Skimming and Harvesting

There is little available detail on the technologies for skimming or harvesting cyanobacteria from natural systems. A large surfactant, flotation, skimming, ozonation technology has been used in a pilot project in Florida (Page et al. 2020) that shows promise for removal of cyanobacteria and possible cyanotoxin destruction. A second project is a skimming application in Southampton, New York (Southampton Press 2019). Although harvesters for submerged aquatic plants are known and used occasionally for removal of invasive submerged grasses, such as Hydrilla spp. (McGehee 1979), data that support the removal of cyanobacteria biomass from concentrated blooms with these techniques are limited.

PLANKTONIC	BENTHIC
EFFECTIVENESS Water body types: Pond, lake/reservoir, bay/estuary, systems allowing scum formation Any surface area or depth Water body uses: Any, except perhaps drinking water sources Any trophic state Any mixing regime Reported (no data) treatment of 100 M gal/day	EFFECTIVENESS No available studies
NATURE OF HCB Scum-forming or floating HCBs Singular or repeating HCBs Toxic and nontoxic HCBs Intervention strategy	NATURE OF HCB No available studies on benthic cyanobacteria
ADVANTAGES Biofuel production from harvested biomass is proposed Low potential for adverse impacts High volumes of surface scum biomass can be harvested	ADVANTAGES No available studies on benthic cyanobacteria
LIMITATIONS Limited data Huge capital investment for reagents, air flotation technology, ozone, and operations and maintenance May not be scalable Hazardous waste designation for collected biomass possible Indiscriminate removal Scum is collected, so there may be surface water criteria concerns Unknown costs Need partners for post-collection commercial use	LIMITATIONS No available studies on benthic cyanobacteria Not selective to cyanobacteria May spread benthic mats that reproduce by fragmentation Disruptive of habitat Generates high turbidity Decay of disrupted macrophytes may negatively impact water quality

The sole estimate found for efficacy of harvesting and skimming is the 2019 Florida pilot project (Page et al. 2020). Unfortunately, much of the cyanobacteria present in this study were subsurface, and there was little cyanotoxin (microcystin) detected. Most results were for nutrient removal, but this method was quite effective in removing nitrogen and phosphorus, which are mostly found in the cyanobacteria biomass. There were two major limitations for the technology, however: huge capital and operations and management costs, as well as very high energy demand. Page et al. (2020) argued that these costs could be reduced if the harvested biomass could then be converted to biofuels and sold, but that technology is still in development.

As both skimming and flotation cannot remove an entire bloom, the remaining populations could re-seed and cause additional blooms. For skimmed cyanobacteria without biofuel conversion, the collected material could be considered hazardous waste with associated costs for its disposal. Subsequent disposal of harvested biomass may be limited depending on cyanotoxin content of the collected biomass.

COST ANALYSIS

Costs are relatively low for simple skimming and very high for surfactant-flotation-skimming-ozone treatment. Specific equipment for skimming or harvesting would be required, and some form of power would be needed. The relative costs below are for skimming only and surfactant-flotation-skimming-ozonation. If harvested biomass can be processed for commercial uses, net overall cost may be reduced. Whether funds recovered from the sale of the collected material are passed on to the lake manager to reduce their costs is unknown.

Relative cost per growing season: Skimming and harvesting

ITEM	RELATIVE COST PER GROWING SEASON
Material	$$–$$$
Personal Protective Equipment	$$
Equipment	$$–$$$
Machinery	$$–$$$
Tools	$–$$$
Labor	$$–$$$
O&M Costs	$–$$$
Delivery	$$$
OVERALL	$$–$$$

REGULATORY AND POLICY CONSIDERATIONS

Collected biomass may include intracellular cyanotoxins, so appropriate use of the harvested biomass will depend on the material’s cyanotoxin concentration. If nontoxic, landfill application or use as wet fertilizer might be possible; composting would likely be allowed, but authorities would need to be contacted for local regulations. If processors can be found for use in the synthesis of commercial products such as foam rubber or biofuels, disposal permitting may not be necessary. If cyanotoxins are present, then permits for use of the collected biomass would be needed, and local and state officials should be contacted. For both toxic and nontoxic biomass, harvesting would remove cellular nitrogen and phosphorus, assisting in nutrient removal from impacted water bodies and therefore possible “credit” for TMDLs in a watershed.

REFERENCES

McGehee, J. T. 1979. “Mechanical hydrilla control in Orange Lake, Florida.”  Journal of Aquatic Plant Management 17:58-61.

Page, Martin A., Bruce A. MacAllister, Angela. Urban, Christopher L. Veinotte, Irene E. MacAllister, Kaytee L. Pokrzywinski, Jim. Riley, Edith Martinez-Guerra, Craig S. White, Chris. Grasso, Alan James Kennedy, Catherine C. Thomas, Justin. Billing, Andrew Schmidt, Dan. Levy, Bill. Colona, David. Pinelli, and Chandy. John. 2020. “Harmful Algal Bloom Interception, Treatment, and Transformation System, “HABITATS”, ERDC TR-20-1.” Champaign, IL: U. S. Army Corps or Engineers. Construction Engineering Research Laboratory. https://hdl.handle.net/11681/35214.

Southampton Press. 2019. “Governor Cuomo and DEC Launch Blue-Green Algae Removal Pilot Program In Southampton Village.” The Southampton Press, 10/3/2019, Environment/Neighborhood. https://www.27east.com/southampton-press/governor-cuomo-and-dec-launch-blue-green-algae-removal-pilot-program-in-southampton-village-1540878/.