Modelling nitrogen fluxes at the landscape scale

The distribution and impacts of different nitrogen pollutants are inextricably linked. To understand the problem fully, the interactions between the different pollutants need to be taken into account. This is particularly important when it comes to abatement techniques, since measures to reduce emissions of one nitrogen pollutant can often lead to an increase in another. This project represents a step towards greater understanding of these issues by linking together new and existing nitrogen flux models into a larger framework. The modelling framework has been constructed and some of the nitrogen flows between fields, farms and the atmosphere have been modelled for a UK study area for typical farm management scenarios.     

Modelling of nitrogen release from MBT waste

The "LaNDy" model (landfill nitrogen dynamics model) is a new mathematical tool for the evaluation of the long-term behaviour of nitrogen in mechanical-biologically pretreated (MBP) waste. LaNDy combines a hydraulic model based on RICHARD's equation with one-dimensional heat flow in landfills, kinetics of biological degradation, gas diffusion, nitrification and denitrification. A suitable temperature-dependent N mineralisation sub-model was based on numerous data from the literature and own LSR-experiments. With the "nitrification modus" of the LaNDy model, kinetic data of nitrification, thermodynamic data of denitrification and diffusion characteristics of gaseous components (especially of oxygen and methane) are used as an additional input for the preliminary calculation of the long-time impact of nitrification and denitrification. Examples of predicted temperature distribution and leachate ammonium concentrations, using different landfill size, age of the landfill (10 to approximately 100 a) and hydraulic conductivity of the MBP waste, are presented in this paper.     

Modelling seasonal variation in biomedical waste generation at healthcare facilities

A mathematical model can help waste planners to optimize waste management systems related to environmental protection. It can also help government bodies set guidelines and regulations, and evaluate prevailing strategies for handling and disposal of waste. In this paper, a technique to develop a mathematical model to correlate the generation rate of biomedical waste (contaminated with blood and body fluid) as a function of bed occupancy and type of ailment (in terms of seasonal changes) using data for two consecutive years from three different healthcare facilities is presented. The data exhibit different trends in biomedical waste generation rates and number of beds occupied in two different years. However, the seasonal variation in biomedical waste production rate remained nearly the same during these 2 years. The fixed trend in biomedical waste generation rate in two consecutive years could be due to similar seasonal illnesses pattern and social factors.     

Measurement and Modelling of Ammonia Emissions at Waste Treatment Lagoon-Atmospheric Interface

Global emissions of ammonia are approximately 75 Tg N/yr (1 Tg =10¹²g). The major global source is excreta from domestic animals ( 32 Tg N ^-1yr^-1). Waste storage and treatment lagoonsare used to treat the excreta of hogs in North Carolina (NC). Proteins and nitrogen rich compounds in the lagoon are convertedto ammonia, through a series of biological and chemical transformations. The process of ammonia emission has been investigated using two different model approaches: (1) CoupledMass Transfer with Chemical Reaction Model (Model I), and (2)Mass Transport without Chemical Reaction Model (Model II). Asensitivity analysis is performed with the models, and the modelresults are compared with ammonia emission experiments at a swinewaste storage and treatment lagoon in NC using a dynamic emissionflux chamber.Results of model predictions of emission flux indicate an exponential increase in ammonia flux with increasing lagoontemperature and pH, a linear increase with increasing lagoontotal ammoniacal nitrogen (TAN), and a secondary degree increasewith the increasing wind speed. In addition, the fluxes predictedby Model I are consistently larger than fluxes predicted by Model II. Experimental values of flux agreed well with model predictions, with the experimental values lying in different positions between the two model predictions under different physical and chemical conditions. Further, when compared to diurnal and seasonal experimental flux values, Model I corroborates the results in calm meteorological conditions (windspeed U10 = 1.5 m s^-1). However, the observed results are better predicted by Model II during unstable conditions, when wind speeds are higher than 2.0 m s^-1 and physical transfer process functions dominate.     

Transformations of nitrogen at the interface between the topsoil and an impervious clay subsoil

Much work has been done on gaseous emissions and leaching of nitrogenous compounds from whole soil profiles and also from soil surface measurements which are assumed to be mainly due to topsoil activity. In soils with an impervious clay subsoil, the boundary between the topsoil and subsoil may provide an interface for microbial activity, including N transformations. In this study, we investigated movement and transformations of two reactive N species (nitrate and urea) at the subsoil interface using a series of replicate, intact soil blocks, under two contrasting watering regimes. We measured fluxes in both liquid and gaseous phases and demonstrated that nitrate reaching the subsoil interface does not necessarily leach into water systems, but may denitrify immediately and could, therefore, add to atmospheric pollution through N₂O production. On the other hand, ammonium reaching the subsoil interface either directly, or after mineralization, appears to be more mobile than expected and has the potential to pollute watercourses.     

