A multicriteria-based methodology for site prioritisation in sediment management

Decision-making for sediment management is a complex task that incorporates the selections of areas for remediation and the assessment of options for any mitigation required. The application of Multicriteria Analysis (MCA) to rank different areas, according to their need for sediment management, provides a great opportunity for prioritisation, a first step in an integrated methodology that finally aims to assess and select suitable alternatives for managing the identified priority sites. This paper develops a methodology that starts with the delimitation of management units within areas of study, followed by the application of MCA methods that allows ranking of these management units, according to their need for remediation. This proposed process considers not only scientific evidence on sediment quality, but also other relevant aspects such as social and economic criteria associated with such decisions. This methodology is illustrated with its application to the case study area of the Bay of Santander, in northern Spain, highlighting some of the implications of utilising different MCA methods in the process. It also uses site-specific data to assess the subjectivity in the decision-making process, mainly reflected through the assignment of the criteria weights and uncertainties in the criteria scores. Analysis of the sensitivity of the results to these factors is used as a way to assess the stability and robustness of the ranking as a first step of the sediment management decision-making process.     

Comparison of bioluminescence and nitrification inhibition methods for assessing toxicity to municipal activated sludge

The aim of this study was to compare two alternative toxicity assessment methods to determine wastewater toxicity and predict treatment plant process upsets. The toxicity of two synthetic organic compounds (triclosan and 4-n-nonylphenol), which are commonly detected in municipal wastewater, and municipal and industrial wastewaters with different heavy metals content were evaluated by the nitrification inhibition assay and bioluminescence toxicity test. Comparison between both assays confirmed that Vibrio fischeri is generally more sensitive than autotrophic bacteria, and, if not calibrated, the bioluminescence method tends to overestimate toxic effects on activated sludge biomass. The nitrification inhibition assay appears to predict plant process upsets more accurately. Both methods showed a significant toxicity decrease through treatment that could be partially attributed to the significant heavy metals removal obtained by primary and secondary treatment. A good correlation for the two assays was obtained, as indicated by a high correlation coefficient (r2 = 0.80).     

Investigation of triclosan fate and toxicity in continuous-flow activated sludge systems

The purpose of this research was to study the fate and toxicity of triclosan (TCS) in activated sludge systems and to investigate the role of biodegradation and sorption on its removal. Two continuous-flow activated sludge systems were used; one system was used as a control, while the other received TCS concentrations equal to 0.5 and 2mgl(-1). At the end of the experiment, 1mgl(-1) TCS was added in the control system to investigate TCS behaviour and effects on non-acclimatized biomass. For all concentrations tested, more than 90% of the added TCS was removed during the activated sludge process. Determination of TCS in the dissolved and particulate phase and calculation of its mass flux revealed that TCS was mainly biodegraded. Activated sludge ability to biodegrade TCS depended on biomass acclimatization and resulted in a mean biodegradation of 97%. Experiments with batch and continuous-flow systems revealed that TCS is rapidly sorbed on the suspended solids and afterwards, direct biodegradation of sorbed TCS is performed. Regarding TCS effects on activated sludge process, addition of 0.5mgl(-1) TCS on non-acclimatized biomass initially deteriorated ammonia removal and nitrification capacity. After acclimatization of biomass, nitrification was fully recovered and further increase of TCS to 2mgl(-1) did not affect the performance of activated sludge system. The effect of TCS on organic substrate removal was minor for concentrations up to 2mgl(-1), indicating that heterotrophic microorganisms are less sensitive to TCS than nitrifiers.     

Household hazardous waste disposal to landfill: using LandSim to model leachate migration

Municipal solid waste (MSW) landfill leachate contains a number of aquatic pollutants. A specific MSW stream often referred to as household hazardous waste (HHW) can be considered to contribute a large proportion of these pollutants. This paper describes the use of the LandSim (Landfill Performance Simulation) modelling program to assess the environmental consequences of leachate release from a generic MSW landfill in receipt of co-disposed HHW. Heavy metals and organic pollutants were found to migrate into the zones beneath a model landfill site over a 20,000-year period. Arsenic and chromium were found to exceed European Union and US-EPA drinking water standards at the unsaturated zone/aquifer interface, with levels of mercury and cadmium exceeding minimum reporting values (MRVs). The findings demonstrate the pollution potential arising from HHW disposal with MSW.     

Extreme Nitrogen Oxide and Ozone Concentrations in Athens Atmosphere in Relation to Meteorological Conditions

In the present study, we investigate the variation of NO _x (NO + NO₂) and O₃ concentrations and the relation between the extreme events (episodes) of NO _x and O₃ concentrations and the relevant meteorological conditions in the urban atmosphere of the Athens basin. Hourly data of NO, NO₂ and O₃ concentrations from 10 representative monitoring sites located in the Athens basin were used, covering the 10-year time period from 1994 to 2003. The results of our analysis show that the concentrations of air pollutants differ significantly from one monitoring site to another, due to the location and proximity of each station to the emission sources. For each site, there are also significant differences in NO _x and O₃ concentrations from day to day, as well as from month to month and/or from season to season. The annual and seasonal variations show higher NO values in winter and lower in summer. On the contrary, NO₂ and O₃ values are higher in summer (photochemical production of O₃) and lower in winter. These differences are attributed, to a large extent, to the prevailing synoptic and meteorological conditions, the most important between them being the wind direction and speed as well as the atmospheric pressure. Our analysis of the identified 179 extreme NO _x air pollution events shows that most of them took place under anticyclonic conditions, associated with calm or weak winds (speed <2.5 ms⁻¹) of mostly southern to southwestern directions, as well as with low air temperatures and intense stable surface atmospheric conditions. There exists a significant decreasing tendency in NO _x air pollution episodic events over the 10-year study period, resulting in very few to none events in the period from 2000 to 2003. As far as it concerns the extreme O₃ concentrations, 34 air pollution events were identified, occurring under high air temperatures, variable weak winds and intense solar irradiation. The trends of O₃ concentrations are stronger in suburban sites than in urban ones.     

Effect of macronutrients and of anaerobic digestate on the heterotrophic cultivation of Chlorella vulgaris grown with glycerol

Environmental Science and Pollution Research - The aim of this work was to investigate the kinetics of the heterotrophic growth of Chlorella vulgaris as a means of producing bio-oil for biodiesel...     

Inference and model determination for temperature-driven non-linear ecological models

Environmental and Ecological Statistics - This paper is concerned with a contemporary Bayesian approach to the effect of temperature on developmental rates. We develop statistical methods using...