Density and sludge volume index estimation in mature aerobic granular sludge by quantitative image analysis and chemometrics tools

Quantitative image analysis (QIA) has already been applied for activated sludge dysfunctions and anaerobic granular sludge processes elucidation and its application to aerobic granular sludge characterization is considered of major interest. In this work, a sequencing batch reactor (SBR) was operated using mature aerobic granular sludge for pharmacologically active compounds (PAC) removal. The physicochemical parameters (total and volatile suspended solids, sludge volume index and density), prior to the introduction of PAC, were determined by analytical methods. The mature aerobic granular and suspended sludge morphological and structural parameters were established by QIA. The objective of this study is to characterize this mature granular sludge by QIA, and establish relationships for physicochemical parameters (aggregates density and SVI30) with QIA data using chemometric tools. Indeed, relevant relationships could be found for both density (R2 of 0.81) and SVI30 (R2 of 0.87).The authors thank the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469 unit, COMPETE 2020 (POCI-01-0145-FEDER-006684) and BioTecNorte operation (NORTE-01-0145-FEDER000004) funded by the European Regional Development Fund under the scope of Norte2020 - Programa Operacional Regional do Norte. Cristiano Leal is recipient of a fellowship supported by a doctoral advanced training (call NORTE-69-2015-15) funded by the European Social Fund under the scope of Norte2020 - Programa Operacional Regional do Norte. A. Val del Rio is supported by Xunta de Galicia (ED418B 2017/075) and program Iacobus (2017/2018).