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.

Integrated production of polyhydroxyalkanoates (PHAs) with municipal wastewater and sludge treatment at pilot scale.

A pilot-scale process was operated over 22 months at the Brussels North Wastewater Treatment Plant (WWTP) in order to evaluate polyhydroxyalkanoate (PHA) production integration with services of municipal wastewater and sludge management. Activated sludge was produced with PHA accumulation potential (PAP) by applying feast-famine selection while treating the readily biodegradable COD from influent wastewater (average removals of 70% COD, 60% CODsol, 24% nitrogen, and 46% phosphorus). The biomass PAP was evaluated to be in excess of 0.4gPHA/gVSS. Batch fermentation of full-scale WWTP sludge at selected temperatures (35, 42 and 55 °C) produced centrate (6-9.4 gCODVFA/L) of consistent VFA composition, with optimal fermentation performance at 42 °C. Centrate was used to accumulate PHA up to 0.39 gPHA/gVSS. The centrate nutrients are a challenge to the accumulation process but producing a biomass with 0.5 gPHA/gVSS is considered to be realistically achievable within the typically available carbon flows at municipal waste management facilities.

Influence of transient substrate overloads on the proliferation of filamentous bacterial populations in an activated sludge pilot plant.

Using oligonucleotide probes directed at the rRNA of filamentous bacteria, this study looks at the influence of the components of transient substrate overloads on the growth of the dominant filamentous bacteria of activated sludge fed by a synthetic substrate. By dissociating the massive input of organic matter from the oxygen shortage that the latter generally induces, it is revealed that each of these factors applied alone, induces only transitory, small-scale growth of the filaments Nostocoida limicola, Haliscomenobacter hydrossis. Thiothrix and of type 021N. In contrast, combining them during a reconstituted transient substrate overload with an artificially created oxygen deficit, induces very fast growth of H. hydrossis which is responsible for establishing major proliferation. This massive proliferation was easily reduced by chlorination.

Filamentous bacterial population dominance in activated sludges subject to stresses.

Evolution of a filamentous bacterial population was monitored on four wastewater treatment pilot plants subject to stresses which have consisted of oxygen deficiencies and/or loading shocks. Fluorescent in situ hybridization (FISH) was used to perform filaments identification and quantification. Results obtained on the different pilot plants have led us to conclude that independently of the nature of the stresses, a single filamentous bacteria species was involved in the increase of the sludge volume index associated to the filamentous growth. In addition, when serial stresses were used, substitutions in dominant filamentous populations occurred: if another filament began to proliferate it caused the regression of the one which was formerly dominant.