Anaerobic co-digestion of cheese whey and the screened liquid fraction of dairy manure in a single continuously stirred tank reactor process: Limits in co-substrate ratios and organic loading rate

• Cheese whey and liquid fraction of dairy manure continuous co-digestion operation.
• Cheese whey proportion and HRT influence on the process was investigated.
• Operation possible with 85% cheese whey fraction in the feed.
• Similar efficiencies observed within the range 15–85% cheese whey in the feed.
• 1.37 m3 CH4 m−3 d−1 reached with 65% whey in the feed at OLR of 5.9 kg VS m−3 d−1.

Mesophilic anaerobic co-digestion of cheese whey and the screened liquid fraction of dairy manure was investigated with the aim of determining the treatment limits in terms of the cheese whey fraction in feed and the organic loading rate. The results of a continuous stirred tank reactor that was operated with a hydraulic retention time of 15.6 days showed that the co-digestion process was possible with a cheese whey fraction as high as 85% in the feed. The efficiency of the process was similar within the range of the 15–85% cheese whey fraction. To study the effect of the increasing loading rate, the HRT was progressively shortened with the 65% cheese whey fraction in the feed. The reactor efficiency dropped as the HRT decreased but enabled a stable operation over 8.7 days of HRT. At these operating conditions, a volumetric methane production rate of 1.37 m3 CH4 m−3 d−1 was achieved.