Adapting R4 simplifications of Anaerobic Digestion Model No. 1 (ADM1-R4) for pump-mixed biogas production

•Innovative reactor with an external pump instead of mechanical stirring.•The model was successfully simplified to 26 equations ODEs, from initial 81.•The simplification does not affect the quality of predictions.•Biogas production mean relative error of 10.68 % for all configurations.•High accuracy for biogas composition prediction – 5.37 % MRE vs unbiased data.