Source segregation and treatment of urine and faeces from dairy cattle reduces GHG and NH3 emissions in covered storage

Managing dairy excreta as slurry can result in significant emissions of ammonia (NH₃) and greenhouse gases (GHGs) during storage and thereafter. Additionally, slurry often has an imbalanced nitrogen (N) to phosphorus (P) ratio for crop fertilization. While various treatments exist to address emissions and nutrient imbalances, each has trade-offs that can result in pollution swapping. An integrated management system, starting with source segregation (SS) in-house to separate faeces and urine into two manageable streams followed by step-wise complementary treatments has been designed to manage nutrients and reduce emissions in the whole chain, but its effect on emissions in storage remains untested. This study investigated NH₃, nitrous oxide (N₂O), and methane (CH₄) emissions and total N losses from integrated storage systems combining SS, mesophilic or thermophilic anaerobic digestion (AD), acidification, drying and zeolite addition and an impermeable cover. These systems were compared to two reference slurry storage systems: in-house uncovered (US) and outside covered (CS). A 30-day lab-scale experiment was conducted at 10 °C, monitoring emissions using an INNOVA1412 gas analyser, while total N losses were assessed using mass balance. Results indicated that the SS fractions treated before covered storage exhibited significantly lower emissions (NH₃ or CH₄ or both) compared to both reference slurry storage systems (US and CS). Source segregation combined with acidification of urine and AD of faeces at 35 °C and an impermeable cover allowed for a 99% reduction in NH₃ emissions, a 45% reduction in CH₄ emissions and had no effect on N₂O emissions as compared to US. When AD of faeces was conducted at 55 °C instead of 35 °C, the CH₄ emission was reduced by 77% compared to US. This study concludes that SS combined with urine and faeces treatment allows a more effective and simultaneous reduction of all emissions in storage as compared to slurry storage systems, while also effectively separating nutrients allowing more precise N and P fertilization with dairy excreta. Further research is necessary to assess emissions and fertilizer value of treated fractions after field application, in addition to the associated costs.