Wetland-based treatment systems are often implemented as a method to remove unwanted substances from contaminated groundwater. Wetlands are effective due to the high biological activity that naturally takes place in the rhizosphere and soil. In support of a demonstration surface wetland system at a site in Columbus, Georgia, laboratory-scale wetland systems were designed to study the effect of different carbon sources and their biodegradability, COD:N ratio and temperature on the rate and extent of nitrate reduction of nitrate-bearing groundwater. Nitrate reducing bacteria are ubiquitous in surface and subsurface wetlands but a major limiting factor for these systems is carbon availability. Two major carbon sources were investigated in both continuous-flow and batch systems: a natural source, hay and a commercial source, MicroC GTM, a concentrated carbohydrate mix. Between these two carbon sources, the nitrate removal rate was not significantly different as long as sufficient biodegradable carbon was provided. The effect of both hydraulic retention time (HRT) and COD:N ratio on nitrate removal were investigated in continuous-flow systems. The specific nitrate removal rate in open to the atmosphere batch reactors was estimated at 0.55 mg N/mg biomass VSS-day. The effluent nitrate concentration in a continuous-flow system maintained with an HRT of 5 days at room temperature (22 to 23°C) was less than 3 mg nitrate-N/L. The COD:N ratio was kept at 6:1 for the majority of the experiments (approximately twice the theoretical requirement) to ensure sufficient carbon loading. Lower COD:N ratios of 5, 4, 3, 2, 1, and 0.5 were also investigated in the continuous-flow system and the minimum required carbon loading to achieve an effluent nitrate concentration below 10 mg N/L for an influent groundwater nitrate concentration between 65 and 70 mg N/L was determined to be 5:1 COD:N. The effect of temperature on the nitrate removal rate was also investigated at 22, 15, 10 and 5°C. As expected, the rate of nitrate reduction decreased with the decrease in temperature, especially below 10°C. Overall, the surface wetland is a feasible solution to treating nitrate-bearing groundwater even at relatively low ambient temperature values, provided that sufficient, biodegradable carbon is present.

