Continuous long-term monitoring of leaching from microplastics into ambient water - A multi-endpoint approach.

Widespread pollution of aquatic environments by microplastics (MPs) is a serious environmental threat. Despite the knowledge of their occurrence and properties rapidly evolving, the potential leaching from MPs remains largely unexplored. In this study, 16 different types of MPs prepared from consumer products were kept in long-term contact with water, while the leachates were continuously analysed. Most of the MPs released significant amounts of dissolved organic carbon, up to approximately 65 mg per g MPs after 12 weeks of leaching, and some MPs also released dissolved inorganic carbon. Other elements identified in the leachates were Al, Ba, Ca, Fe, K, Mg, Mn, Na, Si, and Zn. Of those, Ca, K, and Na were detected most frequently, while Ca reached the highest amounts (up to almost 2.5 mg per g MPs). Additionally, 80 organic individuals were tentatively identified in the leachates, mostly esters, alcohols, and carboxylic acids. Some compounds considered harmful to human health and/or the environment were detected, e.g., bisphenol A or phthalate esters. The current results provide insight into the transfer of various compounds from MPs to ambient water, which might have consequences on the fluxes of carbon and metals, as well as of specific organic contaminants.

Current knowledge in the field of algal organic matter adsorption onto activated carbon in drinking water treatment.

The increasing occurrence of algal and cyanobacterial blooms and the related formation of algal organic matter (AOM) is a worldwide issue that endangers the quality of freshwater sources and affects water treatment processes. The associated problems involve the production of toxins or taste and odor compounds, increasing coagulant demand, inhibition of removal of other polluting compounds, and in many cases, AOM acts as a precursor of disinfection by-products. Previous research has shown that for sufficient AOM removal, the conventional drinking water treatment based on coagulation/flocculation must be often accompanied by additional polishing technologies such as adsorption onto activated carbon (AC). This state-of-the-art review is intended to serve as a summary of the most current research on the adsorption of AOM onto AC concerning drinking water treatment. It summarizes emerging trends in this field with an emphasis on the type of AOM compounds removed and on the adsorption mechanisms and influencing factors involved. Additionally, also the principles of competitive adsorption of AOM and other organic pollutants are elaborated. Further, this paper also synthesizes previous knowledge on combining AC adsorption with other treatment techniques for enhanced AOM removal in order to provide a practical resource for researchers, water treatment plant operators and engineers. Finally, research gaps regarding the AOM adsorption onto AC are identified, including, e.g., adsorption of AOM residuals recalcitrant to coagulation/flocculation, suitability of pre-oxidation of AOM prior to the AC adsorption, relationships between the solution properties and AOM adsorption behaviour, or AOM as a cause of competitive adsorption. Also, focus should be laid on continuous flow column experiments using water with multi-component composition, because these would greatly contribute to transferring the theoretical knowledge to practice.

In Vitro Study of the Toxicity Mechanisms of Nanoscale Zero-Valent Iron (nZVI) and Released Iron Ions Using Earthworm Cells.

During the last two decades, nanomaterials based on nanoscale zero-valent iron (nZVI) have ranked among the most utilized remediation technologies for soil and groundwater cleanup. The high reduction capacity of elemental iron (Fe0) allows for the rapid and cost-efficient degradation or transformation of many organic and inorganic pollutants. Although worldwide real and pilot applications show promising results, the effects of nZVI on exposed living organisms are still not well explored. The majority of the recent studies examined toxicity to microbes and to a lesser extent to other organisms that could also be exposed to nZVI via nanoremediation applications. In this work, a novel approach using amoebocytes, the immune effector cells of the earthworm Eisenia andrei, was applied to study the toxicity mechanisms of nZVI. The toxicity of the dissolved iron released during exposure was studied to evaluate the effect of nZVI aging with regard to toxicity and to assess the true environmental risks. The impact of nZVI and associated iron ions was studied in vitro on the subcellular level using different toxicological approaches, such as short-term immunological responses and oxidative stress. The results revealed an increase in reactive oxygen species production following nZVI exposure, as well as a dose-dependent increase in lipid peroxidation. Programmed cell death (apoptosis) and necrosis were detected upon exposure to ferric and ferrous ions, although no lethal effects were observed at environmentally relevant nZVI concentrations. The decreased phagocytic activity further confirmed sublethal adverse effects, even after short-term exposure to ferric and ferrous iron. Detection of sublethal effects, including changes in oxidative stress-related markers such as reactive oxygen species and malondialdehyde production revealed that nZVI had minimal impacts on exposed earthworm cells. In comparison to other works, this study provides more details regarding the effects of the individual iron forms associated with nZVI aging and the cell toxicity effects on the specific earthworms' immune cells that represent a suitable model for nanomaterial testing.

