Anaerobic ammonium oxidation (ANAMMOX) sludge immobilized by waterborne polyurethane and its nitrogen removal performance-a lab scale study

Abstract

In the present study, to maintain the biomass of anaerobic ammonium oxidation bacteria (ANAMMOX) in water, waterborne polyurethane (WPU) was used to immobilize ANAMMOX sludge. The ANAMMOX granules immobilized by WPU exhibited the best entrapment support, superb bioactivity and highest mechanical stability when compared with the performance of other ANAMMOX immobilized granules of polyvinyl alcohol (PVA), sodium alginate (SA), and the mixed material, PVA–SA. In a continuous-flow experiment, during high volume-load WPU-immobilized granules exhibited a relatively high total nitrogen removal rate, no effluent suspended solids or granule crushing were observed within 100 days. The highest total nitrogen removal rate of 80.98% was observed when the volume load of TN was 1.697 kg per m³ per day with HRT 1.5 h. WPU-immobilized granules exhibited better correlation (R²: 0.945 NH₄⁺–N and 0.989 NO₂⁻–N) with experimental kinetic data for biological nitrogen removal. According to experimental data, good sludge retaining ability, strong resistance to shock-loading and mechanical stability during long-term operation of the granules immobilized by WPU was observed. The formation of volcanic crater-like concaves on the two sides of each bacterium and a large amount of ANAMMOX bacteria growing along the channels inside of the WPU granules were observed by scanning electron microscopy. Finally, the microbial community analysis 16S rDNA cloning revealed that Candidatus Brocadia fulgida (JX243641.1) was the primary ANAMMOX bacteria inside the WPU-immobilized granules. As carriers, immobilization materials protect ANAMMOX bacteria and increase biomass; however, they have no effect on bacteria and bacterial community structure.