Edward J. Bouwer

Biodegradation and removal of pharmaceuticals and personal care products in treatment systems: a review

Pharmaceuticals and personal care products (PPCPs) have been the focus of much recent research as concerns rise about their occurrence in bodies of water worldwide. In an effort to characterize the risk and determine the prevalence of these micropollutants in lakes and rivers, many researchers are examining PPCP removal from impaired water during wastewater treatment and water recycling (soil passage) processes. Biodegradation studies and projects considering combinations of biodegradation and other removal processes have been conducted over a wide range of compound categories and therapeutic classes, as well as across different systems and scales of study. This review summarizes the extent of PPCP removal observed in these various systems.

Reversibility and mechanism of bacterial adhesion

The reversibility and mechanisms of adhesion of various pseudomonads and coryneform bacteria having different hydrophobicities and negative cell surface charges on negatively charged Teflon and glass were studied. Adhesion at an ionic strength of 0.1 M was irreversible and corresponded to activation Gibbs energies for detachment higher than 5 kT for 19 out of 20 combinations of bacterial strains and surfaces. The data further demonstrate the importance of two groups of interactions: (i) the electrostatic and van der Waals interactions as described by the DLVO model, and (ii) the interactions between the outer cell surface macromolecules and the solids (steric interactions). At an ionic strength of 0.1 M, steric interactions control adhesion for all but two bacterium/substratum combinations tested. These interactions are attractive for seven moderately to strongly hydrophobic strains on Teflon and prevented detachment upon decreasing the ionic strength to less than 0.0001 M and also after applying shear forces. In contrast, steric interactions inhibited adhesion for more hydrophilic bacterium/substratum combinations for which detachment occurred upon reducing the ionic strength to less than 0.0001 M and/or after applying shear. The importance of the interactions included by the DLVO model is demonstrated by the following. (i) Two hydrophobic strains adhere irreversibly on glass by strong van der Waals attraction in a secondary DLVO minimum at an ionic strength of 0.1 M and detach when the ionic strength is reduced to less than 0.0001 M. (ii) Electrostatic repulsion inhibits deposition at lower ionic strength. The practical implications of these findings are discussed.

Hydrogen peroxide use to increase oxidant capacity for in situ bioremediation of contaminated soils and aquifers: A review

Abstract Biotransformation of organic pollutants is often most effective and complete under oxic or oxidant-rich conditions. Dissolved oxygen availability is frequently limiting the biotransformation of these organic compounds in the subsurface due to the limited aqueous solubility of oxygen, the relatively slow rate of re-aeration of groundwater in the saturated zone, and the significant biological oxygen demand exerted during aerobic metabolism. Addition of hydrogen peroxide (H2O2) can augment the oxidant capacity of the aquifer. This paper reviews several reactions pertinent to remediating contaminated groundwaters via H2O2 addition. H2O2 is disproportioned by the action of microbial catalase and several inorganic catalysts such as iron oxide species to give 0.5 mol O2 per mole of H2O2 consumed. The resulting dissolved oxygen should then be available for microbial respiration. If disproportionation occurs too quickly, evolution of oxygen gas can form bubles that lower aquifer permeability. Another type of reaction is direct oxidation of organic compounds by H2O2 in the presence of enzymes (peroxidases) or metal oxide catalysts. Molecular oxygen is not evolved as a result of this type of H2O2-consuming reaction. Modifications in treatment strategy may also be necessary to minimize H2O2 toxicity as H2O2 is known to be toxic at a concentration within the cell of 0.1 mM.

Bioremediation of organic compounds — putting microbial metabolism to work

Microorganisms can metabolize many aliphatic and aromatic organic contaminants, either to obtain carbon and/or energy for growth, or as co-substrates, thus converting them to products such as carbon dioxide, water, chloride and biomass. These biotransformations can be exploited for treatment of contaminated soils and ground water.

Biodegradation of aromatic compounds under mixed oxygen/denitrifying conditions: a review

Bioremediation of aromatic hydrocarbons in groundwater and sediments is often limited by dissolved oxygen. Many aromatic hydrocarbons degrade very slowly or not at all under anaerobic conditions. Nitrate is a good alternative electron acceptor to oxygen, and denitrifying bacteria are commonly found in the subsurface and in association with contaminated aquifer materials. Providing both nitrate and microaerophilic levels of oxygen may result in oxidation of the stable benzene rings in aromatic contaminants and allow for the intermediates of this oxidation to degrade via denitrification. The effects of using mixed electron acceptors on biodegradation of subsurface contaminants is unclear. Below some critical oxygen threshold, aerobic biodegradation is inhibited, however high levels of oxygen inhibit denitrification. The mechanisms which regulate electron transfer to oxygen and nitrate are complex. This review: 1) describes the factors which may affect the utilization of oxygen and nitrate as dual electron acceptors during biodegradation; 2) summarizes the incidence of dual use of nitrate and oxygen (aerobic denitrification); and 3) presents evidence of the effectiveness of bioremediation under mixed oxygen/nitrate conditions.

Engineering scale-up of in situ bioremediation processes: a review

To be useful to field practitioners, advances in bioremediation research must be capable of being scaled up from the laboratory to the field. The phenomena which control the rate at which biodegradation proceeds are typically scale-dependent in nature. Failure to understand and account for scale-dependent variables, such as mass transport limitations, spatial heterogeneities and the presence of competing microorganisms, may inhibit the effectiveness of field-scale bioremediation designs. This paper reviews and evaluates the methods available for characterization of the processes effecting bioremediation at scales ranging from the laboratory to the field. Questions facing the field-scale practitioner of bioremediation are addressed in a manner which highlights the current state of research, the reliability of results and the extent to which laboratory-scale research accurately reflects common field conditions. Where gaps or inadequacies exist in our current knowledge or methods, research needs are identified. This review is intended to complement existing work by providing a framework from which to assess the importance of scale of observation to a particular result or conclusion, thereby providing an integrated approach to the scale-up process.

