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Ce travail a étudié deux approches différentes pour optimiser la réduction biologique des sulfates: la première approche consisté à élaborer une stratégie de contrôle de processus pour optimiser l'ajout d'un donneur d'électrons et la deuxième à vérifier la pertinence de l'utilisation d'une source de carbone bon marché, à savoir, le méthane. Une stratégie de contrôle de l'apport du donneur d'électron en se basant sur le suivi de la charge organique a été mis en place. Des conditions d'abondance et de famine ont été appliquées à un bioréacteur à bactéries sulfato-réductrices (BSR) pour stimuler les dynamiques du processus. Ces conditions d'abondance/famine ont donné lieu à l'accumulation de carbone et également de soufre élémentaire (composants de stockage de biomasse réductrice de sulfate). Cette étude a montré que les retards dans le temps de réponse et un gain de commande élevé peuvent être considérés comme les facteurs les plus critiques affectant l'application d'une stratégie de contrôle de sulfure dans des bioréacteurs à BSR. L'allongement du temps de réponse est expliqué par l'induction de différentes voies métaboliques au sein des communautés microbienne des boues anaérobies, notamment par l'accumulation de sous produits de stockage. Le polyhydroxybutyrate (PHB) et les sulfates ont été retrouvés accumulés par la biomasse présente dans le bioréacteur à lit fluidisé inverse utilisé pour cette étude et donc ils ont été considérés comme les produits majoritaires de stockage par les BSR. Sur cette base, un modèle mathématique a été développé, qui montre un bon compromis entre les données expérimentales et simulées, et confirme donc le rôle clé des processus d'accumulation. Afin de comprendre les voies métaboliques impliquées dans l'oxydation anaérobie du méthane couplé à la réduction des sulfates (AOM-SR), différents donneurs et accepteurs d'électrons ont été ajoutés au cours de test d'incubations in vitro visant à enrichir la communauté microbienne impliqué dans l'AOM-SR à haute pression avec plusieurs co-substrats. L'AOM-SR est stimulée par l'addition de l'acétate ce qui n'a pas été rapporté pour d'autres communautés impliqué dans l'AOM-SR. En outre, l'acétate a été généré dans le test de contrôle résultant probablement de la réduction de CO2. Ces résultats renforcent l'hypothèse que l'acétate peut servir d'intermédiaire dans le processus de l'AOM-SR, au moins pour certains groupes de archées anaérobie méthanotrophe (ANME) et les bactéries sulfato-réductrices / This work investigated two different approaches to optimize biological sulphate reduction: to develop a process control strategy to optimize the input of an electron donor and the applicability of a cheap carbon source, i.e., methane. For the design of a control strategy that uses the organic loading rate (OLR) as control input, feast and famine behaviour conditions were applied to a sulphate reducing bioreactor to excite the dynamics of the process. Such feast/famine regimes were shown to induce the accumulation of carbon, and possibly sulphur, storage compounds in the sulphate reducing biomass. This study showed that delays in the response time and a high control gain can be considered as the most critical factors affecting the application of a sulphide control strategy in bioreactors. The delays are caused by the induction of different metabolic pathways in the anaerobic sludge including the accumulation of storage products. Polyhydroxybutyrate (PHB) and sulphate were found to accumulate in the biomass present in the inversed fluidized bed used in this study, and consequently, they were considered to be the main storage compounds used by SRB. On this basis a mathematical model was developed which showed a good fit between experimental and simulated data giving further support to key role of accumulation processes. In order to understand the microbial pathways in the anaerobic oxidation of methane coupled to sulphate reduction (AOM-SR) diverse potential electron donors and acceptors were added to in vitro incubations of an AOM-SR enrichment at high pressure with several co-substrates. The AOM-SR is stimulated by the addition of acetate which has not been reported for any other AOM-SR performing communities. In addition, acetate was formed in the control group probably resulting from the reduction of CO2. These results support the hypothesis that acetate may serve as an intermediate in the AOM-SR process, at least in some groups of anaerobic methanotrophs (ANME) and sulphate reducing bacteria

2006 - 2007 metais atlikus tyrimus skirtingų sezonų metu buvo nustatyta, kad, antropogenizuotų Sudervės (Salotė, Gilužis, Gineitiškės) ir Riešės (Paežeriai, Raudondvaris, Riešė) upių baseinų ežerų vandenyje ir dugno nuosėdose susiformavo palankios aplinkos sąlygos SRB, heterotrofinių ir E. coli bakterijų augimui ir dauginimuisi. Skirtingais sezonais (pavasarį, vasarą, rudenį), tirtųjų ežerų dugno nuosėdose, SRB kiekis stipriai skirėsi ir svyravo nuo 0 iki 106 KSVS/ml. Sudervės upės baseino ežerų dugno nuosėdose, didžiausias šių bakterijų skaičius buvo nustatytas liepos mėnesį ir siekė 104 KSVS/ml. Tuo tarpu didžiausias SRB skaičius Riešės upės baseino ežerų dugno nuosėdose buvo nustatytas rugsėjo mėnesį ir siekė 106 KSVS/ml. Intensyviausiai heterotrofinės bakterijos tirtuose ežeruose vystėsi dugno nuosėdose, tuo tarpu vandens paviršiuje buvo aptkti vidutiniškai 1000 kartų mažesni šių bakterijų kiekiai. Daugiausiai heterotrofinių bakterijų vandens paviršiuje bei dugno nuosėdose, lyginant su kitais tirtaisiais ežerais, buvo aptikta Riešės ežere. Daugiausiai E. coli bakterijų Sudervės ir Riešės upių baseinų ežeruose buvo aptikta vandens paviršiuje liepos mėnesį, esant aukštai vandens temperatūrai (18,4 - 21,8 °C). Didžiausias šių bakterijų kiekis buvo užfiksuotas Gilužio ežere. Vienas pagrindinių veiksnių, skatinusių