Industrial ecotoxicology in focus: The unexplored environmental impacts of pilot-scale advanced filtration in Sc recovery.

The demand within the European Union (EU) for the crucial raw material Scandium (Sc), coupled with the lack of sufficient recovery strategies, has gravitated research into exploiting alternative secondary sources. Utilizing residues from ore-production processes has proven to be a successful attempt for advanced Sc recovery. Despite the emergence of new technologies for Sc recovery from such residues, the potential environmental impacts of byproducts and technology wastes are often disregarded. Our study aimed to assess the environmental efficiency of a pilot-scale Sc recovery technology that relies solely on filtration. We employed a problem-specific ecotoxicity toolkit based on the approach of Direct Toxicity Assessment (DTA). The results of DTA provide an indication of the scale of the adverse effect of (contaminated) samples without the necessity of translating the results into chemical concentration. Standardized test methods (Aliivibrio fischeri bioluminescence inhibition, Daphnia magna lethality and Sinapis al b a root and shoot elongation inhibition) were applied, supplemented by a bioconcentration assessment with the D. magna bioaccumulation test method to gain insight on the bioaccumulation potential of different metals in the case of all samples from the filtration technology. Comprehensive genotoxicity evaluations were also implemented using three distinct test methods (Ames test, Ames MPF test, SOS Chromotest). We conducted a comparative direct toxicity assessment to anticipate the potential environmental impacts of residues generated at each filtration step on the aquatic ecosystem. Our findings indicate that the environmental impact of the generated intermediate and final residues was alleviated by the consecutive filtration steps employed. The pilot-scale application of the Sc recovery technology achieved a high and statistically significant reduction in toxicity according to each test organism during the filtration processes. Specifically, toxicity decreased by 73 %, 86 % and 87 % according to the Aliivibrio fischeri bioluminescence inhibition assay, the Sinapis alba shoot elongation inhibition test, and the Daphnia magna lethality test, respectively. The toolbox of industrial ecotoxicology is recommended to predict the environmental performance of metal recovery technologies related to potential ecosystem effects.

The potential of Hungarian bauxite residue isolates for biotechnological applications.

Bauxite residue (red mud) is considered an extremely alkaline and salty environment for the biota. We present the first attempt to isolate, identify and characterise microbes from Hungarian bauxite residues. Four identified bacterial strains belonged to the Bacilli class, one each to the Actinomycetia, Gammaproteobacteria, and Betaproteobacteria classes, and two to the Alphaproteobacteria class. All three identified fungi strains belonged to the Ascomycota division. Most strains tolerated pH 8-10 and salt content at 5-7% NaCl concentration. Alkalihalobacillus pseudofirmus BRHUB7 and Robertmurraya beringensis BRHUB9 can be considered halophilic and alkalitolerant. Priestia aryabhattai BRHUB2, Penicillium chrysogenum BRHUF1 and Aspergillus sp. BRHUF2 are halo- and alkalitolerant strains. Most strains produced siderophores and extracellular polymeric substances, could mobilise phosphorous, and were cellulose degraders. These strains and their enzymes are possible candidates for biotechnological applications in processes requiring extreme conditions, e.g. bioleaching of critical raw materials and rehabilitation of alkaline waste deposits.

Ecotoxicity characterization assisted performance assessment of electro-bioremediation reactors for nitrate and arsenite elimination.

The performance of combined reduction of nitrate (NO3 - ) to dinitrogen gas (N2 ) and oxidation of arsenite (As[III]) to arsenate (As[V]) by a bioelectrochemical system was assessed, supported by ecotoxicity characterization. For the comprehensive toxicity characterization of the untreated model groundwater and the treated reactor effluents, a problem-specific ecotoxicity test battery was established. The performance of the applied technology in terms of toxicity and target pollutant elimination was compared and analyzed. The highest toxicity attenuation was achieved under continuous flow mode with hydraulic retention time (HRT) = 7.5 h, with 95%, nitrate removal rate and complete oxidation of arsenite to arsenate. Daphnia magna proved to be the most sensitive test organism. The results of the D. magna lethality test supported the choice of the ideal operational conditions based on chemical data analysis. The outcomes of the study demonstrated that the applied technology was able to improve the groundwater quality in terms of both chemical and ecotoxicological characteristics. The importance of ecotoxicity evaluation was also highlighted, given that significant target contaminant elimination did not necessarily lower the environmental impact of the initial, untreated medium, in addition, anomalies might occur during the technology operational process which in some instances, could result in elevated toxicity levels.

