Figure 1: Components of a drum filter
A drum filter was placed at a washing facility to test its performance. Drum filters function by allowing washwater to fall through a circular metal screen. As the screen becomes plugged by solids, the water level rises until it trips a sensor. This signals the machine to rotate the drum and turn on a spray bar which cleans the waste off the screen into a collection tray that exits through an outlet. The water used to rinse is pumped out of the lower portion where filtered water is collected prior to flowing out. It can also be programmed to rotate and rinse on a set schedule.
Figure 2: Solids trapped by the screen (left), spraying the screen clean (middle), and the inflow, left, and outflow, right, from the drum filter (right)
The filter tested is rated to handle 1,000 US gallons/minute with a solid load of 10 mg/L using a 30 micron screen. However, the washwater it was treating had a lower flow rate and a higher solid load. It was installed after a barrel washer for root vegetables and before a biofiltration system intended for dissolved solids and nutrients. Theoretically this drum filter would remove suspended solids larger than 30 microns in size, leaving the finer solids and dissolved portion for the next treatment step.
| Drum filters are able to remove large amounts of solids from a washwater and concentrate it into the waste stream (Figure 3). The outflow can then continue to further treatment processes to remove finer solids which cannot be caught by the screen. The waste stream, however, would also require further work. The goal is to concentrate the waste to the point where it is the consistency of sludge with minimal water and maximum solids. It is then disposed of, for example, through composting. This filter required optimization to produce a sludge-like waste and that process will be more thoroughly explained in an upcoming article. |  Figure 3: From left to right, samples of inflow, waste stream, and outflow |
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