• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 63
  • 23
  • 15
  • 14
  • 12
  • 11
  • 3
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 151
  • 151
  • 43
  • 41
  • 34
  • 27
  • 26
  • 26
  • 24
  • 20
  • 19
  • 17
  • 13
  • 13
  • 13
  • 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.

Reingsresultat, drifterfarenheter och kostnadseffektivitet i svenska våtmarker för spillvattenrening / Treatment results, operational experiences and cost efficiency in constructed wetlands for wastewater treatment in Sweden

Flyckt, Linda January 1984 (has links)
I denna studie har funktionen hos sju anlagda våtmarker för behandling av avloppsvatten i Sverige jämförts över tid med avseende på avskiljning av kväve, fosfor och BOD. Syftet var att undersöka våtmarkernas långsiktiga funktion, skötselåtgärder och relaterade kostnader. Våtmarkerna (1,6 - 28 ha stora) har varit i drift olika länge, mellan 7 och 17 år, och befintliga övervakningsdata samt intervjuer med ansvariga för respektive våtmark användes som grund för studien. Resultaten visade att våtmarkernas reningsfunktion generellt sett varit god utan någon tendens till en försämrad funktion över tid. Våtmarkerna belastades med 1100 - 9900 kg N/ (ha·år) och avskiljde mellan 420 och 2400 kg N/ (ha·år), beräknat som ett medelvärde per anläggning. Belastningen av fosfor var 17 - 145 kg P/ (ha·år) med en avskiljning på 10 - 110 kg P/ (ha·år). En linjär regressionsanalys visade att en högre fosforbelastning också gav en högre avskiljning. Sambandet var svagare för kväve, vilket indikerar att andra faktorer också var viktiga för kväveavskiljningen. Problem med fosforsläpp i våtmarkerna observerades bara där fosforfällning i reningsverken skett med järnbaserad kemikalie, och verkade vara förknippade med tidvisa anaeroba förhållanden i sedimenten. Utgående halter av BOD7 låg på < 5,0 mg/l för alla våtmarker trots stora skillnader i inkommande halt. Kostnaderna för avskiljningen i våtmarkerna var 30 - 190 kr per kg avskilt kväve och 0 - 4700 kr per kg avskilt fosfor. Storleken på kostnaderna var beroende av investeringskostnaden och den årliga driftkostnaden samt hur kostnaden fördelades mellan kväve och fosfor. / In this study, seven constructed free water surface wetlands for wastewater treatment in Sweden were compared, regarding the removal of nitrogen, phosphorous and BOD. The aim was to investigate the long term function, management needs, related costs and look into uncertainties regarding the risk for phosphorous release. The seven wetlands (1.6 - 28 ha) have been in operation for 7-17 years and existing monitoring data were used along with interviews with the staff responsible for the operation. All wetlands performed satisfactorily and there were no indications of a reduced treatment capacity over time. On average, the wetlands received 1100 to 9900 kg N / (ha·yr) and removed 420 to 2400 kg N / (ha·yr). The phosphorous loads varied between 17 and 145 kg P / (ha·yr) and the removal between 10 and 110 kg P / (ha·yr). A linear regression showed that a higher phosphorous load resulted in a higher removal rate. For the removal of nitrogen the linear relationship was weaker, indicating that other factors also were important. Release of bound phosphorous occurred occasionally in wetlands after WWTP using iron based phosphorous precipitation chemicals, and seemed associated with periods when sediments became anaerobic. Effluent concentrations of BOD were < 5.0 mg/l despite varying inflow concentration, and seemed to reflect a background concentration. The costs for the wetland treatment varied between 30 and 190 SEK per kg N removed and between 0 and 4700 SEK per kg P removed. The size of the costs was dependent on investment and management costs as well as how the cost was distributed between nitrogen and phosphorous.

Dynamics of phosphorus transport and retention in a wetland receiving drainage water from agricultural clay soils

Anderson, Malin January 2011 (has links)
A constructed wetland (0.08 ha) receiving drainage water from a small agricultural catchment (22 ha) with clay soil, was investigated with respect to phosphorus dynamics and retention. The aim was to evaluate the function of the wetland with respect to phosphorus retention, and relate that to gross sedimentation as measured with sediment traps. Hydraulic load and phosphorus retention were estimated for 2003-2010 based on monitoring data. Furthermore, water quality dynamics was studied during three intensive sampling periods of 3-5 days during 2010. For each period, phosphorus retention was calculated and the relationship between flow and phosphorus concentrations analysed. Additionally, the gross sedimentation rate was estimated using sediment traps, and the phosphorus, carbon and nitrogen content analysed. The results suggested that there was no net retention of phosphorus during 2003-2010, except for 04/05. During the intensive sampling periods, release of phosphorus from the wetland mainly occurred during high flow. Sediment analyses showed that settling of inflow particles mostly occurred in the inlet pond, while the sediment found in a shallow vegetated area and outlet pond likely originated from internal processes rather than from the catchment. In fact, the gross sedimentation of phosphorus during April-July and July-August, respectively, exceeded the measured phosphorus inflow. The results showed that short periods with rapid flow increases were crucial for the wetlands function and thus high frequency sampling must be done during these periods. Furthermore, it seems that the particles lost from the catchment during high flows are too small to settle in the wetland.

