Oxidation Lagoons

Oxidation Lagoons

	Oxidation Lagoons Oxidation ponds are also known as stabilisation ponds or lagoons. They are used for simple secondary treatment of sewage effluents. Within an oxidation pond, heterotrophic bacteria degrade organic matter in the sewage which results in production of cellular material and minerals which supports the growth of algae in the oxidation pond. Growth of algal populations allows further decomposition of the organic matter by producing oxygen. The production of this oxygen replenishes the oxygen used by the heterotrophic bacteria.
Typically oxidation ponds need to be less than 10 feet deep in order to support the algal growth. In addition, the use of oxidation ponds is largely restricted to warmer climatic regions because they are strongly influenced by seasonal temperature changes. Oxidation ponds also tend to fill (become shallow), due to the settling of the bacterial and algal cells formed during the decomposition of the sewage. Overall, oxidation ponds tend to be inefficient and require large holding capacities and long retention times. The degradation is relatively slow and the effluents containing the oxidised products need to be periodically removed from the ponds. Microbes grow as suspended particles within the water column rather than as biofilms. As oxygenation is usually achieved by diffusion, and by the photosynthetic activity of algae these systems need to be shallow. Sewage is subjected to primary settling and is subsequently channelled through a series of oxidation ponds.
Treated sewage is discharged into surface waters. Partially treated sewage is used for ground water recharge. Primary pond re-aerates the oxygen-depleted water. After settling of most of the algal and bacterial biomass, the water is transferred to large shallow infiltration ponds. From these ponds, water flows through sand and soil layer and slowly returns underground.
Clogging of infiltration ponds (undegraded microbial polysaccharide and accumulation of iron sulphide) is a recurrent problem in ground water treatment operation. Problem is countered by periodic rest periods for infiltration basins which allow degradation of the excess polysaccharides and re-aerates the sediment of oxidation pond with the oxidation of clogging iron sulphide.

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