Coupling anammox and heterotrophic denitrification activity at mainstream conditions in a single reactor unit

Using the upflow biological filter reactor, sulfur denitrification using thiosulfate of hydroponic culture wastewater was examined. Start-up periods of the reactor were one to two weeks. About 90% of nitrogen removal ratio were achieved over 80 days, at 6.3 kg/m3·days of nitrogen loading. Shock loading among 0.56-2.8 kgN/m3· day did not affect the reactor performance. However, when temperature went below 15°C, the effluent characteristics became poor. Suitable S/N and IC/N ratios were calculated as 3.3 and 0.15, respectively. The activities of sulfur denitrification, heterotrophic denitrification and sulfur reduction were examined by the bath experiments under several conditions using biomass grown in the reactor. In the anoxic conditions, denitrification using thiosulfate was occurred stoichiometrically in the presence of thiosulfate. The denitrification activity was highest (17 mgN/gBiomass·hr). When the electron donor was not added to the substrate, denitrification occurred using sulfur granules accumulated in the biomass. Seventy mg of sulfur granule were accumulated in one g of biomass. The denitrification activity using sulfur granules was 2.9-5.0 mgN/gBiomass·hr. Heterotrophic denitrification occurred in the presence of organic matter. The activities were 1.4-5.4 mgN/gBiomass·hr. In the anaerobic conditions, the accumulated sulfur was reduced to sulfide at a rate of 1.4 mgS/gBiomass·hr. These results suggested that sulfur denitrification, heterotrophic denitrification and sulfur reduction bacteria coexisted in the biofilm and sulfur cycle was established in the reactor. Accumulated sulfur plays an important role in the sulfur denitrification.

Alkalinity requirement and the possibility of simultaneous heterotrophic denitrification during sulfur-utilizing autotrophic denitrification were evaluated with sulfur packed bed reactors (SPBRs). SPBR showed >99% NO3--N removal efficiency at influent NO3--N concentration of 1,500 mg/L, although 25-40% of the added NO3--N was recovered as N2O. Complete denitrification without N2O production was achieved when the influent NO3--N concentration decreased to 750 mg/L. When nitrified landfill leachate containing 602–687 mg/L of NO3--N was fed to SPBR, denitrification efficiency was greater than 98%. During leachate treatment, alkalinity consumption was 3.25–3.76 g CaCO3/g NO3--N removed. Most of denitrification activity occurred within bottom 11.5 cm of sulfur layer, meaning that effective HRT of 2.34 hours was enough for the complete denitrification at the loading rate of 2.2 kg NO3--N/m3-day. Complete denitrification was also achieved when methanol was added to nitrified leachate without alkalinity addition. In this case, alkalinity produced by heterotrophs was used for sulfur-utilizing denitrification.

Due to the extensive application of artificial nitrogen-based fertilizers on land, groundwater from the central part of Taiwan faces problems of increasing concentrations of nitrate, which were measured to be well above 30 mg/L all year round. For meeting the 10 mg/L nitrate standard, optimal operations for a heterotrophic denitrification pilot plant designed for drinking water treatment was investigated. Ethanol and phosphate were added for bacteria growing on anthracite to convert nitrate to nitrogen gas. Results showed that presence of high dissolved oxygen (around 4 mg/L) in the source water did not have a significantly negative effect on nitrogen removal. When operated under a C/N ratio of 1.88, which was recommended in the literature, nitrate removal efficiency was measured to be around 70%, sometimes up to 90%. However, the reactor often underwent severe clogging problems. When operated under C/N ratio of 1.0, denitrification efficiency decreased significantly to 30%. Finally, when operated under C/N ratio of 1.5, the nitrate content of the influent was almost completely reduced at the first one-third part of the bioreactor with an overall removal efficiency of 89–91%. Another advantage for operating with a C/N ratio of 1.5 is that only one-third of the biosolids was produced compared to a C/N value of 1.88.

