Domenic Grasso

Chemo-autotrophic biogas purification for methane enrichment: mechanism and kinetics

Off-gas from anaerobic digestion and landfills has significant potential as an alternative energy source. Current technologies to purify off-gas and increase its caloric value have been primarily limited to physicochemical methods. An alternative biological method has been proposed that increases the methane content. Through the use of a chemo-autotrophic methanogen (Methanobacterium thermoautotrophicum), uncoupled methanogenesis techniques and hollow fiber membranes, carbon dioxide is converted to methane and hydrogen sulfide is effectively removed from biological off-gases. This gas stream treatment process improves the quality and caloric value of the biogas. A continuous culture bench-scale system that utilizes hollow fiber membranes was employed to study the process. The gas-phase methane concentrations were found to increase from 60% to 96%.

STRUCTURAL AND BEHAVIORAL CHARACTERISTICS OF A COMMERCIAL HUMIC ACID AND NATURAL DISSOLVED AQUATIC ORGANIC MATTER

Dissolved organic matter (DOM) from two natural surface wa~r sources and a commercial humic acid were analyzed using gel-permeation chromatography, high pressure reverse phase liquid chromatography, and IH-NMR speclroscopy. Results from the chromatographic studies show that the DOM of two natural waters consisted primarily of relatively low molecular weight, polar organic constitoonts, while large and relatively nonpolar macromolecules comprised a significant fraction of the commercial humic acid. The 1H-NMR assays indicated that DOM from the two natural water samples was comprised of nonaromatic organic constituents, while the commercial humic acids tested contained both aromatic and alipha~ moieties. Based upon these composite results of the several different types of analysis employed, it is evident that the humic acid examined, and possibly others prepared in the same way, contain molecular smlcmres which exhibit physical and chemical propeni~ that do not reflect the uue nature of DOM in real aquatic systems. Commercially available humic subsumces of this type may therefore not be suitable surroga~ for naturally occurring DOM in laboratory investigations and analysis of geochemical and environmental ~nsfe~a~ion reactions.

Impact of ozone on stability of montmorillonite suspensions

Abstract A sodium montmorillonite (NaM) suspension (150 mg/liter) was treated with various ozone doses up to 97 μ M (0.65 μmol O 3 /mg NaM). Suspension stability increased with increasing levels of ozonation as evidenced by increases in critical coagulation concentration (CCC) values of Na + , Ca 2+ , and La 3+ . The increase in induced stability of NaM was found to be most pronounced with Na + as an indifferent electrolyte and least noticeable when La 3+ was used. The enhanced stability of NaM can in large measure be attributed to an increase in the surface charge as a result of ozone-induced transformations. The conductivity of the suspending medium (water) was found to increase with ozonation indicating a leaching of ions from the crystal structure. DLVO theory was utilized to interpret the stability behavior of NaM suspensions; however, it underestimated CCC values. This discrepancy was attributed to an additional force resulting from hydrogen-bonding interactions. These interactions were found to be repulsive (hydration pressure) in nature. Hydration pressure increased with ozonation while Liftshitz—van der Waal forces remained largely unaffected. Electrostatic forces were found to be the major component responsible for increased stability of NaM as a result of ozonation, supporting a crystal dissolution hypothesis.

Nitroglycerin biodegradation: Theoretical thermodynamic considerations

Abstract Biochemical transformation of nitroglycerin (glycerol trinitrate, GTN) has been broadly established, yet its mineralization as a sole carbon and energy source has not. This manuscript examines whether there are thermodynamic reasons why GTN can not serve as a sole carbon and energy source for microbial growth based on hypothetical pathways for biochemical transformation, and considers the stoichiometric limitations for the removal of the released nitrite or nitrate ions during GTN transformation. The results of these analyses indicate that growth on GTN as sole carbon and energy source is thermodynamically feasible under both aerobic and anoxic conditions, and that maximal nitrite and nitrate removal is achievable under anoxic conditions when denitrification is incomplete.

An Approach for Incorporating Information on Chemical Availability in Soils into Risk Assessment and Risk-Based Decision Making, Prepared by: The New England Environmentally Acceptable Endpoints Workgroup

A regional workgroup comprised of individuals from regulatory agencies, uni versities, and consulting companies was formed to develop an approach for incor porating information on chemical availability in soils into risk assessment and risk based decision making. The approach consists of the following decision framework for including information on chemical availability: (1) Determine the usefulness of incorporating information on bioavailability; (2) Identify information needs from a conceptual model of exposure for the site and from exposure pathways judged critical to the assessment; (3) Identify soil factors that affect bioavailability; (4) Determine the type or form of information (measures and/or models) that can be used within the risk assessment and risk management process; (5) Select methods (measures and/or models) based on the “weight of evidence” or strength of the bioavailability information they will provide and how that information will be used for risk assessment and risk based decision making; (6) Incorporate information into the risk assessment and risk based decision making. These fac tors can be integrated into existing risk based approaches for site management such as Superfund, state approaches, and the ASTM Risk Based Corrective Action Process (RBCA). Consistent with risk assessment guidance, an assessment of chemical availability in soils must consider current as well as reasonably foresee able conditions. The approach recognizes that information on chemical availabil ity is contextual and depends on the receptor and pathway. Further, the value of information depends on how well it is accepted and/or validated for use in regulatory decision making. The workgroup identified four principles for select ing methods (measures and/or models) for obtaining information on chemical availability and for evaluating information on chemical availability for use in risk assessments: (1) soil chemical relevance, (2) pathway relevance, (3) receptor relevance, and (4) acceptance of the method.

