Melbourne Water’s Western Treatment Plant (WTP) treats 52 per cent of the wastewater from the metropolitan area of Melbourne and 72 per cent of the industrial wastewater. After passing through a sequence of biological processes, including lagoon treatment, a portion of the water is disinfected and released as Class A recycled water. During the warmer months blooms of cyanobacteria (commonly known as blue-green algae), including Microcystis aeruginosa, periodically occur within the lagoons and can lead to interruption of the supply of recycled water from the affected lagoon system due to the presence of the toxin microcystin. This project investigated the effectiveness of recently developed technology for the detection, prevention and reduction of nascent blooms.
Technologies that were investigated include:
- algae on-line analyser (AOA);
- field use “dipstick” methods (the Abraxis strip test);
- ultrasonic algal controllers; and
- solar-powered mixers (SolarBee mixers).
Being relatively new on the market, these items have little operational history and thus little validation of effectiveness. The overall aim of this project was to develop an increased understanding of the effectiveness of this equipment. Activities to do so included:
- Collecting water samples from the inlet and outlet of ponds (with Solar Bee unit) to determine the phytoplankton and zooplankton counts and the water quality parameters were evaluated.
- Suspensions of known cell concentration of M. aeruginosa, Euglena gracilis and Chlorella sp. were prepared in treated water from WTP and their chlorophyll a concentrations were determined by the algae on-line analyser located at WTP.
- Abraxis Microcystin Strip Test Kits (PN 520020 and PN 520022) were used for the determination of extracellular and intracellular microcystin in a range of water matrices of different water quality. The results were compared with those obtained from HPLC analysis,
- Suspensions of known cell concentration of M. aeruginosa, Chlorella sp. and Anabaena circinalis were sonicated for 5-20 minutes using a lab sonicator at varying power intensities (0.043-0.32 W mL-1). Cell concentration and hence cell growth over 7 days was determined by optical density measurement at 684 nm and compared with control samples which were not exposed to sonication. Extracellular microcystin concentrations were measured using Abraxis Microcystin Strip Test Kits.
Using M. aeruginosa as a test cyanobacterium, it has been shown that the algal online analyser can be used to detect populations, and thus imminent blooms, that the Abraxis Strip Test can be used for approximate quantitation of microcystin in wastewater, and that sonication has the potential for the deactivation of cyanobacteria. Thus these technologies have application for the lagoons at WTP and elsewhere, whereas the SolarBee mixer is not suitable for use at WTP and similar shallow lagoon systems.
Details on this project have also been included in the following sources:
- Nguyen, T, Doan, T., Fan, L. and Roddick, F.A. (2010) Using an algal online analyser for detecting the presence of cyanobacteria in biologically treated effluent, 2nd National Cyanobacterial Workshop, Melbourne, 2-3 August.
- Roddick, F.A., Meizler, A., Nguyen, T. and Fan, L. (2011) Detection of microcystin-LR in lagoon-treated water by Abraxis Strip Test, Ozwater 2011, Adelaide, 9-11 May.
- Nguyen, T. Fan, L. and Roddick, F.A. (2011) Experience with an algal online analyser for detecting Microcystis aeruginosa in lagoon-treated effluent, Proceedings IWA Waste Stabilisation Ponds 2011, Adelaide, 1-2 August.
- Rajasekhar, P.,Fan, L. Nguyen,T. and Roddick, F.A.(2011) Impact of sonication at 20 kHz on Microcystis aeruginosa, Anabaena circinalis and Chlorella sp., Water Research , doi:10.1016/j.watres.2011.11.017