Christos Christodoulatos

Treatment of arsenic in Bangladesh well water using a household co-precipitation and filtration system

Laboratory and field tests were conducted to evaluate the effectiveness of a household filtration process and investigate the effects of phosphate and silicate on the removal of arsenic from Bangladesh groundwater by ferric hydroxides. Fe/As ratios of greater than 40 (mg/mg) were required to reduce arsenic to less than 50 microg/L in Bangladesh well water due to the presence of elevated phosphate and silicate concentrations. The household filtration process included co-precipitation of arsenic by adding a packet (approximately 2 g) of ferric and hypochlorite salts to 20 L of well water and subsequent filtration of the water through a bucket sand filter. A field demonstration study was performed to test the treatment system in seven households in Bangladesh in March and April 2000. Experimental results obtained from the participating families proved that the household treatment process removed arsenic from approximately 300 microg/L in the well water to less than 50 microg/L. The participating families liked this simple and affordable process and used it to prepare clean water for drinking and cooking. A larger scale field test is currently underway.

Solubility, Sorption, and Soil Respiration Effects of Tungsten and Tungsten Alloys

This laboratory study addresses issues related to the fate and transport of tungsten and tungsten oxides in the environment (soil-water). Tungsten dioxide and tungsten trioxide were dissolved in aqueous solutions whose pH had been adjusted from 4.0 to 11.0. For initial pH smaller than 10.0, dissolved tungsten concentration remained fairly constant at around 10.0 mg/L for WO2 and increased from 0.3 mg/L to 2.0 mg/L for WO3 with increasing values of initial pH. Large amounts of dissolved tungsten were found when tungsten powder or alloy pieces were exposed to aqueous solutions. The dissolution occurs along depletion in solution pH and dissolved oxygen concentration. Depending upon the alloying elements present, the final dissolved tungsten concentration varied from 70 to 475 mg/L. Reduction in pH, dissolved oxygen depletion, and high levels of dissolved tungsten may be of relevance to environmental forensics. In the presence of alloying elements such as iron, nickel, and cobalt, tungsten strongly sorbed to well-characterized model soils. Sorption of tungsten to illite and montmorillonite clays occurs with an increase in pH and appears to be nonreversible. This behavior may significantly retard tungsten mobility. The mixing of tungsten powder with soils at rates higher than 3% (w/w) resulted in acidification of the soil matrix and had a significant impact on soil microbial community as determined by soil respiration.

Effects of natural organic matter on aggregation kinetics of boron nanoparticles in monovalent and divalent electrolytes

Nano boron is a promising new propellant being considered for military and civilian applications; however, the impact of its release on the environment is largely not known. The early stage aggregation kinetics of boron nanoparticles was investigated in the presence of two kinds of natural organic matter-Suwannee River humic acid (SRHA) and sodium alginate-by dynamic light scattering and transmission electron microscopy (TEM). The addition of SRHA caused the boron nanoparticles to stabilize and resulted in (1) decreased attachment efficiency for the reaction-controlled regime and (2) an increase in the critical coagulation concentration, in CaCl(2) and MgCl(2) solutions. The increase in the electrostatic repulsion is suggested as a main cause of the induced stabilization as indicated by the electrophoretic mobility measurements. Similar behavior was observed in the presence of alginate and MgCl(2). However, the attachment efficiency kept increasing in the presence of CaCl(2) and alginate with the increase in the electrolyte concentration and was greater than unity at>4mM CaCl(2). The destabilization was attributed to bridging of the nanoparticles by the alginate-Ca(2+) system. Results from this study suggest that various NOM and electrolytes play significant and differing roles in the aggregation of boron nanoparticles in natural aquatic environments.

