Peter O. Nelson

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.

Copper, Chromium, and Arsenic Adsorption and Equilibrium Modeling in An Iron-Oxide-Coated Sand, Background Electrolyte System

The adsorption of copper, chromate, and arsenate (CCA)onto iron-oxide-coated sand (IOCS) was examined insingle-metal and mixed-metal systems. Copper andarsenate were strongly adsorbed or formed inner-spheresurface complexes with the IOCS surface while chromatewas weakly adsorbed or formed an outer-sphere surfacecomplex with the IOCS surface. Copper adsorption byIOCS slightly increased in the presence of arsenatebut was not affected by the presence of chromate. Arsenate adsorption was not affected by the presenceof copper and/or chromate. Chromate adsorptionincreased in the presence of copper by the combinationof electrostatic effects and possiblesurface-copper-chromate ternary complex formation. The presence of arsenate significantly decreasedchromate adsorption due to competition for adsorptionsites and electrostatic effects. Using inner-spheresurface complexation constants for copper and arsenateand outer-sphere surface complexation constants forchromate, the triple-layer model (TLM) was successfulin describing adsorption of copper, chromate, andarsenate in single-solute systems. The modelindicated that each metal uses a different number ofadsorption sites. For CCA metals-IOCS systems, theequilibrium constants determined from single-solutesystems were not able to predict adsorption frommulti-solute systems. The TLM does not currentlyaccount for the heterogeneity of oxide surface sitesand the formation of ternary complexes and/or solidphases that do not exist in single-solute systems.

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.

Microbial viability measurements and activated sludge kinetics

Abstract A laboratory study was performed to evaluate the influence of microbial viability information on a widely used steady-state kinetic model of slurry-type biological wastewater treatment processes. Adenosine triphosphate (ATP), determined by the luciferin-luciferase firefly lantern extract method using a liquid scintillation spectrometer to measure light emission, was used as the indicator of microbial viability. It was found that the microbial viability of activated sludge mixed liquor volatile suspended solids (MLVSS) exhibits a functional relationship with biological solids retention time ( θ c ), i.e., being essentially 100% at low values of 0 c and decreasing to a nearly constant value at the higher values of 0 c , typical of activated sludge process operation. Values of the model coefficients were also affected by the microbial viability of the MLVSS. Based on mass balance considerations and ATP measurements, it is proposed that the MLVSS of an activated sludge system treating a soluble organic waste can be divided into the following three fractions: (I) active or viable microbial solids, (2) inert microbial debris solids, and (3) nonviable biodegradable microbial solids. Implications of viability information in design and operation are discussed.

Equilibrium chemical modelling of heavy metals in activated sludge

A chemical speciation distribution model of heavy metals, previously developed by Nelson et al. (J. Wat. Pollut. Control Fed. 53, 1323, 1981), was applied to cadmium in activated sludge from a full-scale wastewater treatment plant. In the model, cadmium adsorption to bacterial solids was quantified by the determination of conditional formation constants based on TOC. Adsorption of cadmium strongly pH-dependent. Soluble cadmium speciation was dominated by the free cadmium ion below pH 6, by cadmium-organic ligand complexation at pH 6 and 7 and by inorganic species at pH 8 and 9. Cadmium adsorbed by bacterial solids increased greatly with pH from near 30% at pH 4 to near 90% at pH 9. Cadmium speciation and distribution was also modelled in an indifferent electrolyte suspension of bacterial solids and in activated sludge using adsorption constants from the indifferent electrolyte medium.

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.

Chemical Solute Mass Balance of Crater Lake, Oregon

ABSTRACT Crater Lake covers the floor of the caldera at the top of Mount Mazama. Surrounded by steep walls, the water surface of the lake occupies 78 percent of the catchment basin. No major rivers empty into the lake, and there is no surface outlet Based on a chemical solute mass balance model, mass inputs of major solute chemical components (Na, Ca, K, Mg, SO4, Cl, Si, and HCO3) from atmospheric deposition and caldera springs do not equal the mass output in seepage from the lake. One or more previously unquantified sources must be present in the lake or watershed system to account for the calculated deficits of mass inputs which range from 50 to 90 percent of mass outputs. A hydrothermal source, with a flow rate of approximately 6 percent of me seepage rate and chemical composition similar to saline fluids found in isolated pockets on the bottom of Crater Lake and to hydrothermal springs in die Cascade Mountain Range, could account for the calculated input mass deficits for major solute chemical compone...

Environmental Impact of Runoff from Highway Construction and Repair Materials: Project Overview

A study was conducted to identify the possible effects of highway construction and repair (C&R) materials on the quality of surface water and groundwater near the highway environment. The scope involved the development of a validated methodology to assess such effects in three phases. Phases 1 and 2 involved a survey of C&R materials, laboratory testing of the chemical and toxicological characteristics of a selected number of these materials, development and validation of a laboratory testing–based screening and evaluation methodology for highway C&R materials, and development of a mathematical model to simulate the fate and transport of water quality constituents, including toxicity, along surface and subsurface pathways in the highway environment. Phase 3 focused on 10 tasks designed to confirm the evaluation methodology, test various hypotheses of the model development, develop additional leaching and sorption data, compare ecotoxicological testing procedures developed during the project with standard Environmental Protection Agency procedures, refine laboratory protocols, enhance the model, and investigate the availability of field data for model testing.

Chapter 6 – Lead Sorption, Chemically Enhanced Desorption, and Equilibrium Modeling in an Iron-Oxide-Coated Sand and Synthetic Groundwater System

Oxides of iron are ubiquitous subsurface mineral constituents and control the mobility of metal ions in soils and groundwater by adsorptive retardation. In this laboratory study, iron-oxide-coated sand (IOCS) is used to model lead chemical behavior in soil using batch and column reactor experiments. Several parameters are varied in order to ascertain their effects: pH, ionic strength, complexation by organic ligands, competing cations, and reaction time. In equilibrium experiments, pH was the major factor that controlled the adsorption process, and increasing ionic strength somewhat decreased Pb adsorption below pH = 5 but had no influence at higher pH values. Using a surface complexation, triple-layer model (TLM), an inner-sphere surface reaction was successful in describing the effect of pH on Pb adsorption on IOCS over a range of Pb concentrations at constant ionic strength. EDTA greatly decreased Pb adsorption at equimolar and greater concentrations, with its effect increasing with pH above 6.0, but with a enhanced adsorption at acidic pHs below about 4.5. Soil column studies of Pb adsorption on IOCS are consistent with expectations from batch studies. Results of this study provide guidance in determining conditions that chemically enhance mobilization or immobilization of Pb in soil and groundwater.

Accumulation of cadmium by abarenicola pacifica

Abstract The bioavailability of trace metals to marine organisms depends on trace metal partitioning among geochemical phases and on the kinetics of uptake from each phase. This study was undertaken to develop a kinetic model for trace metal uptake based on equilibrium partitioning of the metal in aqueous and sedimentary phases. A three compartment model was developed and used to estimate the accumulation of cadmium under short term laboratory conditions. The rate of cadmium uptake from bentonite clay, humic acid, ferric hydroxide, and seawater was measured for the deposit-feeding polychaete Abarenicola pacifica . The results show that, under the conditions of this study, bentonite clay and ferric hydroxide can be more important sources of cadmium than seawater for Abarenicola pacifica .