The 1993 oil spill of Tampa Bay,a scenario for burning?

This viewpoint paper considers the potential of offshore burning of oil in the recent Tampa Bay spill as a generic oil spill response option. While the oil spilled might not have been amenable to burning, the physical constraints of the spill and subsequent environmental conditions provide a scenario for future consideration of this option.     

Comparative occurrence rates for offshore oil spills

Estimates of occurrence rates for offshore oil spills are useful for analysis of potential oil spill impacts and for oil spill response contingency planning. As the Oil Pollution Act of 1990 (U.S. Public Law 101–380, 18 August 1990) becomes fully implemented, estimates of oil spill occurrence will become even more important to natural resource trustees and to responsible parties involved in oil and gas activities. Oil spill occurrence rate estimates have been revised based on U.S. Outer Continental Shelf platform and pipeline spill data (1964–1992) and worldwide tanker spill data (1974–1992). These spill rates are expressed and normalized in terms of number of spills per volume of crude oil handled. The revisions indicate that estimates for the platform spill occurrence rates declined, the pipeline spill occurrence rates increased, and the worldwide tanker spill occurrence rates remained unchanged. Calculated for the first time were estimates of tanker and barge spill rates for spills occuring in U.S. waters, and spill occurrence rates for spills of North Slope crude oil transported by tanker from Valdez, Alaska. All estimates of spill occurrence rates were restricted to spills greater than or equal to 159 m³ (1000 barrels).     

Quantitative analysis of alternate oil spill response strategies using OSCAR

A three-dimensional numerical model of the physical and chemical behavior and fate of spilled oil has been coupled to a model of oil spill response actions. This coupled system of models for Oil Spill Contingency and Response (OSCAR), provides a tool for quantitative, objective assessment of alternative oil spill response strategies. Criteria for response effectiveness can be either physical (‘How much oil comes ashore?’ or ‘How much oil have we recovered?’) or biological (‘How many biologically sensitive areas were affected?’ or ‘What exposures will fish eggs and larvae experience in the water column?’). The oil spill combat module in the simulator represents individual sets of equipment, with capabilities and deployment strategies being specified explicitly by the user. The coupling to the oil spill model allows the mass balance of the spill to be affected appropriately in space and time by the cleanup operation as the simulation proceeds. An example application is described to demonstrate system capabilities, which include evaluation of the potential for both surface and subsurface environmental effects. This quantitative, objective approach to analysis of alternative response strategies provides a useful tool for designing more optimal, functional, rational, and cost-effective oil spill contingency solutions for offshore platforms, and coastal terminals and refineries.     

Oil and water separation in marine oil spill clean-up operations

This paper discusses the changes in spilled oil properties over time and how these changes affect differential density separation. It presents methods to improve differential density, and operational effectiveness when oil-water separation is incorporated in a recovery system. Separators function because of the difference in density between oil and seawater. As an oil weathers this difference decreases, because the oil density increases as the lighter components evaporate. The density also increases as the oil incorporates water droplets to form a water-in-oil emulsion. These changes occur simultaneously during weathering and reduce the effectiveness of separators. Today, the state-of-the-art technologies have limited capabilities for separating spilled marine oil that has weathered.For separation of emulsified water in an emulsion, the viscosity of the oil will have a significant impact on drag forces, reducing the effect of gravity or centrifugal separation. Since water content in an emulsion greatly increases the clean up volume (which can contain as much as two to five times as much water as the volume of recovered oil), it is equally important to remove water from an emulsion as to remove free water recovered owing to low skimmer effectiveness. Removal of both free water and water from an emulsion, has the potential to increase effective skimming time, recovery effectiveness and capacity, and facilitate waste handling and disposal. Therefore, effective oil and water separation in marine oil spill clean-up operations may be a more critical process than credited because it can mean that fewer resources are needed to clean up an oil spill with subsequent effects on capital investment and basic stand-by and operating costs for a spill response organization.A large increase in continuous skimming time and recovery has been demonstrated for total water (free and emulsified water) separation. Assuming a 200 m³ storage tank, 100 m³ h⁻¹ skimmer capacity, 25% skimmer effectiveness, and 80% water content in the emulsion, the time of continuous operation (before discharge of oil residue is needed), increases from 2 to 40 h and recovery of oil residue from 10 to 200 m³.Use of emulsion breakers to enhance and accelerate the separation process may, in some cases, be a rapid and cost effective method to separate crude oil emulsions. Decrease of water content in an emulsion, by heating or use of emulsion breakers and subsequent reduction in viscosity, may improve pumpability, reduce transfer and discharge time, and can reduce oily waste handling, and disposal costs by a factor of 10. However, effective use of emulsion breakers is dependant on the effectiveness of the product, oil properties, application methods and time of application after a spill.     

