1,721,112 research outputs found
Biofouling of spiral wound membrane systems
No full textBiofouling of spiral wound membrane systems High quality drinking water can be produced with membrane filtration processes like reverse osmosis (RO) and nanofiltration (NF). Because the global demand for fresh clean water is increasing, these membrane technologies will increase in importance in the coming decades. One of the most serious problems in RO/NF applications is biofouling - excessive growth of biomass - affecting the performance of the RO/NF systems due to e.g. (i) increase in pressure drop across membrane elements (feed-concentrate channel), (ii) decrease in membrane permeability, (iii) increase in salt passage. These phenomena result in the need to increase the feed pressure to maintain constant production and to clean the membrane elements chemically. In practice, the first phenomenon is most dominant. The objective of this study was to relate biomass accumulation in spiral wound RO and NF membrane elements with membrane performance and hydrodynamics and to determine parameters influencing biofouling. The focus of this research was on the development of biomass in the feed-concentrate (feed-spacer) channel and its effect on pressure drop and flow distribution. These detailed studies can be used to develop an integral strategy to control biofouling in spiral wound membrane systems. Problem analysis Studies to diagnose biofouling in 15 full-scale RO and NF membrane installations with varying feed water types showed that (i) highest biomass concentrations were found at the installation feed side, (ii) the biomass related parameter adenosine-tri-phosphate was suitable for biofouling diagnosis in membrane element autopsies, (iii) measurements of biological parameters in the water were not appropriate in quantifying biofouling, and (iv) there is a need for a representative monitor and sensitive accurate pressure data to enable a reliable evaluation of the development of biofouling (Chapter 2). Based on the practical observations it was decided to develop a set of tools to study biofouling at controlled conditions. Method development A monitor was developed (Chapter 3) in combination with testing of a sensitive differential pressure drop transmitter (Chapter 4). This small monitor named Membrane Fouling Simulator (MFS) uses the same membranes and spacers as present in commercial membrane elements, has similar hydrodynamics and is equipped with a sight window. The MFS is an effective scaled-down version of a full-scale system and allows to study the biofouling process occurring in the first 0.20 m of RO/NF elements. Magnetic Resonance Imaging (MRI) provided in-situ, non-invasive, and spatially-resolved measurements of biofouling and its impact on hydrodynamics and mass transport in spiral wound membrane elements as well as in the MFS (Chapter 5). A three-dimensional computational model was developed to simulate biofouling in membrane elements, with feed spacer geometry as used in practice (Chapter 6). The model combines fluid dynamics, solute transport and biofouling. The methods described in the first part of the thesis have been used to increase the understanding of fundamental aspects of biofouling. Basic studies The development of biomass and related increase in pressure drop was not influenced by the permeate production in the elements (Chapter 7). Irrespective whether a flux was applied or not, the feed-concentrate channel pressure drop and biofilm amount increased in RO and NF membranes in monitor, test-rig, pilot and full-scale installation. Mass transport calculations supported that permeate production plays a minor role in the development of biofouling. Since fouling occurred irrespective of permeate production, the critical flux concept stating that “below a critical flux no fouling occurs” is not applicable to control RO/NF biofouling in extensively pretreated water. In essence, biofouling is a feed spacer channel problem (Chapter 8). This observation is based on (i) practical data and supported by (ii) in-situ visual observations of fouling accumulation using the MFS sight window, (iii) in-situ non-destructive observations of fouling accumulation and velocity distribution profiles using MRI, and (iv) differences in pressure drop and biomass development in monitors with and without feed spacer. MRI studies showed that already a restricted biofilm accumulation on the feed channel spacer influenced the velocity distribution profile strongly, leading to a strong decrease of the effective surface area in the membrane module and probably increasing the salt concentration in the dead-zones of the element leading to increased salt passage. Three-dimensional numerical simulations of biofilm formation and fluid flow were executed and compared with MRI and MFS studies (Chapter 9). The simulations