Floating wetlands

Floating wetlands — Planning and design

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• Overview
• Key considerations
• Planning and design
• Construction and operation
• Links and references

Site selection

Floating wetlands can be located in existing waterways or ponds, or a purpose built pond.

They should be located where flows are generally slow to moderate and where there is permanent water. Large variations in water height or sites with high velocities could damage the floating wetland and will make it challenging to secure the matrix.

Sizing

The area of floating wetland required to treat a subcatchment area is not well documented. Further testing is required to determine optimal sizing for Queensland conditions. One study examined a floating wetland sized to 0.14% of the contributing urban catchment. Despite being subject to highly variable flows it achieved removal rates of: TSS 76%, TP 55% and TN 17%[3].

The size of floating wetland could be calculated according to predicted flow, water volume and desired hydraulic residence times (see sizing under treatment wetlands). Longer hydraulic residence times of 3 to 5 days increase nitrogen removal compared to shorter residence times[1].

To facilitate denitrification, the floating wetland should cover a minimum of between 10% and 50% of the pond s pond/lake surface area coverage is recommended to create the anoxic conditions needed[4].

Most floating wetlands are implemented as a modular technology and can be expanded if results show more floating wetland footprint is required to achieve pollutant reduction within an existing waterbody/lagoon.

Design

• The floating mat or matrix should be arranged to ensure the water requiring treatment interacts with the plant roots, by reducing preferential flow paths around the floating wetlands (Figure 3)[2].
• Water depth of 0.8-1.5m.
• Where turtles are common, a mesh protection for the plant roots is required to prevent them being eaten. In some locations floating wetlands may also requires netting or other protection from birds which may damage plants.
• The floating matrix can be attached to the bank with wires which allow the floating mats to rise and fall with changes in water level. The anchoring needs to have sufficient capacity to accommodate water level changes and projected flow velocity.

References

1. ^ Boonsong, K & Chansiri, M (2008), 'Domestic Wastewater Treatment using Vetiver Grass Cultivated with Floating Platform Technique', Assumption University Journal of Technology, vol. 12, no. 2, pp. 73-80.
2. ^ a b Lucke, T, Walker, C & Beecham, S (April 2019), 'Experimental designs of field-based constructed floating wetland studies: A review', Science of The Total Environment. [online], vol. 660, pp. 199-208. Available at: https://linkinghub.elsevier.com/retrieve/pii/S0048969719300191 [Accessed 20 April 2022].
3. ^ Nichols, P, Lucke, T, Drapper, D & Walker, C (2016), 'Performance Evaluation of a Floating Treatment Wetland in an Urban Catchment', Water, vol. 8, p. 244.
4. ^ Wei, F, Shahid, MJ, Alnusairi, GSH, Afzal, M, Khan, A, El-Esawi, MA, Abbas, Z, Wei, K, Zaheer, IE, Rizwan, M & Ali, S (19 July 2020), 'Implementation of Floating Treatment Wetlands for Textile Wastewater Management: A Review', Sustainability. [online], vol. 12, no. 14, p. 5801. Available at: https://www.mdpi.com/2071-1050/12/14/5801 [Accessed 20 April 2022].

Last updated: 19 April 2022