Analysis of Methods Used in Spill Response Planning: Trajectory Analysis Planner TAP II

Long records of geophysical forcing have been used in numerous studies to estimate a statistical distribution of oil spill scenarios. The resulting set of spill scenarios is then used as a basis for planning a robust response capability that should be able to handle all likely real spills. For model developers to be able to support these expectations there are a number of criteria that must be satisfied: (1) Models must develop and retain the data necessary to answer key response questions; (2) developers must understand the limitations in resolution imposed by the specific algorithms they use; and (3) the cardinality of the long geophysical records (with respect to modeled spill behavior) should be determined and the final collection of spill scenarios must span this set. This paper considers these specific constraints and discusses methods that can be used to quantify some aspects of the uncertainty in the output.     

Summary of Development and Field Testing of the Transrec Oil Recovery System

This paper summarizes the development, field testing and performance evaluation of the Transrec oil recovery system including the Framo NOFO Transrec 350 skimmer and multi-functional oil spill prevention and response equipment and presents performance data, not published before, from full-scale experimental oil spills in the North Sea from 1981 to 1990. The rare data provides useful information for evaluation of mechanical clean-up capabilities and efficiency, in particular, for responders who are using this equipment in many countries around the world.The development of the Transrec oil recovery system represents one of the most comprehensive efforts funded to date by the oil industry in Norway to improve marine and open ocean oil spill response capabilities. The need for improvements was based upon early practical user experience with different oil recovery systems, and test results from experimental oil spills in the North Sea.The result of the development efforts increased: (1) skimmer efficiency from approximately 15–75% (it reached 100% under favorable environmental conditions); (2) oil emulsion recovery rate from approximately 20–300 m³/h; (3) recovery system efficiency from approximately 15–85% in 1.5 m significant wave height; (4) oil emulsion thickness from approximately 15–35 cm; (5) weather-window for mechanical recovery operations from 1.5 to 3.0 m significant wave height; (6) capability for transfer of recovered oil residue to shuttle tankers in up to 4 m significant wave height and 45 knot winds; (7) capability for operations at night.The new Transrec oil recovery system with the special J-configuration virtually eliminated skimming operation downtime, and damage to booms and equipment failures that had been caused by oil spill response vessel (OSRV) problems with maintaining skimming position in the previous three-vessel oil recovery system with the boom towed in U-configuration. The time required to outfit OSRVs dropped from approximately 30–<1 h, reducing time from notification to operation on site by more than 24 h.Improvement in oil recovery resulted in the acceptance of a new oil spill preparedness and response plan. The new plan reduced the need for oil recovery systems from 21 to 14, towing vessels in preparedness from 42 to 18, and personnel on stand-by from 135 to 70, which subsequently reduced the total contingency and operational costs by almost 50%. These cost reductions resulted from lower contingency fees for personnel, fewer towing vessels on stand-by, less expensive open ocean training and exercises, less equipment and reduced storage space to lease, and simplified equipment maintenance.     