Sulphate-reducing bacteria (SRB) mediate the reduction of metals/metalloids directly or indirectly. Bioremediation of arsenic contaminated water could be a cost-effective process provided a cheap carbon source is used. To this end, molasses was tested as a possible source of carbon for the growth of sulphate-reducing bacteria (SRB). Its chemical composition and the tolerance of SRB toward different arsenic species [As (III) and As (V)] were also investigated. Batch culture studies were carried out to assess 1, 2.5 and 5 g l-1 molasses as suitable concentrations for SRB growth. The results indicate that molasses does support SRB growth, the level of response being dependent on the concentration; however, growth on molasses was not as good as that obtained when lactate, the usual carbon source for SRB, was used. The molasses used in this study contained several metals including Al, As, Cu, Fe, Mn and Zn in concentrations ranging from 0.54-19.7 ìg g-1, but these levels were not toxic to the SRB. Arsenic tolerance, growth response and sulphate-reducing activity of the SRB were investigated using arsenite and arsenate solutions at final concentrations of 1, 5 and 20 mg l-1 for each species. The results revealed that very little SRB growth occurred at concentrations of 20 mg l-1 As (III) or As (V). At lower concentrations, the SRB grew better in As (V) than in As (III). Batch cultures of sulphate-reducing bacteria (SRB) in flasks containing pine bark, sand and polystyrene as support matrices and Postgate medium B were used to study formation of biofilms. The effects of the support matrices on the growth of the organisms were evaluated on the basis of pH and redox potential change and the levels of sulphide production and sulphate reduction. Characterisation of the matrix surfaces was done by means of environmental scanning electron microscopy (ESEM). A consortium of SRB growing on polystyrene caused a 49% of original sulphate reduction whereas on sand a 36% reduction occurred. Polystyrene was further examined for its durability as a long-term support material for the growing of SRB in the presence of As(III) and/or As(V) at concentrations of 1, 5 and 20 mg l-1. Both sulphate reduction and sulphide production were greater in this immobilised system than in the matrix-free control cultures. With pine bark as support matrix no significant sulphate reduction was observed. The kinetics of sulphate reduction by the immobilised cells were compared with those of planktonic SRB and found to be superior. The leaching of organic compounds, particularly phenolic substances, from the pine bark had a detrimental effect on the growth of the SRB. Different proportions of pine bark extract were used to prepare media to investigate this problem. Growth of SRB was totally inhibited when 100% pine bark extract was used. Analysis of these extracts showed the concentration of phenolics increased from 0.33 mg l-1 to 7.36 mg l-1 over the extraction interval of 15 min to 5 days. Digested samples of pine bark also showed the presence of heavy metals. The effects of nitrate, iron and sulphate and combinations thereof were investigated on the growth of a mixed culture of sulphate-reducing bacteria (SRB). The addition of 30 mg l-1 nitrate does not inhibit the production of sulphide by SRB when either 50 or 150 mg l-1 sulphate was present. The redox potential was decreased from 204 to -239 mV at the end of the 14 day batch experiment in the presence of 150 mg l-1 sulphate and 30 mg l-1 nitrate. The sulphate reduction activity of the SRB in the presence of 30 mg l-1 nitrate and 100 mg l-1 iron was about 42% of original sulphate, while if no iron was added, the reduction was only 34%. In the presence of 20 mg l-1 either As(III) or As(V), but particularly the former, growth of the SRB was inhibited when the cells were cultured in modified Postgate medium in the presence of 30 mg l-1 nitrate. The bioremoval of arsenic species [As(III) or As(V)] in the presence of mixed cultures of sulphate-reducing bacteria was investigated. During growth of a mixed SRB culture adapted to 0.1 mg l-1 arsenic species through repeated sub-culturing, 1 mg l-1 of either As(III) or As(V) was reduced to 0.3 and 0.13 mg l-1, respectively. Sorption experiments on the precipitate produced by batch cultured sulphate-reducing bacteria (SRB-PP) indicated a removal of about 77% and 55% of As(V) and As(III) respectively under the following conditions: pH 6.9; biomass (2 g l-1); 24 h contact time; initial arsenic concentration,1 mg l-1 of either species. These results were compared with synthetic iron sulphide as adsorbent. The adsorption data were fitted to Langmuir and Freundlich isotherms. Energy dispersive x-ray (EDX) analysis showed the SRB-PP contained elements such as sulphur, iron, calcium and phosphorus. Biosorption studies indicated that SRB cell pellets removed about 6.6% of the As(III) and 10.5% of the As(V) from water containing an initial concentration of 1 mg l-1 of either arsenic species after 24 h contact. Arsenic species were precipitated out of synthetic arsenic-contaminated groundwater by reacting it with the gaseous biogenic hydrogen sulphide generated during the growth of SRB. The percentage removal of arsenic species was dependent on the initial arsenic concentration present. Lastly, laboratory scale bioreactors were used to investigate the treatment of arsenic species contaminated synthetic groundwater. A mixed culture of SRB with molasses as a carbon source was immobilised on a polystyrene support matrix. The synthetic groundwater contained either As(III) or As(V) at concentrations of 20, 10, 5, 1 or 0.1 mg l-1 as well as 0.1 mg l-1 of a mixture with As(III) accounting for 20, 30, 40, 60 and 80% of the total. More that 90% and 60% of the As(V) and As(III) respectively were removed by the end of the 14-day experiment. At an initial concentration of 0.1 mg l-1 total arsenic had been reduced to below the WHO acceptable level of 10 ìg l-1 when the proportion of As(III) was 20 and 30%, while at 40% As(III) this level was reached only when the treatment time was increased to 21 days. The efficiency of As(III) removal was increased by first oxidising it to As(V) using MnO2. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

