Factors Selecting for Polyphosphate- and Glycogen-Accumulating Organisms in Granular Sludge Sequencing Batch Reactors

MicrobialGlycogen-accumulating organisms selectionMicrobial selection in aerobic granular sludgeAerobic granular sludge was studied in dynamicDynamics and steady-state sequencing batch reactorsSequencing batch reactor (SBRSBR). FactorsFactors governing competitionCompetition between polyphosphatePolyphosphate- (PAOsPAO) and glycogenGlycogen-accumulating organisms (GAOsGAO), and biological nutrient removalBiological nutrient removal (BNRBNR), were identified. First, selectionSelection was tracked under gradual changes in the ratioRatio and concentrationsConcentration of acetateAcetate (Ac) and propionatePropionate (Pr) in the influentInfluent of a dynamicDynamics SBRSBR operated without purging excess sludgeExcess sludge. BiomassBiomass growthGrowth was limited when supplying only acetateAcetate. PropionatePropionate fed either as single volatile fatty acidVolatile fatty acid or in mixturesMixture with acetateAcetate sustained the developmentDevelopment of the granular sludgeGranular sludge bedBed and “Ca. AccumulibacterAccumulibacter” (38%). Second, a multifactorial experimental designMultifactorial experimental design was used to examine PAO/GAO competitionPAO/GAO competition. EffectsEffect of 6 main factorsFactors were screened: organicOrganics concentrationConcentration (600–1200 mg CODCOD L−1), Ac/Pr ratioRatio (100:0–50:50%COD), CODCOD/P ratioRatio (35–100 gCOD gP−1), pHPH (6.5–7.5), temperatureTemperature (15–28 °C), redoxRedox during starvationStarvation (aerobicAerobic vs. aerobicAerobic/anoxicAnoxic). Eight SBRsSBR were run over 50 days at fixed sludgeSludge age (15 days) and 4-h cycles of anaerobicAnaerobic feast (100 min) and starvationStarvation (120 min) batchBatch phasesPhase. The PAOPAO “Candidatus Accumulibacter“Candidatus Accumulibacter”” (47%) and P-removalP-removal (80–100%) were selected at pHPH 7.5, < 20 °C and 50%:50% Ac/Pr. The GAOGAO “Ca. CompetibacterCompetibacter” (35%) was selected at pHPH 6.5, 28 °C, 100% Ac and 600 mgCOD L−1, impairing P-removalP-removal (0–44%). GAOGAO conditions selected for TetrasphaeraTetrasphaera-related PAOsPAO (16%). NitrificationNitrification-denitrificationDenitrification was optimal at pHPH 7.5 and > 25 °C. With fixed 2 h of starvationStarvation, P-removalP-removal was only complete under full aerationAeration. This work provided keys to sustain granular sludgeGranular sludge, select PAOsPAO, and enhance BNRBNR. A slightly alkaline pHPH drives higher PAOPAO selectionSelection. The 3-carbonsCarbon propionatePropionate substrateSubstrate yieldsYield more biomassBiomass. Besides non-limiting organicOrganics supplySupply, full BNRFull BNR requires process controlProcess control on durationsDuration of anaerobicAnaerobic feast and aerobicAerobic-anoxicAnoxic starvationStarvation phasesPhase. PurgePurge of excess granular sludgeGranular sludge stabilizes the sludgeSludge age, microbiomeMicrobiome compositionComposition, and BNRBNR. This knowledge can be utilized to engineer BNR granular sludgeBNR granular sludge processesGranular sludge process.