Trapsuutjies is an environmental initiative owned by Susan Botha, who formerly worked at CapeNature. The name Trapsuutjies literally means ‘tread lightly’ and is the Afrikaans word for chameleon.
“The guiding principle of this initiative is to cultivate positive and focussed environmental behavioural change through value adding and innovative partnerships,” says Susan.
Southern Africa has successfully integrated water resource policies, but some areas still lack sustainable water resources. The Water Research Commission (WRC) and its Research, Development and Innovation Roadmap for 2015 to 2025 suggested the use of alternative sources of water and the reuse of wastewater as one such intervention, if this water complied with Green Drop requirements that would allow the use of this suitably treated water.
Trapsuutjies became involved with a pilot project at De Rust Wastewater Treatment Plant (WWTP) in 2017, when an artificial wetland was created to improve water quality with the aim of releasing it into the natural water system.
This project involved the creation of floating islands on the fifth of six ponds at the plant. The islands consisted of pockets made with shade netting and filled with empty, recycled two-litre plastic bottles. Reeds and bulrushes were planted on the rafts.
In 2017, the UN Environmental Programme’s World Water Development Report delivered in Durban noted that reclaiming wastewater could have environmental, economic, and social benefits, and contribute to better health and well-being, water and food security, and support sustainable development.
The wastewater treatment plant at Dysselsdorp before the placement of the floating islands in lane 1.
According to the UNEP report, improved wastewater management should include the five Rs:
- reducing pollution at the source;
- removing contaminants from wastewater;
- reusing the reclaimed water;
- recovering useful by-products; and
- raising social awareness that the use of reclaimed water is okay.
“While the South African government has been quite successful in providing water to most households, they have not been so successful in treating the sewage effluents from households,” said Dieks Theron, then a resident of De Rust, who designed the float. “To expand the sewage works using conventional methods would cost billions of rands, and alternative natural methods should be tested.”
A floating island planted with reeds and bulrushes on a pond at De Rust wastewater treatment plant. (Photo: Tisha Steyn)
The wastewater plant at Blomnek outside de Rust consists of six wastewater ponds, skirted with reeds and bulrushes growing along the edges. A chemical analysis of the reeds indicated that the plants on the edges were not effectively removing chemicals and unwanted bacteria from the water. The water in the last pond therefore did not comply with the standard required to release it into the natural water system or use it for anything else.
Dieks’s floating island design was novel. Here’s how to create it:
• make a pocket by sewing together the sides of a length of shade cloth with rope;
• fill the pocket with empty two-litre plastic bottles;
• affix reeds and bulrushes to the float;
• position the raft on the pond, anchoring it to the edge for easy removal;
• once the reeds are overgrown, pull out the raft to cut leaves for composting.
Perforated drums with bricks inside were placed on the floor of lane one to slow down water flow.
How does the system work?
The roots hanging in the water below the raft function as an anchor for useful bacteria which remove harmful bacteria (E-coli and Staphylococcus) and chemicals from the wastewater. Using an artificial wetland is a less expensive way than engineered approaches and greatly improves the quality of the water.
Käthe Seidel, a German scientist, was the first to experiment with the use of marsh vegetation to improve water quality. In 1957, she created an artificial marsh with bulrushes near Krefeld in Germany. She pumped heavily polluted water from the Rhine River into it. After two weeks, tests showed that the water had a much lower phosphorous and nitrogen content, while the oxygen content had increased. Her success owned her the nickname Bulrush Kate, and today this method is used worldwide to obtain improved water quality.
Floating islands can significantly increase the successful removal of pollutants, including nutrients, suspended solids, heavy metals and other unwanted components from natural and constructed wetlands.
The reduction of pollutants such as nitrogen and phosphorous mainly takes place by means of bacterial biofilms growing within the island matrix and on the roots hanging below the islands. Very little nutrients are taken up by the plants, but the plants are necessary to provide additional anchors for biofilm development, as well as producing oxygen and carbon for the bacteria.