Stochastic Modeling Concepts in Groundwater and Risk Assessment: Potential Application to Marine Problems

Parameter uncertainty is ubiquitous in marine environmental processes. Failure to account for this uncertainty may lead to erroneous results, and may have significant environmental and economic ramifications. Stochastic modeling of oil spill transport and fate is, therefore, central in the development of an oil spill contingency plan for new oil and gas projects. Over the past twenty years, several stochastic modeling tools have been developed for modeling parameter uncertainty, including the spectral, perturbation, and simulation methods. In this work we explore the application of a new stochastic methodology, the first-order reliability method (FORM), in oil spill modeling. FORM was originally developed in the structural reliability field and has been recently applied to various environmental problems. The method has many appealing features that makes it a powerful tool for modeling complex environmental systems. The theory of FORM is presented, identifying the features that distinguish the method from other stochastic tools. Different formulations to the reliability-based stochastic oil spill modeling are presented in a decision-analytic context.     

An approach to evaluate the application of the vulnerability index for oil spills in tropical Red Sea environments

The Egyptian national marine oil pollution contingency plan was urgently initiated after the Nabila oil spill in 1982, to provide an estimate of its environmental effects on the Egyptian Red Sea coastal areas and to determine geomorphological features and cuastal processes, together with physical, chemical and biological baseline data for this tropical environment.The ‘Vulnerability Index’ (VI) was applied to evaluate and calibrate the effect of the Nabila oil spill on the Egyptian Red Sea Coastal area. A detailed in situ coastal survey was conducted during two visits in November 1982 and May 1983 to 80 shore sites from Suez to Ras Banas to monitor the oil pollution and to apply the ‘Vulnerability Index’. A comparative assessment of the index over time by comparing it with a quick ground inspection in November 1993 to some sites to evaluate the applicability of this index for oil spills in such environments. In addition, the physical effects of fresh and weathered crude oil and/with dispersant on water filtration by different beaches were preliminary studied.The geomorphological/Vulnerability Index results show that most of the Egyptian Red Sea coastal environments have medium to high vulnerability to immediate and medium term oil spill damage. The oil pollution spread estimated to be 250 km south of the oil spill and about 200 km north of it. The quantity of oil along the shoreline was reduced by about 60% due to natural and authorities clean up. The third survey after 11 years showed that the VI could be used as a predictive tool for assessment of oil spill effects on such tropical environments.     

Long-term Environmental Impact of Oil Spills

Oil contamination may persist in the marine environment for many years after an oil spill and, in exceptional cases such as salt marshes and mangrove swamps, the effects may be measurable for decades after the event. However, in most cases, environmental recovery is relatively swift and is complete within 2–10 years. Where oil has been eliminated from the scene, the long-term environmental impacts are generally confined to community structure anomalies that persist because of the longevity of the component species.     

The technology windows-of-opportunity for marine oil spill response as related to oil weathering and operations