sulfatų redukcijos proceso intensyvumą tirtų ežerų dugno nuosėdose, buvo sulfatų kiekis. Daugiausiai šio junginio susikaupė vasarą. Todėl sulfatų redukcijos... [toliau žr. visą tekstą] / Investigations were carried out in water layers and bottom sediments of Suderve (Salote, Giluzis, Gineitiskes) and Riese (Paezeriai, Raudondvaris, Riese) rivers lakes, which undergo anthropogenic impact, in different seasons (spring, summer, autumn) of 2006-2007. It was established that the whole complex of abiotic factors formed favorable conditions for the growth of SRB, heterotrophic and E. coli bacteria. The differences in the abundance of sulphate reducing bacteria in bottom sediments did not reflect the intensity of the process. Generally, their amount varied from 0 to 106 colony forming units (CFU) per ml on media with lactate. The highest abundance of SRB in the lakes of Suderve river basin was recorded in July and reached 104 CFU per ml. Meanwhile, the highest abundance of SRB in the lakes of Riese river basin was recorded in September and reached 106 CFU per ml. The highest amount of heterotrophic bacteria was registered in bottom sediments while in water layer it was estimated 1000 times lower amount. In comparison with other investigated lakes the highest abundance of heterotrophic bacteria in water layer and bottom sediments was determined in Lake Riese. The highest amount of E. coli bacteria was determined in water layer by a high water temperature in July (18, 4 - 21, 8 °C) in basins of Suderve and Riese rivers lakes. The highest abundance of these bacteria was recorded in Giluzis Lake. The intensity of sulphate reducing process mainly depends on sulphate... [to full text]

Municipal wastewater and industrial wastewaters like those effluents from brewery, citric acid production, tannery, pulp and paper industry, and mussel processing contain sulphate ranging from 20 mg.L-1 to 11400 mg.L-1. When these wastewaters are treated in an anaerobic system like prefermentors or anaerobic digesters the sulphate is reduced to sulphide by sulphate reducing bacteria (SRB). The presence of sulphate reduction is not desirable as it may reduce methane yield due to partial substrate utilisation by SRB, causes system toxicity and the production of malodor H2S in the gas phase. In this thesis, the effects of operational conditions on sulphate transformation and assimilation was studied in a laboratory scale anaerobic wastewater treatment system. The laboratory scale system consisted of two reactors the first one a well-mixed fermentor (referred to as an acidogenic reactor) and the second an expanded granular sludge blanket reactor (referred to as a methanogenic reactor) with pH and temperature control. Two sets of studies were performed; in the first set both reactors were connected serially to represent a two-stage high-rate anaerobic treatment system. The system was fed molasses and operated at temperature of 35oC. The acidogenic reactor was controlled at pH of 6 while the methanogenic reactor was controlled at pH of 7.2 by automatic addition of caustic. In the second set of experiments only the first reactor was used to represent a prefermentor and the first stage of the two stage. The reactor was fed with glucose at various concentrations, operated at pH of 6 and temperature of 35oC. Information gained from these studies was encapsulated in a mathematical model to describe sulphate reduction in anaerobic treatment systems. This model was also validated using data generated from the experiments. The experimental study showed that · At low sulphate concentrations of about 250 mg.L-1 and COD concentration of 10,000 mg.L-1 in feed, relatively high percentage (up to 35 %) of produced sulphide was assimilated by biomass, while the rest of the sulphur was distributed as unconverted sulphate, dissolved sulphide, H2S gas and to a lesser extent as metallic sulphide precipitates. · The major electron donor for sulphate reduction in both the acidogenic and the methanogenic reactor was hydrogen gas. Therefore, sulphate reduction not only competed with hydrogen utilising methanogens for the available hydrogen, but also changed the distributions of organic acids, which were directly or indirectly influenced by the H2 partial pressure. · Sulphide concentrations of up to 6.5 mM free hydrogen sulphide) at pH of 7.2 was not inhibitory to methanogens · Sulphate reducing bacteria were able to grow even at a low hydraulic retention time of 1.2 hours in the well-mixed acidogenic reactor. It was estimated that the maximum specific growth rate (m) and half saturation constant (ks) of SRB was 1.31 h-1 and 3.8 mg S.L-1, respectively. These values were higher than those reported in literature. · Sulphate reduction was suppressed at high concentration of carbon in the feed. Accumulation of high concentration of volatile organic acids at high feed-carbon concentrations had little effect on sulphate reduction. However, extent of sulphate reduction had a negative correlation with total concentration of biomass. A non-competitive biomass inhibition function was proposed to model the correlation. From this fit it was estimated that a biomass concentration of about 3300 mg-COD.L-1 will completely inhibit sulphate reduction. · Sulphate reduction was affected by redox potential control and pH in the acidogenic reactor. High pH and low redox potential values were essential for sulphate reduction to proceed. At redox potential control of -300 mV, sulphate reduction was inhibited more at pH of 6 than it was at pH of 7. At redox potential values of -250 mV or higher, about 90 % inhibition of sulphate reduction was observed at both pH of 6 and 7. An existing model describing carbohydrate degradation was extended to include sulphate reduction processes. Despite experimentally observing that sulphate reduction only took place from hydrogen, all possible substrates for