Wastewater treatment lagoons are wide spread in the US with more than 6,000 plants in use. Especially in areas with a low population density, lagoons are proven to be a good solution as they require only little construction and operation cost.
However changing influent values due to population growth, new industries or other effects can cause an overloading of the lagoon. The most typical signs of an overloaded lagoon are:
Excessive sludge production and odors
Increasing BOD and TSS influents result in undigested sludge which is settling to the bottom of the lagoon and taking up valuable space. This leads to slow, anaerobic processes so that more and more sludge is built up over time. When the sludge starts to float and odor appears, the lagoon has turned over.
A healthy, efficient wastewater lagoon has a clear sparkling green, blue or brown color. A firm blue-green color however indicates increased algae growth. Excessive algae growth prevents sunlight from reaching deeper areas of the lagoon so that oxygen levels decrease. In summer times the lagoon might also have a green leafy covering of Duckweed. Duckweed has the same effect as excessive algae growth.
White, odorless foams on the surface of the lagoon are normally an indication for detergents or other foam forming materials in the influent. On the other hand brown, dark foam is often a consequence of a wrong F/M ratio.
All of the described indicators of overloaded lagoons go along with changing DO (dissolved oxygen) and PH levels. Therefore, the DO and PH levels of lagoons should be occasionally checked e.g. with portable testing kits. In most cases increased aeration will correct an overloaded lagoon and improve their performance. As water levels in a lagoon plant can normally not be lowered, fixed aeration systems are very difficult to install and lagoon bypasses are expensive. Therefore retrievable diffuser aeration systems – as supplied by AET – are a cost effective solution for oxygen deficient lagoons.