Pre-Filter Updates

A small group meet on Wed from 1-3 to work on the prefilters. We wanted to see if we could get the Tantalus operating on a biosand filter. We decided to remove the sand and check on the cap at the bottom of the filter. As we went to lift the bag of sand out we discovered that the bottom of the bag had disintegrated.

Bag Bottom Completely Open

When we removed the "bag" and the sand stayed behind. We removed the sand and cleaned the top layer of rock to remove all sand from the rock.

Pre-Filter With Sand Removed

We tested the water's ability to flow through the feed bag and found that it flowed through two layers without holes. We tried several ways to put the bag in the container such that it would hold the sand. Each time we added water we noticed ways the water could escape and avoid the sand filtration. When we had just the sand, the water was flowing through the sand too quickly. We finally decided to use another bag. We placed it in the bucket on top of the rock layer and filled to the top of the bucket with sand. We will monitor how long it takes the bag to disintegrate. (This bag was slightly different from the previous feed bag.) We folded the bag top over and placed an empty 5 gallon bucket on top that had 4 holes in it. We discovered the folded over bag top encouraged more spillage.


We finally opted this design: 5 gallon bucket with Tantalus structure from earlier testing (using the cap to build pressure), approx 4 inches of small pebbles, manufactured sand held in a feed bag, and another  5 gallon bucket on top of the sand inside the feed bag. The 5 gallon bucket has 4 holes (the holes were already there--might prefer use 2 holes). The top bucket acts as a storage bucket. It can handle 2 gallons at a time and has a even flow rate. The Tantalus will keep the water in the lower bucket until the water level reaches the top of the filter bucket.

Pre-filter with Tantalus Attached

(This brings to question whether the bags in our main filters are working as an effective barrier layer. If they are not holding up as we thought, it explains the sand getting through.)