• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 130
  • 51
  • 12
  • 8
  • 6
  • 6
  • 5
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 1
  • Tagged with
  • 241
  • 241
  • 62
  • 51
  • 49
  • 47
  • 42
  • 33
  • 30
  • 25
  • 24
  • 23
  • 22
  • 19
  • 18
  • 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.

Chemical engineering modelling of a vegetated submerged reedbed for winery effluent treatment

Sheridan, Craig Michael 25 February 2014 (has links)
Environmental concerns for wineries in South Africa cover not only the conversion of effluent into more benign forms, but the reclaiming of water, a resource that is scarce and precious in a drought-prone country. However, not all waste treatment options are available to small wineries, because many are too sophisticated and expensive to be commercially viable. Accordingly, this study investigated the use of constructed wetlands in the form of Vegetated Submerged Reedbeds (VSR) as a practicable alternative for small-scale wine producers. Winery effluent is known to have a high chemical oxygen demand (COD) and low pH. In this study, effluent was extensively analysed from two cellars, including the temporal changes over the duration of a harvest and the duration of a year. It was found that for raw winery effluent, ethanol contributes approximately 85% to 90% of the COD, with acetic acid being the next significant contributor. The pH showed some dependence on the concentration of acetic acid. The concentration of sodium in the effluent is strongly dependent on the cleaning regime in place at the cellar, and the concentration of potassium has been shown to be linked to the spillage of juice, wine or lees. It was also found that the hydraulic processes occurring within the VSR display significantly non-ideal behaviour. If the feed to the VSR was located on the surface the dead volume accounted for approximately 25% of the non-ideal behaviour of the system and bypass accounted for a further 6% of non-ideal behaviour. In the system studied, there was a preferential flow pattern within with the greatest flow occurring closest the surface and in the centre, and the least at the sidewalls. It was proposed that the flow profile can be conceptualised as being hull-shaped. We believe this hypothesis is correct and as far as we are aware this flow pattern has not been described previously. It was found that this profile was the same for irregularly shaped gravel and for spherically shaped gelatinous beads and it is therefore believed it is not dependent on the geometry of the VSR or the packing medium. This study also investigated the use of three different methods for determining the rate constants for the degradation of winery effluent within a sub-surface flow constructed wetland (CW). These methods comprised using a dispersed plug flow (the Peclet) equation; a tanks-in-series (TIS) equation; and analysing the residence time distribution (RTD) directly. The last of these was called the Convolution Integral (CI) method. Within the CW studied, the principal constituent of the chemical oxygen demand (COD), ethanol, was always fully degraded by the time the flow reached the outlet. It was therefore possible to calculate the rate constant of degradation from the initial eight metres of the CW. Self similarity of the RTDs was also demonstrated, which meant that in general the system’s hydraulics were similar throughout the CW. This meant we could extrapolate the data so as to develop a more complete understanding of the hydraulic properties of the CW and examine how they affected the kinetics of degradation. It was found that whilst both the Peclet and the TIS equation were able to predict concentration within the CW accurately, this required multivariate optimisation. This rendered a result that was more of a modelling exercise than a useful design tool. The CI method, however, could be applied to predict system parameters effectively. This study used the CI to measure the rate constants of removal for both ethanol and potassium, which were found to be the key species that responded to the degradation/treatment of the effluent. The rate constant found for the biodegradation of COD was found to have significantly more uncertainty associated with it than the measurement of the rate of degradation individual components and it was therefore posited that it is better to describe the processes of degradation by tracking individual components rather than lumped parameters. In each chapter, a short abstract is provided in which results are given.

Selecting plant species to optimize wastewater treatment in constructed wetlands

Taylor, Carrie Renee. January 2009 (has links) (PDF)
Thesis (MS)--Montana State University--Bozeman, 2009. / Typescript. Chairperson, Graduate Committee: Catherine A. Zabinski. Includes bibliographical references (leaves 73-80).

Phosphate and ammonium removal from waste water, using constructed wetland systems