showed similar (i) pressure drop development and (ii) patterns in flow distribution and channelling as observed in MRI and MFS studies. Feed spacers showed to have an essential role in biofouling, and are considered a prime target for improving the membrane elements. Based on the gained insights several potential methodologies to minimize the impact of biofouling have been studied and described in the last chapters of the thesis. Control studies The effect of substrate concentration, linear flow velocity, substrate load and flow direction on pressure drop development and biofilm accumulation was investigated in MFSs (Chapter 10). The pressure drop increase was related to the amount of accumulated biomass and linear flow velocity. Biomass accumulation was related to the substrate load. A flow direction change in the pressure vessels instantaneously reduced the pressure drop, accentuating that hydrodynamics, spacers and pressure vessel configuration offer possibilities to restrict the pressure drop increase caused by accumulated biomass. The impact of flow regime on pressure drop, biomass accumulation and morphology was studied (Chapter 11). In RO and NF membrane elements, at linear flow velocities as applied in practice voluminous and filamentous biofilm structures developed in the feed spacer channel, causing a significant increase in feed channel pressure drop. The amount of accumulated biomass was independent of the applied shear, depending on the substrate load. A high shear force resulted in more compact and less filamentous biofilm structure compared to a low shear force, causing a lower pressure drop increase. A biofilm grown at low shear was easier to remove during water flushing compared to a biofilm grown at high shear. Flow regimes manipulated biofilm morphology affecting membrane performance, enabling new approaches to control biofouling. Phosphate limitation as a method to control biofouling was investigated at a full-scale RO installation, characterized by low phosphate and substrate concentrations in the feed water and low biomass amounts in lead membrane modules. MFS studies showed that phosphate limitation restricted the pressure drop increase and biomass accumulation, even in the presence of high substrate concentrations (Chapter 12). Outlook Most past and present methods to control biofouling have not been very successful. Based on insights obtained by the studies described in this thesis, an overview is given of several potential complementary approaches to solve biofouling (Chapter 13). An integrated approach for biofouling control is proposed, based on three corner stones: (i) equipment design and operation, (ii) biomass growth conditions, and (iii) cleaning agents. Although in this stage chemical cleaning and biofouling inhibitor dosing seem inevitable to control biofouling, it is expected that in future – also because of sustainability and costs reasons - membrane systems will be operated without or with minimal chemical cleaning and dosing.BiotechnologyApplied Science
Aerobic granular sludge: Scaling up a new technology
No full textMost conventional wastewater treatment plants need a large surface area for the treatment of their sewage. This is due to the open structure of the biomass used to convert the polluting components in wastewater. Because of the flocculated growth, sludge concentrations in reaction tanks are low and settling times need to be long in order to keep the biomass in the system. This Ph.D. thesis describes the development of a new compact aerobic granular sludge technology, in which the biomass is grown in compact granular structures. The main advantage of this compact growth structure is the higher biomass concentrations that van be reached and that all processes, needed for the treatment of wastewater, can be performed in one (discontinuously operated) reactor. Therefore, 80% less area and 30% less energy is required for the treatment of the wastewater. This process is unique, since by the natural composition of the aerobic granular sludge, combined with different diffusion limitations, all processes for the conversion of the polluting agents can occur in the same granule simultaneously. In the laboratory, biological removal efficiencies of 100% COD (acetate), 94% phosphate and 94% nitrogen (of which full-nitrification) were measured. During the Ph.D. a large-scale design has been made by the engineers of the Dutch consultancy firm DHV. Bottlenecks from practice were translated to scientific research and the results of the research could directly be used in the design. Different bottlenecks that were studied in the laboratory scale research were the influence on conversions and granule morphology of i) the way of influent dosing, ii) the use of a bubble column or airlift (influence of high local shear forces), iii) influence of temperature, iv) type of wastewater. A model for aerobic granular sludge has been developed as well, in order to study the sensitivity of different process parameters on conversion rates and efficiencies. This fast procedure for developing innovations led to a successful pilot scale study at sewage treatment plant Ede, The Netherlands and to the market introduction of this new technology by DHV under the name of NeredaTM.Applied Science
