Anaerobic treatability and residual biogas potential of the effluent stream of anaerobic digestion processes.

Although anaerobic digestion is a well-established technology, the treatment and disposal of the digestate still presents a challenge due to lack of viable methods for processing. The residual organic matter in digestates also creates a significant residual biogas potential. This fact indicates that the digestates need further processing not only to reduce their organic content for disposal, but also to capture the biogas associated with this residual organic content. This study investigated anaerobic treatment and residual biogas potential of digestates obtained from five full-scale farm-based digesters. The results indicated that it was possible to reduce the total chemical oxygen demand (CODt ) of the digestates with an efficiency of 21%-84%. The corresponding biogas yields of digestates ranged between 0.078 and 0.326 Lbiogas /g VSadded . This level of biogas production is comparable to the biogas production potential of several commonly used raw substrates. PRACTITIONER POINTS: Significant CODt reduction and biogas capture can be attained by AD of digestates. The digestates subjected to anaerobic treatment yielded up to 82% CODt removal. Residual biogas yields of digestates ranged between 0.078-0.326 Lbiogas/g VSadded. Biogas yields obtained were comparable to many raw feedstocks of biogas plants.