Retention Pond & Polishing Pond Algae Control

Retention ponds are used in a number of situations to remove pollutants prior to discharge into receiving streams. Small ponds are often seen near parking lots, gas stations, or neighborhoods where the ponds are used to treat for oil sheen, fertilizer run-off, and other pollutants. Larger ponds are often found at the end of wastewater treatment systems and are vital for "polishing" the effluent by removing residual TSS while removing small quantities of BOD, ammonia, phosphate, or other criteria pollutants.

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When operating well, EPA found ponds remove

• TSS  - 67%
• Total Phosphate - 48%
• Total Nitrogen - 31%
• Nitrate - 24%
• Metals - 24.73%

While the ponds are effective and easily managed for much of the year, algae related TSS can become a treatment issue during summer months. The algae bloom is related to long days, warm temperatures and the residual nutrients (N & P) in the water. This algae related TSS increase can create problems with effluent permits, disinfection with UV or chlorine, and odors/appearance issues.

Best Long term Control Strategies

• Add mixers to circulate the contents of the pond. This is the greatest way to improve pond conditions and maintain a stable balance between bacteria, algae and pollution removal. I am a personal fan of the Solar-Bee type mixers from (http://www.medoraco.com)
• Use bacteria additives when needed to remove pollutants such as petroleum (oil sheen) or following periods where loadings have increased or washout occurred. The bacteria can also enhance sludge removal when coupled with mixers. Aster Bio's AB-10 has been tested in various ponds to help with problem pollution degradation and algae control.
  
• Copper sulfate is effective for rapid algae control, but is limited in effectiveness when no mixers are present. It is a short-run solution to the problem at best.
• Dyes that prevent photosynthesis by algae. This solution creates is expensive and makes the water look very unnatural. However, for very shallow, small ponds near a residence it can be a solution.