Aurecon designed a unique vacuum-based sewage collection system believed to be the largest of its kind in the world.
With an in-depth understanding of the sanitation problems experienced by the communities of the Kasane and Kazungula villages in northern Botswana and the growth potential of the region, global engineering and infrastructure advisory company, Aurecon, designed a unique vacuum-based sewage collection system. The technology is new on the African continent and the installed system is believed to be the largest of its kind in the world.
Aurecon was appointed for the Kasane-Kazungula Villages Sanitation Project by the Botswana Department of Waste Management and Pollution Control. This ecologically sensitive area on the banks of the Chobe and Zambezi rivers is very close to Botswana’s Chobe National Park with its nearly 120 000 elephants, and serves as a gateway for tourists intending to visit the Victoria Falls (Zimbabwe), Livingstone (Zambia) and Namibia’s Caprivi Strip.
The existing sanitation system only served a minor proportion of the community and growth in the region had resulted in the already overloaded treatment works overflowing, causing river contamination and health concerns. Due to the area’s topography and ecological sensitivity, Aurecon proposed that a combination of the standard gravity system and a fully-automated, vacuum-based closed sewer system be implemented. This offered lower operating costs, better reliability and reduced maintenance.
It was also proposed that influent be treated using the activated sludge system, ensuring the effluent quality was suitable for discharge into watercourses and ideal for land use and/or irrigation. The effectiveness of this system is evidenced by elephants drinking from the holding ponds on a regular basis.
A vacuum sewer system works by ‘sucking’ the wastewater at high velocity through small diameter pipes to a central collection point, from where it is pumped in the conventional way. It is an ideal solution for the relatively flat terrain in the area as pipes do not need to be laid to specific falls and, in fact, can even be laid uphill. It is also suited to areas where water use is low, as self-cleansing velocities are provided by the vacuum suction.
Designed to eventually serve 30 000 people and accommodate the high volumes of visitors to the area, the scope of the new system includes: 5 vacuum pump stations with 20-25 m³ vessels, 110 km of reticulation pipes (of which 50 km are vacuum pipes), 21 km of transmission lines, a 5 ML/day activated sludge plant, as well as 20 km of access roads.
HDPE pipes were selected for the vacuum system and joined using a sophisticated computerised electrofusion welding process. The success of this process and the careful attention given to training of the operators is evidenced by only two joints needing to be repeated out of the 8 300 sections of pipe involved.
In collaboration with the client, Aurecon ensured that the local communities received optimal added value from the project. Local community members were employed during project construction, material was sourced from a locally-owned quarry and training was given to men and women of the community.
Community members who received training have also been employed by the Water Utilities Corporation of Botswana to manage and maintain the scheme.
The success of the innovative project solution was facilitated by Aurecon’s holistic, inclusive approach to community-focused projects. The company provided strategic design input together with an inception and preliminary design report, as well as the final design report for the new sanitation system. The preliminary design report also involved lengthy consultation with stakeholders to motivate community participation.