Biogrout, ground improvement by microbial induced carbonate precipitation
No full textBiogrout is a new ground improvement method based on microbially induced precipitation of calcium carbonate (MICP). When supplied with suitable substrates, micro-organisms can catalyze biochemical conversions in the subsurface resulting in precipitation of inorganic minerals, which change the mechanical soil properties. This study focuses on one of these biochemical conversions: microbially catalyzed hydrolysis of urea inducing calcium carbonate precipitation in sand. This Biogrout process comprises the following steps: Sporosarcina pasteurii, a bacterial species containing a large amount of the enzyme urease are cultivated, injected in the ground and supplied with a solution containing urea and calcium chloride. Urease catalyzes the conversion of urea into ammonium and carbonate and the produced carbonate precipitates with calcium as calcium carbonate crystals. These crystals form sticking wedges between the sand grains increasing the strength and stiffness of the sand. The remaining ammonium chloride is extracted and disposed. The thesis comprises the necessary steps to develop this process from a laboratory experiment to a practical application, culminating in an unprecedented 100 m3 field scale experiment in which 40 m3 of sand was biologically cemented within 12 days stretching over a distance of 5 m. Engineering tools are established such as empirical correlations between the CaCO3 content and strength or stiffness, which enable to design treatment procedures for several emphasized applications, such as increasing the stiffness of railroad embankment or improving the stability of limestone room and pillar mines. Some of the remaining issues of this Biogrout process include the required removal of ammonium chloride and the use of axenically cultivated aerobic organisms with consequent decaying urease activity in time due to a lack of oxygen in the subsurface. To avoid both these issues the suitability of other possible MICP processes for ground improvement is evaluated and the potential of the most promising alternative, denitrification, is shown in laboratory experiments.BiotechnologyApplied Science
Microbial ecology of phototrophic biofilms
No full textBiofilms are layered structures of microbial cells and an extracellular matrix of polymeric substances, associated with surfaces and interfaces. Biofilms trap nutrients for growth of the enclosed microbial community and help prevent detachment of cells from surfaces in flowing systems. Phototrophic biofilms can best be defined as surface attached microbial communities mainly driven by light as the energy source with a photosynthesizing component clearly present. Eukaryotic algae and cyanobacteria generate energy and reduce carbon dioxide, providing organic substrates and oxygen. The photosynthetic activity fuels processes and conversions in the total biofilm community, including the heterotrophic fraction. This thesis starts with a brief introduction in the ecology of phototrophic biofilms and discusses their actual and potential applications in wastewater treatment, bioremediation, fish-feed production, biohydrogen production, and soil improvement and their role in biofouling. The next chapter describes the diversity of phototrophic bacteria in hot spring microbial mats found on the east coast of Greenland. In this study we utilized a polyphasic approach using a combination of isolation techniques, microscopic observation of morphological features, and cultivation-independent molecular methods. We observed a relationship between the cyanobacterial community composition and the in situ temperatures of different microbial mat parts. Chapter 4 focuses on the successional changes in community composition of freshwater phototrophic biofilms growing under different light intensities. Our results suggest that surface colonization by heterotrophic pioneers facilitates the development of phototrophic biofilms. In Chapter 5 we compared the community composition of phototrophic biofilms cultivated in three microcosm systems operated under identical conditions but placed in different laboratories. Denaturing Gradient Gel Electrophoresis (DGGE) analysis of both 16S and 18S rRNA gene fragments showed that the communities developed differently in terms of species richness and community composition. Chapter 6 demonstrates that nifD gene sequences, coding for a