This paper identifies and estimates time periods as ‘windows-of-opportunity’ where specific response methods, technologies, equipment, or products are more effective in clean-up operations for several oils. These windows have been estimated utilizing oil weathering and technology performance data as tools to optimize effectiveness in marine oil spill response decision-making. The windows will also provide data for action or no-action alternatives. Crude oils and oil products differ greatly in physical and chemical properties, and these properties tend to change significantly during and after a spill with oil aging (weathering). Such properties have a direct bearing on oil recovery operations, influencing the selection of response methods and technologies applicable for clean up, including their effectiveness and capacity, which can influence the time and cost of operations and the effects on natural resources.The changes and variations in physical and chemical properties over time can be modeled using data from weathering studies of specific oils. When combined with performance data for various equipment and materials, tested over a range of weathering stages of oils, windows-of-opportunity can be estimated for spill response decision-making. Under experimental conditions discussed in this paper, windows-of-opportunity have been identified and estimated for four oils (for which data are available) under a given set of representative environmental conditions. These ‘generic’ windows have been delineated for the general categories of spill response namely: (1) dispersants, (2) in situ burning, (3) booms, (4) skimmers, (5) sorbents, and (6) oil-water separators. To estimate windows-of-opportunity for the above technologies (except booms), the IKU Oil Weathering Model was utilized to predict relationships—with 5 m s⁻¹ wind speed and seawater temperatures of 15°C.The window-of-opportunity for the dispersant (Corexit 9527^®) with Alaska North Slope (ANS) oil was estimated from laboratory data to be the first 26 h. A period of ‘reduced’ dispersibility, was estimated to last from 26–120 h. The oil was considered to be no longer dispersible if treated for the first time after 120 h. The most effective time window for dispersing Bonnic Light was 0–2 h, the time period of reduced dispersibility was 2–4 h, and after 4 h the oil was estimated to be no longer dispersible. These windows-of-opportunity are based on the most effective use of a dispersant estimated from laboratory dispersant effectiveness studies using fresh and weathered oils. Laboratory dispersant effectiveness data cannot be directly utilized to predict dispersant performance during spill response, however, laboratory results are of value for estimating viscosity and pour point limitations and for guiding the selection of an appropriate product during contingency planning and response. In addition, the window of opportunity for a dispersant may be lengthened if the dispersant contains an emulsion breaking agent or multiple applications of dispersant are utilized. Therefore, a long-term emulsion breaking effect may increase the effectiveness of a dispersant and lengthen the window-of-opportunity.The window-of-opportunity of in situ burning (based upon time required for an oil to form an emulsion with 50% water content) was estimated to be approximately 0–36 h for ANS oil and 0–1 h for Bonnie Light oil after being spilled. The estimation of windows-of-opportunity for offshore booms is constrained by the fact that many booms available on the market undergo submergence at speeds of less than 2 knots. The data suggest that booms with buoyancy to weight ratios less than 8:1 may submerge at speeds within the envelope in which they could be expected to operate. This submergence is an indication of poor wave conformance, caused by reduction of freeboard and reserve net buoyancy within the range of operation. The windows-of-opportunity for two selected skimming principles (disk and brush), were estimated using modeled oil viscosity data for BCF 17 and BCF 24 in combination with experimental performance data developed as a function of viscosity. These windows were estimated to be within 3–10 h (disk skimmer) and after 10 h (brush skimmer) for BCF 17. Whereas for BCF 24, it is within 2–3 d (disk skimmer) and after 3 d (brush skimmer).For sorbents, an upper viscosity limit for an effective and practical use has in studies been found to be approximately 15,000 cP, which is the viscosity range of some Bunker C oils. Using viscosity data for the relative heavy oils, BCF 17 and BCF 24 (API gravity 17 and 24), the time windows for a sorbent (polyamine flakes) was estimated to be 0–4 and 0–10 d, respectively. With BCF 24, the effectiveness of polyamine flakes, was reduced to 50% after 36 h, although it continued to adsorb for up to 10 d. For BCF 17, the effectiveness of polyamine flakes was reduced to 50% after 12 h, although it continued to adsorb for up to 4 d. The windows-of-opportunity for several centrifuged separators based upon the time period to close the density gap between weathered oils and seawater to less than 0.025 g ml⁻¹ (which is expected to be an end-point for effective use of centrifugal separation technology), were estimated to be 0–18 (ANS) and 0–24 h (Bonnie Light) after the spill. Utilizing the windows-of-opportunity concept, the combined information from a dynamic oil weathering model and a performance technology data base can become a decision-making tool; identifying and defining the windows of effectiveness of different response methods and equipment under given environmental conditions. Specific research and development needs are identified as related to further delineation of windows-of-opportunity.     

The Significance of Oil Spill Dispersants

There is growing acceptance worldwide that use of dispersants to counter the effects of an oil spill offers many advantages and can often result in a net environmental benefit when considered in relation to other response options. A major reason for this growing support and increased reliance on dispersants is the advent of improved dispersant products that are low in toxicity to marine life and more effective at dispersing heavy and weathered oils – oils previously believed to be undispersible. This capability has been demonstrated through extensive laboratory testing, field trials, and dispersant application on actual spills. This paper summarizes recent advances in dispersant R&D and reviews the implications of technology advances.     

