Filter Bags Demonstration Site

One technology under examination by the project is filter bags. They are made out of fabric and are available with different sized pores. Wastewater is pumped into the bag and the sediment is caught by the fabric while treated water is strained out. The water is then collected and continues through further treatment if necessary.

Figure 1: A filter bag on the collection table above a tank with a pipe to return treated water to a settling pond (left) and an expanding bag (right)

In order to test the system, a pump was placed at the inlet of a settling pond to send a sample of carrot washwater to a scaled-down filter bag (Figure 1). The washwater was pumped in and clearer water flowed out of the bag. The bag was successful in straining out both pieces of carrots and soil particles (Figure 2).

Figure 2: Inflow of vegetable washwater at the top and outflow from the filter bag at the bottom (left) and solids filtered by the bag (right)

There were two issues with the system identified by this test. First, the pump sending the water to the bag was plugged several times by large chunks of carrots. Those larger pieces would either have to be removed earlier or chopped prior to the filter bag. Second, the bag clogged due to the colloids in the water and ruptured at the seam when the water had nowhere to exit and pressure built within the bag. The addition of coagulants would reduce this problem by clumping the colloids prior to the bag.

The filter bag system was certainly successful at removing solids from the washwater and since they are collected in a bag, the discarding of the waste is straightforward. Unlike settling ponds, which have to be dug out on a regular basis, the bag can simply be replaced with a new one when full.

A larger sized filter bag will be tested in the future to further review the benefits and challenges this system presents.