[Truncated abstract] An ethanol delivery system, consisting of silicone (poly(dimethylsiloxane)) tubing coiled and shaped as mats, was characterised and evaluated for its potential to act as a permeable reactive barrier (PRB), to promote reducing conditions and enable the enhanced bioremediation of a variety of groundwater contaminants in situ. Aqueous ethanol solutions were recirculated through the inner volume of the silicone polymer tubing in the mat, to allow permeation and delivery of ethanol by diffusion through the tubing walls to a target contamination zone. The aim of the system was to provide control over subsurface geochemistry by overcoming carbon source limitations, and as a result stimulate indigenous bacteria to remove contaminants. The physical properties of the silicone tubing were initially characterised, which included the determination of the ethanol sorption and diffusion properties of the tubing. A model for the mass of ethanol transferred via diffusion from an aqueous solution on the inner volume of a length of polymer tubing was developed to enable prediction of the ethanol delivery capacity of the silicone polymer mats. A number of large-scale laboratory column studies were then conducted to validate this ethanol mass delivery model, and to evaluate the use of silicone polymer mats to deliver ethanol and promote the biodegradation of a range of different contaminated groundwaters. The laboratory column experiments were observed to produce ethanol mass flux delivery statistically similar to that predicted by the model; however this was only with the application of an effective diffusion coefficient within the model, which was determined from the model under subsurface-simulated conditions. Ethanol delivery using the silicone tubing polymer mat system was also quantified in a pilot field-scale demonstration. The mass of ethanol delivery in the field was shown to be within the range of model-predicted ethanol delivery; however delivery was not as consistent and predictable as that observed in the column studies. Successful ethanol enhanced nitrate contamination removal (via denitrification) was observed at a field scale. For field applications, this innovative polymer mat amendment delivery system may provide targeted, predictable and cost-effective amendment delivery compared to aqueous injection methods for groundwater bioremediation, however, knowledge and quantification of the hydrogeology of the particular field site is required. Two other ethanol-driven biologically-mediated contaminant removal processes were also investigated in the laboratory-scale soil column studies, and included the assessment of the removal of dissolved metals/sulfate via sulfate reduction and metalsulfide precipitation, and the removal of trichloroethene via reductive dechlorination.

The objective of this research was to demonstrate the application of ultrasound to field sites having problems with precipitation build up and corrosion. PTW s are passive reactive walls containing zero-valent iron metal for in-situ remediation of contaminated groundwater. However, loss of reactivity over time due to build up of corrosion and other precipitates on the iron surface is a major concern. Ultrasound energy has been established as an effective tool for revitalizing iron surface. This research applied ultrasound energy to a zero-valent iron wall constructed below the ground surface to remove precipitates and iron corrosion, increasing iron reactivity. Two field sites were selected for the ultrasound application research project. These sites have PTWs installed for the remediation of chlorinated compounds such as TCE and its daughter products. The first site is located at Launch Complex 34 (LC 34), Cape Canaveral Air Station, Florida. The second site is located at Denver Federal Center, Lakewood, Colorado. The ultrasound was applied to these sites by introducing an ultrasonic transducer in wells installed within the wall or just upstream of the wall and then applying ultrasonic energy to the entire depth of the wall. The apparatus used for ultrasound application was an omni-directional tubular resonator. Two such ultrasound units with frequencies of 25 kHz and 40 kHz were used for ultrasound treatment. Kinetic batch studies were performed on iron samples taken before and after ultrasound treatment. The degradation rate constants and half-life values for TCE were then calculated and con1pared for pre-ultrasound and post-ultrasound iron san1p les. Sin1ultaneously grounchvater \vas analyzed for di ffercnt VOCs. Soni cation period as brief as 30 n1inutes sho\vcd signi fie ant in1pact on the firstorder rate constants for TCE degradation. An increase in sonication period proved to be even n1ore effective. A sonication period of 90 n1inutes decreased TCE half-life by 30-40% for the 40-kHz resonator and 60-75~o for the 25-kHz resonator, for both the field sites. The 25-kHz resonator proved to be more effective than the 40-kHz resonator. For both field sites, ultrasound treatn1ent significantly increased TCE degradation rates, indicating a ren1oval of corrosion products and precipitates from the iron surface due to ultrasound. This technology has shown a great potential in revitalizing iron reactivity, effectively increasing the PTW life expectancy.

