Applications Sludge Treatment

Conventional anaerobic digestion of sewage sludge is limited by the hydrolysis step (technical digestion limit). Treating (waste activated) sludge with ultrasound overcomes this limit. The anaerobic digestion process is intensified and further degradation is achieved. This reduces the quantity of digested residual sludge, while biogas production increases.

Degradation of the organic sludge fraction by conventional anaerobic sludge stabilisation is limited by the rate-determining hydrolysis step. Degrees of volatile solids degradation of 50% are rarely achieved. The cause of this lies in the difficult to access and degrade bacterial biomass of the waste activated (excess) sludge. By applying the high-power jetsky ultrasound technology this limiting hydrolysis step is overcome. Therefore the sonicated excess sludge biomass is more readily available for the subsequent biological enzymatic degradation process. Ultrasound causes disintegration of the sludge flock structure and release of exoenzymes even with small energy inputs. This also creates more interfaces between the solid and liquid phase and therefore facilitates the enzymatic attack of the active microorganisms. A higher energy input results in the breakdown of bacteria cells, causing the cell contents and endoenzymes to be released.

These enzymes further accelerate the degradation process. The entire digestion process is intensified and the organic fraction is further degraded. An important advantage from this is a significantly increased production of biogas and reduction in the quantity of residual sludge to be disposed of. As a result of the smaller quantity of residual organic matter, the dewater ability of the digested sludge is also facilitated (less flocculent addition) and increased (higher degree of dewatering). This disintegration of the sludge reduces its viscosity. This is important for practical operation, as this facilitates mixing the fermenter content, which in turn results in noticeable energy savings. With the help of ultrasound technology, digesters, which are at the limit of their capacity, can easily continue to be operated long-term. In new installations the digesters can be designed with a shorter retention period.

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