Enrichment and adaptation yield high anammox conversion rates under low temperatures.

This study compared two anammox sequencing batch reactors (SBR) for one year. SBRconstantT was kept at 30 °C while temperature in SBRloweringT was decreased step-wise from 30 °C to 20 °C and 15 °C followed by over 140 days at 12.5 °C and 10 °C. High retention of anammox bacteria (AnAOB) and minimization of competition with AnAOB were key. 5-L anoxic reactors with the same inoculum were fed synthetic influent containing 25.9 mg NH4+-N/L and 34.1 mg NO2--N/L (no COD). Specific ammonium removal rates continuously increased in SBRconstantT, reaching 785 mg NH4+-N/gVSS/d, and were maintained in SBRloweringT, reaching 82.2 and 91.8 mg NH4+-N/gVSS/d at 12.5 and 10 °C respectively. AnAOB enrichment (increasing hzsA and 16S rDNA gene concentrations) and adaptation (shift from Ca. Brocadia to Ca. Kuenenia in SBRloweringT) contributed to these high rates. Rapidly settling granules developed, with average diameters of 1.2 (SBRconstantT) and 1.6 mm (SBRloweringT). Results reinforce the potential of anammox for mainstream applications.

Dynamics of metabolically active bacterial communities involved in PAH and toxicity elimination from oil-contaminated sludge during anoxic/oxic oscillations.

The kinetics of polycyclic aromatic hydrocarbons (PAH) elimination from a contaminated sludge were determined in bioreactors under different conditions: continuously oxic, anoxic, and anoxic/oxic oscillations. The dynamics of metabolically active bacterial communities and their involvement in PAH degradation were followed by T-RFLP targeting 16S rRNA and ring hydroxylating dioxygenase (RHD) transcripts, respectively. PAH degradation was related to toxicity elimination using an aryl hydrocarbon receptor-responsive reporter cell line. Oxygen supply was identified as the main factor affecting the structure of bacterial communities and PAH removal. PAH-degrading bacterial communities were stable throughout the experiment in all conditions according to the presence of RHD transcripts, indicating that bacterial communities were well adapted to the presence of pollutants. Oxic and anoxic/oxic oscillating conditions showed similar levels of PAH removal at the end of the experiment despite several anoxic periods in oscillating conditions. These results highlight the role of dioxygenase activity after oxygen addition. Nevertheless, the higher toxicity elimination observed under oxic conditions suggests that some metabolites or other unidentified active compounds persisted under oscillating and anoxic conditions. Our results emphasize the importance of using complementary biological, chemical and toxicological approaches to implement efficient bioremediation strategies.

Relevant approach to assess performances of wastewater biosolids composting in terms of micropollutants removal.

The presence of organic pollutants in wastewater biosolids and their possible impact to the environment contribute to decrease interest for the agricultural spreading of biosolids. It is thus important to have a better overview of sewage sludge quality in terms of organic pollutant content and ecotoxicity assessment. It is also necessary to better understand the impact of biosolid composting processes on the pollutant and toxicity removal. Therefore, concentrations of oestrogens (E), nonyphenol ethoxylates (NPE), polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB) and linear alkyl benzene sulphonates (LAS) and some of their associated toxic effects were determined at different stages of a composting process using, respectively, chemical analysis and in vitro bioassays (estrogen receptor alpha, dioxin receptor and pregnan X receptor reporter cell lines). Pollutants concentrations were higher in the final compost than in biosolid due to dry matter reduction through composting. Mass balance calculation shows a positive impact of the aerobic treatment on the removal of the most degradable pollutants. The three toxicological activities were measured in both biosolids and in the initial and final compost: oestrogenic activity increased whereas dioxin-like and pregnan X activities decreased. The difficulty in correlating chemical and toxicological results underlines the importance of combining both approaches in order to improve the assessment of the compost quality.