Transformations of nitrogen at the interface between the topsoil and an impervious clay subsoil

Much work has been done on gaseous emissions and leaching of nitrogenous compounds from whole soil profiles and also from soil surface measurements which are assumed to be mainly due to topsoil activity. In soils with an impervious clay subsoil, the boundary between the topsoil and subsoil may provide an interface for microbial activity, including N transformations. In this study, we investigated movement and transformations of two reactive N species (nitrate and urea) at the subsoil interface using a series of replicate, intact soil blocks, under two contrasting watering regimes. We measured fluxes in both liquid and gaseous phases and demonstrated that nitrate reaching the subsoil interface does not necessarily leach into water systems, but may denitrify immediately and could, therefore, add to atmospheric pollution through N₂O production. On the other hand, ammonium reaching the subsoil interface either directly, or after mineralization, appears to be more mobile than expected and has the potential to pollute watercourses.     

Air Pollution Modelling at an Urban Scale – Russian Experience and Problems

Urban concentration fields are extremely inhomogeneous andtheir gradients are very high. It results in specificproblems when modelling air pollution at the urban scalethat are analysed in this paper. Some examples ofmisrepresentation of the urban concentration field,computed with the use of the source-receptor type models,are given here. They can help in understanding the natureof the problems we face and reveal deficiencies of thecomputational technologies in use. Filtering of thecomputed fields is suggested as an instrument for improvingtheir quality. Its efficiency is proved on the test runs.An algorithm for refinement of the filtered fields isintroduced in this paper.     

Slurry phase bioremediation of PAHs in industrial landfill samples at laboratory scale

The effect of Tween 80 and selected bacteria additions on the bioremediation of PAH contaminated landfill soil (70.38mgkg(-1)) was evaluated in a slurry phase bioreactor. A phenanthrene-degrading consortium was selected by enrichment cultures and used as autochthonous inoculum. The Tween 80 addition increased the aqueous concentration of both high and low molecular weight PAHs. In the experiment with Tween 80 and inoculum addition, added microorganisms improved (>90%) the biodegradation of two- and three-ring PAHs as well as of the four-ring PAHs pyrene and fluoranthene. Biodegradation of the higher molecular weight PAHs was about 30% in experiments with Tween 80 addition, with and without inoculum addition.     

Batch separation of shredded bulky waste by gas-solid fluidized bed at laboratory scale

A gas-solid fluidized bed separator using various bed materials was used to separate shredded municipal bulky waste (SBW). Using 290 microm glass beads as the bed material, the apparent density of the fluidized bed was 1.5 g/cm(3) and the SBW could be separated into combustibles such as wood, paper and plastics and incombustibles such as metals and glass. The overall efficiency (Newton's efficiency) of the separation was calculated to be 0.93. In order to obtain high efficiency, the superficial velocity must be adjusted so that the fluidized bed is agitated moderately and at the same time there is no weak fluidized region. Using a mixture of particles of nylon shot and 68 microm glass beads, the apparent density of the fluidized mixture bed could be varied between 0.63 and 0.99 g/cm(3) by changing the mixing ratio of the two materials. In the case of a mixing ratio of 20% for glass beads, an apparent density of 0.65 g/cm(3) was produced, in which wood and paper components were recovered while plastics remained in the bed to give a final overall efficiency of 0.88.     

Improvement actions in waste management systems at the provincial scale based on a life cycle assessment evaluation

This paper reports some of the findings of the ‘GERLA’ project: GEstione Rifiuti in Lombardia – Analisi del ciclo di vita (Waste management in Lombardia – Life cycle assessment). The project was devoted to support Lombardia Region in the drafting of the new waste management plan by applying a life cycle thinking perspective. The present paper mainly focuses on four Provinces in the Region, which were selected based on their peculiarities. Life cycle assessment (LCA) was adopted as the methodology to assess the current performance of the integrated waste management systems, to discuss strengths and weaknesses of each of them and to design their perspective evolution as of year 2020.Results show that despite a usual business approach that is beneficial to all the provinces, the introduction of technological and management improvements to the system provides in general additional energy and environmental benefits for all four provinces. The same improvements can be easily extended to the whole Region, leading to increased environmental benefits from the waste management sector, in line with the targets set by the European Union for 2020.     

The use of life cycle assessment for the comparison of biowaste composting at home and full scale

Environmental impacts and gaseous emissions associated to home and industrial composting of the source-separated organic fraction of municipal solid waste have been evaluated using the environmental tool of life cycle assessment (LCA). Experimental data of both scenarios were experimentally collected. The functional unit used was one ton of organic waste. Ammonia, methane and nitrous oxide released from home composting (HC) were more than five times higher than those of industrial composting (IC) but the latter involved within 2 and 53 times more consumption or generation of transport, energy, water, infrastructures, waste and Volatile Organic Compounds (VOCs) emissions than HC. Therefore, results indicated that IC was more impacting than HC for four of the impact categories considered (abiotic depletion, ozone layer depletion, photochemical oxidation and cumulative energy demand) and less impacting for the other three (acidification, eutrophication and global warming). Production of composting bin and gaseous emissions are the main responsible for the HC impacts, whereas for IC the main contributions come from collection and transportation of organic waste, electricity consumption, dumped waste and VOCs emission. These results suggest that HC may be an interesting alternative or complement to IC in low density areas of population.     

