Darren A. Lytle

A systematic comparison of the electrokinetic properties of environmentally important microorganisms in water

The surface charge of microorganisms is an important factor controlling their stability in aqueous environments and removal during water treatment practices. The electrophoretic mobility (EPM) of a number of environmentally important microorganisms in phosphate buffers was measured. The effect of pH, ionic strength, and cation type (valence) and cation concentration on the EPM was investigated. The results show that microorganisms have significantly different charge properties in water. The surface charge of all microorganisms was impacted by pH, ionic strength and ionic make-up of the water. As a result, direct comparisons of reported surface charge values should be approached with caution. Increasing the pH increased the EPM in the negative direction. Increasing the ionic strength of the suspension by increasing the phosphate buffer concentration or adding simple salts generally decreased the EPM. The EPM was more neutral as the valence state of the cation in the salt increased.

Microbial Survey of a Full-Scale, Biologically Active Filter for Treatment of Drinking Water

ABSTRACT The microbial community of a full-scale, biologically active drinking water filter was surveyed using molecular techniques. Nitrosomonas, Nitrospira, Sphingomonadales, and Rhizobiales dominated the clone libraries. The results elucidate the microbial ecology of biological filters and demonstrate that biological treatment of drinking water should be considered a viable alternative to physicochemical methods.

Formation and release behavior of iron corrosion products under the influence of bacterial communities in a simulated water distribution system

To understand the formation and release behavior of iron corrosion products in a drinking water distribution system, annular reactors (ARs) were used to investigate the development processes of corrosion products and biofilm community as well as the concomitant iron release behavior. Results showed that the formation and transformation of corrosion products and bacterial community are closely related to each other. The presence of sulfate-reducing bacteria (SRB, e.g. Desulfovibrio and Desulfotomaculum), sulfur-oxidizing bacteria (SOB, e.g. Sulfuricella), and iron-oxidizing bacteria (IOB, e.g. Acidovorax, Gallionella, Leptothrix, and Sphaerotilus) in biofilms could speed up iron corrosion; however, iron-reducing bacteria (IRB, e.g. Bacillus, Clostridium, and Pseudomonas) could inhibit iron corrosion and iron release. Corrosion scales on iron coupons could develop into a two-layered structure (top layer and inner layer) with time. The relatively stable constituents such as goethite (α-FeOOH) and magnetite (Fe3O4) mainly existed in the top layers, while green rust (Fe6(OH)12CO3) mainly existed in the inner layers. The IOB (especially Acidovorax) contributed to the formation of α-FeOOH, while IRB and the anaerobic conditions could facilitate the formation of Fe3O4. Compared with the AR test without biofilms, the iron corrosion rate with biofilms was relatively higher (p < 0.05) during the whole experimental period, but the iron release with biofilms was obviously lower both at the initial stage and after 3 months. Biofilm and corrosion scale samples formed under different water supply conditions in an actual drinking water distribution system verified the relationships between the bacterial community and corrosion products.

Microbial Community Profile of a Lead Service Line Removed from a Drinking Water Distribution System

ABSTRACT A corroded lead service line was removed from a drinking water distribution system, and the microbial community was profiled using 16S rRNA gene techniques. This is the first report of the characterization of a biofilm on the surface of a corroded lead drinking water service line. The majority of phylotypes have been linked to heavy-metal-contaminated environments.

Nanoscale Investigation of the Impact of pH and Orthophosphate on the Corrosion of Copper Surfaces in Water

Advanced surface characterization techniques were used to systematically investigate either the corrosion or passivation of copper after immersion in water as impacted by pH and orthophosphate water chemistries. Atomic force microscopy, depth profiling with time-of-flight secondary ion mass spectrometry, and X-ray diffraction were used to evaluate changes in surface chemistry of copper surfaces resulting from various chemical treatments. Nanoscale differences in surface morphology are clearly evident after 6 and 24 h immersion in water samples. Orthophosphate and pH dramatically influence the evolution and progression of changes during surface corrosion. For example, in the absence of orthophosphate the surface of copper exposed to water at pH 6 had formed relatively large cubic crystals on the surface up to 400 nm in height. In the presence of orthophosphate, the morphology and growth rate of corrosion byproduct changed dramatically, and the formation of identifiable crystals diminished. These investigations provide insight into the mechanisms of surface passivation and the evolution of nanoscale mineral deposits on surfaces at very early stages of the corrosion of copper surfaces in water.

Removal of strontium from drinking water by conventional treatment and lime softening in bench-scale studies

The United States Environmental Protection Agency Contaminant Candidate List 3 lists strontium as a contaminant for potential regulatory consideration in drinking water. Very limited data is available on strontium removal from drinking water and as a result, there is an immediate need for treatment information. The objective of this work is to evaluate the effectiveness of coagulation/filtration and lime-soda ash softening treatment methods to remove strontium from surface and ground waters. Coagulation/filtration jar test results on natural waters showed that conventional treatment with aluminum and iron coagulants were able to achieve only 12% and 5.9% strontium removal, while lime softening removed as high as 78% from natural strontium-containing ground water. Controlled batch experiments on synthetic water showed that strontium removal during the lime-soda ash softening was affected by pH, calcium concentration and dissolved inorganic carbon concentration. In all softening jar tests, the final strontium concentration was directly related to the initial strontium concentration and the removal of strontium was directly associated with calcium removal. Precipitated solids showed well-formed crystals or agglomerates of mixed solids, two polymorphs of calcium carbonate (vaterite and calcite), and strontianite, depending on initial water quality conditions. X-ray diffraction analysis suggested that strontium was likely incorporated in the calcium carbonate crystal lattice and was likely responsible for removal during lime softening.

