Microbiology

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Bioremediation of heavy metal polluted waters.
(1995) Meyer, Angela.; Wallis, Frederick Michael.
Microorganisms have the potential to remove heavy metals from polluted waters and effluents and may be used in clean-up processes. Microbial associations were enriched for and adapted to grow in nutrient solutions containing various concentrations of different metals. As immobilised cells are known to be more stable and more efficient in metal uptake than are corresponding planktonic or free-living cells the attachment of the microbial associations was investigated using a model stream and it was found that biofilm development was better on rough surfaces such as ground glass and polystyrene than on smooth surfaces such as unetched glass plates and glass beads. When comparing metal uptake by planktonic and attached microorganisms, attached populations were found to have a greater metal-uptake capacity. The uptake of individual metals from various metal combinations was tested with various proportions of pregrown metal-adapted microbial populations as inoculum and it was found that a particular metal was taken up more readily by microbial associations which had previously been exposed to that metal. Lead (Pb2+) appeared to be taken up more readily than copper (Cu2+) or cadmium (Cd2+) while Cd2+ was more actively removed than Cu2+ from solution. pH also affected metal uptake and the optimum range for Cu2+ uptake by the Cu2+ -adapted microbial association was found to be between 5.8 and 7.0. Dead microbial biomass was investigated and found to have efficient metal uptake capacity. Living mycelium from an isolated Aspergillus species showed poor uptake of Cu2+ initially, but when this fungus was pregrown and subsequently killed by moist heat treatment the non-living mycelium was efficient in removal of Pb2+ and Cu2+ ions. The optimum mycelial biomass concentration for metal uptake was also determined. The mechanism of metal uptake by this Aspergillus species was determined, using electron microscopy and EDX techniques, to be metabolism-independent biosorption onto the hyphal surface. Thus the microbial associations and fungal cultures used in this study were shown to have the potential for use in the removal of heavy metals from polluted waters.
Installation, commissioning and preliminary microbiological and operational investigations of full-scale septic tank digestion of sewage.
(1997) Taylor, Michelle Anne.; Senior, Eric.
This study investigated the commissioning and maintenance of a Pennells two-tank bioreactor system with specific reference to its application in rural areas of KwaZulu- Natal, South Africa to treat sewage and generate biogas. The septic tank configuration was installed in a community which lacked electricity and domestic waste disposal. An artificial wetland was constructed at the outlet of the system to facilitate further treatment. Inefficient operation and maintenance of the system occurred due to various social/community-related problems which are typical of a field- and community-based project of this nature in a rural region of a Third World African country. These problems affected both maintenance and digester performance. The Pennells system was characterized by incomplete anaerobiosis which limited methanogenesis. Despite this, and attendant problems of low temperatures and elevated pH values, COD removal resulted. Laboratory-scale batch cultures, in conjunction with fluorescence and scanning electron microscopy, were used to identify a suitable anaerobic digester sludge for inoculation purposes. Perturbation experiments with locally used detergents and toxic compounds demonstrated the inimical effects of these agents. In contrast, low concentrations of penicillin and tetracycline promoted methanogenesis. Further analysis with light, fluorescence and scanning electron microscopy identified the acidogens as the predominant bacterial species, whilst fluorescence microscopy confirmed the absence of methanogens in the bioreactor.
A laboratory scale study to investigate the effects of solids concentration on the efficiency of anaerobic digestion.
(1995) Naidoo, Valerie.; Senior, Eric.; Buckley, Christopher Andrew.
With the exceptions of mixing and heating mechanisms, and the recycling of settled solids, no radical changes or improvements have been made to conventional anaerobic digesters treating municipal sewage. These digesters usually function with a hydraulic retention time of 30 to 60 days and at a total solids concentration of 2.6 %(m/v). Volumetric loading is limited since high loadings effect the displacement of the slow growing methanogens. Thus, the hydraulic retention time is coupled to the solids retention time. A crossflow microfiltration unit has been constructed at Northern Waste Water Treatment Works, Durban, to concentrate sludge from a conventional anaerobic digester and, thus, facilitate operation with a higher solids concentration. In addition, this process should result in the retention of the active biomass which would otherwise be lost as a waste product of the treatment process. The solids retention time is, thus, decoupled from the hydraulic retention time. The net result could be higher volumetric loadings, increased microbial activity and increased volatile solids destruction and, hence, improvement in the efficiency of anaerobic digestion of sewage sludge. To test these, different experiments were conducted to specifically determine the effect of higher solids loads. Preliminary experiments were undertaken to determine the biodegradability of primary sludge from the Northern Waste Water Treatment Works. Results showed that primary sludge of 76% VS could be reduced to approximately 48 to 50% VS during an experimental period of 85 days. Reduction of the first 20% VS was rapid if conditions were optimum but subsequent reduction from 55 to 50% VS was slow. It was calculated that approximately 0.88 l gas was produced for every g volatile solids catabolised. Further experiments were conducted to investigate the effects of different solids concentrations on microbial activity. The results showed that the volume of gas produced increased as the solids concentration increased from 2 to 6%(m/v). Digesters with solids concentrations of 6 to 13%(m/v) produced similar volumes of gas. Digesters with solids concentrations of 6 to 13%(m/v) TS produced approximately 300 ml more gas than the control during the 20 days experimental period. The rate of gas production also increased as the solids concentration increased. However, digesters containing 11%(m/v) and 13%(m/v) TS produced similar rates. These results indicate that the introduction of concentrated sludge into the digester improves digestion efficiency. Finally, a semi-continuous digester was operated at a 30 days retention time and at optimum temperature to investigate the efficacy of digesters with increased solids concentrations. The results showed that the rate of gas production increased as the solids concentration increased from 2%(m/v)(control) to 3.8%(m/v). However, the digester operated with 4.7%(m/v) TS produced gas at a rate lower that the digester with 3.8%(m/v) TS. The volatile solids concentrations of all four digesters were similar, indicating neither favourable nor unfavourable effects from increased solids concentrations. The digesters operated with 3.8%(m/v) and 4.7%(m/v) TS produced higher concentrations of volatile acids than the control. The alkalinity concentrations (>_4000 mg t-1 ) were similar for all four digesters.
