In this article
The most reliable way to prevent algae in a wastewater lagoon is to keep the water moving: aeration and surface mixing block the calm, sunlit conditions algae need. Covers, barley straw, dyes and ultrasound can help, while chemicals kill algae but can upset treatment. Algae matter because they are usually the main source of effluent TSS and BOD.
Key takeaways
- Algae drive high effluent TSS and BOD, DO swings, odors and sludge.
- Prevention beats treatment: aeration and mixing that reach the whole surface work best long term.
- Covers, barley straw and ultrasound help; chemicals can harm treatment bacteria and need approval.
Why is algae a problem in a wastewater lagoon?
- High TSS and BOD. Each mg/L of algal TSS adds roughly 0.5 mg/L of BOD. Algae can push effluent TSS and BOD above what came in.
- DO swings. Algae make oxygen by day and use it at night, leaving less for BOD-removing bacteria. A sudden die-off can crash DO.
- Nutrient feedback. Algae take up ammonia and phosphorus, then release them as they die.
- Odors. Low DO and decaying mats cause earthy, grassy or rotten odors.
- Sludge. Dead algae sink and add to the sludge blanket.
What are the options for lagoon algae control?
| Method | Prevents or treats | Effort | Main drawback |
|---|---|---|---|
| Aeration and mixing | Prevents | Low once installed | Upfront cost; must move the whole surface |
| Hydraulic retention time (HRT) | Prevents | Design change | Shorter HRT can hurt BOD and pathogen removal |
| Baffles | Prevents | Moderate | Construction; mainly stops short-circuiting |
| Controlled discharge | Limits algae in effluent | Low | Needs extra storage |
| Covers or dyes (shading) | Prevents | Moderate | Covers cut oxygen transfer; some regulators ban dyes |
| Barley straw | Prevents (not existing blooms) | Replace every 1–2 months | Adds BOD and sludge as it breaks down |
| Ultrasound | Prevents | Low | Less proven in wastewater than in lakes |
| Chemicals (copper sulfate, chlorine) | Treats | Low to moderate | Can harm treatment bacteria; copper builds up in sludge |
| Filtration | Treats effluent | High | Backwash returns algae to the lagoon |
| Raking or skimming | Treats | Very high | Rarely keeps up |
How does each method work?
Aeration and mixing
Surface turbulence limits the sunlight algae need, helps strip excess CO2 and keeps slower-growing algae from taking hold. Coarse-bubble systems create the most surface turbulence; fine-bubble systems create mild turbulence but transfer more oxygen. Surface aerators create a lot of turbulence near the unit, but the energy often does not reach the rest of the lagoon. Ares Aeration® combines fine and coarse bubble in one portable unit.
Retention time
Lagoon pioneer Linvil Rich of Clemson University called hydraulic retention time the most influential factor in algae growth: the shorter the HRT, the less time algae have to grow. HRT still has to be long enough to treat BOD and pathogens.
Baffles
Splitting a lagoon into smaller cells prevents short-circuiting and lets you discharge from the cell with the best water. See how to prevent lagoon short-circuiting.
Controlled discharge
Discharge from the cell with the best water quality, a few inches below the sunlit surface layer where there are fewer algal cells. Algae move up and down with the light, so discharging at night is usually cleaner than in the afternoon.
Covers and dyes
Floating insulated covers such as AlgaeProtect block the sunlight algae need, over all or part of the surface. Dyes do the same, but some regulators do not allow dye in the discharge. Any surface cover also blocks oxygen transfer from the air, so plan for supplemental aeration. Duckweed shades out algae too, but brings its own problems; see duckweed control.
Barley straw
Rotting barley straw releases compounds that inhibit algae. It prevents new growth but does not treat existing blooms, so put it in early in spring, before the water warms, and replace it every month or two. Research notes it works best with good aeration, neutral to alkaline pH and open, sunlit water. More in Can barley straw prevent lagoon algae?
Ultrasound
Sound waves inhibit algae growth and can be tuned to the type of algae present. Ultrasound uses little power and has worked in lakes and drinking water reservoirs; results in wastewater lagoons are less proven.
Chemicals
Copper sulfate and chlorine kill algae quickly, but they can upset the lagoon’s biology and slow BOD treatment. Copper builds up in sludge and complicates disposal, and a sudden die-off can crash DO. Check with your regulator before using any additive.
Filtration and raking
Intermittent sand filters can remove algae, but returning the backwash to the lagoon just recycles it. Raking or skimming is labor-intensive and rarely keeps up.
Prevention beats treatment
Algae blooms are both a symptom (high nutrients, calm water) and a cause (higher BOD and TSS). A properly aerated and mixed lagoon should see only minor algae at the edges in the hottest months. If blowers or aerators are out of service, fixing them comes first. If the system is undersized or worn out, compare lagoon aeration options.
Frequently asked questions
What is the best way to prevent algae in a wastewater lagoon?
Keep the water moving. Aeration and mixing that reach the whole surface limit the calm, sunlit conditions algae need.
Do lagoon covers prevent algae?
Yes. Covers block the sunlight algae need, but they also block oxygen transfer from the air, so the lagoon usually needs supplemental aeration.
Does barley straw work in wastewater lagoons?
It can prevent new growth if it goes in before the water warms, but it does not kill existing algae and adds BOD and sludge as it breaks down.
Is copper sulfate safe for a lagoon?
It kills algae but can harm treatment bacteria, builds up in sludge and may need a permit. Use it only with your regulator’s approval.
Why is my lagoon effluent TSS high in summer?
Algae are usually the main cause. See troubleshooting high pond TSS.
Stop algae before it starts. Ares Aeration® pairs fine-bubble oxygen transfer with coarse-bubble mixing to keep the whole lagoon moving.
