Turning industrial wastewater into productive use

Most industries produce wastewater, with current world trends being to minimize or recycle such waste within the production process. Wastewater from food processing plants such as abattoirs is bio-degradable and non-toxic, but has high concentrations of biochemical oxygen demand and suspended solids which create unsuitable environmental conditions for aquatic life.

Right at the heart of Kampala, Uganda’s capital, lies the biggest abattoir in the country supplying meat to a city with a population of more than 1.5 million people according to the 2014 population census. It also supplies neighbouring towns with meat.

The abattoir processes on average 600 cattle and 120 goats and sheep per day. This produces 200 000 litres of wastewater daily, which mixes with other drainage and spring water to produce an average of 400 000 litres of wastewater. It eventually drains into the Nakivubo channel that discharges into Lake Victoria at Inner Murchison bay.

According to Joseph Kyambadde, a senior lecturer at Uganda’s Makerere University, the wastewater from the abattoir has very high organic content from animal blood and undigested feed.

“This, when discharged into surface water, uses dissolved oxygen to facilitate its decomposition thereby depleting oxygen required by aquatic organisms like fish,” says Kyambadde.

The decomposition process also produces toxic products which kill fish besides the noxious stench which pollutes the air.

The huge amount of effluent from the abattoir affects the community living around it by creating a bad smell of hydrogen sulfide produced during the discharge of protein-rich blood and undigested feeds. The effluent also contaminates water at Inner Murchison Bay, four kilometres downstream at the Ggaba Water Works, which is the source for Kampala City and neighbouring towns.

In 2010 scientists from Makerere University, with support from Bio-resource Innovations Network for Eastern Africa Development (Bio-Innovate), set up a pilot waste treatment unit for production of biogas and bio-fertilizer at the Kampala abattoir.

“The waste-to-energy implementation project was initiated in 2013,” Kyambadde says. “The slaughterhouse waste and wastewater is run through a fermentation process that releases methane, which is then captured and burned to produce electricity”.

The project has the raw wastewater pumped into an anaerobic digester plant which creates biogas. “The produced biogas is piped to a generator that runs on 70 % gas and 30 % diesel,” explains Kyambadde.

The digester sludge is released into a drying bed and processed into organic fertilizer. The generator is operated mainly at night to power the lights and fridges at the abattoir.

Kyambadde says that across East Africa, increases in the processing of agricultural products is being accompanied by a growth in organic waste dumped into bodies of water and open landfills.

The Kampala Abattoir project is one example in East Africa where research and development are not only being used for a cleaner environment, but also to inform national policies. The region acknowledges the need to reduce dependence on scarce fossil fuels and non-renewable resources.

This project shows that biomass processing technology can assist the transformation of inefficient and polluting bio-based industries, like abbatoirs, into modern bio-refineries for a large array of renewable products with lower emissions.

The agro/bio-wastes from the abattoir will result in a continuous supply of energy for industrial processing, as well as nutrient-rich organic fertilizers.

Since economies of Eastern Africa countries are based on agriculture, application of organic fertilizer will result in increased income for farmers, provide more feedstock for processing enterprises, and affordable and clean energy.

The reduction in greenhouse gas emissions through recovery of biogas from the bio-waste treatment plants, and the discharge of treated effluent that meets acceptable international discharge standards, will contribute towards climate change mitigation.

Access to clean water and sanitation services is a public good. The majority of agricultural processing industries in Eastern Africa are located close to water resources. Untreated effluent is released into nearby streams and contaminates drinking water sources with nutrients and pathogens which contribute to waterborne diseases.

Therefore, Kampala Abattoir project will ensure that downstream communities sharing the same water resources are protected through upstream treatment of waste prior to release into the environment.

The project, according to Kyambadde, is worth replicating in other regions with similar waste effluent challenges.

*Ochieng’ Ogodo is a science journalist based in Kenya.

This series of news articles is part of the Wastewater Management and Sanitation Provision in Africa Project, a partnership between the African Development Bank (AfDB), UN Environment and GRID-Arendal. The project is supported by the AfDB through its Rural Water Supply and Sanitation Initiative (funded by the Governments of Burkina Faso, Canada, Denmark, France, Italy, Switzerland and the Netherlands), and the Multi-Donor Water Partnership Programme (funded by the Governments of Canada and Denmark). The project is also funded by the Government of Norway and UNEP, and technically supported by GRID-Arendal.