What causes algae growth?
ROLE OF ALGAE IN LAGOON SYSTEMS
In lagoon systems algae play a natural role in biological
waste treatment. Algae are photosynthetic organisms
(require sunlight) and prefer warmer temperatures,
long hydraulic retention times, light, high phosphorus
concentrations, and inorganic materials (alkalinity is an
inorganic carbon). Algae produce oxygen during the
daylight hours, and consume oxygen at night. The
oxygen they produce is necessary for treatment, and
in facultative lagoon systems that don’t have
supplemental aeration, this and aeration from wind
Actinastrum Green Algae
and turbulence are the only means of dissolved
oxygen. Algae consume alkalinity (carbon dioxide and
carbonate) and if alkalinity is limited, this can increase the pH to above 9 in some instances, which
precipitates phosphorous (a form of phosphorus removal). While algae grow naturally in lagoon
processes, overgrowth can cause problems of increased suspended solids and BOD in the final effluent
and should be avoided.
COMMON CONTROL STRATEGIES FOR ALGAE
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Reducing Sunlight
Reducing Phosphorus
o Including phosphate released from bottom (benthic layer)
Dissolved Air Floatation in effluent or tertiary filtration
Reducing Hydraulic Retention Time
Taking a cell with an algae bloom offline and waiting for the algae to die off
Duckweed Cover
o If not maintained properly, can be a major source of effluent BOD
Addition of algae competitor (such as daphnia and rotifers)
Constructed wetlands to polish effluent
Chemical Addition such as Copper Sulfate
o Must be applied carefully and before the algae bloom occurs
Chlorination
o At low doses, can flocculate the algae, at higher doses, will cause cell lysis which can
increase effluent BOD