a multilevel perspective can give a broader understanding of environmental trade‐offs.
Highlights
Biogas production with an anaerobic digestion approach captures methane (CH4) from manure as a source of energy which would otherwise be an emission (Burton & Turner, 2003)
To build up the model, we did these steps following the instruction of the Substance Flow Analysis (SFA) approach: Step 1: Identify the most common biogas production options on a dairy farm Step 2: Set the system boundaries, processes, and nitrogen flows included in each biogas production option Step 3: Quantify the nitrogen flows of all biogas production options Step 4: Use indicators to compare the nitrogen flows between biogas production options
This study points out significant trade-offs between biogas production and nitrogen problems
Summary
Biogas production with an anaerobic digestion approach captures methane (CH4) from manure as a source of energy which would otherwise be an emission (Burton & Turner, 2003). While biogas production reduces methane emissions, it can bring up the trade-offs with regard to the nitrogen issues of the dairy farms. Nitrogen is the primary and the largest nutrient that is required for plant growth (Ohyama, 2010) but it is involved in several types of emissions (NH3, NOx, N2O, NO3−) on the dairy farms. These emissions result in various impacts such as climate change, ozone depletion, air pollution, and eutrophication (Fields, 2004; Leip et al, 2015)
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