Why Dust Mitigation?

Dust and desertification are growing issues around the world, threatening millions of people with increasingly unstable soil and eroding infrastructure (Middleton and Kang, 2017). According to our own interviews, the U.S. Air Force also struggles with dust eroding infrastructure. Dust leads to increased accident rates, extensive repairs, and thousands of additional man hours a year. Becuase of its small size and varying composition, dust can enter the smallest gaps, eroding machinery and infrastructure both within the military and society at large. In aerospace applications, dust mitigation is a promising method to reduce low visibility “brown outs” as well as reducing the maintenance needed to upkeep vital systems saving money and time.

Cycle 1: Attempting to Measure Dust

Design

Our main objective with dust mitigation was to stabilize soil, increasing it's resistance to wind erosion. However, dustiness on small scale can be difficult to measure. Our first iteration of this test attempted to quantify dust by using a fan to blow dust away and measure the difference in mass.

Build

Using several petri dishes, we cemented different sand groups with various cementation solutions. The goal being that each petri dish could be tested independently under fan winds so that the amount of dust lost could be measured. Each dish was filled as level as possible and left to cement over a three day period.

Test

The cemented sand was tested with both a fan and compressed air, but results were not what we had hoped. A scale was used to measure the weight of each Petri dish before and after the test, which was our method of determining dust loss. For the first iteration, the fan was first angled downward towards the Petri dish and put on full blast, then angled more forward. Nothing blew off of the Petri dishes with cemented soils, making gathering meaningful data impossible. Similarly, untreated controls lost minimal sand mass making taking meaningful data difficult.

For the second iteration, a bottle with pressurized air was put on its side on top of a test tube rack and the spout angled downward towards the Petri dish. The trigger was pulled to maximum for a duration of 3 seconds to release the pressurized air. The Petri dish with Escherichia coli (E. coli) and INP-sil was not affected at all, but the Petri dish with the control (only sand) had the sand almost blown off entirely.

Learn

The first round of testing had several shortcomings as mentioned previously. First, most of the biocemented soils were fairly resistant to the fan and did not yield significant results. Second, there was no quantifiable way of measuring the strength of the wind – for example, it was very difficult to precisely pull the pressurized air bottle’s trigger for consistent air pressure or at a consistent angle. The same was true of the fan, it was difficult to measure how much wind was being produced, as different brands of fans would have different strengths of wind.

Cycle 2: Penetrometer Testing

Design

Our main objective with dust mitigation was to minimize the erosion of topsoil/sand. Some considerations with this goal are the environmental friendliness, as well as figuring out a method of measuring “dustiness” in a quantifiable manner. We initially tested this with a fan and pressurized air, but this did not give significant results, nor did it present a quantifiable way of measuring the dustiness or soil strength. As a result, we began looking at ways to obtain data on soil strength. We came across penetrometer testing, which seemed to be a promising method to measure soil strength.

Build

Several ideas were implemented to standardize the experiment and procedure. Culturing was performed using the same procedure as the biocemented and biosilicification bricks. This procedure is backed in literature and has been shown to yield powerful bricks. Petri dishes were selected to test small but relevant amounts of cemented soil and sand. Additionally, a Petri dish proved beneficial to create a standard soil sample using a standardized and replicable procedure. Filling to the top and tapping to ensure standard amounts, consistent treatment, and 3 days of drying before ensured minimal variability within the test subjects.

Test

A penetrometer proved to obtain the most optimal data on soil strength and compaction while maintaining a standardized procedure for each Petri dish.

The penetrometer rod was driven into the soil once for each Petri dish, and released once the soil was past its breaking point. The rod was generally driven into the middle of the Petri dish, or evenly flat areas in order to prevent variability in the soil depth level. The penetrometer tip was wiped off every time afterwards in order to prevent cross-contamination of the cemented soils in the Petri dishes. The pressure taken from the penetrometer, measuring kg/cm², was then recorded and shown in Figure 1 below.

Results:

In previous literature, as well as our own tests, biocement made using S. pasteurii has shown significant strength (4.1 kg/cm²), but can be difficult to implement due to ammonium production and other adverse enviornmental effects. While a small sample size with a relatively large standard error, this data shows increased soil strenth using E. coli INP-sil in a TB-Si solution. Reading with a penetrometer reading of 2.385 kg/cm², biosilicified sand shows greater pressure resistance than that of untreated sand. This indicates success in the biosilicification process, and a promising option for combatting dust mitigation in a more environnmentally conscious way.

Project Achievements:

Both cycles revealed valuable information about the biosilicification of sand mixtures, and indicate the benefits of biosilicification in dust mitigation applications. E. coli INP-sil with TB-Si solution showed greater strength than non-treated sand. While not reaching the strength of biocemented sand, these experiments still indicate that the soil stability provided by biosilicification is relevant. In the future, we would like to continue with additional experiments, larger experiment sizes, and additional biosilicification solutions in order to find the most effective biosilicification process possible.

Sources

• Middleton, N., & Kang, U. (2017). Sand and dust storms: Impact mitigation. Sustainability, 9(6), 1053.