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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Investigation of the Effects of Biofouling on the Hydraulic Properties of Wells in Fractured Bedrock Aquifers

Cooke, Brenda Elizabeth 18 December 2007 (has links)
The objective of this study is to improve the understanding of the effect of biofilm growth and biofouling on well performance in a fractured rock aquifer. The study was conducted by investigating biofouling in several recently drilled and much older wells. The study was conducted at three field sites using six groundwater wells in Perth, Portland and Cambridge Ontario. The well located in Perth was drilled in the spring of 2006 and after preliminary hydraulic testing; biofilm was grown in the well by the addition of nutrients (steel wool, Difco beef peptone and gelatin). The wells located in Portland and Cambridge are more than 10 years old and were already biofouled. In each case, the well was hydraulically tested using open- well pumping methods and via slug testing using a straddle packer system (1.7m spacing) in which measurements were obtained contiguously from the bottom to the top of the well. This provided distinct measurements of the hydraulic properties of the individual fracture zones along the length of each hole. The five older wells in Portland and Cambridge were cleaned following the initial testing using recirculation of hydrochloric acid followed by recirculation of 35% hydrogen peroxide. Once the cleaning was completed, the hydraulic testing was repeated. Each of the wells were videotaped using a downhole camera at various stages during the study. Samples were obtained on three occasions for bacterial typing using the BART™ system. Transmissivity data from the different states of fouling (drilled, fouled or cleaned) were compared and it was determined that fractures with low transmissivity values are more susceptible to the effects of biofouling than those with high transmissivity. The reduction in transmissivity was as much as 50% percent. Fractures with low transmissivity are of small apertures which are easily plugged by biofilm. The cleaning process did not markedly improve total wellbore performance for those wells where a comparison was made following cleaning. The presence of any form of iron, (i.e. steel well casing or steel pump parts) in the well will contribute significantly to the biofouling, based on the results of the laboratory study. / Thesis (Master, Civil Engineering) -- Queen's University, 2007-12-11 11:11:24.327

Marine biofilm development on titanium with particular reference to seawater heat exchange systems

Gunn, N. January 1988 (has links)
No description available.

Optimisation of sodium hypochlorite dosing at Wylfa Power Station : an experimental study with Mytilus edulis

Thompson, Ina Sharon January 1998 (has links)
No description available.

Biofouling in salmon aquaculture: the effectiveness of alternative netting materials and coatings in coastal British Columbia.

Edwards, Courtney D. 28 August 2012 (has links)
Biofouling in salmon aquaculture is an important issue. The use of copper based antifoulants contributes to marine pollution and managing biofouling on untreated nets incurs a heavy cost on the industry. What is needed is an antifoulant coating that balances the needs of the industry with good environmental practices. This study describes the effectiveness of seven alternative netting treatments and two copper based treatments as compared to an untreated nylon net. Effectiveness was measured in terms of percent net occlusion, percent cover of major fouling groups and biomass. Following eight months immersion, results show that the alternative treatments did not out-perform the untreated nylon control, and that the two copper treatments significantly outperformed the control and all of the alternative treatments tested in this study. The results demonstrate that the alternative treatments tested in this study were unable to meet the performance standards set by industry, that more research is needed into alternative antifoulant coatings for aquaculture, and that the effectiveness of copper based treatments will continue to be a barrier to the implementation of alternative antifouling treatments. / Graduate

Monitoring microbial biofilms

Brain, Stephen January 1996 (has links)
No description available.

Selbstreinigungseigenschaften der Haut des Pilotwales, Globicephala melas

Baum, Christof. Unknown Date (has links) (PDF)
Techn. Universiẗat, Diss., 2002--Berlin.

