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PubMed2005

Hydrodynamic aspects of particle clogging in porous media.

Data from 6 filtration studies, representing 43 experiments, are analyzed with a simplified version of the single-parameter O'Melia and Ali clogging model. The model parameter displays a systematic dependence on fluid velocity, which was an independent variable in each study. A cake filtration model also explains the data from one filtration study by varying a single, velocity-dependent parameter, highlighting that clogging models, because they are empirical, are not unique. Limited experimental data indicate exponential depth dependence of particle accumulation, whose impact on clogging is quantified with an extended O'Melia and Ali model. The resulting two-parameter model successfully describes the increased clogging that is always observed in the top segment of a filter. However, even after accounting for particle penetration, the two-parameter model suggests that a velocity-dependent parameter representing deposit morphology must also be included to explain the data. Most of the experimental data are described by the single-parameter O'Melia and Ali model, and the model parameter is correlated to the collector Peclet number.

Equipment Failure↗

PubMed2002

Selection of microbial consortia for treating metal-working fluids.

The aim of this research was to determine the effectiveness of a strategy for constructing microbial consortia for treating chemically mixed industrial effluent, based on a more thorough understanding of communities within waste metal-working fluids (MWFs). Complementary phenotypic and genotypic methods revealed that the microbial communities in spent MWFs had low diversity and were very similar in species composition in samples originating from different locations and uses. Of 65 bacterial isolates studied, only 9 species were identified using fatty acid methyl ester (FAME) analysis. The results of genotypic analysis by denaturing gradient gel electrophoresis (DGGE) were congruent with observations made using FAME analysis. The metabolic potential of the isolates was assessed in terms of assimilation ability and tolerance of co-contaminants. The three isolates, selected (Clavibacter michiganensis, Methylobacterium mesophilicum, and Rhodococcus erythropolis) to form a consortium, were representative of three of the four most abundant populations and when combined could utilise or tolerate all of the individual MWF components, including the biocide and the recalcitrant compound benzotriazole.

Bacteria↗

PubMed2004

Mixing characteristics and whey wastewater treatment of a novel moving anaerobic biofilm reactor.

A novel moving anaerobic biofilm reactor was used to treat whey wastewater. In this process, biofilm was grown on a plastic biofilm media module, which was vertically moved up and down in the bulk fluid. The objectives of the study were to investigate the mixing and performance characteristics of the new process in treating whey wastewater. The mixing efficiency was indicated by a dispersion number, D(L)/uL. D(L)/uL was up to 1.34, showing that the anaerobic reactor can be taken as a completely mixed reactor. At mesophilic conditions (35+/-2 degrees C), the admissible volumetric COD loading rate up to 11.6kg COD m(-3) day(-1) was achieved with the COD removal efficiency of 89% and the hydraulic retention time (HRT) of 1 day. When the HRT was 0.6 days, the volumetric COD loading rate was 15.2 kg COD m(-3) day(-1), but COD removal efficiency decreased to 81%. The percentage of methane (CH4) in the biogas was 63% on average and the yield of methane was 333.4 L CH4 kg(-1) COD removal at ambient conditions.

Bacteria, Anaerobic↗

PubMed2003

Design of hard water stable emulsifier systems for petroleum- and bio-based semi-synthetic metalworking fluids.

