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At least 253 records · Page 14Linked to original sources
PubMed2003

Biofouling assessment using an infrared monitor.

The paper details the design of an infrared monitor for detecting biofilm accumulation on surfaces in flowing systems. It is based on the principle that the amount of infrared radiation absorbed by a biofilm, is proportional to the amount of biofilm present. The test surface in the monitor has to be transparent in order to allow the passage of the radiation, so that the radiation absorbed is solely due to the presence of the biofilm. Since the biofilm structure is very dependent upon the conditions under which it was formed, e.g. fluid flow, nutrient and cell concentrations and temperature, it cannot be made to give absolute values of biofilm accumulation. Nevertheless the device is extremely useful for comparison purposes, such as the evaluation of biocide efficacy under different operating conditions. Correlations of biofilm thickness with infrared absorbance can be made, however, for specified operating conditions. The value of the monitor is demonstrated in some typical examples. The infrared absorbance shows a clear distinction between the accumulation of biofilm under two different velocity regimes, three pH values and three chlorine concentrations at two water velocities. It is suggested that in addition to laboratory use, the monitor could be used effectively for biofilm control in cooling water circuits.

Biofilms↗
PubMed2002

Development of a simulator for ozone/UV reactor based on CFD analysis.

A new CFD (Computational Fluid Dynamics) simulator for an O3/UV reactor where ozone dissolved water flows under the irradiation of UV, has been developed by combining a fluid dynamics model with a complex radical reaction model. The radical reaction model used in this simulator was found to be reasonable, because the results obtained from the simulation of a completely stirred tank reactor (CSTR) system were in good agreement with the experimental results, e.g., the concentrations of total organic carbon (TOC), hydrogen peroxide and dissolved ozone obtained from a lab-scale CSTR. Furthermore, by using this CFD simulator, the distributions of substances such as hydroxyl radical (OH*) and hydrogen peroxide in the O3/UV reactor have been investigated. These distributions showed that this CFD simulator was considered to be reasonable. In addition, the simulation results suggested that conventional reactors were not optimized.

Computer Simulation↗
PubMed2003

Membrane treatment by nanofiltration of exhausted vegetable tannin liquors from the leather industry.

A rational use of water in the leather industry is described by applying the criteria of "clean technologies" by means of membrane processes. A nanofiltration (NF) process was used for recovering tannins and water from exhausted baths and reusing them as tanning agents and washings. Results of experiments performed on laboratory and semi-industrial pilot scale plants, operating and fluid-dynamic conditions and mass balance of the NF process are reported and discussed. Chemical and physical analytical values measured on skins treated with the recovered solutions were very similar to those measured on control skins tanned with standard solutions. According to the obtained results, a process scheme is suggested. It permits both to recover water and to increase the tannin/non tannin (T/NT) ratio in the retentate solution, starting from exhausted tanning baths and by using a NF membrane purification/concentration. The final volume reduction factor of tested exhausted baths was 5.25, the increase of T/NT ratio was from 1.1 to 2.3 and the average permeate flux was 12.5l/m(2)h. Advantages are in terms of: reduction of environmental impact (up to 75% of COD reduction of the global effluent), simplification of cleaning-up processes of wastewaters, decrease of disposal costs, saving of chemicals and water.

Conservation of Natural Resources↗
PubMed2003

Biological treatment of mixed industrial wastewaters in a fluidised bed reactor.

A study has been carried out on the operating parameters that influence the biodegradation of petroleum and brewery wastewaters, with a low-density biomass support. The biodegradation rate of a mixture of two wastes was compared with that of the separate wastes. A low aspect ratio reactor was employed, and this made it possible to operate at low superficial gas and liquid velocities. The gas distributor used created a fluid flow pattern similar to that of a draft tube, which enhanced axial mixing. At a particles loading of 12% (v/v), the optimum superficial gas velocity was 2.5 cm/s for the mixture. The interstice structure of the biomass-support particles, improved microbial attachment due to the resulting large surface area. There was a low biomass concentration when petroleum wastewater was treated alone, however, for a mixture of petroleum and brewery wastewaters, an increase in the concentration was observed. There was a higher gas hold up in the mixture than in the petroleum wastewater, but lower than in the brewery wastewater. An improved biodegradation was achieved when a mixture of brewery and petroleum wastewaters was treated, and this gave an indication that nutrient deficient wastes can be treated together with phosphate and nitrate rich food industry wastewaters.

