Coffee Wastewater: The Environmental Challenge Behind Wet Processing
Why washed coffee generates a high-strength wastewater stream — and what happens when it reaches the environment
Coffee is one of the world's largest agricultural commodities. Global coffee production is forecast to reach 178.8 million 60-kg bags in 2025/26, equivalent to approximately 10.7 million tonnes of green coffee.
A significant share of this coffee is processed using wet or washed methods. One detailed global assessment estimated that approximately 39% of coffee production is processed using the washed method. This is an estimate rather than a precise global measurement, but it gives an indication of the scale involved.
That would correspond to approximately 4.2 million tonnes of green coffee undergoing washed processing each year.
But green coffee is only the final product. Before it reaches that form, substantially more coffee cherry must pass through the washing station.
Using a commonly applied 6:1 fresh-cherry-to-green-coffee ratio, this represents roughly 25 million tonnes of fresh coffee cherries.
And processing those cherries generates a significant wastewater stream.
01 / A GLOBAL WASTEWATER STREAM
Approximately 125 billion litres
Published estimates of water consumption and wastewater generation vary substantially between processing systems. One review reports wastewater generation of approximately 5 m³ per tonne of fresh coffee fruit for processes involving pulping, mucilage removal and washing, while the wider literature reports water consumption and wastewater discharge ranging from approximately 1.5 to 23 m³ per tonne depending on the process.
Using the estimated 25 million tonnes of fresh cherries associated with washed coffee production and the representative figure of 5 m³ of wastewater per tonne gives an illustrative annual volume of approximately:
≈125 BILLION LITRES
This is a calculated illustration, not a measured global wastewater total. Actual volumes vary significantly according to processing technology, water availability, recycling and operating practices.
But even this conservative calculation illustrates the scale of the issue.
And volume is only part of the problem.
What makes coffee wastewater particularly challenging is what is dissolved and suspended in that water.
02 / WHAT MAKES COFFEE WASTEWATER DIFFERENT?
Coffee wastewater is not simply water that has been used to wash coffee.
During pulping, fermentation and washing, water comes into contact with the coffee fruit and carries away dissolved and suspended material.
This includes sugars, pectins, organic acids, proteins, phenolic compounds, tannins, alkaloids and other organic substances, together with suspended coffee residues. Reviews of coffee-processing wastewater consistently describe it as a high-strength organic effluent.
The composition changes depending on:
coffee variety;
processing method;
fermentation conditions;
water consumption;
equipment;
and the point at which the wastewater is sampled.
This variability is important. There is no single chemical profile that represents every coffee washing station.
But several characteristics appear repeatedly:
High organic loading.
Strong acidity.
Suspended organic solids.
Nutrients and other dissolved compounds.
Together, these characteristics can have significant effects once the wastewater enters a natural water body.
03 / THREE KEY CHARACTERISTICS OF COFFEE WASTEWATER
Coffee wastewater is particularly challenging because of a combination of high organic loading, high oxygen demand and strong acidity. Three parameters are especially useful for understanding the problem: Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and pH.
01 — HIGH ORGANIC LOAD: BOD
Biological Oxygen Demand (BOD) indicates how much dissolved oxygen microorganisms require to biologically break down biodegradable organic matter.
In simple terms:
More biodegradable organic matter → more microbial activity → more oxygen consumed.
Published literature reports BOD concentrations in coffee-processing wastewater of up to approximately 20,000 mg/L.
For comparison, UK government guidance gives a typical BOD concentration of approximately 380 mg/L for domestic sewage. Actual domestic wastewater varies considerably, so this is a reference value rather than a universal standard.
The upper reported coffee-wastewater value is therefore approximately:
53× higher than typical domestic sewage.
02 — CHEMICAL OXYGEN DEMAND: COD
Chemical Oxygen Demand (COD) measures the amount of oxygen equivalent required to chemically oxidize substances in wastewater. It captures a broader range of oxidizable material than BOD.
Coffee wastewater can contain exceptionally high COD concentrations, with published values reaching approximately 50,000 mg/L*.
For comparison, UK government guidance gives a typical COD concentration of approximately 677 mg/L for septic-tank discharge. Again, this is a reference value rather than a universal standard.
The upper reported coffee-wastewater value is approximately:
74× higher than the reference level.
At these reported concentrations, coffee wastewater can contain BOD and COD levels hundreds of times above permissible discharge limits used in environmental regulations.
These BOD and COD values illustrate why coffee wastewater is classified as a high-strength organic effluent.
03 — STRONG ACIDITY: pH
Coffee wastewater can also be strongly acidic, with published studies reporting pH values below 4, although actual values vary considerably between facilities and sampling conditions.
The pH scale is logarithmic. A solution at pH 4 has approximately 1,000 times the hydrogen-ion concentration of a solution at pH 7.
This does not mean that acidity alone determines the wastewater's environmental toxicity. Rather, it illustrates how chemically different strongly acidic coffee wastewater can be from the freshwater environment into which it may be discharged.