Metalworking fluids (MWFs) increase productivity and the quality of manufacturing operations by cooling and lubricating during metal forming and cutting processes. Despite their widespread use, they pose significant health and environmental hazards throughout their life cycle. An obvious environmental improvement to MWF technology would be to improve the lifetime of the fluid while utilizing more environmentally friendly and less energy-consuming materials without compromising existing performance levels. This investigation focuses on the design of mixed anionionc:nonionic emulsifier systems for petroleum and bio-based MWFs that improve fluid lifetime by providing emulsion stability under hard water conditions, a common cause of emulsion destabilization leading to MWF disposal. Experimental conditions were designed to evaluate the impact of emulsifier structural characteristics (straight chain, branched tail, branched head) and the molar ratios of anionic to nonionic surfactant and oil to total surfactant. Results from the 2500 formulations generated indicate that the use of a twin-headed anionic surfactant can provide improved hard water stability for both mineral oil- and vegetable oil-based formulations, even in the absence of a chelating agent and a coupler. Results also suggest that an oil:total surfactant molar ratio of 0.5 or less is necessary for particle size stability in hard water conditions for these systems. The newly developed petroleum and bio-based formulations with improved hard water stability are competitive with commercially available MWFs in performance evaluations for tramp oil rejection, contact angle, and tapping torque efficiency. These results can be used to design MWF formulations with fewer components and extended lifetime under hard water conditions, both of which would lead to a reduction in the life cycle environmental impact of MWFs.

Calcium Chloride↗

PubMed2004

Modelling a spatially heterogeneous biofilm and the bulk fluid: selected results from benchmark problem 2 (BM2).

The numerical simulation of mass transfer and conversion in spatially heterogeneous biofilms on the meso-scale requires an accurate description of the hydrodynamics in the biofilm systems and of spatial effects. This leads to systems of three-dimensional nonlinear partial differential equations that are numerically very expensive to solve and to data requirements that are not easy to meet. In this paper several modeling approaches to reduce the physical complexity and, hence, accelerate the computation are compared. They range from a mere reduction of dimensionality by lumping the problem along a secondary flow direction to global mass balances or empirical correlations, at the core of which a one-dimensional boundary value problem must be solved. It is found that even strongly simplified models can describe the qualitative behaviour of the model with regard to variations in the geometrical and hydrodynamic model parameters quite well. In order to obtain also quantitatively reliable results the hydrodynamics must be considered in an appropriate manner.

Bacteria↗

PubMed2003

Development of guidelines for improved hydraulic design of waste stabilisation ponds.

Pond hydraulic behaviour is influenced by the inlet/outlet configuration, baffles and wind, but design information relating to these factors is still very limited. This paper reviews the development of "Guidelines for the Improved Hydraulic Design of Waste Stabilisation Ponds" and summarises some of the key findings and recommendations. This work was based on review of previous research, laboratory experimentation, field studies and mathematical modelling using computational fluid dynamics. The inlet design can have a significant influence on the flow regime in a pond. Poorly considered positioning of the inlet and the outlet can create hydraulic short-circuiting problems. As an example of the nature of the work undertaken in this project, the use of a small horizontal inlet pipe was compared against a vertical inlet design. A practical method of assessing the relative significance of wind versus inlet power input was presented. The application of this analysis may allow engineers to size inlet pipes to help control the flow patterns in ponds for efficient performance. Extensive testing has been undertaken on a wide range of baffle configurations. An example of this research showed how short stub baffles could provide similar improvements to longer "traditional" baffle designs, potentially offering significant savings in construction costs. For traditional baffle designs a minimum of two baffles is recommended. For the pond modelled in this work, it was found that any more than four baffles gave only marginal improvements.

Bioreactors↗

PubMed2004

Direct energy recovery from primary and secondary sludges by supercritical water oxidation.

Supercritical water oxidation (SCWO) oxidizes organic and biological materials virtually completely to benign products without the need for stack gas scrubbing. Heavy metals are recovered as stabilized solid, along with the sand and clay that is present in the feed. The technology has been under development for twenty years. The major obstacle to commercialization has been developing reactors that are not clogged by inorganic solid deposits. That problem has been solved by using tubular reactors with fluid velocities that are high enough to keep solids in suspension. Recently, system designs have been created that reduce the cost of processing sewage sludges below that of incineration. At 10 wt- % dry solids, sludge can be oxidized with virtually complete recovery of the sludge heating value as hot water or high-pressure steam. Liquid carbon dioxide of high purity can be recovered from the gaseous effluent and excess oxygen can be recovered for recycle. The net effect is to reduce the stack to a harmless vent with minimal flow rate of a clean gas. Complete simulations have been developed using physical property models that accurately simulate the thermodynamic properties of sub- and supercritical water in mixtures with O2, N2, CO2, and organics. Capital and operating cost estimates are given for sewage sludge treatment, which are less costly than incineration. The scenario of direct recovery of energy from sludges has inherent benefits compared to other gasification or liquefaction options.

