Tastes and Odours in Reservoirs Research Report 73 Research Report 73 Tastes and Odours in Reservoirs Peter Hobson1, Caroline Fazekas1, Jenny House1, Rob Daly1, Tim Kildea1, Steve Giglio1, Michael Burch1, Tsair-Fuh Lin2, Yan-Min Chen2 1Australian Water Quality Centre, South Australian Water Corporation, GPO Box 1751, Adelaide, South Australia, 5001 2Department of Environmental Engineering, National Cheng Kung University, 1 University Road, Tainan City, Taiwan 70101 (ROC) Research Report No 73 TASTES AND ODOURS IN RESERVOIRS DISCLAIMER The Cooperative Research Centre for Water Quality and Treatment officially ended October 2008, and has been succeeded by Water Quality Research Australia Limited (WQRA), a company funded by the Australian water industry. WQRA and individual contributors are not responsible for the outcomes of any actions taken on the basis of information in this research report, nor for any errors and omissions. WQRA and individual contributors disclaim all and any liability to any person in respect of anything, and the consequences of anything, done or omitted to be done by a person in reliance upon the whole or any part of this research report. This research report does not purport to be a comprehensive statement and analysis of its subject matter, and if further expert advice is required the services of a competent professional should be sought. 0 Water Quality Research Australia Limited 2010 Location: WQRA Head Office Level 3, 250 Victoria Square, Adelaide SA 5000 Postal Address: GPO BOX 1751, Adelaide SA 5001 For more information about WQRA visit the website www.wqra.com.au Tastes and Odours in Reservoirs Research Report 73 ISBN 18766 16997 MARCH 2010 2 CRC FOR WATER QUALITY AND TREATMENT – RESEARCH REPORT 73 FOREWORD Research Report Title: Tastes and Odours in Reservoirs Research Officers: Peter Hobson Peter Baker Greg Ingleton Paul Hackney Tim Kildea Kathy Cinque Project Leader: Michael Burch Research Nodes: Australian Water Quality Centre South East Queensland Water Corporation Ltd Melbourne Water Corporation Hunter Water Corporation CRC for Water Quality and Treatment Project No. 2.0.2.2.2.0 – Tastes and Odours in Reservoirs 3 TASTES AND ODOURS IN RESERVOIRS EXECUTIVE SUMMARY A range of organisms that grow naturally in source water are known to cause taste and odour (T&O) problems in drinking water supplies. The scientific literature and practical experience indicates that these can include cyanobacteria and algae, actinomycete bacteria, fungi and other aquatic microbiota. The organisms can be free-living in the water column (i.e. planktonic) or grow as benthic populations on the sediments; and depending upon the source water, they can be seasonally abundant. This project aimed to investigate the occurrence of these different organisms in Australian reservoirs and to better understand their relative potential to produce significant tastes and odours which affect water quality. The background to this study was that in 2005 a survey of 37 drinking water providers in Australia, representing 5 million customers, found that 78% of the providers had experienced problems with earthy/musty odours and half had not positively identified the problem compounds and were not carrying out routine chemical analysis. Interestingly, only five respondents reported a definite link between algal numbers and T&Os, indicating a need for further investigation. Further feedback from a range of water quality managers in the Australian water industry assisted in scoping the project. The project set out to characterise the occurrence of T&Os produced by benthic cyanobacteria and actinomycetes in a range of Australian reservoirs. These micro-organisms have been implicated as a possible cause of unexplained T&O incidents during the last few years where planktonic cyanobacteria were absent at the time in drinking water reservoirs in South Australia, Victoria, New South Wales, Queensland and Western Australia. The first component of the project involved a field survey of reservoirs in four states to characterise T&O organisms. This study then developed a conceptual model and then a mass balance model that incorporated processes for production and loss of odour metabolites in a reservoir. The model led to specific investigations and experiments that were designed to calibrate the rates of the component processes identified in the model. While there is considerable experience with the management of planktonic cyanobacteria there is very little knowledge or experience with the control and management of benthic cyanobacteria. The study evaluated the use of desiccation or ‘drying out’ by changing water level as a possible control technique. A discussion on management of benthic cyanobacteria is provided in this report, however