Widespread harmful algae bloom (HAB) outbreaks have profound negative impacts: threats to human health and safety, stress on ecological systems, diminished quality of life, and significant economic loss to water-based recreational and commercial activities. They occur due to decades worth of nitrogen and phosphorus nutrient runoff deposited into our freshwater lakes and water bodies. Now, excess nutrient runoff and human activity have contributed to an uncontrollable rise in HABs across the globe. This ongoing accumulation of nutrients into our shrinking freshwater supplies combined with warmer temperatures has turned these precious water bodies into petri dishes for harmful algae growth. Removing the overabundance of nutrients is essential to restoring these water bodies and preventing the growth of future HABs.
Toxic Algae in Florida
To prevent flooding during the summer months in Florida, billions of gallons of Lake Okeechobee water are discharged through the Caloosahatchee River to the West and to the St. Lucie Canal on the East. But heavy rains in May 2018 caused excess nutrient pollution to be discharged into both waterways. This created an ecological catastrophe in which a rapid buildup of toxic algae created a hazardous green slime that coated the waterways, killed thousands of fish and marine life, and caused an unprecedented detrimental effect on downstream water quality. Residents left their homes, and businesses closed. In a mere three weeks, the bloom coverage grew from 30% to 90% of the lake's surface. Shortly thereafter, due to the significant areas of HABs in the surrounding seven counties, the governor declared a state of emergency.
Nutrient Interceptor and Removal System
Because of its ability to harvest algae cells intact, AECOM’s Nutrient Interceptor and Removal System (NIRS) harvesting technology was seen as the only viable technology that could help mitigate this crisis. By physically removing algae cells, which contain the key nutrients of nitrogen and phosphorus, NIRS eliminates the food source for algae growth. Yet, the removal of HABs and treatment of the toxic blue-green algae containing microcystin via the NIRS had never been conducted in a field application. Fortunately, a range of relevant disciplines allowed AECOM’s HAB team to quickly develop what is now a scalable, modular practical solution—and one that provided immediate relief for Florida.
NIRS uses a concept similar to the type of skimmers that are used to recover oil from the water’s surface during a spill. It selectively removes live algae from the phototrophic zone. This enables our system to capture highly concentrated algae cells in the water column, before they die and float to the surface. The collected algae is separated from the water and concentrated into a dense biomass. The separated water is then filtered within the NIRS system into a crystal-clear water stream and returned to the water body. The biomass is transformed into a paste that has re-use potential such as feedstock in the creation of biofoams or as an energy source for a biocrude that can be used to fuel the waterway’s own remediation process.
NIRS can capture and remove intact algal cells from the water column continuously throughout the year. It can be used to drastically reduce the nutrient loading into waterways and/or to restore eutrophic lake conditions by physically removing nutrients from the water. But most importantly, harvesting enables the platform to allow nutrient-rich water bodies to restore themselves over time. In addition, NIRS’ modular design and floatation separation technology allows the system to effectively operate in a wide range of environmental conditions. The modular system allows for cost-effective scalability to any size, which helps to address seasonal variability.
Additional Benefits
NIRS, the centerpiece of AECOM’s Algae Harvesting and Nutrient Reduction Program, provides a framework for restoring nutrient-impacted waterways worldwide. But improvement to water quality is not the only benefit. Because NIRS removes the algae cells intact, it yields a biomass that can be used as a feed stock for energy production and commercial products: renewable gas, fertilizer, shoes, and even surfboards. For example, algae biofoam is now being used as a replacement for toxic Ethylene Vinyl Acetate to provide a more environmentally sustainable product for the footwear industry.
Converting toxic algae into useful products demonstrates the potential of moving toward a more sustainable circular economy. The successful cleanup in Florida drew attention from the U.S. Department of Energy (DOE) Bioenergy Technologies Office Laboratories for NIRS’ potential to create a biocrude fuel source. And AECOM is currently collaborating with DOE’s National Renewable Energy Laboratory on a pilot test to determine the biofuel value of the recovered biomass.
AECOM is also in collaboration with the U.S. Army Corps of Engineers' Engineer Research and Design Center on a research program to demonstrate a scalable Hazardous Algal Bloom Interception, Treatment, and Transformation System (HABITATS) that can rapidly skim algae from impacted waterways, concentrate the algae suspension into a paste, and transform the concentrated paste into biocrude that can be used to fuel the remediation operation.
In freshwater systems, HABs have caused an estimated $4 billion in economic damages and losses annually in the United States. EPA has described nutrient pollution as “one of America’s most widespread, costly and challenging environmental problems.” It poses serious health risks to swimmers and the public in general, making these water bodies unsafe for human exposure. Across the globe, excess nutrient runoff and human activity have contributed to an uncontrollable HAB rise. Affected areas worldwide will likely continue to worsen year after year, especially if accompanied by population growth and uncontrolled nonpoint source discharges into our freshwater lakes and water bodies. Physically removing nutrients by harvesting live algae cells from our nutrient-impacted waterways provides one of the best sustainable solutions to combating this emerging ecological crisis. AECOM’s NIRS provides a practical, cost-effective solution to combating toxic algae blooms by physically removing nutrients that fuel algae growth from our waterways. The technology has been proven—and, importantly, can be implemented today.