Ways to reduce coffee pollution: Common wastewater treatment methods

Wastewater generated coffee processing plants contain high amounts of organic matter and dark coloured pigments that are toxic to aquatic and human lives. While biological treatment types are typically used to treat wastewaters, non-biodegradables in coffee effluents may still hinder the water quality of treated water (Tomizawa et al., 2016). As such, researchers look into combining biological with physicochemical methods to improve the water quality derived from wastewater treatment (Mohamed, 2015; Blanco et al., 2014).

The most common biological method would be the anerobic/aerobic wastewater treatment. Both of which requires bacteria or other micro-organisms to breakdown the organic compound from the wastewater via biological oxidation to form sediments, which can then be removed (Mohamed, 2015). However, it is noted that the process is too time consuming, and requires the effluents to be of a consistent condition for the process to be efficient (Ijanu et al., 2020). Hence, scientists and engineers have explored the possibilities to improve wastewater treatment effectiveness via pairing up with physicochemical methods.

A common physicochemical method is the photon-Fenton process. Based on Dong et al. (2020), a photo-Fenton reaction is a kind of advanced oxidation process, which conventionally combines  Fe2+ ions with H2O2. It was found that this reaction generates a strongly oxiding radical species that can degrade organic pollutants into non-toxic materials, without the need for a harsh environment and special equipment. Notably, this reaction requires a low pH of 2.8 to reach maximum efficiency (O'dowd et al., 2020), making it a less desirable choice for wastewater treaters.

Above are common biological and physicochemical methods to treat coffee wastewater, and of course, the list of effective treatment methods are not limited to these. As each methods have its pros and cons, it is up to the wastewater treatment facility to decide which method best fit the situation they face (e.g. cost of operation, efficiency in removing pollutants).

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.