Succession of Phenotypic, Genotypic, and Metabolic Community Characteristics during In Vitro Bioslurry Treatment of Polycyclic Aromatic Hydrocarbon-Contaminated Sediments

ABSTRACT Dredged harbor sediment contaminated with polycyclic aromatic hydrocarbons (PAHs) was removed from the Milwaukee Confined Disposal Facility and examined for in situ biodegradative capacity. Molecular techniques were used to determine the successional characteristics of the indigenous microbiota during a 4-month bioslurry evaluation. Ester-linked phospholipid fatty acids (PLFA), multiplex PCR of targeted genes, and radiorespirometry techniques were used to define in situ microbial phenotypic, genotypic, and metabolic responses, respectively. Soxhlet extractions revealed a loss in total PAH concentrations of 52%. Individual PAHs showed reductions as great as 75% (i.e., acenapthene and fluorene). Rates of 14C-PAH mineralization (percent/day) were greatest for phenanthrene, followed by pyrene and then chrysene. There was no mineralization capacity for benzo[a]pyrene. Ester-linked phospholipid fatty acid analysis revealed a threefold increase in total microbial biomass and a dynamic microbial community composition that showed a strong correlation with observed changes in the PAH chemistry (canonicalr2 of 0.999). Nucleic acid analyses showed copies of genes encoding PAH-degrading enzymes (extradiol dioxygenases, hydroxylases, and meta-cleavage enzymes) to increase by as much as 4 orders of magnitude. Shifts in gene copy numbers showed strong correlations with shifts in specific subsets of the extant microbial community. Specifically, declines in the concentrations of three-ring PAH moieties (i.e., phenanthrene) correlated with PLFA indicative of certain gram-negative bacteria (i.e., Rhodococcus spp. and/or actinomycetes) and genes encoding for naphthalene-, biphenyl-, and catechol-2,3-dioxygenase degradative enzymes. The results of this study suggest that the intrinsic biodegradative potential of an environmental site can be derived from the polyphasic characterization of the in situ microbial community.

Transformations of trace halogenated aliphatics in anoxic biofilm columns

Abstract The transformability of trihalomethanes, carbon tetrachloride, 1,1,1-trichloroethane, 1,2-dibromoethane, tetrachloroethylene, hexachloroethane, and dibromochloropropane was studied under conditions of denitrification, sulfate respiration, and methanogenesis. These compounds at concentrations commonly found in groundwater were continuously administered to anoxic biofilm columns that resembled groundwater environments. Acetate was the primary substrate to support microbial growth. All of the compounds studied were transformed under methanogenesis. Bromoform, bromodichloromethane, carbon tetrachloride, and hexachloroethane were transformed even under the less reducing conditions of denitrification. Some of the compounds were partially mineralized to CO 2 . However, reductive dehalogenation appeared to be the predominant mechanism for removal. Characterization of the available electron acceptors in the subsurface is important for assessing organic micropollutant biotransformation. Reaction rates observed in the laboratory biofilms indicate that biotransformation could be responsible for significant removals of these halogenated compounds in the subsurface.

The effects of alternative pretreatment strategies on anaerobic digestion and methane production from different algal strains

The effect of various pretreatment strategies on methane yields following anaerobic digestion (AD) of five different microalgal strains was investigated. Pavlova_cf sp., Tetraselmis sp. and Thalassiosira weissflogii exhibited substantial methane yields of 0.4-0.5L/g volatile solids (VS) without pretreatment, providing up to 75-80% of theoretical values. In contrast, methane yields from Chlorella sp. and Nannochloropsis sp. were around 0.35L/g VS, or 55-60% of the theoretical values, respectively. Alkali treatment was not effective and thermal pretreatment only enhanced Nannochloropsis methane yields. Thermochemical pretreatment had the strongest impact on biomass solubilization with methane yields increasing by 30% and 40% for Chlorella and Nannochloropsis, respectively. The lipid content had a strong beneficial impact on the theoretical and observed methane yields as compared to protein and carbohydrate content. Other features such as cell-wall composition are also likely to be important factors dictating algal biodegradability and methane yields addressed in part by thermochemical pretreatment.

Trace determination of pharmaceuticals and other wastewater-derived micropollutants by solid phase extraction and gas chromatography/mass spectrometry.

The presence of pharmaceuticals and other wastewater-derived micropollutants in surface and groundwaters is receiving intense public and scientific attention. Yet simple GC/MS methods that would enable measurement of a wide range of such compounds are scarce. This paper describes a GC/MS method for the simultaneous determination of 13 pharmaceuticals (acetaminophen, albuterol, allopurinol, amitriptyline, brompheniramine, carbamazepine, carisoprodol, ciclopirox, diazepam, fenofibrate, metoprolol, primidone, and terbinafine) and 5 wastewater-derived contaminants (caffeine, diethyltoluamide, n-butylbenzene sulfonamide, n-nonylphenol, and n-octylphenol) by solid phase extraction (SPE) and derivatization with BSTFA. The method was applied to the analysis of raw and treated sewage samples obtained from a wastewater treatment plant located in the mid-Atlantic United States. All analytes were detected in untreated sewage, and 14 of the 18 analytes were detected in treated sewage.