One-stage single cell protein production from hemp (Cannabis sativa L.) biomass residues and cheese whey through sequential anaerobic-aerobic fermentation

Abstract

Single cell protein (SCP) is emerging as a viable alternative to conventional protein sources thanks to their low environmental footprint and resource upcycling potential. This study investigated the production of SCP from hemp (Cannabis sativa L.) biomass residues (HBRs) and cheese whey (CW) in an innovative one-stage sequential anaerobic–aerobic fermentation process, through which the anaerobically produced volatile fatty acids (VFAs) were converted into SCP in the aerobic step. The best performance in terms of VFA and biomass yields (i.e., 0.85 mg HAc ∙ mg sCOD^-1 and 0.21 g TSS ∙ g sCOD^-1, respectively) as well as of protein content (i.e., 51 %) was obtained by working with a consecutive residence time of two and one days for, respectively, the anaerobic and the aerobic phase. A preliminary techno-economic assessment was performed to calculate the total production cost of the SCP, which ranged between 1.71 and 3.23 € ∙ kg TSS^-1.

Abbreviations: HAc, acetic acid equivalent; TSS, total suspended solids; HH, hemp hurds; Mix, mix of leaves and inflorescences; LA, lactic acid; LAB, lactic acid bacteria; co-AF, acidogenic co-fermentation; AeF, aerobic fermentation; HRT, hydraulic retention time; VS, volatile solids; SRT, solid retention time; VSS, volatile suspended solids; sCOD, soluble chemical oxygen demand; CBHs, carbohydrates; HPLC, high-performance liquid chromatography; Π, VFA volumetric productivity, mg HAc ∙ L^-1∙ d^-1; Γ, VFA yield, mg HAc ∙ mg sCOD^-1; B, biomass volumetric productivity, g TSS ∙ L^-1∙ d^-1; PP, protein volumetric productivity, g protein ∙ L^-1∙ d^-1; Y, biomass yield coefficient, g TSS ∙ g COD^-1; CAPEX, capital expenditures; OPEX, operating expenditures; DW, dry weight; RA, relative abundance; HOB, hydrogen oxidizing bacteria; PHAs, polyhydroxyalkanoates; OLR, organic loading rate.