Nitrogen removal in a shallow maturation pond with sludge accumulated during 10 years of operation in Brazil.

Accumulated sludge in polishing (maturation) ponds reduces the hydraulic retention time (smaller useful volume), and this could potentially lead to a decrease in performance. However, settled biomass, present in the sediments, can contribute to nitrogen removal by different mechanisms such as nitrification and denitrification. This study investigated the influence of the bottom sludge present in a shallow maturation pond treating the effluent from an anaerobic reactor on the nitrification and denitrification processes. Nitrification and denitrification rates were determined in sediment cores by applying ammonia pulses. Environmental conditions in the medium were measured and bacteria detected and quantified by real-time polymerase chain reaction (real-time PCR). The pond showed daily cycles of mixing and stratification and most of the bacteria involved in nitrogen removal decreased in concentration from the upper to the lower part of the sludge layer. The results indicate that denitrifiers, nitrifiers and anammox bacteria coexisted in the sludge, and thus different metabolic pathways were involved in ammonium removal in the system. Therefore, the sediment contributed to nitrogen removal, even with a decrease in the hydraulic retention time in the pond due to the volume occupied by the sludge.

Bacterial community involved in the nitrogen cycle in a down-flow sponge-based trickling filter treating UASB effluent.

The bacterial community composition of a down-flow sponge-based trickling filter treating upflow anaerobic sludge blanket (UASB) effluent was investigated by pyrosequencing. Bacterial community composition considerably changed along the reactor and over the operational period. The dominant phyla detected were Proteobacteria, Verrucomicrobia, and Planctomycetes. The abundance of denitrifiers decreased from the top to the bottom and it was consistent with the organic matter concentration gradients. At lower loadings (organic and nitrogen loading rates), the abundance of anammox bacteria was higher than that of the ammonium-oxidizing bacteria in the upper portion of the reactor, suggesting that aerobic and anaerobic ammonium oxidation occurred. Nitrification occurred in all the compartments, while anammox bacteria prominently appeared even in the presence of high organic carbon to ammonia ratios (around 1.0-2.0 gCOD gN(-1)). The results suggest that denitrifiers, nitrifiers, and anammox bacteria coexisted in the reactor; thus, different metabolic pathways were involved in ammonium removal in the post-UASB reactor sponge-based.

Diversity and dynamics of ammonia-oxidizing bacterial communities in a sponge-based trickling filter treating effluent from a UASB reactor.

Changes in ammonia-oxidizing bacterial (AOB) population dynamics were examined in a new sponge-based trickling filter (TF) post-upflow anaerobic sludge blanket (UASB) reactor by denaturating gradient gel electrophoresis (DGGE), and these changes were linked to relevant components influencing nitrification (chemical oxygen demand (COD), nitrogen (N)). The sponge-based packing media caused strong concentration gradients along the TF, providing an ecological selection of AOB within the system. The organic loading rate (OLR) affected the population dynamics, and under higher OLR or low ammonium-nitrogen (NH4(+)-N) concentrations some AOB bands disappeared, but maintaining the overall community function for NH4(+)-N removal. The dominant bands present in the upper portions of the TF were closely related to Nitrosomonas europaea and distantly affiliated to Nitrosomonas eutropha, and thus were adapted to higher NH4(+)-N and organic matter concentrations. In the lower portions of the TF, the dominant bands were related to Nitrosomonas oligotropha, commonly found in environments with low levels of NH4(+)-N. From a technology point of view, changes in AOB structure at OLR around 0.40-0.60 kgCOD m(-3) d(-1) did not affect TF performance for NH4(+)-N removal, but AOB diversity may have been correlated with the noticeable stability of the sponge-based TF for NH4(+)-N removal at low OLR. This study is relevant because molecular biology was used to observe important features of a bioreactor, considering realistic operational conditions applied to UASB/sponge-based TF systems.

Granular biomass selection in a double-stage biogas collection UASB reactor: effects on SMA, abundance and diversity of the methanogenic population.

The present work aimed at investigating biomass selection in a pilot-scale double-stage biogas collection (DSBC) upflow anaerobic sludge bed (USAB) reactor treating domestic wastewater. Specific methanogenic activity (SMA) measurements and FISH countings were applied to sludge samples collected during 102 days of operation of the DSBC-UASB and of a control reactor. Results showed that both reactors presented similar SMA values in early stages of operation however the UASB-DSBC reactor showed much higher SMA after day 45, when the biomass was in granular stage. In terms of archaeal abundance, no statistical difference was observed between the reactors. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) revealed a similar composition of the archaeal communities in the two reactors and during the operational period, mainly constituted by Methanosaeta concilii. The results suggest that cell activity rather than archaeal abundance or diversity drive the methane production in the UASB reactors.