In many areas, wastewater and stormwater go through facultative or moderately aerated lagoon systems prior to discharge. These lagoons remove residual oragnics, nutrients, and solids that can pass through the upstream treatment. In the case of stormwater, the lagoons remove nutrients from fertilizer runoff and hydrocarbons from parking lots/roads. Unlike modern wastewater treatment sytems, the lagoons have low levels of biomass (MLSS) that can range from 30 - 100 mg/L volatile solids. The solids component consists of:
The reason for ammonia appearing and AOB growing during summer months is a phenomenon related to sludge degradation on the pond bottom. While the sludge layer degrades all year, the rate of anaerobic lysis increases with summer temperatures. The pond bottom remains anaerobic/anoxic producing organic acids, methane, and nutrients (N, P). The upper layers have oxygen present from algae photosynthesis, natural diffusion from the surface, and action of mixers/aerators if present. In ponds with more sludge, the problems related to ammonia release and algae blooms tend to cause more problems. So what can be done to control this other than a big mechanical dredging project?
- Residual TSS from wastewater treatment - both living organisms and non-living components
- Facultative bacteria that thrive in the low F/M environment (we actually see AOB thriving in ponds with high sludge levels during summer months)
- Algae - both eukaryotic and cyanobacteria. Often excess phosphorus can trigger a cyanobacteria bloom causing problems with TSS, odors, and pH.
The reason for ammonia appearing and AOB growing during summer months is a phenomenon related to sludge degradation on the pond bottom. While the sludge layer degrades all year, the rate of anaerobic lysis increases with summer temperatures. The pond bottom remains anaerobic/anoxic producing organic acids, methane, and nutrients (N, P). The upper layers have oxygen present from algae photosynthesis, natural diffusion from the surface, and action of mixers/aerators if present. In ponds with more sludge, the problems related to ammonia release and algae blooms tend to cause more problems. So what can be done to control this other than a big mechanical dredging project?
- Add mixers for low velocity, high volume movement. The mixer circulates water from anerobic zone to the upper aerobic regions, allowing for more effective sludge stabilization/nutrient removal. We are also seeing benefits from adding new micro & nanobubble aeration technologies here too.
- If mixers are not enough to control the problem, you can then use algae control methods inclusing sonic systems, copper sulfate, and biological algae control methods.
- If sludge layer is visible at the surface and has produced "islands" - then it is time to evaluate dredging or various biodgredging technologies. If the sluge has a high organic fraction, then biodredging may prove less costly and effective.
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