sulphate reducion was considered. These included: lactic acid, butyric acid, propionic acid, acetic acid and hydrogen. Kinetic parameters for sulphate reduction processes were obtained from documented literature. Inhibition of sulphate reduction by biomass and sulphur assimilation by biomass were included in the model. A new approach to calculate caustic consumption at given pH values was also included. A modification to hydrogen regulation function was also made to better predict product distributions as a function of gas-phase hydrogen concentration. Model validation was performed using data from dynamic experiments. Comparison to actual data was undertaken on several key variables in the acidogenic and methanogenic reactors such as: organic acid concentrations, gas compositions, gas production rates, sulphate and sulphide concentrations and caustic consumption rates. The model satisfactorily predicted sulphate and sulphide concentrations in both reactors. However, discrepancy between predicted and experimental data on organic carbon concentrations was seen, especially during organic carbon concentration step changes.

Municipal wastewater and industrial wastewaters like those effluents from brewery, citric acid production, tannery, pulp and paper industry, and mussel processing contain sulphate ranging from 20 mg.L-1 to 11400 mg.L-1. When these wastewaters are treated in an anaerobic system like prefermentors or anaerobic digesters the sulphate is reduced to sulphide by sulphate reducing bacteria (SRB). The presence of sulphate reduction is not desirable as it may reduce methane yield due to partial substrate utilisation by SRB, causes system toxicity and the production of malodor H2S in the gas phase. In this thesis, the effects of operational conditions on sulphate transformation and assimilation was studied in a laboratory scale anaerobic wastewater treatment system. The laboratory scale system consisted of two reactors the first one a well-mixed fermentor (referred to as an acidogenic reactor) and the second an expanded granular sludge blanket reactor (referred to as a methanogenic reactor) with pH and temperature control. Two sets of studies were performed; in the first set both reactors were connected serially to represent a two-stage high-rate anaerobic treatment system. The system was fed molasses and operated at temperature of 35oC. The acidogenic reactor was controlled at pH of 6 while the methanogenic reactor was controlled at pH of 7.2 by automatic addition of caustic. In the second set of experiments only the first reactor was used to represent a prefermentor and the first stage of the two stage. The reactor was fed with glucose at various concentrations, operated at pH of 6 and temperature of 35oC. Information gained from these studies was encapsulated in a mathematical model to describe sulphate reduction in anaerobic treatment systems. This model was also validated using data generated from the experiments. The experimental study showed that · At low sulphate concentrations of about 250 mg.L-1 and COD concentration of 10,000 mg.L-1 in feed, relatively high percentage (up to 35 %) of produced sulphide was assimilated by biomass, while the rest of the sulphur was distributed as unconverted sulphate, dissolved sulphide, H2S gas and to a lesser extent as metallic sulphide precipitates. · The major electron donor for sulphate reduction in both the acidogenic and the methanogenic reactor was hydrogen gas. Therefore, sulphate reduction not only competed with hydrogen utilising methanogens for the available hydrogen, but also changed the distributions of organic acids, which were directly or indirectly influenced by the H2 partial pressure. · Sulphide concentrations of up to 6.5 mM free hydrogen sulphide) at pH of 7.2 was not inhibitory to methanogens · Sulphate reducing bacteria were able to grow even at a low hydraulic retention time of 1.2 hours in the well-mixed acidogenic reactor. It was estimated that the maximum specific growth rate (m) and half saturation constant (ks) of SRB was 1.31 h-1 and 3.8 mg S.L-1, respectively. These values were higher than those reported in literature. · Sulphate reduction was suppressed at high concentration of carbon in the feed. Accumulation of high concentration of volatile organic acids at high feed-carbon concentrations had little effect on sulphate reduction. However, extent of sulphate reduction had a negative correlation with total concentration of biomass. A non-competitive biomass inhibition function was proposed to model the correlation. From this fit it was estimated that a biomass concentration of about 3300 mg-COD.L-1 will completely inhibit sulphate reduction. · Sulphate reduction was affected by redox potential control and pH in the acidogenic reactor. High pH and low redox potential values were essential for sulphate reduction to proceed. At redox potential control of -300 mV, sulphate reduction was inhibited more at pH of 6 than it was at pH of 7. At redox potential values of -250 mV or higher, about 90 % inhibition of sulphate reduction was observed at both pH of 6 and 7. An existing model describing carbohydrate degradation was extended to include sulphate reduction processes. Despite experimentally observing that sulphate reduction only took place from hydrogen, all possible substrates for sulphate reducion was considered. These included: lactic acid, butyric acid, propionic acid, acetic acid and hydrogen. Kinetic parameters for sulphate reduction processes were obtained from documented literature. Inhibition of sulphate reduction by biomass and sulphur assimilation by biomass were included in the model. A new approach to calculate caustic consumption at given pH values was also included. A modification to hydrogen regulation function was also made to better predict product distributions as a function of gas-phase hydrogen concentration. Model validation was performed using data from dynamic experiments. Comparison to actual data was undertaken on several key variables in the acidogenic and methanogenic reactors such as: organic acid concentrations, gas compositions, gas production rates, sulphate and sulphide concentrations and caustic consumption rates. The model satisfactorily predicted sulphate and sulphide concentrations in both reactors. However, discrepancy between predicted and experimental data on organic carbon concentrations was seen, especially during organic carbon concentration step changes.