Aggregation and deposition behavior of boron nanoparticles in porous media

New kinds of solid fuels and propellants comprised of nanomaterials are making their way into civilian and military applications yet the impact of their release on the environment remains largely unknown. One such material is nano boron, a promising solid fuel and propellant. The fate and transport of nano boron under various aquatic systems was investigated in aggregation and deposition experiments. Column experiments were performed to examine the effects of electrolyte concentration and flow velocity on the transport of boron nanoparticles under saturated conditions, whereas aggregation tests were conducted to assess the effects of electrolytes on the aggregation of the boron nanoparticles. Aggregation tests indicated the presence of different reaction-controlled and diffusion-controlled regimes and yielded critical coagulation concentrations (CCC) of 200 mM, 0.7 mM and 1.5 mM for NaCl, CaCl(2), and MgCl(2), respectively. Aggregation and deposition experimental data corresponded with the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) model and the constant attachment efficiency filtration model, respectively. Theoretical calculations indicated that both the primary and secondary energy minima play important roles in the deposition of nano boron in sand columns.

Plasmochemical degradation of volatile organic compounds (VOC) in a capillary discharge plasma Reactor

We report the results of parametric and kinetic studies of the plasmochemical degradation of volatile organic compounds (VOCs) present in respirable atmospheres using a nonthermal ambient-pressure plasma generated in a pin-to-plate capillary plasma electrode (CPE) discharge reactor. Parameters studied included the reactor volume, contaminant residence time, energy density, and influent contaminant concentration. A kinetic model was developed based on a plug-flow regime and a second-order kinetic expression with respect to the reactive plasma species and contaminant concentration. Experimental data were fitted to the proposed model using nonlinear regression techniques, and plasmochemical degradation rate constants were determined for toluene, ethylbenzene, and m-xylene as model compounds.

Destruction of Bacillus Subtilis cells using an atmospheric-pressure capillary plasma electrode discharge

We report the results of experiments aimed at the investigation of the destruction of spore-forming bacteria, which are believed to be among the most resistant micro-organisms, using a novel atmospheric-pressure capillary plasma electrode discharge plasma. Various well-characterized cultures of Bacillus Subtilis were prepared, subjected to atmospheric-pressure plasma jets emanating from a plasma-shower reactor operated either in He or in air (N/sub 2//O/sub 2/ mixture) at various power levels and exposure times, and analyzed after plasma treatment. Reductions in colony-forming units ranged from 10/sup 4/ (He plasma) to 10/sup 8/ (air plasma) for plasma exposure times of less than 10 min.

Anaerobic biodegradation of nitroglycerin

Abstract Nitroglycerin (C 3 H 5 (ONO 2 ) 3 ) or glycerol trinitrate (GTN), a constituent of various propellant formulations and a vasodilator prescribed to treat angina pectoris and other heart diseases, was completely mineralized in serum vials under strict anaerobiosis by mixed cultures from an anaerobic digester. Anaerobic biodegradation occurred via successive denitration of the parent molecule and production of glycerol dinitrate (GDN), and glycerol mononitrate (GMN), which was converted to a utilizable carbon source, most likely glycerol. Both isomeric forms of GDN were detected, namely glycerol 1,3-dinitrate (1,3-GDN) and glycerol 1,2-dinitrate (1,2-GDN), which were converted to glycerol 1-mononitrate (1-GMN) and glycerol 2-mononitrate (2-GMN). Significant regioselectivity of the enzymatic degradation was observed with preferential attack at the secondary (C2) nitro group, which favored production of 1,3-GDN and 1-GMN. Addition of cosubstrates substantially enhanced the rates of conversion of GTN; however, biodegradation also occurred in the absence of external carbon sources. The rates of biodegradation were significantly decreased at each successive denitration, with conversion of GMN to glycerol being the rate limiting step. The destruction of the GDN and GMN intermediates, which are more soluble than the parent compound, and possibly more toxic and mutagenic, is extremely important for the treatment of wastewater and soils contaminated with GTN. Nitrate and nitrite, the main nitrogen products of denitration, were also removed under anaerobic conditions.

