Coffee wastewater
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Coffee wastewater, also known as coffee effluent, is a byproduct of
coffee processing Coffee production is the industrial process of converting the raw fruit of the coffee plant into the finished coffee. The coffee cherry has the fruit or pulp removed leaving the seed or bean which is then dried. While all green coffee is proce ...
. Its treatment and disposal is an important environmental consideration for coffee processing as
wastewater Wastewater is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of domestic, industr ...
is a form of industrial
water pollution Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water ...
. The unpicked
fruit In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...
of the coffee tree, known as the coffee cherry, undergoes a long process to make it ready for
consumption Consumption may refer to: *Resource consumption *Tuberculosis, an infectious disease, historically * Consumption (ecology), receipt of energy by consuming other organisms * Consumption (economics), the purchasing of newly produced goods for curren ...
. This process often entails use of large quantities of
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
and the production of considerable amounts of solid and liquid waste. The type of waste is a result of the type of process that the coffee cherries go through. The conversion of the cherry to ''oro''Stemming from the Spanish word for gold, due to the colour of the dried bean or ''green bean'' (the dried coffee bean which is ready to be exported) is achieved through either a dry, semi-washed or fully washed process.


Processing


Dry

The coffee cherries are dried immediately after they are harvested through sun drying, solar drying or artificial drying. In sun drying, the coffee cherries are placed on a clean floor and left to dry in the open air. In solar drying, the cherries are placed in a closed cabinet, which has ventilation holes to let moisture out. Artificial drying is used mostly during the wet season, when the low level of sunlight extends the time needed for solar drying and the cherries are prone to mold growth. After being dried, the cherries are hulled. In this process the dried outer layer of the cherry, known as the
pericarp Fruit anatomy is the plant anatomy of the internal structure of fruit. Fruits are the mature ovary or ovaries of one or more flowers. They are found in three main anatomical categories: aggregate fruits, multiple fruits, and simple fruits. Aggre ...
, is removed mechanically.


Semi-washed

In semi-washed processing, the cherries are de-pulped to remove the pericarp. After this the slimy
mucilage Mucilage is a thick, gluey substance produced by nearly all plants and some microorganisms. These microorganisms include protists which use it for their locomotion. The direction of their movement is always opposite to that of the secretion of m ...
layer which covers the bean is removed. This is done mechanically by feeding the beans into a cylindrical device which conveys them upward. While the friction and pressure exerted on the beans by this process is enough to remove most of the mucilage, a small amount of it will still remain in the centre-cut of the beans. This technique is used in Colombia and Mexico in order to reduce the water consumption from the long fermentation process and the extensive washing.


Becolsub

In order to reduce the contamination generated by the wet process of coffee fruits, scientists at Cenicafé developed a technology that avoids using water when not needed and uses the right water when needed. The technology, called ''Becolsub'' (taken from the initials of the Spanish for ecological wet coffee process with by-products handling: ''Beneficio Ecologicos Sub-productos''), controls more than 90% of the contamination generated by its predecessor. The quality of the coffee processed this way is the same as for coffee processed by natural fermentation. The Becolsub technology consists of pulping without water, mechanical demucilaging and mixing the by-products (fruit outer-skin and mucilage) in a screw conveyor. The technology also includes a hydromechanical device to remove floating fruits and light impurities, as well as heavy and hard objects, and a cylindrical screen to remove the fruits whose skin was not separated in the pulping machine. Scientists at Cenicafé discovered that a coffee fruit with mucilage (immature and dry fruits have no mucilage) has enough water inside for the skin and seeds to be separated in conventional pulping machines without water, that the liquid was only required as a conveying means and that pulping without water avoids 72% of the potential contamination. Mucilage removal has been done through a fermenting process, which takes between 14 and 18 hours, until the mucilage is degraded and can easily be removed with water. Washing fermented mucilage requires, in the best case, 5.0 L/kg of DPC. Scientists at Cenicafé developed a machine to remove the mucilage covering the coffee seeds. 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. In the screw conveyor the retention is greater than 60%, which means a 20% additional control of potential contamination. The two by-products are widely used as worms' substrate to produce natural fertilizers. However, the high concentration of the mucilage obtained from the demucilager provides opportunity for industrializing the by-product.


