Assessment of Constructed Wetlands’ Potential for the Removal of Cyanobacteria and Microcystins (MC-LR)

Guna Bavithra,João Morais,Alexandre Campos,Joana Azevedo,C Marisa R Almeida,Vitor Vasconcelos,Isabel M.P.L.V.O Ferreira,Edgar Pinto,Flávio Oliveira

doi:10.3390/w12010010

Guna Bavithra, João Morais + Show 7 more

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https://doi.org/10.3390/w12010010

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Abstract

Microcystis blooms and the subsequent release of hepatotoxic microcystins (MCs) pose a serious threat to the safety of water for human and livestock consumption, agriculture irrigation, and aquaculture worldwide. Microcystin-LR (MC-LR), the most toxic variant of MCs, has been widely detected in a variety of environments such as water, sediments, plants, and many aquatic organisms. Conventional solutions of water treatment are costly, requiring specific infrastructure, as well as specialized personnel and equipment. Therefore, these solutions are not feasible in many rural areas or in the treatment of large reservoirs. In this regard, low-cost and low-technology solutions, such as constructed wetlands (CWs), are attractive solutions to treat surface waters contaminated with toxic cyanobacteria blooms from lakes, ponds, reservoirs, and irrigation systems. In line with this, the main aim of this work was to evaluate the potential of CWs for the treatment of water contaminated with MC-LR produced by Microcystis aeruginosa—LEGE 91094. For that, microcosms (0.4 × 0.3 × 0.3 m) simulating CWs were assembled with Phragmites australis to treat lake water contaminated with Microcystis aeruginosa cells and MCs. Results showed removal percentages of M. aeruginosa cells above 94% and about 99% removal of MC-LR during 1 week treatment cycles. CWs maintained their functions, regardless the presence of MC-LR in the system, and also showed significant removal of nutrients (ammonium ion removal up to 86%) and organic matter (removal reaching 98%). The present work indicates that CWs have the potential for removal of cyanobacterial cells and cyanotoxins, which can be useful for the treatment of eutrophic waters and provide water of sufficient quality to be used, for instance, in agriculture.

Highlights

Cyanobacteria occur in diverse environments, being highly prevalent in the aquatic environment, for example, in fresh water, brackish water, oceans, andWater 2020, 12, 10; doi:10.3390/w12010010 www.mdpi.com/journal/waterWater 2020, 12, 10 hot springs
During the 2 weeks of acclimation, MC-low range (LR) removals in constructed wetlands (CWs) were higher than 90%
The lake water was doped with M. aeruginosa culture

Summary

Introduction

Cyanobacteria (previously known as blue-green algae) occur in diverse environments, being highly prevalent in the aquatic environment, for example, in fresh water, brackish water, oceans, and. They are either present as biofilms or benthic mats, or dispersed in the water column as planktonic organisms. Cyanobacteria frequently reach high cell densities, forming the so-called blooms [1]. Cyanobacterial blooms were regarded as an aesthetic problem due to their scum-like appearance (green, brown, or red) and strong disagreeable odour. Cyanotoxin poisoning was first reported in an Australian lake in 1878 [2], and since the increased frequency of fish death, unknown hepatotoxic/neurotoxic diseases, and animal poisonings have led to an increased research interest and public awareness of harmful cyanobacterial blooms [1]

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