The use of wastewater treatment lagoons, or stabilization ponds, is a common practice for rural municipalities and industrial facilities. Through the years there have been numerous designs for these ‘sludge settling basins,’ ranging from facultative, partial aerated, and fully aerated systems. But the primary reason for these systems is to utilize relatively shallow earthen ponds, or lagoons, for the purpose of sludge settling and stabilization. Over the years, the technologies for these lagoons has changed little except to line them to protect groundwater from contamination and the addition of multicelled lagoon systems for the purpose of adding mechanical oxidation for quicker treatment and effluent water polishing.
The other things that have changed are the encroachment of growing populations and plant expansions that often pose problems for both the lagoons and the populations around them. Noxious odors, which are caused by the insufficient digestion and buildup of the sludge on the bottom of aerated lagoons, become a primary problem. Space limitations become a major problem as populations grow, and new, or larger, cells are required in the lagoon system. Finally, the efficiency of these lagoons is dependent on a myriad of conditions that range from environmental to design limitations. Sludge reducing bacteria populations must constantly be assessed, sludge depth and water temperatures are usually in constant flux and aeration equipment and the energy to run them is expensive and causes ever increasing maintenance and maintenance costs.
The Lagoon Aeration Process
In the more advanced waste lagoon systems there is an aeration process that is supposed to –
- Provide oxygen to aerobic bacteria that convert and oxidize the organic material in the wastewater.
- Provide mixing in order to distribute dissolved oxygen and bring aerobic organisms into contact with organic sludge.
- Provide enough mixing to allow solids to become suspended for quicker digestion and oxidation by the aerobic bacteria. If this does not take place, solids will build up on the bottom, eventually requiring the very expensive process of sludge removal from the lagoon bottom.
Over the years the methods of aerating these lagoons has changed little. The primary aeration techniques used for earthen waste lagoons are:
- Hose bubbler systems that utilize large, housed, industrial blowers.
- Diffused air grids that also utilize large industrial blowers.
- Low horsepower spray aerators.
- Paddle-wheel, or brush, aerators.
- Large circular surface mixers.
- Floating air induction aerators.
- Solar powered mixers.