Field test of Chitosan sock as effective flocculant for settling sediment fines
Honokōwai powerline road below preserve
Paul Sturm, Casey Gunn & Tova Callender
Join us for field trials of the chitosan sock method!
Quick glossary:
Turbidity - Turbidity is defined as the measure of relative clarity of a liquid (by the USGS). In a sample of clear water, most of the light passes through. There are few suspended particles to scatter the light. In a murky sample of water with many suspended particles, much of the light bounces and scatters.
Flocculant - Flocculation is the process of particles suspended in a liquid clumping together. A flocculant is a substance that encourages the clumping process. Particles stay suspended in water - clumps sink! This process reduces turbidity.
Chitosan - Chitosan is derived from the exoskeletons of crab, shrimp & other crustaceans. It is widely included in dietary supplements… but can this fishery by-product help the planet? We’ve been working with partners on testing chitosan as a flocculant.
OK, let’s go to the field!
6 months ago: kickout with four rows of vetiver planted
Before the trial: compost sock pre-wetted with irrigation water by sprinkler
Water released from the tank created runoff in the kickout
Samples Collected (below the second row of vetiver)
1) Before the flocculant sock was added
2) After floc-sock was added & became saturated
(floc-sock is made with burlap case in left photo)
Differences in the turbidity of the samples became evident as they settled
Using a Hach turbidity meter borrowed from Hui O Ka Wai Ola, we measured turbidity (NTU) for each of the samples
After noticing how swirling the sample seemed to make the sample post floc-sock even cleaner, we tried swirling vs. shaking and inverting for both sample types
Readings were taken in close succession as soon as the meter had locked on the previous value (all three in ~ less than a minute)
Results of turbidity testing
Comparing Settling Rates
Figure Credit: Tova Callender, West Maui Ridge to Reef
There are two orders of magnitude between the turbidity in the control and post flocculant sample, and one order of magnitude difference in settling time
Observations
It really works! Chitosan was very effective at reducing turbidity of run off immediately
Swirling movement seems to facilitate more settling, so could it be incorporated in a micro basin design (round features?)