Efficiencies of indigenous South African plant biofilters for urban stormwater runoff water quality improvement with a focus on nutrients and metals

Abstract

In South Africa, urban activities contribute high levels of pollution to rivers and groundwater via stormwater runoff. In reducing urban stormwater loads of engineered plant biofiltration, an effective and self-sustaining component of green infrastructure is a treatment option. The country's extensive natural biodiversity offers untapped potential of indigenous species' use in plant biofilters. This paper presents the findings of a plant biofilter column experiment, which investigated the performance of nine indigenous plant species under varied urban stormwater pollutant load strengths. Average significant loads of dissolved Cd (>98%), Cu (>84%), Pb (>99%) and Zn (>95%), as well as NH3-N (>93%), were removed by the plant biofilters, whereas the removal of -N (−37–79%) and -P (−81 to 63%) was more variable. Biofilters equipped with indigenous plant species were on average at least 11% more efficient than unvegetated soil in the removal of urban nutrient and metal pollutants. Over time, planted biofilters improved nutrient and metal removal efficiencies. The results support the inclusion of indigenous plants in biofilters within urban stormwater green infrastructure initiatives. Further research to inform plant biofilter design practicalities and assess plant biofilter performance in the field is warranted.

How well do endemic wetland plant species perform in water purification?

“…Likewise C. textilis performed well relative to results of a review of eight studies, conducted mainly in China, which found that phosphorus uptake rates for numerous plant species, including Canna indica, P. australis, J. effusus and Typha species, varied between 2 and 163 mgP.m − 2 .d − 1 (Wang et al, 2020). A study conducted after ours, investigating the use of nine South African endemic plant species for use in bio lters, also con rmed that C. textilis and P. serratum consistently showed some of the best results in terms of nutrient removal relative to the other seven species (Jacklin et al, 2021b).…”

“…Due to increasing demand for wastewater treatment, there is a need for more innovative, affordable and sustainable decentralised technologies to treat wastewater -particularly for developing nations (Kivaisi, 2001). Extensive research into design considerations and optimization has resulted in various types of constructed wetlands being developed for different wastewater types (Babatunde et al, 2008;Batchelor and Loots, 1997;Jacklin et al, 2021b;Wood and Pybus, 1992;Wu et al, 2015; S. Yeh et al, 2015). Floating wetlands, a type of constructed wetland, are manufactured buoyant structures designed to support emergent wetland plants.…”