JoAnn Silverstein

Effects of ultrafiltration membrane surface properties on Pseudomonas aeruginosa biofilm initiation for the purpose of reducing biofouling

Biofilm fouling is one of the major obstacles hindering the use of membranes in water processing systems. There are a series of events that take place during biofilm formation, one of the most interesting and important issues of biofouling is the initial attachment of microorganisms to the surface. Therefore, effects that surface properties have on biofilm fouling are important to attachment and were examined. Hydrophobicity, surface charge and roughness were measured for several polymeric surfaces of interest in water processing membrane systems. These surfaces were then subjected to conditioning layer formation and biofilm fouling, both of which were quantified. The results show that biofilm initiation by a strain of Pseudomonas aeruginosa increases as the surface becomes more rough and more hydrophobic, while fouling is minimal when surface charge is minimized and increases with increasing charge, whether positive or negative.

Development and Application of Small-Subunit rRNA Probes for Assessment of Selected Thiobacillus Species and Members of the Genus Acidiphilium

ABSTRACT Culture-dependent studies have implicated sulfur-oxidizing bacteria as the causative agents of acid mine drainage and concrete corrosion in sewers. Thiobacillus species are considered the major representatives of the acid-producing bacteria in these environments. Small-subunit rRNA genes from all of the Thiobacillus andAcidiphilium species catalogued by the Ribosomal Database Project were identified and used to design oligonucleotide DNA probes. Two oligonucleotide probes were synthesized to complement variable regions of 16S rRNA in the following acidophilic bacteria:Thiobacillus ferrooxidans and T. thiooxidans(probe Thio820) and members of the genus Acidiphilium(probe Acdp821). Using 32P radiolabels, probe specificity was characterized by hybridization dissociation temperature (Td) with membrane-immobilized RNA extracted from a suite of 21 strains representing three groups of bacteria. Fluorochrome-conjugated probes were evaluated for use with fluorescent in situ hybridization (FISH) at the experimentally determinedTds. FISH was used to identify and enumerate bacteria in laboratory reactors and environmental samples. Probing of laboratory reactors inoculated with a mixed culture of acidophilic bacteria validated the ability of the oligonucleotide probes to track specific cell numbers with time. Additionally, probing of sediments from an active acid mine drainage site in Colorado demonstrated the ability to identify numbers of active bacteria in natural environments that contain high concentrations of metals, associated precipitates, and other mineral debris.

Effect of molecular size and charge on biofilm sorption of organic matter

Abstract Packed-bed reactors were used to examine the effects of molecular size and charge on biofilm sorption of organic compounds selected for their similarity to the size and charge ranges of aquatic natural organic matter (NOM). In addition, the sorbate compounds were chosen for nonbiodegradability, which was verified by BOD tests. In experiments using uncharged NOM-surrogate compounds it was found that as sorbate molecular size increased, biofilm sorption decreased. Also, negatively charged NOM-surrogate compounds were found to be less well sorbed to biofilm than neutral molecules. Apparently biofilm sorption of small molecules is enhanced by diffusion of the sorbate into the porous biofilm matrix; whereas larger sorbate molecules probably accumulate at the biofilm-water interface because they are excluded from the biofilm pores. The observed decrease in biofilm sorption of anionic organic molecules compared to removal of neutral sorbates was thought to be the result of electrostatic repulsion between the negatively-charged sorbate and the negatively-charged biofilm particularly slowing diffusion of the sorbate molecules within the biofilm.

Inhibition of perchlorate reduction by nitrate in a fixed biofilm reactor

Perchlorate and nitrate were reduced simultaneously in fixed biofilm reactors. Reduction of 1000 microg L(-1) perchlorate decreased slightly with the addition of 10-16 mg L(-1) NO(3)-N when excess acetate was supplied while denitrification was complete. When influent acetate was reduced by 50% to well below the stoichiometric requirement, perchlorate reduction decreased by 70% while denitrification decreased by only 20%, suggesting that competition for electrons by nitrate was a factor in inhibition. Reduction of nitrate was favored over perchlorate, even though reactor biofilm had been enriched under perchlorate-reducing conditions for 10 months. When excess acetate was restored, perchlorate and nitrate returned to initial levels. The average most probable numbers of perchlorate- and nitrate-reducing bacteria during excess substrate operation were not significantly different and ranged between 2.0 x 10(5) and 7.9 x 10(5)cells cm(-2) media surface area. The effect of nitrate on chloride generation by suspensions of perchlorate-reducing populations was studied using a chloride ion probe. The rate of reduction of 2mM perchlorate decreased by 30% in the presence of 2mM nitrate when excess acetate was added. When acetate was limited, perchlorate reduction decreased by 70% in the presence of equi-molar nitrate.

Iodine disinfection of a model bacteriophage, MS2, demonstrating apparent rebound

Abstract MS2 coliphage viruses suspended in buffered distilled water were rapidly inactivated by

Effect of ozonation on sorption of natural organic matter by biofilm

Abstract Experiments were conducted to determine the effects of ozonation on sorption of aquatic natural organic matter (NOM) onto biofilm using bench-scale packed-bed reactors. It was found that 18–22% of NOM measured as dissolved organic carbon (DOC), and 28–30% measured as chloroform formation potential, was removed from the water without biodegradation. The bulk of the NOM removal was attributed to biosorption of low-molecular-weight compounds—less than 3000 Da. At a dose of 1 g-O 3 g-DOC , ozonation was not found to have a significant effect on biosorption of NOM. Ozonation simultaneously decreased the molecular size and increased the acidity of NOM compounds, and it was concluded that the effects counterbalanced each other at an ozone dose of 1:1, resulting in no significant change in NOM sorption.

