Daeik Kim

Encapsulation of lead from hazardous CRT glass wastes using biopolymer cross-linked concrete systems.

Discarded computer monitors and television sets are identified as hazardous materials due to the high content of lead in their cathode ray tubes (CRTs). Over 98% of lead is found in CRT glass. More than 75% of obsolete electronics including TV and CRT monitors are in storage because appropriate e-waste management and remediation technologies are insufficient. Already an e-waste tsunami is starting to roll across the US and the whole world. Thus, a new technology was developed as an alternative to current disposal methods; this method uses a concrete composite crosslinked with minute amounts of biopolymers and a crosslinking agent. Commercially available microbial biopolymers of xanthan gum and guar gum were used to encapsulate CRT wastes, reducing Pb leachability as measured by standard USEPA methods. In this investigation, the synergistic effect of the crosslinking reaction was observed through blending two different biopolymers or adding a crosslinking agent in biopolymer solution. This CRT-biopolymer-concrete (CBC) composite showed higher compressive strength than the standard concrete and a considerable decrease in lead leachability.

A NEW GENERATION OF PORTABLE COARSE, FINE, AND ULTRAFINE PARTICLE CONCENTRATORS FOR USE IN INHALATION TOXICOLOGY

This study presents the development of prototype portable coarse, fine and ultrafine particle concentrators. A single-round nozzle virtual impactor operating at an intake flow of 120 L/min is used to concentrate coarse particles (e.g., 2.5–10 µm) by a factor up to 40 depending on the minor flow rate. Fine and ultrafine particles are concentrated by first growing to supermicrometer sizes via supersaturation. This is accomplished by first drawing these particles over a pool of warm, deionized, distilled water to achieve saturation and then through a condenser that allows the particles to grow to supermicrometer size, followed by concentration in a virtual impactor. After concentration, particles are returned back to their original size distribution and relative humidity by removing excess moisture in a diffusion drier. The performance of these concentrators was evaluated using generated monodisperse particles as well as ambient air particles. Average concentration enrichment factors were 9.5, 20, and 37 for a minor flow of 12, 6, and 3 L/min, respectively. The average concentration enrichment based on particulate sulfate and nitrate was by a factor of 20 and 22.6, respectively. The HEADS sampler was used as the reference sampler. The enrichment values based on particulate nitrate indicate that no nitrate loss occurs during particle concentration enrichment. The concentration of particular elemental (EC) and organic carbon (OC) was also evaluated, using the MOU DI as a reference sampler. The average concentration enrichment factors obtained for EC and OC were 20.4 and 21.6, respectively. Our experimental results indicated that the enrichment in concentration is not dependent on particle size and chemical composition. Because of their compact size and high concentration efficiency, the concentrators described in this study are inexpensive and portable so can be moved easily to several locations over seasons that differ in PM chemical composition and source profiles.

Stabilization of Metals in Subsurface by Biopolymers: Laboratory Drainage Flow Studies

Environmental contamination with heavy metals and radionuclides remains a major problem worldwide. The current clean-up methodologies are based on energy-intensive engineering processes, which are disruptive and costly. A new universal technology targeted for the permanent enclosure and fixation of nuclear and other extreme hazardous metallic wastes in subsurface sites is needed. Such technology will be useful in treating contamination at many sites in the U.S., with specific applications to Department of Energy (DOE) sites. Biopolymers are potential tools for such an innovative technology. Biopolymers have repeated sequences, and therefore provide ample opportunity for chemical reactions with metals, soil particles, and other biopolymers. They also have the additional ability of creating cross-linking interpenetrating networks that can encapsulate the contaminants. Based on this concept, in the present work five biopolymers (xanthan, chitosan, polyhydroxy butyrate, guar gum, polyglutamic acid) were investigated for potential use in the stabilization of metals in the subsurface. The effects of these biopolymers (used alone and in combinations) on soil characteristics (permeability, shear strength) and their metal uptake ability have been studied using laboratory drainage flow systems. Biopolymer solutions were run through the experimental sandpack columns, followed by copper solution and leaching agents (distilled water and hydrochloric acid). The permeability and shear strength of sand were evaluated. Copper uptake capacity of each biopolymer and combination of biopolymers was also studied along with subsequent leaching. All biopolymers tested improved sand characteristics (by decreasing permeability and increasing shear strength) and had good metal uptake ability (60–90%) with relatively low leachability (10–22%). While biopolymers used alone were more efficient in metal uptake, the combination of two biopolymers (xanthan and chitosan) had an increasing plugging effect. These results show the potential of using biopolymers in subsurface metal stabilization.

Evaluation of biopolymer-modified concrete systems for disposal of cathode ray tube glass.

Abstract Cathode ray tubes (CRTs) from computer monitors and television sets, which contain significantly high percentage of lead (Pb) by weight, represent an enormous and growing hazardous waste problem in the United States and worldwide. As a result, new technologies are needed to cope with current CRT waste stream and increased hazard and build new markets for its recycled components, developing commercially viable concrete composites, as well as minimizing CRT disposal problems. In this study, commercially available biopolymers, such as xan-than gum, guar gum, and chitosan, were used to encapsulate CRT glass waste, reducing the Pb leachability. The biopolymers utilized contain a number of useful functional groups, such as carboxyl (xanthan), hydroxyl (guar), and amino groups (chitosan), which play important roles in binding and stabilizing Pb onto concrete structures. The use of biopolymers in concrete systems can create a stable interpenetrating cross-linking composite that will last for many years. Results from these new composites show 30% higher compressive strength than standard concrete and a sharp decrease in lead leachability from several thousand milligrams per liter initially to an amount of three-tenths milligrams per liter or lower values (much lower than the U.S. Environment Protection Agency standard for hazardous waste of 5 mg/L by the toxicity characteristic leaching procedure test), and for some of the composites leachability is below even the standard for drinking water. This efficient and cost-effective CRT–biopolymer-concrete composite is a new class of biopolymer-modified material that can potentially perform a significant role in relieving the current CRT issue.