The acidity is partly associated with the fermentation and decomposition of organic material, during which microorganisms transform organic compounds and produce organic acids among other products.
04 / WHAT HAPPENS WHEN IT REACHES A RIVER?
The most important environmental consequence of high BOD and COD is what happens to dissolved oxygen.
When organic-rich wastewater enters a river, microorganisms begin breaking down the organic material.
That biological activity consumes oxygen.
If oxygen is consumed faster than the water can replenish it, dissolved oxygen concentrations fall.
Aquatic organisms depend on dissolved oxygen for respiration.
A field study of 11 rivers and streams associated with traditional wet coffee processing plants in Ethiopia found coffee effluent with COD as high as 7,200 mg/L and BOD₅ as high as 871 mg/L. The study found that this organic load depleted dissolved oxygen to as little as 0.25 mg/L.
That number needs context.
A separate study of coffee-affected rivers notes that around 5 mg/L is a level needed to support aquatic organisms, while concentrations below 2 mg/L can be lethal to many fish.
So 0.25 mg/L is only 5% of 5 mg/L.
At that point, the problem is no longer simply that the water is "polluted."
The oxygen conditions themselves can become incompatible with aquatic life.
05 / THE IMPACT IS NOT ONLY OXYGEN DEPLETION
BOD and COD explain one major pathway of environmental damage:
organic matter → microbial decomposition → oxygen consumption → aquatic stress
But coffee wastewater can affect water quality through several pathways simultaneously.
Its low pH can alter the chemical conditions of receiving waters.
Nutrients can contribute to eutrophication.
Suspended solids can increase turbidity and affect aquatic habitats.
And coffee-processing wastewater contains a complex mixture of dissolved organic compounds, including phenolics, tannins and alkaloids, which have been identified in the scientific literature as contributors to the wastewater's environmental effects.
The result is not one single pollutant acting in isolation.
It is a combined chemical and biological disturbance.
06 / WHEN THE RIVER IS ALSO THE COMMUNITY'S WATER SOURCE
The environmental impact does not stop at aquatic ecosystems.
In many coffee-producing regions, rivers and streams are part of everyday community life. They may be used for washing, livestock, irrigation, recreation and, in some locations, domestic purposes.
A 2023 study in Ethiopia specifically examined rivers receiving effluent from wet coffee-processing plants that were used by local communities.
Researchers found significantly higher concentrations of total coliforms and E. coli at discharge and downstream sites, particularly during the coffee-processing season. The study recorded E. coli concentrations as high as 213 CFU/100 mL at one discharge point.
The researchers concluded that the organic-rich wastewater contributed to microbial proliferation and deterioration of river water quality. They also reported community observations of bad odour, colour changes and skin irritation associated with contact with polluted water.
This distinction matters.
Coffee wastewater does not necessarily "create" pathogens. Rather, the combination of organic pollution and contaminated receiving waters can support increased microbial populations, while E. coli and other coliforms can indicate faecal contamination and potential health risks.
The same river can therefore become both: an ecological receptor and a community resource at risk.
07 / THE PROBLEM DOES NOT LOOK THE SAME AT EVERY WASHING STATION
Coffee-processing wastewater management varies enormously between countries and facilities.
Some larger washing stations have treatment or water-recycling systems. Others rely on settling ponds or lagoons (or even discharge wastewater without treatment).
But conventional infrastructure is not always sufficient.
Small and medium-sized washing stations may have limited treatment infrastructure, while poorly designed or undersized lagoons can overflow during periods of heavy processing or rainfall. In some producing regions, untreated wastewater may still be discharged directly to surrounding land, streams or rivers. Scientific studies in Ethiopia, for example, have documented direct or indirect discharge of untreated coffee effluent and inadequate treatment infrastructure.
As coffee production and environmental expectations increase, transparency, monitoring and enforcement will become increasingly important.
08 / COFFEE WASTEWATER IS ALSO A CLIMATE ISSUE
The environmental footprint of untreated coffee wastewater extends beyond water quality.
When highly organic wastewater is retained in oxygen-depleted conditions, such as poorly managed ponds, anaerobic microbial processes can generate methane.
Life-cycle studies have identified wastewater as a major greenhouse-gas hotspot at some wet mills.
One Kenyan study found that processing wastewater accounted for approximately 97% of processing-stage greenhouse-gas emissions at the wet mills studied. The study reported a mean processing carbon footprint of 2.6 kg CO₂e per kg of coffee parchment and identified wastewater as the dominant emission hotspot.
The 97% figure should not be interpreted as a universal value for the coffee industry. It is the result of a specific study and its system boundaries.
But it demonstrates an important point:
Wastewater treatment is not only a water-quality issue. Under some processing systems, it can also be a significant part of the carbon footprint of wet coffee processing.
09 / REGULATION IS BEGINNING TO CATCH UP
The environmental regulation of coffee wastewater is not uniform globally.
Some countries regulate coffee processing specifically, while others regulate it through broader industrial or agro-industrial wastewater frameworks.