These islands can remove up to 4,6 g/m2 /day of phosphorous and up to 8,1 g/m2 /day ammonia, while at the same time removing nitrogen and nitrogen gas.
It is essential to remove excess plant growth on top of the raft to encourage root growth.
Nitrogen-based nutrients are mostly removed as nitrogen gas. Phosphorous is primarily deposited as organic-rich sediment, which accumulates within or beneath the floating islands. This material should regularly be removed, for when it loses oxygen, it returns the phosphorous to the water column. This could lead to algal and bacterial blooms, which will degrade the quality of the water.
“At Blomnek, decreases of approximately 90% in coliform count and approximately 60% in phosphate concentrations were recorded,” says Susan. Despite good results, the water was still below the standard for irrigation.
When this project was halted because of incessant theft and vandalism, the focus shifted to the Dysselsdorp WWTP in 2019. Like the pilot project at De Rust, the Dysselsdorp project was funded by the Gouritz Cluster Biosphere Reserve (GCBR) and in coordination with the local Oudtshoorn Municipality.
Dysselsdorp wastewater plant
Learning from De Rust experience and with the involvement of various partners, the Dysselsdorp project was a much larger version of the pilot project.
Sampling of the water was done once a month to establish whether the purification was successful.
According to Susan, the contact channel on-site is divided into seven lanes, six of which are connected in a serpentine pattern, while the seventh, where chlorination takes place, is walled off.
About thirty floats, each planted with about twenty bulrush plants, were placed in lanes two, four and six.
Different floats were used. The first floats consisting of bamboo poles fastened with wire, were soon replaced with floats constructed of four two-metre 110 mm PVC pipes, attached with silicone with 90-degree elbows to form a square. Three wooden droppers per float were used to attach the plants to.
During phase two, thirty additional, slightly larger floats and filtration cells were placed in the first lane. Fifteen filtration cells, consisting of 210-litre plastic drums with holes drilled into them and filled with reject porous bricks, help to slow down water flow, which aids nutrient uptake.
“As the Dysselsdorp plant has a history of being reported as being non-compliant to the Department of Environmental Affairs and Development Planning (DEA&DPs) requirements, it made sense to utilise the funding to assist the municipality to work towards continued Green Drop compliance,” says Susan.
A diagram of the floating islands above and the drums filled with bricks in lane 1.
While the municipal processes manage faecal coliforms to some extent, no nutrient removal was done. The aim of the floating wetlands was to reduce these nutrients to make the water suitable for use. The testing is done monthly to determine the nutrient values. Research and Development (R&D) funding from the United Nations Development Programme (UNDP and Water Research Commission (WRC) made provision for added testing for heavy metals, to implement filtration cells and increase the number of floating wetlands.
If the water is suitable, it could be used to establish a local economic development (LED) project, such as a plant nursery, which would add value to the existing municipal processes.
The floating islands create valuable employment opportunities in a town that has very limited economic opportunities. It also contributes to water reuse strategies to ensure environmental and human health, especially in a
drought-stricken area.
For more information contact Susan Botha at (+27)83-500-5900 or send an e-mail to sbotha0@gmail.com.
References
Frers, C. (2014, April 30). The use of aquatic plants to treat waste water. Fourth Corner Nurseries. https://fourthcornernurseries.com/the-useof-aquatic-plants-to-treat-wastewater/
Käthe Seidel (Last updated: 2021, July 27) Wikipedia https://en.wikipedia.org/wiki/K%C3%A4the_Seidel
Masters, B. (2012, March 1). The ability of vegetated floating Islands to improve water quality in natural and constructed wetlands: a review. Water Practice and Technology (2012) 7 (1): wpt2012022. IWA Publishing
https://doi.org/10.2166/wpt.2012.022
The United Nations World Water Development Report (2017). Wastewater: The untapped resource. Available at: https://wedocs.unep.org/handle/20.500.11822/20448