Fully washed

This process is mainly used when processing ''
Coffea arabica ''Coffea arabica'' (), also known as the Arabic coffee, is a species of flowering plant in the coffee and madder family Rubiaceae. It is believed to be the first species of coffee to have been cultivated and is currently the dominant cultivar, r ...
''. After de-pulping, the beans are collected in
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...
tanks where bacterial removal of the mucilage takes place over 12 to 36 hours. 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 Off-flavours or off-flavors ( see spelling differences) are taints in food products caused by the presence of undesirable compounds. They can originate in raw materials, from chemical changes during food processing and storage, and from micro-organ ...
like ''sour coffee'' and ''onion-flavour''. However, wet processing is believed to yield higher quality coffee than the other processes since small amounts of
off-flavors Off-flavours or off-flavors ( see spelling differences) are taints in food products caused by the presence of undesirable compounds. They can originate in raw materials, from chemical changes during food processing and storage, and from micro-organ ...
give the coffee its particular taste and "body". When fermentation is complete, the beans are washed thoroughly to remove fermentation residues and any remaining mucilage. If not removed, these cause decolouring of the parchment and make the beans susceptible to yeasts. After washing, the beans are dried. When the drying process is not rapid enough earthy and musty taints, like ''Rio-flavor'' come up.


Water usage

The amount of water used in processing depends strongly on the type of processing. Wet fully washed processing of the coffee cherries requires the most fresh water, dry processing the least. Sources indicate a wide range in water use. Recycling of water in the de-pulping process can drastically reduce the amount needed. With reuse and improved washing techniques, up to 1 to 6 m3 water per tonne of fresh coffee cherry is achievable; without reuse a consumption of up to 20 m3/tonne is possible.


General

Water used in processing coffee leaves the coffee processing unit with high levels of
pollution Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...
. The main component is
organic matter Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
, stemming from de-
pulping Pulp is a Lignocellulosic biomass, lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibers from wood, fiber crops, Paper recycling, waste paper, or cotton paper, rags. Mixed with water and other chemica ...
and
mucilage Mucilage is a thick, gluey substance produced by nearly all plants and some microorganisms. These microorganisms include protists which use it for their locomotion. The direction of their movement is always opposite to that of the secretion of m ...
removal. The majority of
organic material Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
in the wastewater is highly resistant and
COD Cod is the common name for the demersal fish genus '' Gadus'', belonging to the family Gadidae. Cod is also used as part of the common name for a number of other fish species, and one species that belongs to genus ''Gadus'' is commonly not call ...
values, the amount oxygen required to stabilize organic matter by using a strong oxidant, make up 80% of the pollution load, with values as high as 50 g/L. The BOD, the amount of oxygen required for the biological decomposition of organic matter under aerobic conditions at a standardized temperature and time of incubation, coming from
biodegradable Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegradati ...
organic material can reach values of 20 g/L. With a (rough) screening and removal of the pulp COD and BOD values become considerably lower. Values in the range of 3–5 g/L for COD and 1.5–3 g/L for BOD5BOD values after 5 days were found. Recorded values of 2.5 g/L for COD and 1.5 g/L for BOD5. A large part of the organic matter,
pectin Pectin ( grc, πηκτικός ': "congealed" and "curdled") is a heteropolysaccharide, a structural acid contained in the primary lamella, in the middle lamella, and in the cell walls of terrestrial plants. The principal, chemical component of ...
s, precipitates as mucilated solids and could be taken out of the water. When these solids are not removed and pH values rise and an increase in COD can be observed. In order to optimize the
anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...
processing of the wastewater pH values should be between 6.5 and 7.5, instead of the generally present values of pH=4, which is highly acidic. This is obtained by adding
calcium hydroxide Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca( OH)2. It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed or slaked with water. It has m ...
(CaOH2) to the wastewater. This resulted in a regained solubility of the pectins, raising COD from an average of 3.7 g/L to an average of 12.7 g/L. The water is further characterised by the presence of
flavonoid Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans. Chemically, flavonoids ...
compounds, coming from the skin of the cherries. 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 Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...
processes and growth and nutrient transformations by (especially) rooted water plants. Many efforts in
olive The olive, botanical name ''Olea europaea'', meaning 'European olive' in Latin, is a species of small tree or shrub in the family Oleaceae, found traditionally in the Mediterranean Basin. When in shrub form, it is known as ''Olea europaea'' ...
and
wine Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are m ...
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
polyphenol Polyphenols () are a large family of naturally occurring organic compounds characterized by multiples of phenol units. They are abundant in plants and structurally diverse. Polyphenols include flavonoids, tannic acid, and ellagitannin, some of ...
ics and flavonoid compounds by species of wood digesting fungi (
Basidiomycetes Basidiomycota () is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Ba ...
) in a submerged solution with
aeration Aeration (also called aerification or aeriation) is the Systems engineering process, process by which air is circulated through, mixed with or solvation, dissolved in a liquid or other substances that act as a fluid (such as soil). Aeration proces ...
using compressed air. These complex processes seemed to be able to remove the colour compounds, but simplified, cheaper techniques using other types of fungi (i.e. ''
Geotrichum Geotrichum is a genus of fungi found worldwide in soil, water, air, and sewage, as well as in plants, cereals, and dairy products; it is also commonly found in normal human flora and is isolated from sputum and feces. It was first described in ...
'', ''
Penicillium ''Penicillium'' () is a genus of ascomycetous fungi that is part of the mycobiome of many species and is of major importance in the natural environment, in food spoilage, and in food and drug production. Some members of the genus produce pe ...
'', ''
Aspergillus ' () is a genus consisting of several hundred mold species found in various climates worldwide. ''Aspergillus'' was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli. Viewing the fungi under a microscope, Miche ...
'') only thrived in highly diluted wastewaters. Coffee wastewater is not a constant flow of water with uniform loadings of contamination. The processing of coffee cherries is a batch process and regarding water flows, two processes can be determined: de-pulping and fermentation/washing.


