Effect of the stirring speed, the type of impeller and the feed strategy in a mechanically stirred pilot-scale anaerobic sequencing batch reactor

Author(s)

Luciano Farias de Novaes

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de São Carlos (EESC/SBD)
• Defense date: 2008-05-30

Examining board members

José Alberto Domingues Rodrigues; Mario Takayuki Kato; Deovaldo de Moraes Junior; Arnaldo Sarti; Marcelo Zaiat

• Advisor: José Alberto Domingues Rodrigues

Abstract

The objective of this work was to assess the effect of the stirring speed, the type of impeller and the feed strategy in a mechanically stirred pilot-scale (\'da ordem de\' 1 \'M POT.3\') anaerobic sequencing batch reactor to two configurations: a containing granulated biomass (ASBR) and the other containing immobilized biomass (AnSBBR). Domestic wastewater was treated in 8-h cycles. Three impeller types (turbine with six-flat blades, turbine with six 45º-inclined blades and helix with three blades) were assessed at two different stirring speeds (40 and 80 rpm), totaling six experimental conditions. The stirring speed and the impeller that resulted in the best combination was used in work of the feed strategy . The reactors were operated at room temperature at four different feed strategies (fed batch during 25%, 50% and 75% of the cycle, and conventional fed-batch). The results allowed conclude that: in the AnSBBR increasing the stirring speed from 40 rpm to 80 rpm showed to improve mass transfer, with consequent increase in substrate consumption; in the ASBR increasing the stirring speed from 40 rpm to 80 rpm showed desestabilization in system, because of the disruption caused in the granules witth greater agitation; operation with the helix impeller showed some advantages over the turbine impellers, such as: improved efficiency in solids removal, higher value of the first order kinetic constant and higher alkalinity production; both for the ASBR as for the ASBBR the best performance in wastewater treatment was obtained when the reactors were operated at conventional batch, fed-batch during 50% and 75% of the cycle; no significant difference in performance was observed among these three conditions. Despite poor performance of the conventional fed-batch and fed-batch during 25% of the cycle compared to the other conditions, both these conditions presented operational stability. Hence, the anaerobic sequencing batch reactors presented operational flexibility as far as feed strategy is concerned. (AU)