New Research Update: The Impact of Coffee Processing on River Water in Ethiopia

By Emma Sage, Coffee Science Manager, SCAA

A new study, published in the Journal of Environmental Monitoring and Assessment, has investigated the specific environmental impact of coffee waste on river water in the Jimma Zone of Ethiopia. This research was undertaken by collaborators from Ethiopian, US and Belgium Universities, as well as the local Jimma Agricultural Research Center. The article was first published online on December 9, 2011, and can be found at the journal website.

Most of us are probably aware that coffee processing can use a lot of water and impact the chemistry of that water, but this has not been quantified extensively in many growing regions. It is especially important to understand this coffee-related pollution as we progress further down the rabbit hole of climate change and dwindling natural resources.

First, some background: let’s talk about eutrophication. This happens to water all over the world, especially where agriculture is present. It is a result of the leaching of nutrients into water, which run downstream and are added to the natural watershed. Nitrogen and phosphorus are essential nutrients for life and key ingredients in agricultural fertilizers. This is why agricultural areas are particularly susceptible to eutrophication. An over-abundance of these elements in a watershed with many sources of nitrogen pollution leads to many organisms (such as algae or plankton) growing very quickly to unprecedented abundances (sometimes this is called a “bloom”). These organisms then use up much of the oxygen in their area, creating what is called hypoxia, or an aquatic environment with too little oxygen to sustain life. You can learn more about this at Science or at the The National Oceanic and Atmospheric Administration.

The Jimma zone in Ethiopia produces more than 32,000 tons of processed coffee every year (data from the Jimma Agricultural Resource Center), and other studies have calculated that pulping alone can consume 6–7 cubic meters (or 6000–7000 liters) of water per ton of coffee cherries. That means a lot of water! Wet processing in the Jimma Zone of Ethiopia typically uses this water to remove the coffee pulp. This water ends up contaminated with lots of organic matter. We can think of this waste water as “fertilized” water, as it has leached out nutrients from the coffee fruit.

In this new study, the authors looked at 23 coffee-processing plants and at 18 corresponding rivers, making it the most extensive study of its type in Ethiopia. They compared the rainy and dry seasons to see how well the rivers recovered from the peak processing, which typically occurs just after the rainy season. They monitored the oxygen, organic load, total dissolved solids, pH, phosphorus, nitrate, and ammonia (nitrogenous compounds) downstream in each river.

For controls they simply sampled various locations upstream of the processing plants. They also monitored the diversity of macroinvertebrate communities in affected rivers to help understand the ecological impacts of these chemical changes. (If you are wondering why macroinvertebrates are important, just think of a food chain diagram. They are snails, worms, mussels, leeches, beetles, flies, and other insects. They are generally thought of as indicators of watershed health. For more information on them, you can check out the EPA website.).

In this study, the authors found significant reductions in water quality downstream from coffee processing plants during the wet season. During the wet season, they saw a large increase in organic loads, nutrients, and solids, which resulted in dissolved oxygen levels to as little as 0.1 mg/L water. They also found that during the processing peak that the average pH of river waters was lowered from 7 to 6.2. This combination of changes led to a decrease in diversity of macroinvertebrates.

During the dry season, the scientists found that the organic load, dissolved oxygen, solids, and pH had recovered to mostly normal levels. They found that the overall macroinvertebrate diversity was restored during this time period, but that the most sensitive taxa remained at low percentages, indicating a longer-term impact on the ecosystem. Interestingly, since the dissolved oxygen was reduced so drastically, scientists found that the water pollution by nitrogen was unable to recover during the dry season. This is because some oxygen is necessary during the nitrogen cycle in order to transform it to its volatile form and expel it from the river water. With this information, they determined that oxygen levels, organic load, and nitrate were all causal for the shift in invertebrate diversity. The authors considered this a very serious finding and worried that without fast action many of these rivers would pose a risk to not only ecosystem but human health.

What can be done about this? You may be aware that different coffee growing regions have implemented various techniques to reduce water use or pollution from coffee waste. For example, some recycle waste water, use coffee waste as animal feed, or compost it for fertilizer. Others have implemented filtration sieves to remove the solid coffee debris from water before it re-enters the natural watershed, preventing further leaching of pollutants in river water. Recently some have even suggested it for biodiesel fuel production. However, according to this research article, none of these practices have been implemented in this region of Ethiopia.

Article Citation: Beyene A, Kassahun Y, Addis T, Assefa F, Amsalu A, Legesse W, Kloos H & Triest L. Published online Dec 9, 2011. The impact of traditional coffee processing on river water quality in Ethiopia and the urgency of adopting sound environmental practices. 

Environmental Monitoring and Assessment In press.

Photo: Seth Lieberman via flickr.