Anaerobic co-digestion of potato tuber and its industrial by-products with pig manure

The possible use of potato tuber and its industrial by-products (potato stillage and potato peels) on farm-scale co-digestion with pig manure was evaluated in a laboratory study. The methane yields (m3 kg−1 volatile solids (VS)added waste) achieved on semi-continuous co-digestion at loading rate of 2 kg VS m−3 day−1 in continuously stirred tank reactors at 35 °C were 0.13-0.15 at 100:0 (VS% pig manure to VS% potato co-substrate), 0.21-0.24 at 85:15 and 0.30-0.33 at 80:20 feed ratio. Increasing the loading rate from 2 to 3 kg VS m−3 day−1 at a feed VS ratio of 80:20 (pig manure to potato waste) produced methane yields of 0.28-0.30 m3 kg−1 VSadded waste. Post-digestion (60 days) of the digested materials in batches produced 0.12-0.15 m3 kg−1 VSadded waste of methane at 35 °C. The results suggest that successful digester operation can be achieved with feed containing potato material up to 15-20% of the feed VS and that under similar feed VS, loading rate, retention time and feed VS ratio, the methane yields and process performance for potato tuber would be similar to that of its industrial residues. Thus, co-digestion of potatoes and/or its industrial by-products with manures on a farm-scale level would generate renewable energy and provide a means of waste treatment for industry.