Understanding the microbial trends in a nitritation reactor fed with primary settled municipal wastewater

Granulation of partial denitrification sludge: Advances in mechanism understanding, technologies development and perspectives

The high-rate and stably efficient nitrite generation is vital and still challenges the wide application of partial denitrification (PD) and anammox technology. Increasing attention has been drawn to the granulation of PD biomass. However, the knowledge of PD granular sludge is still limited in terms of granules characterization and mechanisms of biomass aggregation for high nitrite accumulation. This work reviewed the performance and granulation of PD biomass for high nitrite accumulation via nitrate reduction, including the system start-up, influential factors, granular characteristics, hypothetical mechanism, challenges and perspectives in future application. The physiochemical characterization and key influential factors were summarized in view of nitrite production, morphology analysis, extracellular polymer substance structure, as well as microbial mechanisms. The PD granules exhibit potential advantages of a high biomass density, good settleability, high hydraulic loading rates, and strong shock resistance. A novel granular sludge-based PD combined with anammox process was proposed to enhance the capability of nitrogen removal. In the future, PD granules utilizing different electron donors is a promising way to broaden the application of anammox technology in both municipal and industrial wastewater treatment.

Organic carbon bioavailability: Is it a good driver to choose the best biological nitrogen removal process?

Organic carbon can affect the biological nitrogen removal process since the Anammox, heterotrophic and denitrifying bacteria have different affinities and feedback in relation to carbon/nitrogen ratio. Therefore, we reviewed the wastewater carbon concentration, its biodegradability and bioavailability to choose the appropriate nitrogen removal process between conventional (nitrification-denitrification) and Anammox-based process (i.e. integrated with the partial nitritation, nitritation, simultaneous partial nitrification and denitrification or partial-denitrification). This review will cover: (i) strategies to choose the best nitrogen removal route according to the wastewater characteristics in relation to the organic matter bioavailability and biodegradability; (ii) strategies to efficiently remove nitrogen and the remaining carbon from effluent in anammox-based process and its operating cost; (iii) an economic analysis to determine the operational costs of two-units Anammox-based process when compared with the commonly applied one-unit Anammox system (partial-nitritation-Anammox). On this review, a list of alternatives are summarized and explained for different nitrogen and biodegradable organic carbon concentrations, which are the main factors to determine the best treatment process, based on operational and economic terms. In summary, it depends on the wastewater carbon biodegradability, which implies in the wastewater treatment cost. Thus, to apply the conventional nitrification/denitrification process a COD_b/N ratio higher than 3.5 is required to achieve full nitrogen removal efficiency. For an economic point of view, according to the analysis the minimum COD_b/gN for successful nitrogen removal by nitrification/denitrification is 5.8 g. If ratios lower than 3.5 are applied, for successfully higher nitrogen removal rates and the economic feasibility of the treatment, Anammox-based routes can be applied to the wastewater treatment plant.

Salinity is the major driver of the global eukaryotic community structure in fish-canning wastewater treatment plants

Fish-canning wastewater is characterized frequently by a high content of salt (NaCl), making its treatment particularly difficult; however, the knowledge of the effect of NaCl on eukaryotic communities is very limited. In the present study, the global diversity of eukaryotes in activated sludges (AS) from 4 different wastewater treatment plants (WWTPs) treating fish-canning effluents varying in salinity (0.47, 1.36, 1.72 and 12.76 g NaCl/L) was determined by sequencing partial 18S rRNA genes using Illumina MiSeq. A greater diversity than previously reported was observed in the AS community, which comprised 37 and 330 phylum-like and genera-like groups, respectively. In this sense, the more abundant genus-like groups (average relative abundance (RA) > 5%) were Adineta (6.80%), Lecane (16.80%), Dictyostelium (7.36%), Unclassified_Fungi7 (6.94%), Procryptobia (5.13) and Oocystis (5.07%). The eukaryotic communities shared a common core of 25 phylum-like clades (95% of total sequences); therefore, a narrow selection of the eukaryotic populations was found, despite the differences in the abiotic characteristics of fish-canning effluents and reactor operational conditions inflicted. The differences in NaCl concentration were the main factor that influenced the structure of the eukaryotic community, modulating the RAs of the different phylum-like clades of the common core. Higher levels of salt increased the RAs of Ascomycota, Chlorophyta, Choanoflagellata, Cryptophyta, Mollusca, Nematoda, Other Protists and Unclassified Fungi. Among the different eukaryotic genera here found, the RA of Oocystis (Chlorophyta) was intimately correlated to increasing NaCl concentrations and it is proposed as a bioindicator of the global eukaryotic community of fish-canning WWTPs.