Phosphorus retention in a constructed wetland - the role of sediment accretion

Johannesson, Karin January 2008 (has links)
A low-loaded constructed wetland was investigated with respect to phosphorus retention. Since the main long-term phosphorus retention mechanism is sedimentation and sediment accretion, the study focused on these processes. The purpose of the study was 1) to investigate how the calculated value of phosphorus retention (Pin – Pout), corresponded with the measured amount of phosphorus in the sediment, 2) to find out where in the wetland the phosphorus had accumulated, and in what form it was retained, and 3) to investigate the role of vegetation. The calculated value was 12 kg ha-1 and the measured value was 104 kg ha-1, which indicated the importance of internal phosphorus circulation, where plants probably take phosphorus from the underlying clay. Hence, vegetation could possibly increase the total phosphorus content in the wetland. The composition of phosphorus in the sediment was analysed using sequential fractionation. The dominating form of phosphorus in the sediment was iron-bound phosphorus (29 %). In total, 48 % of the phosphorus was stable, i.e. tightly bound in the sediment, and 35 % was relatively stable. The bioavailable fraction, which could cause eutrophication in downstream waters, was 17 % of the total phosphorus content, or 41 kg ha-1. The amount of total phosphorus was significantly higher near the inlet, compared to the outlet, which is explained by rapid sedimentation of particulate phosphorus entering the wetland. The phosphorus amount near the inlet represented 80 % of the total phosphorus load – which indicates the importance of internal circulation of phosphorus, both biological and geochemical.

Treatment of Endocrine Disrupting Chemicals (EDCs) by Constructed Wetlands

Zen, Yi-peng 15 July 2010 (has links)
Alkylphenol polyethoxylates (APEOs), a class of nonionic surfactants, have been widely used for industrial, agricultural and household applications. The biodegradation metabolites of APEOs, such as nonylphenol and octylphenol, are more persistent and known to disrupt endocrine function in wildlife and human. These compounds are also recognized as endocrine disrupting chemicals (EDCs). The objectives of this study were to investigate the distribution and removal efficiencies of EDCs, including nonylphenol diethoxylates (NP2EO), nonylphenol monoethoxylates (NP1EO), nonylphenol (NP) and octylphenol (OP), of wastewater treated by the constructed wetland systems along the Dahan River and around the Dapeng Bay, respectively. In addition, the method of risk quotient was used to evaluate the potential ecological risk of APEOs to aquatic organisms in current study. The water samples collected from 32 sampling sites in the Dapeng Bay National Scenic Area including Datan, Pengcun and Linbain right bank constructed wetlands. The samples were then concentrated by solid phase extraction, and analyzed for target compounds by HPLC/fluorescence. According to the results, nonylphenol diethoxylates, nonylphenol monoethoxylates, nonylphenol and octylphenol were found approximately equal to 29.9, 47.3, 20.5 and 57.7 %, respectively of the samples from three constructed wetlands with concentrations ranged from <3.3 to 968.7, <3.3 to 226.5, <1.3 to 238.4 and <1.0 to 1458.7 ng/L, respectively. Temporal variation of APEOs showed a decreasing in the order of summer¡Öspring¡Öwinter¡Öautumn. The removal efficiencies of APEOs in these constructed wetlands showed a decreasing order of Datan wetland¡ÖPengcun wetland¡ÖLinbain right bank wetland. In addition, the samples collected from 18 sampling sites from the constructed wetlands along the riparian of Dahan River including Daniaopi, Hsin-Hai Bridge Phases I and II constructed wetlands. According to the results, nonylphenol diethoxylates, nonylphenol monoethoxylates, nonylphenol and octylphenol were found approximately equal to 91.9¡B84.8¡B17.1 and 73.7 %, respectively of samples collected from three constructed wetlands with concentrations ranged from <3.3 to 11191.5, <3.3 to 6069.0, <1.3 to 671.0 and <1.0 to 5581.9 ng/L, respectively. The removal potential of APEOs in these constructed wetlands showed a decreasing order of Hsin-Hai Bridge Phases II¡ÖDaniaopi¡ÖHsin-Hai Bridge Phases I constructed wetland. Regarding the ecological assessment in this research, the calculated risk quotients were up to 30 times higher in the constructed wetland systems of Dahan River than those in the Dapeng Bay National Scenic Area, indicating that the existing concentrations of these EDCs in wetland systems might cause potential ecological risks to aquatic organisms. Furthermore, the decreasing risk quotient from influent to effluent indicating the capabilities of treating alkylphenolic compounds in these constructed wetlands.