nitrogenase subunit, can be used to detect and identify diazotrophic cyanobacteria in natural communities. PCR products generated using primers homologous to conserved regions in the cyanobacterial nifD genes were subjected to DGGE and clone library analysis in order to determine the genetic diversity of diazotrophic cyanobacteria in environmental samples. In the last chapter we describe the development of PCR primers targeting conserved regions within the cyanobacterial hupS gene family. This gene is involved in the hydrogen metabolism of diazotrophic microorganisms. We analyzed hupS diversity and transcription in cultivated phototrophic biofilms by the direct retrieval and analysis of mRNA that was reverse transcribed, amplified with hupS specific primers, and cloned. Overall, the community composition and species richness of phototrophic biofilms was shown to be highly variable. Cultivation-independent molecular methods proved very useful to study diversity and function in phototrophic biofilms.Applied Science
Magic granules
No full textBook 1 Chapter 1 gives a short overview of the history of aerobic granular sludge technology and finishes with an outline of the thesis. Chapter 2 deals with segregation of biomass as a function of height of the sludge bed. Phosphate accumulating organisms were found to dominate at the bottom of the sludge bed, whereas Glycogen accumulating organisms dominated at the top of the sludge bed. By selective removal of glycogen accumulating organisms dominated sludge from the top of the sludge bed, more than 95% P removal efficiencies were achieved at 30°C. Based on current knowledge this is the first process in which a stable biological P-removal could be maintained at 30°C. In chapter 3 the selective sludge removal was studied within this enhance biological phosphorous removal (EBPR) system in more detail. At 30°C the removal of bottom sludge from the PAO-rich part of the sludge bed in minor proportions did not negatively affect P-removal and allowed to obtain biomass with a lower ash content. The research further shows that at 20ºC, selective removal of PAOs was not crucial for a stable bioP removal and biomass can be removed equally throughout the sludge bed. Our results indicate that high ash content and density of bottom granules positively correlated with the presence of PAO-dominated granules. In chapter 4 we studied the competition for nitrite between nitrite oxidizing bacteria (NOB) and anaerobic ammonium oxidizing bacteria (Anammox) at low temperatures. White granules were dominated by NOB bacteria and were mainly located at the top of the settled sludge bed whereas red granules were dominated by Anammox bacteria and were located at the bottom. Granules from the top of the sludge bed were smaller and therefore had a larger aerobic volume fraction. These smaller granules also furthermore had a lower density then larger granules and consequently a slower settling rate. Selective sludge removal from the top of the settled sludge bed selectively removed NOB resulting in an increased overall biomass specific N-conversion. This forms an option for obtaining a stable Anammox process at lower temperatures in municipal wastewater treatment systems. Chapter 5 investigates the effect of granular density on the settling velocity of individual granules. The granule was divided in different layers each occupying a certain volume fraction consisting out of either bacteria, extra polymeric substances or precipitates. The density of each fraction was estimated experimentally. Each volume fractions was coupled with the corresponding densities to calculate a total density of a granule. This was used to calculate settling velocities. Results revealed that Phosphate accumulating organisms (PAO) had a higher density than glycogen accumulating organisms leading to significantly higher settling velocities for PAO dominated granules explaining earlier observations of the segregation of the granular sludge bed inside reactors. The model showed that a small increase in the volume fraction of precipitates (1-5%) strongly increased the granular density and thereby the settling velocity. For nitritation-anammox granular sludge the settling model shows that density differences are not very important and segregation of the biomass in the bed is mainly caused by variations in granule radius. In chapter 6 we showed that the temperature and ionic strength dependent density and viscosity changes of water have great impact on settling velocity of granular sludge. The corresponding slow settling of small granules at decreased water viscosities and increased water densities as caused by a lower temperature can be an important reason for the reported troublesome start-up of granular sludge reactors at low temperatures. Settling velocities also decreased with increasing salt concentrations. Changes