Ecotoxicity attenuation by acid-resistant nanofiltration in scandium recovery from TiO2 production waste.

The lack of high-grade scandium (Sc) ores and recovery strategies has stimulated research on the exploitation of non-ore-related secondary sources that have great potential to safeguard the critical raw materials supply of the EU's economy. Waste materials may satisfy the growing global Sc demand, specifically residues from titanium dioxide (TiO2) production. New technologies are being developed for the recovery of Sc from such residues; however, the possible environmental impacts of intermediary products and residues are usually not considered. In order to provide a comprehensive ecotoxicity characterisation of the wastes and intermediate residues resulting from one promising new technology, acid-resistant nanofiltration (arNF), a waste-specific ecotoxicity toolkit was established. Three ecotoxicity assays were selected with specific test parameters providing the most diverse outcome for toxicity characterisation at different trophic levels: Aliivibrio fischeri (bacteria) bioluminescence inhibition (30 min exposure), Daphnia magna (crustacean) lethality and immobilisation (24 h exposure) and Lemna minor (plant) growth inhibition with determination of the frond number (7 d exposure). According to our results, the environmental impact of the generated intermediate and final residues on the aquatic ecosystem was mitigated by the consecutive steps of the filtration methods applied. High and statistically significant toxicity attenuation was achieved according to each test organism: toxicity was lowered based on EC20 values, according to the A. fischeri bioluminescence inhibition assay (by 97%), D. magna lethality (by 99%) and L. minor frond number (by 100%), respectively, after the final filtration step, nanofiltration, in comparison to the original waste. Our results underline the importance of assessing chemical technologies' ecotoxicological and environmental impacts with easy-to-apply and cost-effective test methods to showcase the best available technologies.

Passive electrobioremediation approaches for enhancing hydrocarbons biodegradation in contaminated soils.

Electrobioremediation technologies hold considerable potential for the treatment of soils contaminated by petroleum hydrocarbons (PH), since they allow stimulating biodegradation processes with no need for subsurface chemicals injection and with little to no energy consumption. Here, a microbial electrochemical snorkel (MES) was applied for the treatment of a soil contaminated by hydrocarbons. The MES consists of direct coupling of a microbial anode with a cathode, being a single conductive, non-polarized material positioned suitably to create an electrochemical connection between the anoxic zone (the contaminated soil) and the oxic zone (the overlying oxygenated water). Soil was also supplemented with electrically conductive particles of biochar as a strategy to construct a conductive network with microbes in the soil matrix, thus extending the radius of influence of the snorkel. The results of a comprehensive suite of chemical, microbiological and ecotoxicological analyses evidenced that biochar addition, rather than the presence of a snorkel, was the determining factor in accelerating PH removal from contaminated soils, possibly accelerating syntrophic and/or cooperative metabolisms involved in the degradation of PH. The enhancement of biodegradation was mirrored by an increased abundance of anaerobic and aerobic microorganisms known to be involved in the degradation of PH and related functional genes. Plant ecotoxicity assays confirmed a reduction of soils toxicity in treatments receiving electrically conductive biochar.

Effects of microscale particles in red mud amended artificial soils on bioaccumulation of elements in E. fetida.

Red mud (RM) contains large quantities of microscale particles < 1 µm and high concentrations of potentially toxic elements. In this research, we have used two types of RM of similar chemical properties but containing different quantities of micro-particles, to test whether their size plays a role in the uptake of chemical elements by earthworm Eisenia fetida. Earthworms were exposed for seven days to artificial soils (prepared in the laboratory following a protocol) amended with increasing quantities of RM. Mortality of 86 % occurred when earthworms were exposed to amended soil containing 46 % of particles below 1 µm. Surprisingly, tissue analyses have shown decreased concentrations of metals instead of the expected toxic effect. SEM analysis revealed that micro-particles strongly adhere to the earthworm epidermis putting them under the large stress. Micro-particles in RM clog their minute dermal pores of 90 nm-735 nm in diameter, which size depends on whether the earthworm's body is contracted or stretched. Strong adhesion of micro-particles to earthworms' epidermis and blockage of their microsize pores prevented normal dermal respiration and absorption of chemical elements through their epithelium resulting in a decrease of most measured metals, especially essential elements potassium, calcium and iron, followed by the lethal outcomes.

