Microphyte and macrophyte-based lagooning in tropical regions

A 720 m² plant made of 8 ponds in series, set in Yaounde (Cameroon), was successively operated as a macrophyte-based system (type M) from November 1997 to October 98, a microphyte-based system (type m) from October 1999 to September 2000 and a combination of macrophyte and microphyte ponds (type M+m) from May to July 2001. Average applied loads varied over the years; from 420 kg. BOD₅ ha⁻¹ d⁻¹ on the year 1997/98, the loads reached 510 kg BOD₅ ha⁻¹ d⁻¹ in 1999/2000 and 500 in 2001. Though the system became more and more overloaded and sludge accumulated rapidly in the first ponds, it provided average removals of SS, BOD₅ and COD that were always higher than 90% whatever the type of lagooning. Performances in the removal of SS, organic matter and the abatement of N-NH₄⁺ and PO₄³⁻ did not significantly differ according to the type of lagooning and the applied load. Macrophyte lagooning did not show any definitive superiority as to nutrient removal when compared to microphyte lagooning. Microphyte lagooning was the most effective process in faecal indicators removal.