published_or_final_version / Civil and Structural Engineering / Master / Master of Philosophy

The biological treatment of wastewater has evolved significantly from simple single sludge systems practicing organic carbon removal to ones which now include either nitrification/denitrification (N/DN) and / or phosphorus (P) removal. The inclusion of more biological processes have increased the complexity of current wastewater systems which has subsequently led to the development of more complex mathematical models. The operation of plants can be assessed and improved by the use of mathematical modelling tools which require accurate input data. Thus, knowledge of the wastewater characteristics is an important step towards the optimum modelling, design and operation of present and future plants. However, for these tools to be effective, the input data needs to be accurate which is dependent on the current methods used to determine them. Wastewater is a complex substrate consisting of compounds of differing biodegradability. Biokinetically, these compounds have been divided into readily biodegradable (RBCOD), slowly biodegradable (SBCOD) and unbiodegradable substrate groups. Compounds with intermediate biodegradability i.e. compounds which fall between the RBCOD and SBCOD groups, have been termed readily hydrolyzable organic substrates (RHCOD). The organic matter is discussed in terms of chemical oxygen demand (COD). The readily biodegradable and readily hydrolyzable COD fractions of wastewater can be determined by respirometric tests such as the oxygen utilization rate (OUR) and nitrate-N utilization rate (NUR) tests. The principal aim of this project was to investigate the NUR test as a tool for wastewater characterization and to study denitrification kinetics in batch reactors. In addition, an experimental readily biodegradable substrate, acetate, was used to determine the reliability of the NUR tests. Acetate was also used to ascertain utilization profiles and rates of a typical readily biodegradable substrate during denitrification. Biodegradable COD characterizations with enhanced biological phosphorus removal (EBPR) sludges were also investigated to determine the impact of anoxic phosphorus removal on NUR tests. The results obtained from the numerous NUR tests added to the undestanding of the NUR test. Samples from 22 wastewater treatment plants were tested, most of which were located in France. Four South African plants were also tested. Data obtained from the NUR tests were used to calculate the RBCOD and RHCOD fractions. The SBCOD, however, could not be determined directly from the 6 h NUR batch tests. The readily biodegradable COD (RBCOD) fractions ranged between 7 and 25 % of the total COD concentration of raw wastewater, with majority of those results falling within the 10-20 % (of the total COD) range. The results also showed that the initial rapid rate associated with readily biodegradable COD utilization was sometimes followed by a short intermediate phase (i.e. short duration, 2 to 3 h). The intermediate fraction was found to range between 5 and 29 % of the total COD concentration and was classed as a readily hydrolyzable COD component of raw wastewater since the magnitude of the RHCOD fraction was too small to be classed as slowly biodegradable COD which comprises approximately 30 to 60 % of the total COD found in raw wastewaters. The variability of the RHCOD fractions suggests that this fraction is either very variable or that the NUR test does adequately or accurately characterize it. Another possibility is that the RHCOD (or second biodegradable fraction) calculated from the NUR test is a component of the RBCOD of the influent wastewater. In this case, the bacteria may have used some of the RBCOD directly for energy and accumulated or stored the rest as part of a survival mechanism which allows them to be more competitive under dynamic operating conditions. Once the readily biodegradable COD becomes limiting, the bacteria will use the accumulated or stored compounds. This hypothesis is substantiated by tests done with acetate as substrate. An intermediate phase was also observed when acetate was the sole substrate. Thus, it was possible with the 3-phase profiles to calculate a second biodegradable fraction. Results suggest that a significant part of the added acetate (as COD) was stored and the second phase is in fact an 'apparent or residual' phase