Mesophilic anaerobic co-digestion of cow manure and biogas crops in full scale German biogas plants: A model for calculating the effect of hydraulic retention time and VS crop proportion in the mixture on methane yield from digester and from digestate storage at different temperatures

Data from 24 full scale biogas plants in Germany digesting cow manure and crops were evaluated. Special emphasis was given to the effect of hydraulic retention time HRT and proportion of crops in the mixture (VS basis) p(VS,Crops)(lnp) on the methane yield from the digester y(CH4)(D,VSlnp) and the storage tank y(CH4,T)(S,VSlnp) at 37 and 22 degrees C. The evaluation has shown model parameters for maximal methane yield of manure and crops y(maxCH4)(eff,VSlnp) at 270 and 420 L kg(-1), respectively. For example, at HRT of 60 days, maximum methane yield result to 249 and 388 L kg(-1) for a crop proportion in the input of 0.0 and 1.0, respectively. The calculation of y(CH4,T)(S,VSlnp) considers first order reaction rates and a temperature term f(T). Hence, at any arbitrary temperature in the range of 12 degrees C < T < 37 degrees C the values of y(CH4,T)(S,VSlnp) in the course of time can be calculated, which correspond to methane emissions for uncovered storage tanks. (C) 2013 Elsevier Ltd. All rights reserved.