Drizo, Aleksandra January 1998 (has links)
Phosphorus and nitrogen in waste water from sewerage systems contribute to excessive nutrient enrichment of surface waters, presenting a threat to nature conservation, domestic and industrial water supplies, and recreation. The general objective of this research was to investigate phosphate and ammonium removal from waste water by constructed wetland systems (CWS), which are increasingly being used for low-cost water treatment. Phosphate (P) adsorption capacity and other properties of potential CWS substrate materials (bauxite, shale, burnt oil shale, limestone, zeolite, light expanded clay aggregates (LECA) and fly ash) were investigated. Fly ash and shale had the highest P adsorption values, which were significantly correlated with porosity and hydraulic conductivity. Longer - term experiments with shale and bauxite gave maximum P uptake values of 730 and 355 mg P kg- I, respectively. Phragmites australis (common reed) seedlings grew satisfactorily in shale, bauxite, LECA and fly ash. Shale was selected as the most suitable substrate, and used in a pilot-scale CWS in plastic tanks in a greenhouse, with and without P. australis, at two input nutrient concentrations and a loading rate of 0.02 m3 m-2 d-1. Both planted and unplanted systems removed 98 - I 00% of P from a synthetic sewage over ll months. Removal of ammonium N was also complete in the planted tanks, but only 40 - 75% was removed in the unplanted ones. Corresponding nitrate N removal was 85 - 95% and 45 - 75%. The systems performed as well at high as at low concentration for both phosphate and ammonium. The variations in P and N removal could not be attributed to differences in pH, Eh and temperature, which did not differ significantly between planted and unplanted tanks. During the experiment, P and N concentrations were determined at 3 depths and 4 positions along the length of the tanks. H2P04- - P and NH/ - N concentrations were low ( < I. 0 g m-3) at all locations in the planted systems, whereas the P concentrations were sometimes twice as high in the unplanted ones. NH4 + -N in the unplanted systems was relatively high (l 0 - 30 g m"3) throughout the experiment. N03--N concentrations were very low by comparison. P. precipitation on shale and P. australis root and rhizome surfaces was examined by X-ray fluorescence analysis, and by chemical extraction with ammonium acetate, 0.1 M HCI and 2%> citric acid. This showed that P, Fe and Al had precipitated on all these surfaces. However. it was not possible to quantify the surface deposits, and further research is necessary. The hydraulic residence time. flow characteristics and permeability of the shale was investigated by a bromide tracer. The tracer breakthrough curves showed a similar pattern in all tanks, with ca 66% of the flow occurring through the bottom zone. However, the actual hydraulic residence time (6 days) was slightly higher than the theoretical one Although there was a significant difference (p < 0.02) between the distribution of flow in planted and unplanted tanks. there was no reduction in the reactive pore volume observed in any of the tanks. This confirmed that shale has good permeability properties. Monitoring of the full-scale systems was carried out during June - September 1995. Although P removal in a planted bed was between 50-75%, the overall performance of the full-scale systems was disappointing, especially for ammonium removal. This was attributed to high loading rates, visibly non-uniform flow and clogged gabions. A bromide tracer study carried out on these systems confirmed the short hydraulic retention times and heterogeneous flow mechanisms in both the unplanted and planted systems. Results obtained from the pilot scale study do not necessarily provide a quantitative prediction of the performance of larger-scale systems. However, the potential value of a shale-based system has been demonstrated, and this opens a new direction in the design of CWS; most systems built to date in the UK use gravel as a substrate. Shale has proved to have superior properties for P removal and is cheap and readily available in Scotland. Its application as a substrate in a full-scale system remains a subject for further investigation.

Pilot-Scale Constructed Wetlands Combined with Phosphorus Removing Slag Filters for Treating Dairy Wastewater

Lee, Martin 02 October 2009 (has links)
Pilot-scale constructed wetlands (CW), with electric arc furnace steel slag phosphorus removing filters were built and implemented for treating dairy wastewater on the Paul Miller Dairy Farm at the University of Vermont. Two distinct CW types were used in the study, hybrid and integrated. Hybrid CWs consist of more than one CW in-series, and in this research three hybrid CW systems were tested. Two hybrid CWs used a vertical saturated flow (VF) CW followed in-series by a horizontal saturated flow (HF) CW. One hybrid CW used a HF CW followed in series by a second HF CW. In this study, three integrated CW systems were implemented which consisted of a CW followed by a phosphorus removing slag filter. Two integrated CW systems consisted of a VF CW followed in-series by a saturated horizontal flow slag filter. One integrated CW system consisted of a HF CW followed by a horizontal saturated flow slag filter. All individual CWs and slag filters had the same dimensions; a length, width, and height of 1.7m, 1.1 m, and 0.5 m, respectively. CWs were filled with 2 cm diameter gravel, topped with 3 cm of compost, and planted with river bulrush (Schoenoplectus fluviatilis). Slag filters were filled with 2-5 cm diameter slag, having a porosity of 0.42. From August to December of 2007 the six CW systems were fed with a pulse flow of dairy wastewater with a hydraulic loading rate of 1.9 cm/day. This gave a nominal retention time of ~10 days for each CW system. From May to September of 2008 the flow was changed to a continuous inflow, and resulted in a hydraulic loading rate of 3.9 cm/day. A nominal retention time of ~5 days for each CW system was calculated. Weekly monitoring was carried out for five-day biochemical oxygen demand (BOD5), total suspended solids (TSS), ammonium (NH4+), dissolved reactive phosphorus (DRP), and pH. Integrated CWs and hybrid CWs were monitored for their ability to treat dairy wastewater. The analyses focused on determining if there were important differences in pollutant treatment efficiencies between the two distinct systems. Time series temporal semivariogram analysis of the measured water parameters illustrated that different treatment efficiencies existed in the beginning of the 2008 summer (early summer) compared to the end of the 2008 summer (late summer). Furthermore, the CWs were found to have significantly different (p-value < 0.0001) treatment performances, in terms of TSS and BOD5 removal, from early to late summer 2008. Integrated CWs remove significantly more DRP than hybrid CWs (p-value < 0.05). During the late summer of 2008, the integrated CWs removed significantly more ammonium (p-value < 0.05) then all other CW systems. Hybrid and integrated CWs were both efficient in removing organics, but the hybrid systems were significantly (p-value < 0.05) more efficient during the period of highest macrophyte biomass. Mechanisms of pollutant removal in these CW systems were further analyzed. Ultimate BOD laboratory experiments were used to determine the maximum amount of biologically available organic matter and the corresponding rate constants for the removal kinetics of organic matter in the dairy wastewater. Geochemical modeling of the minerals that form on steel slag show that hydroxyapatite controls the activities of phosphate and calcium ions. The geochemical modeling results show a similar finding to field results, because as the wastewater:slag ratio decreases the pH increases (pH > 11) and phosphorus is removed.