Bacteria↗
PubMed2005

Profiling and modelling of thermal changes in a large waste stabilisation pond.

A thermal profiling study was undertaken at four depths at each of nine sites, and at the inlets and outlets of a large waste stabilisation pond (WSP). Results were collected simultaneously using a network of 42 thermistors and dataloggers. Profiles at each site were categorised as either "stratified" or "unstratified", and persistence analysis was used to determine the frequency and persistence of stratification events at each of the nine sites. Stratification was found to persist most strongly at the site furthest upwind in the WSP, with respect to prevailing wind during the study, leading to the conclusion that stratification induced short-circuiting will be greatest in this region of the WSP. A computational fluid dynamics (CFD) model was constructed of the WSP, including an energy balance to predict the bulk stratification gradient in the pond. Environmental conditions and WSP inlet temperature during one day in June 2001 were used as boundary conditions. The pond thermal profiles measured during the profiling study, together with outlet temperature during the day, were used to validate the CFD model results. The model predicted mean pond temperature with a high degree of accuracy (r2 = 0.92). However it was evident that even modest winds (> or = 1.5 m/s) partially broke down stratification, leading to poor prediction of the gradient by the CFD model, which did not directly account for the impact of wind shear stress on mixing in the WSP.

Models, Biological↗
PubMed2003

Dynamic response of biofilm to pipe surface and fluid velocity.

Biofouling in pipelines is a function of the inner roughness of the specific piping material that is used in distribution systems and the concomitant biofilm formation. To test the effect of velocity on the growth of biofilm, a Roto-Scope was designed and built to imitate different materials and flow conditions in potable water distribution systems. Biofilm formation was monitored using DAPI staining and the total number of viable bacteria. Increased velocity in the system resulted in a specific detaching velocity, where the formation of biofilm was limited. Most of the time these detaching velocities were not the highest velocities tested. The range of detaching velocities was between +/- 3 m x s(-1) and 4 m x s(-1). A flow velocity within this range would thus be ideal for achieving reduced biofilm growth in a distribution system.

Biofilms↗
PubMed2005

The efficiency of a sequencing batch biofilm reactor in organic carbon and phosphorus removal.

A laboratory sequencing batch biofilm reactor (SBBR), operated for a period of 158 days, was used to treat domestic-strength synthetic effluent. The biofilm reactor comprised a bulk fluid reactor, a biofilm plastic module, a synthetic wastewater feed tank, and pneumatic devices with pneumatic controls. The reactor cycle time was 8 h, and its operation consisted of five phases: feeding (59 min), mixing (1 min), anoxic/anaerobic (3 h), aerobic (3 h), and settling (1 h). At total chemical oxygen demand (CODT) loading rates of 8.8 g CODT m(-2) d(-1) and 1.2 kg CODT m(-3) d(-1), expressed in terms of the plastic module surface area and reactor volume, respectively, the SBBR had average removal rates of 8.3 g CODT m(-2) d(-1) and 1.1 kg CODT m(-3) d(-1), or 94%. Total orthophosphorus (PO4-PT) and filtered orthophosphorus (PO4-PF) removals were 44% and 50%, respectively.

Biofilms↗
PubMed2003

The spatial significance of water quality indicators in waste stabilization ponds--limitations of residence time distribution analysis in predicting treatment efficiency.