Occurrence and fate of microplastics at two different drinking water treatment plants within a river catchment.

Microplastics (MPs) are emerging globally distributed pollutants of aquatic environments, and little is known about their fate at drinking water treatment plants (DWTPs), which provide a barrier preventing MPs from entering water for human consumption. This study investigated MPs ≥ 1 µm in raw and treated water of two DWTPs that both lie on the same river, but the local quality of water and the treatment technology applied differ. In the case of the more complex DWTP, MPs were analysed at 4 additional sampling sites along the treatment chain. The content of MPs varied greatly between the DWTPs. There were 23 ±â€¯2 and 14 ±â€¯1 MPs L-1 in raw and treated water, respectively, at one DWTP, and 1296 ±â€¯35 and 151 ±â€¯4 MPs L-1 at the other. Nevertheless, MPs comprised only a minor proportion (<0.02%) of all detected particles at both DWTPs. With regard to size and shape of MPs, the majority (>70%) were smaller than 10 µm, and only fragments and fibres were found, while fragments clearly prevailed. The most frequently occurring materials were cellulose acetate, polyethylene terephthalate, polyvinyl chloride, polyethylene, and polypropylene. Much higher total removal of MPs was achieved at the DWTP with a higher initial MP load and more complicated treatment (removal of 88% versus 40%); coagulation-flocculation-sedimentation, deep-bed filtration through clay-based material, and granular activated carbon filtration contributed to MP elimination by 62%, 20%, and 6%, respectively. Additionally, results from this more complex DWTP enabled to observe relationships between the removal efficiency and size and shape of MPs, particularly in the case of the filtration steps.

Influence of COM-peptides/proteins on the properties of flocs formed at different shear rates.

Coagulation followed by floc separation is a key process for the removal of algal organic matter (AOM) in water treatment. Besides optimizing coagulation parameters, knowledge of the properties of AOM-flocs is essential to maximizing AOM removal. However, the impact of AOM on the floc properties remains unclear. This study investigated how peptides/proteins derived from the cellular organic matter (COM) of the cyanobacterium Microcystis aeruginosa influenced the size, structure, and shape of flocs formed at different shear rates (G). Flocs formed by kaolinite, COM-peptides/proteins and a mixture of the same were studied, and the effect of intermolecular interactions between floc components on floc properties was assessed. The coagulation experiments were performed in a Taylor-Couette reactor, with aluminum (Al) or ferric sulphate (Fe) utilized as coagulants. Image analysis was performed to gauge floc size and obtain data on fractal dimension. It was found that floc properties were affected by the presence of the COM-peptides/proteins and the coagulant used. COM-peptides/proteins increased floc size and porosity and widened floc size distributions. The Fe coagulant produced larger and less compact flocs than Al coagulant. Moreover, the decrease in floc size that occurred in parallel with increase in shear rate was not smooth in progress. A rapid change for the kaolinite-coagulant suspension and two rapid changes for the suspensions containing COM were observed. These were attributed to various intermolecular interactions between floc components participating in coagulation at different G. Based on the results obtained, shear rates suitable for efficient separation of flocs containing COM were suggested.

