Activated carbon in sediment remediation : benefits, risks and perspectives

Klassieke verontreinigingen zoals hydrofobe organische verbindingen (HOCs) komen uiteindelijk vaak in waterbodems terecht. Deze waterbodems kunnen hierdoor zelf een bron van verontreiniging worden en zo een risico vormen voor aquatische organismen en voor de mens. Traditionele manieren om waterbodems te reinigen, zoals baggeren en in situ capping, zorgen voor een grote verstoring van het benthische milieu en zijn niet altijd effectief, terwijl zij wel hoge kosten met zich meebrengen. Daarom is het nodig om nieuwe methoden voor reiniging van waterbodems te ontwikkelen die makkelijker zijn, minder kosten en minder verstorend zijn dan de bestaande methoden. De afgelopen jaren is de mogelijkheid onderzocht om adsorberende materialen zoals actieve kool (AC) toe te voegen aan verontreinigde waterbodems om zo de HOC concentratie in het water te verminderen. Dit onderzoek heeft als doel om het effect van toevoegen van AC op HOC blootstelling en toxiciteitsafname voor bentische organismen en gemeenschappen beter te begrijpen, om zo het gat tussen laboratorium en veld te dichten

Bioremediation in marine ecosystems: a computational study combining ecological modeling and flux balance analysis

The pressure to search effective bioremediation methodologies for contaminated ecosystems has led to the large-scale identification of microbial species and metabolic degradation pathways. However, minor attention has been paid to the study of bioremediation in marine food webs and to the definition of integrated strategies for reducing bioaccumulation in species. We propose a novel computational framework for analysing the multiscale effects of bioremediation at the ecosystem level, based on coupling food web bioaccumulation models and metabolic models of degrading bacteria. The combination of techniques from synthetic biology and ecological network analysis allows the specification of arbitrary scenarios of contaminant removal and the evaluation of strategies based on natural or synthetic microbial strains. In this study, we derive a bioaccumulation model of polychlorinated biphenyls (PCBs) in the Adriatic food web, and we extend a metabolic reconstruction of Pseudomonas putida KT2440 (iJN746) with the aerobic pathway of PCBs degradation. We assess the effectiveness of different bioremediation scenarios in reducing PCBs concentration in species and we study indices of species centrality to measure their importance in the contaminant diffusion via feeding links. The analysis of the Adriatic sea case study suggests that our framework could represent a practical tool in the design of effective remediation strategies, providing at the same time insights into the ecological role of microbial communities within food webs

Stabilisering av fibersediment : Förstudie av hållfasthet och föroreningsläckage

Massaindustrin har gett ifrån sig stora mängder träfibrer och processkemikalier från olika utsläppskällor vid Sveriges östkust. Fibrer och föroreningar som är bundna till dem (både metaller och organiska föroreningar), ligger idag ackumulerade utanför eller nedströms de olika utsläppskällorna och bildar så kallade fiberbankar (huvudsakligen fibermaterial) och fiberhaltiga sediment (fibermaterial uppblandat med naturliga sediment bestående mestadels av leror). Naturlig översedimentering av fiberbankar med nya, renare sediment har konstaterats i enskilda fall men är inte vanligt förekommande. Ett kontinuerligt läckage, tillsammans med andra naturliga processer som t.ex. landhöjning och undervattensskred samt mänskliga aktiviteter i områdena som utbyggnad av hamnar och olika typer av ledningar kan bidra till att föroreningar som ligger begravda riskerar att spridas. Sanering av fiberbankar kan i olika grad vara problematisk på grund av fiberbankars låga kompakt- och skrymdensitet. Det finns därför ett stort behov av effektiva metoder för att kunna hantera en storskalig förvaltning och sanering av fiberbankar.  Syftet med denna förstudie har varit att undersöka möjligheter att stabilisera fiberbanksmaterial och fiberrikt sediment för att förbättra materialens hållfasthets- och deformationsegenskaper och samtidigt fastlägga förekommande föroreningar. Detta har gjorts genom att bestämma hållfasthet och lakbarhet hos provkroppar tillverkade på laboratorium.  Undersökningarna visar att densiteten och hållfasthetsegenskaperna hos fiber och fiberrikt sediment kan förbättras betydligt genom stabilisering. Vilken hållfasthet som kan uppnås beror av egenskaperna hos det ursprungliga sedimentet. Skakförsöken visade emellertid att stabilisering medförde betydligt högre lakvattenhalter av kobolt, koppar, kvicksilver, och nickel, samt alla detekterade PAH och PCB kongener. För krom, bly och zink minskade däremot lakvattenhalterna efter stabilisering. Ytutlakningsförsöken visade att den ackumulerade mängden av tungmetaller steg med tiden och för PAH tycks ökningen vara relativt linjär men i de flesta fall kunde en avklingning ses.