in salt concentration will cause a strong time dependent effect of settling of granules due to the slow diffusion of salts into the granules. Conductivity and temperature measurements can therefore be used as an additional operational factor to stabilize and improve biomass retention in granular sludge technology. Book 2 Chapter 1 gives a short introduction in microbial ecology. Chapter 2 of the second book reports the differences in the microbial community composition of flocculent sludge and granular sludge. Their total bacterial community composition were very dissimilar whereas the community assessment showed that both systems had on average a similar species richness entropy, and evenness, suggesting that although the bacterial groups where very dissimilar a same stability in microbial community and function was obtained. The AOB population showed more unevenness than it was the case for the total bacterial populations. A correlation between the ammonium oxidizing bacterial population and changes in ammonium removal efficiency as well as temperature was found for both systems, whereas the bacterial population correlated with total nitrogen removal efficiencies. Chapter 3 aims to unravel the reasons for the disproportion in the ratio of AOB and NOB in aerobic granular sludge. In this study, we analysed the nitrifying microbial community (ammonium-oxidizing bacteria - AOB and nitrite-oxidizing bacteria - NOB) within three different aerobic granular sludge treatment systems as well as within one flocculent sludge system. Fluorescent in situ hybridization (FISH) and quantitative-PCR (qPCR) showed that Nitrobacter was the dominate NOB in acetate fed aerobic granules. In the conventional system, both Nitrospira and Nitrobacter were present in similar amounts. This suggested that the growth of Nitrobacter within aerobic granular sludge was partly uncoupled from the lithotrophic nitrite supply from AOB. This was supported by activity measurements which showed a 3 fold higher nitrite oxidizing capacity than ammonium oxidizing capacity. Based on these findings, two hypotheses were considered: either Nitrobacter grew mixotrophically by acetate-dependent dissimilatory nitrate reduction (ping-pong effect) or a nitrite oxidation/nitrate reduction loop (nitrite loop) occured in which denitrifiers reduced nitrate to nitrite supplying additional nitrite for the NOB apart from the AOB. The disproportion of the amount of AOB and NOB in granular sludge should be investigated further to confirm the hypothesis made in this work. In chapter 4 the specific solid retention time for different bacteria within flocculent and granular sludge was determined. Samples were collected from reactor and effluent sludge and the number of a specific bacterial group was evaluated in respect to the total bacterial community by the means of quantitative polymerase chain reaction (qPCR). Operational data were combined with molecular techniques and the SRT of each individual microorganism could be calculated. It was further observed that protozoa were grazing on the bacterial community within the system indicating that they have the potential to shorten the specific SRT of bacteria. Archea were not found in the flocculent system but were present in small amounts within the granular system. Chapter 5 gives outlook about possible applications molecular techniques in wastewater treatment.Environmental BiotechnologyDelft University of Technolog
PHA Production in Aerobic Mixed Microbial Cultures
No full textPolyhydroxyalkanoate (PHA) is a common intracellular energy and carbon storage material in bacteria, which is considered as a bioplastic due to its plastic like properties. PHAs are versatile materials which are biodegradable and made from renewable resources. Commercial production of PHAs is currently based on pure culture processes employing either natural PHA producers or genetically modified bacteria. Pure culture processes use generally pure sterile substrates and axenic reactors, leading to high production costs and thus relatively expensive products. An alternative approach for the production of PHAs is the use of mixed culture biotechnology, using non-sterile waste streams as a substrate and open reactors. The use of cheaper substrates, less energy (no sterilization of substrate or reactors) and cheaper equipment could reduce the production costs compared to pure culture processes. However, the mixed culture PHA production process requires optimization for higher cellular PHA contents to be competitive with pure culture processes. The research described in this thesis aimed at improving the cellular PHA contents that can be achieved in open mixed cultures. A two-step process consisting of (i) a culture enrichment and growth step and (ii) a PHA production step was used. For the enrichment of a mixed culture with PHA