Effect of drying on leaching testing of treated municipal solid waste incineration APC-residues

Air-pollution-control (APC) residues from waste incinerators are hazardous waste according to European legislation and must be treated prior to landfilling. Batch and column leaching data determine which type of landfill can receive the treated APC-residues. CEN standards are prescribed for the batch and column leaching test; however, these standards do not specify whether or not the residue samples should be dried prior to the leaching testing. Laboratory tests were performed in parallel (dried/non-dried) on treated APC-residue samples and evaluated with respect to Cr, Cd, Cu, Pb and Zn leaching. The effect of drying of the wet APC-residue samples was particularly dramatic regarding the leaching of Cr. Drying resulted in 10-100 times more Cr leaching in both batch and columns test. Drying also affected the leaching of Cd, Cu and Pb. Initial Cd leaching was up to 100 times higher in column tests with dried APC-residue than in tests with wet residues. The effect of drying appeared to be a combination of decreasing the reduction capacity of the sample (Cr), decreasing pH (Cd, Cu) and in column tests also a wash-out of salts (probably affecting Cd and Pb). If the leaching tests are intended to mimic landfill conditions, the results of this paper suggest that the tests should be done on wet, non-dried residue samples, although this may be less practical than testing dried samples.     

The Introduction of the Precautionary Principle in Danish Environmental Policy: The Case of Plant Growth Retardants

In this paper, we investigate the Precautionary Principle (PP) in action. Precaution is a fairly new concept in environmental policy. It emerged back in the 1960s but did not consolidate until the 1980s, as it formed part of the major changes taking place in environmental policies at that time. The PP is examined in three contexts. Firstly, we look at the meaning of the concept and how it is disseminated through the media and public discourses to the political arenas of Denmark. Then we examine how the idea is adopted to the political level. Thirdly, we look briefly at the first Danish translation of the principle into a practical context, which includes translations into concrete scientific practices. It is concluded that if the PP shall be more than a simple “idea” or a frequently used “term,” emphasis must be put on the transformation of the concept into concrete practices, like e.g., the alternative testing regimes that we show in the case of plant growth-retarding pesticides presented in this paper.     

Leaching from MSWI bottom ash: evaluation of non-equilibrium in column percolation experiments

Impacts of non-equilibrium on results of percolation experiments on municipal solid waste incineration (MSWI) bottom ash were investigated. Three parallel column experiments were performed: two columns with undisturbed percolation and one column with two sets of 1-month-long flow interruptions applied at liquid-to-solid (L/S) ratios of L/S 2L/kg and 12L/kg, respectively. Concentrations of Na, K, Cl(-), Ca, Si, SO(4)(2-), Al, Cu, Ni, Mo, Ba, Pb, Zn, and dissolved organic carbon (DOC) were monitored throughout the entire leaching period; geochemical modeling was used to identify non-equilibrium-induced changes in the solubility control. Despite both physical and chemical non-equilibrium, the columns were found to provide adequate information for readily soluble compounds (i.e., Na, Cl(-), and K) and solubility-controlled elements (i.e., Ca, SO(4)(2-), Ba, Si, Al, Zn, and Pb). The leaching of Cu and Ni was shown to depend strongly on DOC leaching, which was likely affected by physical non-equilibrium during flow interruptions. Consequently, the leaching of Cu and Ni in the undisturbed columns was shown to be by about one order of magnitude lower compared with the interrupted column. The results indicate that the leaching of DOC-related metals in laboratory column experiments may be considerably underestimated compared with full-scale scenarios in which the impacts from non-equilibrium may be significantly lower. The leaching of Mo (or MoO(4)(2-)) may be controlled solely by its availability in the mobile zone, which in turn appeared to be controlled by diffusion from the stagnant zone; no Mo controlling minerals were predicted by the geochemical modeling.     

Life cycle assessment of disposal of residues from municipal solid waste incineration: recycling of bottom ash in road construction or landfilling in Denmark evaluated in the ROAD-RES model

Two disposal methods for MSWI bottom ash were assessed in a new life cycle assessment (LCA) model for road construction and disposal of residues. The two scenarios evaluated in the model were: (i) landfilling of bottom ash in a coastal landfill in Denmark and (ii) recycling of bottom ash as subbase layer in an asphalted secondary road. The LCA included resource and energy consumption, and emissions associated with upgrading of bottom ash, transport, landfilling processes, incorporation of bottom ash in road, substitution of natural gravel as road construction material and leaching of heavy metals and salts from bottom ash in road as well as in landfill. Environmental impacts associated with emissions to air, fresh surface water, marine surface water, groundwater and soil were aggregated into 12 environmental impact categories: Global Warming, Photochemical Ozone Formation, Nutrient Enrichment, Acidification, Stratospheric Ozone Depletion, Human Toxicity via air/water/soil, Ecotoxicity in water/soil, and a new impact category, Stored Ecotoxicity to water/soil that accounts for the presence of heavy metals and very persistent organic compounds that in the long-term might leach. Leaching of heavy metals and salts from bottom ash was estimated from a series of laboratory leaching tests. For both scenarios, Ecotoxicity(water) was, when evaluated for the first 100 yr, the most important among the twelve impact categories involved in the assessment. Human Toxicity(soil) was also important, especially for the Road scenario. When the long-term leaching of heavy metals from bottom ash was evaluated, based on the total content of heavy metals in bottom ash, all impact categories became negligible compared to the potential Stored Ecotoxicity, which was two orders of magnitudes greater than Ecotoxicity(water). Copper was the constituent that gave the strongest contributions to the ecotoxicities. The most important resources consumed were clay as liner in landfill and the groundwater resource which was potentially spoiled due to leaching of salts from bottom ash in road. The difference in environmental impacts between landfilling and utilization of bottom ash in road was marginal when these alternatives were assessed in a life cycle perspective.     