Carbon Dioxide↗

PubMed2004

Colloid formation at waste plume fronts.

Highly saline and caustic tank waste solutions containing radionuclides and toxic metals have leaked into sediments at U.S. Department of Energy (DOE) facilities such as the Hanford Site (Washington state). Colloid transport is frequently invoked to explain migration of radionuclides and metals in the subsurface. To understand colloid formation during interactions between highly reactive fluids and sediments and its impact on contaminant transport, we simulated tank waste solution (TWS) leakage processes in laboratory columns at ambient and elevated (70 degrees C) temperatures. We found that maximum formation of mobile colloids occurred at the plume fronts (hundreds to thousands times higher than within the plume bodies or during later leaching). Concentrations of suspended solids were as high as 3 mass %, and their particle sizes ranged from tens of nanometers to a few micrometers. Calcium carbonate is always one of the dominant phases of the plume front colloids, while the other phases varied with solution pH and temperature. During infiltration of the leaked high-Na+ waste solution, rapid and completed Na+ replacement of exchangeable Ca2+ and Mg2+ from the sediment caused accumulation of these divalent cations at the moving plume front. Precipitation of supersaturated Ca2+/Mg2+-bearing minerals caused dramatic pH reduction atthe plume front. In turn, the reduced pH caused precipitation of other minerals. This understanding can help predict the behavior of contaminant trace elements carried by the tank waste solutions and could not have been obtained through conventional batch studies.

Adsorption↗

PubMed1993

Comparison of glass wool and glass powder methods for concentration of viruses from treated waste waters.

Enumeration of cultivable virus particle in sewage requires the samples to be concentrated. Two adsorption-elution methods, the glass wool cartridge method and the glass powder fluid layer method were compared. Firstly, it was demonstrated that virus could be readily recovered from the head, first 25 ml, of eluate of glass wool rather than from a reconcentration of the entire eluate, either by organic flocculation: 83% of positivity vs 44% respectively or double precipitation by PEG: 85% of positivity vs 61% respectively. Concentration on glass wool allowed the rescue of a greater number of positive samples (33/35) than on glass powder (16/35) as well as a higher mean titer of indigenous viruses, respectively 19 MPNCU/l vs 6 MPNCU/l (F1(34) = 36.02, P < 0.0001). Enteroviruses were the most frequently isolated viruses: found in 34/35 samples by either method, in 32/35 samples by glass wool, and in 14/35 samples by glass powder. Of the 12 enterovirus types identified by either method, a majority was Echovirus 6 (10 samples), Echovirus 11 (7 samples), Coxsackievirus B5 (4 samples) and also Coxsackievirus A7, A16, A21, B1, B6, Echovirus 1, 4, 12 and 19. Adenovirus types 1 and 5 were isolated from 4 samples by either method.

Adsorption↗

PubMed2006

Purification and characterization of an alkaline lipase from Pseudomonas aeruginosa isolated from putrid mineral cutting oil as component of metalworking fluid.

Extracellular lipase was isolated and purified from the culture broth of Pseudomonas aeruginosa, an extremophile which naturally grows in water-soluble mineral cutting oil (pH 10) used as metalworking fluid (MWF) for cooling and lubrication in industrial metalworking processes. The molecular mass of the purified lipase was estimated by SDS-PAGE to be 54 kDa. The optimum pH and temperature were 11 and 70 degrees C, respectively. The enzyme is stabile over a broad pH range (pH 4-11.5). The lipase preferably acted on triacylglycerols with medium-chain fatty acids. The lipase was inhibited strongly by Zn(2+), Hg(2+), Cu(2+) and slightly by Ca(2+) and Mg(2+). Non-ionic detergents and sodiumdeoxycholate enhanced lipase activity. Alkaline lipase from P. aeruginosa, capable of growing in a water-restricted medium has excellent properties and good potential for biotechnological applications in the metal industry. Its marked stability and activity in organic solvents suggest that this lipase is highly suitable as a biotechnological tool in a water-restricted medium with a variety of applications including organosynthetic reactions and the control and prevention of MWF putrification in the metal industry.