Municipal wastewater and industrial wastewaters like those effluents from brewery, citric acid production, tannery, pulp and paper industry, and mussel processing contain sulphate ranging from 20 mg.L-1 to 11400 mg.L-1. When these wastewaters are treated in an anaerobic system like prefermentors or anaerobic digesters the sulphate is reduced to sulphide by sulphate reducing bacteria (SRB). The presence of sulphate reduction is not desirable as it may reduce methane yield due to partial substrate utilisation by SRB, causes system toxicity and the production of malodor H2S in the gas phase. In this thesis, the effects of operational conditions on sulphate transformation and assimilation was studied in a laboratory scale anaerobic wastewater treatment system. The laboratory scale system consisted of two reactors the first one a well-mixed fermentor (referred to as an acidogenic reactor) and the second an expanded granular sludge blanket reactor (referred to as a methanogenic reactor) with pH and temperature control. Two sets of studies were performed; in the first set both reactors were connected serially to represent a two-stage high-rate anaerobic treatment system. The system was fed molasses and operated at temperature of 35oC. The acidogenic reactor was controlled at pH of 6 while the methanogenic reactor was controlled at pH of 7.2 by automatic addition of caustic. In the second set of experiments only the first reactor was used to represent a prefermentor and the first stage of the two stage. The reactor was fed with glucose at various concentrations, operated at pH of 6 and temperature of 35oC. Information gained from these studies was encapsulated in a mathematical model to describe sulphate reduction in anaerobic treatment systems. This model was also validated using data generated from the experiments. The experimental study showed that · At low sulphate concentrations of about 250 mg.L-1 and COD concentration of 10,000 mg.L-1 in feed, relatively high percentage (up to 35 %) of produced sulphide was assimilated by biomass, while the rest of the sulphur was distributed as unconverted sulphate, dissolved sulphide, H2S gas and to a lesser extent as metallic sulphide precipitates. · The major electron donor for sulphate reduction in both the acidogenic and the methanogenic reactor was hydrogen gas. Therefore, sulphate reduction not only competed with hydrogen utilising methanogens for the available hydrogen, but also changed the distributions of organic acids, which were directly or indirectly influenced by the H2 partial pressure. · Sulphide concentrations of up to 6.5 mM free hydrogen sulphide) at pH of 7.2 was not inhibitory to methanogens · Sulphate reducing bacteria were able to grow even at a low hydraulic retention time of 1.2 hours in the well-mixed acidogenic reactor. It was estimated that the maximum specific growth rate (m) and half saturation constant (ks) of SRB was 1.31 h-1 and 3.8 mg S.L-1, respectively. These values were higher than those reported in literature. · Sulphate reduction was suppressed at high concentration of carbon in the feed. Accumulation of high concentration of volatile organic acids at high feed-carbon concentrations had little effect on sulphate reduction. However, extent of sulphate reduction had a negative correlation with total concentration of biomass. A non-competitive biomass inhibition function was proposed to model the correlation. From this fit it was estimated that a biomass concentration of about 3300 mg-COD.L-1 will completely inhibit sulphate reduction. · Sulphate reduction was affected by redox potential control and pH in the acidogenic reactor. High pH and low redox potential values were essential for sulphate reduction to proceed. At redox potential control of -300 mV, sulphate reduction was inhibited more at pH of 6 than it was at pH of 7. At redox potential values of -250 mV or higher, about 90 % inhibition of sulphate reduction was observed at both pH of 6 and 7. An existing model describing carbohydrate degradation was extended to include sulphate reduction processes. Despite experimentally observing that sulphate reduction only took place from hydrogen, all possible substrates for sulphate reducion was considered. These included: lactic acid, butyric acid, propionic acid, acetic acid and hydrogen. Kinetic parameters for sulphate reduction processes were obtained from documented literature. Inhibition of sulphate reduction by biomass and sulphur assimilation by biomass were included in the model. A new approach to calculate caustic consumption at given pH values was also included. A modification to hydrogen regulation function was also made to better predict product distributions as a function of gas-phase hydrogen concentration. Model validation was performed using data from dynamic experiments. Comparison to actual data was undertaken on several key variables in the acidogenic and methanogenic reactors such as: organic acid concentrations, gas compositions, gas production rates, sulphate and sulphide concentrations and caustic consumption rates. The model satisfactorily predicted sulphate and sulphide concentrations in both reactors. However, discrepancy between predicted and experimental data on organic carbon concentrations was seen, especially during organic carbon concentration step changes.

