Facultative lagoons

Anaerobic ponds are loaded such that anaerobic conditions prevail throughout the Hquid volume. One of the major problems with anaerobic ponds is the generation of odors. The odor problem can frequentiy be eliminated by the addition of sodium nitrate at a dosage equal to 20% of the appHed oxygen demand. An alternative is the use of a stratified facultative lagoon, in which aerators are suspended 3 meters below the Hquid surface in order to maintain aerobic surface conditions, with anaerobic digestion occurring at the lower depths. 

Effluent quahty from facultative lagoons is related primarily to the suspended solids created by living and dead microbes. The long retention period in the lagoons allows the microbes to die off, leaving a small particle that settles slowly. The release of nutrients from the dead microbes permits the algae to survive by recycling the nutrients. 

Phases gas-hquid bio solid liquid plus bio solid. Liquid plus bio solid anaerobic digesters (conventional first stage) batch microbiological treatment of municipal sludge no mixing use for <50 mVs. Other options include anaerobic ponds, facultative lagoons and ponds, and aerobic ponds. 

Facultative lagoons and ponds use when the price of land is inconsequential. Low flows with COD about 500 mg COD/L and TSS about 500 mg TSS/L. 

Facultative lagoon with surface aeration residence time = 7-20 d, usually 4-8 d, and longer in cold temperatures loading 40-130 pg BOD5/S m depth 2.4-4.S m surface aeration power to oxygenate. 

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