Operational experiences of industrial scale AD: Lessons for the future

In this paper we discuss operational experiences of two large industrial anaerobic digestion facilities processing brewery waste and maize. The raw effluent from the brewery waste has COD ranging from 5500 mg/l to 41400 mg/l, with variable flow rate and suspended solids up to 4800 mg/l. The Anaerobic Digestion (AD) treatment uses 900m³ EGSB reactor. The two-year monitoring of data includes Ripley´s Ratio, Volatile Fatty Acids, and pH. These parameters indicate lower performance and certain instability before the planned maintenance works, followed by the much improved performance afterwards. The average biogas production is 3540 Nm³/day but the variance of the biogas flow remains an issue. The combined Heat and Power (CHP) production from energy crops uses ensilaged, purposely grown maize with 28-34% dry matter and chop length of 6-9 mm. The available three-year data for this AD facilities indicate great process stability. It uses 150 t/day of maize, and result in energy production of 21 GW/year which is 7000 homes equivalent. This energy is evenly split between the sewage treatment works and injection to the public electricity grid. Depending on the dry solids content, the digestate is either stored and spread on the land, or sold to farmers.