Papers by Christos Christodoulatos
High loadings of nutrients such as phosphorus (P) are a major source of eutrophication that is th... more High loadings of nutrients such as phosphorus (P) are a major source of eutrophication that is threatening natural water quality worldwide. The excessive concentrations of P present in water bodies originate in agricultural and wastewater effluents, storm water runoff, etc. The disruption of the terrestrial P cycle by anthropogenic activities along with a growing awareness that P is a limited resource call for effective methods to remove and retain P before it reaches natural waters. This study investigates the removal of orthophosphate species (PO4-P) by adsorption onto aragonite as a natural adsorbent under a wide range of environmental conditions. Aragonite is a renewable and economical material; it can be used jointly with any best-management practices or as a post-secondary treatment in a wastewater treatment plant to enhance the phosphorus removal and consequently mitigate eutrophication in surface waters. Moreover, the aragonite-adsorbed P product can be used directly as a fe...
Bookmarks Related papers MentionsView impact
CRC Press eBooks, Feb 13, 2022
Bookmarks Related papers MentionsView impact
Journal of Hazardous Materials, Mar 1, 2009
Ultra high-performance liquid chromatography (UHPLC) utilizes columns packed with sub-2-mum stati... more Ultra high-performance liquid chromatography (UHPLC) utilizes columns packed with sub-2-mum stationary-phase particles and allows operation with pressures of up to 15,000 psi to yield increased resolution, speed, and sensitivity versus conventional HPLC. This promising new technology was used for the analysis of energetic compounds (RDX, HMX and CL-20) and a selective method was developed on an Acquity UPLC. A fast UHPLC method was applied to determine alkaline hydrolysis reaction kinetics of major energetic compounds. Activation energies of alkaline hydrolysis reaction for CL-20, RDX and HMX were comparable to those in literature, however they were determined in a shorter amount of time due to the speed of analysis of the chromatographic method. The use of liophilic salts (KPF(6)) as mobile-phase additives for the enhancement of separation selectivity of energetic compounds was demonstrated.
Bookmarks Related papers MentionsView impact
identification of areas containing radioactive contamination provide an excellent test case for e... more identification of areas containing radioactive contamination provide an excellent test case for environ-mentally responsible training. These training sites have restricted access, and operations are conducted in compliance with a current Nuclear Regulatory Commission license. In order for the training to be realistic, the ranges have been amended with thorium oxide to simulate a plutonium spill. The environ-mental concern from the operation of these ranges is thorium migration through three mechanisms: wnd, surface water, and vertical migration to groundwater. Field measurements have mapped thorium-232 distribution at the site, and led to laboratory experimente to determine mobilit} ' mechanisms. Column leaching experiments have shown that vertical migration is minimal, in agreement with field results. Soil extraction experiments indicate that thorium desorption from soil is colloidal. Additionally, electrokinetic experiments suggest thorium migration as a negative complex, pos...
Bookmarks Related papers MentionsView impact
Resources, Conservation and Recycling, 2022
Bookmarks Related papers MentionsView impact
Due to recent demilitarization activities in United States, Eastern Europe, and former Soviet Uni... more Due to recent demilitarization activities in United States, Eastern Europe, and former Soviet Union, a large quantity of propellants, explosives, and pyrotechnics are to be disposed in an environmental safe manner. The nitroaromatic compound 2,4-Dinitrotoluene (DNTT) is a precursor for the manufacture of 2,4,6-trinitrotoluene and polyurethane foam and extensively used in manufacturing propellants and explosives. A number of treatment technologies have been proposed to convert DNT to innocuous products or to separate it before it reaches the waste stream. Recently a basidiomycete, Phanerochaete chrysosporium, commonly known as a `white rot fungus` have been shown to be a potential microorganism for mineralizing DNT. Use of this fungus has been tested for decontaminating explosive contaminated soil. The objective of this study is to enhance the degradation rate of DNT by selecting proper reactor configuration and subsequently to model the degradation kinetics for scale-up purpose to t...
