Municipalities may generate recycled water that is susceptible to cyanotoxin-producing cyanobacteria when the nutrient rich water is stored in warm, shallow holding ponds prior to distribution. Standard water quality management practices to prevent cyanobacteria blooms in natural waterbodies seek to decrease external nutrient loadings and control nutrients that have accumulated in the sediment. However, notably decreasing nutrient levels in recycled water ponds would require costly upgrades to wastewater treatment plants that generate the recycled water. Thus, common lake and reservoir management techniques need to be modified or used in combination with other approaches to control cyanobacteria blooms within recycled water storage ponds.
A municipality requested RBI’s assistance in developing a mitigation and management plan to address toxin-producing cyanobacteria in their recycled water storage ponds. RBI conducted an engineering feasibility study to provide a cost-effective management approach for the municipality to implement in their recycled water holding ponds. RBI incorporated on-site equipment that was already owned by the municipality as part of the feasibility study to control costs. In developing the plan, RBI considered a range of mitigation options and developed a cost-benefit analysis. Municipality preferences for equipment types were incorporated when developing potential mitigation strategies. The mitigation strategies were then evaluated in terms of effectiveness in limiting cyanobacteria production, capital costs, operation and maintenance costs, and impacts to facility operations. A proposed mitigation strategy was determined based on the ability to minimize cyanobacteria production and impacts to facility operations, and maximize cost-effectiveness.