brought about by the consumption of the stored or accumulated acetate products. This is suggested in two ways: (1) the calculation of the yield coefficient is lower and closer to the 0.5 mg/l values, cited in the literature, when the COD calculated from phases 1 and 2 are considered, and (2) the acetate mass balances were found to be approximately 100 % when phases 1 and 2 were used to calculate the amount of acetate utilized under anoxic conditions. The results obtained with sodium acetate as a readily biodegradable substrate were used to formulate several conclusions on acetate utilization during denitrification. Firstly, from acetate mass balances it was found that acetate may be used exclusively for denitrification (100 % acetate was accounted for). In this case, the sludge contains a significant proportion of denitrifiers and little or no polyphosphate accumulating organisms. This observation was made only when non-EBPR (enhanced biological phosphorus removal) sludges were used. Secondly, acetate mass balances which were found to be < 100 % suggest that acetate could be used for denitrification and the production of storage products like polyhydroxyalkanoates (PHA's). These sludges probably contained a higher proportion of polyphosphate accumulating organisms which competed for the available acetate in the bulk liquid. This observation was made for both EBPR and non-EBPR sludges. Thirdly, acetate could be used for denitrification by denitrifiers and for polyhydroxyalkanoate synthesis by denitrifying polyphosphate accumulating organisms. The stored PHA's in the denitrifying polyphosphate accumulating organisms are subsequently utilized during denitrification. This secondary utilization is manifested in the second denitrification phase and is supported by the observation of phosphorus uptake. These results showed that wastewaters high in volatile fatty acids (VFA's) were also subject to denitrifying polyphosphate accumulating organism activity even though the sludge was sampled from non enhanced biological phosphorus removal systems (non EBPR). Several of the NOx profiles revealed either 2 or 3 rates due to the control of the substrate to biomass ratio (S/X: :<_0.1 mgO2 / mgO2). Majority of the samples (i.e. 85%) tested produced initial maximum specific denitrification rates (k1) between 3 and 6 mgN/gVSS.h. The intermediate denitrification rate (k2) was found to vary between 2 and 3 mgN/gVSS.h. Denitrification rates (k3) obtained from utilization of influent and. endogenous slowly biodegradable COD (SBCOD) varied between 1.0 and 1.5 mgN/gVSS.h. This latter rate is significantly higher than the endogenous denitrification rates cited in the literature. One of the reasons for these higher rates could be be linked to the the reuse of stored or accumulated products by the microorganisms. In addition, a comparative study on RBCOD determination of wastewaters with enhanced biological phosphorus removal and non-EBPR sludges. It was found that the RBCOD values derived by NUR tests with EBPR sludge were consistently lower (4 to 5 %) than those with non-EBPR sludge. Thus, the NUR tests with EBPR sludge resulted in a 4 to 5 % underestimation of the RBCOD fraction of raw wastewaters. This loss in RBCOD to polyphosphate accumulating organisms appears to be linked to the influent raw wastewater acetate concentration. These tests showed that the RBCOD fraction could be adequately characterized using the NUR method. The accuracy of the tests appears to be compromised when enhanced biological phosphorus removal sludges are used in the NUR tests. Moreover, it was found that non-EBPR sludges can also consume some of the acetate that is present in the system for the production and replenishment of storage compounds. Fortunately, for the wastewaters tested, the acetate component of the RBCOD fraction was small and therefore, did not significantly affect the results. Mechanisms such as substrate accumulation and storage may also impact on substrate removal and hence, the determination of the readily biodegradable COD concentration of municipal wastewaters. Thus, while the results showed that the NUR is a useful characterization tool for wastewaters, it will continue to be a more tedious characterization tool than the oxygen utilization rate test, until a suitable nitrate/nitrite electrode is developed to automate the test. / Thesis (Ph.D.)-University of Natal, Durban, 1999.

