Integrated biorefinery wastewater design

Regardless of their feedstock, all ethanol-producing biorefineries face the common challenges of treating their effluent efficiently and economically to meet local discharge requirements, and minimising their net water consumption. In terms of process integration, these twin requirements can be addressed by (i) improving existing secondary (i.e. biological) treatment methods to maximise COD reduction, (ii) incorporating a tertiary ‘polishing’ stage to remove colour, and (iii) using (reverse osmosis) membrane technology to recover process water. This paper considers disposal and/or treatment options for the post-biological treatment of ethanol stillage. The illustrative examples presented show how the secondary and tertiary treatment stages in a biorefinery can be energy integrated via the (biogas derived) power from the anaerobic digester.