Proceedings

The Crown sludge disintegration system utilises mechanical forces to cause cavitation in surplus activated sludge (SAS). Cavitation ruptures the cell structure releasing the otherwise locked in resource for digestion enhancement or as a carbon source for biological treatment enhancement. This paper discusses the performance data from several existing operational disintegration plants for digestion enhancement and from the first full scale plant for biological treatment enhancement.

The first full scale Crown disintegration system for digestion enhancement was installed in March 2002 and since then a further ten plants have been installed and are fully operational throughout Europe. After the first three months of operation in this application the system has shown itself to be highly effective in increasing the Biogas yield from existing sludge treatment facilities. Yields have risen in almost all cases in excess of 30%. Sludge volumes for disposal after digestion have decreased by 20% or more. Sludge dewatering has improved by an average of 5 percentage points.

Biogas yield is becoming more important as energy derived from sludge now attracts a premium sales price due to the introduction of Renewable Options Credits (ROC’S). With disposal to land costs at an all time high and likely to increase further in future the cost benefit of digestion enhancement is further enhanced. Typically Crown Disintegration system operators are achieving paybacks of less than two years. The paper will look at a number of examples of the system in its digestion enhancement role and discuss the technical and commercial benefits.

In the autumn of 2003 the first full scale Crown Disintegration plant was installed, for the city of Wiesbaden, in its Biological treatment enhancement role. The city of Wiesbaden suffers from population loss during summer and winter months leading to problems with final effluent quality. The biological tanks have previously suffered with considerable foaming problems when the carbon levels were low. Wiesbaden had tried a number of solutions to the problem including diverting primary sludge to the biological phase and the import of Methanol as a carbon source. Both solutions improved the effluent discharge quality however the former caused problems due to ragging of various plant equipment and the latter was very expensive.

The Crown system was installed in 2003 and was operational for the winter months when the nitrogen discharge limits are most at risk. The system was monitored by the City of Wiesbaden over the key risk period. The paper will discuss the details of the operation and confirm the systems ability to release carbon from thickened RAS as a substitute for other imported carbon sources.

At Wiesbaden the biological aeration input volumes to the tanks are automatically regulated by the ammonia level monitoring equipment. Since the Crown system has been installed substantial reductions have been noted in the volume of oxygen required and significant energy savings have been realised. The City of Darmstadt University is currently studying the effect on the overall sludge load to digestion and the paper will report on interim findings.

KEY WORDS Carbon source, Crown, Digestion enhancement, Disintegration, Total Nitrogen, Wiesbaden