Using an Integrated Approach to Monitor Algal Blooms
Most drinking water utilities enter high-alert mode upon testing positive for microcystin. Staff at the city of Wichita Falls, Texas, Water Purification Laboratory responded calmly when they received that dreaded phone call in July 2018 because of their progressive approach to monitoring cyanobacteria. Climate conditions are conducive to harmful algae blooms and taste-and-odor events with increasing frequency and intensity. As a result, USEPA regulations are moving toward requiring cyanobacteria monitoring. Proactive drinking water utilities are seeking a streamlined approach to monitoring cyanobacteria and nuisance algae.
No single method answers all the questions needed to make cyanobacteria treatment decisions and ensure a safe water supply, including: 1) Are cyanobacteria present in the reservoir? 2) What quantity is present? 3) Can the species produce toxins? 4) What’s the concentration of cyanotoxins? The city of Wichita Falls poses these questions to identify nascent problems. When a cyanobacteria spike occurs, it’s important to treat a reservoir while contamination levels are low to diminish large-scale Microcystis outbreaks and cyanotoxin issues.
An Integrated Monitoring Approach
The city incorporated FlowCam®, a flow imaging microscope from Yokogawa Fluid Imaging Technologies, with three other methods—quantitative polymerase chain reaction (qPCR) with CyanoDTec from Phytoxigene, liquid chromatography–tandem mass spectrometry (LC/MS/MS) outsourced to a private laboratory, and gas chromatography–mass spectrometry (GC–MS) from Thermo Fisher Scientific—in an integrated strategy to monitor two lakes and one reservoir. The methods build on one another.
The city uses FlowCam to run samples three times each week in the summer and once each week in the winter. The FlowCam instrument is used to identify and enumerate filter-clogging algae, taste-and-odor algae, and cyanobacteria. Besides an initial capital investment, there’s no cost per sample and no limit to the number of samples that can be analyzed. FlowCam works quickly; it used to take the city three to four hours to do algae counts in the summer, but now it takes 15 minutes. Elevated counts for filter-clogging diatoms or taste-and-odor producers are used to trigger immediate treatment. In Wichita Falls, Dolichospermum concentrations of 100–200 chains/mL indicate an oncoming taste-and-odor event. Microcystis concentrations of 500 colonies/mL trigger immediate qPCR tests.
The city uses qPCR once each week to confirm if cyanobacteria in samples have toxin-producing genes. Having Microcystis in a sample doesn’t mean the source water will have the neurotoxin microcystin. If the toxin-producing genes aren’t present or activated, then microcystin will not be present. In fact, Wichita Falls sees Microcystis, Dolichospermum, and Oscillatoria in its reservoirs, and all three can produce microcystin.
If the qPCR results are positive for the presence of toxin-producing genes, it’s time to do a toxin test. For example, one city sample tested positive using an LC/MS/MS toxin test for microcystin. LC/MS/MS analysis is currently conducted by a third party for Wichita Falls, with a standard turnaround time of two weeks (or five days at double the price).
GC–MS analyses are also part of the toolkit the city of Wichita Falls uses to monitor taste-and-odor taxa. These analyses run three days each week to monitor 2-methylisoborneol (MIB) and geosmin, common taste-and-odor compounds in drinking water. A FlowCam count exceeding 200 chains/mL for Dolichospermum may indicate a taste-and-odor event is on the horizon because geosmin can increase with high Dolichospermum counts.
Texas faces formidable ecological conditions that are conducive to cyanobacteria blooms and taste-and-odor events. The city’s water quality team has leveraged the best technologies to keep its water clean and its customers happy. Wichita Falls’ multifaceted approach has reduced outbreak size and has all but eliminated taste-and-odor complaints. It’s been almost six years since the city’s last taste-and-odor outbreak.
