Ordering Information:
ORDER NUMBER:  91199
DATE AVAILABLE: Spring 2008

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PRINCIPLE INVESTIGATORS:
Justin Brookes, Robert Daly, Rudi H. Regel, Michael Burch, Lionel Ho, Gayle Newcombe, Daniel Hoefel, Chris Saint, Thomas Meyne, Michele Burford, Maree Smith, Glen Shaw, Peyi Peyi Guo, David Lewis, and Matthew Hipsey

OBJECTIVES:
The goals of this project were to investigate cyanobacterial toxin degradation in reservoirs, identify toxin-degrading organisms, and develop reservoir management approaches for the control of toxin production.

BACKGROUND:
The water industry has been actively seeking methods to control cyanobacteria. However, controlling them to a level that ensures no taste-and-odor problems is difficult.

Even low numbers of cyanobacteria can produce concentrations of compounds that cause tastes and odors that attract customer complaints. The most sustainable long-term solution for reducing toxins, tastes, and odors is to control cyanobacterial growth through mixing and a reduction in nutrient levels.

HIGHLIGHTS:
The toxin degradation kinetics and rates describing degradation were determined and incorporated into the ecological Computational Aquatic Ecosystem Dynamics Model (CAEDYM). The ecological model can be coupled with the hydrodynamic Dynamic Reservoir Simulation Model (DYRESM) to enable prediction of cyanobacterial growth, toxin production, and toxin degradation in any reservoir.

A series of fact sheets are presented that summarize the current knowledge on cyanobacterial toxins, water treatment for toxin removal, and management of cyanobacteria within lakes and reservoirs.

APPROACH:
Biodegradation studies were undertaken on two cyanobacterial toxins, cylindrospermopsin and microcystin. These studies consisted of spiking natural waters with known concentrations of toxin and measuring toxin degradation through time. Sand column biofilters were also spiked with microcystin and the evolution of a microbial community able to degrade the toxins was examined. The microbial community was screened, using molecular techniques, for organisms capable of degrading toxins.

RESULTS/FINDINGS:
Microcystin degradation within two natural water sources that experience Microcystis blooms was reasonably rapid, with microcystin concentrations reaching undetectable levels after 6–8 days from an initial concentration of 20 µg L ^-1. However, these rates were slower than those within sand filters, which degrade microcystin toxin from 20 µg L ^-1 to undetectable concentrations within 4 minutes. Some natural aquatic organisms have the capacity to degrade soluble Cylindrospermopsin, and degradation was observed at all sites in North Pine Dam, QLD, Australia, from initial concentrations ranging from 3 to 76 µg L ^-1.

Reservoir hydrodynamics and growth of the phytoplankton species was successfully simulated with the DYRESM-CAEDYM computer model. The timing and magnitude of blooms was similar for the field and the simulated data sets. The CAEDYM model was extended to include toxin production and degradation, which can be applied to any reservoir to predict the risk of cyanobacterial toxins.

Utilities cannot rely on biodegradation to control the cyanobacterial toxins, microcystin and cylindrospermopsin, in drinking water reservoirs. Toxins can be present in the water column without degrading bacteria being present. Cylindrospermopsin can persist for months in the water column suggesting that biodegradation does not always occur. Additionally, screening with PCR for microcystin degrading organisms revealed that these organisms were not always present in toxic blooms of Microcystis aeruginosa.

IMPACT:
Operators are better equipped to manage the hazards in both the reservoir and water treatment plant when using the DYRESM-CAEDYM model to predict the risk from cyanobacteria in any given reservoir. There is a data requirement for model use, but the expense associated with this is considered modest compared with the improved operation and health and aesthetic outcomes that are realized with better system understanding and management.

RESEARCH PARTNER:
Cooperative Research Centre for Water Quality and Treatment

PARTICIPANTS:

• Veolia Water
• SE Queensland Water