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At least 235 records · Page 13Linked to original sources
PubMed2004

Biofilm modeling with AQUASIM.

AQUASIM is a computer program for the identification and simulation of aquatic systems. The program includes a one-dimensional multisubstrate and multispecies biofilm model and represents a suitable tool for biofilm simulation. The program can be used to calculate substrate removal in biofilm reactors for any user specified microbial system. One-dimensional spatial profiles of substrates and microbial species in the biofilm can be predicted. The program also calculates the development of the biofilm thickness and of the substrates and microbial species in the biofilm and in the bulk fluid over time. Detachment and attachment of microbial cells at the biofilm surface and in the biofilm interior can be considered, and simulations of sloughing events can be performed. Furthermore, AQUASIM allows pseudo two-dimensional modeling of plug flow biofilm reactors by a series of biofilm reactor compartments. The most significant limitation of the model is that it only considers spatial gradients of substrates and microbial species in the biofilm in the direction perpendicular to the substratum.

Bacteria↗
PubMed1999

Degradation of polydimethylsiloxane fluids in the environment--a review.

Due to their insolubility in water and high adsorption coefficient, liquid polydimethylsiloxanes (PDMS) discharged as effluent will adsorb to particulate matter and, therefore, will become a component of sewage sludge during waste water treatment. The subsequent environmental fate of PDMS will depend on the fate of the sludge. Due to increasing practices of soil amendment with sewage sludge the principal environmental compartment receiving PDMS fluids is the soil. Degradation of PDMS is a common process taking place in many different types of soils. It occurs through a unique combination of environmental degradation processes. Initial hydrolysis of PDMS is catalysed by clay minerals, the principal component of soil. The primary hydrolysis product, dimethylsilanediol (DMSD), is then either biodegraded, or evaporated into the atmosphere, where it is subsequently oxidised in the presence of sunlight. The end products in both cases are expected to be CO2, SiO2 and H2O.

Biodegradation, Environmental↗
PubMed2001

Carbonaceous oxidation using a new vertically moving biofilm system.

This laboratory study consisted of the construction and testing of a new experimental biofilm system for the carbonaceous oxidation of a synthetic wastewater. In the system, a biofilm cuboid module with a high surface area was vertically and repeatedly immersed in and lifted out of the wastewater in a reactor. The performance of two different biofilm modules were compared: one module was constructed from crossflow corrugated plastic sheets with a specific surface area of 410 m2m(-3) and had a calculated surface area of 6.24 m2; the other consisted of honeycombed plastic with hexagonal vertical columns and an estimated surface area of about 2.8 m2. Filtered chemical oxygen demand (COD) removal rates per bulk fluid volume for the corrugated and honeycombed modules of 7.2 kg COD m(-3) d(-1) and 7.6 kg COD m(-3) d(-1) were respectively achieved and these rates compare favourably with other wastewater treatment systems. The new biofilm system was simple to construct and operate, and was very effective in removing biodegradable COD from the synthetic wastewater. The system offers potential for reduced reactor volumes, energy saving, low solids production and easy solids removal.

Biodegradation, Environmental↗
PubMed2003

A method for the numerical assessment of sediment interceptors.

The problems associated with the presence of sediments in sewers and stormwater drainage systems represent a major engineering challenge. Their accumulation can result in operational difficulties, including low restriction and premature overflows. Sediments themselves are known to contribute significantly to the polluting load of storm overflows. The use of sediment interceptors within sewer systems or downstream of stormwater intakes represents one way of alleviating these problems. A study of stormwater sediment interceptors using Computational Fluid Dynamics (CFD) has identified that the ability of a chamber to retain, as well as remove, sediments is an important performance characteristic. A methodology for the assessment of such characteristics using CFD is presented in the context of a study of different chamber types. This concludes that primitive chambers, for example, gully pots, are likely to be far more prone to flushing out during high flow inputs than advanced systems such as vortex separators.

Facility Design and Construction↗
PubMed2003

A pilot plant study using a vertically moving biofilm process to treat municipal wastewater.