Biotechnology↗

PubMed2006

Examining the effect of length/width ratio on the hydro-dynamic behaviour in a DAF system using CFD and ADV techniques.

Dissolved air flotation (DAF) is a solid-liquid separation system that uses fine bubbles rising from the bottom to remove particles in water. In this study, we investigated the effect of L/W(L; length, W; width) on the hydrodynamic behavior in a DAF system using CFD (computational fluid dynamics) and ADV (acoustic Doppler velocimetry) technique. The factual full-scale DAF system, L/W ratio of 1:1, was selected and various UW ratio conditions (2:1, 3:1,4:1 and 5:1) were simulated with CFD. For modelling, 2-phase (gas-liquid) flow equations for the conservation of mass, momentum and turbulence quantities were solved using a Eulerian-Eulerian approach based on the assumption that a very small particle is applied in the DAF system. Also, for verification of CFD simulation results, we measured the actual velocity at some points in the full-scale DAF system with the ADV technique. Both the simulation and the measurement results were in good accordance with each other. We concluded that the L/W ratio and outlet geometry play an important role for flow pattern and fine bubble distribution in the flotation zone. In the ratio of 1:1, the dead zone is less than those in other cases. On the other hand, in the ratio of 5:1, the fine bubbles were more evenly distributed.

Waste Disposal, Fluid↗

PubMed1978

Acetic acid and hydrogen metabolism during coculture of an acetic acid producing bacterium with methanogenic bacteria.

Two microorganisms originally existing as a mixed culture obtained from an anaerobic digester fluid were separated for pure and coculture studies. One of these was motile, Gram-negative, and non-sporeforming, and it required yeast extract for growth and acetic acid production. This isolate produced H2 and did not need H2 and (or) CO2 for growth and acetate formation. The other isolate was a methanogen whick resembled Methanobacterium arbophilicum in morphology and substrate specificity. Coculture growth of the two isolates in yeast extract broth (80% N2--20% CO2 gas phase) indicated that the non-methanogen produced up to four to five times more H2 than when grown separately. Although the growth of the non-methanogen was not enhanced by the removal of H2 by the methanogen, the hydrogen produced was essential for the growth of methanogen. Similar results were obtained when the non-methanogen was cocultured with Methanospirillum hungatti GP1. Cultivation of the non-methanogen in the presence of M. hungatti GP1 (under abundance of 80% H2--20% CO2) indicated that the acetate produced was consumed by M. hungatii, without inhibiting the growth of the other culture.

Acetates↗

PubMed2005

Modeling of a vapor-phase fungi bioreactor for the abatement of hexane: fluid dynamics and kinetic aspects.

During some previous works, a packed-bed lab-scale biofilter (177 . 10(-6) m3), inoculated with a selected strain of Aspergillus niger had been tested for the abatement of hexane vapors, showing a maximum elimination capacity of 200 g hexane/m3 reactor/h. A steady-state mathematical model taking into account axial dispersion effect was applied to describe the process and predict experimental results, but many model parameters could not be calculated from experimental data. The aim of the present work was to carry out further investigations to accurately determine the dispersion coefficient and the kinetics parameters to verify the effective validity of the model. Analysis of residential time distribution revealed the presence of a certain degree of axial dispersion (dispersion coefficient D of 1.22 . 10(-4) m2/s). Experimental data from kinetic trials carried out in reduced height reactors, together with data from full-scale runs, were elaborated to estimate the kinetic saturation constant (K(s)), the coefficient yield (Y), the maximum growth rate (mu(max)) and maximum substrate degradation rate (r(max)). All these parameters were introduced into the model, which was then solved by simulation software finding a good correlation between experimental and theoretical results.