Municipal wastewater and industrial wastewaters like those effluents from brewery, citric acid production, tannery, pulp and paper industry, and mussel processing contain sulphate ranging from 20 mg.L-1 to 11400 mg.L-1. When these wastewaters are treated in an anaerobic system like prefermentors or anaerobic digesters the sulphate is reduced to sulphide by sulphate reducing bacteria (SRB). The presence of sulphate reduction is not desirable as it may reduce methane yield due to partial substrate utilisation by SRB, causes system toxicity and the production of malodor H2S in the gas phase. In this thesis, the effects of operational conditions on sulphate transformation and assimilation was studied in a laboratory scale anaerobic wastewater treatment system. The laboratory scale system consisted of two reactors the first one a well-mixed fermentor (referred to as an acidogenic reactor) and the second an expanded granular sludge blanket reactor (referred to as a methanogenic reactor) with pH and temperature control. Two sets of studies were performed; in the first set both reactors were connected serially to represent a two-stage high-rate anaerobic treatment system. The system was fed molasses and operated at temperature of 35oC. The acidogenic reactor was controlled at pH of 6 while the methanogenic reactor was controlled at pH of 7.2 by automatic addition of caustic. In the second set of experiments only the first reactor was used to represent a prefermentor and the first stage of the two stage. The reactor was fed with glucose at various concentrations, operated at pH of 6 and temperature of 35oC. Information gained from these studies was encapsulated in a mathematical model to describe sulphate reduction in anaerobic treatment systems. This model was also validated using data generated from the experiments. The experimental study showed that · At low sulphate concentrations of about 250 mg.L-1 and COD concentration of 10,000 mg.L-1 in feed, relatively high percentage (up to 35 %) of produced sulphide was assimilated by biomass, while the rest of the sulphur was distributed as unconverted sulphate, dissolved sulphide, H2S gas and to a lesser extent as metallic sulphide precipitates. · The major electron donor for sulphate reduction in both the acidogenic and the methanogenic reactor was hydrogen gas. Therefore, sulphate reduction not only competed with hydrogen utilising methanogens for the available hydrogen, but also changed the distributions of organic acids, which were directly or indirectly influenced by the H2 partial pressure. · Sulphide concentrations of up to 6.5 mM free hydrogen sulphide) at pH of 7.2 was not inhibitory to methanogens · Sulphate reducing bacteria were able to grow even at a low hydraulic retention time of 1.2 hours in the well-mixed acidogenic reactor. It was estimated that the maximum specific growth rate (m) and half saturation constant (ks) of SRB was 1.31 h-1 and 3.8 mg S.L-1, respectively. These values were higher than those reported in literature. · Sulphate reduction was suppressed at high concentration of carbon in the feed. Accumulation of high concentration of volatile organic acids at high feed-carbon concentrations had little effect on sulphate reduction. However, extent of sulphate reduction had a negative correlation with total concentration of biomass. A non-competitive biomass inhibition function was proposed to model the correlation. From this fit it was estimated that a biomass concentration of about 3300 mg-COD.L-1 will completely inhibit sulphate reduction. · Sulphate reduction was affected by redox potential control and pH in the acidogenic reactor. High pH and low redox potential values were essential for sulphate reduction to proceed. At redox potential control of -300 mV, sulphate reduction was inhibited more at pH of 6 than it was at pH of 7. At redox potential values of -250 mV or higher, about 90 % inhibition of sulphate reduction was observed at both pH of 6 and 7. An existing model describing carbohydrate degradation was extended to include sulphate reduction processes. Despite experimentally observing that sulphate reduction only took place from hydrogen, all possible substrates for sulphate reducion was considered. These included: lactic acid, butyric acid, propionic acid, acetic acid and hydrogen. Kinetic parameters for sulphate reduction processes were obtained from documented literature. Inhibition of sulphate reduction by biomass and sulphur assimilation by biomass were included in the model. A new approach to calculate caustic consumption at given pH values was also included. A modification to hydrogen regulation function was also made to better predict product distributions as a function of gas-phase hydrogen concentration. Model validation was performed using data from dynamic experiments. Comparison to actual data was undertaken on several key variables in the acidogenic and methanogenic reactors such as: organic acid concentrations, gas compositions, gas production rates, sulphate and sulphide concentrations and caustic consumption rates. The model satisfactorily predicted sulphate and sulphide concentrations in both reactors. However, discrepancy between predicted and experimental data on organic carbon concentrations was seen, especially during organic carbon concentration step changes.