The aim of process industries is to produce products and intermediates from raw materials and other intermediates. Inevitably, there are waste products to be disposed of and if these are of no use, they must be returned to the air, water or land environments. Such returns should be carried out in such a way as to minimise any adverse effects on the environment, otherwise the waste is bound to cause pollution to the environIDent. Wastewater is one such product that has to be returned to the environment. A weakness in the current practice of wastewater treatment is that the potential toxicity of the effluent is only addressed through the prevention of specific types of waste being discharged to the sewer. The discharge of effluents containing toxic or inhibitory substances is currently not directly addressed or controlled by many industries and local authorities. While cost recovery is important, due consideration must be given to the possible effect on the receiving environment. The magnitude of the problem of toxic components in the inflow to wastewater treatment plants in South Africa is largely unknown. However, it is thought by some treatment authorities to be relatively serious. In addition, there has been no attempt to quantify the effect of individual toxicants on the performance of the treatment processes and thus put a monetary value to individual discharges. Nitrification is one of the important biological processes that takes place in wastewater treatment plants, which may be affected by toxicants from wastewater. The toxicants may inhibit the nitrification process and create problems in the treatment plant. The aim of this study was to determine if the Amanzimtoti Wastewater Treatment Plant is experiencing inhibition of nitrification, and if so, determine whether large industries discharging into the plant contribute to this problem. The study site used in this research was the Amanzimtoti Wastewater Treatment Plant, located at Isipingo, in Durban, together with some selected industries that discharge their effluents into this treatment plant. In this study, the Amanzimtoti Wastewater Treatment Plant together with lO industries that discharge effluent into it, were surveyed for inhibition of nitrification. A screening method for estimation of inhibition of nitrification at municipal wastewater treatment plants described by Jonsson (2001) was used in the investigations. This involved testing inhibition of nitrification at various dilutions of wastewater effluent from 20% to 80% dilution. An investigation was conducted of inhibitory substances within influent wastewaters to the Amanzimtoti Wastewater Treatment Plant, and inhibitory substances were detected in all four sampling weeks. The level of inhibition was in general up to 29%, with the greatest inhibition being observed at 20% and the least at 80% dilution. In order to investigate the source of inhibition, inhibition of nitrification was measured in the sewage influent during times when industries are open and when they are closed. Inhibition was significantly lower during December when industries close, supporting the hypothesis that industrial effluent contributes to inhibition of nitrification. Comparison of wastewater from different industries showed that of 10 surveyed industries, 9 generated wastewaters that were found to be inhibitory, with Industry D showing the highest inhibition of approximately 30% over the 4 dilutions. The least inhibitory effluent was from Industry C with an average of 10%. Industry A was found to stimulate nitrification. There was no correlation found between the daily volume contribution of the industries to the treatment plant, and the inhibition of nitrification. There was also no correlation found between the inhibition of nitrification and the chemical oxygen demand and settleable solids concentration of wastewater from each of the industries.. At 80% dilution, the nitrification inhibition results obtained for all nine industries were similar and it was difficult to distinguish between them, whereas at 20% dilution, the differences among the industrial effluents on nitrification could be clearly evaluated. Industries B, D, E, G and J were found to have higher inhibition than the other four surveyed industries. Results obtained at the 20% dilution could therefore be used as a decision making tool by wastewater pollution officers to identify industries requiring close monitoring. From the study, it was clear that the inhibition of nitrification that resulted from mixtures of industrial wastewaters cannot be readily predicted from nitrification inhibition by the individual wastewaters. New compounds may be formed during mixing in the sewer network that are more or less inhibitory than if the wastewaters are not mixed. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2005.