The pilot plant study comprised the construction and monitoring of a new vertically moving biofilm system (VMBS) for treating municipal wastewater. The system operated on site for 11 months. The biofilm module in this system, consisting of high surface area plastic media, was vertically and repeatedly moved in cycles up into the air and down into the wastewater. The vertical movement of the biofilm module supplied sufficient oxygen for the removal of the organic carbon in the wastewater. The overall physical oxygen transfer coefficient (Kla) measured at the cycle speed of six cycles per minute was 2.53 per hour. During the pilot study, dissolved oxygen (DO) concentrations in the bulk fluid were in the range of 1.5-5 mg/l. It was found that the areal removal rate of filtered chemical oxygen demand (COD) was up to 35 g COD/(m(2)day) and the bulk fluid volumetric filtered COD removal rate was 2.62 kg COD/(m(3)day). The field experiment showed that clogging commonly found in other biofilm systems did not occur in this system. The power consumption was in the range of 0.09-0.25 k Wh/m(3) wastewater flow, 0.40-2.19 k Wh/kg COD removal and 1.24-1.74 k Wh/kg BOD removal. The new biofilm system offers potential for reduced reactor volumes, energy saving, simple construction and easy operation.

Biofilms↗
PubMed2000

Experimental investigation into the incineration of wool scouring sludges in a novel rotating fluidised bed.

The main purpose of this research was to investigate the possibility of incineration of wool scouring sludges in a novel vertical axis rotating fluidized bed (RFB). A small-scale RFB was designed and constructed with an internal diameter (ID) of 200 mm and height of 50 mm to carry out the experiments. In phase one of the experiments, a cold test was conducted to investigate the fluidization performance of the RFB, which eventually led to the optimisation of the operating parameters, i.e., sand particle size, rotation speed and bed loading (bed thickness) which ensures complete fluidization and minimum particle elutriation. Sand particle size of 0.5 to 0.6 mm, rotation speed of 200 to 400 rpm and bed loading of 1 kg (equivalent to bed thickness of 27 mm) were found optimal. These information generated were useful for the second phase of the experiments, which was the hot test, in investigating the possibility of incinerating wool scouring sludges in the RFB. Nine wool sludges from different process routes generated from the wool scouring industries were analysed for their compositions. Most of these sludges were highly moist, had high volatile matter and high ash content with low level of fixed carbon. These characteristics made incineration difficult. Hence, the effect of varying the moisture content, rotation speed and sludge feed rate on the incineration of the three selected sludges were studied in the hot test. With 5% support methane, all sludges with a maximum moisture up to 70% as-received could be successfully burned in the RFB at rotating speeds of 200 and 300 rpm. The combustion was found to be intense with a high efficiency due to the good turbulence and mixing in the RFB. The combustion gases produced, i.e., CO, CO(2) and NO(x) were reasonably low due to the high combustion intensity and efficiency. To study the dynamics of the bed and freeboard region in the RFB, the velocity flow field was simulated using a computational fluid dynamics (CFD) model to generate information of the flow pattern. The special advantages of swirling flow would benefit the gas combustion in the RFB. The experimental results obtained have suggested that the incineration was successful and the ash particles elutriated were fine due to the good mixing and turbulence in the RFB. This also reflects the RFB as an effective incinerator.

Animals↗
PubMed2002

Early warning of disturbances in a laboratory-scale MSW biogas process.

The use of near-infrared spectroscopy (NIR) to monitorthe dynamics of a biogas process was evaluated using multivariate data analysis. The digester was a completely stirred 8 I tank reactor fed with the organic fraction of source-sorted MSW. Intermittently the digester was overloaded with feed. Before and after overload on-line monitoring of NIR spectra and off-line analysis in the liquid and the gas phase of traditional chemical variables and microbial biomass, determined as total concentration of phospholipid fatty acids (PLFA and PLEL), were done. The dynamics that occurred due to overloading could be followed using principal component analysis of the obtained NIR-spectra. In addition, the response to changes in the digester fluid was reproducible and could be detected within five minutes, which can be considered as real-time monitoring. Selected wavelengths in the region 800-2,000 nm were used to make a PLS1 -regression with propionate. The regression resulted in a good correlation for propionate (R= 0.94 and RMSEP of 0.21 g/l in the range of 0.3-3 g/l). The results indicate the possibility to develop an early warning biogas control system based on near-infrared spectroscopy monitoring of propionate.

Automation↗
PubMed2001

Modeling of organic pollutant destruction in a stirred-tank reactor by ozonation.

Destruction of organic contaminants in water by ozonation is a gas-liquid process which involves ozone mass transfer and fast irreversible chemical reactions. Ozonation reactor design and process optimizing require the modeling of the gas-liquid interactions within the reactor. In this paper a theoretical model combining the fluid dynamic and reaction kinetic parameters is proposed for predicting the destruction rates of organic pollutants in a semi-batch stirred-tank reactor by ozonation. A simple expression for the enhancement factor as our previous work has been applied to evaluate the chemical mass transfer coefficient in ozone absorption, 2,4-dichlorophenol (2,4-DCP) and 2,6-DCP or their mixture are chosen as the model compounds for simulating, and the predicted DCP concentrations are compared with some measured data.

