Amendment of arsenic and chromium polluted soil from wood preservation by iron residues from water treatment

An iron-rich water treatment residue (WTR) consisting mainly of ferrihydrite was used for immobilization of arsenic and chromium in a soil contaminated by wood preservatives. A leaching batch experiment was conducted using two soils, a highly contaminated soil (1033 mg kg⁻¹ As and 371 mg kg⁻¹ Cr) and slightly contaminated soil (225 mg kg⁻¹ As and 27 mg kg⁻¹ Cr). Compared to an untreated reference soil, amendment with 5% WTR reduced leaching in the highly contaminated soil by 91% for Cr and 98% for As. No aging effect was observed after 103 d. In a small field experiment, soil was mixed with 2.5% WTR in situ. Pore water was extracted during 3 years from the amended soil and a control site. Pore water arsenic concentrations in the amended soil were more than two orders of magnitude lower than in the control for the upper samplers. An increased release of arsenic was observed during winter in both fields, mostly in the deepest samplers. This is likely due to the formation of a pseudo-gley because of precipitation surplus. Stabilization of arsenic and chromium contaminated soil using WTR is a promising method but the transformation of ferrihydrite in soil proves a concern in case of waterlogged soils. Still the amendment minimized the leaching of arsenic, even in cases of seasonal releases.     

Water hyacinths as a resource in agriculture and energy production: a literature review

Water hyacinths are becoming a problem in lakes, ponds and waterways in many parts of the world. This paper contains a literature study of different ways to use water hyacinths, mainly in agricultural or alternative energy systems. The literature review indicated that water hyacinths can be rich in nitrogen, up to 3.2% of DM and have a C/N ratio around 15. The water hyacinth can be used as a substrate for compost or biogas production. The sludge from the biogas process contains almost all of the nutrients of the substrate and can be used as a fertiliser. The use of water hyacinth compost on different crops has resulted in improved yields. The high protein content makes the water hyacinth possible to use as fodder for cows, goats, sheep and chickens. Water hyacinth, due to its abundant growth and high concentrations of nutrients, has a great potential as fertiliser for the nutrient deficient soils of Africa and as feed for livestock. Applying the water hyacinths directly without any other processing than sun drying, seems to be the best alternative in small-scale use due to the relatively small losses of nutrients and workload required. To meet the ever-growing energy demand, biogas production could be one option but it requires investments and technological skills that would impose great problems in developing countries where the water hyacinth is often found. Composting as an alternative treatment has the advantage of a product that is easy to work into the soil compared with dried water hyacinths, because of the decomposed structure. Harvesting and transport of water hyacinths can be conducted manually on a small scale and does not require a new harvesting technique to be introduced. Transporting of fresh water hyacinths means, if used as fertiliser in amounts large enough to enhance or effect crop growth, an unreasonably large labour requirement. Based on the labour need and the limited access to technology, using dried water hyacinths, as green manure is a feasible alternative in many developing countries.     

Patch dynamics of mussel beds near São Sebastião (São Paulo), Brazil

In permanent quadrats on exposed and protected shores near São Sebastião (São Paulo), Brazil, changes in percent cover of mussels [Brachidontes solisianus (d'Orbigny)] and barnacles [Chthamalus stellatus bisinuatus (Pilsbury)] were followed from November 1979 through December 1982. Mussels gradually disappeared from both shores, while barnacles came to dominate the exposed, but not the protected, shore. Decreases in percent cover of mussels were related to periods of higher temperatures. Mussels were only transient dominants of the mid-intertidal zone due to lack of recruitment and high summer mortality. This is probably because the study was carried out near the northern limit of their occurrence as a dominant of mid-intertidal communities.Deceased     

Chemical composition of material fractions in Danish household waste

The chemical composition of Danish household waste was determined by two approaches: a direct method where the chemical composition (61 substances) of 48 material fractions was determined after hand sorting of about 20 tonnes of waste collected from 2200 households; and an indirect method where batches of 80–1200 tonnes of unsorted household waste was incinerated and the content of the waste determined from the content of the outputs from the incinerator. The indirect method is believed to better represent the small but highly contaminated material fractions (e.g., batteries) than the direct method, because of the larger quantities included and the more homogenous material to sample from. Differences between the direct and the direct methods led to corrections in the of heavy metal concentration of a few fractions.The majority of the energy content of the waste originates from organic waste like paper, cardboard and organic fractions. The single fraction contributing most to the total energy content is the non-recyclable plastic fraction, contributing 21% of the energy content and 60% of the chlorine content, although this fraction comprises less than 7% by weight. Heavy metals originate mainly from inert fractions, primarily batteries.     

Successive identification of biodegradation rates for multiple sequentially reactive contaminants in groundwater.

At the field scale, the biodegradation rate is usually estimated from analytical solutions to single species transport with first-order reactions, using measured data as input. Because many contaminants, e.g., chlorinated solvents, are degraded in a sequential pattern, with degradation products further reacting to produce new species, it is of great interest to quantify the transformation rate of every reaction. The conventional inverse solutions for identifying the transformation rates are limited to single species problems. In the present study, we propose a successive optimization approach to identify the biodegradation rate for each species by using a previously developed analytical solution to multi-species first-order reactive transport using data obtained at the field scale. By specifying a link between analytical solutions to sequentially reactive transport problems and optimization methods and assuming constant transport parameters (velocity, dispersivities, and retardation factors), the first-order transformation rates are optimized successively from parent species to its daughter species.     

Mitigation of methane emission from an old unlined landfill in Klintholm,Denmark using a passive biocover system

Methane generated at landfills contributes to global warming and can be mitigated by biocover systems relying on microbial methane oxidation. As part of a closure plan for an old unlined landfill without any gas management measures, an innovative biocover system was established. The system was designed based on a conceptual model of the gas emission patterns established through an initial baseline study. The study included construction of gas collection trenches along the slopes of the landfill where the majority of the methane emissions occurred. Local compost materials were tested as to their usefulness as bioactive methane oxidizing material and a suitable compost mixture was selected. Whole site methane emission quantifications based on combined tracer release and downwind measurements in combination with several local experimental activities (gas composition within biocover layers, flux chamber based emission measurements and logging of compost temperatures) proved that the biocover system had an average mitigation efficiency of approximately 80%. The study showed that the system also had a high efficiency during winter periods with temperatures below freezing. An economic analysis indicated that the mitigation costs of the biocover system were competitive to other existing greenhouse gas mitigation options.     

The Potential for Double-Loop Learning to Enable Landscape Conservation Efforts

As conservation increases its emphasis on implementing change at landscape-level scales, multi-agency, cross-boundary, and multi-stakeholder networks become more important. These elements complicate traditional notions of learning. To investigate this further, we examined structures of learning in the Landscape Conservation Cooperatives (LCCs), which include the entire US and its territories, as well as parts of Canada, Mexico, and Caribbean and Pacific island states. We used semi-structured interviews, transcribed and analyzed using NVivo, as well as a charrette-style workshop to understand the difference between the original stated goals of individual LCCs and the values and purposes expressed as the collaboration matured. We suggest double-loop learning as a theoretical framework appropriate to landscape-scale conservation, recognizing that concerns about accountability are among the valid points of view that must be considered in multi-stakeholder collaborations. Methods from the social sciences and public health sectors provide insights on how such learning might be actualized.