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 and thus, are 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 them with beneficial properties such as protective functions against other organisms. Besides odor and taste substances, species such as AnabaenaAphanizomenonCylindrospermopsisMicrocystisNodularia and Oscillatoria generate a range of intra- and extracellular hepato-, neuro-, derma- and endotoxins harmful to animals, birds and humans. Intoxications with so called cyanotoxins are 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 even human poisoning, and in some cases subsequent deaths, have been associated with cyanotoxins – and are still happening as documented in recent reports and reviews. These toxic compounds can mainly be found in the aquatic environment, posing a major risk to surface waters intended for drinking and recreational purposes; especially as the (anthropogenic) eutrophication of our waterbodies increases, providing a very fruitful habitat for cyanobacteria and thus promoting more frequently occurring toxic 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. The research on cyanobacteria and cyanotoxins as well as appropriate removal techniques is still in progress and there is a lack of crucial knowledge. Many countries have not yet enforced strict regulations regarding maximum tolerable cyanotoxin levels in drinking water. Furthermore, the WHO currently proposed a provisional guideline value for only a single cyanotoxins - 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, France and New Zealand went 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 effectiveness and 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, 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.

What happened so far

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 review and analysis are 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 identified 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 % of the studies. 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 was published as deliverable to the EU in summer 2018 and a brief overview of the results of this literature review was presented at the SETAC Europe meeting in Rome in May 2018.

Besides this literature-based work, first experiments using ozone and Fenton’s reagent (Fe2+ in combination with hydrogen peroxide) for the removal of a selected (less studied) cyanotoxin cylindrospermopsin were conducted. Furthermore, during a secondment at the Leibniz Institute for Plasma Science and Technology in Greifswald, Germany, different plasmas were screened for their applicability for the removal of cyanotoxins. Following the initial screening, two plasmas, a pulsed corona discharge and a pulsed dielectric barrier discharge were selected for more in-depth studies. The data from this research is currently processed and the results will presumably be prepared for publication in the first half of 2019. They will also be presented at conferences during 2019. In addition, more experiments with ozone and Fenton oxidation will be conducted in the near future.

In 2019, ESR12 will participate at two NaToxAq Ph.D. Schools in Barcelona and Leipzig as well as at secondments at non-academic partners – water-treatment companies - Aigües de Barcelona, Barcelona, and Veolia, Copenhagen.