South Africa (SA) currently faces a major pollution problem from mining impacted water, including acid rock drainage (ARD), as a consequence of the mining activities upon which the economy has been largely built. The environmental impact of ARD has been further exacerbated by the country's water scarce status. Increasingly scarce freshwater reserves require the preservation and strategic management of the country's existing water resources to ensure sustainable water security. In SA, the primary focus on remediation of ARDcontaminated water has been based on established active technologies. However, these approaches are costly, lead to secondary challenges and are not always appropriate for the remediation of lower volume discharges. Mostly overlooked, ARD discharges from diffuse sources, associated with the SA coal mining industry, have a marked impact on the environment, similar to those originating from underground mine basins. This is due to the large number of deposits and their broad geographic distribution across largely rural areas of SA. Semi-passive ARD treatment systems present an attractive alternative treatment approach for diffuse sources, with lower capital and operational costs than active systems as well as better process control and predictability than traditional passive systems. These semi-passive systems typically target sulphate salinity through biological sulphate reduction catalysed by sulphate reducing bacteria (SRB). These anaerobic bacteria reduce sulphate, in the presence of a suitable electron donor, to sulphide and bicarbonate. However, the hydrogen sulphide product generated is highly toxic, unstable, easily re-oxidised and poses a significant threat to the environment and human health, so requires appropriate management. An attractive strategy is the reduction of sulphate to sulphide, followed by its partial oxidation to elemental sulphur, which is stable and has potential as a value-added product. A promising approach to achieve partial oxidation is the use of sulphide oxidising bacteria (SOB) in a floating sulphur biofilm (FSB). These biofilms develop naturally on the surfaces of sulphide rich wastewater streams. Its application in wastewater treatment and the feasibility of obtaining high partial oxidation rates in a linear flow channel reactor (LFCR) has been described. The use of a floating sulphur biofilm overcomes many of the drawbacks associated with conventional sulphide oxidation technologies that are costly and require precise operational control to maintain oxygen limiting conditions for partial oxidation. In the current study a hybrid LFCR, incorporating a FSB with biological sulphate reduction in a single reactor unit, was developed. The integration of the two biological processes in a single LFCR unit was successfully demonstrated as a ‘proof of concept'. The success of this system relies greatly on the development of discrete anaerobic and microaerobic zones, in the bulk liquid and at the airliquid interface, that facilitate sulphate reduction and partial sulphide oxidation, respectively. In the LFCR these environments are established as a result of the hydrodynamic properties associated with its design. Key elements of the hybrid LFCR system include the presence of a sulphate-reducing microbial community immobilised onto carbon fibres and the rapid development of a floating sulphur biofilm at the air-liquid interface. The floating sulphur biofilm consists of a complex network of bacterial cells and deposits of elemental sulphur held together by an extracellular polysaccharide matrix. During the Initial stages of FSB development, a thin transparent biofilm layer is formed by heterotrophic microorganisms. This serves as ‘scaffolding' for the subsequent attachment and colonisation of SOB. As the biofilm forms at the air-liquid interface it impedes oxygen mass transfer into the bulk volume and creates a suitable pH-redox microenvironment for partial sulphide oxidation. Under these conditions the sulphide generated in the bulk volume is oxidised at the surface. The biofilm gradually thickens as sulphur is deposited. The produced sulphur, localised within the biofilm, serves as an effective mechanism for recovering elemental sulphur while the resulting water stream is safe for discharge into the environment. The results from the initial demonstration achieved near complete reduction of the sulphate (96%) at a sulphate feed concentration of 1 g/L with effective management of the generated sulphide (95-100% removal) and recovery of a portion of the sulphur through harvesting the elemental sulphur-rich biofilm. The colonisation of the carbon microfibres by SRB ensured high biomass retention within the LFCR. This facilitated high volumetric sulphate reduction rates under the experimental conditions. Despite the lack of active mixing, at a 4-day hydraulic residence time, the system achieved volumetric sulphate reduction rates similar to that previously shown in a continuous stirred-tank reactor. The outcome of the demonstration at laboratory scale generated interest to evaluate the technology at pilot scale. This interest necessitated further development of the process with a particular focus on evaluating key challenges that would be experienced at a larger scale. A comprehensive kinetic analysis on the performance of the hybrid LFCR was conducted as a function of operational parameters, including the effect of hydraulic residence time, temperature and sulphate loading on system performance. Concurrently, the study compared the utilisation of lactate and acetate as carbon source and electron donor as well as the effect of reactor configuration on system performance. Comparative assessment of the performance between the original 2 L LFCR and an 8 L LFCR variant that reflected the pilot scale design with respect