The effect of polymer addition on granulation in an anaerobic baffled reactor (ABR). Part I: process performance

Abstract

The stability and performance of an anaerobic baffled reactor (ABR) treating an ice-cream wastewater at several organic loading rates have been investigated. Specifically, it was determined whether an ABR would promote phase separation and if a polymer additive was capable of enhancing granule formation in an ABR. In order to achieve these goals, two ABRs, having identical dimensions and configurations, were used to study the above objectives using a synthetic ice-cream wastewater. The ABR proved to be an efficient reactor configuration for the treatment of a high-strength synthetic ice-cream wastewater. An organic loading rate of around 15 kg CODm(-3) d(-1) was treated with a 99% COD removal efficiency. From the jar test and inhibition assay, it was concluded that Kymene SLX-2 was the most effective and least inhibitory polymer tested. The methane yield was higher in the polymer-amended reactor compared to the control reactor. In addition, polymer addition resulted in a considerably higher degree of biomass retention and lower solids washout from the ABR. Consequently, it demonstrated that there was a considerable potential for sludge conditioning in ABRs by facilitating better biomass retention within the reactor which in turn led to better process performance. Granulation was achieved in both ABRs within 3 months. However, the granules from the polymer-amended reactor appeared earlier and were generally larger and more compact, although this was not quantified in detail during the present study. The main advantage of using an ABR comes from its compartmentalised structure. The first compartment of an ABR may act as a buffer zone to all toxic and inhibitory material in the feed thus allowing the later compartments to be loaded with a relatively harmless, balanced and mostly acidified influent. In this respect, the latter compartments would be more likely to support active populations of the relatively sensitive methanogenic bacteria and partly explains why the best granules and the highest methane yield were obtained in Compartment 2. It is unlikely that a complete separation of phases (acidogenic and methanogenic) occurred within the ABRs since methane production was observed in all compartments, although this was low (approximately 40% of all gas composition) in Compartment 1, becoming higher (approximately 70%) in the following compartments.