Absorption↗
PubMed2002

Methanobrevibacter acididurans sp. nov., a novel methanogen from a sour anaerobic digester.

A novel acid-tolerant, hydrogenotrophic methanogen, isolate ATMT, was obtained from an enrichment performed at pH 5.0 using slurry from an acidogenic digester running on alcohol distillery waste. The original pH of the slurry was 5.7 and the volatile fatty acid concentration was 9000 p.p.m. Cells of isolate ATMT were Gram-positive, non-motile and 0.3-0.5 microm in size. They did not form spores. The isolate could grow in the pH range 5.0-7.5, with maximum growth at pH 6.0. The optimum temperature for growth was 35 degrees C. Formate, acetate, methanol, trimethylamine, 2-propanol and 2-butanol were not utilized as growth substrates. Rumen fluid and acetate were required for growth on H2/CO2. Coenzyme M and 2-methylbutyric acid were not required in the presence of rumen fluid. 16S rDNA sequence analysis confirmed the signature sequence of the genus Methanobrevibacter. Morphological and biochemical characteristics of the isolate, together with the 16S rDNA sequence analysis, clearly revealed that the isolate could not be accommodated within any of the existing species of the genus Methanobrevibacter. Therefore, it is proposed that a novel species of the genus Methanobrevibacter should be created for this isolate, Methanobrevibacter acididurans sp. nov., and the type strain is

Anaerobiosis↗
PubMed2003

The utilisation of engineered invert traps in the management of near bed solids in sewer networks.

Large existing sewers are considerable assets which wastewater utilities will require to operate for the foreseeable future to maintain health and the quality of life in cities. Despite their existence for more than a century there is surprisingly little guidance available to manage these systems to minimise problems associated with in-sewer solids. A joint study has been undertaken in the UK, to refine and utilise new knowledge gained from field data, laboratory results and Computational Fluid Dynamics (CFD) simulations to devise cost beneficial engineering tools for the application of small invert traps to localise the deposition of sediments in sewers at accessible points for collection. New guidance has been produced for trap siting and this has been linked to a risk-cost-effectiveness assessment procedure to enable system operators to approach in-sewer sediment management pro-actively rather than reactively as currently happens.

Cities↗
PubMedDate not supplied

Identifying the determinants of viable microorganisms in the air and bulk metalworking fluids.

Exposure assessment was conducted for an epidemiologic study of the respiratory effects of exposure to metalworking fluids (MWF). As part of the study, airborne microorganisms were collected with a two-stage microbial impactor, and a sample of the bulk soluble MWF was collected from each machine sump, as well as information about the work environment. These data were then used to develop multivariate statistical models of the determinants bulk MWF and airborne microbial levels. Microbial concentrations in the bulk MWF ranged from 5 x 10(4) to 5 x 10(10) colony-forming units (CFU)/mL, with a geometric mean of 3.4 x 10(7) CFU/mL. The geometric mean airborne microbial level was 182 CFU/m3 (for particles size <8 microm) with a range of 1 to 8,308 CFU/m3. In modeling the determinants of bulk microorganisms, fluid-related factors were the most important characteristics associated with microbial levels, followed by process-related and environmental factors. The final full multivariate model predicted a significant reduction in bulk microbial levels by increasing pH of the fluid and reducing the amount of tramp oil leaking into the fluid. For the airborne microbial models, process-related factors were the major characteristics associated with microbial levels, followed by factors related to worker activities and environmental factors. The final full multivariate model predicted a significant control of airborne microorganisms by increasing worker distance from the machine, reducing the number of machines within 10 feet of the worker, decreasing the bulk microbial levels, and adding machine enclosures. These models can be used to prioritize nonbiocidal interventions to control microbial contamination of the bulk MWF and the air.

Air Microbiology↗
PubMedDate not supplied

Modeling the development of biofilm density including active bacteria, inert biomass, and extracellular polymeric substances.