to aspect ratio was conducted. Pseudo-steady state kinetics was assessed based on carbon source utilisation, volumetric sulphate reduction, sulphide removal efficiency and elemental sulphur recovery. Additionally, the hybrid LFCR provided a unique synergistic environment for studying the co-existence of the sulphate reducing (SRB) and sulphide oxidising (SOB) microbial communities. The investigation into the microbial ecology was performed using 16S rRNA amplicon sequencing. This enabled the community structure and the relative abundance of key microbial genera to be resolved. These results were used to examine the link between process kinetics and the community dynamics as a function of hydraulic residence time. Results from this study showed that both temperature and volumetric sulphate loading rate, the latter mediated through both sulphate concentration in the feed and dilution rate, significantly influenced the kinetics of biological sulphate reduction. Partial sulphide oxidation was highly dependent on the availability and rate of sulphide production. Volumetric sulphate reduction rates (VSRR) increased linearly as hydraulic residence time (HRT) decreased. The optimal residence time was determined to be 2 days, as this supported the highest volumetric sulphate reduction rate (0.21 mmol/L.h) and conversion (98%) with effective sulphide removal (82%) in the 2 L lactate-fed LFCR. Lactate as a sole carbon source proved effective for achieving high sulphate reduction rates. Its utilisation within the process was highly dependent on the dominant metabolic pathway. The operation at high dilution rates resulted in a decrease in sulphate conversion and subsequent increase in lactate metabolism toward fermentation. This was attributed to the competitive interaction between SRB and fermentative bacteria under varying availability of lactate and concentrations of sulphate and sulphide. Acetate as a sole carbon source supported a different microbial community to lactate. The lower growth rate associated with acetate utilising SRB required longer start-up period and was highly sensitive to operational perturbations, especially the introduction of oxygen. However, biomass accumulation over long continuous operation led to an increase in performance and system stability. Microbial ecology analysis revealed that a similar community structure developed between the 2 L and 8 L lactate-fed LFCR configurations. This, in conjunction with the kinetic data analysis, confirmed that the difference in aspect ratio and scale had minimal impact on process stability and that system performance can be reproduced. The choice of carbon source selected for distinctly different, highly diverse microbial communities. This was determined using principle co-ordinate analysis (PCoA) which highlighted the variation in microbial communities as a function of diversity and relative abundance. The SRB genera Desulfarculus, Desulfovibrio and Desulfomicrobium were detected across both carbon sources. However, Desulfocurvus was found in the lactate-fed system and Desulfobacter in acetate-fed system. Other genera that predominated within the system belonged to the classes Bacteroidetes, Firmicutes and Synergistetes. The presence of Veillonella, a lactate fermenter known for competing with SRB, was detected in the lactate-fed systems. Its relative abundance corresponded well with the lactate fermentation and oxidation performance, where an apparent shift in the dominant metabolic pathway was observed at high dilution rates. Furthermore, the data also revealed preferential attachment of selective SRB onto carbon microfibers, particularly among the Desulfarculus and Desulfocurvus genera. The microbial ecology of the floating sulphur biofilm was consistent across both carbon sources. Key sulphur oxidising genera detected were Paracoccus, Halothiobacillus and Arcobacter. The most dominant genera present in the FSB were Rhizobium, well-known nitrogen fixing bacteria, and Pannonibacter. Both genera are members of the class Alphaproteobacteria, a well-known phylogenetic grouping in which the complete sulphur-oxidising, sox, enzyme system is highly conserved. An aspect often not considered in the operation of these industrial bioprocess systems is the microbial community dynamics within the system. This is particularly evident within biomass accumulating systems where the proliferation of non-SRB over time can compromise the performance and efficiency of the process. Therefore, the selection and development of robust microbial inoculums is critical for overcoming the challenges associated with scaling up, particularly with regards to start-up period, and long-term viability of sulphate reducing bioreactor systems. In the current study, long-term operation demonstrated the robustness of the hybrid LFCR process to maintain relatively stable system performance. Additionally, this study showed that process performance can be recovered through re-establishing suitable operational conditions that favor biological sulphate reduction. The ability of the system to recover after being exposed to multiple perturbations, as explored in this study, confirms the resilience and long-term viability of the hybrid process. A key feature of the hybrid process was the ability to recover the FSB intermittently without compromising biological sulphate reduction. The current research successfully demonstrated the concept of the hybrid LFCR and characterised sulphate reduction and sulphide oxidation performance across a range of operating conditions. This, in conjunction with a clearer understanding of the complex microbial ecology, illustrated that the hybrid LFCR has potential as part of a semi-passive approach for the remediation of low volume sulphate-rich waste streams, critical for treatment of diffuse ARD sources.

