As a part of the design work for the Screencap project, BWA executed in close cooperation with Waterboard AA en Maas a pilot test to validate the design that was made in cooperation with IV-Water.
The CellCap finescreens to be installed at the facilities of Aarle-Rixtel can be equipped with filter meshes, having a different pore size. Important in this case is not only the capacity to treat, but also the efficiency of the screens by means of TSS, BOD and Nitrogen. Specifically the BOD:N ratio that will be discharged is important to ensure the denitrification process. To determine the design specifications a pilot scale CellCap finescreen was installed at the facilities and operated under the circumstances as the future installation will have as well.
In December 2015, in a period when the variations in wastewater are large and the temperature is only limited, a pilot scale CellCap finescreen was installed and operated for 3 weeks.
The Cellcap finescreen is designed for high efficiency solids removal from municipal and industrial wastewater streams. It is particularly effective for treating wastewater at beef processing facilities, reducing total suspended solids (TSS) by 50-80% and biochemical oxygen demand (BOD5) by 20 -30%. This significantly improves the water quality and wastewater discharge options. The unit is designed to handle wastewater streams which, besides solids, may contain high concentrations of fats, oils, or grease (FOG).
The finescreen, depending of the application, is equipped with a filtercloth having a mesh opening size of 30 to 840 microns. The feed water is continuously fed into the unit in which the free water escapes through the mesh. The suspended solids that are separated by the mesh form a pre-coat which increases the efficiency, by catching smaller particles.
The movement of the mesh is continuously, where the speed is controlled, based upon the liquid level in the unit.
To improve separation of solids it is possible to add chemicals as an option (inorganic or polyelectrolyte).
The filtrate (free water) first collected behind the filter cloth in the frame and will be discharged.
The solids will be removed from the filter cloth by means of a patented cleaning system (airdoctor), using air pressure at the end of the filtration area.
During the test samples were taken from the feed water, while the flow to the treatment plant was registered. This to determine the characteristics of the wastewater in relation to the feed flow of the treatment plant and to the time of day. At the same time samples were taken of filtrate and rejection water, while operational parameters of the CellCap screen were registered.
The conclusion of the pilot was that the design made and written in the tenderbook was sufficient for the results targeted at the start of the project. With regards to a choice of filtermesh, there remained some uncertainty, meaning that during the full-scale start-up period some additional tests should be executed to determine the optimal selection of mesh opening. This will however not influence the overall design of the plant.
The graph below shows the efficiencies achieved during one week of the pilot tests.
The tests proved that with the CellCap finescreen, the efficiency of different parameters can be controlled in a wide range.