Correlation between nitrite accumulation and the concentration of AOB in a nitritation reactor

AbstractNitritation is an innovative biological nitrogen removal method in wastewater, and it has the advantages of energy and economy. The correlation between a nitrite conversion rate and the gene copy numbers of ammonia oxidizing bacteria (AOB) in a nitritation reactor was examined to measure the effectiveness of removing a nitrogen content in a biological nitrogen removal process, using a biological process of nitritation. A laboratory scale reactor was prepared and operated for over a year, using digester supernatant to induce a stable nitritation, and to optimize the operational conditions by adjusting various operating factors. The relationship between operational results of nitritation reactor and the AOB gene copies was approximated through identification and quantitative analysis of AOB. A stable nitritation can be artificially led with the control of SRT, while treating anaerobic digester supernatant from MWTPs. And AOB gene copies showed a correlation with free ammonia (FA) inhibition and performance of nitritation, and AOB activity. Thus, AOB gene copies were found important when it comes to analyzing nitritation.

Mechanism and kinetics of reductive dehalogenation of PBB (polybrominated biphenyl) in the sonolytic and ketyl radical system

The kinetics and mechanism of reductive destruction of aqueous polybrominated biphenyl (PBB) were studied. Complete degradation was achieved within 30 min of ultrasound-assisted chemical process (UACP), which involved sonication, ketyl radical and its anion, and metal catalyst (ferrous ion). Reductive dehalogenation of PBB is a first-order reaction between PBB concentration and UACP reaction time. The kinetic condition of PBB degradation was optimized in terms of temperature, dosage of radical initiator, and metal catalyst. Mechanism of reductive debromination was also proposed to explain the function of ketyl and aryl radicals on the debromination of bromobiphenyl. Two kinetic models were studied to elucidate the debromination mechanism pathway. Laboratory observed data were found to fit model predicted values obtained from equilibrium and differential equations.

Feasibility study on cross-linked biopolymeric concrete encapsulating selenium glass wastes

Feasibility study was conducted to encapsulate the selenium (Se) contained in glass waste, using the biopolymer-modified concrete. Biopolymer has unique characteristics to provide the chemical sites to metals or toxic compounds through the three-dimensional cross-linked structure. Very minute amount of biopolymer enhanced the characteristics of cementitious material. The resulting biopolymeric composite with selenium glass waste showed 20% higher compressive strength than ordinary concrete and the lower leaching concentration than the equipment detection limit. For a qualitative measurement, X-ray diffraction (XRD; X-ray powder diffractogram) was used to characterize the biopolymeric concrete. The optimum waste content percentage with appropriate biopolymer concrete mixture ratio was identified for its possible commercial use. Implications: The selenium waste from a glass manufacturer initiated this study. Biopolymer-modified concrete system is of importance in encapsulating hazardous wastes, which is unique, unlike the conventional waste solidification method.

Naval derusting wastewater containing high concentration of iron, treated in UV photo-Fenton-like oxidation.

The UV photooxidation with Fe(III) and H2O2 was employed to treat a naval derusting wastewater, which contains the high COD (chemical oxygen demand) and various metal concentrations exceptionally with high concentrations of citric acid and iron. Because of its iron containment, the Fenton-like reaction automatically took place with the added amount of H2O2. The decomposition rate was found in a sequence of: UV/H2O2/Fe(III) > UV/H2O2 > Fe(II)/H2O2. Two H2O2 injection methods, single and multiple points, were evaluated. The multiple-point H202 injection was more efficient to decompose the citric acid. The decomposition of the synthetic citric acid and the real derusting citric acid wastewater was also compared. The 93% COD reduction of the derusting wastewater was achieved using the UV/H2O2/Fe(III) treatment.

Devulcanization of Scrap Tire Through Matrix Modification and Ultrasonication

The development of an economical process for recycling used tires will alleviate the disposal program of the scrap tires. Vulcanized rubber, because of its three-dimensional structure, cannot flow into the manufacturing processes, therefore limiting the scope of recycling used tires. Devulcanization technology was investigated in order to develop a feasible process to minimize the stockpiles of waste tires. This process induces the cleavage of the cross-linked networks in the tire structure through the combinational methods of ultrasonic and chemical devulcanization. The products from devulcanized tires are the major original components of tires. Rubber, carbon black, and extended oil were the main materials recovered, and sulfur was separated out in this technology. These recovered materials have many applications as reusable materials for the manufacturing sector.

Measuring the Applicability of Biosensors to Detect Possible Terror Chemicals in Water Distribution Network

Instant and accurate detection of chemical contamination in a water distribution system is significant in protecting public health and water resource. Using water quality surrogates to signal a contamination occurrence offers the advantage of detecting a large number of chemicals. This article describes how the indigenous biofilm in a contaminated drinking water system may provide an effective indirect surrogate response with either turbidity or ultraviolet changes (UV254). Rotating annular bioreactors (RAB) and pipe loops were used to quantify biofilm along with turbidity and UV254 measurements. The number of biofilm cells on the polyvinyl chloride (PVC) analytical coupons was also enumerated, using automated fluorescence microscopy. Measuring the biosensing capacity, the analytical coupons were submersed into beakers with potential chemical contaminants such as aldicarb, cyanide, cycloheximide, nicotine, sodium arsenate, and sodium fluoroacetate. Resulting data indicated that turbidity was a useful surrogate for forensically monitoring chemical contaminants. Turbidity measurement can make an inexpensive biosensor for the security of a water distribution system.