Effects of particle size and acid addition on the remediation of chromite ore processing residue using ferrous sulfate

A bench-scale treatability study was conducted to assess the effects of particle size and acid addition on the remediation of chromite ore processing residue (COPR) using ferrous sulfate. The remediation scheme entailed the chemical reduction of hexavalent chromium [Cr(VI)] and the mitigation of swell potential. Leaching tests and the EQ3/6 geochemical model were used to estimate the acid dosage required to destabilize Cr(VI)-bearing and swell-causing minerals. The model predicted greater acid dosage than that estimated from the batch leaching tests. This indicated that mass transfer limitation may be playing a significant role in impeding the dissolution of COPR minerals following acid addition and hence hindering the remediation of COPR. Cr(VI) concentrations determined by alkaline digestion for the treated samples were less than the current NJDEP standard. However, Cr(VI) concentrations measured by X-ray absorption near edge structure (XANES) were greater than those measured by alkaline digestion. Greater Cr(VI) percentages were reduced for acid pretreated and also for smaller particle size COPR samples. Upon treatment, brownmillerite content was greatly reduced for the acid pretreated samples. Conversely, ettringite, a swell-causing mineral, was not observed in the treated COPR.

Tungsten speciation and toxicity: acute toxicity of mono- and poly-tungstates to fish.

Tungsten is a widely used transition metal for which very limited information on environmental and toxicological effects is available. Of particular interest is the lack of information linking tungsten speciation and environmental effects. Tungsten anions may polymerize (depending upon concentration, pH, and aquatic geochemistry) in aquatic and soil systems. However, to this date, of all soluble tungstate species only monotungstates have been scrutinized to a fair extent in toxicological studies. The objective of this work is a comparative assessment of the acute toxicity of monotungstates (sodium tungstate, Na(2)WO(4)) and polytungstates (sodium metatungstate, 3Na(2)WO(4).9WO(3)) to Poecilia reticulate. The experiments have been performed according to the OEDC protocols 203 and 204. LD50 values for 1-14 days show that sodium metatungstate is significantly more toxic to fish than sodium tungstate. Based on LD50 (0.86-3.88gL(-1) or 4.67-21.1x10(-3)molNa(2)WO(4)L(-1)), sodium tungstate may be classified as a chemical of low toxicity to fish. Sodium metatungstate caused similar fish mortality to sodium tungstate when it was introduced in 55-80 times lower concentrations (in terms of molL(-1)) than sodium tungstate. LD50 values for sodium metatungstate range from 0.13 to 0.85gWL(-1) or 5.69 to 38.71x10(-5)mol 3Na(2)WO(4).9WO(3)L(-1). Based on these values sodium metatungstate can be classified as a moderate toxic agent to fish.

Leaching mechanisms of Cr(VI) from chromite ore processing residue.

Batch leaching tests, qualitative and quantitative x-ray powder diffraction (XRPD) analyses, and geochemical modeling were used to investigate the leaching mechanisms of Cr(VI) from chromite ore processing residue (COPR) samples obtained from an urban area in Hudson County, New Jersey. The pH of the leaching solutions was adjusted to cover a wide range between 1 and 12.5. The concentration levels for total chromium (Cr) and Cr(VI) in the leaching solutions were virtually identical for pH values >5. For pH values <5, the concentration of total Cr exceeded that of Cr(VI) with the difference between the two attributed to Cr(III). Geochemical modeling results indicated that the solubility of Cr(VI) is controlled by Cr(VI)-hydrocalumite and Cr(VI)-ettringite at pH >10.5 and by adsorption at pH <8. However, experimental results suggested that Cr(VI) solubility is controlled partially by Cr(VI)-hydrocalumite at pH >10.5 and by hydrotalcites at pH >8 in addition to adsorption of anionic chromate species onto inherently present metal oxides and hydroxides at pH <8. As pH decreased to <10, most of the Cr(VI) bearing minerals become unstable and their dissolution contributes to the increase in Cr(VI) concentration in the leachate solution. At low pH ( <1.5), Cr(III) solid phases and the oxides responsible for Cr(VI) adsorption dissolve and release Cr(III) and Cr(VI) into solution.