Impact of water quality on chlorine demand of corroding copper.

Copper is widely used in drinking water premise plumbing system materials. In buildings such as hospitals, large and complicated plumbing networks make it difficult to maintain good water quality. Sustaining safe disinfectant residuals throughout a building to protect against waterborne pathogens such as Legionella is particularly challenging since copper and other reactive distribution system materials can exert considerable demands. The objective of this work was to evaluate the impact of pH and orthophosphate on the consumption of free chlorine associated with corroding copper pipes over time. A copper test-loop pilot system was used to control test conditions and systematically meet the study objectives. Chlorine consumption trends attributed to abiotic reactions with copper over time were different for each pH condition tested, and the total amount of chlorine consumed over the test runs increased with increasing pH. Orthophosphate eliminated chlorine consumption trends with elapsed time (i.e., chlorine demand was consistent across entire test runs). Orthophosphate also greatly reduced the total amount of chlorine consumed over the test runs. Interestingly, the total amount of chlorine consumed and the consumption rate were not pH dependent when orthophosphate was present. The findings reflect the complex and competing reactions at the copper pipe wall including corrosion, oxidation of Cu(I) minerals and ions, and possible oxidation of Cu(II) minerals, and the change in chlorine species all as a function of pH. The work has practical applications for maintaining chlorine residuals in premise plumbing drinking water systems including large buildings such as hospitals.

Microwave-Assisted Combustion Synthesis of Nano Iron Oxide/Iron-Coated Activated Carbon, Anthracite, Cellulose Fiber, and Silica, with Arsenic Adsorption Studies

Combustion synthesis of iron oxide/iron coated carbons such as activated carbon, anthracite, cellulose fiber, and silica is described. The reactions were carried out in alumina crucibles using a Panasonic kitchen microwave with inverter technology, and the reaction process was completed within a few minutes. The method used no additional fuel and nitrate, which is present in the precursor itself, to drive the reaction. The obtained samples were then characterized with X-ray mapping, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), selected area diffraction pattern (SAED), transmission electron microscopy (TEM), X-ray diffraction (XRD), and inductively coupled plasma (ICP) spectroscopy. The size of the iron oxide/iron nanoparticle-coated activated carbon, anthracite, cellulose fiber, and silica samples were found to be in the nano range (50–400 nm). The iron oxide/iron nanoparticles mostly crystallized into cubic symmetry which was confirmed by SAED. The XRD pattern indicated that iron oxide/iron nano particles existed in four major phases. That is, γ-Fe2O3, α-Fe2O3, Fe3O4, and Fe. These iron-coated activated carbon, anthracite, cellulose fiber, and silica samples were tested for arsenic adsorption through batch experiments, revealing that few samples had significant arsenic adsorption.

Deposition behavior of residual aluminum in drinking water distribution system: Effect of aluminum speciation

Finished drinking water usually contains some residual aluminum. The deposition of residual aluminum in distribution systems and potential release back to the drinking water could significantly influence the water quality at consumer taps. A preliminary analysis of aluminum content in cast iron pipe corrosion scales and loose deposits demonstrated that aluminum deposition on distribution pipe surfaces could be excessive for water treated by aluminum coagulants including polyaluminum chloride (PACl). In this work, the deposition features of different aluminum species in PACl were investigated by simulated coil-pipe test, batch reactor test and quartz crystal microbalance with dissipation monitoring. The deposition amount of non-polymeric aluminum species was the least, and its deposition layer was soft and hydrated, which indicated the possible formation of amorphous Al(OH)3. Al13 had the highest deposition tendency, and the deposition layer was rigid and much less hydrated, which indicated that the deposited aluminum might possess regular structure and self-aggregation of Al13 could be the main deposition mechanism. While for Al30, its deposition was relatively slower and deposited aluminum amount was relatively less compared with Al13. However, the total deposited mass of Al30 was much higher than that of Al13, which was attributed to the deposition of particulate aluminum matters with much higher hydration state. Compared with stationary condition, stirring could significantly enhance the deposition process, while the effect of pH on deposition was relatively weak in the near neutral range of 6.7 to 8.7.

Characterization of the cell surface properties of drinking water pathogens by microbial adhesion to hydrocarbon and electrophoretic mobility measurements.

The surface characteristics of microbial cells directly influence their mobility and behavior within aqueous environments. The cell surface hydrophobicity (CSH) and electrophoretic mobility (EPM) of microbial cells impact a number of interactions and processes including aggregation, adhesion to surfaces, and stability of the cells within the aqueous environments. These cell characteristics are unique to the bacterial species and are a reflection of the large diversity of surface structures, proteins, and appendages of microorganisms. CSH and EPM of bacterial cells contribute substantially to the effectiveness of drinking water treatment to remove them, and therefore an investigation of these properties will be useful in predicting their removal through drinking water treatment processes and transport through drinking water distribution systems. EPM and CSH measurements of six microbiological pathogen or surrogate species suspended in phosphate-buffered water are reported in this work. Two strains of Vibrio cholerae were hydrophobic, while three strains of Escherichia coli were hydrophilic. Bacillus cereus was categorized as moderately hydrophobic. The strains of E. coli had the highest (most negative) EPM. Based on the measurements, E. coli species is predicted to be most difficult to remove from water while V. cholerae will be the easiest to remove.