Boosting municipal sludge digesters: two full scale pilots started
10 - 20% more sludge breakdown and 20 - 30% higher biogas yield are the reasons why Wetterskip Fryslan and Waterschap Brabantse Delta decided to test the fermentation process at the Burgum and Bath wastewater treatment plants.
The core of the test
The core of the trial involves periodic small doses to the sludge feed to the digester of microporous granular silica particles 200 - 600 microns in size, grafted with selected microbial material developed by US-based Drylet. The technology has been extensively tested in the United States.
The dosing accelerates the anaerobic sludge degradation in the reactor and increases the biogas production. The effect becomes well visible after two sludge residence times in the digester.
The trials will last six months, so that the practical results will be known by the end of 2021. If the targets are met, this will make a good contribution to the policy goals of the water boards: reducing the production of sludge of the water boards and striving for energy neutrality.
At rwzi Burgum the material is dosed into the supply pipe of the sludge digester, after sludge thickening. The sludge digester consists of two digester tanks in series, each with a volume of 1,000 m3. The trials started in April 2021 and will continue until October 2021.
At the Bath sewage works, dosing takes place in the sludge recirculation pipeline of one of the two digesters, each with a volume of 5,400 m3so that a direct comparison of the performance of both fermentation tanks can be made.
Brightwork supervises both trials and reports the results in close cooperation with the waterboards. Previously, the positive results were published of similar duration tests with Drylet material, performed on the water line of WWTP Halsteren of Waterboard Brabantse Delta. In 2019 and 2020, the impact of the dosage was tested there on the sluice sludge production and the performance of the treatment plant. Those tests showed that 25% less flushing sludge was produced, while the effluent quality of the treatment plant remained stable and good. See also our recent publication.