South Arne Field Development: An Environmental Impact Assessment of Oil Spills

The South Arne field being developed by Amerada Hess A/S is located in 60 m water depth approximately 200 km from the Danish mainland, in block 5604/29 of the Danish sector of the North Sea.As part of the development of the field, a comprehensive environmental impact assessment has been carried out, including the assessment of the impact from oil spills. The Danish authorities required that a ‘worst case’ oil spill be chosen as the basis for the assessment on birds and aquatic organisms including plankton, fish eggs and larvae and benthos.A well blow-out at the surface was chosen as the worst case for the impact on birds, and a seabed blow-out for aquatic organisms.The oil spill modelling was carried out with the DEEPBLOW, SLIKMAP and OSCAR models from SINTEF. The modelling identified environmentally sensitive areas which could potentially be influenced by an oil spill. These included the Dogger Bank, western Skagerrak, south-western Norwegian Trench, the eastern German Bight and the Wadden Sea.Historical meteorological and hydrodynamic scenarios were chosen from a long period of records to ensure that the plume passed through the environmentally sensitive resource areas.For birds, a scan of the literature and available databases was made to determine the numbers and species of birds in the areas swept by the surface slick, the number of fatalities was estimated and finally the recovery time for each species population was estimated.The impact on aquatic organisms was estimated using the predicted environmental concentration/predicted no effect concentration (PEC/PNEC) method of the CHARM model. This method is normally applied to continuous discharges, but here has been used to estimate the impact of a transient pollution cloud resulting from an oil spill.     

Chemical and Ecotoxicological Characterisation of Oil–Water Systems

An ongoing chemical and ecotoxicological study of Water Accommodated Fraction of oils is presented and the preliminary findings are discussed. The study aims at obtaining improved and realistic data on potential environmental effects of various oils released and weathered at sea. Such data will be used for improving algorithms in present fate and effect models for damage assessment studies and “Net Environmental Benefit Analysis” of response alternatives in various spill scenarios. Preliminary results show that models used to assess effects in the water column will need to resolve the water soluble fraction of oils into more than one single bulk parameter to produce realistic estimates of effects.     

Toxicity Evaluation with the Microtox Test to Assess the Impact of In Situ Oiled Shoreline Treatment Options: Natural Attenuation and Sediment Relocation

Changes in the toxicity levels of beach sediment, nearshore water, and bottom sediment samples were monitored with the Microtox^® Test to evaluate the two in situ oil spill treatment options of natural attenuation (natural recovery--no treatment) and sediment relocation (surf washing). During a series of field trials, IF-30 fuel oil was intentionally sprayed onto the surface of three mixed sediment (pebble and sand) beaches on the island of Spitsbergen, Svalbard, Norway (78°56^′ N, 16°45^′ E). At a low wave-energy site (Site 1 with a 3-km wind fetch), where oil was stranded within the zone of normal wave action, residual oil concentrations and beach sediment toxicity levels were significantly reduced by both options in less than five days. At Site 3, a higher wave-energy site with a 40-km wind fetch, oil was intentionally stranded on the beach face in the upper intertidal/supratidal zones, above the level of normal wave activity. At this site under these experimental conditions, sediment relocation was effective in accelerating the removal of the oil from the sediments and reducing the Microtox^® Test toxicity response to background levels. In the untreated (natural attenuation) plot at this site, the fraction of residual oil remaining within the beach sediments after one year (70%) continued to generate a toxic response. Chemical and toxicological analyses of nearshore sediment and sediment-trap samples at both sites confirmed that oil and suspended mineral fines were effectively dispersed into the surrounding environment by the in situ treatments. In terms of secondary potential detrimental effects from the release of stranded oil from the beaches, the toxicity level (Microtox^® Test) of adjacent nearshore sediment samples did not exceed the Canadian regulatory limit for dredged spoils destined for ocean disposal.     

