Vacuum-enhanced anaerobic fermentation: Achieving process intensification, thickening and improved hydrolysis and VFA yields in a single treatment step

Basem Haroun; Gholamreza Bahreini; Masuduz Zaman; Eunkyung Jang; Frances Okoye; Elsayed Elbeshbishy; Domenico Santoro; John Walton; Ahmed Al-Omari; Chris Muller; Kati Bell; George Nakhla

doi:10.1016/j.watres.2022.118719

Vacuum-enhanced anaerobic fermentation: Achieving process intensification, thickening and improved hydrolysis and VFA yields in a single treatment step

Water Res. 2022 Jul 15:220:118719. doi: 10.1016/j.watres.2022.118719. Epub 2022 Jun 7.

Authors

Affiliations

¹ Chemical and Biochemical Engineering, University of Western Ontario, Canada; Water Pollution Research Department, National Research Center, 33 El Bohoth St., P.O.12622, Dokki, Giza, Egypt.
² Chemical and Biochemical Engineering, University of Western Ontario, Canada.
³ USP Technologies, Canada.
⁴ Civil Engineering Department, Ryerson University, Canada.
⁵ Brown and Caldwell, USA.
⁶ Chemical and Biochemical Engineering, University of Western Ontario, Canada; Civil and Environmental Engineering, University of Western Ontario, Canada. Electronic address: gnakhla@uwo.ca.

PMID: 35704979
DOI: 10.1016/j.watres.2022.118719

Abstract

This study assessed the feasibility of a novel vacuum-enhanced anaerobic digestion technology, referred to as IntensiCarb^TM (IC), under mild vacuum pressure (110 mbar), compared to a control (conventional fermenter), and evaluated the impact of the vacuum on the activities of various microbial groups. Both fermenters (test and control) were operated with mixed (50% v/v) municipal sludge at solids concentrations of 2-2.5%, pH of 7.8-8.1, 40-45 °C, a theoretical solids retention time (SRT) of 3 days with different hydraulic retention times (HRT). The intensification factor (IF) of the IC, defined as SRT/HRT, was controlled at 1.3 and 2.0. Simultaneous thickening and fermentation intensification were achieved. Compared with the control, the IC, despite the shorter HRTs, achieved 29.5 to 90.2% increase in the VFA yield (79 to 116 mg ΔVFA/ g VSS vs 61 mg ΔVFA/ g VSS), and 16.2% to 56.4% increase (280 to 377 mg ΔsCOD/ g VSS vs 241 mg ΔsCOD/ g VSS), in the hydrolysis yield. Fermentate from the IC exhibited comparable specific denitrification rates to acetate. Further, the solids-free condensate contained low nutrient concentrations, and thus was far superior to a typical centrates from dewatering as a carbon source. No adverse effects of vacuum on the activity of fermentative bacteria and methanogens were observed. This study demonstrated that the IC can be deployed as an intensification technology for both fermentation and anaerobic digestion of biosolids with the additional significant advantage, i.e. elimination of sidestream ammonia treatment requirements.

Keywords: Advanced biosolid treatment; Anaerobic fermentation; Evaporation; Vacuum fermentation.

MeSH terms

Anaerobiosis
Bioreactors*
Fermentation
Hydrolysis
Sewage* / microbiology
Vacuum

Substances

Sewage