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
WIT Transactions on Ecology and the Environment, 1970
Bookmarks Related papers MentionsView impact
ABSTRACT Summary form only given. Electrical discharges in gas bubbles in water are investigated ... more ABSTRACT Summary form only given. Electrical discharges in gas bubbles in water are investigated by applying microsecond long rectangular pulses of 6-20 kV to needle-to-plane electrodes submerged in water. Ar or O2 bubbles; 1-5 mm in diameter, are introduced through the Pt needle that serves as the negative electrode. A bubble remains on the needle through numerous discharge processes. The voltage across the electrodes and the current to the ground are measured. Electrical measurements suggest that a corona-type atmospheric-pressure discharge is ignited in the gas bubble (composed of Ar or O2 gas and water vapor) without the electrical breakdown of the entire water filled electrode gap. The discharge characteristics are investigated as a function of the applied voltage, the distance between the electrodes, the bubbled gas (Ar or O2), the size of the gas bubble, and the pH and conductivity of the water. Optical and electrical measurements are used to explore the properties of the discharge. The size of the bubble as compared to the electrode distance affects the electrical characteristics of the discharge. The liquid water-metal interface and the liquid water-gas interface both play an important role in the initiation and the development of the electrical discharge in the gas bubbles. Evidence from environmental application studies supports the strong dependence of the discharge properties, active species production, and cleaning efficiency on all the parameters mentioned above including the applied voltage, the electrode distance, bubble size, and the initial characteristics of the solution
Bookmarks Related papers MentionsView impact
Journal of Cleaner Production, Aug 1, 2021
Abstract The amount of water removed from harvested algae and the required quantity of solvent fo... more Abstract The amount of water removed from harvested algae and the required quantity of solvent for efficient oil recovery impact the overall economic viability of transforming algae to bioenergy. Thus, in this study, the effect of total solids (TS) content and solvent-to-biomass ratio on oil recovery from Nannochloropsis oculata and Nannochloropsis salina (both referred to in this work as Nannocloropsis spp. and representative of marine species of algae) and Scenedesmus obliquus (a freshwater specie) was studied using modified Bligh & Dyer (B-D) method and Soxhlet extraction (with either hexane or ethanol as solvent). Adopting the modified B-D method, a maximum oil content exists between 10 and 20 wt% TS. Oil recovered with ethanol (with no pretreatment) and hexane (on acid hydrolyzed algae) with thimble increases with both TS (varied from 10 to 20 wt%) and solvent-to-biomass ratio (varied from 10 to 25). Conversely, oil yield increases with solvent-to-biomass ratio but reduces with TS due to enhanced mixing and mass transfer, increase in partition coefficient of lipids during downstream separation at lower TS, and implementation of hexane extraction without thimble. Hexane extraction was subsequently performed on acid hydrolyzed algae in a scale-up model and a 98% performance was achieved while about 60% of algal oil at the optimum data point was transformed to biodiesel with no significant impact by the solvent-to-biomass ratio or scale-up. Ethanol recovers mostly polar lipids and potentially forms an azeotrope with water which makes green diesel production less favorable and solvent recoverability challenging, respectively while the use of a large quantity of chloroform is unsafe. Thus, ethanol extraction and modified Bligh-Dyer methods were not performed in the scale-up model. Results from the application of our techno-economic analysis (TEA) model indicate that predicted sale price of Hydrotreated Algal Oil (HTAO) at each of the oil extraction data points decreases with increase in the oil content of algae, using a base case of 10000 barrel per day of HTAO with credits from animal feed and nutraceutical production. At the optimum data point, the predicted sale price of HTAO is $8.59 per gallon.