Long-term effects of grain husk and paper fibre sludge biochar on acidic and calcareous sandy soils - A scale-up field experiment applying a complex monitoring toolkit.

Biochar is produced from a wide range of organic materials by pyrolysis, specifically for improvement of poor quality soils. One of the main issues nowadays in studying biochar as soil amendment is to upscale experiments and move from short-term, laboratory conditions to long-term field trials. This paper presents a long-term field study, being the final step of a scale-up technology development, on grain husk and paper fibre sludge biochar application for soil improvement with focus on two degraded soil types of a temperate region. The effects of biochar on an acidic and a calcareous sandy agricultural soil were studied applying a complex approach including physico-chemical, biological and ecotoxicological methods. Our study demonstrated that the applied biochar had positive direct and indirect influences on the acidic sandy soil, but these effects were different in terms of extent and time. 30 t/ha biochar addition improved the pH of the acidic sandy soil by 24% and also increased significantly the nutrient concentrations (P2O5 by 68%, K2O by 11% and organic matter by 33%), and the water-holding capacity after 30 months. Furthermore, biochar addition improved also the microbiological activity and diversity in the acidic sandy soil. Biochar application did not induce any negative effects. Biochar had no toxic effect on the plants and the biochar-treated soil provided a more liveable habitat for soil living animals than the untreated acidic sandy soil. The favourable biochar-mediated influences on soil properties were manifested mainly in the acidic sandy soil, proving that the biochar-related advantages have to be verified for different soil types. The benefits of grain husk and paper fibre sludge biochar application in an acidic sandy soil were confirmed on the long term by the applied tiered approach.

Biochemical and reproductive effects of red mud to earthworm Eisenia fetida.

Red mud (RM) is the main waste of alumina production whose disposal poses a problem. The research of various possible effects of red mud on soil organisms has been scarce. We have exposed earthworms (Eisenia fetida) to red mud: artificial soil mixtures. The tested samples of red mud were of different origin: Croatian (CRRM) and Hungarian (HURM). The effects of exposure on the metabolic and oxidative status of earthworms were measured using several biochemical biomarkers (acetylcholinesterase, catalase and glutathione S-transferase activity and metallothionenin content) and reproductive success was assessed upon counting the number of hatched juveniles. The LC50 value for CRRM was 40% and for HURM 62% of red mud in the growth medium on weight basis, respectively. A significant effect (p < 0.001) of the RM concentration and origin, as well as significant interactions between the origin of RM and the applied concentrations on all measured biomarkers were observed. CRRM had a higher content of different metals as well as a higher conductivity in comparison to HURM. The reproduction was inhibited after exposure to both RMs. Namely, 25% CRRM caused a 53.26% reduction in the number of juveniles, whereas 18% HURM caused a 68.84% reduction, and 50% HURM caused 97.9% reduction, respectively. Both RMs caused changes in the measured biomarkers related to an oxidative stress. Consequently, the possible adverse effects on soil organisms before the environmental application of red mud should be assessed to avoid further environmental damage.

Re-using bauxite residues: benefits beyond (critical raw) material recovery.

Since the world economy has been confronted with an increasing risk of supply shortages of critical raw materials (CRMs), there has been a major interest in identifying alternative secondary sources of CRMs. Bauxite residues from alumina production are available at a multi-million tonnes scale worldwide. So far, attempts have been made to find alternative re-use applications for bauxite residues, for instance in cement / pig iron production. However, bauxite residues also constitute an untapped secondary source of CRMs. Depending on their geological origin and processing protocol, bauxite residues can contain considerable amounts of valuable elements. The obvious primary consideration for CRM recovery from such residues is the economic value of the materials contained. However, there are further benefits from re-use of bauxite residues in general, and from CRM recovery in particular. These go beyond monetary values (e.g. reduced investment / operational costs resulting from savings in disposal). For instance, benefits for the environment and health can be achieved by abatement of tailing storage as well as by reduction of emissions from conventional primary mining. Whereas certain tools (e.g. life-cycle analysis) can be used to quantify the latter, other benefits (in particular sustained social and technological development) are harder to quantify. This review evaluates strategies of bauxite residue re-use / recycling and identifies associated benefits beyond elemental recovery. Furthermore, methodologies to translate risks and benefits into quantifiable data are discussed. Ultimately, such quantitative data are a prerequisite for facilitating decision-making regarding bauxite residue re-use / recycling and a stepping stone towards developing a zero-waste alumina production process. © 2018 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Influence of red mud on soil microbial communities: Application and comprehensive evaluation of the Biolog EcoPlate approach as a tool in soil microbiological studies.

