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 fea tures, which sets ii apart from the well known categories of wastewater. Up to now, there is a definite lack of practical experience and know-how in t he treatment of those effluents. In view of the increasingly wide acceptanc e awarded to the fermentation process, it appears necessary, however, to in clude the treatment of the generated wastewater in the overall process and to grant it the same priority as the fermentation step. In this study, pilo t-scale experiments were conducted over 200 days in a sequencing batch reac tor (SBR), with the wastewater from a full-scale Bavarian biowaste digestio n plant. Characterization of the influent implementing molecular size distr ibution studies showed that 97% of the components were either in particular form or <1 kD. The main classes of compounds present in these fractions ha ve been identified. The treatment objectives of the SBR plant were carbon a nd nitrogen removal. Soluble COD removal efficiencies were comprised betwee n 40 and 60%, yielding a residual, refractory COD concentration of about 20 00 mg/L in the effluent. Ammonium removal efficiencies averaged 96% and den itrification occurred with the addition of acetic acid or pretreated biowas te as a carbon source. Pretreated biowaste also showed synergetic effects a s a cc-substrate for COD removal.