Research - Results: Pilot installation

Membrane filtration
The most important results for the membranes of the pilot installation are as follows:

• The so-called Clean Water Permeability (CWP), which is indicative of the quality of the membranes, is characteristic for high-end Zenon ZW500d membranes. The membranes were approved on the basis of these measurements.
• Although the tests were performed at relatively high process temperatures, the membrane results were good. Most tests will be performed again in the winter in order to evaluate the functioning of the membranes at lower temperatures.
• The chemical purification of the membranes was optimised in the simulation unit. The use of hydrogen peroxide proved to be ineffective due to the relatively high grease content of the local wastewater. Good results were obtained using a combination of sodium hydroxide and warm water.
• A significant reduction of the energy consumption of the membrane installation seems possible on the basis of energy optimisation testing. Further research at lower temperatures and during longer testing periods should provide more insight.

Biological process
The first biological start-up procedure of the simulation unit was cut short due to software problems. As a result, the simulation unit did not receive sufficient wastewater during the start-up procedure, leading to poor sludge quality and excessive foaming. After the software had been repaired, the biological process was restarted on 7 June 2004.

Although the initial research objectives of the simulation unit did not include demonstrating the effectiveness of the biological processes, the results are promising. The effluent requirement for the Varsseveld MBR plant is 5.0 mg Ntotal/l. The nitrogen content of the effluent stayed below this level during the entire study period, with the exception of a few minor exceedances. During a period of a few weeks, we even managed to achieve the MTR standard value of 2.2 mg Ntotal/l. This makes the simulation unit at Varsseveld the first installation in the Netherlands to meet the MTR standard for nitrogen removal without dosage from a carbon source. These positive results can largely be explained by the favourable composition of the influent, the advantageous process conditions and the optimal process design.

The phosphate content of the effluent is largely dependent on the values set for iron dosage. Since the beginning of September 2004, we have managed to achieve a phosphate content of approximately 0.1 to 0.3 mg Ptotal/l at an iron dosage level of approximately 0.8 mol Fe/mol P. Iron dosage was discontinued at the beginning of November 2004. The effects of relocating the dosage point will be examined during a later stage of the study.

The pilot installation was dismantled on Thursday 20 January 2005. The biological media were removed and the filtration unit was relocated and directly connected to the full-scale MBR plant. The key research objective for the filtration unit is the continuing investigation of energy savings in process mode (permeate extraction) and in stand-by mode (no permeate extraction).

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