8. Preliminary Thoughts on Wet-mill Water Use at Origin

It’s been awhile. Turns out graduate school is just a little bit harder than undergrad. Honestly though, I thought my undergrad engineering homework was impossible. There is a faint light at the end of the tunnel and that is my thesis (fingers crossed).

Aside from coffee leaf rust, the industry’s other major environmental concern is what is going on with wet-milling! Diligent research is being performed to figure out exactly what we should do with the wastewater produced from this process and if the water required to process coffee is removing valuable drinking water downstream. Michael Sheridan of CRS wrote a great post in 2012 on water challenges facing the coffee industry. The questions he raised directly influenced my direction in graduate school and I hope to share with you some of the interesting discoveries that I’ve dug up the past few weeks.

1. In 2011, a major hydrology study on coffee agroforestry was published. Delgado et al. monitored and tracked every drop of water that entered a square kilometer coffee plot and developed a model that aims to predict how much rain is retained by the entire system and how much of it finds its way to the stream in the center of the plot. They found that coffee agroforestry systems exhibited excellent aquifer recharge and erosion control.

2. Although the previous researches were successful in mapping all but 10% of the incoming water, their system did not have a wet-mill and its impact on incoming water and downstream resources is still unknown. However, using their published data, I was able to extrapolate on some of their initial findings and what I found was not at all what I expected.

Performing a back of the envelope calculation, I imposed a virtual wet-mill on the watershed and found that it used only 2% of the available water to process the coffee of the entire plantation, not just the coffee in the watershed. This was significantly lower than I anticipated and it was assuming perfect coffee yield with no lost crops. So perhaps the water requirement isn’t significant in some watersheds, but there may exist other environmental issues stemming from wet-mills.

3. Treatment solutions for coffee wastewater are abundant and water recycling can help reduce the amount of water used in processing. Of course, if these technologies exist why is this still an issue and why am I even writing a blog post on it? Mainly because few countries have adopted treatment technologies due to typical barriers to implementation (i.e. economics and policy) and the unknown effectiveness recycling wastewater. Currently, there is a lot of interest in using constructed wetlands to treat the pollution from wet-mills. Although they have been extremely successful in removing pollution, I see major hurdles to this technology. Specifically, long retention times and the size of such wetlands. These wetlands must retain the wastewater for up to 45 days, which is a problem when polluted water is constantly flowing out of the wet-mill and unless this water is stored until the wetland is ready for the next batch, it will just bypass treatment and flow straight into the nearby river. I believe the larger problem is the land requirement involved in wetlands. From my understanding of farming, which isn’t much, a farmer’s land is their primary asset. I can only imagine how difficult it will be to convince a coffee farmer that they should convert some of their usable coffee land into a bog to treat fermenting wastewater.


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