The application of anaerobic digestion (AD) for the co-treatment of waste activated sludge (WAS) and of the organic fraction of municipal solid waste (OFMSW) results in the production of an anaerobic effluent which has particular characteristics and must receive adequate post-treatment for the removal of nutrients. In this work, the short-cut nitrogen removal (SCNR) and denitrifying phosphorus removal via nitrite (DPRN) were studied using a sequencing batch reactor (SBR) for the treatment of the anaerobic supernatant. The long-term stability and behaviour of the biological via-nitrite processes were examined under ordinary and extraordinary operation of the full scale AD plant and the dewatering process. Nutrients removal was tested at low volumetric nitrogen loading rates (vNLR = 0.2 kg m-3d-1), at the vNLR of the system’s nitrifying capacity (0.8 kg m-3d-1) and above its nitrifying capacity (1.1 kg m-3d-1). The feasibility of applying low-cost external carbon sources produced from the pre-treatment of OFMSW and other biowaste was tested; these include fermentation liquid (FL) and liquid drainage (LD) from OFMSW, and FL from cattle manure and maize silage (CM&MS). Complete washout of nitrite oxidizing bacteria (NOB) was accomplished (i.e. 100% NO2-N/NOx-N) at all times, even when the free ammonia (FA) concentration in the reactor was very low (<0.45 mg NH3-N L-1). The type of external carbon source critically impacted on the specific nitrite uptake rate (sNUR) with acetic acid and CM&MS resulting in high specific denitrification rates. DPRN was very effective when all three carbon sources were used and particularly when FL from OFMSW was applied.
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