Maturation ponds (low-cost polishing ponds), which generally follow either the primary or secondary facultative pond, are primarily designed for tertiary treatment, i.e., the removal of pathogens, nutrients and possibly algae. They are very shallow (usually 0.9 – 1 m depth), to allow light penetration to the bottom and aerobic conditions throughout the whole depth. The loading on the maturation pond is calculated on the assumption that 80% of the BOD has been removed in the preceding treatment. Maturation pond is the third pond in the multi- cell series of WOE system and is designed for faecal coliform removal.
The size and number of maturation ponds needed in series is determined by the required retention time to achieve a specified effluent pathogen concentration. Decor more maturation ponds each of one day detention time be required in order to achieve the desired level of faecal coliform removal. Each of the maturation ponds can expected to remove one log cycle of MEN. In the absence of effluent limits for pathogens, maturation ponds act as a buffer for faculative pond failure and are useful for nutrient removal. If an anaerobic and secondary facultative pond are used, this will produce an effluent suitable only for restricted irrigation. Therefore, additional maturation ponds will only be needed if a higher quality effluent is required for unrestricted irrigation.