Microplastics in drinking water treatment - Current knowledge and research needs.

Microplastics (MPs) have recently been detected in oceans, seas and freshwater bodies worldwide, yet few studies have revealed the occurrence of MPs in potable water. Although the potential toxicological effects of MPs are still largely unknown, their presence in water intended for human consumption deserves attention. Drinking water treatment plants (DWTPs) pose a barrier for MPs to enter drinking water; thus, the fate of MPs at DWTPs is of great interest. This review includes a summary of the available information on MPs in drinking water sources and in potable water, discusses the current knowledge on MP removal by different water treatment processes, and identifies the research needs regarding MP removal by DWTP technologies. A comparison of MPs with other common pollution agents is also provided. We concluded that special attention should be given to small-size MPs (in the range of several micrometres) and that the relationship between MP character and behaviour during distinct treatment processes should be explored.

The impact of pre-oxidation with potassium permanganate on cyanobacterial organic matter removal by coagulation.

The study investigates the effect of permanganate pre-oxidation on the coagulation of peptides/proteins of Microcystis aeruginosa which comprise a major proportion of the organic matter during cyanobacterial bloom decay. Four different permanganate dosages (0.1, 0.2, 0.4 and 0.6 mg KMnO4 mg-1 DOC) were applied prior to coagulation by ferric sulphate. Moreover, changes in sample characteristics, such as UV254, DOC content and molecular weight distribution, after pre-oxidation were monitored. The results showed that permanganate pre-oxidation led to a reduction in coagulant dose, increased organic matter removals by coagulation (by 5-12% depending on permanganate dose), microcystin removal (with reductions of 91-96%) and a shift of the optimum pH range from 4.3 to 6 without to 5.5-7.3 with pre-oxidation. Degradation of organic matter into inorganic carbon and adsorption of organic matter onto hydrous MnO2 are suggested as the main processes responsible for coagulation improvement. Moreover, permanganate prevented the formation of Fe-peptide/protein complexes that inhibit coagulation at pH about 6.2 without pre-oxidation. The study showed that carefully optimized dosing of permanganate improves cyanobacterial peptide/protein removal, with the benefit of microcystin elimination.

A comparison of the character of algal extracellular versus cellular organic matter produced by cyanobacterium, diatom and green alga.

This study investigated characteristics of algal organic matter (AOM) derived from three species (cyanobacterium Microcystis aeruginosa, diatom Fragilaria crotonensis and green alga Chlamydomonas geitleri) which dominate phytoplanktonic populations in reservoirs supplying drinking water treatment plants. Algal growth was monitored by cell counting, optical density and dissolved organic carbon concentration measurements. Extracellular organic matter (EOM) released at exponential and stationary growth phases and cellular organic matter (COM) were characterised in terms of specific UV absorbance (SUVA), peptide/protein and non-peptide content, hydrophobicity and molecular weight (MW). It was found that both EOM and COM were predominantly hydrophilic with low SUVA. COM was richer in peptides/proteins, more hydrophilic (with about 89% of hydrophilic fraction for all three species) and had lower SUVA than EOM. MW fractionation showed that both EOM and COM of all three species contain large portions of low-MW (<1 kDa) compounds and high-MW (>100 kDa) polysaccharides. Peptides/proteins exhibited narrower MW distribution than non-peptide fraction and it widened as the cultures grew. The highest amount of peptides/proteins with a significant portion of high-MW ones (22%) was observed in COM of M. aeruginosa. The results imply that the knowledge of AOM composition and characteristics predetermine which processes would be effective in the treatment of AOM laden water.

Coagulation of peptides and proteins produced by Microcystis aeruginosa: Interaction mechanisms and the effect of Fe-peptide/protein complexes formation.

