Coffee wastewater
Its treatment and disposal is an important environmental consideration for coffee processing as wastewater is a form of industrial water pollution.
This process often entails use of large quantities of water and the production of considerable amounts of solid and liquid waste.
This technique is used in Colombia and Mexico in order to reduce the water consumption from the long fermentation process and the extensive washing.
The technology, called Becolsub (taken from the initials of the Spanish for ecological wet coffee process with by-products handling: Beneficio Ecologicos Sub-productos[2]), controls more than 90% of the contamination generated by its predecessor.
The Becolsub technology consists of pulping without water, mechanical demucilaging and mixing the by-products (fruit outer-skin and mucilage) in a screw conveyor.
This machine, called Deslim (the initial letters of the Spanish demucilager, the mechanical washer and cleaner) removes more than 98% of the total mucilage (same as a well conducted fermentation) by exerting stress and generating collisions among beans, using only 0.7 L/kg of DPC.
The resulting highly concentrated mixture of water, mucilage and impurities is viscous and is added to the separated fruit skin in a screw conveyor.
[3] After de-pulping, the beans are collected in fermentation tanks where bacterial removal of the mucilage takes place over 12 to 36 hours.
[4] The fermentation phase is important in the development of the flavour of the coffee, which is partially due to the microbiological processes that take place.
The emergence of yeasts and moulds in acidic water can lead to off-flavors like sour coffee and onion-flavour.
Flavonoid compounds result in dark colouration of the water at a pH=7 or higher, but they do not add to BOD or COD levels of the wastewater, nor have major environmental impacts.
Lower levels of transparency, however, can have a negative impact on photosynthetic processes and growth and nutrient transformations by (especially) rooted water plants.
Many efforts in olive and wine processing industries, with relatively large funds for research, have been trying to find a solution for this problem.
Calvert mentions research done into the removal of polyphenolics and flavonoid compounds by species of wood digesting fungi (Basidiomycetes) in a submerged solution with aeration using compressed air.
[21] These complex processes seemed to be able to remove the colour compounds, but simplified, cheaper techniques using other types of fungi (i.e. Geotrichum, Penicillium, Aspergillus) only thrived in highly diluted wastewaters.
Other components in pulping water are acids and toxic chemicals like polyphenolics (tannins) or alkaloids (caffeine).
Washing of the fermented beans leads to wastewater containing mainly pectins from the mucilage, proteins and sugars.
This is because COD levels cannot be determined onsite during the washing process and discharge of the wastewater into surface waters is based on visual inspection.
