Click on “Download PDF” for the PDF version or on the title for the HTML version.

If you are not an ASABE member or if your employer has not arranged for access to the full-text, Click here for options.

Highlights

Three rigorous, methods for estimating influent-effluent mass flow differences due to biogas generation in manure-based anaerobic co-digestion systems are presented.

Abstract. During co-digestion of dairy manure and off-farm organic waste in farm anaerobic co-digestion (AcoD) systems, the process‘s conversion of biodegradable organics to biogas reduces the volumetric mass (or mass-volume) of the effluent discharged compared to the mass-volume fed. In this study, we present three methods for estimating the mass-flow difference between influent and effluent due to conversion to biogas based on widely accepted, rigorously applied, biological and engineering principles. Monthly operating data from three full-scale AcoD systems, operated under different conditions for a full year were used to compare results using the three calculation methods. Results revealed that the predictions of influent mass flow loss obtained using a simplified input-based method primarily based on influent volumetric flow rates and biodegradability data were in good agreement with those obtained using more accurate, real-time data, namely methane concentration and biogas production. For AcoD systems adding off-site wastes at around 30% or less of the total influent volatile solids (VS), the estimated reduction in effluent flow was in the range of 3% or less. In one case, for VS additions up to approximately 60% of the AcoD system‘s influent load, the reduction was 12%. Accepted fundamental water vapor relationships were also applied to biogas generation. Biogas water vapor loses were estimated to comprise approximately 0.2% of the total biogas mass-volume typically produced. Since in most anaerobic digestion systems, biogas condensate water is returned to the influent, this insignificant amount may be ignored.