Kenneth J. Williamson

Model of trace-metal partitioning in marine sediments.

An equilibrium adsorption model is developed to predict the partitioning of trace metals between different geochemical phases in aquatic sediments. The model uses conditional equilibrium constants determined from linear portions of adsorption isotherms. As an example of how the model can be used, the adsorption and the partitioning of Cu and Cd on several select artificial geochemical phases were studied. Conditional equilibrium constants for adsorption of Cu and Cd on bentonite clay, Fe(OH)S, MnOz, and humic acid in seawater show the model’s applicability for trace-metal concentrations existing in natural environments. The adsorption constants for Cu were much higher than for Cd for all solid phases. The affinity of the metals for humic acid relative to other phases was high for Cu and low for Cd. The model predicts that the clay fraction is a major sink for Cu and Cd for the artificial geochemical phases used.

Combined aerobic heterotrophic oxidation, nitrification and denitrification in a permeable-support biofilm

Abstract A biofilm reactor, termed the permeable-support biofilm (PSB), was developed in which oxygen was supplied to the interior of the biofilm through a permeable membrane. The reactor was tested on filtered sewage supplemented with nutrient broth; the bulk solution was anoxic and the interior of the biofilm was supplied with pure oxygen. All tests were performed on a non-steady state biofilm with a depth of 1 mm. Mass balances on total organic carbon, ammonia, organic nitrogen and nitrate showed that combined heterotrophic oxidation of organics, denitrification and nitrification occurred simultaneously within the biofilm. The advantages of such a reactor are discussed.

Sulfide control of cadmium and copper concentrations in anaerobic estuarine sediments

Equilibrium concentrations of the toxic trace metals copper and cadmium were calculated for the physico-chemical conditions characterizing pore waters of anaerobic estuarine sediments using available thermodynamic data and assuming simple sulfide minerals control solubilities. Polysulfide complexes are responsible for the solubility of copper in the cuprous (Cu(I)) oxidation state. Predicated copper concentrations, assuming covellite (CuS) is the controlling solid phase, are in reasonable agreement with copper analyses in a wide range of sulfidic waters and sediment pore waters. In the absence of thermodynamic data, no account could be taken of possible polysulfide complexes of cadmium. However, bisulfide complexes appear to account satisfactorily for observed solubilities assuming the existence of greenockite (CdS) as the controlling solid phase. Anaerobic estuarine sediments may act as a sink for copper and cadmium in the common situation in which free sulfide concentrations are controlled by the coexistence of iron sulfide and iron oxide minerals. However, where free sulfides reach high concentrations of 10−3 M or more, the concomitant increase in concentration of bisulfide and polysulfide complexes may result in the sediments acting as a source of copper and cadmium.

Cooxidation of naphthalene and other polycyclic aromatic hydrocarbons by the nitrifying bacterium, Nitrosomonas europaea

The soil nitrifying bacterium Nitrosomonas europaea has shown the ability to transform cometabolically naphthalene as well as other 2- and 3-ringed polycyclic aromatic hydrocarbons (PAHs) to more oxidized products. All of the observed enzymatic reactions were inhibited by acetylene, a selective inhibitor of ammonia monooxygenase (AMO). A strong inhibitory effect of naphthalene on ammonia oxidation by N. europaea was observed. Naphthalene was readily oxidized by N. europaea and 2-naphthol was detected as a major product (85%) of naphthalene oxidation. The maximum naphthol production rate was 1.65 nmole/mg protein-min in the presence of 240 μM naphthalene and 10 mM NH4+. Our results demonstrate that the oxidation between ammonia and naphthalene showed a partial competitive inhibition. The relative ratio of naphthalene and ammonia oxidation, depending on naphthalene concentrations, demonstrated that the naphthalene was oxidized 2200-fold slower than ammonia at lower concentration of naphthalene (15 μM) whereas naphthalene was oxidized only 100-fold slower than ammonia oxidation. NH4+- and N2H4-dependent O2 uptake measurement demonstrated irreversible inhibitory effects of the naphthalene and subsequent oxidation products on AMO and HAO activity.

Environmental impact of highway construction and repair materials on surface and ground waters. Case study: crumb rubber asphalt concrete.

The practice of incorporating certain waste products into highway construction and repair materials (CRMs) has become more popular. These practices have prompted the National Academy of Science, National Cooperative Highway Research Program (NCHRP) to research the possible impacts of these CRMs on the quality of surface and ground waters. State department of transportations (DOTs) are currently experimenting with use of ground tire rubber ( crumb rubber) in bituminous construction and as a crack sealer. Crumb rubber asphalt concrete (CR-AC) leachates contain a mixture of organic and metallic contaminants. Benzothiazole and 2(3H)-benzothiazolone (organic compounds used in tire rubber manufacturing) and the metals mercury and aluminum were leached in potentially harmful concentrations (exceeding toxic concentrations for aquatic toxicity tests). CR-AC leachate exhibited moderate to high toxicity for algae ( Selenastrum capriconutum) and moderate toxicity for water fleas ( Daphnia magna). Benzothiazole was readily removed from CR-AC leachate by the environmental processes of soil sorption, volatilization, and biodegradation. Metals, which do not volatilize or photochemically or biologically degrade, were removed from the leachate by soil sorption. Contaminants from CR-AC leachates are thus degraded or retarded in their transport through nearby soils and ground waters.