The Role of Enhanced Heterotrophic Bacterial Growth on Iron Oxidation by Acidithiobacillus ferrooxidans

Addition of organic carbon substrate (glucose) profoundly affected the growth of cultures of acidophilic bacteria typical of acid mine drainage (AMD) sites: the iron-oxidizing autotrophic bacteria, Acidithiobacillus ferrooxidans , and a common heterotrophic strain, Acidiphilium acidophilum . Growth of A. ferrooxidans on soluble ferrous iron media was significantly inhibited in the presence of 1,000 mg/L glucose, regardless of the initial cell density, and in spite of favorable pH and aeration conditions. Interestingly, inhibition of A. ferrooxidans was reduced with addition of the heterotroph, apparently due to the consumption of glucose because the onset of iron oxidation coincided with reduction in glucose concentration in the medium. Another mechanism, local production of CO 2 by A. acidophilum provided inorganic carbon required by A. ferrooxidans cells, was investigated. Although no direct proof of interspecies CO 2 exchange was identified, iron oxidation was enhanced and glucose inhibition reduced with incubation of A. ferrooxidans cultures with 5% CO 2 in air. When oxygen was limited and glucose was added to the acidic coculture, the ultimate amount of iron oxidized was significantly lower and the ferric iron produced was subsequently reduced by the heterotrophs as conditions became anoxic. Attribution of ferric iron reduction to A. acidophilum was confirmed in pure culture experiments where a zero-order iron-reduction rate of 458 - 26.9 w mol Fe/L-day (25.6 - 1.5 mg Fe/L-day) was observed. Bacterial iron reduction also led to an increase in pH from 2.5 to 4.0. Thus, the addition of glucose or some other organic electron donor could provide an in situ or ex situ bioremediation strategy to raise pH at AMD sites resulting in a lower amount of metal leaching into drainage water by promoting reducing conditions favorable to iron reduction.

Bacterial Kinetics of Sulfur Oxidizing Bacteria and Their Biodeterioration Rates of Concrete Sewer Pipe Samples

The importance of bacteria in catalyzing microbially induced concrete corrosion was evaluated. Experiments were conducted to determine the optimum pH and growth kinetics of four selected bacterial strains (Thiobacillus neapolitanus C2, Thiobacillus thioparus H1, Acidithiobacillus thiooxidans, and Acidiphilium cryptum LHET2). Combinations of these strains were inoculated into flasks containing ∼42 g concrete blocks half-submerged in 600 mL of synthetic wastewater with hydrogen sulfide in the headspace air. Controls not inoculated with bacteria lost 0–3 mg/g concrete over 227 days; in the aqueous phase the minimum pH was 6–6.7 and 19–23 mg of calcium/g concrete was released. Systems inoculated with two species of neutrophilic sulfur oxidizing microorganisms (SOM) lost 8 mg/g concrete; in the aqueous phase the minimum pH was 4.5 and 25 mg of calcium/g concrete was released. The concrete samples incubated with neutrophilic and acidophilic SOM and an acidophilic heterotroph experienced the greatest deteriorati...

Effect of average flow and capacity utilization on effluent water quality from US municipal wastewater treatment facilities.

There is increasing interest in decentralization of wastewater collection and treatment systems. However, there have been no systematic studies of the performance of small treatment facilities compared with larger plants. A statistical analysis of 4 years of discharge monthly report (DMR) data from 210 operating wastewater treatment facilities was conducted to determine the effect of average flow rate and capacity utilization on effluent biochemical oxygen demand (BOD), total suspended solids (TSS), ammonia, and fecal coliforms relative to permitted values. Relationships were quantified using generalized linear models (GLMs). Small facilities (40 m³/d) had violation rates greater than 10 times that of the largest facilities (400,000 m³/d) for BOD, TSS, and ammonia. For facilities with average flows less than 40,000 m³/d, increasing capacity utilization was correlated with increased effluent levels of BOD and TSS. Larger facilities tended to operate at flows closer to their design capacity while maintaining treatment suggesting greater efficiency.

Iron respiration by Acidiphilium cryptum at pH 5

The growth of acidophilic iron respiring bacteria at pH > 4.5 may be a key to the transition from acidic to circumneutral conditions that would occur during restoration of acid mine drainage sites. Flasks containing Acidiphilium cryptum ATCC 33463 were incubated initially under aerobic conditions in liquid medium containing Fe(2)(SO(4))(3) and glucose at an initial pH of 5. Significant iron respiration was observed after flasks were sealed to prevent oxygenation; at the same time, medium pH increased from 4.5 to 6. No soluble Fe(III) was detected throughout the experiments, consistent with pH conditions, indicating that bacteria were able to respire using precipitated ferric iron species. In addition, the concentration of soluble Fe(2+) reached a plateau, even though iron respiration appeared to continue, possibly due to precipitation of mixed Fe (II)/Fe(III)-oxide as magnetite. Results suggest that A. cryptum has a wide range of pH tolerance, which may enable it to play a role in controlling acid generation by means of establishing growth conditions favorable to neutrophilic bacteria such as sulfate reduction.