Characterization and treatment of the liquid effluents from the anaerobic digestion of biogenic solid waste

The process wastewater generated by the fermentation of biogenic fractions of solid waste (biowaste) is characterized by very specific composition features, which sets it apart from the well known categories of wastewater. Up to now, there is a definite lack of practical experience and know-how in the treatment of those effluents. In view of the increasingly wide acceptance awarded to the fermentation process, it appears necessary, however, to include the treatment of the generated wastewater in the overall process and to grant it the same priority as the fermentation step. In this study, pilot-scale experiments were conducted over 200 days in a sequencing batch reactor (SBR), with the wastewater from a full-scale Bavarian biowaste digestion plant. Characterization of the influent implementing molecular size distribution studies showed that 97% of the components were either in particular form or <1 kD. The main classes of compounds present in these fractions have been identified. The treatment objectives of the SBR plant were carbon and nitrogen removal. Soluble COD removal efficiencies were comprised between 40 and 60%, yielding a residual, refractory COD concentration of about 2000 mg/L in the effluent. Ammonium removal efficiencies averaged 96% and denitrification occurred with the addition of acetic acid or pretreated biowaste as a carbon source. Pretreated biowaste also showed synergetic effects as a co-substrate for COD removal.