Inorganic carbon limitation during nitrogen conversions in sponge-bed trickling filters for mainstream treatment of anaerobic effluent.

Anaerobic sewage treatment is a proven technology in warm climate regions, and sponge-bed trickling filters (SBTFs) are an important post-treatment technology to remove residual organic carbon and nitrogen. Even though SBTFs can achieve a reasonably good effluent quality, further process optimization is hampered by a lack of mechanistic understanding of the factors influencing nitrogen removal, notably when it comes to mainstream anaerobically treated sewage. In this study, the factors that control the performance of SBTFs following anaerobic (i.e., UASB) reactors for sewage treatment were investigated. A demo-scale SBTF fed with anaerobically pre-treated sewage was monitored for 300 days, showing a median nitrification efficiency of 79% and a median total nitrogen removal efficiency of 26%. Heterotrophic denitrification was limited by the low organic carbon content of the anaerobic effluent. It was demonstrated that nitrification was impaired by a lack of inorganic carbon rather than by alkalinity limitation. To properly describe inorganic carbon limitation in models, bicarbonate was added as a state variable and sigmoidal kinetics were applied. The resulting model was able to capture the overall long-term experimental behaviour. There was no nitrite accumulation, which indicated that nitrite oxidizing bacteria were little or less affected by the inorganic carbon limitation. Overall, this study indicated the vital role of influent characteristics and operating conditions concerning nitrogen conversions in SBTFs treating anaerobic effluent, thus facilitating further process optimization.

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.

Performance of plastic- and sponge-based trickling filters treating effluents from an UASB reactor.

The paper compares the performance of two trickling filters (TFs) filled with plastic- or sponge-based packing media treating the effluent from an upflow anaerobic sludge blanket (UASB) reactor. The UASB reactor was operated with an organic loading rate (OLR) of 1.2 kgCOD m(-3) d(-1), and the OLR applied to the TFs was 0.30-0.65 kgCOD m(-3) d(-1) (COD: chemical oxygen demand). The sponge-based packing medium (Rotosponge) gave substantially better performance for ammonia, total-N, and organic matter removal. The superior TF-Rotosponge performance for NH(4)(+)-N removal (80-95%) can be attributed to its longer biomass and hydraulic retention times (SRT and HRT), as well as enhancements in oxygen mass transfer by dispersion and advection inside the sponges. Nitrogen removals were significant (15 mgN L(-1)) in TF-Rotosponge when the OLRs were close to 0.75 kgCOD m(-3) d(-1), due to denitrification that was related to solids hydrolysis in the sponge interstices. For biochemical oxygen demand removal, higher HRT and SRT were especially important because the UASB removed most of the readily biodegradable organic matter. The new configuration of the sponge-based packing medium called Rotosponge can enhance the feasibility of scaling-up the UASB/TF treatment, including when retrofitting is necessary.

Feasibility of UASB/trickling filter systems without final clarifiers for the treatment of domestic wastewater in small communities in Brazil.

The paper analyses the concept and performance of different configurations of compact UASB/TF systems, without the final clarification stage, in relation to the removal of organic matter. The experiments were carried out in two sets of UASB/TF systems operating without secondary clarifiers, as follows: (i) four shallow (2.50 m height) TFs, each one filled with a different packing material; and (ii) two deep (4.20 m height) TFs, one filled with polyethylene corrugated sheets and the other with mixed polyethylene and sponge sheets. For the conditions tested (different packing material in shallow and deep TF), the UASB/TF systems had consistently complied (90 to 100% of the results) with the Brazilian discharge standards regarding to BOD, COD, and TSS parameters. The average BOD, COD and TSS effluent concentrations stayed below 40 mg BOD L(-1), 100 mg COD L(-1) and 50 mg TSS L(-1), respectively. UASB/TF systems can constitute an attractive alternative for domestic wastewater treatment in small communities in developing countries, especially considering its operational simplicity and very low running costs.

Experience with the design and start up of two full-scale UASB plants in Brazil: enhancements and drawbacks.

This paper discusses the main drawbacks and enhancements experienced with the design and start up of two full-scale UASB plants in Brazil. The topics addressed are related to blockage of inlet pipes, scum accumulation, seed sludge for the start-up, corrosion and gas leakage, odour generation and sludge management. The paper describes the main improvements achieved.

Development of compact UASB/trickling filter systems for treating domestic wastewater in small communities in Brazil.

The paper analyses the concept and performance of compact UASB/TF systems in relation to configuration, use of innovative packing media and operational conditions. For the conditions tested, the UASB/TF systems had consistently complied with the Brazilian discharge standard regarding to COD, BOD and TSS parameters. However, some enhancements are still necessary in order to increase nitrification in the process. The conditions to promote nitrification in shallow TF (packed bed up to 2.50 m height) seem to be compatible with the proposed simplification in the flowsheet, which is to operate the system without secondary clarifiers.