We present the unified multi-component cellular automaton (UMCCA) model, which predicts quantitatively the development of the biofilm's composite density for three biofilm components: active bacteria, inert or dead biomass, and extracellular polymeric substances. The model also describes the concentrations of three soluble organic components (soluble substrate and two types of soluble microbial products) and oxygen. The UMCCA model is a hybrid discrete-differential mathematical model and introduces the novel feature of biofilm consolidation. Our hypothesis is that the fluid over the biofilm creates pressures and vibrations that cause the biofilm to consolidate, or pack itself to a higher density over time. Each biofilm compartment in the model output consolidates to a different degree that depends on the age of its biomass. The UMCCA model also adds a cellular automaton algorithm that identifies the path of least resistance and directly moves excess biomass along that path, thereby ensuring that the excess biomass is distributed efficiently. A companion paper illustrates the trends that the UMCCA model is able to represent and shows a comparison with experimental results.

Algorithms↗
PubMed2002

Pilot-scale study of an anaerobic baffled reactor for the treatment of domestic wastewater.

Large proportions of South Africans live in areas with inadequate sanitation and a poor infrastructure for waterborne sanitation. Service providers are looking for alternative wastewater treatment options. The anaerobic baffled reactor is being considered as a decentralised sanitation option in these areas. A 3,200 L reactor was built and is currently being evaluated at a wastewater treatment works. The reactor was built based on experiences gained from working with a laboratory reactor (10 L) and predicted flow patterns observed on a computational fluid dynamics model. The design and construction of the reactor will be discussed in this paper. The feed to the reactor consists of screen degritted sewage and the flow to the reactor is maintained by means of a programmable logic controller. The pilot-plant layout is discussed in this paper. Samples are analysed for chemical oxygen demand, pH, alkalinity, ammonia, phosphorus, solids and ash content. Reductions of between 70 and 80% are obtained for COD and the pH values for the effluent samples are within the discharge limits.

Bioreactors↗
PubMedDate not supplied

Legal aspects and technical alternatives for the treatment of reservoir brines at the Activo Luna oilfield, Mexico.

Deep formation water, extracted as an undesired byproduct from on-shore production wells at the Activo Luna oilfield and processed in adjacent oil fields, are highly enriched in salt minerals, especially in sodium chloride (NaCl) (262 000 mg/L), but also in metals and nonmetals, such as strontium (Sr) (2068 mg/L), bromine (Br) (2034 mg/L), boron (B) (396 mg/ L), iodine (I) (43.4 mg/L), selenium (Se) (3.74 mg/L), and arsenic (As) (0.55 mg/L). Direct reinjection of the brine underground is not possible because of elevated pressure conditions within the petroleum reservoir. The disposal into near shore areas of the Gulf of Mexico without treatment must be rejected because of a) elevated concentrations of some toxic elements, such as B, silver (Ag), thallium (Tl), Se and cadmium (Cd), which exceed permissible limits of environmental legislation for surface discharge (Official Mexican norms NOM-001-ECOL-1998 and CE-CCA-001/89), and b) differences in density that could cause the descent of hypersaline fluid to the ocean floor, potentially affecting the diversity and survival of the benthic ecosystem. Conventional treatment techniques, such as microfiltration or reverse osmosis, are not suitable for the Activo Luna brines because of their extreme mineralization, which will cause pressure conditions exceeding 200 bars across the membrane. As an alternative process, the evaporation of the entire brine volume of approximately 200 m3/day by solar ponds or industrial crystallization plants is suggested. The residual precipitated residuals are composed mainly of chlorine (Cl) (9460 tons/year), sodium (Na) (4230 tons/ year), calcium (Ca) (1028 tons/year), potassium (K) (207 tons/year), and magnesium (Mg) (65.8 tons/year). As an alternative to its disposal on a dumpsite, some special minerals (especially NaCl, Mg, Sr, and Br) could be recovered for its economic value.

Animals↗
PubMed2001

Numerical and experimental hydrodynamic studies of a lagoon pilot.

The determination of residence time is of major interest in terms of the characterisation, design and modelling of most environmental engineering processes, where a proper and homogeneous fluid distribution is often essential, and especially in the domain of wastewater or waste material treatment. In this paper, two different numerical methods for obtaining theoretical predictions of residence time distributions using the finite volume method are used. The first one consists of solving a transport equation of the local mean age of the fluid, which is the average time that a fluid particle takes to reach any point of the domain from a supply inlet. The result obtained is a spatial distribution of the local mean age of the fluid, which may be displayed as isocontours in the space domain considered. The second one consists of injecting a virtual particle stream (i.e. a fluid particle having the same density as the surrounding fluid, and treated numerically as a tracer) and measuring the time elapsed between the injection and the termination of the trajectory using a Lagrangian reference frame. The result obtained is expressed as an exit time distribution and may be displayed as a histogram. Finally, a comparison with measurements of mean residence times of tracers in a lagoon is made in order to establish the relevance of this method in concrete form. The prediction enables the instantaneous determination of the geometrical characteristics of the flow that contribute actually to the residence time dispersion. Its appropriate use prior to the design of water treatment and waste material treatment installations should contribute to prevent undesirable flow patterns such as short-circuiting and dead spaces.