Critical Loads and Dynamic Modelling to Assess European Areas at Risk of Acidification and Eutrophication

European critical loads and novel dynamic modelling data have been compiled under the LRTAP Convention by the Coordination Centre for Effects. In 2000 9.8% of the pan-European and 20.8% of the EU25 ecosystem area were at risk of acidification. For eutrophication (nutrient N) the areas at risk were 30.1 and 71.2%, respectively. Dynamic modelling results reveal that 95% of the area at risk of acidification could recover by 2030 provided acid deposition is reduced according to present legislation. Insight into the timing of effects of exceedances of critical loads for nutrient N necessitates the further development of dynamic models.     

Rapid full‐scale bioremediation of perchlorate in soil at a large brownfields site

The former Bermite site north of Los Angeles, California, was used to manufacture various explosives and related products containing energetic compounds, including perchlorate. Remediation of perchlorate in site soil and groundwater is being conducted to meet regulatory requirements and allow planned redevelopment activities to proceed. The general approach to perchlorate remediation of shallow soil at the site includes excavation of affected soils followed by ex situ bioremediation. Glycerin was chosen for use as an electron donor because of its stability, safety, low cost, and regulatory acceptance. However, full‐scale bioremediation operation with glycerin initially resulted in inconsistent results despite consistent perchlorate biodegradation observed in treatability study microcosms. To eliminate the inconsistency and optimize the biotreatment process, additional studies were performed in the field on parallel tracks to determine crucial factor(s) that influenced inconsistent breakdown of perchlorate in site soils. Total Kjeldahl nitrogen (TKN) was determined to be a significant factor limiting perchlorate biodegradation. The addition of di‐ammonium phosphate (DAP) resulted in the consistent and complete perchlorate removal, generally within two weeks of incubation with a median destruction rate of about 200 μg/kg/day. Soil processing rates were gradually increased over the year, and, by the summer, approximately 2,000 to 2,500 tons of soil were being processed per day with a total of approximately 160,000 tons processed by the end of July. The total unit treatment cost for the process is about approximately $35/ton. The glycerin‐DAP process is playing a major role in the remediation of this 1,000‐acre former industrial site. © 2008 Wiley Periodicals, Inc.     

Modelling the compression behaviour of landfilled domestic waste

This paper discusses the mechanisms involved in the compression of domestic waste, and how the resulting compression behaviour may be modelled. Reference is made to experimental data illustrating the effect of gas content and pore water pressure on bulk density and drainable porosity, and a theoretical model able to reproduce some but not all features of the data is presented.     

Modelling of organic matter dynamics during the composting process

Composting urban organic wastes enables the recycling of their organic fraction in agriculture. The objective of this new composting model was to gain a clearer understanding of the dynamics of organic fractions during composting and to predict the final quality of composts. Organic matter was split into different compartments according to its degradability. The nature and size of these compartments were studied using a biochemical fractionation method. The evolution of each compartment and the microbial biomass were simulated, as was the total organic carbon loss corresponding to organic carbon mineralisation into CO₂. Twelve composting experiments from different feedstocks were used to calibrate and validate our model. We obtained a unique set of estimated parameters. Good agreement was achieved between the simulated and experimental results that described the evolution of different organic fractions, with the exception of some compost because of a poor simulation of the cellulosic and soluble pools. The degradation rate of the cellulosic fraction appeared to be highly variable and dependent on the origin of the feedstocks. The initial soluble fraction could contain some degradable and recalcitrant elements that are not easily accessible experimentally.     

Modelling the biochemical degradation of solid waste in landfills

This paper describes the concept of a generic spatially distributed numerical model that has been developed to contain and link sub-models of landfill processes in order to simulate solid waste degradation and gas generation in landfills. The model includes the simulation of the transport of leachate and gases, and the consolidation of the solid waste. The structure of the model consists of linked discrete constant volume elements. The paper outlines the theoretical background that provides the framework to contain the numerical procedures that make up the model. Details are also given of the approach to the modelling of the chemistry and microbiology of solid waste degradation.     

Modelling the effects of waste components on cement hydration

Ordinary Portland Cement (OPC) is often used for the solidification/stabilization (S/S) of waste containing heavy metals and salts. These waste components will precipitate in the form of insoluble compounds on to unreacted cement clinker grains preventing further hydration. In this study the long term effects of the presence of contaminants in solidified waste is examined by numerically simulating cement hydration after precipitation of metal salts on the surface of cement grains. A cement hydration model was extended in order to describe pore water composition and the effects of cement grain coating. Calculations were made and the strength development predicted by the model was found to agree qualitatively with experimental results found in literature. The complete model is useful in predicting the strength and leaching resistance of solidified products and developing solidification recipes based on cement.     

Valorization of marine sediments in geopolymer mortars: physico-mechanical,microstructural and environmental investigations at laboratory scale

Journal of Material Cycles and Waste Management - The high consumption of natural sand and the accumulation of mineral wastes in landfills such as dredged sediments make it necessary to valorize...