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

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.

Role of Rhizospheric Microbiota as a Bioremediation Tool for the Protection of Soil-Plant Systems from Microcystins Phytotoxicity and Mitigating Toxin-Related Health Risk

“…MC extraction from plant samples was conducted as described by Bavithra et al (2020) [ 47 ]. Freeze-dried roots and shoots were ground into fine powder in liquid nitrogen.…”

Progress in Multi-Soil-Layering Systems for Wastewater Treatment

“…Among the MCs, the most toxic is MC-LR [57]. Although slow sand filtration [58] and CW technologies [59] have shown good performance for MC-LR treatment, more studies are required for large-scale applications of slow sand filtration. In addition, CWs require large land areas.…”

Multi-Soil-Layering Technology: A New Approach to Remove Microcystis aeruginosa and Microcystins from Water

“…Eco-technological purification systems for the removal of cyanobacterial contaminants include constructed wetlands (CWs) using various types of plants [165][166][167], depending on whether these plants have purifying effects on the cyanotoxins in question or household slow sand filters [165][166][167]. For instance, a study with CWs [167] found MC-LR reductions from 5.55 g L −1 to less than 0.1 g L −1 , as well as a 2.39 log 10 unit reduction in Microcystis aeruginosa, while Bavithra et al [165] showed 94-99% cyanobacteria and microcystins (MC-LR) removal from lake water in CWmicrocosms. Moreover, in these eco-technologies, some propose the development of biofilm-based reactors by recycling reverse osmosis (RO) membranes used in desalination plants that have reached the end of their working life.…”

“…For example, studies have shown that clays such as montmorillonite, kaolinite, smectite, and illite interact electrostatically with MCs due to their chemical composition, allowing adsorption and trapping of these molecules on the surface of clay particles. Similarly, incorporating porous materials [165] such as zeolite, pumice, or pozzolan plays a crucial role in the simultaneous removal of cyanobacteria and cyanotoxins, especially when these materials have considerable porosity in the form of meso-and macropores [102,159].…”