Water Science and Technology

The activity of denitrifying methanotrophic bacteria at 11–30 °C was assessed in short-term experiments. The aim was to determine the feasibility of applying denitrifying methanotrophic bacteria in low-temperature anaerobic wastewater treatment. This study showed that biomass enriched at 21 °C had an optimum temperature of 20–25 °C and that activity dropped as temperature was increased to 30 °C. Biomass enriched at 30 °C had an optimum temperature of 25–30 °C. These results indicated that biomass from low-temperature inocula adjusted to the enrichment temperature and that low-temperature enrichment is suitable for applications in low-temperature wastewater treatment. Biomass growth at ≤20 °C still needs to be studied.

We investigated the bacterial community compositions and phosphorus removal performance under sludge bulking and non-bulking conditions in two biological wastewater treatment systems (conventional A2/O (anaerobic/anoxic/aerobic) and inverted A2/O (anoxic/anaerobic/aerobic) processes) receiving the same raw wastewater. Sludge bulking resulted in significant shift in bacterial compositions from Proteobacteria dominance to Actinobacteria dominance, characterized by the significant presence of filamentous ‘Candidatus Microthrix parvicella’. Quantitative real-time polymerase chain reaction (PCR) analysis revealed that the relative abundance of ‘Candidatus Accumulibacter phosphatis’, a key polyphosphate-accumulating organism responsible for phosphorus removal, with respect to 16s rRNA genes of total bacteria was 0.8 and 0.7%, respectively, for the conventional and inverted A2/O systems when sludge bulking occurred, which increased to 8.2 and 12.3% during the non-bulking period. However, the total phosphorus removal performance during the bulking period (2-week average: 97 ± 1 and 96 ± 1%, respectively) was not adversely affected comparable to that during the non-bulking period (2-week average: 96 ± 1 and 96 ± 1%, respectively). Neisser staining revealed the presence of large polyphosphate granules in ‘Candidatus Microthrix parvicella’, suggesting that this microbial group might have been responsible for phosphorus removal during the sludge bulking period when ‘Candidatus Accumulibacter phosphatis’ was excluded from the systems.

A sustainable option for nitrogen removal is the anaerobic ammonium-oxidizing (anammox) process in which ammonium is oxidized to nitrogen gas with nitrite as electron acceptor. Application of this process, however, is limited by the availability of anammox biomass. In this study, two Brocadia-like anammox phylotypes were successfully enriched, detected and identified from an activated sludge taken from a domestic wastewater treatment plant (Minas Gerais, Brazil) employing a Sequencing Batch Reactor (SBR). The dominant phylotype was closely related to ‘Candidatus Brocadia sinica’, but one clone seemed to represent a novel species for which we propose the name ‘Candidatus Brocadia brasiliensis’. Based on Fluorescence in situ hybridization (FISH) analysis, this enrichment led to a relative population size of 52.7% (±15.6) anammox bacteria after 6 months of cultivation. The cultivation process can be divided into three phases: phase 1 (approximately 25 days) was characterized by heterotrophic denitrification metabolism, phase 2 was the propagation phase and phase 3 (from the 87th day onwards), in which significant anammox activity was detected. A long-term performance of the SBR showed a near perfect removal of nitrite based on the influent NO2−-N concentration of 61–95 mg L−1. The average ammonia removal efficiency was 90% with the influent NH4+-N concentration of 55–82 mg L−1. Therefore, anammox cultivation and enrichment from activated sludge was possible under a controlled environment within 3 months.