No description available.

No description available.

This research identifies the well components, operation factors, and the soil and hydrogeological parameters that influence the recovery of Light-Non-Aqueous-Phase-Liquids (LNAPL) in an heterogeneous environment using pumping wells. The purpose of this research is to improve the analysis of sites contaminated by LNAPLs to efficiently recover the feasible amounts of LNAPL in the sites. The focus is on heterogeneous soil environments. The model adapted to analyze the recovery of LNAPL from the contaminated sites was improved to account for a high degree of vertical heterogeneity, including the vertical variation of one or several of the soil properties within the same layer. This research also studies the optimization of the recovery of LNAPL for the system of wells both at the level of one well and a system of wells. The developed model and method are applied to a real site. Thus, the model’s ability to estimate the performance of a system of recovery wells is evaluated using real soil data and performance measurements. This research constitutes a robust background regarding the design, operation, analysis, and optimization of a system of recovery wells in a heterogeneous soil environment. / text

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Batch microcosm studies were carried out to screen for microorganisms from the subsurface of Hanford DOE site that could cometabolically transform chloroform (CF) under aerobic conditions. The potential need for CF bioremediation at the Hanford site has resulted from the large release of carbon tetrachloride (CT) to the subsurface, of which a fraction anaerobically transformed to CF. Potential cometabolic substrates were screened for their ability to promote aerobic cometabolism of CF. The potential cometabolic substrates tested were isoprene, propene, octane, ammonia, methane, propane, and butane. Microcosms were constructed with 125 ml batch serum bottles filled with 25 g of aquifer solids, 50 ml of synthetic groundwater, and 60 ml of headspace air. Consumption of methane, butane, propane, and propene was slow, while the consumption of ammonia was very slow. Microorganisms stimulated on propene and octane showed no ability to transform CF. Limited CF was transformed in microcosms stimulated on ammonia and methane. Over 90% transformation of CF was observed in microcosms stimulated on either butane or propane during the initial incubation. Successive addition studies with methane, propane, and butane microcosms were conducted, because these substrates showed the most potential for driving CF cometabolism. The studies indicated that the most effective CF transformation was achieved by butane-utilizers. CF transformation was correlated with the consumption of the primary substrate. Propane- and butane-utilizers grown in the absence of CF showed transformation yields 3 times greater than those grown in the presence of CF. In butane fed microcosms, CF transformation was linked with butane and oxygen consumption, indicating that an oxygenase enzyme of the butane-utilizers was likely responsible for CF transformation. The butane-utilizers showed no ability to transform CT, which also suggests the possibility of CF transformation by an oxygenase enzyme. In butane microcosms, complete transformation of 55 pg of CF (1200 ��g/L of CF in aqueous solution) was observed. The maximum transformation yield of 0.03 g CF transformed/g substrates consumed was achieved by the butane-utilizers. A stoichiometric amount of chloride was released to solution from CF during CF transformation, indicating that complete dehalogenation of CF was achieved by butane-utilizers. In our knowledge, these were the first observations, demonstrating butane as a cometabolic substrate for CF transformation. / Graduation date: 1997

D. Tech. Water care. / Groundwater is the main source of drinking in most rural areas of South Africa and is supplied to the communities without prior treatment. However, the contamination of groundwater sources by pathogenic bacteria poses a public health concern to these communities. This study was aimed at developing and evaluating the effectiveness of filter materials coated with silver nanoparticles for the removal of pathogenic microorganisms from groundwater as well as the inhibition of biofilm formation in drinking water systems.