ESR12 Marcel Schneider – University of Copenhagen

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ESR12 Marcel Schneider

Project: Water treatment operations to remove natural toxins from surface water

Principal supervisor: Prof. Luděk Bláha, Ph.D.

Intro to project: 

Cyanobacteria, also known as blue-green algae, are phototrophic prokaryotes inhabiting the earth for billions of years being one of the oldest known groups of microorganisms. They utilize photosynthesis in order to produce energy and metabolize inorganic and organic matter. As secondary metabolites, some cyanobacteria produce toxic substances assumingly providing protective functions against other organisms. Besides odor and taste substances, species such as Anabaena, Aphanizomenon, Cylindrospermopsis, Microcystis, Nodularia and Oscillatoria generate a range of intra- and extracellular hepato-, neuro-, derma- and endotoxins harmful to animals, birds and humans. Intoxication with so called cyanotoxins is evidently known for almost 150 years, raising interest and concern of farmers, scientists and water treatment plant operators since then. Until now, numerous incidences of pet, livestock and/or wildlife or human poisoning, and in some cases subsequent deaths, have been associated with cyanotoxins – and are still happening. These toxic compounds can mainly be found in the aquatic environment, posing a major risk towards surface waters intended for drinking and recreational purposes; especially as the (anthropogenic) eutrophication of our waterbodies seems to increase, providing a very fruitful habitat for cyanobacteria and thus promoting more and more frequent blooms.

Most people know cyanobacteria only from newspaper articles or signs at beaches advising them not to ingest or come into contact with algal mats, but are not aware of the struggles environmental authorities and water treatment plant operators are facing in order to provide cyanobacteria-free and harmless drinking water. Since the research on cyanobacteria, cyanotoxins and appropriate removal techniques is still in progress and lacks crucial knowledge, many countries have not yet enforced strict regulations regarding maximum tolerable cyanotoxin levels in drinking water. Furthermore, the WHO only proposed a provisional guideline value for microcystin-LR of 1 μg/L in drinking water, mainly due to the lack of ecological and toxicological data for other cyanotoxins. Only few countries, e.g. Australia, Czech Republic, France and New Zealand go beyond this suggestion and added limiting values for other cyanotoxins within their drinking water directives/regulations. One of the main problems in regard to this topic is the diversity of these toxins which sometimes can result in insufficient removal when conventional water treatment processes are applied.

As part of the NaToxAq network, ESR12 focuses on water treatment operations targeting selected cyanotoxins by assessing various techniques for their removal efficiencies, including mainly emerging methods such as advanced oxidation processes and non-thermal plasma-based approaches. As the degradation of cyanotoxins during drinking water treatment does not necessarily lead to complete mineralization of these compounds, one objective of this project is to identify potential degradation intermediates and products formed during the treatment, propose possible degradation pathways and assess their toxicological properties using in vitro tests.

Progress in the first year

The first objective of this project is focused on preparing an extensive literature review in the context of “Treatment techniques for the removal of cyanotoxins from drinking water” to summarize and assess the current state-of-the-art and to identify information gaps. In order to do so, the currently available scientific literature for this specific topic was examined to reveal preferences in research towards i) certain cyanotoxins in regard to their removal from drinking water, and ii) treatment techniques used to remove cyanotoxins from drinking water. This analysis is based on the number of publications found within this search employing a range of pre-selected and defined search parameters using the Web of Knowledge service. More than 500 publications were found reporting the removal of cyanotoxins from drinking water employing either Advanced Oxidation Processes (AOPs) or conventional and other emerging treatment techniques. About 78 % of all publications focus on the treatment of microcystins, which are the most commonly occurring and thus, most commonly studied cyanotoxins. In terms of preferences in applied treatment techniques, conventional and other emerging methods (incl. biodegradation, adsorption, chemical oxidation and others) are reportedly used in about 62 % of all publications, whereas AOPs (incl. photolysis/-catalysis, ozonation, Fenton oxidation, non-thermal plasmas and others) account for about 38 %. In general, treatment techniques that are already widely applied in drinking water treatment seem to receive more attention than techniques that were originally not meant to be used for water treatment, for example non-thermal plasmas, radiolysis or electrochemical oxidation. A more detailed review will be published as deliverable to the EU in summer 2018 and a brief overview of the results of this literature review will be presented at this year’s SETAC Europe meeting in Rome in May 2018.

Besides this literature-based work, first preliminary experiments using ozone for the removal of cylindrospermopsin were conducted. Further and more extensive experiments as well as the first secondment at the Leibniz Institute for Plasma Science and Technology (INP) in Greifswald, Germany, where non-thermal plasmas will be examined for their application for the removal of cyanotoxins are planned and prepared at this moment.