Tag Archives: sewage treatment

WEC Projects devises sewage treatment plant plan for Mothae diamond mine

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WEC Projects, a South Africa-based EPC contractor specialising in water and wastewater treatment solutions, says it will soon complete the installation of a new WEC Model B packaged sewage  treatment plant at the Mothae diamond mine in Lesotho.

The mine is 70% owned by Lucapa Diamond Company and 30% by the Government of Lesotho.

Rudolf de Koning, Sales Representative at WEC Projects, says: “The mine lacked a sustainable sewage solution. Producing 60 cu.m of domestic raw sewage per day, Mothae utilised honeysuckers – sewage trucks – to dispose of the sewage at the nearest disposal facility, almost 130 km away. This was obviously a very costly method of sewage disposal. WEC proposed the installation of its Model B conventional activated sludge treatment plant with a daily capacity of 80 cu.m, which allows for future upgrading and expansions of the mine operations.”

The R3.2 million ($194,817) installation is a combined activated sludge and clarification treatment plant. Its modular design simplifies the logistics involved in transporting to the site and simplifies assembly as well as ensures a smaller overall footprint, according to WEC Projects. The Mothae installation also integrates a Wastemaster that includes screening, de-gritting and oil removal to cope with fats and oils present in the sewage which could adversely affect the aerobic process in the plant’s reactor. The Wastemaster removes the oils, fats and non-biodegradable material upstream from the treatment process. The plant will treat the mine’s grey and black water piped to the current septic system.

“Besides the high fat and oil levels, another factor which could affect the treatment plant’s effectiveness was the high altitude of the site which results in low, fluctuating temperatures,” de Koning explains. “The biological population growth occurs optimally at around 19°C and above. In order to ensure the proper ambient temperature is maintained, the plant will be assembled within a larger enclosed facility.”

In addition to making the mine more environmentally compatible through the effective treatment of its domestic sewage, the plant also reduces the costs of transporting waste to the nearest disposal facility, it says. Another consideration is that water availability reduces considerably in the area during the winter. The new plant can help the mine reduce its water consumption.

Thato Tsephe, Project Foreman at Mothae, says: “We worked closely with WEC Projects on-site to develop a sustainable solution. WEC Projects had previously installed a sewage treatment plant at the neighbouring Letseng Mine and it was that facility that encouraged us to approach them. What is critical for us, what is critical for us is to complete the civil works and installation and commissioning of the plant during the winter season with the harsh climate posing many challenges.”

WEC Projects looks to nature for Lucara Karowe sewage treatment plant

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WEC Projects has secured a R3 million ($187,460) contract to supply a new sewage treatment plant for the expansion of Lucara Diamond’s Karowe diamond mine in Botswana.

The mine, near the village of Letlhakane in the eastern Kalahari Basin region of Botswana, is planning to cease open-pit activities by 2026 after which it will continue mining underground, extending its operational life to around 2040. More than 1,000 m above sea level, the mine operates in a region where temperatures average 35°C and water is scarce; so much so that the Government of Botswana has legislated mandatory water saving requirements for industry.

WEC Projects installed the original treatment plant in 2012 and will integrate the new system into the existing facility, increasing throughput from 100 cu.m/d to 150 cu.m/d to meet the requirements of an increase in the number of staff at the mine. While the treatment plant itself is a fairly standard installation, the mine requested a variation to the original project scope – a man-made natural reed bed wetland system that will provide a “polishing” phase to the treatment process, using natural organisms and filtration processes to further clean the wastewater, WEC Projects said.

Wayne Taljaard, Managing Director of WEC Projects, said: “This is a particularly unique feature for a mine as usually such reed bed wetlands are built for much larger installations such as municipal sewage treatment. The government’s mandate for water conservation has forced companies in Botswana to apply creative thinking to overcome the challenge of operating in an arid country.”

The main sewage treatment facility will consist of a WEC Projects Model A treatment plant, an extended aeration system using conventional activated sludge to process the sewage. The wastewater passes through a mechanical screen which removes solids and is then treated by a biological reactor which integrates anoxic, aerobic and clarification zones.

After treatment, the water will enter the reed bed wetland area where it will percolate through the reed bed allowing microorganisms to breakdown contaminants such as sulphur, heavy metals and chlorine. The water produced by this process, while not for human consumption, will be reused by the mine for applications such as irrigation and dust suppression, according to the company.

To create the wetland, a shallow dam will be built, its bottom to be filled with gravel and reeds planted. The water from the treatment plant will feed into the wetland area where nature will be left to take its course.

Taljaard added: “The reed bed solution offers a number of advantages for the mine as the effluent will be relatively odourless and is flexible enough to cope with fluctuations in input. It also requires little maintenance once it is up and running and will ensure that the mine remains within the constructs of the law.”