Effects of Media Characteristics on Performance of Upflow Anaerobic Packed-Bed Reactors

Abstract

The effects of media specific surface area, porosity, pore size as well as the role of suspended biomass on the performance of upflow anaerobic packed-bed reactors (APBRs) treating synthetic protein-carbohydrate waste were examined in the laboratory. The results showed that the reactor packed with media of the largest media pore size and porosity demonstrated the highest chemical oxygen demand (COD) removal efficiencies at loading rates of 8, 12, and 16 g COD/L·d. An increase of over 40% in specific surface area in an APBR had not improved the removal efficiency, instead it produced 16% lower in COD removal efficiency at loading rate of 16 g COD/L·d. The superiority in treatment performance of the media having the largest porosity and pore size indicates that, a substantial amount of the COD removal was associated with the suspended biomass entrapped in the interstitial void spaces within the media. Quantitative indication of methane production by the suspended biomass based on a batch serum bottle technique indicated that, suspended biomass contributes approximately one half of the total methane production. The amount of methane production associated with the suspended biomass determined from the test was as high as 56% at 12 g COD/L·d and increased to 58% at higher loading rate of 16 g COD/L·d. The results suggest that media pore size and porosity play a more significant role than media specific surface area in the performance of upflow APBRs. The media with larger pore size and porosity are likely to cause higher growth of entrapped suspended biomass or sludge granules leading to superiority in waste treatment.