Harmful Algae Monitoring and Control System for Drinking Water Reservoirs

Climate change and extensive agricultural activities are endangering drinking water reservoirs in many countries. Eutrophication has turned water dams into favorable environments for harmful algae blooms. Controlling blooms of phytoplankton, including cyanobacteria, has become a top priority for aquatic system managers, especially concerning drinking water protection, recreational activities, and aquaculture production.

A serious issue is that some cyanobacteria produce compounds that cause unpleasant tastes and odors, such as geosmin and 2-Methylisoborneol (MIB). These compounds result in off-flavors in drinking water, negatively impacting water quality and requiring significant investment in water treatment measures. Furthermore, cyanobacteria can also synthesize harmful biological toxins that pose health risks and contribute to high fish mortality rates.

Managing lakes, reservoirs, and rivers to monitor cyanobacterial blooms is crucial for protecting human health. A notable example is the project at the Solingen waterworks in Germany, where a series of measures have been implemented to control the harmful cyanobacteria Planktothrix rubescens.

Sample project: Solingen waterworks

The harmful cyanobacterium Planktothrix rubescens is one of the primary causes of harmful algae blooms and is a frequent producer of microcystin toxins, which can cause liver damage and cancer. In the spring of 2013, following reports of dog deaths after drinking water from the Sengbach dam, studies identified an increase in Planktothrix rubescens and subsequently a large algal bloom in the Sengbach dam water.

The waterworks had to suspend water production for three months to conduct daily laboratory tests and supplement with continuous monitoring using the AlgaeOnlineAnalyser starting from early May 2013. The use of this device significantly reduced the time required for traditional microbiological analysis and established an alarm threshold for continuous 24/7 monitoring of harmful algae.

1. Continuous Monitoring with AlgaeOnlineAnalyser

To address the situation, the Sengbach waterworks deployed the AlgaeOnlineAnalyser starting in early May 2013. This device significantly reduced the time required for traditional microscopic analysis and provided continuous 24/7 monitoring of harmful algae growth. The AlgaeOnlineAnalyser not only measures algae concentration but also assesses algae activity, offering crucial information about the dynamics of algae blooms. This helps optimize the drinking water treatment process.

2. Rapid Laboratory Analysis with AlgaeLabAnalyser

In addition to continuous monitoring, the waterworks also utilized the AlgaeLabAnalyser to quickly and accurately test algae concentration in water samples collected from surrounding lakes and rivers. This method ensures timely responses to harmful algae incidents, contributing to improved quality of the input water for the plant.

Fluorometric measurement is a reliable method that allows real-time, on-site determination of algae concentration. Comparisons between laboratory analysis (cell counting) and AlgaeOnlineAnalyser measurements are consistent—see the image below.

The AlgaeOnlineAnalyser also measures algae activity to provide information on bloom dynamics. This information helps optimize the drinking water treatment process.

3. Algae Layer Measurement with FluoroProbe

Planktothrix rubescens often concentrates at the thermocline in the reservoir. To determine the optimal water intake depth, the FluoroProbe was used to measure algae stratification. The results indicated that a depth of 12 meters is the best point for water intake with the lowest algae content, ensuring the highest water quality for drinking water production.

Results Achieved and Practical Application

After implementing the comprehensive monitoring and control solutions, algae concentration at the Sengbach dam was significantly reduced and maintained at safe levels, below the WHO alarm threshold. This not only helps protect public health but also minimizes the costs and efforts associated with water treatment.

The WHO recommends that cyanobacteria concentrations in drinking water should be below 1 µg/l. During peak times, cyanobacteria levels at the Solingen waterworks exceeded 20 µg/l. However, thanks to the use of the AlgaeOnlineAnalyser, managers were able to control and maintain algae concentrations at safe levels.

Conclusion

A comprehensive solution for monitoring and controlling harmful algae is crucial for ensuring the quality and safety of drinking water. Technologies such as AlgaeOnlineAnalyser, AlgaeLabAnalyser, and FluoroProbe have proven effective in protecting public health and optimizing the water treatment process. This model is one that other waterworks can learn from and apply to protect their own drinking water sources.