Impact of slurry removal frequency on CH₄ emission and subsequent biogas production; a one-year case study

Anaerobic digestion of animal slurry to produce biogas is the dominated treatment approach and a storage period is normally applied prior to digestion. Pre-storage, however, contributes to CH₄ emissions and results in loss of biogas potential. Manure management was found to be an efficient approach to reduce not only the on-site CH₄ emission but may also have extended influence on CH₄ emission/losses for storage and subsequent biogas process, while the connection remains unclear. The objective of this study was therefore to evaluate the impact of slurry management (e.g. removal frequency) on CH₄ emission (both on-site and storage process prior to biogas) and biogas yield. An experimental pig house for growing-finishing pigs (30-110 kg) and the relevant CH₄ emission was monitored for one year. In addition, the specific CH₄ activity (SMA) test was conducted and used as an alternative indicator to reflect the impact. Results showed that the manure management affected both on-site and subsequent methane emission; with increased manure removal frequencies, the methane emission became less dependent on variation of temperatures and the specific methanogenesis activity was significantly lower. The highest SMA (100 mL CH₄ gVS^-1), for instance, was observed from the slurries with limited emptied times, which was 10 times of that from the slurries being emptied three times a week. These findings could enlighten the development of environmentally friendly strategies for animal slurry management and biogas production.