Vetiver grass infiltration pits and wetlands are an affordable, eco-friendly coffee wastewater treatment technique. Photo credit: TechnoServe
Coffee processing generates large amounts of effluents that have high concentrations of organic matter, suspended solids, and chemical substances like tannins, phenolics, and alkaloids. This effluent is highly acidic with a pH as low as 3.5 and has a high Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD), as well as high Total Suspended Solids (TSS). Discharging this effluent without treating it leads to high oxygen depletion in water bodies, eutrophication, and chemical contamination affecting not just aquatic life but also human health. Downstream users who rely on rivers and other water bodies for potable and domestic use are heavily impacted as the water contaminated with effluents becomes unfit for consumption.
“Treating coffee wastewater is very important for people and the planet. In Peru, for example, farmers use an estimated 11 million liters of water to process their coffee each year. In Ethiopia, where wastewater from central wet mills often overflows into rivers, TechnoServe found that the BOD of the contaminated river water was equivalent to that of raw sewage. The pollution and stench was particularly bad during harvest and the local government would often force wet mills to shut down, depriving the farmers of a strong market for their crop,” says Carole Hemmings, Global Coffee Sustainability Director, TechnoServe.
Using Vetiver Grass for Coffee Wastewater Treatment
A significant portion of effluent produced worldwide on coffee farms is discharged into the environment without adequate treatment. Among the small percentage of producers who treat the wastewater, the commonly used technique is sedimentation ponds. However, sedimentation pits often overflow and can also be dangerous for children. Additionally, they are generally unlined leading to vertical leakage of effluents into groundwater.
Vetiver infiltration pits are another technique with huge potential that overcomes the pitfalls of sedimentation ponds while still being very affordable for producers.
“Vetiver grass has deep, strong roots that help it filter and absorb the wastewater, removing the pollution before it can contaminate waterways or the soil,” explains Carole. Vetiver wetlands have been implemented in Ethiopia, Kenya, Tanzania, Costa Rica, Peru, Vietnam, India, Colombia, and Honduras. The results are promising.
“Average ranges from multiple studies have shown that vetiver treatment systems can reduce BOD levels by 70 to 90% and COD by 60 to 85%. The exact reduction depends on wastewater composition, retention time, and system design. An 80% reduction in TSS, 50 to 70% reduction in total nitrogen content, and 40 to 70% reduction in total phosphorus content has also been observed,” explains The Vetiver Network International team.
Vetiver infiltration pits are affordable and easy to build and maintain. Ideally, artificial wetlands are preferred to build the vetiver wetlands, but that can increase the initial capital cost. Pits are a close second option but the flow of effluents into the pits has to be controlled to prevent overflow. The pits are generally layered with a 30cm layer of coarse gravel to aid drainage, a 20cm layer of sand over the gravel to aid filtration and a final topsoil cover on which the vetiver grass is planted.
“Through our CAFE and MOCCA programs, we have supported hundreds of farmers to create vetiver wetlands. In Peru, they only need 12 square meters of land to effectively filter the wastewater for a regular farm. The required materials include vetiver grass, compost, and PVC pipes, with a total cost of less than $100,” explains Carole.
Vetiver infiltration pits and wetlands can remove suspended solids and other contaminants rapidly. It is an eco-friendly and affordable wastewater treatment technique. The only maintenance required is regular checking to prevent clogging and overflow, periodic trimming of vetiver grass to promote growth, and annual removal of accumulated sludge from the bottom of the pits (or as needed). This simple method can make a huge difference to the environment, without burdening the producers economically.