Bookmarks Related papers MentionsView impact
Langmuir, Nov 10, 2020
As a commercial adsorbent, TiO2 shows a high adsorption capacity for lead (Pb(II)). However, the ... more As a commercial adsorbent, TiO2 shows a high adsorption capacity for lead (Pb(II)). However, the molecular structure of Pb(II) adsorption on TiO2 is still unknown. Meanwhile, as a widely used corrosion inhibitor, phosphate (PO4) is usually added into drinking water, and its influential mechanism on Pb(II) removal by TiO2 remains unknown. Here, the mechanisms of Pb(II) adsorption on TiO2 and the effect of PO4 were systematically investigated using a combination of spectroscopic analyses and surface complexation modeling. The adsorption structure of Pb(II) on TiO2 was revealed as a tridentate mononuclear configuration by the extended X-ray absorption fine structure (EXAFS) analysis. In the presence of 0.1-5 mg/L PO4, Pb(II) was removed mainly by adsorption on TiO2 rather than precipitation. Ternary complexation between Pb(II) and PO4 on TiO2 surfaces was found based on EXAFS and in situ Fourier transform infrared characterizations. These complexation structures were used to build a surface complexation model to accurately simulate and predict Pb(II) removal under different conditions. This study provides essential information about the mechanisms of Pb(II) removal by TiO2 and develops a model to predict adsorption behaviors, especially in the presence of PO4.
Bookmarks Related papers MentionsView impact
Geosciences Journal, Jun 1, 2007
Bookmarks Related papers MentionsView impact
Social Science Research Network, 2022
Bookmarks Related papers MentionsView impact
Summary form only given. Pulsed electrical discharges in water find environmental applications in... more Summary form only given. Pulsed electrical discharges in water find environmental applications in water sterilization and decoloration due to the production of active species, such as ozone, hydrogen peroxide, O, H, and OH radicals. We investigated the production of active species and the decomposition of organic compounds using electrical discharges between horizontal mesh-to-mesh electrodes in water with Ar or Oxygen
Bookmarks Related papers MentionsView impact
Chemical Engineering Journal, May 1, 2020
Bookmarks Related papers MentionsView impact
Social Science Research Network, 2022
Bookmarks Related papers MentionsView impact
Nanoscale, 2022
Bio-enhanced carbonate precipitation for CO2 mineralization.
Bookmarks Related papers MentionsView impact
Science of The Total Environment, Apr 1, 2020
The soil major component of clay plays an important role in governing the fate and transport of e... more The soil major component of clay plays an important role in governing the fate and transport of engineered nanomaterials (e.g., the most commonly used titanium dioxide nanoparticles; nTiO2) in the subsurface environments via forming nTiO2-clay aggregates. This research is designed to unravel the interplay of naturally-occurring bacteria (Escherichia coli) and phosphate on the transport and retention of nTiO2-kaolin aggregates in water-saturated porous media. Our results showed that nTiO2-nTiO2 homoaggregates and nTiO2-kaolin heteroaggregates dominated in the nTiO2-kaolin nanoaggregate suspension. Transport of nTiO2-kaolin aggregates was enhanced with the copresence of E. coli and phosphate, particularly at the low pH of 6.0. This effect is due to the greater adsorption of phosphate and thus the greater enhancement in repulsive interaction energies between aggregates and sand grains at pH 6.0 (vs. pH 9.0). The charged “soft layer” of E. coli cell surfaces changed the aggregation state and the heterogeneous distribution of nTiO2-kaolin aggregates, and subsequently stabilized the nTiO2-nTiO2 homoaggregates and nTiO2-kaolin heteroaggregates via TEM-EDX measurements and promoted the physical segregation between the aggregates (separation distance = 0.486 vs. 0.614 μm without vs. with the presence of E. coli) via 2D/3D AFM identifications, both of which caused greater mobility of nTiO2-kaolin aggregates with the presence of E. coli. Nonetheless, transport of nTiO2-kaolin aggregates was lower with the copresence of E. coli and phosphate vs. the singular presence of phosphate due to the competitive adsorption of less negatively charged E. coli (vs. phosphate) onto the aggregates. Taken altogether, our findings furnish new insights into better understanding the fate, transport, and potential risks of nTiO2 in real environmental settings (soil and sediment aquifer) where clay, bacteria, and phosphate ubiquitously cooccur.
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Uploads
Papers by Christos Christodoulatos