Aspergillus niger↗

PubMed2004

Influence of ion accumulation on the emulsion stability and performance of semi-synthetic metalworking fluids.

The metalworking industry is one of the largest in the United States. Although metalworking fluids (MWFs) are ubiquitous in manufacturing as coolants and lubricants, these emulsified fluids have a significant environmental impact over their life cycle. Accordingly, it has become necessary to better understand emulsion destabilization mechanisms that lead to MWF deterioration and disposal so that MWF formulations can be designed for increased longevity. This paper investigates the impact of pH and a wide range of hard water salts on MWF emulsion stability. While expected trends from the emulsion science literature are observed, it is shown that MWF destabilization can lead to an increase in the microbial load that the MWF can sustain while only slightly improving manufacturing performance as measured by the tapping torque test. Experimental observations also indicate that these trends are strongly correlated with increased emulsion particle size, regardless of whether increased particle size is achieved by aging, by reductions in pH, or by the addition of hard water salts. In MWF systems, these conditions typically result from the accumulation of divalent and trivalent cations over time due to hard water additions and exposure to metal workpieces and tools. While MWFs are formulated with EDTA to avoid emulsion destabilization due to cation accumulation, it is shown that EDTA can be ineffective or highly inefficient for this purpose due to direct interactions between EDTA and the MWF emulsifier system. Given the ineffectiveness of EDTA and commonly utilized MWF emulsifier systems to maintain stable emulsion size in the presence of high concentrations of hard water salts, a more effective and environmentally preferable technological change to the MWF formulation design is proposed and successfully demonstrated.

Emulsions↗

PubMed2003

Bioadsorber efficiency, design, and performance forecasting for alachlor removal.

This study discusses a mathematical modeling and design protocol for bioactive granular activated carbon (GAC) adsorbers employed for purification of drinking water contaminated by chlorinated pesticides, exemplified by alachlor. A thin biofilm model is discussed that incorporates the following phenomenological aspects: film transfer from the bulk fluid to the adsorbent particles, diffusion through the biofilm immobilized on adsorbent surface, adsorption of the contaminant into the adsorbent particle. The modeling approach involved independent laboratory-scale experiments to determine the model input parameters. These experiments included adsorption isotherm studies, adsorption rate studies, and biokinetic studies. Bioactive expanded-bed adsorber experiments were conducted to obtain realistic experimental data for determining the ability of the model for predicting adsorber dynamics under different operating conditions. The model equations were solved using a computationally efficient hybrid numerical technique combining orthogonal collocation and finite difference methods. The model provided accurate predictions of adsorber dynamics for bioactive and non-bioactive scenarios. Sensitivity analyses demonstrated the significance of various model parameters, and focussed on enhancement in certain key parameters to improve the overall process efficiency. Scale-up simulation studies for bioactive and non-bioactive adsorbers provided comparisons between their performances, and illustrated the advantages of bioregeneration for enhancing their effective service life spans. Isolation of microbial species revealed that fungal strains were more efficient than bacterial strains in metabolizing alachlor. Microbial degradation pathways for alachlor were proposed and confirmed by the detection of biotransformation metabolites and byproducts using gas chromatography/mass spectrometry.

Acetamides↗

PubMed2006

Biofilm growth and characteristics in an alternating pumped sequencing batch biofilm reactor (APSBBR).

