Total nitrogen removal in two-step biofiltration

Abstract

A one-year study was carried out on two semi-industrial submerged up-flow biofilters - a pre-denitrification (pre-DN) step followed by a nitrifying (N) step, designed to treat the primary settled municipal wastewater of a full scale plant for both carbon and nitrogen removal. Performances of the pre-DN step have been investigated showing high removal denitrifying capacities – 1 to 1.2 kg NO3−–N removed per m3 of reactor per day–, obtained with high TSS and carbon loading rates, at a water velocity up to 21.5 m3/ m2.h. The complete treatment plant – primary settlement + pre-DN/N loop – has demonstrated a nitrogen removal efficiency ranging from 70% without any additional carbon, up to 85% with methanol. COD and TSS removal rates were 91% and 97% respectively. The above results show that two submerged biofilters in series form a treatment line suitable for nitrogen removal. This technical choice leads to very compact full scale plants such as Ahlen WWTP (Germany, 85 000 PE).

Optimization of a full‐scale site to achieve total nitrogen removal through implementation of a denitrification‐submerged anoxic filter

“…The nitrate concentration in the feed was observed to vary between 2 and 18 mg NO 3 /L (with an average of 7.7 mg NO 3 /L; loading of 0.07–0.63 kg NO 3 /m 3 day) and the concentration of COD between 140 and 440 mg COD/L (an average of 315 mg COD/L) with loads between 2.4 and 5.9 kg COD/m 3 day. These values are in agreement with the literature that recommends nitrate‐loading rates of 0.6–1.2 kg NO 3 /m 3 day (Pujol & Tarallo ) and 1.9 kg NO 3 /m 3 day (Dee et al . ).…”

“…Loadings above 0.5 kg NO 3 /m 3 day, there was a complete utilization of the media, showing considerable removal in every cell of the anoxic SAF. The maximum loading rate could not be determined in this study but others investigating predenitrification submerged filters recommend nitrate loading rates between 0.6 and 1.2 kg NO 3 /m 3 day (Pujol & Tarallo 2000), 1.9 kg NO 3 /m 3 day (Dee et al 1994) for feed wastewater with COD < 450 mg/L, similar to the study here presented. Others studies present significantly higher nitrate loading rates for higher strength wastewaters, between 4.3 and 5.7 kg NO 3 /m 3 day for high C:N ratio of 10, that is, with an average influent BOD of 414 mg/L (Nikolavcic et al 2000) and critical nitrate loading rates of 9 kg NO 3 /m 3 day for C:N ratios between 3 and 3.9 using methanol dosing (Oh et al 2001).…”

“…Loadings above 0.5 kg NO 3 /m 3 day, there was a complete utilization of the media, showing considerable removal in every cell of the anoxic SAF. The maximum loading rate could not be determined in this study but others investigating pre‐denitrification submerged filters recommend nitrate loading rates between 0.6 and 1.2 kg NO 3 /m 3 day (Pujol & Tarallo ), 1.9 kg NO 3 /m 3 day (Dee et al . ) for feed wastewater with COD < 450 mg/L, similar to the study here presented.…”

“…Because the lowest retention time data (around 30 min) corresponded to the highest nitrate loadings into the anoxic SAnoF, it was difficult to establish a minimum admissible retention time. There is limited information available in the literature on the influence of HRT on denitrification efficiency on submerged filters, but HRT below 60 min have been demonstrated for nitrate‐loading rates between 0.6 and 1.2 kg NO 3 /m 3 day (HRT of 40–60 min) (Pujol & Tarallo ), 1.9 kg NO 3 /m 3 d (HRT of 15–60 min) (Dee et al . ), comparable with the study here presented.…”

Factors Affecting the Design and Operation of Biologically Active Filters

“…About 60 to 70% NO 3 -N removal was achieved in the pre-denitrification reactor at loading rates ranging from 0.1 to 0.6 kg NO 3 -N/m 3 ·d. During a one-year study, Pujol and Tarallo (2000) achieved about 68% NO 3 -N removal (or 0.9 kg NO 3 -N/m 3 ·d) with typical wastewater feed to the predenitrification BAF and up to 90% removal when additional substrate (methanol) was added. A range of recycle rates (150 to 350%) and corresponding filtration velocities (9.4 to 16.9 m 3 /m 2 ·h) also were tested.…”