Red mud can be applied as soil ameliorant to acidic, sandy and micronutrient deficient soils. There are still knowledge gaps regarding the effects of red mud on the soil microbial community. The Biolog EcoPlate technique is a promising tool for community level physiological profiling. This study presents a detailed evaluation of Biolog EcoPlate data from two case studies. In experiment "A" red mud from Ajka (Hungary) was mixed into acidic sandy soil in soil microcosms at 5-50 w/w%. In experiement "B" red mud soil mixture was mixed into low quality subsoil in a field experiment at 5-50 w/w%. According to average well color development, substrate average well color development and substrate richness 5-20% red mud increased the microbial activity of the acidic sandy soil over the short term, but the effect did not last for 10months. Shannon diversity index showed that red mud at up to 20% did not change microbial diversity over the short term, but the diversity decreased by the 10th month. 30-50% red mud had deteriorating effect on the soil microflora. 5-20% red mud soil mixture in the low quality subsoil had a long lasting enhancing effect on the microbial community based on all Biolog EcoPlate parameters. However, 50% red mud soil mixture caused a decrease in diversity and substrate richness. With the Biolog EcoPlate we were able to monitor the changes of the microbial community in red mud affected soils and to assess the amount of red mud and red mud soil mixture applicable for soil treatment in these cases.

The potential application of red mud and soil mixture as additive to the surface layer of a landfill cover system.

Red mud, the by-product of aluminum production, has been regarded as a problematic residue all over the world. Its storage involves risks as evidenced by the Ajka red mud spill, an accident in Hungary where the slurry broke free, flooding the surrounding areas. As an immediate remediation measure more than 5cm thick red mud layer was removed from the flooded soil surface. The removed red mud and soil mixture (RMSM) was transferred into the reservoirs for storage. In this paper the application of RMSM is evaluated in a field study aiming at re-utilizing waste, decreasing cost of waste disposal and providing a value-added product. The purpose was to investigate the applicability of RMSM as surface layer component of landfill cover systems. The field study was carried out in two steps: in lysimeters and in field plots. The RMSM was mixed at ratios ranging between 0 and 50% w/w with low quality subsoil (LQS) originally used as surface layer of an interim landfill cover. The characteristics of the LQS+RMSM mixtures compared to the subsoil (LQS) and the RMSM were determined by physical-chemical, biological and ecotoxicological methods. The addition of RMSM to the subsoil (LQS) at up to 20% did not result any ecotoxic effect, but it increased the water holding capacity. In addition, the microbial substrate utilization became about triple of subsoil (LQS) after 10months. According to our results the RMSM mixed into subsoil (LQS) at 20% w/w dose may be applied as surface layer of landfill cover systems.

Direct toxicity assessment - Methods, evaluation, interpretation.

Direct toxicity assessment (DTA) results provide the scale of the actual adverse effect of contaminated environmental samples. DTA results are used in environmental risk management of contaminated water, soil and waste, without explicitly translating the results into chemical concentration. The end points are the same as in environmental toxicology in general, i.e. inhibition rate, decrease in the growth rate or in yield and the 'no effect' or the 'lowest effect' measurement points of the sample dilution-response curve. The measurement unit cannot be a concentration, since the contaminants and their content in the sample is unknown. Thus toxicity is expressed as the sample proportion causing a certain scale of inhibition or no inhibition. Another option for characterizing the scale of toxicity of an environmental sample is equivalencing. Toxicity equivalencing represents an interpretation tool which enables toxicity of unknown mixtures of chemicals be converted into the concentration of an equivalently toxic reference substance. Toxicity equivalencing, (i.e. expressing the toxicity of unknown contaminants as the concentration of the reference) makes DTA results better understandable for non-ecotoxicologists and other professionals educated and thinking based on the chemical model. This paper describes and discusses the role, the principles, the methodology and the interpretation of direct toxicity assessment (DTA) with the aim to contribute to the understanding of the necessity to integrate DTA results into environmental management of contaminated soil and water. The paper also introduces the benefits of the toxicity equivalency method. The use of DTA is illustrated through two case studies. The first case study focuses on DTA of treated wastewater with the aim to characterize the treatment efficacy of a biological wastewater treatment plant by frequent bioassaying. The second case study applied DTA to investigate the cover layers of two bauxite residue (red mud) reservoirs. Based on the DTA results the necessary toxicity attenuation rate of the cover layers was estimated.

