Value-adding conversion and volume reduction of sewage sludge by anaerobic co-digestion with crude glycerol

- Anaerobic co-digestion of sewage sludge and a crude glycerol was evaluated.
- Co-digestion yielded methane, hydrogen, and 1,3-PDO as value-added products.
- Increasing glycerol levels significantly increased hydrogen and 1,3-PDO production.
- By adjusting glycerol content, hydrogen and methane fermentation was controlled.
- Addition of crude glycerol promoted the solubilization of sewage sludge.

In this study, conversion of sewage sludge to biogas by anaerobic co-digestion with crude glycerol was examined. When 0.126 g/L crude glycerol was added to the reactor, only methane was produced. Upon addition of 5.04 g/L crude glycerol, hydrogen production occurred, and a significant amount of 1,3-propanediol (1,3-PDO) was generated in the liquid phase. On day 6, the dry weight was largely composed of organic acids (48%) and 1,3-PDO (17%), which are water-soluble. Degradation of 1,3-PDO was very slow, which is advantageous for recovery. Crude glycerol, which contains alkaline substances, promoted organic matter degradation by microorganisms, which possibly affected biogas and 1,3-PDO production. Addition of 0.630-2.52 g/L glycerol initially led to hydrogen production, followed by methane production a few days later, which stabilized within 1 week. In conclusion, adjustment of the crude glycerol concentration allows controllable conversion to value-added products for co-digestion.