Over the past fifty years, considerable research in waste stabilization pond operation has led to the development of a number of models used to describe the hydraulic regime and predict treatment efficiency. Models range in complexity from plug or completely mixed simplifications to computational fluid dynamics (CFD) models which are able to predict flow hydraulics at a local level. Information about the exit age of pond effluent can be used to estimate pollutant decay. However, a mechanistic approach to understanding pond operation highlights the importance of knowing both the time and spatial history of pond effluent. A CFD model of a large pond system was constructed to demonstrate various hydraulic scenarios under different boundary conditions. Two scenarios were compared to visually demonstrate the effects of differing hydraulic conditions. Typical mechanistic models were applied to each condition to quantify biological differences. This simple example indicates that integrating biological and localised flow models will lead to a more holistic understanding of pond operation and treatment efficiency.

Bioreactors↗
PubMed2004

An accurate approach to the design of channel hydraulic flocculators.

The design of flocculators for water treatment continues to be based on the generalized and simplistic concept of mean velocity gradient within the reaction zone. This approach makes little sense for hydraulic flocculators in which the turbulence conditions are heterogenous. A theoretical, experimental and computational fluid dynamics study is presented, in which a point-to-point approach is derived, allowing variations in turbulent kinetic energy to be taken into account in determining flocculation efficiency. Results for the point-to-point calculation are compared with experimental measurements of flocculation efficiency in a full-scale model of a channel hydraulic flocculator, and an extremely good fit is obtained, demonstrating the point-to-point approach to be an accurate method of determining flocculation efficiency in channel hydraulic flocculators. A design example is presented showing how the point-to-point approach can be used in practice. It is concluded that the point-to-point approach is a much better method of design than that based on the mean velocity gradient.

Equipment Design↗
PubMed2005

CFD (computational fluid dynamics) modelling of baffles for optimizing tropical waste stabilization pond systems.

CFD modelling of the incorporation of two baffles equally spaced along the longitudinal axis of the pond and with a length equal to 70% of the pond breadth, indicated a potential improvement in the removal of E. coli in a 4-day secondary facultative pond at 25degrees C from 5 x 10(6) per 100 ml in the effluent from a 1-day anaerobic pond to 4 x 10(4) per 100 ml; the reduction in an un-baffled pond was an order of magnitude less effective. The addition of a similarly baffled 4-day primary maturation pond reduced the effluent E. coli count to 340 per 100 ml; the reduction in an un-baffled series was two orders of magnitude less effective. Well designed baffles thus have considerable potential for reducing pond area requirements and hence costs in the hot tropics. These very promising results highlight the need for field studies on baffled pond systems to validate (or allow calibration) of the CFD model used in this study.

Biodegradation, Environmental↗
PubMed2004

Biological nitrogen removal using a vertically moving biofilm system.

In this study, a biological nitrogen removal process using a vertically moving biofilm system was used to treat synthetic wastewater. The process consisted of two pre-denitrification units, one combined carbonaceous removal/nitrification unit and three nitrification units. Each unit employed biofilm growth on a plastic module. In the anoxic units, the modules were vertically moved, while always submerged, in the bulk fluid; in the aerobic units, they were moved vertically up into the air and down into the wastewater. Three small-scale experiments, having different recirculation ratios and influent loadings, were conducted at a controlled temperature of 11 degrees C. In this system, the carbonaceous removal efficiency was in the range of 94-96% and the total nitrogen removal efficiency was 77-82%. In the anoxic units, the denitrification efficiency was 94-98% and the areal denitrification rates, based on the surface area of the biofilm modules, were 2.9-3.8 g NO3-N/(m2 x d). The nitrification efficiency occurring in the aerobic tanks was up to 95% and the maximum areal ammonium removal rates were 1.3-1.8 g NH4-N/(m2 x d).

Bacteria↗
PubMed2002

Investigation of anaerobic zone short-circuiting using computational fluid dynamics.

Flow characteristics of anaerobic zone was investigated using the computational fluid dynamics technique. The tank is an inlet/outlet baffle tank with two impellers to provide additional energy to prevent solid settlement. The turbulent flow was modelled using the standard k-e model and the rotation of the impellers was modelled using the multiple rotating frame of reference technique. The model simulated tracer results and was in reasonable agreement with measurement. Solid settlement was tracked using the Lagrangean disperse phase tehnique. Flow in anaerobic zone exhibited completely mixed behaviour with short-circuiting. A number of options were investigated. All exhibited the general completely mixed system, which resulted from the flow circulation around the central baffle. Some options, however, led to major short circuiting and were avoided. The function of the impellers was to maintain the flow circulation and to prevent solid settlement.