given that knowledge on the ecology of these organisms is relatively limited it is difficult to develop a comprehensive management plan at this stage. Components of the project are summarised below. Survey of Australian Reservoirs A survey was carried out of major drinking water supply reservoirs in four states: Hope Valley and Happy Valley Reservoirs (South Australia), North Pine Dam (Queensland), Grahamstown Dam (New South Wales) and Yan Yean Reservoir (Victoria). The aim was to characterise the benthic community (cyanobacteria and actinomycetes) and determine their relative contribution to odour production in these reservoirs. The initial focus of investigation was on benthic cyanobacteria, however, actinomycetes have recently been identified in the literature as possible sources of T&Os in water supplies and were also included. In addition, historical data collected from both Hope Valley and Happy Valley Reservoirs by SA Water since 1997 were analysed to determine relationships between cyanobacteria and odour episodes. Both planktonic Anabaena and the benthic cyanobacterium Phormidium were shown to contribute significantly to the total geosmin content in Hope Valley and possibly Happy Valley Reservoir. Total geosmin present in water entering Hope Valley Reservoir treatment plant on some occasions came entirely from Phormidium. These results showed the important role that historical data can provide in identifying sources of T&Os in reservoirs. A detailed spatial survey was undertaken at these two reservoirs in spring and summer to gain a better understanding about the ecology of both benthic cyanobacteria and actinomycetes. The survey 4 CRC FOR WATER QUALITY AND TREATMENT – RESEARCH REPORT 73 consisted of ten transects equally spaced around the perimeter where samples were collected at various depths down to 2 m. The aim was to assess the variation both within and between locations. The density of benthic cyanobacteria, Oscillatoria sp., Phormidium sp. and Pseudanabaena sp. varied significantly from site to site at both Hope Valley and Happy Valley Reservoirs. These organisms were found at all depths at some sites and were completely absent from other sites. This suggested variations in micro-environments and habitats within the reservoirs at relatively closely spaced locations. Growth was also found to vary seasonally with growth at some sites in spring but not in summer and vice versa. There was a significant increase (p<0.05) in numbers of Oscillatoria sp. with increasing depth in both spring and summer for Happy Valley Reservoir and summer for Hope Valley Reservoir. This suggested that Oscillatoria sp. preferred lower irradiance and possibly lower temperatures which are both found in deeper waters. Such observations of differences in growth preferences are important for developing a monitoring program for particular reservoirs. Actinomycetes producing both geosmin and MIB were isolated from Hope Valley and Happy Valley Reservoirs. These were all members of the genus Streptomyces. All but one isolate from a total of 92 produced geosmin and approximately 40% of isolates from both reservoirs produced both geosmin and MIB in varying ratios. Correspondingly the remaining 60% of isolates produced geosmin only. The presence of T&O producing actinomycetes in these reservoirs confirms that they could be contributing to the reservoir odour load but further work is required to determine their significance. An issue with the technique of culture isolation used in this study is that it is not possible to determine whether the isolates that grew from reservoir samples were from actively growing cells or from dormant spores and it is therefore not possible to determine whether they were producing geosmin. The relationship between actively growing actinomycetes and geosmin production requires further study. The benthic cyanobacterium, Phormidium sp., was identified in the sediments of Grahamstown Reservoir at a single depth at one site only. Large areas of the reservoir supported a dense coverage of torpedo grass (Panicum repens) which grew down to a depth of approximately 1 m and which could retard the growth of benthic cyanobacteria by shading and light limitation. However, an epiphytic community consisting of Pseudanabaena sp. and Anabaena sp. was found attached to the macrophytes indicating that they provide a substrate to support cyanobacterial growth. Actinomycetes were detected in the sediments at all 10 sites surveyed, but not at all depths, and included both Streptomyces sp. and Actinomycetale sp. Both species were found to produce only geosmin. The water levels at both North Pine Dam and Yan Yean Reservoir were historically low at the time of the study, which was a result of drought conditions. As a consequence