Effect of Different Scenarios of Dairy Manure Processing on Emissions and Economics

Keywords: dairy management, manure, slurry separation, emissions, ammonia, methane, greenhouse gases.

Manure is an unavoidable by-product of the production of milk and meat. However, this manure or products of manure processing can play a significant role in closing nutrient cycles and reducing the environmental impact of dairy farming. The project NL Next Level Manure Valorisation aims to initiate new breakthroughs in the manure value chain from housing to application. In the project animal feed manufacturers, and dairy and meat processing companies are working together with the Dutch foundation for manure valorisation and Wageningen University and Research towards a transition in the production and use of animal nutrients. Within the work packages Technology and Animal Housing several analyses for different livestock sectors have been worked out. This paper describes the analyses for dairy farming

The vast majority of Dutch dairy cows are housed on a concrete slatted floor. In this housing system faeces and urine are collected and stored together and applied as slurry on grass and arable land. However, new, sometimes innovative, floor concepts aiming to reduce ammonia emission from housing also have the possibility to keep faeces and urine separated. Together with slurry treatment techniques (i.e. separation or digestion) this opens new possibilities for a sustainable use of nutrient from animal production.

The aim of this study was to determine the effect of different dairy manure treatment scenarios on ammonia and greenhouse gas emissions and compare them to a reference scenario in which faeces and urine are stored and applied as slurry. Through this study, optimal nitrogen cycling with minimal losses and emissions can be determined.

The results indicated that a combination of separation of the solid and liquid fractions, combined with nitrogen stripping and anaerobic digestion achieved the largest reduction in ammonia emissions.

The minimum farm size above which anaerobic digestion of manure is profitable depends on the freshness of the manure and the cost of electricity and heat. In the market circumstances before 2022 the tipping point of farm size was around 250 dairy cows. The current market situation in 2022 will reduce this threshold.