Monitoring and forecasting cyanobacteria risk for a drinking water plant in Spain

Abstract

Abstract Cyanobacterial harmful algal blooms are a critical risk for public health since the release of cyanotoxins can reach hazardous levels in drinking water. In this study, a cost-effective monitoring programme has been developed and applied by a Spanish water operator to detect cyanobacteria presence in a drinking water plant reservoir; a total of 65 phytoplankton genera and seven cyanobacterial taxa were identified. Based on these monitoring data, different analysis techniques such as classification trees have been used to identify the potential situations of risk and to forecast cyanobacteria evolution in surface water. As a result, a new operational risk management plan has been developed and applied by the water operator since 2019. The main improvements concern the classification of the situations of risk in six groups (from low to very high, according to chlorophyl-a and cyanobacteria concentrations), the planning of the actions required under each situation (monitoring, management practice and treatment), and the use of the risk forecast to perform some of these actions from 2–3 days in advance. The methodology can be replicated to other case studies to facilitate the management of cyanobacteria risk and comply with the requirements of the revised European Drinking Water Directive adopted in 2020.