Stabilisering med alternativa bindemedel : Sammanställning av geotekniska egenskaper, klimatpåverkan och kostnad

Stabilization with lime/cement columns is a common method for soil reinforcement for road and railway construction. The production of lime and cement, however, has been associated with a major negative impact on the environment and climate. There is potential to reduce this impact by partially replacing cement and lime with alternative binders such as slag or fly ash. At present, there is uncertainty in the industry about the geotechnical and environmental properties of materials stabilized with alternative binders. This project gives an overview of geotechnical and chemical properties of materials stabilized with both traditional and alternative binders, compares prices for different binders, and makes an assessment of climate impact of different binders and stabilization alternatives using life-cycle analysis (LCA). The project discusss key stages in the planning cycle of a stabilization project and presents a workflow for the selection of binders and stablization method taking into consideration life cycle perspective

In situ sorption of hydrophobic organic compounds to sediment amended with activated carbon

Contaminated sediments can be remediated by adding carbonaceous materials (CM), e.g. activated carbons (AC). Here, we analyze published datasets from AC amendment trials to identify variation in the effectiveness of AC in reducing porewater concentrations of hydrophobic organic contaminants (HOCs). The analysis uses a model that separates the contribution of HOC sorption to AC by parameterzing the sorption contributions by amorphous organic matter and black carbon (BC). It appears that sorption to BC increased with LogKOW, whereas sorption to AC showed a relatively narrow range of affinity properties with a median Freundlich LogKF,AC value of 7.2 (µg/kgAC)/(µg/L)n (IQR = 7.0–7.5) for polychlorinated biphenyls (PCBs) and 8.6 (IQR = 8.3–8.8) for polycyclic aromatic hydrocarbons (PAHs). Estimated Freundlich exponents were nF,AC = 0.74 for PCBs and 0.82 for PAH. Sorption to AC was stronger than to BC for chemicals below LogKOW = 6.3–6.6. For HOC risk reduction this is favorable, because chemicals with low KOW show generally higher bioavailable concentrations

Modeling Trade-off between PAH Toxicity Reduction and Negative Effects of Sorbent Amendments to Contaminated Sediments

Adding activated carbon (AC) to contaminated sediment has been suggested as an effective method for sediment remediation. AC binds chemicals such as polycyclic aromatic hydrocarbons (PAHs), thus reducing the toxicity of the sediment. Negative effects of AC on benthic organisms have also been reported. Here, we present a conceptual model to quantify the trade-off, in terms of biomass changes, between the advantageous PAH toxicity reduction and the negative effects of AC on populations of benthic species. The model describes population growth, incorporates concentration-effect relationships for PAHs in the pore water and for AC, and uses an equilibrium sorption model to estimate PAH pore water concentrations as a function of AC dosage. We calibrated the model using bioassay data and analyzed it by calculating isoclines of zero population growth for two species. For the sediment evaluated here, the results show that AC may safely protect the benthic habitat against considerable sediment PAH concentrations as long as the AC dosage remains below 4%

Community effects of carbon nanotubes in aquatic sediments

Aquatic sediments form an important sink for manufactured nanomaterials, like carbon nanotubes (CNT) and fullerenes, thus potentially causing adverse effects to the aquatic environment, especially to benthic organisms. To date, most nanoparticle effect studies used single species tests in the laboratory, which lacks ecological realism. Here, we studied the effects of multiwalled CNT (MWCNT) contaminated sediments on benthic macroinvertebrate communities. Sediment was taken from an unpolluted site, cleaned from invertebrates, mixed with increasing levels of MWCNTs (0, 0.002, 0.02, 0.2 and 2 g/kg dry weight), transferred to trays and randomly relocated in the original unpolluted site, which now acted as a donor system for recolonization by benthic species. After three months of exposure, the trays were regained, organic (OC) and residual carbon (RC) were measured, and benthic organisms and aquatic macrophytes were identified. ANOVA revealed a significantly higher number of individuals with increasing MWCNT concentrations. The Shannon index showed no significant effect of MWCNT addition on biodiversity. Multivariate statistics applied to the complete macroinvertebrate dataset, did show effects on the community level. Principal Component Analysis (PCA) showed differences in taxa composition related to MWCNT levels indicating differences in sensitivity of the taxa. Redundancy Analysis (RDA) revealed that MWCNT dose, presence of macrophytes, and spatial distribution explained 38.3% of the total variation in the data set, of which MWCNT dose contributed with 18.9%. Still, the net contribution of MWCNT dose was not statistically significant, indicating that negative community effects are not likely to occur at environmentally relevant future CNT concentrations in aquatic sediments

Extraction of sediment-associated polycyclic aromatic hydrocarbons with granular activated carbon

Addition of activated carbon (AC) to sediments has been proposed as a method to reduce ecotoxicological risks of sediment-bound contaminants. The present study explores the effectiveness of granular AC (GAC) in extracting polycyclic aromatic hydrocarbon (PAH) from highly contaminated sediments. Four candidate GAC materials were screened in terms of PAH extraction efficiency using single-step 24-h GAC extractions, with traditional 24-h Tenax extraction as a reference. Subsequently, sorption of native PAHs to the best performing GAC 1240W (0.45–1.70¿mm) was studied for sediment only and for GAC–sediment mixtures at different GAC–sediment weight ratios, using 76-µm polyoxymethylene (POM) passive samplers. Granular AC sorption parameters for PAHs were determined by subtracting the contribution of PAH sorption to sediment from PAH sorption to the GAC–sediment mixture. It appears that the binding of PAHs and the effectiveness of GAC to reduce sediment porewater concentrations were highly dependent on the GAC–sediment mixing ratio and hydrophobicity of the PAH. Despite the considerable fouling of GAC by organic matter and oil, 50 to 90% of the most available PAH was extracted by the GAC during a 28-d contact time, at a dose as low as 4%, which also is a feasible dose in field-scale applications aimed at cleaning the sediment by GAC addition and removal