Stabilization pond

Stabilization pond technology - sometimes also called facultative pond technology - is a natural method for wastewater treatment.

Technology

Stabilization ponds ^[1]consist of shallow man-made basins comprising a single or several series of anaerobic, facultative or maturation ponds. The primary treatment takes place in the anaerobic pond, which is mainly designed for removing suspended solids, and some of the soluble element of organic matter (BOD). During the secondary stage in the facultative pond most of the remaining BOD is removed through the coordinated activity of algae and heterotrophic bacteria. The main function of the tertiary treatment in the maturation pond is the removal of pathogens and nutrients (especially nitrogen).

Application and suitability

Stabilization ponds are particularly well suited for tropical and subtropical countries because the intensity of the sunlight and temperature are key factors for the efficiency of the removal processes. ^[2] It is also recommended by the WHO for the treatment of wastewater for reuse in agriculture and aquaculture, especially because of its effectiveness in removing nematodes (worms) and helminth eggs.^[3]

Stabilization ponds, as described here, use no aerators. High-performance lagoon technology with aerators has much more in common with that of activated sludge. Such aerated lagoons are common in small towns in the United States, among other places.^[4]

Cost considerations

According to the IRC International Water and Sanitation Centre, stabilization pond technology is the most cost-effective wastewater treatment technology for the removal of pathogenic micro-organisms.^[5] A World Bank study carried out in Sana’a, Yemen, in 1983 makes a detailed economic comparison of waste stabilization ponds, aerated lagoons, oxidation ditches and trickling filters. According to this study, stabilization pond technology is a cheaper option up to a land cost of US$ 7.8/m2. Above this cost, oxidation ditches become the cheapest option. ^[6] However, often the main constraint against selecting this technology is not land cost but land availability. If land is available, stabilization ponds have the advantage of very low operating costs since they use no energy compared to other wastewater treatment technologies.

Use

Stabilization ponds are used for municipal waste water treatment in many countries with ample sunshine, including Colombia, El Salvador, Guatemala, Honduras, Israel, Jordan, Morocco, Nicaragua, Tunisia and Uganda.^[7] They are typically used in smaller towns where land availability and cost is less of a constraint. In some cities larger stabilization ponds have been replaced in the early 2000s by activated sludge waste water treatment plants, such as in Amman (Jordan) and in Adelaide (Australia) in 2004.^[8]

Removal of pathogens

A study of ten stabilization ponds in Honduras has shown that they were effective in removing helminth eggs, a pathogen, from the effluent and to satisfy the World Health Organization microbiological guidelines for Category B irrigation with wastewater effluent. However, sludge from all ponds was heavily contaminated with helminth eggs.^[9]

External links

• EPA Wastewater Technology Fact Sheet: Facultative Lagoons

References

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