Biological sulphate reduction (BSR) has been identified as a promising alternative technology for the treatment of acid mine drainage. BSR is a process that uses sulphate reducing bacteria to reduce sulphate to sulphide using substrates as nutrients under anaerobic conditions. The performance of BSR is dependent on several factors including substrate, pH, temperature and hydraulic retention time (HRT). In a quest to find a cost effective technology, Mintek conducted bench-scale tests on BSR that led to the commissioning of a pilot plant at a coal mine in Mpumalanga province, South Africa. This current study forms part of the ongoing tests that are conducted to improve Mintek’s process. The purpose of this study was to investigate the robustness of Mintek’s process and to develop a tool that can be used to predict the process’ performance with varying pH, temperature and HRT. Design Expert version 11.1.2.0 was used to design the experiments using the Box-Behnken design. In the design, pH ranged from 4 to 6, temperature from 10 °C to 30 °C and HRT from 2 d to 7 d with sulphate reduction efficiency, sulphate reduction rate and sulphide production as response variables. Experiments were carried out in water jacketed packed bed reactors that were operated in a down-flow mode. The reactors were packed with woodchips, wood shaving, hay, lucerne straw and cow manure as support for sulphate reducing bacteria (SRB) biofilm. Cow manure and lucerne pellets were used as the main substrates and they were replenished once a week. These reactors mimicked the pilot plant. The data obtained were statistically analysed using response surface methodology. The results showed that pH did not have a significant impact on the responses (p>0.05). Temperature and HRT, on the other hand, greatly impacted the process (p<0.05) and the interaction between these two factors was found to be strong. Sulphate reduction efficiency and sulphate reduction rate decreased by over 60 % with a decrease in temperature 30 °C to 10 °C. Generally, a decrease in sulphide production was observed with a decrease in temperature. Overall, a decrease in HRT resulted in a decline of sulphate reduction efficiency and sulphide production but favoured sulphate reduction rate. This study demonstrated that Mintek’s process can be operated at pH as low as 4 without any significant impact on the performance. This decreases the lime requirements and sludge production during the pre-neutralisation stage by close to 50 %. There was, however, a strong interaction between temperature and HRT which can be used to improve the performance especially during the winter season. / Dissertation (MEng)--University of Pretoria, 2020. / Chemical Engineering / MEng / Unrestricted

Quando as wetlands alcançam a máxima capacidade de tratamento para remover metais pesados, a remoção ainda pode ocorrer por precipitação na forma de sulfetos devido a redução biológica de sulfato. Para alcançar este objetivo, devem ser promovidas condições anaeróbias, uma fonte de sulfato deve existir e uma fonte adequada de carbono/energia deve estar presente. No presente trabalho, a macroalga Sargassum filipendula e bagaço de cana-de-açúcar (materiais lígneo-celulósicos) foram selecionados como fontes de carbono, devido ao seu acentuado conteúdo de compostos orgânicos de degradação lenta e serem resíduos de alta disponibilidade. Experimentos foram simultaneamente conduzidos em operação contínua em duas colunas (0,5 L cada), uma contendo a macroalga e/ou bagaço de cana-de-açúcar e a outra contendo os materiais inoculados com um lodo anaeróbio. Neste trabalho, foi estudada a remoção de cádmio e zinco, devido à presença deles em efluentes de operações de mineração/metalurgia. Os ensaios foram realizados sob três diferentes condições experimentais no que se refere à quantidade de lodo anaeróbio inoculado no reator e o material empregado como fonte de carbono/energia. Os resultados indicaram que o reator inoculado foi capaz de tratar o efluente mais eficientemente que o reator não inoculado, considerando o período dos testes / When wetlands reach maximum treatment capacity to remove heavy metals, removal can still take place through precipitation as sulphides, due to biological reduction of sulphate. To achieve this goal, anaerobic conditions must be attained, a sulphate source must exist, and an adequate carbon/energy source must be present. In the present work, the seaweed Sargassum filipendula and sugarcane bagasse (ligneous-cellulosic materials) have been selected as carbon sources, due to their high content of slow degradation organic compounds and high availability as waste materials. Experiments were simultaneously conducted in continuous operation in two columns (0.5 L each), one containing the seaweed and/or sugarcane bagasse and another containing the materials inoculated with an anaerobic sludge. In this work, the removal of cadmium and zinc was studied, due to their presence in effluents from mining/metallurgy operations. The rehearsals were accomplished under three different experimental conditions in what refers to the amount of anaerobic mud inoculated in the reactor and employed material as carbon/energy source. The results obtained indicated that the inoculated reactor was able to treat the effluent more efficiently than the non inoculated reactor, considering the time-course of the tests