Proceedings

Since 2005 Dutch water authorities aim at energy-neutral sewage treatment plants with maximizing recovery of natural resources. This aim led to a renewed interest in anaerobic digestion, initiating the development of new sludge digestion technologies. Royal HaskoningDHV developed, amongst others, the Ephyra® technology, a high-rate plug flow digster, consisting of two to four reactors in series, with a recycle flow from the last to the first reactor. Ephyra® retention time can be as low as 4-8 days. Since December 2017 a full-scale Ephyra® digester is in operation at wastewater treatment plant Tollebeek in The Netherlands with a VSS reduction of more than 50% without additional energy consuming pretreatment; two other new full scales are under construction. The presentation will give an overview of the operational results at Tollebeek since December 2017, including results of struvite production and dewatering. Besides Ephyra® operational results also the results of parallel PhD research at the Technical University of Delft is presented. The results show that compartmentalized plug flow digester design improves sludge digestion and sludge digestion rate, as indicated by the measured protein en cellulose hydrolysis rates. A shorter residence time per Ephyra® compartment increases specific hydrolysis rates and higher concentrations of cellulases and proteases.