The use of impulse response tracer experiments in horizontal subsurface flow constructed wetland development

Pieters, Werner January 2016 (has links)
A research proposal submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfillment of the requirements for the degree of Master of Science in Engineering. Johannesburg, 2016 / In the past three decades there has been an increased interest in constructed wetlands (CW) and their effectiveness in treating water. The hydraulic efficiency of a CW can be determined by using chemical reactor theory to develop residence time distribution (RTD) parameters such as effective volume (Veff), normalized variance (σ2) and mean residence time (τm). Five experiments were conducted to study the effects on these RTD parameters in a CW by using a glass pilot-scale laboratory rig and varying the inlet-outlet positions. The rig made use of a glass tank 250x250x500mm filled with clear superabsorbent polymer balls as a packing. The clear tank and balls made it possible for the flow to be observed when a FWT red impulse tracer dye was inserted into the system. The flow was photographed at specific time intervals for visual analysis and comparison. . The visual results showed the formation of a hull-shaped velocity profile in all the experiments. The RTD was obtained by collecting tracer samples at specific outlet positions during the course of each experiment. The five inlet-outlet configurations RTD parameters results showed; a straight flow path from a single inlet to outlet yielded the lease desirable hydraulic performance with dead volumes contributing to up to 67% of the CW. An increase in the number of outlets and changing the direction of flow diagonally showed up to a 96% improvement to the effective volume of the system could be achieved when compared with single inline inlet-outlet flow. The best result was achieved by combining the visual and RTD data to make changes to the rigs geometry in order to eliminate dead zones and yielded up to a 148% improvement in the effective volume of the system when compared with single inline inlet-outlet flow. A well designed CW with respect to inlet-outlet position can result in reduced land requirements and construction costs by minimizing the dead volume and improving hydraulic efficiency. / MT2016

Treatment of Industrial Wastewater by Gravel-type Constructed Wetlands

Lin, Hsin-Yi 07 September 2000 (has links)
In this study, we discussed the treatment efficiencies of different types of industrial wastewaters by several lab-scale constructed wetlands. The purpose this study is to decrease certain pollutants in the effluents from the industrial wastewaters treatment plants investivate the feasibility of water reuse and recovering. We divided the experiment into two stages, and three types of industry wastewaters ,including paper, steel and refiring, are in this study. In the first stage, the treatment efficiencies of controlling the flow rate at 6 mL/min higher that those controlling at 4 mL/min. However, sinece the amounts of phosphur were smalls in the industrial weatewaters, the removal efficiencies are not high enough. Thus, we added sewage and phousphate into the wastewaters in second stage of experiments with the best ratio of N : P of 4 : 1. The performance work of these two stage experiments did help to clean the nutrient of nitrogenous in the industrial wastewater, especially the refining industry comparing to the other two types of industries.

Impact of Wildlife on Escherichia coli in a Constructed Wetland.

Orosz-Coghlan, Patricia Anne January 2001 (has links) (PDF)
Thesis (M. S. - Soil, Water and Environmental Science)--University of Arizona, 2001. / Includes bibliographical references (leaves 48-50).

Reduction of enteric organisms in small scale, subsurface flow constructed wetlands

Nokes, Rita Lynn. January 1998 (has links) (PDF)
Thesis (M.S. - Soil, Water, and Environmental Science)--University of Arizona. / Includes bibliographical references (leaves 119-122).

Establishment vegetation patterns in an artificial urban wetland as a basis for management /

Conran, Leigh Garde. January 1991 (has links) (PDF)
Thesis (M. Env. St.)--University of Adelaide, Mawson Graduate Centre for Environmental Studies, 1993. / Includes bibliographical references (leaves [34-40]).

Designing a constructed wetland to treat landfill leachage /

Scott, Jennifer E. January 1900 (has links)
Thesis (M. Sc.) (Hons)--University of Western Sydney, Hawkesbury, 1994.

Page generated in 0.0921 seconds