Influence of the suspended and attached biomass on the nitrification in a two submerged biofilters in series system

The performance and stability of a system formed by two submersed filters i n series for removing organic matter, solids and ammonia nitrogen from urba n wastewater were tested. The wastewater was pretreated through a fine scre ening (through a 1.5 mm sieve) and primary settlement, before entering the first filter. The hydraulic retention time (HRT) in both filters was adjust ed to 2 hours. Superficial velocities of 1 m/h for the liquid and 8 m/h for the air were maintained throughout all the experiments. The averaged remov al percentages of organic carbon and solids were the following: 84% of TSS, 85% of VSS, 88% of total GOD, 86% of soluble COD and 93% of total BOD5. Fi lter backwash was conducted when the observed head loss through the filter raised up to 1.2 m of water column. Substratum particles were sampled from both filters for measuring the conce ntration of retained biomass in the two forms: attached (as Volatile Attach ed Solids, VAS) and suspended (as Volatile Suspended Solids, VSS) biomass. The activity of these solids was also determined by closed respirometry ass ays, which revealed that the biomass retained between the substratum partic les as suspended biomass showed much higher activity that the attached biom ass. The suspended biomass retained in the filter was responsible for remov ing most of the soluble COD and ammonia, while most of the nitrite oxidizer s were inside the biofilm.