Rural Wastewater Treatment Lagoon Enhancement with Dome Shaped Submerged Bio-film Devices

Shallow lagoon systems are the most common form of engineered domestic wastewater treatment in the United States and the world. Municipalities, particularly smaller rural communities, use this low cost treatment method. These lagoon systems are generally effective at reducing biochemical oxygen demand (BOD) to acceptable levels prior to discharge. They are generally ineffective at nutrient removal, specifically nitrogen and phosphorous compounds dissolved in the discharge water. The biological removal of nitrogen compounds takes place in two stages when naturally occurring nitrifying, then denitrifying bacteria consume them. Biological removal of dissolved phosphorous compounds occurs through uptake by a class of bacteria known as polyphosphate accumulating organisms (PAOs). In open lagoon systems, these nutrient consuming bacteria are generally out-competed by the more robust bacteria that consume the carbonaceous BOD, and do not proliferate. Because of this, municipalities using lagoon systems often have difficulties meeting nutrient discharge requirements. To promote the proliferation of nitrifying and denitrifying bacteria and PAOs in shallow lagoon systems, specially designed aerated dome structures (Poo-Gloos) have been developed. These dome structures are nested hemispheres made out of ABS black plastic. Fine-bubble diffuser hose is attached in the gap between the inner and outer annulus around the bottom of each dome. Nested dome structures are mounted on a sturdy base and rest on the bottom of a lagoon so they are fully submerged. The space between the dome shells is filled with a high surface area to volume packing material made out of polypropylene plastic. Low-pressure air is supplied to the diffusers and the released bubbles travel up the inside of each dome. The dome structures retard the upward movement of the aeration bubbles, forcing the bubbles against naturally occurring bio-film colonizing the surfaces, promoting oxygen transfer. The rising air bubbles also drag the wastewater up from near the bottom of the lagoon, along through the insides of the dome structures, and out the top. This promotes micro-mixing of nutrients into the bio-film. By providing surface area, oxygen, mixing, and blocking of sunlight, these dome structures greatly enhance the growth and metabolism of nitrifying bacteria. In addition, denitrifying bacteria proliferate in the deeper portions of the inside bio-film surfaces as well as the non-aerated backside surfaces of the domes and during times the aeration bubbles are cycled off. The performance of PAOs is also enhanced by aeration cycling. This cycling should provide the necessary aerobic/anoxic/ anerobic phases for these bacteria. The benefit to rural communities will be a low-cost technology that can be manufactured in rural areas, and can be easily added to existing lagoon systems. The installed dome structures will increase lagoon performance, allowing the communities to meet increasingly stringent nutrient level discharge requirements while retaining existing lagoon systems.