Bean on a Journey: Turning over a new leaf?

With the enlightenment on the possible pollution that coffee wastewater can do to the environment in recent decades, there is a greater sense of urgency to mitigate the pollution. Hence, it is apt to introduce some wastewater treatment techniques that help reduce pollution derived from wet processing to conclude the Bean on a Journey series. Further discussions about the effectiveness of techniques will be discussed in the next series.

1. Physiochemical treatment

In recent years, physicochemical treatment has garnered popular votes from wastewater treaters, as it is efficient and effective in breaking down complex compounds in the wastewaters (Ijanu et al., 2020). Some examples of physicochemical treatment include:

- zero-valent iron treatment
- photo-fenton method
- ultraviolet radiation catalysis
- electro-oxidation

2. Biological treatment

Biological treatment has been widely practised, as it is effective in removing biological oxygen demand (BOD) in wastewaters (Ijanu et al., 2020), and cheaper to implement on a large scale (Muthukumar et al., 2021). Some examples of biological treatment methods include:

- expanded granular sludge bed bioreactor
- chemical coagulation and flocculation
- adsorption

 3. Ion-exchange 

While the ion-exchange technique is not foreign to the wastewater treatment industry, it does not seem to be a widely adopted technique to treat coffee effluent. Ijanu et al. (2020) and Campos et al. (2021) briefly mentioned the technique in relation to coffee effluent and recognised the method as cheap and environmentally friendly.

4. Membrane filtration

Membrane filtration is commonly used to complement the other methods mentioned above. As per its name, membrane filtration filters sediments and large bacteria from the wastewaters (Pamula, 2018). Following this train of thought, the membrane is rendered useless when faced with chemical compounds that need to be separated (Ijanu et al., 2020).

While there seem to be many options for wastewater treatment, many such techniques are still not frequently employed in coffee plants. To increase the uptake of these pollution reduction methods, instead of purely educating the types of techniques available, it would be wiser to recommend a method that is most desirable to their circumstance.

Bean on a Journey: Wet processing

Specialty grade arabica beans are typically produced via wet processing as it is said to produce a cleaner taste and brighter acidity, which improves the flavour profile of coffee. While wet processing increases the desirability factor of coffee in terms of taste, it certainly does not do the same for sustainability. In this instalment of Bean on a Journey, we explore how depulping, fermentation and washing of coffee cherries contribute to water pollution.

Coffee cherries are first depulped, and the pulps are washed away, exposing the seeds that is wrapped in a layer of mucilage. The mucilage is then gotten rid of through a long fermentation process and intensive washing. 

Figure 1: Coffee cherry anatomy. Image from: https://ulinzi-conservation-coffee.com/blogs/coffee/the-coffee-cherry

The first and major pollutant is the coffee pulps, as a series of damages occur after its introduction into a water system. According to Ratten et al., 2015, coffee pulps contain large amounts of organic matter that require high amounts of oxygen to decompose. Their "oxygen-loving" tendencies causes waters to become anaerobic, leading to fishkills and bacteria growth that threaten human and aquatic health (Ijanu et al., 2020; Ratten et al., 2015).

As a result of anaerobic water conditions, mucilage (another pollutant), which is soluble and largely made up of proteins and sugars, becomes tougher to decompose. While Tosif et al (2021) suggested the usefulness of muscilages for humans, the muscilage that get precipitated out in rivers can clog up waterways and worsen anaerobic conditions of the waters (Ratten et al., 2015).

Besides pulps and mucilages, a large amount of phosphorus have been found in coffee effluents. Coffee effluents refer to the wastewater discharged into water systems when the beans are washed. A study by Genanaw et al. (2021) found that phosphate contents in rivers near coffee processing plants be more than 5 times the amount under normal conditions. Such high amounts of phosphate encourages algae growth, which may lead to eutrophication (O'Niell et al., 2011).

Based on the pollutants released from wet processing, it seems that specialty coffees are not sustainable for the environment. However, the coffee industry does not back down from such set backs. Instead, wastewater treatment and other sustainable practices have been developed to reduce pollution during the processing phase. Next in the series, we will be exploring some mitigation strategies to manage these pollutants.

Bean on a Journey: An overview

From a farm to a cup, coffee beans undergo different processes before they are ready for consumption. Throughout these processes, conventional methods of production account for about 15.33kg of carbon dioxide per 1kg of green coffee (from Nab and Maslin, 2020), which is equivalent to the mass of 750 sushis! With more than 100 million bags of 60kg coffee being produced annually, one can only imagine the amount of carbon footprint produced. In this week's series of Bean on a Journey, we start by understanding the flow of coffee production. In the next two parts of the series, we will focus on the wet processing phase, which has recently gained more attention among the coffee community.

Generally, an avid consumer of coffee would understand the flow of production similar to what is shown in figure 1. Based on this knowledge, farming seemed to be understood as the most notorious for pollution due to the chain impacts caused by deforestation and farming processes (from Varcho, n.d.). Such impacts include water pollution from soil erosion and overfertilization, and air pollution from releasing sequestered carbon during deforestation. 

Figure 1: Coffee production process. Adapted from: https://ecoffee.vn/hanh-trinh-ki-dieu-mang-ten-from-farm-to-cup/

Other commonly known processes that contribute to pollution are roasting and brewing. During both processes, coffee grounds are usually disposed of as waste. As coffee grounds are organic, they release carbon dioxide and methane when they decompose in landfills, polluting the air, and contributing to global warming.

In between the mentioned processes, is the often-neglected coffee processing phase (refer to figure 2), which has recently risen in prominence due to sustainability efforts. Wet processing, in particular, is subjected to hot debates as it is water-intensive, and accounts for 54% of the water required in the entire production process (from Giraldi-Diaz et al., 2018). This suggests that a high magnitude of pollutants is being released during this process, and as such, garnering more attention to itself over the past few years.

Figure 2: Detailed flow of coffee production. The red box indicates the processes in question. Adapted from: Giraldi-Diaz et al., 2018

In this first instalment of Bean on a Journey, we explored the general flow of coffee production and briefly understood the impacts of the commonly known production processes. While lesser-known, coffee processing is gradually gaining prominence in its role in contributing to pollution. Hence, in the next instalment, we will ride the trend to explore the impacts of coffee processing in our environment.