The Treatment of Swine Wastewater by Horizontal Biofilter and Subsurface Constructed Wetland

Hsieh, Hsiao-Yu 09 August 2011 (has links)
Swine wastewater is one of the major pollutions in Taiwan. The abundant nutrition and organic matters in it may lead eutrophication of water body. Meanwhile, the low dissolved oxygen level and high suspended solids concentration may also make it more difficult to handle the wastewater treatment. At present facility of swine wastewater in Taiwan is the three-process treatment which includes the solid-liquid separation, anaerobic digestion, and activated sludge system. Even though the three-process treatment is widely used, the efficiency of sediment and filter effectively to remove the nutrition, e.g., ammonia and phosphate is still in question. On the other hand, the activated sludge system is a difficult technique that the swine farmers can¡¦t easily to operate. Based on these reasons, an efficient swine wastewater treatment process should be established. In this study, we replace the activated sludge system in three-process treatment with the horizontal biofilter (HBF) and subsurface system constructed wetland (SFSCW) to assess the practicability of improving the traditional process. HBF is a fix-biofilm system which is superior to the suspended growth of activated sludge system by its simple operation and no need to return the sludge from the final clarifier. Porosity in the gravel of SFSCW and the root zone of Canna indica can also help to remove the nutrients from the outflow of HBF. The tested HRT (hydraulic retention time) has been controlled at about 30 hours and results show that SS, BOD and COD removal efficiencies as 84.07%, 86.48%, and 68.45%, respectively. HBF and SFSCW provided approximate 70~80% and 10~20% removal efficiencies, respectively. This design of combining HBF and SFSCW system has high potential to treat the swine wastewater, and adding the backwash unit may further facilitate the operation in the future.

A study of benthic invertebrate community and environmental factors of salty artifical wetlands

Dai, Li 07 September 2011 (has links)
The objectives of this study are to investigate the biodiversity in different unit of treatment systems, and to detect the function in a salt water type of constructed wetland. We investigated the benthic invertebrate community in different stage from 2010 July to 2011 May, while the parameters of TKN, NH3-N, organic nitrogen, TP, TOC and particle size were measured in the sediments of each sampling site at the same time in the wetland system. The results show that concentrations of organic matter and nutrients in the sediments were increased with time monthly. In May of 2010, the concentration of NH3-N were found the highest one(ANOVA, p<0.05). The particle size in sampling site 1 were the highest (ANOVA, p<0.05), while in November of 2010 all sampling sites were found exhibiting significantly different with other months (ANOVA, p<0.05). Further more, for the diversity of benthic invertebrate, we found that the parameter of the temperature was strongly negatively related to the species diversity, species abundance and species evenness, respectively (r=-387[H¡¦]¡F-533[d]¡F-438[J¡¦] ). The species diversity was increased with organic nitrogen concentrations in the sediments (r=0.492[TKN]¡F0.408[NH3-N]¡F0.493[org-N]), and were negatively related to the parameters of DO and particle size(r=-0.402[Particle size]¡F-0.287[DO] ). In addition, PCA shows that the parameters of particle size¡Borg-N¡BNH3-N¡BTKN and TOC were all important factors. Generally, it was concluded that the constructed systems, which is functioned of wetland was wastewater treatment mainly, exhibit no significant function in biodiversity.

A study of the Nitrogen Cycling Processes and the Operational Mechanisms in Vertical flow Constructed Wetlands

Tasi, Hao-cheng 30 May 2007 (has links)
The main contents of campus sewage are BOD and inorganic nutrients. Conventional secondary treatment processes can remove BOD efficiently, whereas the inorganic nutrients remain mostly left. Therefore, the effluents may cause eutrophication to the receiving water bodies. Using constructed wetland treatment system to reduce nutrients become more and more popular recently. Vertical flow type subsurface process is particularly efficient in nitrogen transformations. In this research we studied the nitrogen transformation dynamics by using different types vertical flow constructed wetland system with various natural materials as the media to treat the secondary effluents from a campus sewage treatment plant. Six self designed experiment columns with broken concrete blocks, oyster shells, different sizes of marble granules, and river sands were used for this study as vertical flow constructed wetland systems. The methods of operation included batch type, continuous flow with filled water and trickling filter type, which were tested by controlling the influent flows into those six test columns. The efficiencies of various combinations in treatments and their mechanisms were discussed in the study. The experimental results showed that the best ammonium nitrogen removal efficiency was measured equal to 46.6% in batch type operations, while the continuous flow with filled water type operation showed the best performance by using concrete blocks as the media (42.8%). However, the best ammonium nitrogen removal rate in the trickling operation was found in the column with media of 3 mm marble granules (91.1%). The medium of river sand obtained the best phosphorous removal rate by using a batch flow operation. Vegetating presented only minor contributions in the column with medium of smaller grain size materials. The optimum C/N ratios for denitification tests are 3.5 and 3 by using the media of concrete and oyster, respectively.