Models, Theoretical↗
PubMed2003

Nitrogen removal using a vertically moving biofilm system.

The aim of this laboratory study was to establish the efficacy of a new experimental biofilm system for the removal of nitrogen from synthetic wastewater. The system consisted of six reactors in series: one anaerobic, one anoxic and four aerobic reactors. In both the anaerobic and anoxic reactors, a plastic cuboid module was repeatedly moved up and down in the wastewater, while being totally submerged at all times. In each of the aerobic reactors, an identical module to that used in the anaerobic and anoxic reactors was intermittently and repeatedly immersed in and lifted out of the wastewater. All the individual reactors had a bulk fluid volume of 28.2 litres and the average temperature of the wastewater was about 10 degrees C. Each module consisted of crossflow corrugated plastic sheets with a surface area of 1.824 m2. The nitrate recycle flow from the fourth aerobic tank to the anoxic tank was twice the inflow to that tank. In the anoxic reactor, filtered COD was removed at an average rate of 2.22 kg COD/m3 x d and nitrate-nitrogen was denitrified at a rate of 0.42 kg NO3-N/m3 x d. The average nitrification rate in the second aerobic reactor was 0.12 kg NH4-N/m3 x d. The new biofilm system was simple to construct and operate.

Bacteria, Aerobic↗
PubMed1978

Cholera: possible infection from aircraft effluent.

This paper presents the hypothesis that some cases of cholera might be due to effluent discharge from aircraft. The theoretical case is borne out by inspection of data on the physical conditions pertaining between high altitudes and ground level. A study of the distribution of isolated outbreaks and single cases of disease and their relation to major airline routes showed a reasonable correspondence. Sporadic outbreaks of cholera in Europe between 1970 and 1975 were found to lie within the flight paths of regular airline services from Calcutta, where cholera is endemic, to the Northern Hemisphere. Laboratory studies on the stability of Vibrio cholerae to conditions likely to be encountered in droplets falling from high altitude to the ground suggested that significant numbers of organisms might survive. It should be noted that in this study no account was taken of the effect of ultra-violet light on viability and it is known that at high altitides the ultraviolet light component of solar radiation is much higher than at ground level. Results of experiments where small numbers of organisms were inoculated into relatively poor media showed that rapid growth ensued and that sufficient organisms were produced to give an infective dose of Vibrio cholerae in 1-10 ml/fluid. It could be concluded that human infection could easily occur by ingestion of fluids such as milk or soup which had some time earlier received a fortuitous but slight contamination from the air. Investigation of one disinfectant (chloramine T) showed that it reacted rapidly and in a complex manner with peptone. One effect of this reaction was the elimination of bactericidal activity and it seems likely that, as at present employed, chloramine T is of doubtful value in aeroplane hygiene. One important conclusion that arises from this work is that if cholera can be spread, even only occasionally, by effluent from aircraft then close investigation should be made of the possibility of other bacteria and viruses being spread in a similar way.

Aircraft↗
PubMed2004

Nutrient removal in a sequencing batch biofilm reactor (SBBR) using a vertically moving biofilm system.

In this paper, the performance of a sequencing batch biofilm reactor (SBBR) using an anoxic/anaerobic phase followed by an aerobic phase for nutrient removal from wastewater was investigated. In the laboratory SBBR unit, biofilm was grown on a plastic biofilm media module, which was vertically moved up into the air and down into the bulk fluid during the aerobic phase. The vertical movement of the biofilm module supplied oxygen to the microorganisms. The module was submerged in the wastewater during the anoxic/anaerobic phase. The percentage removals of total chemical oxygen demand (COD), total nitrogen (TN) and soluble orthophosphate (PO4-P) were 95.4%, 68.3% and 89.5% respectively at influent concentrations of COD 773 mg l(-1), TN 49.9 mg l(-1) and PO4-P 16.5 mg l(-1). The effluent COD was 35 mg l(-1), NH4-N 10.2 mg l(-1), NO3-N 5.5 mg l(-1), soluble PO4-P 1.7 mg l(-1) and suspended solids (SS) 19 mg l(-1).

Biofilms↗