THE TREATMENT TRILOGY OF FLOATING FILTERS - FROM PILOT TO PROTOTYPE TO PLANT

The basic kinetic expressions developed in non-aerated biofilms (denit rification and RBCs) were verified on granular floating media in aerat ed filters. The limiting parameters of biofilms were verified on a sma ll scale lab unit, using wastewater and media from full scale. It coul d be shown that the observed relationships corresponded to theoretical expectations and half-order kinetics as well as the significant const ants were established. Maximum surface removal rates were measured as 1.7 g N-NH4/m(2) d for nitrification, and the most limiting parameter was a half-order oxygen concentration close to saturation. Similar kin etics as on small scale were observed on a full-scale prototype of a n ew floating aerated biofilter, which can be used for both nitrificatio n and denitrification, as well as complete nitrogen removal from settl ed wastewater in one reactor. The mixed biofilm nitrified 15 % less th an pure tertiary treatment, and 20 % performance was lost between lab and full scale, due mainly to aeration limitations. Also, 35 % lower d enitrification rates were observed between ethanol and sewage as carbo n source, but addition of ethanol raised the full-scale performance to nitrate removal rates of 1,4 g N-NO3/m2 d. After pilot testing and fu ll-scale demonstration, the process was implemented on several treatme nt plants, one of which was located in Denmark,to achieve nitrogen res iduals below 8 mg TN/1. This plant uses 8 filters of 63 m2 to treat 12 000 m3/d, and the biological reactor occupies a surface similar to th e existing conventional primary settler. The results of the first few months of operation are given: as long as the ratio between biodegrada ble COD and total nitrogen at the filter inlet is above 5, nitrogen re moval of 80 % is achieved.