The purpose of this research is to hydraulically characterize an engineered wetland in Albany, Oregon. The wetland receives treated wastewater from both Albany Millersburg Water Reclamation Facility (AMWRF) and ATI Wah Chang. AMWRF's water is municipal waste water. ATI Wah Chang's water comes from its nearby metal processing plant. The wetland is designed to remove thermal input as well as nitrogen species from both sources. ATI Wah Chang effluent has significant nitrate concentrations. A reliable model is needed to estimate the denitrification potential of the wetland. In order to construct a model, accurate hydraulic parameters such as residence time and flow rate are needed. In the first few days after ATI started flow, the aquatic conductivity level of the wetland increased significantly. Conductivity was used as a tracer to estimate residence times in the wetland as well as to measure the split ratios from different water sources in the wetland (ATI Wah Chang and AMWRF). A pilot test on conductivity and flow rate was carried out on a single pond. The pilot test was designed to accurately measure the influent and effluent from a single pond. Using this information, rates of infiltration as well as unintended flow paths could be identified. A third tracer test was performed using Rhodamine W.T. This test allowed for the determination of the residence time of each pond, the wetland as a whole, and identified stagnant zones within the ponds. To simulate the nitrogen transportation and transformation process, a numerical model was developed. The model's input parameters include reaction rate constants for nitrification and denitrification, volume of each pond, flow rate, flow path connections, and temperature. The model simulated the tracer test that was performed on the wetland to verify its accuracy. The model is also capable of predicting denitrification potential in both pilot scale and field scale. It is also temperature sensitive because temperatures vary significantly; for instance, in winter when the average temperature in Albany is <5��C, denitrification rates decrease significantly. Through this research, hydraulic characterization as well as current denitrification rates in the wetland were identified. Strategies for increasing the denitrification rate were also identified through this research. / Graduation date: 2012

Orientador: Basilio Ernesto de Almeida Milani / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-04T02:32:56Z (GMT). No. of bitstreams: 1 VargasLara_JoseMaria_D.pdf: 1539805 bytes, checksum: cb3f1db3ea06ddceb5dac7d0f33c587c (MD5) Previous issue date: 2005 / Resumo: Este trabalho trata da síntese de um controlador preditivo adaptativo, baseado em modelos reduzidos obtidos mediante identificação orientada para controle preditivo. A metodologia proposta envolve duas áreas importantes para o sucesso do experimento de identificação. Na primeira, projeto de sinais de excitação, é mostrado como sinais de excitação pseudo-aleatórios multi-níveis podem ser projetados para atender com eficácia requisitos que sinais de excitação relevantes para controle devem satisfazer. Na segunda, modelagem de preditores, é abordada a modelagem por identificação de preditores de horizonte estendido. O objetivo central da metodologia proposta é o controle da remoção de matéria nitrogenada de uma planta de tratamento de esgotos por lodos ativados com pré-desnitrificação. A metodologia é aplicada para controlar a concentração de amônia mediante o controle do set-point de oxigênio dissolvido. A metodologia também é aplicada para o controle da concentração de nitrato no reator desnitrificante. Os controladores são avaliados em um estudo de simulação, mostrando a eficácia da metodologia proposta para o controle das concentrações de amônia e nitrato / Abstract: This work deals with the synthesis of an adaptive predictive controller, based on reduced models obtained via identification oriented to predictive control. The methodology proposed involves two important areas for the success of the identification experiment. In the first one, excitation signal design, it is shown how pseudo-random multilevel signals can be designed to effectively satisfy the requirements that excitation signals relevant for control should satisfy. In the second, predictor modelling, the identification of long-range horizon predictors is approached. The main objective of the proposed methodology is the control of the nitrogen removal in an predenitrifying activated sludge wastewater treatment plant. This methodology is applied to control the ammonium concentration in the denitrifying reactor. The controllers are evaluated in a simulation study, showing the effectiveness of the proposed methodology to control ammonium and nitrate concentrations / Doutorado / Automação / Doutor em Engenharia Elétrica

