Department Process Engineering

Many WWTPs are reaching their maximum treatment and clarification capacities, and solutions must be found to upgrade those existing plants. One relevant approach is to replace conventional primary settlers by micro-sieves, in order to recover reactor volume that can then be used for BOD and nutrient removal. Micro-sieves have been developped over the past few years and are characterised by a mesh size of 10 to 500 µm. Micro-screens are extremely compact technologies and can capture between 20-65% of solids and up to 40 % of the BOD, thus offering a relevant alternative over conventional primary settler. Different micro-sieving technologies are being developped: drum-screen, rotating-belt filter, in combination or not with coagulation/flocculation. 

The research at Eawag on the micro-sieving of municipal WW mainly focuses on:

• Evaluating the performances of the different micro-sieving technologies to capture solids, organic substrate, etc.
• Quantifying their impact on the overall energy balance of the WWTP (production of biomethane, aeration savings, energy for running the sieve)
• Characterising the composition of the sieved sludge, in comparison with sludge from primary settler (volatil solid content, cellulose content, etc.)
• Evaluating different routes of valorisation of the sieved material, e.g., in the form of organic acids, biomethane, bioplastic or simply cellulose.

Eawag has been involved in several pilot-scale tests of micro-sieving technologies at various WWTPs:

• Pilot-test of the drum-screen LIQUID from Huber, at the WWTP of Sihtal (ZH Canton). Collaboration between Hunzicker Betatech AG, Huber-Picatech, Sihtal WWTP and Eawag. 
• Pilot-test of the Sobye rotating-belt filter of Nordic Water at the WWTP of Cully (Vaud canton). Collaboration between CSD Ingénieur, Alpha Wassertechnik AG, EPFL and Eawag.
• Comparion of the DynaDrum drum-screen and Sobye rotating-belt filter of Nordic Water at the WWTP of Münchwilen (Thurgau Canton). Collaboration between Kuster-Hager ingenieurbüro AG, Alpha Wassertechnik AG, Münchwilen WWTP and Eawag