Evaluation of solid-liquid separation of dairy manure with different separator screen sizes on the resource recovery and greenhouse gas emissions reduction

Solid-liquid separation is a critical step for the treatment of dairy manure, and the separator screen size plays an important role in determining the separation. Despite its importance, the impact of screen size on subsequent resource recovery and greenhouse gas (GHG) emissions reduction remains largely undetermined and varied. In this study, the influence of separator screen size for solid-liquid separation on resources recovery (bedding materials, biogas and nutrients) and GHG emissions reduction was evaluated. Taking a dairy farm with a stock of 1000 cows as an example, with the increasing of separator screen size from 0.5 mm to 5 mm, the results show that the annual bedding materials production decreased from 987.0 tons to 597.6 tons (dry basis), the annual biogas production increased from 32.5 × 10⁴ m³ to 50.9 × 10⁴ m³, the annual total nitrogen (TN) recovery increased from 35.8 tons to 44.4 tons, and the annual total phosphorus (TP) recovery increased from 8.2 tons to 10.1 tons. The annual economic benefits from resource recovery ranged from 28.7 × 10⁴ ¥ to 34.8 × 10⁴ ¥. Annual total GHG emissions increased with the increasing separator screen size and reached approximately 0.7 t CO₂ equivalent/cow·year. These findings provide guidance for the selection of separator screen size for the solid-liquid separation of dairy manure.