producing bacteria a selective pressure in the form of alternating periods of short presence of the carbon substrate (feast phase) and long absence of the carbon substrate (famine phase) under fully aerobic conditions was employed. PHA storing bacteria generally outcompete other bacteria in such a feast-famine system due to their very high substrate uptake rate (which is not limited by the growth rate) and due to the ability to grow in a more balanced way throughout feast and famine phase. A sequencing batch reactor (SBR) was used to establish the feast-famine regime. The cultures enriched in the first step under different operational conditions were tested for their ability to produce PHA in the second step, the PHA production step. For this purpose the cultures were supplied with an excess of carbon source (fed-batch reactor) while withholding a suitable nitrogen source in order to avoid growth and direct as much carbon as possible into PHA storage. To simplify the system for the optimization studies a mineral medium with acetate as the sole carbon substrate was used in all experiments rather than real wastewater. Acetate yielded pure polyhydroxybutyrate (PHB) as the storage polymer. In order to compare different operational conditions, specific reaction rates and observed yields had to be calculated for the key compounds acetate, biomass, PHB, carbon dioxide, oxygen and the nitrogen source ammonia from measurements performed during a stable SBR cycle or fed-batch experiment. Both SBR and fed-batch reactor were highly dynamic systems with changing reaction rates and liquid volumes, making the evaluation of experimental data a complex task. A very detailed data analysis was carried out for each SBR cycle measurement and fed-batch experiment. The data analysis included for example the correction of measurements for sampling effects and liquid volume changes, the computation of oxygen consumption and carbon dioxide evolution, and the calculation of the best estimates for all reaction rates and total conversions at each time point with the help of a metabolic model (Chapter 2). The metabolic model was used in order to be able to describe the dynamics of the system and in order to ensure that material balances would close. The metabolic model described the measurements generally very well. The reaction rates computed with the metabolic model showed clearer trends than those calculated without the help of the model. Different operational conditions were tested for the biomass enrichment step (SBR). The first two process parameters investigated were low sludge residence times (SRTs) of 4 d, 1 d and 0.5 d and the impact of different degrees of nitrogen versus carbon limitation (Chapter 3). Low SRTs are required for a high biomass productivity in the first step. The impact of nitrogen limitation was investigated, because many waste streams that are suitable substrates for mixed culture PHA production are nutrient limited. Enrichment of a PHA storing community was successful at 4 d and 1 d SRT, but less successful at 0.5 d SRT. Nitrogen limitation in the SBR generally led to competition for nitrogen and consequently to a selective pressure for high growth rates. Carbon limitation in the SBR led to a PHB storage strategy (high acetate uptake rate) and usually to higher PHB contents (about 70 wt%) in subsequent fed-batch experiments compared to cultures enriched under nitrogen limitation. Carbon limitation in the SBR allowed PHB storing bacteria to benefit more from their ability to store PHB by being able to grow throughout the famine phase. Carbon limitation and SRTs higher than 0.5 d were identified as favourable conditions for the biomass enrichment step in the SBR. Nutrient limited wastewaters may require supplementation with nutrients for this step. Another parameter that was investigated was the reactor temperature (Chapter 4). The reactor temperature will influence the reaction rates, but also the selective pressure in the SBR. The influence on the reaction rates can be investigated by applying short-term temperature changes (i.e. one SBR cycle) while the combined effect on reaction rates and selective pressure can be studied in long-term temperature change experiments. In short-term temperature change experiments the reactor temperature of a stable SBR operated at 20°C was changed for one cycle to 15, 25, 30 or 35°C. It was found that reaction rate changes in the famine phase could be described over the whole temperature range with the Arrhenius equation with one temperature coefficient. For the feast phase different temperature coefficients were estimated for acetate uptake, PHB production and growth. These were only valid for temperatures 5°C higher or lower than the steady state temperature. After long-term changes to either 15 or 30°C the reactor performance changed considerably: At lower temperatures