Constantinos P. Halvadakis

Siting MSW landfills on Lesvos island with a GIS-based methodology.

The siting of Municipal Solid Waste (MSW) landfills in Greece is a difficult process due to land resource limitations, the country’s mountainous, insular and primarily water permeable terrain as well as an exacerbated public opposition (NIMBY syndrome). A GIS-based methodology is presented here with the goal to identify and rank the candidate landfill sites for the entire island of Lesvos. The initial step of the methodology comprises a GIS-based spatial analysis that uses 10 criteria, by excluding all areas unsuitable for any waste disposal activity. The pre-selected areas are then further assessed by fieldwork and candidate landfill sites are determined. The candidate sites are ranked using 19 criteria with predefined weight coefficients on a 0 to 10 grading scale. The weight coefficients are estimated for each criterion using the Analytic Hierarchy Process (AHP), while the grading scheme is based on pre-defined guidelines. An overall suitability index is produced for each candidate site allowing comparison and best case selection. A case study for the island of Lesvos is presented here, in which eight candidate landfill sites were finally selected and ranked. Social factors highly determined the ultimate selection of the site in Lesvos, since the third rather than the first site suggested by the methodology, was finally approved by local authorities.

Removal of total phenols from olive-mill wastewater using an agricultural by-product, olive pomace

The purpose of this study was to investigate the sorption of total phenols, which are contained in olive-mill wastewater (OMWW), on solid by-products of olive pomace processing mills. Preliminary batch experiments were conducted using three different types of olive pomace, dried olive pomace (OP-1), dried and solvent extracted olive pomace (OP-2) and dried, solvent extracted and incompletely combusted olive pomace (OP-3). According to the results, OP-3 showed high performance for total phenols sorption and stability. For sorbent concentration of 10gL(-1) and sorbate concentration of 50mgL(-1), more than 40% of initial total phenols concentration was removed. Sorption kinetics was well described by the pseudo-second order rate model (R2>0.99). Total phenols removal efficiency was improved by increasing sorbent concentration and solutions pH or decreasing particle size of the sorbent material. The Langmuir and Freundlich isotherms sufficiently described OP-3 sorption capacity for the concentration range studied (50-500mgL(-1)). Fixed bed sorption experiments showed that lower flow rates and smaller particle size of sorbent resulted in longer column exhaustion time and higher initial removal efficiency. Experiments with thermally or chemically regenerated OP-3 showed that sorption capacity deteriorated after regeneration.

Modelling gas production in managed sanitary landfills

Gas production and recovery from managed sanitary landfills can be simulated by describing the time and space variation of the total pressure and composition of the mixture of gases (CH4, CO2, and N2) in the landfill. The variation of the total pressure and the composition of the gas mixture is described by the equations for mass conservation for each component (including a generation term for CH4 and CO2), the equation of motion, and the equation of state. Simulations of gas production compare well with field data from the Mountain View controlled landfill project field experiment. The function used to approximate the shape of the methanogenesis curve (based on equations describing the biochemical processes) consists of a rising hyperbolic branch and a decaying exponential branch. The conceptual framework of the model has been designed to incorporate equations describing the physics, biology, and chemistry of gas production in landfills.

A Methodology to Estimate Odors around Landfill Sites: The Use of Methane as an Odor Index and Its Utility in Landfill Siting

Abstract The estimation of odor production and dispersion from landfill sites is a very complicated task because of the different chemical species that exist in biogas. To site a new landfill, it is necessary to know the distance that odors can travel around the landfill under atmospheric conditions that increase the concentration of pollutants. Although CH4 is an odorless gas, it can be used as an index to determine the dispersion of low-reactivity odorous species around a landfill site. Methane production rates, estimated by biogas production models, were used by an air dispersion model to determine the spatial distribution of CH4 around landfill sites. By utilizing dispersion models under extreme atmospheric conditions, a maximum CH4 concentration around the landfills was determined. Based on the ratio between CH4 and odorous chemical species, the spatial distribution of the concentration of an odorous species was determined for those species with low reactivity in the atmosphere. For odorous species with high reactivity in the atmosphere, a dispersion-reaction model must be used. In this way, the acceptable distance between new landfills and residential areas can be determined. The proposed methodology could be used as a design tool for those who are interested in landfill siting.

Dewatering of wastewater sludge through a solar still

Wastewater sludge was passed through a laboratory solar still in order to determine the dewatering process. A number of parameters describing the distillate and the sludge were measured at the end of each day in order to determine the process behavior under conditions of relatively high solar radiation and temperature levels. It was realized that dewatering is accelerated and further analysis is needed in order to determine optimum conditions and design parameters for a demonstration plant that will operate towards reducing the sludge volume.

Atmospheric methane transport near landfill sites

Methane production rates that have been estimated by a biogas production model (MICROGEN) are combined with an air dispersion model in order to determine the spatial distribution of methane around landfill sites. By utilising dispersion models under extreme atmospheric conditions, a maximum methane concentration around the landfills can be determined. The factors that enhance the maximum methane concentrations, using the meteorological model CALMET in conjunction with the dispersion model CALPUFF, are found to be the wind speed and the percentage of cloud cover. The rates of temperature and pressure variation, as well as the land use category seem to have no effect on the maximum methane concentrations. A rapid reduction of methane concentration is observed a few metres away from the landfill centre while a slower reduction is observed at distances greater than 300 m from it. The performance of this methodology is evaluated by comparing measured concentrations with model predictions.