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Theses

Cold anammox for energy-positive sewage treatment : impact of temperature and organic carbon on performances and microbiota

Abstract : This thesis aimed to increase the understanding of the short and long-term impact of low temperature on anammox rates, -enrichment, -adaptation of anaerobic ammonium-oxidizing or anammox bacteria (AnAOB) and their ability to compete with heterotrophic bacteria (HB) in the presence of organic carbon (OC).Short term effect of decreasing temperature on AnAOB activityThe short-term effect of temperature decrease on the anammox rates was evaluated in anoxic batch tests between 30-10°C. Results showed that biomass types containing the largest aggregates (>315 μm) and rich in the Ca. Kuenenia were less sensitive to a decrease in temperature. Differences in sensitivity were more likely attributed to the genus rather than to aggregate size. Optimization of Arrhenius modelling by splitting into two temperature intervals (rather than using one global equation) improved the overall goodness of fit (R2) and allowed to obtain more accurate θ-values enabling realistic process rate predictions which could in term help improve modelling for process design purposes.Long term effect of decreasing temperature on AnAOB activity and enrichmentTwo anammox sequencing batch reactors (SBR) with identical inoculum were operated under anoxic conditions on synthetic influent (60 mg N/L) and compared for one year. One was kept at 30°C while temperature in the other was step-wisely decreased from 30°C to 10°C. Minimal competition and high AnAOB retention (SRTs = 168d) resulted in the formation and retention of well settling granules at both 30°C and 10°C, indicating that lowering temperature is not detrimental to granulation and can even increase granule size. The observed AnAOB enrichment and adaptation (at genus level) contributed to achieving unprecedented removal rates of 82 and 92 mg NH4+-N/g VSS/d at 12.5 and 10°C respectively.Impact of temperature and organic carbon on the competition between AnAOB and HBThe impact of low concentrations of slowly biodegradable organic carbon on the competition between anammox and denitrification and how it is impacted by temperature was assessed by adding 30 mg OC/L (90% starch and 10% acetate to mimic HRAS effluent) the influent of the above-mentioned reactors at 30°C and 10°C. With relatively low OC/nitrite removal ratios (0.3 in both reactors), overall nitrogen conversion ratios were close to the anammox stoichiometry. No significant competition between AnAOB and HB for nitrite was observed under the tested conditions as (1) starch hydrolysis was rate limiting for denitrification and (2) HB preferred nitrate over nitrite. Flocs developed in both reactors which transitioned from purely granular to hybrid systems. While flocs became predominant at 30°, the system at 10°C remained predominantly granular, likely due to poorer floc formation and therefore higher floc wash-out, reflected in a lower SRT at 10°C (19d) compared to 30°C (26d). AnAOB abundance decreased greatly (87 to 37%) at 30°C and to a lesser extent (91 to 74%) at 10°C. Despite the observed decrease in AnAOB abundance, removal rates remained high in both reactors and rates of up to 112 mg NH4+-N/gVSS/d were reached at 10°C. Interestingly, addition of organic carbon addition did not impact the dominant genera which remained Ca. Brocadia and Ca. Kuenenia in SBR30°C and SBR10°C, respectively. These findings showed how application of differential SRT (here via the imposed settling time) can help microbial resource management for achieving mainstream PN/A.The finding from this research project show the potential of ‘cold anammox’ and provide some insights that can contribute to the development of a suitable microbial resource management strategy for the implementation of mainstream PN/A applications.
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Pieter de Cocker. Cold anammox for energy-positive sewage treatment : impact of temperature and organic carbon on performances and microbiota. Other. INSA de Toulouse; UNIVERSITE DE GHENT-BELGIQUE, 2018. English. ⟨NNT : 2018ISAT0050⟩. ⟨tel-03396694⟩

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