Sludge processing accounts for one quarter of the operational costs in a wastewater treatment plant. Waterboards have long been looking for a means of cutting these costs. Within the TKI Water Technology project on Hydrodynamic Cavitation for effective sludge disintegration, Delfluent Services BV, KWR and WhirlWind International have researched a method to maximise the methane production and dewatering performance of the sludge, and therefore to reduce costs. The VibroCav tool, developed by Whirlwind International, makes use of active hydrodynamic cavitation: a vibrating element in a transport pipe causes the formation of bubbles under low pressure (cavitation) in the sludge. Sludge treatment with the VibroCav tool results in an increase in methane production of 10%, and possibly more. The effect of the VibroCav tool on the sludge’s dewatering performance is still unknown. An exploration of the impact on the dewatering performance is therefore advisable.
Sludge processing is a big cost item in operating a wastewater treatment plant. The project researched whether pre-treatment using cavitation would reduce costs. Generating cavitation with active hydrodynamic cavitation consumes less energy than does passive cavitation with a venturi pipe (a narrowing of the transport pipe). The project therefore involved the application of cavitation equipment consisting of a self-vibrating element (ball) in a venturi pipe. To optimise the generated cavitation, different parameters can be set in the equipment, for instance backpressure, the diameter of the ball, the space between the ball and the pipe wall, and the flow rate. The effectiveness of pre-treatment with cavitation is measured with the automatic methane potential test system (AMPTS II), a test that determines the methane yield on the basis of pressure. The cavitation tool was tested under various conditions, and the results indicate that a methane yield increase of 10% can be expected. Further research into the optimal operational environment for this tool could lead to even better methane yields.
The use of the VibroCav tool leads to the formation of fine particles and changes the properties of the sludge. Finer particles can change the dewatering in a centrifuge. A better dewatering performance also significantly decreases sludge processing costs.
Pre-treatment with the VibroCav tool also involves energy consumption. The assessment of the financial feasibility took into account this energy consumption (assumption: 2.0 kW/m3) as well as the increased methane production (10%). In addition, a sensitivity analysis was conducted on the impact of the dewatering performance on the financial feasibility. This calculation shows that the VibroCav tool can be profitable if the (absolute) dewatering performance improves by 0.5%. Exploratory dewatering performance tests were carried out and indicate that it would be interesting to further explore the innovative VibroCav tool.