Georgios Bartzas

Solid phase studies and geochemical modelling of low-cost permeable reactive barriers

A continuous column experiment was carried out under dynamic flow conditions in order to study the efficiency of low-cost permeable reactive barriers (PRBs) to remove several inorganic contaminants from acidic solutions. A 50:50 w/w waste iron/sand mixture was used as candidate reactive media in order to activate precipitation and promote sorption and reduction-oxidation mechanisms. Solid phase studies of the exhausted reactive products after column shutdown, using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), confirmed that the principal Fe corrosion products identified in the reactive zone are amorphous iron (hydr)oxides (maghemite/magnetite and goethite), intermediate products (sulfate green rust), and amorphous metal sulfides such as amFeS and/or mackinawite. Geochemical modelling of the metal removal processes, including interactions between reactive media, heavy metal ions and sulfates, and interpretation of the ionic profiles was also carried out by using the speciation/mass transfer computer code PHREEQC-2 and the WATEQ4F database. Mineralogical characterization studies as well as geochemical modelling calculations also indicate that the effect of sulfate and silica sand on the efficiency of the reactive zone should be considered carefully during design and operation of low-cost field PRBs.

Inorganic Contaminant Fate Assessment in Zero-Valent Iron Treatment Walls

This article discusses the fate assessment of several inorganic contaminants in zero-valent iron treatment walls used for the cleanup of acidic plumes and the prevention of groundwater contamination in active or abandoned mixed sulphide and coal mining sites. The fate assessment of contaminants provides useful information for potential forensics investigations carried out in affected mining and waste disposal sites. Laboratory studies using sodium chloride as conventional tracer were carried out to identify transport-related issues and assess the performance and long-term reactivity of iron walls. Transport parameters, such as residence time, dispersion, and heterogeneity, were determined by fitting chloride breakthrough curves (BTCs) to the convection-dispersion equation using time moment analysis and the CXTFIT 2.1 curve-fitting software. First moment analysis of breakthrough curves revealed modest increase in pore-water velocity over time, indicative of decreasing porosity within the reactive mass, mainly due to the formation of mineral precipitates. Geochemical modeling of the process, including interactions between iron filings, heavy metal ions, and sulphates; interpretation of the ionic profiles; and calculation of porosity loss was also carried out by using the speciation/mass transfer computer code PHREEQC-2 and the WATEQ4F database.

Efficiency of pecan shells and sawdust biochar on Pb and Cu adsorption

AbstractIn the present study, two different by-products, pecan shells, and sawdust obtained from the region of Chania, Crete, Greece, were subjected to slow pyrolysis over a temperature range of 250–550°C, for the production of biochar. The quality of the produced biochars was assessed by evaluating their main properties, namely pyrolysis yield, pH, volatile matter and char content, surface area, and C, H, S, N content. Thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy were used for the identification of the morphology and structure of the produced biochars. The potential of selected pecan shells and sawdust biochars to adsorb Pb and Cu from synthetic solutions was also assessed.

Modeling of Reaction Front Progress in Fly Ash Permeable Reactive Barriers

The aim of this article is to predict, through reactive transport modeling, the progress of the reaction front in lignite-based fly ash permeable reactive barriers by taking into account media compositional changes and degradation rates as well as the drop in reactivity due to precipitation and clogging, metal ion concentration, and removal mechanisms. In order to simulate field conditions, synthetic solutions with the quality of leachates generated at waste disposal sites (in terms of pH and toxic load) were pumped upflow in two 40-cm-long laboratory columns placed in series. In addition, this article aims to introduce engineering and science tools in understanding the mechanisms and the geochemical processes that determine the fate of contaminants during migration of acidic plumes in environmental media. The following methodological approach may be helpful in forensic investigations aiming to establish the contamination history at waste disposal sites.