[Truncated abstract] The use of constructed wetlands for tertiary purification of municipal wastewater has received increasing attention around the world because direct discharge of secondary-treated municipal wastewater to water bodies has caused eutrophication. Plant species selection and vegetation management may enhance nutrient removal efficiency in constructed wetlands. However, there is a lack of knowledge on the relations between plant growth and nutrient removal efficiency in constructed wetlands. The objective of this study is to better understand how plant growth and resource allocation are influenced by nutrients in wastewater and how nutrient removal efficiencies are affected by plant species and vegetation management. The preliminary experiment was conducted to select macrophytes, especially ornamental species, to grow in the wastewater in the wetland microcosms. Ten plant species, comprising six ornamental species: Alocasia macrorrhiza, Canna indica, Iris louisiana, Lythrum sp., Zantedeschia aethiopica, Zantedeschia sp., and four sedge species: Baumea articulate, Baumea juncea, Carex tereticaulis and Schoenoplectus validus, were planted in the wetland microcosms and fed a simulated wastewater solution in the concentrations similar to the secondary-treated municipal wastewater. C. indica has shown vigorous and healthy growth, and a relatively high potential of rooting-zone aeration and nutrient removal efficiency. B. articulata and S. validus also showed relatively high nutrient removal efficiency. ... The high nutrient availability and optimum N/P ratio were required for stimulating plant growth, resulting in allocation of more resources to above-ground tissues compared to below-ground parts, and enhancing nutrient removal efficiency. Nutrient removal efficiencies were significantly influenced by growth of C. indica and S. validus, nutrient loading rates and N/P ratios in the wastewater. The nutrient uptake kinetics of C. indica and S. validus were investigated to elucidate the differences in nutrient uptake between species. Wetland plant species have shown differential nutrient uptake efficiency and different preferences for inorganic N source, with C. indica preferring NO3-N and S. validus preferring NH4-N. C. indica had greater capacity than S. validus to take up PO4-P when the concentration of PO4-P in the solution was relatively low, whereas S. validus was more capable than C. indica to take up NO3-N when the concentration of NO3-N in the solution was relatively low. The PO4-P uptake capacity was higher in younger than older plants. Overall, the study has suggested that different plant species have differential capacity to take up nutrients. In addition to nutrient uptake, plants have significant other roles in terms of nutrient removal from the wastewater (such as leaking oxygen into the rhizosphere in which oxidation of substances like ammonia can occur). The properly high nutrient availability and optimum N/P ratio are required to stimulate the plant growth, resulting in enhancing the treatment performance in the wetlands. These findings have important implications for improving our ability to engineer ecological solutions to the problems associated with nutrient-rich wastewater.

The primary objective of this study was to evaluate the rates of nitrate removal for a nitrate containing, low organic carbon wastewater interacting with four different carbon-containing solid substrates (alder woodchips, corn silage, manure and woodchip biochar). Batch systems were tested for nitrate removal, and systems with a combination of three carbon substrates (75% woodchips, 12.5% silage, and 12.5% manure or woodchip biochar by mass) produced average nitrate removal rates of 571 and 275 mg-N L⁻¹ D⁻¹, and systems containing the carbon substrates individually produced rates between 11.4 - 3.3 mg-N L⁻¹ D⁻¹. Silage proved to be the dominant carbon substrate providing high quantities of organic carbon to fuel denitrification. With the introduction of semi-continuous flow, all systems had nitrate removal rates that converged to 13.3 – 6.4 mg-N L⁻¹ D⁻¹, which is approximately two orders of magnitude smaller than the rates of the mixture systems in the batch experiment. Silage appeared to be removed from of the systems with liquid exchange potentially causing the rate decreases. Columns filled with various volume fractions of woodchips (100%, 25%, 12.5%, and 0%) produced nitrate removal rates between 30.8 – 2.4 mg-N L⁻¹ D⁻¹ at a 24 hour and 12 hour hydraulic residence time (HRT). Greater nitrate removal was achieved with higher HRTs and larger fractions of woodchips (the 100% woodchip system at a 24 hour HRT produced the fastest nitrate removal rate of 30.8 mg-N L⁻¹ D⁻¹). When rates were normalized to the amount of woodchips in each column, higher efficiency was found in lower woodchip fraction systems (the 12.5% woodchip column produced the highest normalized nitrate removal rate of 56 mg-N L⁻¹ D⁻¹ L[subscript woodchips]⁻¹). Woodchips proved to be best suited as a long term carbon substrate for nitrate removal in a system containing a nitrate concentrated, low organic carbon wastewater. However, large amounts of woodchips were necessary to achieve nitrate removal greater than 50%. A 41 acre hypothetical wetland with a 3.3 day HRT and a nitrate influent concentration of 45 mg-N L⁻¹ would require 30,000 yd³ of woodchips to achieve 68% nitrate removal based on the values obtained in the bench scale column experiment. / Graduation date: 2012