The main components of coffee wastewater are sugars, mucilage, organic matters, and flavanoids. According to the NRDC, over a period of 6 months in 1988, the coffee processed in Central America polluted 110,000 cubic meters of water per day. Hence, it is important that these wastes and residues are treated.
Sugars: These sugars come from the mucilage or the pulp. During fermentation, the sugar is converted into alcohol and CO2. The alcohol is subsequently converted into acetic acid, as a result the water's pH is lowered. The pH of coffee wastewater is usually around 3.8.
The mucilage: It is made up of proteins, sugars and pectin. The mucilage is difficult to degrade. It precipitates out of the solution and forms a black crust on the surface. This crust can clog up waterways and reduce the amount of oxygen in the water.
The organic matters: These matters are slowly broken down by micro-organisms. In the process, these micro-organisms use up dissolved oxygen in the water. The amount of oxygen needed for these micro-organisms to completely break down the organic matters present is called biological oxygen demand (BOD).
Coffee waste water has a BOD of about 20g/l, 200 times higher than paper-mill wastewater. In Costa Rica, in the early 1980s, two-thirds of the total BOD in the country's rivers came from coffee wastewater.
Due to the high BOD, the dissolved oxygen in water is used up, and anaerobic conditions are created. This causes rotten smells and potential health problems to people who use this water for drinking.
Flavanoids: These are chemicals which give coffee berries their red colour. They are harmless, but turn the coffee wastewater dark green or black, hence the lake/river becomes unsightly.
Low pH kills wildlife: If directly discharged into natural water bodies such as lakes and rivers, the pH of these water bodies can be lowered creating an acidic environment. Many aquatic organisms cannot survive in such an acidic environment.
High BOD kills wildlife: The higher the BOD, the higher the oxygen consumption. This reduces the availability of oxygen required for aquatic life, which is essential for their survival.
The low pH and high BOD slowly wipes out the aquatic life that would have otherwise survived in this environment.
“An Introduction to Good Manufacturing Practices for Post Harvest Processing of Arabica Coffee in Vietnam” - Jan. C von Enden. “Chemistry – The Central Science” – International Edition (8th) Theodore L. Brown, H. Eugene LeMay, Jr., Bruce E. Bursten
Natural Resources Defense Council
The Trade and Environment Database