Sludge volume index and suspended solids estimation of mature aerobic granular sludge by quantitative image analysis and chemometric tools

Aerobic granular sludge (AGS) is considered a promising technology for wastewater treatment. Furthermore, it is recognized that the stability of the process is related to the balanced growth of the suspended (floccular) and granular fractions. Therefore, the development of adequate techniques to monitor this balance is of interest. In this work the sludge volume index (SVI), volatile suspended solids (VSS) and total suspended solids (TSS) of mature AGS were successfully predicted with multilinear regression (MLR) models using data obtained from quantitative image analysis (QIA) of both fractions (suspended and granular). Relevant predictions were obtained for the SVI (R2 of 0.975), granules TSS (R2 of 0.985), flocs TSS (R2 of 0.971), granules VSS (R2 of 0.984) and flocs VSS (R2 of 0.986). The estimation of the granular fraction ratio from the predicted TSS and VSS was also successful (R2 of 0.985). The predictions help to avoid instability episodes of the AGS system, such as changes in biomass morphology, structure and settling properties.The authors thank the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469 unit, BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020 – Programa Operacional Regional do Norte and the project AGeNT – PTDC/BTA-BTA/31264/2017 (POCI-01-0145-FEDER031264). We would also like to thank the scientific collaboration under the FCT project UID/Multi/50016/2019. Cristiano Leal is recipient of a fellowship supported by a doctoral advanced training (call NORTE-692015-15) 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).