Weevil and Aflatoxin resistant Containers


The Problem:
Current storage methods of grains and other harvests that are used in developing countries are not capable of protecting from heat, moisture, and pests. This results in as many as 4.5 billion people suffering from chronic aflatoxin (mold) exposure (link). Our group is working to address this problem by designing a container that is cheap, easy to use, and provides the necessary protectionTarget Demographic: Malawi and Sierra Leone
Although this remains a problem in many communities in rural Africa and other regions in which corn, grains and other affected products are the main food staple, our team has chosen to focus on starting with communities within the countries of Malawi and Sierra Leone. Malawi is a country in southeastern Africa with a total population of about 17 million, as of 2015, and Sierra Leone is a country In West Africa, with a total population of about 6.5 million, as of 2015.

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Malawi (red) and Sierra Leone (yellow)

Category Malawi Sierra Leone
Life Expectancy 60.5 57.1
Population and Population Density
17.2 M, 126/sq km 6.45 M, 81.8/sq km
Population density (SLO) 1347/sq km
Children and Elderly
per 100 adults
92.9/100 83.3/100
Child Mortality Rate
(under age 5/1000 births)
~967,920 total
~774,000 total
Number of people
in poverty
No data 3.32 M
Crude Births 42.5/1000 births
~629,000 total
41.5/1000 births
~267,675 total
Death Rate 12.9 deaths/1000
~190,920 total
3.29% increase
16.5 deaths/1000
~106,425 total
2.5% increase
HIV deaths annually 67,000 1100

Climate (source)
The weather during summer, November to April, is hot and humid. These months it is also the rainy season. These hot and humid conditions greatly increase the . The coolest months are June and July when daytime temperatures hover around 21 degrees Celsius (70 Fahrenheit) and nights can be much cooler, ranging from 7-15 degrees Celsius (45-59 Fahrenheit).
Variations in altitude in Malawi lead to wide differences in climate. The vast water surface of Lake Niassa has a cooling effect, but because of the low elevation, the margins of the lake have long hot seasons and high humidity, with a mean annual temperature of 24° C (75° F ). Average rainfall is heaviest along the northern coast of Lake Malawi, where the average is more than 163 cm (64 in) per year; about 70% of the country averages about 75? 100 cm (30-40 in) annually. Lilongwe, in central Malawi, at an elevation of 1,041 m (3,415 ft), has a moderately warm climate with adequate rainfall. The average daily minimum and maximum temperatures in November, the hottest month, are 17° C (63° F ) and 29° C (84° F), respectively; those in July, the coolest month, are 7° C (45° F ) and 23° C (73° F ).

What Do These Numbers Look Like?
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Nkhota Kota, Malawi and Kabala, Sierra Leone average annual temperature (pink line) and precipitation (green bars)

What We’ve Done So Far:
For the first couple of week working on this project, our team conducted research to learn more about the target communities (demographic information, climate, lifestyle choices, etc.) and about Aflatoxin and its risks, causal factors, preventative measures, etc. Because of the range of problems that accompany the storage methods used by the people of these communities, we had a range of angles from which we would be able to approach our project; these different options include creating a dryer, which would remove moisture from the harvested products; a container that would be resistant to weevils and other pests, moisture and heat; a separator that would remove affected product from the stock of good and usable product; and humidity strips that would indicate the humidity levels within any stock of harvested product. To help us in our decision making and moving forward with our project to help these communities, we created this Design Matrix that indicates the benefits and disadvantages of each approach to the project.


Criteria Cost of Use Cost of Building Feasibility Complexity Time to build Maintenence Change to Process Ease for Consumer Fit Culture Total
Weight 20 10 20 15 10 15 20 10 20 140
Percentage 14.29% 7.14% 14.29% 10.71% 7.14% 10.71% 14.29% 7.14% 14.29%
Dryer 3 3 6 3 3 4 7 7 5 41
Container 8 6 10 7 7 9 9 8 9 73
Separator 2 2 4 1 2 3 5 10 5 34
Humidity Strip 5 7 7 5 8 9 8 4 7 60

Our Design:
After careful consideration we decided to go with creating a bag that would remove the moisture in the grain. We decided that a desiccant was our best option by looking at price and how readily available these products were. We made a sealed plastic bag out of polypropylene and then sealed another bag inside of it with the desiccant in it. We are then going to put our bag into an insulated hole in the ground to keep the grain cooler and away from the humidity.

The Hole at the SEF


Our Sketch


Here is a sketch of our desired result for the hole at the SEF. Our plan is to widen the hole you see above and repurpose the straw by mixing it with clay and sand to make cob which will line the hole and keep it more thermally stable by using the direct contact with the ground.
After the cob layer, there will be a plastic liner made of the same material of our bag to prevent bug infestation. We plan on refitting the lid of the stove with more wood that sits into the hole and sealing that with weather stripping to prevent liquid and air into the hole. We will have to refashion the handles as well so that the whole lid can be lifted up easily by a community member. We initially researched putting insecticides or pesticides in our cob mixture to deter infestation, but the information we found stated that the bugs have to eat the borax in order for it to be effective. We decided to not add insecticide to the mixture and rely on the plastic lining of the hole as well as the bag to keep pests out.

What Is a Desiccant:
A desiccant is a substance or material that is hygroscopic, meaning it has tendency to absorb moisture. There are many types of desiccants that we use every day and although many are salt based, there are some that aren’t. For example, when opening a packaged food item there is often silica gel packets.
How Do You Choose The Right One:
We decided that we wanted a more natural desiccant rather then one that was manufactured in a lab. Some of the things we looked at were salt, rice, non-dairy powdered creamer, and calcium chloride (another kind of salt). We found these test results.

I took one cup each of silica gel, salt, rice, calcium chloride, plaster of Paris, and non-dairy creamer, poured them in separate bowls, then lined the bowls up on a table in the cellar. Relative humidity was in the 65-75% range. I weighed them in the beginning, gross and tare, and at the end of 40 days.”

The ending result was that calcium chloride absorbed gained 56% of weight in moisture of content while the next best thing was the non-dairy powdered creamer at around 20%. We decided to go with calcium chloride figuring that would be more readily available than the powdered creamer.
Overall the bag and hole combo seemed to work. We are currently on day 24 with no mold on the corn yet. One of the big things that we should consider, that we looked into but don’t know without going there, is whether to use the bag as a whole unit with the desiccant attached or to use the same bag that people have been using and giving them an insert.
One of the biggest failures for us was communication. We were really good at the beginning with communicating everything with Peggy, but then it died off as we continued our project. Another failure was it took roughly 5 or 6 tries to figure out the correct order to seal the bag with the desiccant. We ended wasting quite a bit of material because we would be half way through sealing and ended up having to double seal which melts the bag.

– good progress. Please show some of your work. Check your figures (images). Put in captions for the figures. Financial costs?

The Team:
(from left to right)
Sophia, Nick, Chris, Phoebe
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Chris Chaboya: chrischaboya@yahoo.com
Phoebe Conrad: pnconrad07@gmail.com
Nicholas Crawford: nrcrawfo@calpoly.edu
Sophia Michelletti: michelettisophia@gmail.com

We will also be working with Peggy Papathakis from Cal Poly’s Nutrition Department, as well as Dr. Mark Manary from Washington University School of Medicine in St. Louis.