Margarida Ribau Teixeira

Aggregation kinetics and surface charge of CuO nanoparticles: the influence of pH, ionic strength and humic acids

Environmental context The high demand and use of nanomaterials in commercial products have led to increased concerns about their effect on the environment and human health. Because CuO nanoparticles are widely used in several products, it is necessary to understand and predict their behaviour and fate in the environment. We report a study on the aggregation and surface charge of CuO nanoparticles under environmentally relevant conditions to better predict the mobility and bioavailability of these materials in natural waters. Abstract In this study, the role of pH, ionic strength and humic acids (HAs) on the aggregation kinetics and surface charge of commercial copper oxide (CuO) nanoparticles were examined. Results show that the aggregation of CuO nanoparticles is favoured near pH 10, which was determined as the isoelectric point where the hydrodynamic diameter of the aggregates is the greatest. The aggregation of CuO nanoparticles is also ionic strength dependent. The increase in the ionic strength reduces the zeta potential, which leads to an increase in aggregation until 0.15M. After this point an increase in ionic strength has no influence on aggregation. In the presence of HA for concentrations below 4mgCL–1, aggregation was enhanced for acidic to neutral pH, whereas for higher concentrations, at all pH tested, aggregation does not change. The influence of HA on CuO nanoparticles is due to steric and electrostatic interactions. The sedimentation rates of CuO nanoparticles showed a relation between particle diameter and zeta potentials values confirmed by Derjaguin–Landau–Verwey–Overbeek calculations. The results obtained have important implications for predicting the stability and fate of CuO nanoparticles in natural water.

Investigating dissolved air flotation performance with cyanobacterial cells and filaments

Dissolved air flotation (DAF) performance with two different naturally occurring cyanobacterial morphologies was investigated with respect to the biomass removal efficiency, the toxin release to water and the coagulant demand by different water background natural organic matter (NOM). Coagulation (C)/Flocculation (F)/DAF bench-scale experiments (2 min coagulation at 380 s(-1) with polyaluminium chloride (0.5-4 mg/L Al(2)O(3), the dose depending on the water NOM content); 8 min flocculation at 70 s(-1); 8 min DAF with 5 bar relative pressure and 8% pressurised recycle) were performed with single cells of Microcystis aeruginosa and Planktothrix rubescens filaments spiked in synthetic waters with different NOM contents (hydrophobic vs. hydrophilic NOM; moderate (2-3 mgC/L) vs. moderate-high concentration (ca. 6 mgC/L)). For both morphologies, the results show no apparent cyanobacterial damage (since the water quality did not degrade in dissolved microcystins and the removal of intracellular microcystins matched the removal of chlorophyll a) and high biomass removal efficiencies (93-99% for cells and 92-98% for filaments) provided optimal coagulant dose for chlorophyll a removal was ensured. Charge neutralisation by the polyaluminium chloride was the main coagulation mechanism of the M. aeruginosa cells and most likely also of the P. rubescens filaments. The specific coagulant demand was severely affected by NOM hydrophobicity, hydrophobic NOM (with a specific UV(254nm) absorbance, SUVA, above 4 L/(m mgC)) requiring ca. the triple of hydrophilic NOM (SUVA below 3 L/(m mgC)), i.e. 0.7 vs. 0.2-0.3 mg Al(2)O(3)/mg DOC.

pH adjustment for seasonal control of UF fouling by natural waters

Abstract Natural surface waters in Algarve, Portugal, have important seasonal variations in natural organic matter (NOM) content, that influences ultrafiltration (UF) performance. This paper addresses the evaluation of the pH adjustment for seasonal control of UF fouling at a laboratory scale, using a plate and frame polysulphone membrane of 47 kDa MWCO. Results of two types of natural water (clear water, 3–5 NTU, and turbid water, 33–34.6 NTU) and three different water pH values (acid, neutral and basic) demonstrated that the pH adjustment could be used for seasonal control of UF fouling: when the water has less NOM (in dry periods, clear water), the acid pH will improve the UF performance, while during and after intense rainfall periods (turbid water with high NOM concentration) basic pH will be advantageous, because it minimizes membrane fouling. This behaviour is explained for clear water in terms of charge effects on membrane size. For turbid water, the electrostatic repulsion between membrane surface and NOM and turbidity particles is reduced at pH 4.13 and protonation of the NOM functional groups decreases the hydrodynamic radii of humic substances while increasing their hydrophobicity and their tendency to adsorb. Therefore, a dense fouling layer develops and flux is lower at pH 4.13 than at pH 8.33. These results together with the observed raw water feed concentrations decline and rejection decrease with WRR confirm the extensive adsorption on the membrane enhanced by the moderate hardness cation of this water.

Effects of silver nanoparticles exposure in the mussel Mytilus galloprovincialis

Silver nanoparticles (Ag NPs) have emerged as one of the most commonly used NPs in a wide range of industrial and commercial applications. This has caused increasing concern about their fate in the environment as well as uptake and potential toxicity towards aquatic organisms. Accordingly, mussels Mytilus galloprovincialis were exposed to 10 μg L(-1) of Ag NPs and ionic silver (Ag+) for 15 days, and biomarkers of oxidative stress and metal accumulation were determined. Accumulation results show that both Ag NPs and Ag+ accumulated in both gills and digestive glands. Antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase) were activated by Ag NPs and Ag+, showing different antioxidant patterns in both gills and digestive glands. Moreover, metallothionein was inducted in gills, directly related to Ag accumulation, while in the digestive glands only a small fraction of Ag seems to be associated with this protein. Lipid peroxidation was higher in gills exposed to Ag NPs, whereas in the digestive glands only Ag+ induced lipid peroxidation. Ag NPs and Ag+ cause oxidative stress with distinct modes of action and its not clear if for Ag NPs the observed effects are attributed to free Ag+ ions associated with the nanoparticle effect.