De-pulping

The water used for de-pulping of the cherries is referred to as pulping water. It accounts for just over half of the water used in the process. According to Von Enden and Calvert, "pulping water consists of quickly fermenting sugars from both pulp and mucilage components. Pulp and mucilage consists to a large extent of proteins, sugars and the mucilage in particular of pectins, i.e. polysaccharide carbohydrates. These sugars are fermenting using the enzymes from the bacteria on the cherries. Other components in pulping water are acids and toxic chemicals like polyphenolics (tannins) or alkaloids (caffeine). Pulping water can be reused during the de-pulping of the harvest of one day. This results in an increase in organic matter and a decrease in pH. Research in Nicaragua showed COD averages rising from 5,400 mg/L up to 8,400 mg/L with most of the pulp removed. The drop in pH can be attributed to the start of fermentation of the pulping water. This drop continues until fermentation is finished and pH levels of around 4 are reached. The nutrient content of the pulping water at the maximum COD load, which was considered to reflect maximum pollution, was determined during this research. Total nitrogen (TN) concentration in the samples ranged from 50 to 110 mg/L with an average over all samples of 90 mg/L. Total phosphorus (TP) concentration in the samples ranged from 8.9 to 15.2 mg/L with an average over all samples of 12.4 mg/L.


Washing

Washing of the fermented beans leads to wastewater containing mainly pectins from the mucilage, proteins and sugars. The fermentation of the sugars (disaccharide carbohydrates) into ethanol and CO2 leads to acid conditions in the washing water. The
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
is converted in acetic acids after reaction with oxygen, lowering the pH to levels of around 4. The high acidity can negatively affect the treatment efficiency of treatment facilities treating the coffee wastewater like an anaerobic reactor or constructed wetlands and is considered to be detrimental for aquatic life when discharged directly into
surface water Surface water is water located on top of land forming terrestrial (inland) waterbodies, and may also be referred to as ''blue water'', opposed to the seawater and waterbodies like the ocean. The vast majority of surface water is produced by prec ...
s. During the washing process the research in Nicaragua showed a clear decrease in contamination of the wastewater. The COD values drop from an average of 7,200 mg/L to less than 50 mg/L. Despite the fact that wastewater with COD values below 200 mg/L is allowed to be discharged in the natural waterways in Nicaragua it is advisable to redirect all the wastewater to the treatment system. 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. When the water is "clear" it is considered to be clean enough but the COD values measured during the research showed that discharge generally was to soon, resulting in wastewater with higher levels of COD than permitted. Another positive effect of diverting the wastewater to a treatment system is the dilution of the wastewater which enables better treatment by anaerobic bacteria due to more favourable pH values and better post-treatment due to lower concentrations of ammonium. TN concentration in the samples of wastewater stemming from washing ranged from 40 to 150 mg/L with an average over all samples of 110 mg/L. TP concentration in the samples ranged from 7.8 to 15.8 mg/L with an average over all samples of 10.7 mg/L.


See also


Notes


References


Bibliography

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Further reading

* * {{Coffee Coffee production Waste