Microbiological investigations into granular sludge from two anaerobic digesters differing in design and industrial effluent purified.
(1995) Howgrave-Graham, Alan R.; Wallis, Frederick Michael.
Due to a combination of selection criteria, sludges from upflow anaerobic digesters treating industrial waste waters consist primarily of well-settling, dense agglomerates called granules. Quantification of the component mixed microbial populations of these granules has been severely restricted by the inability of researchers to disrupt them without concomitantly destroying numerous cells. In situ quantification using light and electron microscopy is complicated by the high cell numbers and bacterial diversity; the small cell size; and the destructive nature of electron microscopy preparative techniques preventing the viewing of more than a small percentage of the population at a time. For these reasons, in this investigation, standardization of qualitative electron microscopic techniques was performed prior to their application to granules. Isolation and electron and light microscopic techniques were applied to granules from a fullscale clarigester treating effluent from a maize-processing factory. In addition, a method using montaged transmission electron micrographs (TEMs) taken along a granule radius, and image analysis, was developed for bacterial quantification within granules. This method, together with antibody probe quantification, was applied to granules from an upflow anaerobic sludge blanket (UASB) digester treating a brewery effluent. The clarigester granules contained a metabolically and morphologically diverse population of which many members were not isolated or identified. By contrast, the UASB digester granules consisted primarily of morphotypes resembling Methanothrix, Methanobacterium and Desulfobulbus, in order of predominance. However, only about one-third of the population reacted with antibody probes specific to strains of bacterial species expected to occur within these granules. According to the antibody probe library used, the Methanobacterium-like cells observed in TEMs were probably Methanobrevibacter arboriphilus. From this study it is apparent that different anaerobic digester designs, operational parameters, and the chemical composition of the waste water purified, are factors which influence the formation and maintenance of granules differing with respect to their microbial populations. Until the difficulties associated with quantification are overcome, the processes governing granule formation and/or population selection will remain obscure.
Molecular and physiological characterization of thiosulphate-oxidizing microbial associations prior to use in hydrogen sulphide biofiltration.
(2000) Laughlin, Jamie B. A.; Senior, Eric.
Interacting microbial associations capable of utilizing thiosulphate as an energy source were enriched/isolated from activated sludge, landfill site [mal covering soil and soil from an acid mine water drainage site. The isolates were designated Lf-I, Ws-2 and Am-3, respectively. Although hydrogen sulphide was the target molecule for gas biofiltration, thiosulphate, which is a key oxidized intermediate, was used in this study due to the difficulty of working with a toxic gas. Together with thiosulphate oxidation, the microbial associations were assessed for their abilities to oxidize dissolved sulphide to elemental sulphur. Physiological analyses (temperature, pH and substrate concentration optimization) were made with closed and open cultures while morphological characterization and species compositional changes were monitored by light and scanning electron microscopy (SEM). To investigate further functional and structural responses to physiological changes, denaturing-gradient gel electrophoresis (DGGE) separation of PCR-amplified 16S DNA gene fragments and Biolog GN microtitre plates were used. The associations were found to be active metabolically between 0 and 35°C, 15 and 50°C, and 15 and 45°C, with optimum temperatures of 25, 40 and 35°C for Lf-l, Ws-2 and Am-3, respectively. The optimum pH range for microbial association Lf-l was between 3 and 4. The maximum specific growth rates of associations Lf-l , Ws-2 and Am-3 were 0.08, 0.06 and 0.03 h~l , respectively. Components of all three Gram negative rod-dominated associations were motile and displayed anaerobiosis. During open culture cultivation the species complement of Lf-l , as determined by morphological analysis, changed. The same association oxidized sulphide (40 ppm) to sulphur although Ws-2 and Am-3 did not have this capacity. Biolog GN plates detected pH-effected species compositional changes in Lf-l and these were confirmed by DGGE. The same technique showed that enrichment had occurred in the Biolog GN wells. Species composition changes also resulted in response to different pH values (2 to 9), temperatures (5 to 40°C) and dilution rates (0.003 to 0.09 h-1 ), but activity changes were not always accompanied by population profile changes.

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Browsing Microbiology by Subject "Anaerobic bacteria--Industrial applications."