Abstract

Nitrification yield can be affected by fixed biomass or biofilm density. Infact, biofilm detachment may influence the nitrification. The present experiment investigated the effect of detachment biomass cells on nitrifying bacteria expressed via nitrification rate. We monitored nitrification rates before and after biomass detachment from gravel sampled in a small-scale model of wastewater treatment using macrophytes in vertical and horizontal filtersystems. The ammonia-oxidizing bacteria (AOB) number decreased after cell detachment whereas the number of nitrite-oxidizing bacteria (NOB) was lower and saving a constant value of 3.0 MPN/100 ml. Despite this detachment, the yield of ammonium oxidation in the vertical filter remains constant but the reaction required more time. After washing, the NO₃^--N concentration at the bottom of horizontal filter with fine gravel is more important (1.24 mg/l) than that observed at the medium (1.1 mg/l) and the top (0.8 mg/l) of basin; whereas, at the horizontal filter with coarse gravel, the nitrification performance is more important at the medium of basin with NO₃^--N concentration value of 1.14 mg/l than those obtained at the top (0.7 mg/l) and the bottom (0.98 mg/l).

Key words: Autotrophic bacteria, detachment, nitrification, turbidity.