Wastewater Solutions

Minimizing the amount of water used

Factories should practice water conservation. In Papua New Guinea, the coffee is fully washed and the water recycled, so the amount of water used for processing is reduced to 4 - 8m³ per ton of fresh berry. This is a vast difference compared to Vietnam, where the coffee is fully washed without recycling of water: the amount of water required is 4 - 15m³ per ton of fresh berry.

Processing wastewater before discharging

Wastewater must NOT be discharged directly into the environment. Instead, the wastewater should be treated adequately prior to discharge. The best treatment approach would be to first divert the wastewater into a long and shallow acidification tank. Here, the water is fully fermented and acidified. Raw mucilage would form a black crust on top, while sediments (e.g.: pulp components) would sink to the bottom and the middle layer would contain clear acidic water. The mucilage and the sediments are regularly removed and would be further processed into compost.

The acidic water is fed into tanks. Here, natural limestone (CaCO₃ - calcium carbonate) is added. The ensuing reaction helps raise the pH to 6 - 7.

Next, the organic matter in this neutralised water is completely broken down, so its BOD is reduced. This can be done in a number of different ways:

• Anaerobic settling ponds: The water is left in ponds, where the organic matters are broken down by anaerobic micro-organisms.
• Artificial aeration: The water is aerated (pumped high into the air) to increase the amount of dissolved oxygen.
• Biogas reactors: The water is left in biogas reactors, where anaerobic bacteria consume the organic matter and release methane. Methane is an energy source and often used for drying parchment coffee.
• Wetlands: The water is released into a wetland (real or constructed). Wetland plants such as reeds and rushes help to increase the amount of dissolved oxygen, and they also use up some nutrients in this neutralised wastewater.

The BOD of the water is monitored frequently and once it has reached a suitable level, the water can be discharged into the environment.

The methods listed above are often used in combinations. For example, a pilot waste water treatment plant in Khe Sanh (Vietnam) simultaneously utilises three different methods for processing waste water: biogas reactors, settlement tank as well as constructed wetlands.

The economic side of wastewater treatment

Factories are reluctant to take action due to high installation and subsequent management costs. The extra income from the wastes recovered alone is often not enough to subsidise the cost. Hence, in certain countries, strict laws and high penalties are adopted to force the processors to treat the wastewater.

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