Update of Comparative Occurrence Rates for Offshore Oil Spills

Estimates of occurrence rates for offshore oil spills are useful for analyzing potential oil-spill impacts and for oil-spill response contingency planning. With the implementation of the Oil Pollution Act of 1990 (US Public Law 101-380, August 18, 1990), estimates of oil-spill occurrence became even more important to natural resource trustees and to responsible parties involved in oil and gas activities.Oil-spill occurrence rate estimates have been revised based on US Outer Continental Shelf (US OCS) platform and pipeline spill data (1964 through 1999), worldwide tanker spill data (1974 through 1999), and barge spill data for US waters (1974–1999). These spill rates are expressed and normalized in terms of number of spills per volume of crude oil handled. All estimates of spill occurrence rates were restricted to spills greater than or equal to 1000 barrels (159 m³, 159 kl, 136 metric tonnes, 42,000 US gallons).The revisions compared to the previously published rates calculated through 1992 (Anderson and LaBelle, 1994) indicate that estimates for the US OCS platform spill occurrence rates continue to decline, primarily because no spills have occurred since 1980. The US OCS pipeline spill occurrence rates for spills greater than or equal to 1000 barrels remained essentially unchanged. However, the rate for larger OCS pipeline spills (greater than or equal to 10,000 barrels) has decreased significantly. Worldwide tanker spill rates, rates for tanker spills in US waters, and rates for barge spills in US waters decreased significantly. The most recent 15-year estimates for 1985–1999 (compared to rates for the entire data series) showed that rates for US OCS platforms, tankers, and barges continued to decline.     

Australia's National Plan to Combat Pollution of the Sea by Oil and Other Noxious and Hazardous Substances – Overview and Current Issues

Australia's National Plan to Combat Pollution of the Sea by Oil and Other Noxious and Hazardous Substances (the National Plan) has operated since 1973. The objectives of the National Plan are based on Australia's obligations as a signatory to the International Convention on Oil Pollution Preparedness, Response and Co-operation 1990 and a responsibility to protect natural and artificial (man made) environments from the adverse effects of oil pollution and minimise those effects where protection is not possible.The Australian Maritime Safety Authority (AMSA) is the managing agency of the National Plan, working together with the States and Northern Territory governments, other Commonwealth agencies, ports, and the shipping, oil and exploration industries, to maximise Australia's marine pollution response capability.The 1990s have been a period of significant change for oil spill response arrangements in Australia. The National Plan was extended in 1998 to cover chemical spills and is currently in the process of implementing the oil spill response incident control system (OSRICS). A fixed wing aerial dispersant spraying capability was implemented in 1996 and a research and development program has been put in place. The development of a computer-based National Oil Spill Response Atlas was a major project completed during 1999.     

The Oil Pollution Act of 1990: A Decade Later

Analysis of oil spills data confirms that accidental oil spills are natural phenomenon and that there is a relationship between accidental oil spills and variables like vessel size, vessel type, time and region of spill. The volume of oil spilled bears relationship with the volume of petroleum imports and domestic movement of petroleum and proportion of large oil spills. Finally, navigational risk increases with increase in marine traffic and is also determined by variables like hydrographic and meteorological conditions, water configuration, maneuvering space, obstructions and nuisance vessels. The Oil Pollution Act, 1990 (OPA 90) was passed by the US Congress in the aftermath of 11 million gallon spill of crude oil in Prince William Sound, Alaska. The objective of OPA 90 was to minimize marine casualties and oil spills by addressing preventive, protective, deterrent and performance aspects of accidental oil spills. The arm of various regulations like double-hull tankers and vessel response plans extended to both US flagged and foreign-flagged tank vessels. The cost–benefit analysis of major regulations shows that the estimated costs exceed estimated benefits. We observe from USCG data on oil spills by size, by vessel type, Coast guard district and type of petroleum product that there have been significant reductions in the number and the quantity of oil spills. Our regression results show that the quantity of oil spilled increases with increase in oil imports but increases at a decreasing rate. The quantity of oil spilled decreases with increases in the domestic oil movements. Furthermore, percent of oil spills larger than 10,000 gallons also increases the potential quantity of oil spilled. OPA 90 has been a deterrent to accidental oil spills but the finding is not conclusive.     

