Performance of high-loaded ANAMMOX UASB reactors containing granular sludge

The performance of high-loaded anaerobic ammonium oxidizing (ANAMMOX) upflow anaerobic sludge bed (UASB) reactors was investigated. Two ANAMMOX reactors (R1 with and R2 without effluent recycling, respectively) were fed with relatively low nitrite concentration of 240 mg-N L ^-1 with subsequent progressive increase in the nitrogen loading rate (NLR) by shortening the hydraulic retention time (HRT) till the end of the experiment. A super high-rate performance with nitrogen removal rate (NRR) of 74.3-76.7 kg-N m ^-3 day ^-1 was accomplished in the lab-scale ANAMMOX UASB reactors, which was 3 times of the highest reported value. The biomass concentrations in the reactors were as high as 42.0-57.7 g-VSS L ^-1 with the specific ANAMMOX activity (SAA) approaching to 5.6 kg-N kg-VSS ^-1 day ^-1. The high SAA and high biomass concentration were regarded as the key factors for the super high-rate performance. ANAMMOX granules were observed in the reactors with settling velocities of 73-88 m h ^-1. The ANAMMOX granules were found to contain a plenty of extracellular polymers (ECPs) such as 71.8-112.1 mg g-VSS ^-1 of polysaccharides (PS) and 164.4-298.2 mg g-VSS ^-1 of proteins (PN). High content of hemachrome (6.8-10.3 μmol g-VSS ^-1 ) was detected in the ANAMMOX granules, which is supposed to be attributed to their unique carmine color.