Uncoupling mass transfer limitations of gaseous substrates in microbial systems

Abstract Hollow fiber membranes were used to enhance gas—liquid transport in a chemo-autotrophic methanogenic completely mixed batch reactor. Studies of the material transfer for gaseous substrates are typically based on the assumption that the primary resistance is transfer through the gas—liquid interface. We uncoupled the gas—liquid and liquid—microbe resistances, and evaluated their relative contributions. A reduction in the velocity gradient under a constant substrate flux into the bulk liquid shifted the observed limiting resistance from the gas—liquid interface to the liquid—microbial interface. This shift was manifested as an increase in the apparent half-saturation value. The result of this work significantly influences biochemical reactor design and/or evaluation. Although a reactor can be categorized as being completely mixed, based on spatial invariability of the biomass concentration, we demonstrated that significant mass transfer resistance may continue to reside in the liquid—microbe boundary layer.

Modeing nucleophilic substitution reactions to investigate the feasibility of elution processes

A mathematical model was developed to investigate the efficacy of nucleophilic substitution reactions to enhance contaminant mobility during elution processes. The model describes the hydrolysis (SN2 reaction) of N‐2,4,6‐tetranitro‐N‐methylaniline (tetryl), adsorbed onto soil. The reaction products include picrate, methylamine, and nitrite. Picrate the major hydrolysis product (88%) is considerably more soluble than tetryl as well as being biodegradable. Tetryl is recalcitrant to biodegradation. A model was developed to provide a basis for the design of an experimental protocol to investigate the feasibility of this process. The model describes a continuously stirred batch reactor and provides temporal profiles of the contaminant concentrations in both the aqueous and solid phases under a variety of conditions. Although somewhat preliminary in nature, the results indicate that the use of nucleophilic substitution reactions may substantially enhance the efficacy of elution processes for hydrophobic contami...

Impact of Sodium and Potassium on Environmental Systems

Health effects associated with sodium-cycle water softening has led to the consideration of potassium-cycle ion exchange as an attractive alternative. Regulatory agencies, however, have expressed concern regarding the environmental impacts associated with discharge of potassium-laden brine. To assist in providing guidance regarding the relative environmental impacts deriving from discharge of sodiumand potassium-cycle softener regeneration brine, this article summarizes available literature exploring systems potentially impacted by brine discharge. The literature indicates that replacing sodium chloride with potassium chloride as a water softener régénérant appears to result in a more environmentally benign scenario and may, in certain circumstances, be environmentally beneficial. Some areas where potassium chloride may be advantageous are land application of sewage sludge, viral inactivation, mobility in soil, effects on soil properties and impacts on plant life. There are no significant differences between sodium chloride and potassium chloride in effect on engineered physicochemical processes of in aquatic life systems. The impact of sodium may be detrimental to the environment because the uptake of phosphorus by algae was reportedly enhanced by sodium. Potassium, on the other hand, was not reported to enhance phosphorous uptake. Some questions remain about the impact of potassium and sodium on septic tank bacteria, biological waste treatment processes, and effects on natural flora. The literature reviewed on these topics was somewhat conflicting. Further efforts to assess the impact of potassium and sodium should be directed at resolving these literature discrepancies. •This study was supported, in part, under a grant from Kalium Canada Ltd., Regina, Saskatchewan.

Closed-Loop Recovery of Site Remediation Gas Phase Contaminants

A novel gas phase treatment system (contaminant absorption and recovery [CAR]) for removal and subsequent recycling of gas phase VOCs from soil vapor extraction/gas stripping systems has been developed. Gas phase removal efficiencies using a packed column contactor exceed 99 percent The VOC-laden absorption fluid is subsequently vacuum-stripped of the VOCs, allowing potential condensation into liquid solvent concentrates. Partition coefficients for trichloroethylene (TCE) in triethylene glycol (TEG) ranged to ca. 5.0 mole fraction gas/mole fraction liquid, indicating a significant capacity for removal from the gas phase. Results of pilot-scale operation indicate favorable removal efficiencies and cost-effective performance in comparison to GAC or thermal destruction processes. System mass transfer coefficient predictions were done, using a variety of mathematical models and compared to experimental results. A modified Mangers and Ponten correlation was found to describe system mass transfer coefficients w...

Impact of alternative oxidants on the formation of disinfection by‐products and assimilable organic carbon

Abstract Pilot scale studies were conducted to investigate the effect of oxidation at various stages of water treatment process. Impact of pre‐ and postoxidation (before coagulation and after filtration, respectively), on the formation of disinfection by‐products (DBPs) and assimilable organic carbon (AOC) was investigated. Based upon the oxidant (ozone or ozone + hydrogen peroxide) dosages evaluated, no consistently significant differences, in terms of DBP reduction and AOC formation, were observed in pre‐ vs. postoxidation scenarios. The ozone dosage required in postoxidation was found to be less than half of that required in preoxidation to achieve similar DBP reductions and AOC results. Addition of hydrogen peroxide along with ozone did not result in consistently improved treatment performance. Bench and pilot scale studies were conducted to investigate the effect of ozone oxidation pathway on the reduction of DBPs. It was found that, while ozone alone was not particularly effective for long term redu...