Grassification Pilot: System Design for Biogas Production from Grass Waste

The Grassification pilot project designs a 1750 m³ anaerobic digester for converting 200 tonnes of low-quality grass waste into biogas, yielding 100 Nm³ per tonne with a calorific value of 500–600 kWh/t. The system uses HDPE-lined cells with recirculation heating (50°C via 21kW heater) and inline gas analysis to monitor oxygen levels (<0.3%) and maintain process stability. Key components include a drainage system, buffer layer, sand bed, and leachate management via pumps. Organic load is managed through staged digestion (hydrolysis to methanogenesis), with pH and FOS/TAC monitoring ensuring process control. Trials use roadside grass clippings, digestate, and chicory chips, with on-site and lab analysis for quality verification. The design supports renewable heat and electricity production (200–250 kWh each per tonne), with temperature and circulation control critical for consistent biogas output.