the feast phase was long and a growth strategy prevailed. This culture had a very low PHB storage capacity (about 35 wt%). At 30°C the feast phase was short and a PHB storage strategy dominated. This culture was able to store 84 wt% PHB. Higher SBR temperatures appear to be a good strategy to support the enrichment of PHB storing bacteria. In Chapter 5 we report the most successful operating strategy applied during this thesis. A SBR culture was enriched that was able to store 89 wt% PHB within only 7.6 h in a fed-batch experiment. This culture had been enriched with a longer cycle length of 12 h as compared to our previous studies (4 h cycle length), at 1 d SRT, 30°C and carbon limitation. Another key to the high PHB content was the long operating time under these conditions of over a year. The maximum PHB storage capacity of this culture had improved with time. The long cycle length combined with a low SRT was found to favour growth of bacteria that can store a high amount of PHB at a high rate, since this is needed in order to continue to grow throughout the much longer famine phase. After the operating conditions in the SBR had been optimized, also the PHA production step in the fed-batch reactor was investigated. The temperature in fed-batch experiments did not influence the maximum PHB storage capacity, but only the reaction rates (Chapter 4). Fed-batch experiments were typically conducted using fed-batch systems without nitrogen source in the feed. With the aim of using waste streams as a substrate for PHA production, nutrient limitation or starvation may not always be feasible. We therefore investigated the influence of nitrogen starvation, nitrogen limitation and nitrogen excess on the maximum PHB content obtained in fed-batch experiments (Chapter 6). Under nitrogen starvation conditions the biomass reached a maximum PHB content of 89 wt%, under nitrogen limitation 77 wt% and under nitrogen excess 69 wt%. In the latter two experiments PHB contents decreased after these maxima were reached, because growth led to a dilution of the PHB pool. Nutrient starvation seems thus to be the best strategy for maximal PHB production in the fed-batch step. Chapter 7 summarizes and integrates the findings from all individual studies. In this chapter also some remaining issues are discussed and recommendations for future research are provided. With the aim of using real waste streams in the future and producing other PHAs apart from PHB, the next steps would be the use of more diverse carbon source mixtures and eventually a scale-up of the system. In conclusion, mixed culture PHB production has been successfully optimized in this thesis. A mixed culture was established with the capacity to produce PHB levels as high as in pure culture production processes, and at very high PHB production rates. Cultivation conditions have been identified that lead to a selection of a stable mixed microbial culture with a superior PHA production capacity. Compared to previous work with mixed cultures, a more than four times higher cellular PHB content was obtained. Herewith a highly competitive process has been established that may contribute to the development of a more sustainable and renewable biopolymer production in a future bio-based economy.BiotechnologyApplied Science
Treatment of source separated urine and its effects on wastewater systems
No full textAbstract not availableApplied Science
Polyhydroxyalkanoates production by bacterial enrichments
No full textPolyhydroxyalkanoates (PHAs) is a natural bacterial storage compound, which can be used as carbon and electron source. Their remarkable similarities in physical properties to conventional plastics, such as polypropylene, attract great commercial interest. This thesis focuses on PHAs production by bacterial enrichments. As compared to the current pure culture biotechnology, mixed culture biotechnology is much less dependent on the well defined substrate and sterile process. These properties of mixed culture biotechnology can greatly reduce the price of the final products. The major aims of this thesis are to optimize the process to select bacterial enrichments with superior PHAs-producing capacity and analyze the microbial community compositions in these enrichments. In my PhD studies, the main findings are: (1) both the maximal bacterial PHAs content and biomass specific PHAs productivity have been significantly improved. (2) the new selective pressure to enrich bacterial species with superior PHA producing capacity has been found. (3) several novel bacterial speices have been isolated and characterized. Based on these findings, converting argo-industrial waste to valuable chemical compounds can be achieved. Currently, a demo-scale production reactor is being constructed.BiotechnologyApplied Science
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