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Title: Management and control of taste and odour problems associated with geosmin and 2-methylisoborneol in drinking water supplies
Author: Woodfield, Ria
ISNI:       0000 0004 5917 3328
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2014
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Two secondary metabolites, geosmin (GSM) and 2-methylisoborneol (MIB) cause the majority of taste and odour (T/O) problems in surface waters. This research focused primarily on identifying biological sources, and both abiotic and biotic factors associated with the production and release of these compounds in three Wessex Water (WW) drinking water reservoirs. Historical water quality data, collected by WW over 9 - 10 years was interrogated. Planktonic filamentous cyanobacteria in Durleigh and Sutton Bingham reservoirs and benthic cyanobacteria in Nutscale were identified as the most likely key producers of GSM. Corroborating evidence in support of this came from the isolation of a dominant GSM-producing strain of the planktonic cyanobacterium Aphanizomenon gracile (Aph-ll01) from Durleigh reservoir and two GSM-producing cyanobacterial strains, tentatively identified as members of the genus Phormidium were isolated from benthic mats. Geosmin and/or MIB producing actinobacteria were also isolated from each site. Concentrations of MIB in all reservoirs typically fell below the human odour threshold concentration (OTC) of 15 ng L-1, however, GSM concentrations frequently exceeded the human OTC of 3.8 ng L-1. Regression tree analysis revealed that all three reservoirs were typically characterised by elevated GSM concentrations, during periods of low DIN:SRP (typically < 10 by mass). Hydrological conditions were also highlighted as important, particularly at Nutscale reservoir where increased reservoir capacity, coupled with longer residence times since 2007, may have promoted the development of benthic mats, potentially explaining the significant increase in GSM concentrations observed over the study period. Understanding the relative proportions of intra- and extracellular GSM can have implications for the removal of these compounds by water companies, as extracellular GSM is more difficult to remove. An evaluation was made of the solid-phase extraction (SPE) method coupled with gas chromatography-mass spectrometry (the protocol commonly used in the UK water industry) and an additional step was introduced enabling the quantification of intra- and extracellular GSM concentrations in microbial cultures. A full method validation confirmed that SPE offered a viable high throughput alternative to the solid-phase microextraction (SPME) method for measuring GSM, which is typically reported in the scientific literature. Investigations revealed that in vitro, Aph-ll01 produced GSM throughout its growth period in batch culture and retained the majority (64-95%) of its GSM intracellularly. The keystone grazer Daphnia pulex consumed Aph-ll01, releasing intracellular GSM from the filaments into the medium. Grazing was identified as an important route for elevating the ratio of intracellular: extracellular GSM in reservoirs. Although no empirical evidence was gained in support of virus-mediated GSM release, the potential role of both lytic and temperate cyanophage was discussed in relation to T/0 outbreaks.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available