Objectives: To assess the effect of adding solid manure fractions on the biomethane potential (BMP) of liquid dairy cow manure and on the biokinetic parameters of the process.
Results: The methanogenic potential of liquid dairy cow manure was strongly effected by adding a solid manure fraction. The 90/10 % (w/w) liquid/solid manure fraction mixture was the best substrate for CH4 production. This substrate mixture improved by 50 % the final CH4 production per g substrate and decreased the lag time by 220 % relative to the reference BMP test without the addition. Moreover, the addition of 20 % solid manure fraction adversely affected both the final CH4 production and the maximum methane production rate, while increased the lag time by 400 % compared to the reference BMP test without addition.
Conclusions: Liquid dairy cow manure should be supplemented with no more than 10 % of solid manure fraction in order to improve the biomethane potential of this important agro-industrial residue.
Keywords: Anaerobic digestion; Biogas; Biokinetic parameters; Biomethane potential; Dairy cow manure.