A novel biofilm reactor-alternating pumped sequencing batch biofilm reactor (APSBBR)-was developed to treat synthetic dairy wastewater at a volumetric chemical oxygen demand (COD) loading rate of 487 g COD m(-3) d(-1) and an areal loading rate of 5.4 g COD m(-2) d(-1). This biofilm reactor comprised two tanks, Tanks 1 and 2, with two identical plastic biofilm modules in each tank. The maximum volume of bulk fluid in the two-tank reactor was the volume of one tank. The APSBBR was operated as a sequencing batch biofilm reactor with five operational phases-fill (25 min), anoxic (9 h), aerobic (9 h), settle (6 h) and draw (5 min). The fill, anoxic, settle and draw phases occurred in Tank 1. In the aerobic phase, the wastewater was circulated between the two tanks with centrifugal pumps and aeration was mainly achieved through oxygen absorption by micro-organisms in the biofilms when they were exposed to the air. In this paper, the biofilm growth and characteristics in the APSBBR were studied in a 98-day laboratory-scale experiment. During the course of the study, it was found that the biofilm thickness (delta) in Tank 1 ranged from 1.2 to 7.2 mm and that in Tank 2 from 0.5 to 2.2 mm; the biofilm growth against time (t) can be simulated as delta=0.07t0.99 (R2 = 0.97, P = 0.002) in Tank 1 and delta = 0.08t0.66 (R2 = 0.81, P = 0.04) in Tank 2. The biomass yield coefficient, Y, was 0.18 g volatile solids (VS) g(-1) COD removal. The biofilm density in both tanks, X, decreased as the biofilm thickness increased and can be correlated to the biofilm thickness, delta .

Absorption↗

PubMed2005

Flow pattern visualization in a mimic anaerobic digester using CFD.

Three-dimensional steady-state computational fluid dynamics (CFD) simulations were performed in mimic anaerobic digesters to visualize their flow pattern and obtain hydrodynamic parameters. The mixing in the digester was provided by sparging gas at three different flow rates. The gas phase was simulated with air and the liquid phase with water. The CFD results were first evaluated using experimental data obtained by computer automated radioactive particle tracking (CARPT). The simulation results in terms of overall flow pattern, location of circulation cells and stagnant regions, trends of liquid velocity profiles, and volume of dead zones agree reasonably well with the experimental data. CFD simulations were also performed on different digester configurations. The effects of changing draft tube size, clearance, and shape of the tank bottoms were calculated to evaluate the effect of digester design on its flow pattern. Changing the draft tube clearance and height had no influence on the flow pattern or dead regions volume. However, increasing the draft tube diameter or incorporating a conical bottom design helped in reducing the volume of the dead zones as compared to a flat-bottom digester. The simulations showed that the gas flow rate sparged by a single point (0.5 cm diameter) sparger does not have an appreciable effect on the flow pattern of the digesters at the range of gas flow rates used.

Bacteria, Anaerobic↗

PubMed2004

Anaerobic biodegradation of aircraft deicing fluid in UASB reactors.

A central composite design was employed to methodically investigate anaerobic treatment of aircraft deicing fluid (ADF) in bench-scale Upflow Anaerobic Sludge Blanket (UASB) reactors. A total of 23 runs at 17 different operating conditions (0.8% 1.6% ADF (6000-12,000mg/L COD), 12-56h HRT, and 18-36gVSS/L) were conducted in continuous mode. The development of four empirical models describing process responses (i.e. COD removal efficiency, biomass-specific acetoclastic activity, methane production rate, and methane production potential) as functions of ADF concentration, hydraulic retention time, and biomass concentration is presented. Model verification indicated that predicted responses (COD removal efficiencies, biomass-specific acetoclastic activity, and methane production rates and potential) were in good agreement with experimental results. Biomass-specific acetoclastic activity was improved two-fold from 0.23gCOD/gVSS/d for inoculum to a maximum of 0.55gCOD/gVSS/d during ADF treatment in UASB reactors. For the design window, COD removal efficiencies were higher than 90%. The predicted methane production potentials were close to theoretical values, and methane production rates increased as the organic loading rate is increased. ADF toxicity effects were evident for 1.6% ADF at medium organic loadings (SOLR above 0.5gCOD/gVSS/d). In contrast, good reactor stability and excellent COD removal efficiencies were achieved at 1.2% ADF for reactor loadings approaching that of highly loaded systems (0.73gCOD/gVSS/d).

Acetates↗