Photo-oxidation and Photo-toxicity of Crude and Refined Oils

The fate and effects of an oil spill are effected by solar radiation through the action of photo-oxidation and photo-toxicity. Photo-oxidation, an important process in the weathering of oil, produces a variety of oxidized compounds, including aliphatic and aromatic ketones, aldehydes, carboxylic acids, fatty acids, esters, epoxides, sulfoxides, sulfones, phenols, anhydrides, quinones and aliphatic and aromatic alcohols. Some of these compounds contribute to the marine biota toxicity observed after an oil spill. Photo-toxicity occurs when uptake of certain petroleum compounds, e.g. certain polycyclic aromatic hydrocarbons and benzothiophenes, is followed by solar exposure which results in much greater toxicity than after dark uptake. The mechanism of PAH photo-toxicity includes absorbance of solar radiation by the PAH which produces a free radical and this free radical in turn reacts with oxygen to produce reactive oxygen species that can damage DNA and other cellular macromolecules. While most studies on photo-toxicity have been carried out in the laboratory, there are studies showing that water from an oil spill is photo-toxic to bivalve embryos for at least a few days after the spill. Other studies have found that oil contaminated sediments are photo-toxic to several marine invertebrates. More studies are required to determine if marine fauna at an oil spill site are effected by the action of photo-toxicity and photo-oxidation.     

Real time oil spill forecasting during an experimental oil spill in the arctic ice

The oil spill trajectory and weathering model OILMAP was used to forecast spill trajectories for an experimental oil spill in the Barents Sea marginal ice zone. The model includes capabilities to enter graphically and display environmental data governing oil behavior: ice fields, tidal and background current fields, and wind time series, as well as geographical map information. Forecasts can also be updated from observations such as airplane overflights. The model performed well when wind was ‘off-ice’ and speeds were relatively low (3–7 m s⁻¹), with ice cover between 60 and 90%. Errors in forecasting the trajectory could be directly attributed to errors in the wind forecasts. Appropriate drift parameters for oil and ice were about 25% of the wind speed, with an Ekman veering angle of 35° to the right. Ice sheets were typically 1 m thick. When the wind became ‘on-ice’, wind speeds increased to about 10 m s⁻¹ and trajectory simulations began to diverge from the observations, with observed drift parameters being 1.5% of the wind speed, with a 60° veering angle. Although simple assumptions for the large scale movement of oil in dense ice fields appear appropriate, the importance of good wind forecasts as a basis for reliable trajectory prognoses cannot be overstated.     

Life cycle assessment of management alternatives for sludge from sewage treatment plants in Chile: does advanced anaerobic digestion improve environmental performance compared to current practices?

Sludge generation is currently one of the most important issues for sewage treatment plants in Chile. In this work, the life cycle environmental impacts of four sludge management scenarios were studied, focusing on the comparison of current practices and advanced anaerobic digestion (AD) using a sequential pre-treatment (PT). The results show that AD scenarios presented lower potential impacts than lime stabilization scenarios in all assessed categories, including climate change, abiotic depletion, acidification, and eutrophication in terrestrial, marine and freshwater ecosystems. The overall environmental performance of advanced digestion was similar to conventional digestion, with the main difference being a decrease in the climate change potential and an increase in the abiotic depletion potential. Acidification and eutrophication categories showed similar performances in both conventional and advanced AD. The effect of PT in the AD scenarios was related to energy recovery, sludge transport requirements and nutrient loads in the sludge and supernatant after digestate dewatering. Considering the results, PT could be a useful strategy to promote sludge valorization and decrease the environmental burdens of sludge management in Chile compared to the current scenario.