MechChem Africa September-October 2022

WEC packaged wastewater plants: ideal for Africa’s varied needs Gunter Rencken and Rudolf de Koning of WEC Projects talk to MechChem Africa about distributed wastewater treatment using packaged plants that can be purpose-customised and factory-built for easy shipping to, and assembly on, remote sites all over Africa.

W EC Projects, a South African EPC contractor specialis ing in water and wastewater treatment solutions, is about to complete the installationof anewWECModel B packaged sewage treatment plant at the Mothae Diamond Mine in the Maluti Mountains of Lesotho. “The mine lacked a sustainable sewage solution for the 60 m 3 per day of domestic raw sewage it was producing,” says Rudolf de Koning, sales representative for WEC Projects. “The mine used sewage trucks, also known as honeysuckers, to dispose of the sewage at the nearest disposal facility almost 130 km away. This was obviously a very costly method of dealing with locally produced wastewater, so we proposed the installation of one of our wastewater treatment solutions –ourModel Bconventional activated sludge (CAS) treatment plant with a daily capacity of 80 m 3 , which can accommodate future upgrading and expansions of the mine’s operations.” The WEC Model B CAS plant is part of WEC’s modular range of sewage treatment plants that starts with the single reactor Model A plant and goes up to a Model D consisting of four reactors in parallel. “Within each reactor there are anoxic and aerobic stages, along with a clarification tank. Each plant works as a completewastewater treat mentmodule, taking rawsewage inat oneendanddeliveringdischarge quality water at the other, and the remaining sludge is pumped out to drying beds or mechanical dewatering devices,” explains de Koning. A single reactor WEC Model A packaged plant can recycle 60 m 3 of wastewater per day, with every additional module adding a further 60m 3 /dayof sewage treatment capacity. “SoaModel Bpackagedplant, like the one we are currently installing at the Mothae Diamond Mine, consists of two reactor modules that can treat up to 120m 3 /day if the need arises. Andwe can put up to four packaged units in parallel to get amaximumcapacityof 240m 3 /h fromthismodular packaged solution,”

he says. Gunter Rencken,WECProjects’ technical director continues: “We're talkinghere about a relatively small volumeper dayof domestic wastewater treatment. In the flowrange starting at 50-60m 3 /day, one reactor can meet the needs of about 300 to 600 people, depending on howmuch wastewater each household in a community produces. “When it comes to greater volumes, though, it becomes a question of economics. For requirements greater than 240 m 3 /day a Model D packaged plant with additional reactors no longer makes economic sense, because one Model R self-contained packaged plant – which is built using a circular construction – offers cost and space savings com paredtomore than four rectangularmodules,”he tells MechChemAfrica. De Koning says that a key advantage of the packaged approach is that units can be manufactured and pre-assembled at WEC’s local premises, where they can be properly configured and tested before being disassembled, loaded onto trucks and shipped to site. The units are easy to transport and the installation time is significantly reduced, as is the overall footprint of the plants. “Model A to D and Model R plants are usually above ground and require very fewcivil works. Each plant simply requires a small pump sump or a buffer tank to absorb any shock flow, and a few concrete slabs for the reactor modules to sit on. The blowers used for the aeration zone, the dosing units and MCC panels are all housed in a container,” de Koning tells MechChem Africa . “This makes these units ideal for mining camps such as theMothae DiamondMine, as well for smallermunicipalities – in SouthAfrica and across the sub-Saharan African region,” Rencken adds. The modular Model B plant at Mothae also integrates a WEC Wastemaster, which screens, de-grits and removes any oils, fats and non-biodegradable material upstream of the treatment process. “Besides the high fat and oil levels of thiswastewater, the high altitude plant is also susceptible to lowandfluctuating temperatures. Biological population growth occurs optimally at around 19 °C and above. In

12 ¦ MechChem Africa • July-August 2022