Treatment of oil refining and steel-milling wastewater by constructed wetland

Lo, Wei-Chi 23 July 2002 (has links)
Constructd wetland system is one of the ecological engineering technologies used on wastewater treatments. In this study, we discussed the treatment efficiencies of oil refining and steel-milling wastewater by four lab-scale constructed wetland systems (0.8-m long by 0.4-m wide by 0.7-m deep), which were all filled with gravel media, and planted with Phragmites communis. The constructed wetland systems were designed into two types: free water surface (FWS) and subsurface flow (SSF) wetland systems, which were discharged with two different types of wastewater (oil refining and steel-milling). The experiments of this study were run by five stages. The experimental results showed that almost all of the contaminants could be reliably removed from wastewater by the constructed wetland systems, especially in the SSF systems. During the experiments, the second stage of the experiments had the best treatment efficiencies, in which the flowrate was controlled at 5mL/min. The hydraulic retention time (HRT) in FWS and in SSF werecalculated equal to 7.5days, and 5.36days, respectively.

Treatment of oil-refining and steel-milling wastewater by pilot-scale constructed wetland

Hu, Chih-Ching 04 July 2003 (has links)
In recent years, interest in wastewater treatment through constructed wetlands has been significantly increased because of their low cost and energy requirement. In this study, pilot-scale constructed wetland systems were developed to evaluate the efficacy and effectiveness on the treatment of oil-refining and steel-milling wastewater. The constructed wetland used to treat the oil-refining wastewater included one free water surface system (FWS) filled with sandy media and one subsurface flow system filled with gravel media. The plants grown on the wetland were Phragmites communis. The hydraulic retention time for the two systems was approximately 7 and 5 days, respectively. A two-stage subsurface flow constructed wetland system was used to treat steel-milling wastewater. This system, which filled with gravel media were planted with Phragmites communis (the first stage) and Typha orientalis (the second stage). The hydraulic retention time for this system was approximately 7 days. Experimental results showed that the two constructed wetland systems for the oil-refining wastewater treatment could remove most of the wastewater pollutants. Moreover, the first system (FWS) played a more important role on the wastewater treatment. The efficiency of the first stage of the wetland system, which was used for steel-milling wastewater treatment was not significant due to the inhibition of the plant growth by the wastewater. However, the treatment efficiency was increased at the second stage after planting new plants. Results from the two-stage treatment system indicate that higher treatment efficiencies were observed except for ammonium. Results from this study would be very useful in the design of constructed wetlands for practical application to treat oil-refining and steel-milling wastewaters.

Batch Operation of Pilot-Scale Salty Water Constructed Wetlands in Dapeng Bay

Chen, Hsiao-Hua 11 June 2008 (has links)
Recently, the use of constructed wetlands to treat nutritions and containing wastewater, has quite been in vogue. However, since salts aquacultural wastewater contains massive nutrients and salts, the common aquatic plant species are not suitable to treat it. Therefore the purpose of this research is mainly to use pilot-scale salty water constructed wetland systems operated under batch conditions to removal efficiency of nutrients. The pilot-scale have nine pools, the influent was from discharge channels containing aquacultural wastewater and community sewage near by Dapeng Bay. The experiment designs altogether has four stages.In the first stage to the third stage, the HRT was continued at 7 days. Last stage, the HRT was continued at one month. Experimental period has used waste brick bat, oyster shell, 9mm stone and mix stone (9mm stone and 3mm stone mix) as filter medium. The 9mm stone pool and mix stone pool coordinates differently to test the stage planter differently to plant the species. The plant aspect has Avicennia marina(L2¡BL3 pool ), Lumnitzera racemosa and Phragmites australis. (First, the second stage plants the Phragmites australis , the third stage starts to plant Lumnitzera racemosa). The experimental results showed that the filter media used with the mix stone presented the highest removal efficiency for the nutrients,whice the oyster shell exhibited the lowest removal efficiency for the nutrients. The oyster shell system was also found nutrients releaseal to the system. For using plants to remove the nutrients, we found that plants, did not show better performace than the systems without plants(p¡Ö0.05). However, for the condition of vegetation, the plant species of Avicennia marina exhibited the best performace.

Page generated in 0.0828 seconds