Bacterial Growth Potential of Antiscalants used in Reverse Osmosis Systems using Seawater Autochthonous Microbial Communities

Hasanin, Ghadeer Abdullah 11 1900 (has links)
Antiscalants are chemicals used in membrane-based water desalination processes to prevent the scaling of salts on the membrane. Previous studies suggested that antiscalants could lead or contribute biological fouling by providing growth-promoting factors such as source of biodegradable carbon or phosphorus. However, the test in previous studies were conducted using drinking water and pure cultures of bacteria isolated from freshwater. These conditions do not reflect those of desalination systems. In this study, we determined the microbial growth potential of eight antiscalants under conditions relevant to desalination plants. To this end, autochthonous microbial communities from the Red Sea were used, and we exposed them to chemically diverse antiscalants. The chemical characterization of the antiscalants showed that their carbon content ranged from 0.02 to 0.15 mg C/ mg antiscalant. Fourier transform infrared and nuclear magnetic resonance spectroscopy allowed us to classify the eight tested antiscalants into three types based on their chemical structure. These types were phosphonate-based, natural inulin-based, and polyacrylate-based antiscalants. The growth potential of the antiscalants was determined by incubating seawater with antiscalants (50 mg/L) and an initial bacterial cell content of 20,000 cells/ml at 30$^o$C. A reference without antiscalant addition was used for comparisons. The microbial growth was followed by measuring the cell concentrations over time by flow cytometry. Four phosphonate-based antiscalants promoted microbial growth to different degrees, while distinctively one phosphonate did not increased growth significantly under all tested conditions. At the same time, inulin and polyacrylate-based antiscalants did not increase bacterial growth compared to the reference. The growth potential of 8 antiscalants used presently in practice desalination plants ranges between 1,479,793 and 2,074,106 cells/ml based on the results of the growth potential test, strongly suggesting that antiscalant selection and optimization contributes to biofouling prevention and control.

Micronanobubbles as cleaning strategies for SWRO biofouling

Alvarez Sosa, Damaris 07 1900 (has links)
Water desalination has the potential to alleviate a significant part of the world’s thirst, with a majority of desalinated water capacity coming from seawater reverse osmosis (SWRO). However, SWRO membrane systems suffer from the loss of performance due to biofouling leading to economic costs. There is no control or preventive strategy for SWRO biofouling and current industry practices recommend chemical treatments to restore membrane performance. Chemical cleaning results in high economic costs due to chemical acquisition, storage, transportation, long plant downtimes and ultimately shorter membrane lifetime and early replacement; in addition to the environmental impact associated with disposing of chemicals. Therefore, there is a need for novel effective green cleaning strategies for SWRO to meet the increasing demand for desalinated water while taking care of the environment. Micronanobubbles (MNBs) consist of small gas cavities formed in aqueous solutions. This study evaluates the efficiency of both air-filled micronanobubbles (AMNBs) and CO2 nucleated MNBs as: i) curative cleaning-in-place (CIP) treatments and ii) preventive daily treatments for biofouling over long-term studies. Experiments were performed using the membrane fouling simulator (MFS) under conditions that are representative of SWRO membrane systems. Pressure drop was implemented as the main biofilm growth monitoring parameter as used by standard industry practices. Curative studies showed that both MNBs CIP treatments had high cleaning efficiencies of 49-56% pressure drop recovery. MNBs pressure drop recovery values were close to the conventional chemical cleaning (NaOH/HCl) at 51% and were significantly higher than the hydraulic flush (HF) physical cleaning control at 24%. The pressure drop recovery results were supported by the optical coherence tomography (OCT) images before and after CIP and biomass autopsy results. Similarly, preventive MNBs daily treatments showed a significant delay in the system’s performance decline. This delay was 5.1 days for the CO2 MNBs experiments, 4 days for the AMNBs, and only 0.6 days for the hydraulic flushing treatments compared to the control. Compared to the control the duration of the operation was doubled in time before the cleaning criteria was met. OCT images confirmed biofilm growth delay with lower biomass occurrence.