Several major coffee-producing countries have introduced specific environmental requirements for coffee processing. Colombia, for example, has established coffee-specific wastewater discharge requirements, while other producing countries regulate coffee wastewater under broader industrial effluent standards.
Other major coffee-producing countries, including Brazil, Uganda, Vietnam and Mexico, operate broader environmental frameworks governing industrial wastewater discharge and water-quality protection.
Taken together, the 15 largest coffee-producing countries account for approximately 94.7% of global coffee production (based on the USDA 2025/26 forecast) and have environmental regulations governing wastewater treatment and discharge, either through general effluent standards or requirements specific to coffee processing.
The significance is clear: environmental compliance is increasingly becoming part of the operating environment for the global coffee supply chain.
But regulation alone does not install treatment infrastructure.
Where monitoring and enforcement are still developing or regulations are not yet effectively enforced, direct discharge and inadequate treatment can continue. Where producers are required to comply, they may also face practical constraints around land availability, capital expenditure, seasonal throughput and operating complexity.
10 / THE ENGINEERING CHALLENGE
Coffee wastewater is therefore an unusual treatment challenge.
The wastewater can be:
Highly acidic
Extremely rich in biodegradable organic matter
High in suspended solids
Chemically complex
Highly variable during the harvest
And the facilities generating it are often located in rural areas where:
land may be limited;
technical expertise may be scarce;
electricity may be unreliable;
processing volumes change dramatically during harvest;
treatment systems must operate alongside a seasonal production process.
Traditional approaches such as settling ponds, lagoons and biological treatment can play an important role and are widely documented in the literature. But each approach has its own requirements, limitations and environmental trade-offs.
Some require substantial land.
Some require significant retention time.
Some require careful biological control.
Some address organic pollution effectively but do not necessarily solve all water-quality or emissions challenges.
Some require substantial CapEx.
The question is therefore not simply whether coffee wastewater can be treated.
It is:
How can it be treated reliably, at the scale and under the operating conditions of real coffee washing stations?
That is an engineering question.
11 / WHAT TECHNOLOGIES ARE AVAILABLE?
A wide range of technologies has been investigated for coffee-processing wastewater, including biological treatment, anaerobic systems, constructed wetlands, coagulation and flocculation, membrane processes, adsorption and advanced oxidation. Reviews of the field show that no single approach is universally suitable for every wastewater stream or operating environment.
The choice depends on wastewater composition, required discharge quality, processing volume, available infrastructure, land, energy requirements, operating capacity and cost.
In our next Insights article, we will examine the principal technologies used and investigated for coffee wastewater treatment — how they work, what they remove, their infrastructure requirements, and where each approach has practical limitations.
Next in Insights
Coffee Wastewater Treatment: Technologies, Approaches and Their Trade-offs
References
1. USDA Foreign Agricultural Service. Coffee: World Markets and Trade, December 2025. Global 2025/26 production forecast: 178.8 million 60-kg bags.
2. Gururaj et al. (2021). Coffee Processing Wastewater Management: An Overview. Review of wastewater volumes, pollution characteristics and environmental impacts.
3. Murthy, P.S. & Naidu, M.M. (2015). A comprehensive review on utilization of wastewater from coffee processing. Renewable and Sustainable Energy Reviews. Reports BOD up to 20,000 mg/L, COD up to 50,000 mg/L and pH below 4.
4. Ijanu, E.M., Kamaruddin, M.A. & Norashiddin, F.A. (2020). Coffee processing wastewater treatment: a critical review on current treatment technologies with a proposed alternative. Applied Water Science.
5. Dadi, D. et al. (2018). Assessment of the effluent quality of wet coffee processing wastewater and its influence on downstream water quality. Ecohydrology & Hydrobiology, 18(2), 201–211. The study assessed 11 rivers/streams and reported maximum COD of 7,200 mg/L, BOD₅ of 871 mg/L and dissolved oxygen depletion to 0.25 mg/L.
6. Genanaw, W. et al. (2021). Effect of Wastewater Discharge From Coffee Processing Plant on River Water Quality, Sidama Region, South Ethiopia.
7. Amare, G., Dobo, B. & Haile, E. (2023). The Effect of Wet Coffee Processing Plant Effluent on Physicochemical and Bacteriological Quality of Receiving Rivers Used by Local Community: Case of Aroresa District, Sidama, Ethiopia. The study examined four rivers and documented changes in BOD, COD, pH, dissolved oxygen, total coliforms and E. coli, together with reported community impacts.
8. Maina, J.J., Mutwiwa, U.N., Kituu, G.M. & Githiru, M. (2016). Evaluation of Greenhouse Gas Emissions along the Small-Holder Coffee Supply Chain in Kenya. Journal of Sustainable Research in Engineering.
9. Colombia, Ministry of Environment. Resolution 631 of 2015. Specific wastewater discharge parameters for coffee processing.
10. Uganda National Environment Management Authority. National Environment (Standards for Discharge of Effluent into Water or Land) Regulations 2020.
Comments