Environmental assessment of waste incineration in a life-cycle-perspective (EASEWASTE).

A model for life-cycle assessment of waste incinerators is described and applied to a case study for illustrative purposes. As life-cycle thinking becomes more integrated into waste management, quantitative tools for assessing waste management technologies are needed. The presented model is a module in the life-cycle assessment model EASEWASTE. The module accounts for all uses of materials and energy and credits the incinerator for electricity and heat recovered. The energy recovered is defined by the user as a percentage of the energy produced, calculated on the lower heating value of the wet waste incinerated. Emissions are either process-specific (related to the amount of waste incinerated) or input-specific (related to the composition of the waste incinerated), while mass transfer to solid outputs are governed by transfer coefficients specified by the user. The waste input is defined by 48 material fractions and their chemical composition. The model was used to quantify the environmental performance of the incineration plant in Aarhus, Denmark before and after its upgrading in terms of improved flue gas cleaning and energy recovery. It demonstrated its usefulness in identifying the various processes and substances that contributed to environmental loadings as well as to environmental savings. The model was instrumental in demonstrating the importance of the energy recovery system not only for electricity but also heat from the incinerator.     

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.     

Environmental assessment of solid waste systems and technologies: EASEWASTE.

A new model has been developed for evaluating the overall resource consumption and environmental impacts of municipal solid waste management systems by the use of life cycle assessment. The model is named EASEWASTE (Environmental Assessment of Solid Waste Systems and Technologies) and is able to compare different waste management strategies, waste treatment methods and waste process technologies. The potential environmental impacts can be traced back to the most important processes and waste fractions that contribute to the relevant impacts. A model like EASEWASTE can be used by waste planners to optimize current waste management systems with respect to environmental achievements and by authorities to set guidelines and regulations and to evaluate different strategies for handling of waste. The waste hierarchy has for decades been governing waste management but the ranking of handling approaches may not always be the most environmentally friendly. The EASEWASTE model can identify the most environmentally sustainable solution, which may differ among waste materials and regions and can add valuable information about environmental achievements from each process in a solid waste management system.     

Method for determination of methane potentials of solid organic waste

A laboratory procedure is described for measuring methane potentials of organic solid waste. Triplicate reactors with 10 grams of volatile solids were incubated at 55 degrees C with 400 ml of inoculum from a thermophilic biogas plant and the methane production was followed over a 50-day period by regular measurements of methane on a gas chromatograph. The procedure involves blanks as well as cellulose controls. Methane potentials have been measured for source-separated organic household waste and for individual waste materials. The procedure has been evaluated regarding practicality, workload, detection limit, repeatability and reproducibility as well as quality control procedures. For the source-separated organic household waste a methane potential of 495 ml CH4/g VS was found. For fat and oil a lag-phase of several days was seen. The protein sample was clearly inhibited and the maximal methane potential was therefore not achieved. For paper bags, starch and glucose 63, 84 and 94% of the theoretical methane potential was achieved respectively. A detection limit of 72.5 ml CH4/g VS was calculated from the results. This is acceptable, since the methane potential of the tested waste materials was in the range of 200-500 ml CH4/g VS. The determination of methane potentials is a biological method subject to relatively large variation due to the use of non-standardized inoculum and waste heterogeneity. Therefore, procedures for addressing repeatability and reproducibility are suggested.     

METHOD TO IDENTIFY EFFECTWE RIPARIAN BUFFER WIDTHS FOR ATLANTIC SALMON HABITAT PROTECTION1

ABSTRACT: Successful restoration of declining anadromous species is dependent upon effective riparian buffer zone management. Natural resource managers, policy developers and local conservation groups require science‐based information concerning the width at which a given buffer will be effective for its stated purpose. This paper summarizes a method developed in 1999 to determine effective riparian buffer widths for Atlantic salmon habitat protection as part of the Atlantic Salmon Conservation Plan for Seven Maine Rivers. A major assumption of the method is that no two buffers are alike with respect to their effectiveness and that various buffer characteristics dictate the required width for a given level of effectiveness. The method uses a predictive model that generates suggested riparian buffer widths as a function of specific, measurable buffer characteristics (such as slope, soil characteristics, and plant community structure and density) that affect buffer function. The method utilizes a variable‐width, two‐zone approach and specifies land uses that are consistent with desired buffer function within the two zones.