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Integrated fixed-film activated sludge ANITA™Mox process – a new perspective for advanced nitrogen removal
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2013
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ANITA™Mox is a Veolia moving‑bed biofilm reactor that has been validated at full scale for energy‑ and cost‑effective autotrophic nitrogen removal from sidestream effluent using anammox bacteria. The study seeks to boost ANITA™Mox performance under diverse operating conditions by improving substrate transport and accessibility within the biofilm. Two laboratory‑scale reactors—one IFAS and one MBBR—were operated and the distribution of anammox and ammonia‑oxidizing bacteria in sludge and biofilm was quantified with qPCR. The IFAS configuration achieved up to 8 g N m⁻² d⁻¹, 3–4 times higher than MBBR, because high MLSS promotes a 96 % biofilm‑resident anammox and 93 % suspended‑phase ammonia oxidizer distribution, a result confirmed in ongoing full‑scale trials and indicating a compact, robust process for mainstream and sidestream nitrogen removal.
ANITA™Mox is a Veolia process using moving-bed biofilm reactor (MBBR) technology tested and validated in full-scale for energy- and cost-effective autotrophic N-removal from sidestream effluent using anammox (ANaerobic AMMonium OXidation) bacteria. In order to increase the ANITA™Mox process performances under different operating conditions (e.g. mainstream and sidestream application), substrate transport and accessibility inside the biofilm must be enhanced. In this work, (i) two laboratory scale biofilm ANITA™Mox reactors were operated using different configurations (IFAS – integrated fixed-film activated sludge – and MBBR) and (ii) the distribution of the anammox (AnAOB) and ammonia-oxidizing bacteria (AOB) in the suspended sludge and the biofilm was characterized using molecular tools (qPCR). This study showed that in IFAS configuration, the ANITA™Mox process achieved very high N-removal rate (up to 8 gN/m².d), which was three to four times higher than that achieved in the pure MBBR mode. The high concentration of suspended solids (mixed liquor suspended solids (MLSS)) in the bulk obtained within the IFAS mode induces a very efficient bacterial distribution between the AOB and AnAOB population. AnAOB activity mainly occurs in the biofilm (96% of total AnAOB in the reactor), whereas nitritation by AOB mostly takes place in the suspended phase (93% of total AOB). This spatial distribution observed in the IFAS reactor results from a natural selection due to more easily substrate accessibility for AOB in the bulk (NH4+, O2) creating higher nitrite concentration in the bulk liquid compare to pure MBBR mode. The efficient control of MLSS level in the IFAS reactor is a key parameter to enhance the nitrite production by AOB and increase the substrate availability in the AnAOB-enriched biofilm leading to higher N-removal rate. These promising results obtained at laboratory scale have been further confirmed in on-going full-scale IFAS ANITA™Mox trials opening new roads for the widespread application of a very compact and robust ANITA™Mox process for sidestream but also mainstream cost-effective N-removal.