The high performance digester – an efficient process for sewage sludge digestion
Morawe, B., Krafft, S. and Guasch, V., Schwarting Biosystem Gmbh, Germany
(free)
Abstract In waste water treatment plants, sewage sludge is treated in order to reduce the amount of mass to be disposed. This is done using either aerobic or anaerobic processes. The latter has one big advantage: biogas is produced, which is a source for thermal and electrical energy.
The high performance digester developed by Schwarting Biosystem is characterised by treating sewage sludge within a short retention time of only 5 to 10 days. In comparison to this, conventional digesters (CSTR type) are operated with a retention time of more than 25 days.
The reason for the shorter retention time, and hence a smaller reactor volume, of the high performance digester, is it’s optimised process technology: The digester is an upstream plug flow reactor, with the mixing achieved by means of an energy saving impulse mixing system, and with its slim and tall tank design resulting in a very low space demand.
Today there are 10 plants operating successfully in Germany and South Korea.
Keywords Waste water treatment, sewage sludge, process optimisation, reactor theory, reaction kinetics, high performance digester
Introduction Anaerobic sewage sludge treatment as well as biogas plants both use the biological process of anaerobic digestion, but with a different focus. Biogas plants predominantly attempt to be most profitable optimizing substrate conversion efficiency and linked costs. In contrast, sewage sludge digestion focusses on sludge stabilization (pathogen and odour minimisation) and reduction of sludge disposal costs; hence a cheap solution associated with inefficient sludge conversion is not an option.
The main drawback of conventional digesters is that they need large reactor volumes to ensure good conversion of the substrate since their conversion rate is low. This leads to large building space demands and is accompanied by relatively high mixing efforts. The reason for this lies in the characteristics of the reactor type and the reaction kinetics of the biological conversion. www.ewwmconference.com Organised by Aqua Enviro Technology Transfer 7th European Waste Water Management Conference www.ewwmconference.com Organised by Aqua Enviro Technology Transfer A new digester type was developed to achieve a better conversion while reducing the space and mixing energy demands.