Bacteria, Anaerobic↗
PubMed1994

[Study of the efficacy of sewage treatment systems for fluid waste on pig farms in Slovakia].

Bacteriological, helminthological and physico-chemical examinations were carried out to investigate the technological procedure in three water treatment plants treating slurry from large-capacity pig farms (Kosická Polianka, Spisské Vlachy, Vel'ký Dur). Our investigations were focused on the testing of effectiveness of mechanical, chemical and biological treatment system most frequently used in Slovakia. Our investigations revealed that water-treatment plants, operating on pig farms, fulfil only the supplies management requirements concerning the treated water, discharged into the recipient. From the hygienic viewpoint further processing or utilization of the solid fraction remains unsolved. This fraction contains considerable concentrations of bacteria and parasitic germs (Ascaris suum, Trichuris suis, Isospora sp., Eimeria sp.) most of which exhibit high tenacity in the environment. It is recommended to process this solid fraction by composting before it is applied as a manure. However, the measured values did not exceed the reference hygienic limits. The technological stage of chemical treatment, which follows after the separation and utilizes some coagulants (aluminium sulphate, ferrous sulphate), can increase the chemical load of water stripped of crude organic pollutants, by some undesirable chemical elements.

Animal Husbandry↗
PubMed2005

Treatment of oil-in-water emulsions: performance of a sawdust bed filter.

The effect of operating conditions on the performance of a sawdust bed filter used for the treatment of an oil-in-water emulsion was investigated. A metalworking fluid (3 vol.% oil) was used as oil-in-water emulsion and sawdust as filter medium and sorbent. Because of the high stability of the emulsion, small amounts of inorganic salt (calcium sulphate) were mixed with the sorbent, acting as coagulant to achieve the emulsion breakdown. The influence of flow rate, bed height, temperature and the amount of coagulant salt added was studied. Experimental results show that several processes are involved in oil removal from oil-in-water emulsions, i.e. coagulation, coalescence, adsorption or straining. More than 99% of oil content in the influent stream was removed. Experimental results show that low-cost sorbents like sawdust are feasible to be used in the treatment of oil-in-water emulsions if small amounts of coagulant salts are added to the filter media.

Adsorption↗
PubMed2006

Modelling of wastewater treatment plants--how far shall we go with sophisticated modelling tools?

Several levels of complexity are available for modelling of wastewater treatment plants. Modelling local effects rely on computational fluid dynamics (CFD) approaches whereas activated sludge models (ASM) represent the global methodology. By applying both modelling approaches to pilot plant and full scale systems, this paper evaluates the value of each method and especially their potential combination. Model structure identification for ASM is discussed based on a full-scale closed loop oxidation ditch modelling. It is illustrated how and for what circumstances information obtained via CFD (computational fluid dynamics) analysis, residence time distribution (RTD) and other experimental means can be used. Furthermore, CFD analysis of the multiphase flow mechanisms is employed to obtain a correct description of the oxygenation capacity of the system studied, including an easy implementation of this information in the classical ASM modelling (e.g. oxygen transfer). The combination of CFD and activated sludge modelling of wastewater treatment processes is applied to three reactor configurations, a perfectly mixed reactor, a pilot scale activated sludge basin (ASB) and a real scale ASB. The application of the biological models to the CFD model is validated against experimentation for the pilot scale ASB and against a classical global ASM model response. A first step in the evaluation of the potential of the combined CFD-ASM model is performed using a full scale oxidation ditch system as testing scenario.

Models, Theoretical↗
PubMedDate not supplied

Fate and toxicity of aircraft deicing fluid additives through anaerobic digestion.

