Co-digestion is a fairly new concept in which more than two or more substrates are digested together. Previous studies have indicated that co-digestion offers several advantages including additional gas production, improved nutrient balance and potential tipping fees for waste treatment.
On the other hand, it requires additional facilities for gas handling and treatment, increases solids loading to dewatering facilities and may have impacts on recycle stream, mixing and heating requirement and quality of biosolids produce. Therefore, the merits and limits need to be thoroughly
investigated. This paper reviews the technologies suitable for co-digestion and co-digestion experiences in terms of feed mixture, organic loading rates and other operational parameters. Based on literature findings a bench-scale co-digestion study was performed co-digesting biosolids and
three different foodwastes (tomato, cheese and salad dressing) in mesophilic and thermophilic digesters. The preliminary results have shown that mesophilic operation was superior to thermophilic operation in terms of VS reduction and gas production. Thermophilic operation was sensitive to
organic loading and exhibited severe inhibition. More contact time (>15 days) was required for co-digestion of cheese waste than those for other foodwaste mixtures. In the end of experiments (28 days), the ultimate gas productions were virtually same for each foodwaste mixture. The testing
approach, foodwaste selections and complete results will be discussed in an upcoming paper.
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