Effect of anaerobic digester inoculum preservation via lyophilization on methane recovery.

Affiliation

Department of Environmental Science and Technology, University of Maryland, College Park, MD 20742, USA. Electronic address: [Email]

Abstract

A robust anaerobic digestion (AD) inoculum is key to a successful digestion process by providing the abundant bacteria needed for converting substrate to useable methane (CH4). While transporting digester contents from one AD to another for digester startup has been the norm, transportation costs are high, and it is not feasible to transport wet inoculum to remote locations. In this study, the impact of preservation of AD inoculum via lyophilization was investigated for the purposes of digester startup and restabilization. The effect of lyophilizing inoculum on CH4 production using food waste as the substrate was tested using biochemical methane potential (BMP) tests under the following conditions: (1) three inoculum sources, (2) two inoculum to substrate ratios (ISR), (3) two cryoprotectants, and (4) two inoculum growth phases. After lyophilization with skim milk, the three inocula produced 144-146 mL CH4/g volatile solids (VS) and 194-225 mL CH4/g VS at a 2:1 and 4:1 ISR, respectively, with 33-57% more CH4 at the 4:1 ISR. Preservation with 10% skim milk exhibited complete recovery of CH4 production, while 10% glycerol and 10% glycerol/skim milk mixture yielded 76% and 4% CH4 recovery, respectively. Inoculum growth phase before preservation (mid-exponential or stationary growth phase) did not significantly affect CH4 recovery. The study indicates that inoculum can be preserved via lyophilization using 10% skim milk as a cryoprotectant and reactivated for food waste digestion. The results provide a systematic quantification of the conditions needed to successfully preserve a mixed AD inoculum.

Keywords

Biochemical,Cryoprotectant,Food waste,ISR,Lag phase,Startup,

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