Concluding Remarks and Outlook

Granular sludgeGranular sludge reduces costsCosts for biological nutrient removalBiological nutrient removal (BNRBNR) from wastewaterWastewater. The microbial resourceResource is managed in granular sludgeGranular sludge using principles of microbial ecologyMicrobial ecology, biofilm gradientsBiofilm gradient, and process engineeringProcess engineering. Microbial selectionMicrobial selection phenomenaPhenomena were elucidated in the microbiomeMicrobiome of BNR granular sludgeBNR granular sludge. A rational wet-labWet-lab and dry-labDry-lab biomolecularBiomolecular methodologyMethodology was used to profileProfile microbiomesMicrobiome with fast analytical throughputThroughput and high taxonomic and temporal resolutionsResolution. The conceptual ecosystem modelConceptual ecosystem model of BNR granular sludgeBNR granular sludge was built to foster functional analysesFunctional analyses and microbial community engineeringMicrobial community engineering. GranulationGranulation mechanisms and granuleGranule architecturesArchitecture rely on predominant phylotypesPhylotype and their physiologies. BiomassBiomass wash-outWash-out drives rapid granulationGranulation but affects the microbiomeMicrobiome balanceBalance. Controlling the organic loading rateOrganic loading rate, the anaerobic contact timeAnaerobic contact time, and the starvationStarvation phase lengthPhase length is the key for selecting for polyphosphatePolyphosphate-accumulating organism (PAOsPAO) and promoting a stable granulationGranulation and EBPREBPR, while out-selecting bulking bacteriaBulking bacteria and preventing process failuresProcess failure. A careful designDesign of the anaerobic selectorAnaerobic selector is necessary to fully remove organicsOrganics prior to switching on aerationAeration. Hydraulic-biokineticBiokinetic modeling supports the designDesign of the anaerobicAnaerobic up-flow feedingUp-flow feeding selectorSelector. A slightly alkaline pHPH selects for the PAOPAO “Candidatus Accumulibacter“Candidatus Accumulibacter”” over glycogenGlycogen-accumulating competitors. FractionsFraction of active PAOsPAO and the EBPREBPR potentialPotential of sludgeSludge can be rapidly measured in an electrical-conductivityConductivity-based metabolic batch testMetabolic batch test and a polyphosphatasePolyphosphatase enzymatic assayEnzymatic assay. The robustnessRobustness of the biosystemBiosystem relies on feedFeed-forward and feedFeed-back controlsControl in functionFunctions of operational variations, granuleGranule size distributions, bedBed volume, and biochemical conversionsConversion. An applied methodologyMethodology is proposed to guide an ecological engineeringEcological engineering of BNR granular sludgeBNR granular sludge. Although granulesGranule and flocsFlocs differ in density, metricsMetrics and gradientsGradient, the last 100 years of activated sludgeActivated sludge research should not be forgotten when designing granular sludgeGranular sludge technologiesTechnology.