Comparison of semi-batch vs. continuously fed anaerobic bioreactors for the treatment of a high-strength, solids-rich pumpkin-processing wastewater

Abstract

The objective of this work was to compare two different high-rate anaerobic bioreactor configurations – the anaerobic sequencing batch reactor (ASBR) and the upflow anaerobic solid removal (UASR) reactor – for the treatment of a solid-rich organic wastewater with a high strength. The two, 4.5-L reactors were operated in parallel for close to 100 days under mesophilic conditions (37°C) with non-granular biomass by feeding a pumpkin wastewater with ∼4% solids. The organic loading rate of pumpkin wastewater was increased periodically to a maximum of 8 g COD L⁻¹ d⁻¹ by shortening the hydraulic retention time to 5.3 days. Compositional analysis of pumpkin wastewater revealed deficiencies in the trace metal cobalt and alkalinity. With supplementation, the ASBR outperformed the UASR reactor with total chemical oxygen demand (COD) removal efficiencies of 64% and 53%, respectively, achieving a methane yield of 0.27 and 0.20 L CH₄ g⁻¹ COD fed to the ASBR and UASR, respectively. The better performance realized with the ASBR and this specific wastewater was attributed to its semi-batch, dynamic operating conditions rather than the continuous operating conditions of the UASR reactor.

Keywords:

• anaerobic digestion
• pumpkin wastewater
• anaerobic sequencing batch reactor
• upflow anaerobic solid removal reactor
• high-strength wastewater

Acknowledgement

The authors thank James McCarthy and Mark Pfeifer at Nestlé for initiating the study and for providing actual pumpkin wastewater.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Cornell University Agricultural Experiment Station federal formula funds, Project No. NYC-123452 from the NIFA, US Department of Agriculture, International Masters of Science in Environmental Technology and Engineering (IMETE) program, which is co-sponsored by the Erasmus+ programme of the EU, and New York State Energy Development Authority (NYSERDA) under agreement #28264.