This paper focuses on elucidation of the mechanisms involved in the coagulation of peptides and proteins contained in cellular organic matter (COM) of cyanobacterium Microcystis aeruginosa by ferric coagulant. Furthermore, coagulation inhibition due to the formation of Fe-peptide/protein surface complexes was evaluated. The results of coagulation testing imply that removability of peptides and proteins is highly dependent on pH value which determines charge characteristics of coagulation system compounds and therefore the mechanisms of interactions between them. The highest peptide/protein removal was obtained in the pH range of 4-6 owing to charge neutralization of peptide/protein negative surface by positively charged hydrolysis products of ferric coagulant. At low COM/Fe ratio (COM/Fe <0.33), adsorption of peptides/proteins onto ferric oxide-hydroxide particles, described as electrostatic patch model, enables the coagulation at pH 6-8. On the contrary, steric stabilization reduces coagulation at pH 6-8 if the ratio COM/Fe is high (COM/Fe >0.33). Coagulation of peptides and proteins is disturbed at pH 6-7 as a consequence of Fe-peptide/protein complexes formation. The maximum ability of peptides/proteins to form soluble complexes with Fe was found just at pH 6, when peptides/proteins bind 1.38 mmol Fe per 1 g of peptide/protein DOC. Complex forming peptides and proteins of relative molecular weights of 1, 2.8, 6, 8, 8.5, 10 and 52 kDa were isolated by affinity chromatography.

The effect of global velocity gradient on the character and filterability of aggregates formed during the coagulation/flocculation process.

This paper describes the influence of the global velocity gradient G on the properties of aggregates formed during the coagulation/flocculation process. The methods of image and fractal analysis were used to determine aggregate size and structure, respectively. The influence of these aggregate properties on separation using depth filtration is also described. Experiments were conducted in a pilot plant operation. The suspension was formed in a flow mixing tank with global velocity gradients ranging from 28.4-307.2 s(-1) and ferric sulphate used as a coagulant. Filtration velocities were 3 and 6 m h(-1). Predictably, it was shown that the aggregate size decreased with increasing global velocity gradient G. Furthermore it was demonstrated that, with increasing G, the aggregates became more compact and regular (the D2 fractal dimension increased) and the suspension became more homogeneous in size. The aggregates with the smallest diameter and highest D2 fractal dimension displayed the best filterability, i.e. penetrated throughout the full depth of the filter bed and generated a minimum pressure drop.

Optimized reaction conditions for removal of cellular organic matter of Microcystis aeruginosa during the destabilization and aggregation process using ferric sulfate in water purification.

The efficiency of removal of cellular organic matter (COM) of cyanobacteria Microcystis aeruginosa from water with ferric sulfate is influenced primarily by coagulant dosage and reaction pH. Therefore, optimization of the reaction conditions is a prerequisite for efficient purification of surface waters. Because the isoelectric point of COM occurs at a low pH, the purification of waters containing this organic matter should take place in an acidic pH range. It was also found that proteins are removed more efficiently than other organic substances (mainly polysaccharides).

Evaluation of the production, composition and aluminum and iron complexation of algogenic organic matter.

This paper aims at the characterization of algogenic organic matter (AOM) produced by the cyanobacteria Anabaena flos-aqua and Microcystis aeruginosa and the green algae Scenedesmus quadricauda. Further, it is focused on the description of differences in the composition of extracellular organic matter (EOM) and intracellular organic matter (IOM), and on the demonstration of AOM affinity to aluminum and iron coagulants. The results from the conducted analyses imply a significant difference in the amount and properties of the proteins contained in EOM in comparison to IOM. The differences in the production of proteins also depend on the species of microorganism observed and its growth phase; ageing of the culture is accompanied by a gradual increase of the portion of proteins forming AOM. Using affinity chromatography (AC), the proteins with relative molecular weight around 60 kDa were isolated as a component of AOM of cyanobacteria A. flos-aqua and M. aeruginosa. These proteins are able to form complex compounds with iron and aluminum.