Acidic sandy soil improvement with biochar - A microcosm study.

Biochar produced from a wide range of organic materials by pyrolysis has been reported as a means to improve soil physical properties, fertility and crop productivity. However, there is a lack of studies on the complex effects of biochar both on the degraded sandy soil physico-chemical properties and the soil biota as well as on toxicity, particularly in combined application with fertilizer and compost. A 7-week microcosm experiment was conducted to improve the quality of an acidic sandy soil combining variations in biochar types and amounts, compost and fertilizer application rates. The applied biochars were produced from different feedstocks such as grain husks, paper fibre sludge and wood screenings. The main purpose of the microcosm experiment was to assess the efficiency and applicability of different biochars as soil amendment prior to field trials and to choose the most efficient biochar to improve the fertility, biological activity and physical properties of acidic sandy soils. We complemented the methodology with ecotoxicity assessment to evaluate the possible risks to the soil as habitat for microbes, plants and animals. There was clear evidence of biochar-soil interactions positively affecting both the physico-chemical properties of the tested acidic sandy soil and the soil biota. Our results suggest that the grain husk and the paper fibre sludge biochars applied to the tested soil at 1% and 0.5 w/w% rate mixed with compost, respectively can supply a more liveable habitat for plants and soil living animals than the acidic sandy soil without treatment.

Ecotoxicity of fluvial sediments downstream of the Ajka red mud spill, Hungary.

An integrated assessment of biological activity and ecotoxicity of fluvial sediments in the Marcal river catchment (3078 km(2)), western Hungary, is presented following the accidental spill of bauxite processing residue (red mud) in Ajka. Red mud contaminated sediments are characterised by elevated pH, elevated trace element concentrations (e.g. As, Co, Cr, V), high exchangeable Na, and induce an adverse effect on test species across a range of trophic levels. While background contamination of the river system is highlighted by adverse effects on some test species at sites unaffected by red mud, the most pronounced toxic effects apparent in Vibrio fischeri bioluminescence inhibition, Lemna minor bioassay and Sinapis alba root and shoot growth occur at red mud depositional hotspots in the lower Torna Creek and upper Marcal. Heterocypris incongruens bioassays show no clear patterns, although the most red mud-rich sites do exert an adverse effect. Red mud does however appear to induce an increase in the density of aerobic and facultative anaerobic bacterial communities when compared with unaffected sediments and reference sites. Given the volume of material released in the spill, it is encouraging that the signal of the red mud on aquatic biota is visible at a relatively small number of sites. Gypsum-affected samples appear to induce an adverse effect in some bioassays (Sinapis alba and Heterocypris incongruens), which may be a feature of fine grain size, limited nutrient supply and greater availability of trace contaminants in the channel reaches that are subject to intense gypsum dosing. Implications for monitoring and management of the spill are discussed.

Dispersal and attenuation of trace contaminants downstream of the Ajka bauxite residue (red mud) depository failure, Hungary.

This paper identifies the spatial extent of bauxite processing residue (red mud)-derived contaminants and modes of transport within the Marcal and Rába river systems after the dike failure at Ajka, western Hungary. The geochemical signature of the red mud is apparent throughout the 3076 km² Marcal system principally with elevated Al, V, As, and Mo. Elevated concentrations of Cr, Ga, and Ni are also observed within 2 km of the source areas in aqueous and particulate phases where hyperalkalinity (pH < 13.1) is apparent. Although the concentrations of some trace elements exceed aquatic life standards in waters (e.g., V, As) and fluvial sediments (As, Cr, Ni, V), the spatial extent of these is limited to the Torna Creek and part of the upper Marcal. Source samples show a bimodal particle size distribution (peaks at 0.7 and 1.3 µm) which lends the material to ready fluvial transport. Where elevated concentrations are found in fluvial sediments, sequential extraction suggests the bulk of the As, Cr, Ni, and V are associated with residual (aqua-regia/HF digest) phases and unlikely to be mobile in the environment. However, at some depositional hotspots, association of As, Cr, and V with weak acid-extractable phases is observed.