Life cycle analysis of pistachio production in Greece

In the present paper, a life cycle assessment (LCA) study regarding pistachio (Pistacia vera L.) cultivation in Aegina island, Greece, was performed to evaluate the energy use footprint and the associated environmental impacts. In this context, a detailed life cycle inventory was created based on site-survey data and used for a holistic cradle-to-farm gate LCA analysis using the GaBi 6.5 software. The main impact categories assessed were acidification potential (AP), eutrophication potential (EP), global warming potential (GWP), ozone depletion potential (ODP), photochemical ozone creation potential (POCP) and cumulative energy demand (CED). In order to reveal the main environmental concerns pertinent to pistachio production and in turn propose measures for the reduction of environmental and energetic impacts, three scenarios were compared, namely the Baseline scenario (BS) that involves current cultivation practices, the Green Energy (GE) scenario that involves the use of biological fertilizers i.e. compost, and the Waste Utilization (WU) scenario that involves the production of biochar from pistachio and other agricultural wastes and its subsequent soil application to promote carbon sequestration and improve soil quality. Based on the results of this study, the use of compost for fertilization (GE scenario), which results in approximately 9% savings in terms of energy consumption and the five environmental impact categories studied compared to BS scenario, is considered a promising alternative cultivation strategy. Slightly higher savings (10% on average) in terms of the five calculated environmental impact categories, compared to the BS scenario, were indicated when the WU scenario was considered. Regarding energy consumption, the WU scenario results in minor increase, 3%, compared to the BS scenario. Results of uncertainty analysis performed using the Monte Carlo technique and contribution analysis showed that GE and WU scenarios offer reliable and significant eco-profile improvements for pistachio production in the study area compared to the current situation.

Removal of heavy metals from leachates using organic/inorganic permeable reactive barriers

ABSTRACT In the present experimental study, the efficiency of permeable reactive barriers (PRBs) containing organic material mixed with zero-valent iron, fly ash or red mud to remove heavy metals from leachates was assessed. Upflow laboratory column experiments were carried out to assess system efficiency in terms of Cu, Zn, Ni and Mn removal. The initial concentration of each metal ion in the feed was 50 mg/L. X-ray diffraction as well as scanning electron microscopy and energy dispersive spectrometry were used to identify new mineral phases and to identify metal removal mechanisms. Results and analyses show that sorption and precipitation of metals as sulphides, hydroxides and other hydrated phases are the dominant metal removal mechanisms.

Assessment of Aquifer Vulnerability in an Agricultural Area in Spain Using the DRASTIC Model

The assessment of aquifer vulnerability is a very important task, especially in agricultural areas because the quality and availability of groundwater affects both the sustainability of agriculture and the quality of life. In this study, an integrated approach is considered, with the use of the generic and agricultural DRASTIC models as well as a geographic information system (GIS), to assess groundwater vulnerability in the agricultural area of Barrax, in the province of Albacete, in Spain. Seven parameters—depth to water, net recharge, aquifer media, soil media, topography, impact of vadose zone media, and hydraulic conductivity of the aquifer (DRASTIC)—have been considered as weighted layers to enable an accurate groundwater risk mapping. The results of the generic DRASTIC model indicated very low vulnerability to contamination for Barrax groundwater due to limited urban and industrial development in the wider area. However, agricultural activities impose pressure to groundwater resources and the results of the agricultural DRASTIC model show that 6.86% of the study area is characterized by very high, 2.29% by high, 47.28% by medium, 38.28% by low, and the remaining 5.29% by no vulnerability to groundwater contamination. The distribution of nitrate concentration in groundwater in the area under study is quite well correlated with the agricultural DRASTIC vulnerability index. Sensitivity analysis was also performed to acknowledge statistical uncertainty in the estimation of each parameter used, to assess its impact, and thus to identify the most critical parameters that require further investigation. Depth to water and impact of vadose zone are the parameters that had the most noticeable impact on the generic DRASTIC vulnerability index followed by the soil media and topography. In contrast, the agricultural DRASTIC method is more sensitive to the removal of the depth to water parameter followed by the topography and the soil media parameters.