Benzotriazole derivatives are widely used corrosion inhibitors and their fate during wastewater treatment processes is unknown. The purpose of this research was to study the toxic effects and fate of the two commercially significant benzotriazole isomers used in aircraft deicing fluids (4-, and 5-, methylbenzotriazole [MeBT]) during anaerobic digestion. Experiments were executed in microcosms using mesophilic anaerobic biomass co-digesting wastewater sludge and propylene glycol. Sorption of MeBT to digesting solids could be approximated with a Freundlich model, and no anaerobic breakdown of either MeBT isomer was detected. Digesters fed more than 300 mg/L MeBT responded with a significant decrease in methanogenic microbial activity and volatile solids production and a concomitant increase in accumulation of volatile fatty acids. Direct microscopic measurements using fluorescent phylogenetic probes applied to digesting biomass revealed that members of both Archaea and Bacteria domains were sensitive to MeBT. Granular activated carbon (GAC) (volatile solids: GAC = 10%) reduced the apparent toxic effects of MeBT; GAC addition nearly restored the baseline activity of digesters fed MeBT (500 to 1000 mg/L).

Aircraft↗
PubMed2003

Hydrodynamics of biological aggregates of different sludge ages: an insight into the mass transport mechanisms of bioaggregates.

Internal permeation and its role in mass transport to biological aggregates are investigated through detailed settling experiments. Three groups of bacterial aggregates (0.8-3.2 mm), which were different in fractal dimension and porosity, were generated in batch activated sludge reactors with biomass residence times (BRTs) of 5, 10, and 20 days. An apparatus of vertically connected double settling columns, which were filled respectively with water and an EDTA solution of a higher density, was used to characterize the settling and permeability features of individual aggregates. The settling velocities observed in water were in good agreement with those predicted by Stokes' law for porous but impermeable aggregates. The BRT10 and BRT20 aggregates, with porosities that were generally less than 0.92, had fluid collection efficiencies ranging from 0 to 0.1, while the BRT5 aggregates with porosities that were generally higher than 0.97 were almost completely impermeable. It is suggested that bioaggregates with either a tightly or a loosely packed structure cannot be as highly permeable as characterized for nonbiological fractal aggregates. While falling from water into the denser EDTA liquid, many BRT10 and BRT20 aggregates stopped and stayed below the interface of the two liquids for a period that was more than an order of magnitude shorter than the prediction based on the assumption of molecular diffusion as the predominant mass transport mechanism to the aggregates. The results indicate that limited intra-aggregate convection, which may not be important to the hydrodynamic properties of bioaggregates, could significantly enhance mass transport to suspended aggregates in biological wastewater treatment reactors.

Biomass↗
PubMed2003

Aerobic biological treatment of synthetic municipal wastewater in membrane-coupled bioreactors.

Membrane-coupled bioreactors (MBRs) offer many benefits compared to conventional biological wastewater treatment systems; however, their performance characteristics are poorly understood. Laboratory-scale MBRs were used to study bacterial adaptations in physiology and community structure. MBRs were fed a mixture of starch, gelatin, and polyoxyethylene-sorbitan monooleate to simulate the polysaccharide, protein, and lipid components of municipal wastewater. Physiological adaptations were detected by measuring ectoenzyme activity while structural dynamics were studied by denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA gene fragments. As cell biomass accumulated in the MBRs, pollutant removal efficiency initially improved and then stabilized with respect to effluent concentrations of chemical oxygen demand, protein, and carbohydrate. Comparison of the MBR effluent to filtered reactor fluid indicated that a portion of the observed pollutant removal was due to filtration by the membrane rather than microbial activity. The rates of ectoenzyme-mediated polysaccharide (alpha-glucosidase) and protein (leucine aminopeptidase) hydrolysis became relatively constant once pollutant removal efficiency stabilized. However, the maximum rate of lipid hydrolysis (heptanoate esterase) concomitantly increased more than 10-fold. Similarly, alpha-glucosidase and leucine aminopeptidase ectoenzyme affinities were relatively constant, while the heptanoate esterase affinity increased more than 30-fold. Community analysis revealed that a substantial community shift occurred within the first 7 days of operation. A Flavobacterium-like bacterial population dominated the community (>50% of total band intensity) and continued to do so for the remainder of the experiment.

Adaptation, Physiological↗