Activated sludges taken from full-scale membrane separation processes, building wastewater reuse system (400m3/d), and two nightsoil treatment plants (50m3/d) as well as laboratory scale membrane separation bioreactor (0.062m3/d) were analyzed to characterize membrane separation activated sludge processes (MSAS). They were also compared with conventional activated sludges(CAS) taken from municipal wastewater treatment plants. Specific nitrification activity in MSAS processes averaged at 2.28gNH4-N/kgMLSS.h were higher than that in CAS processes averaged at 0.96gNH4-N/kgMLSS.h. The denitrification activity in both processes were in the range of 0.62-3.2gNO3-N/kgMLSS.h without organic addition and in the range of 4.25-6.4gNO3-N/kgMLSS.h with organic addition. The organic removal activity in nightsoil treatment process averaged at 123gCOD/kgMLSS.h which was significantly higher than others. Floc size distributions were measured by particle sedimentation technique and image analysis technique. Flocs in MSAS processes changed their sizes with MLSS concentration changes and were concentrated at small sizes at low MLSS concentration, mostly less than 60 μm. On the contrary, floc sizes in CAS processes have not much changed with MLSS concentration changes and they were distributed in large range. In addition, the effects of floc size on specific nitrification rate, denitrification rate with and without organic carbon addition were investigated. Specific nitrification rate was decreased as floc size increased. However, little effect of floc size on denitrification activity was observed.

AbstractFreshwater lakes are essential hotspots for the removal of excessive anthropogenic nitrogen (N) loads transported from the land to coastal oceans. The biogeochemical processes responsible for N removal, the corresponding transformation rates and overall removal efficiencies differ between lakes, however, it is unclear what the main controlling factors are. Here, we investigated the factors that moderate the rates of N removal under contrasting trophic states in two lakes located in central Switzerland. In the eutrophic Lake Baldegg and the oligotrophic Lake Sarnen, we specifically examined seasonal sediment porewater chemistry, organic matter sedimentation rates, as well as 33-year of historic water column data. We find that the eutrophic Lake Baldegg, which contributed to the removal of 20 ± 6.6 gN m−2 year−1, effectively removed two-thirds of the total areal N load. In stark contrast, the more oligotrophic Lake Sarnen contributed to 3.2 ± 4.2 gN m−2 year−1, and had removed only one-third of the areal N load. The historic dataset of the eutrophic lake revealed a close linkage between annual loads of dissolved N (DN) and removal rates (NRR = 0.63 × DN load) and a significant correlation of the concentration of bottom water nitrate and removal rates. We further show that the seasonal increase in N removal rates of the eutrophic lake correlated significantly with seasonal oxygen fluxes measured across the water–sediment interface (R2 = 0.75). We suggest that increasing oxygen enhances sediment mineralization and stimulates nitrification, indirectly enhancing denitrification activity.

Fifty years ago when only BOD was removed at municipal WWTPs primary clarifiers were designed with 2–3 hours hydraulic retention time (HRT). This changed with the introduction of nitrogen removal in activated sludge treatment that needed more BOD for denitrification. The HRT of primary clarification was reduced to less than one hour for dry weather flow with the consequence that secondary sludge had to be separately thickened and biogas production was reduced. Only recently the ammonia rich digester liquid (15–20% of the inlet ammonia load) could be treated with the very economic autotrophic nitritation/anammox process requiring half of the aeration energy and no organic carbon source compared to nitrification and heterotrophic denitrification. With the introduction of this new innovative digester liquid treatment the situation reverts, allowing us to increase HRT of the primary clarifier to improve biogas production and reduce aeration energy for BOD removal and nitrification at similar overall N-removal.

AbstractTo research the roles of rare earth minerals in denitrification via the NH3-SCR, a mixture was made by certain ratio of rare earth concentrates and rare earth tailings, then treated by microwave roasting, and acids and bases to form a denitrification catalyst. The mineral phase structure and surface morphology of the catalyst were characterized by XRD, BET, SEM and EDS. The surface properties of the catalyst were tested by TPD and XPS methods, and the denitrification activity of the catalyst was evaluated in a denitrification reactor. The results showed that the denitrification efficiency increased up to 82% with complete processing. XRD, BET, SEM, and EDS spectrum analysis stated that the treated minerals contained cerium oxides and Fe−Ce composite oxides. The surface of the modified minerals became rough and porous, the surface area increased, and the surface-active sites were exposed. The results of NH3-TPD and NO-TPD showed that the catalyst surface could gradually adsorb more NH3 and NO after each step. XPS analysis indicated that there were more Ce3+, Fe2+, and lattice oxygen in rare earth minerals catalyst after each treatment step.