Healthcare waste management practices and risk perceptions: findings from hospitals in the Algarve region, Portugal.

The management of healthcare wastes is receiving greater attention because of the risks to both human health and the environment caused by inadequate waste management practices. In that context, the objective of this study was to analyse the healthcare waste management practices in hospitals of the Algarve region, Portugal, and in particular to assess the risk perceptions of, and actual risk to, healthcare staff. The study included three of the six hospitals in the region, covering 41% of the bed capacity. Data were collected via surveys, interviews, and on-site observations. The results indicate that waste separation is the main deficiency in healthcare waste practice, with correct separation being positively related to the degree of daily contact with the waste. Risk perceptions of healthcare staff show the highest levels for the environment (4.24) and waste workers (4.08), and the lowest for patients (3.29) and visitors (2.80), again being positively associated with the degree of daily contact. Risk perceptions of healthcare staff are related to the difficulties of the correct separation of wastes and the lack of knowledge concerning the importance of that separation. The risk of infection with needlesticks/sharps is higher during patient care than during waste handling, and the frequency of these injuries is related to the daily tasks of each healthcare group (doctors, nurses, and housekeepers). Furthermore, legislative definitions and classifications of healthcare wastes appear to have conditioned the management practices associated with, and the perceptions of risk concerning, healthcare wastes.

Quantitative performance targets by using balanced scorecard system: application to waste management and public administration.

This article demonstrates how decision-makers can be guided in the process of defining performance target values in the balanced scorecard system. We apply a method based on sensitivity analysis with Monte Carlo simulation to the municipal solid waste management system in Loulé Municipality (Portugal). The method includes two steps: sensitivity analysis of performance indicators to identify those performance indicators with the highest impact on the balanced scorecard model outcomes; and sensitivity analysis of the target values for the previously identified performance indicators. Sensitivity analysis shows that four strategic objectives (IPP1: Comply with the national waste strategy; IPP4: Reduce nonrenewable resources and greenhouse gases; IPP5: Optimize the life-cycle of waste; and FP1: Meet and optimize the budget) alone contribute 99.7% of the variability in overall balanced scorecard value. Thus, these strategic objectives had a much stronger impact on the estimated balanced scorecard outcome than did others, with the IPP1 and the IPP4 accounting for over 55% and 22% of the variance in overall balanced scorecard value, respectively. The remaining performance indicators contribute only marginally. In addition, a change in the value of a single indicator’s target value made the overall balanced scorecard value change by as much as 18%. This may lead to involuntarily biased decisions by organizations regarding performance target-setting, if not prevented with the help of methods such as that proposed and applied in this study.

Phosphorus recovery from waters using nanofiltration

Recovery of phosphorus has been gaining importance due to its natural scarcity and expensive price. In this work, nanofiltration (NF) has been tested as a technology to treat surface waters with phosphorus and simultaneously recover that phosphorus. Two membranes of same material, but different molecular size were tested (NF270 and NF90). Results showed that membrane fluxes were more affected by the presence of salts, natural organic matter, and especially microcystins than phosphorus. In addition, phosphorus removals were very high (>90%) and varied with the membrane type, feed conductivity, and dissolved organic carbon (DOC). The increase in feed conductivity and DOC originated higher phosphorus removals. Furthermore, the presence of microcystins did not affect the high-phosphorus removals. Results show that more than 96% of the total phosphorus mass can be recovered using NF membranes. NF is therefore a technology that should be considered for phosphorus recovery from surface waters.

Life Cycle Assessment of Soil and Groundwater Remediation: Groundwater Impacts of Electrokinetic Remediation

The growing concern about the sustainability of soil remediation technologies and operations lead to the development of different support decision methods. Life cycle assessment (LCA) methodologies have well-developed methods for assessing environmental impacts for emissions to air, surface water, and surface soil, but deep soil emissions and emissions to groundwater have received little attention. Regional impact of groundwater extractions has largely not been considered in LCA as well, nor their relation to surface water bodies and groundwater-dependent ecosystems. These aspects are now compulsory in the management of water resources in Europe, under EU Water Framework Directive. Future developments in LCA will necessarily have to include these relations in the characterization of the impacts. Given the strong retardation that many pollutants undertake in the soil, the temporal factor is relevant in the groundwater compartment, as contamination may extend for decades. Moreover, groundwater contamination due to industrial sources, including soil remediation, tends to be spatially concentrated, dispersing from the point of origin depending on hydrogeologic conditions, soil retention capacity, pollutant’s degradation rates, and time. Exposure to contaminated groundwater is frequently assessed by modeling; however, the proposed models require detailed information about soil properties, which is usually not available, nor is it possible to obtain in the scope of a life cycle assessment. Simpler methods are therefore needed. The present article discusses some of these alternatives, in particular applied to soil remediation with electrokinetic methods. The use of in situ electrokinetics for the remediation of fine-grained soils requires contaminants to move from their initial location to an electrode. The migration path can be long and there could be stagnant zones between wells where the rate of migration is slow, both of which can result in an incomplete remediation and to potential impacts on groundwater.