A bacterial bioassay for assessment of wastewater toxicity

A bioassay using freeze-dried Nitrobacter as the test organism has been shown to successfully detect various toxicants in municipal and industrial wastewaters. The test is simple, sensitive, rapid and inexpensive; as a result, this test shows potential as a quantitative measurement technique for wastewater toxicity. The bioassay technique was applied in the analysis of a wastewater treatment system at a fiberboard plant near Portland, Oregon. The fiberboard is manufactured from a slurry of chipped wood, shavings and sawdust. Wastewater from the process is treated at an on-site facility consisting of settling ponds, activated sludge basin, clarifier and holding ponds. Treated water is recycled to the mill for reuse. Recently the removal of BOD by the activated sludge system dropped significantly and soluble and particulate organics began to accumulate. The influent and effluent flows for the treatment facility were tested with the Nitrobacter bioassay and both were determined to have significant toxicity. Further tests at points in the process showed that the toxicity was not associated with a single waste stream and was prevalent throughout the entire wastewater treatment system. In an effort to identify the toxicant, toxicity tests were conducted for known chemicals used in the process. The wastewater was treated with various physical and chemical unit processes to determine the most effective method for toxicity removal. Due to the complexity of the wastewater composition, no specific agents have been identified as solely responsible for the observed toxic response, however, several possible explanations for the apparent toxicity are discussed.

Kinetics of trace metal partitioning in model anoxic marine sediments

Abstract A model anaerobic sediment consisting of humic acid, clay, ferrous sulfide, sand, and seawater was utilized to study the partitioning of Cu, Cd, Pb, and Zn between different geochemical phases. An extraction scheme was developed that was selective for each geochemical phase. Metals were dosed on one phase separately, and then mixed into the other undosed phrases. The kinetics of partitioning were rapid, regardless of which phase was initially dosed; equilibrium was reached within 2–5 days. The stoichiometry of distribution was also indepencent of the initially dosed phase. The final metal distributions showed that the metal sulfide phase was not necessarily the dominant trace metal sink in anaerobic sediments.

Bacterial toxicity and metabolism of hydrazine fuels

The toxicity of hydrazine, monomethyl hydrazine, and unsymmetrical dimethyl hydrazine were determined for mixed and uniculture cultures of nitrifying bacteria, denitrifying bacteria, and anaerobic methanogenic bacteria. Monomethyl hydrazine was more toxic than hydrazine, which was more toxic than dimethyl hydrazine. The toxicity levels were low enough to preclude biological waste treatment of these compounds. Hydrazine was cometabolized to nitrogen gas byNitrosomonas.

Pathway, inhibition and regulation of methyl tertiary butyl ether oxidation in a filamentous fungus, Graphium sp

The filamentous fungus Graphium sp. (ATCC 58400) co-metabolically oxidizes the gasoline oxygenate methyl tertiary butyl ether (MTBE) after growth on gaseous n-alkanes. In this study, the enzymology and regulation of MTBE oxidation by propane-grown mycelia of Graphium sp. were further investigated and defined. The trends observed during MTBE oxidation closely resembled those described for propane-grown cells of the bacterium Mycobacterium vaccae JOB5. Propane-grown mycelia initially oxidized the majority (∼95%) of MTBE to tertiary butyl formate (TBF), and this ester was biotically hydrolyzed to tertiary butyl alcohol (TBA). However, unlike M. vaccae JOB5, our results collectively suggest that propane-grown mycelia only have a limited capacity to degrade TBA. None of the products of MTBE exerted a physiologically relevant regulatory effect on the rate of MTBE or propane oxidation, and no significant effect of TBA was observed on the rate of TBF hydrolysis. Together, these results suggest that the regulatory effects of MTBE oxidation intermediates proposed for MTBE-degrading organisms such as Mycobacterium austroafricanum are not universally relevant mechanisms for MTBE-degrading organisms. The results of this study are discussed in terms of their impact on our understanding of the diversity of aerobic MTBE-degrading organisms and pathways and enzymes involved in these processes.

ENVIRONMENTAL IMPACT OF CONSTRUCTION AND REPAIR MATERIALS ON SURFACE WATER AND GROUNDWATER: DETAILED EVALUATION OF WASTE-AMENDED HIGHWAY MATERIALS

An evaluation methodology was developed to help transportation agencies make prudent decisions about the reuse of waste materials and by-products in highway construction. The primary objective of this evaluation process was to assess the potential impact on surface water and groundwater of constituents released from these materials. Test materials included coal fly ash, bottom ash, blast furnace slags, scrap tires, foundry sand, and recycled asphalt pavement. Test materials were screened for potential aquatic impact in their raw form. Then they were amended with either asphalt or aggregate for detailed assessment, including leaching (batch and flat plate or column tests) and environmental removal, reduction, and retardation (soil sorption, volatilization, photolysis, and biodegradation) tests. Short-term bioassays were used to measure directly the potential aquatic impact of derived leachates as a supplement to chemical analyses. For most materials, amendment with asphalt or aggregate largely reduced or eliminated any impact on the aquatic organisms. Among environmental factors, soil sorption appeared to be the most effective contaminant-removal mechanism. All waste-amended asphalts and aggregates exhibited no measurable impact on target organisms after soil sorption. However, for materials such as pressure-treated wood and deck sealer (used as is), environmental tests showed little or no effect in reducing their aquatic impact.