Enhancing Stormwater Ponds with Biological Treatment

Hydraulic retention basin setup to treat stormwater. Note the mixer and native plants in the photo.

Stormwater ponds are often designed to slow runoff from rainfall surging into local waterways. When operators notice hydrocarbon sheen, you often see oil adsorbent booms or vacuum truck skimming. To help reduce downstream pollution levels and eutrophication, we need to realize storm water ponds are biological treatment units and can be operated to improve non-point source pollution entering local waters. Enhancing biological treatment can involve aeration, mixing, and promoting microbial populations. With a biologically active stormwater system, you can achieve an ecological balance that can better degrade hydrocarbons, pesticides, herbicides, and excess nutrients.

Aeration and Mixing: Oxygen as a Catalyst
Aeration is essential for maintaining aerobic conditions, which support beneficial microbial activity. Proper aeration helps break down hydrocarbons and remove nutrients while preventing stagnation that can lead to poor water quality. Example aeration strategies include: 

• Diffused aeration systems including newer micro & nanobubble systems which elivering oxygen directly into deeper pond areas, encouraging aerobic degradation.
• Surface aerators or fountains for enhancing oxygen transfer while promoting circulation. 
• Mechanical mixers for preventing stratification and to ensure pollutants are evenly distributed for treatment. 
  
  

Managing Ecological Relationships in Stormwater Treatment
A balanced interaction between bacteria, algae, and plants is essential for optimizing the biological treatment process. With each playing distinct role: 

• Bacteria
  These microorganisms break down hydrocarbons and other pollutants while transforming excess nutrients into forms that plants and algae can assimilate. At times, it is beneficial to use bioaugmentation to encourage and maintain a diverse bacterial population. 
• Algae
  While excessive algal growth can be problematic, controlled algae populations contribute to nutrient cycling and oxygen generation through photosynthesis. Ensuring an optimal balance prevents harmful algal blooms while promoting natural water purification. 
• Aquatic Plants
  Rooted vegetation and floating wetlands help stabilize nutrient levels by absorbing excess phosphorus and nitrogen. They also support bacterial growth by providing habitat surfaces for microbial communities. 
  
  

Strategies for maintaining the target biological mix include: 

• Selective bioaugmentation
  Introducing beneficial bacteria strains that enhance pollutant degradation without promoting excessive algae growth. 
• Integrated plant management
  Selecting native species that efficiently uptake nutrients while minimizing competition with bacterial activity. 
• Natural cycling optimization
  Using seasonal adjustments, organic nutrient supplementation, and controlled aeration to maintain ecological balance. 

By combining these approaches, stormwater ponds can become dynamic treatment systems capable of improving water quality naturally. Biological treatment not only enhances pollutant removal but also supports biodiversity and reduces reliance on chemical interventions. Implementing these strategies ensures stormwater ponds continue serving as effective and sustainable water management tools in urban environments.