Beschreibung
Ecological and economical aspects of separation and disposal of used bentonite suspensions (slurries) are one of the biggest challenges in hydroshield tunnelling and the construction of diaphragm walls. To support the separation process of the slurry and to reduce separation time and costs, chemicals like metal salts and polymers are added to the slurry prior to its treatment in a chamber filter press or a centrifuge. The thesis presents an alternative support method for fine separation processes by means of electrocoagulation. This electrochemical process causes coagulation and destabilisation of the suspension by applying an electrical current. It has a similar effect on the subsequent fine separation as the addition of chemicals but offers the advantage that no water hazardous substances are required and the water consumption on the construction site decreases.
To investigate the applicability of this method, an experimental setup was designed and bentonite suspensions were subjected to extensive parametric studies. First studies were performed with laboratory-size electrocoagulation cells which had a volume of 2 to 4 l. Based on the results, the technology was scaled up to a mid-scale cell with a volume of 320 l. A calculation model was developed to determine the fine separation capacity with the use of electrocoagulation for any given suspension. The results showed the advantages of this method compared to the conventional separation: the fine separation capacity was improved and the water consumption was reduced.
The thesis includes design recommendations for a real-scale electrocoagulation prototype as well as ideas for further research. The experimental procedure and analysis developed in this thesis allow the investigation of any given used suspension.
