Problem och lösningar vid processoptimering av ... - BOFFE.COM

Summary
The interest in sludge treatment at Swedish wastewater treatment plants has
increased noticeably in recent years. There are several driving forces for this
development. First of all, the possibilities for external utilisation of biogas have
increased, which has motivated energy saving measures and optimisation of the
digestion process. Also, the environmental legislation has become more stringent.
The upcoming requirement for hygienisation of sludge and the ban on landfill
of organic waste both greatly impact the external demands on wastewater treatment
plants and have brought to the fore processes such as thermophilic digestion
and pasteurisation along with methods to reduce the sludge amounts. Further,
a generally augmented level of environmental and cost awareness has led to increased
efforts to minimise costs and use of resources.
Upgrading measures that – for the reasons above – have been implemented at
different plants have in some cases led to unwanted consequences and operational
difficulties since the experience from “new” processes and methods often has been
limited. The purpose of this study is to point out different possibilities and limitations
in sludge treatment and to compile and share the different experiences
made at the Swedish WWTPs in recent years. The intention is to, in a long-term
perspective, contribute to improved and more cost-effective technical solutions.
The study is a review and analysis of different sludge treatment stages (thickening,
anaerobic digestion and final dewatering) and the associated handling
processes (pumping, stirring, heating, heat recovery). Experiences and pitfalls at
the different stages are discussed and possible enhancement measures are specified.
Conclusions and recommendations are made.
The review was carried out in cooperation with 12 reference plants associated
with the study. Operational and process data from these plants were collected to
illustrate and exemplify different aspects of the sludge treatment. Certain key
figures (such as energy consumption per tonne of dry solids) were estimated for
the different stages.
The study shows that the energy consumption for sludge treatment varies
greatly among different wastewater treatment plants, that many plants are not
optimally designed and that there are great possibilities for energy savings, both
of electricity and of heat. The greatest potential for energy savings appear to
exist at the small and medium sized plants.
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