Tributyltin pollution and the bioindicator Nucella lapillus : population recovery and community level responses

Proud, Sarah Victoria January 1994 (has links)
The detrimental effects of tributyltin (TBT) have been recorded on many marine organisms. As a result the UK Government imposed a partial ban on the use of organotin antifouling paints on boats less than 25 m in length, in 1987. In 1988 the Isle of Man Government followed suit introducing a licensing procedure restricting all uses of organotins. At concentrations less than 0.5 ng Sn/I female Nucella lap/Nus develop imposex - the superimposition of male sexual characteristics. To date there have been few studies measuring the recovery of Nucella populations after the introduction of restrictions. This study produces evidence of the extent of recovery in Nucella populations from sites in the south-west of England and on the Isle of Man. The recovery observed was measured by decreasing values of relative penis size, vas deferens sequence and the percentage of sterile adult females in the population. Following the 1987 ban the recovery of Nucella populations in the south-west has shown a linear response allowing predictions to be made for the time scale of complete recovery. In addition concentrations of TBT in the water and tissues of selected indicator organisms also showed decreases. Around the Isle of Man the illegal use of TBT paints was identified and later discouraged by the Marine Administration which was followed by a reduction in TBT concentrations in the water at sites around the Isle of Man. Levels of imposex in dogwhelk populations around the Isle of Man have decreased. Although effects of TBT on Nuce/la have been well documented at the cellular and individual level, the knock on effects on the community have not been investigated. Manipulative field experiments were used to demonstrate the role of Nucella lapd/us in structuring shore communities to allow predictions of the effect of TBT to be made. Rather than using the traditional approach of fences and cages, dogwhelks were removed by hand on regular visits to experimental sites creating treatments with reduced abundances of dogwhelks akin to shores affected by TBT. The role of Nucel/a was examined at different stages of a cycle existing on moderately exposed Manx shores where Fucus vesiculosus and Semibe/anus balanoides fluctuate in abundance. The removal of dogwhelks increased the abundance of Semibalanus ba/anoides on the shore and as a result likelihood of algal escapes from grazing by Patella vulgate also increased. In addition the removal of Nucela increased the size and longevity of newly established Fucus vesiculosus clumps. In a factorial experiment the role of Patella vulgate and Nucella lapillus were examined simultaneously. Nuce/la was found to have an significant effect but less than that of Patella. The presence of Nucella did, however, mediate the effect of Patella. In addition Nucella was found to have a direct effect on the level of Semibalanus balanoides settlement in the field with the number of barnacles settling in cleared areas being reduced on areas which had been previously occupied by Nucella.

Co-culturing green sea urchins, Strongylocentrotus droebachiensis, with blue mussels, Mytilus edulis, to control biofouling at an integrated multi-trophic aquaculture site

Bartsch, Andrea 02 September 2011 (has links)
Prevention and removal of biofouling from nets and product is a huge expense in the aquaculture industry. Of the many technologies that slow the accumulation of biofouling, copper-based coatings are used most commonly as they are a relatively inexpensive and effective option. However, they can leach into the marine environment and have potentially harmful impacts on marine life. In previous studies, sea urchins have shown potential as a non-toxic alternative to control fouling. In this field study, five different stocking densities (i.e. 0, 30, 60, 90, 120 urchins net-1 or 0, 2.46, 4.91, 7.37, 9.82 urchins m-2) of green sea urchins, Strongylocentrotus droebachiensis, were randomly placed in 30 mussel predator exclusions nets (with six replicates per density treatment) in order to test the effect of urchin density on biofouling intensity and urchin/mussel growth. Mussel predator exclusion nets were chosen to house the urchins since they are necessary to protect mussels from diving ducks and sea otters on the west coast of Vancouver Island, British Columbia, Canada. The urchins provide a means of controlling biofouling as well an additional marketable crop to offset predator net expenses. After 174 days, the percent net occlusion, mussel growth, and urchin growth were quantified. Nets with urchins were significantly less fouled than those without urchins. Fouling on nets with higher stocking densities of urchins (90 and 120 urchins net-1) was significantly less than that on nets with the lowest stocking density (30 urchins net-1). Fouling was no longer significantly reduced at densities >60 urchins net-1 or 4.91 urchins m-2. While fouling was significantly reduced in the presence of urchins, it was not completely eliminated as they were only able to access the inside surface of the nets. There was no significant difference in mussel growth at the different urchin stocking densities, but urchin somatic growth and gonad growth did decline with increasing urchin stocking density. Mussels and sea urchins can be successfully co-cultured with no food inputs, but there is a trade-off between biofouling control and urchin growth. / Graduate

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