No abstract

Inoculation dose is a key operational parameter for the solid-state anaerobic digestion (SS-AD) of lignocellulosic biomass, maximum methane recovery, and stable digester performance. The novelty of this study was the co-digestion of unamended full-strength grape marc and cheese whey for peak methane extraction at variable inoculation levels. An acclimatised digestate from a preceding anaerobic treatment was used as a downstream inoculum. The impact of inoculum size (wet weight) was evaluated at 0/10, 5/5, 7/3 and 9/1 substrate-to-inoculum (S/I) ratios, corresponding to an initial concentration of 20–30% total solids (TS) in digesters over 58 days at 45°C. The optimal 7/3 S/I produced the highest cumulative methane yield, 6.45 L CH4 kg-1 VS, coinciding with the lowest initial salinity at 11%; the highest volumetric methane productivity rate of 0.289±0.044 L CH4 LWork-1 d-1; the highest average COD/N ratio of 9.88; the highest final pH of 9.13, and a maximum 15.07% elemental carbon removal; for a lag time of 9.4 days. This study identified an optimal inoculation dose and opens up an avenue for the direct co-digestion of grape marc and cheese whey without requirements for substrate pretreatment, thus improving the overall bioenergy profile of the winery and dairy joint resource recovery operations.

At the end of fermentation, wine contains approximately 20% (w/v) of solid material, known as grape marc (GM), produced at a yield of 2 t/ha. Cheese manufacture produces cheese whey (CW), which is over 80% of the processed milk, per unit volume. Both waste types represent an important fraction of the organic waste being disposed of by the wine and dairy industries. The objective of this study was to investigate the bioenergy potential through anaerobic codigestion of these waste streams. The best bioenergy profile was obtained from the digestion setups of mixing ratio 3/1 GM/CW (wet weight/wet weight). At this ratio, the inhibitory salinity of CW was sufficiently diluted, resulting in 23.73% conversion of the organic material to methane. On average, 64 days of steady bioenergy productivity was achieved, reaching a maximum of 85 ± 0.4% CH4 purity with a maximum cumulative methane yield of 24.4 ± 0.11 L CH4 kg−1 VS. During the fermentation there was 18.63% CODt removal, 21.18% reduction of conductivity whilst salinity rose by 36.19%. It can be concluded that wine and dairy industries could utilise these waste streams for enhanced treatment and energy recovery, thereby developing a circular economy.

No abstract

Renewable and green energy resources are paramount to environmental sustainability. Microbial fuel cells (MFCs) are potential candidates for these alternatives but there is need to search for cheaper fuels to drive the MFCs for realistic large scale applications. A high strength effluent such as whey, which poses a serious environmental threat, is a good candidate for fueling the MFCs with an added advantage of bioremediation. Thus, cheese whey was evaluated for its ability to drive MFCs and the extent of whey remediation was also investigated during the operation of MFCs in this study. Three experimental anodic setups: Raw (unamended) whey alone, heat treated (sterile) whey inoculated with Enterobacter cloacae subspecies dissolvens, and raw whey inoculated with E. cloacae where employed. Native whey microbes achieved 44.7 ± 0 .2% total chemical oxygen demand (tCOD) removal efficiency and 0.04% coulombic efficiency ( cb ). The maximum power density generated was 0.4 W/m 2 (normalized to the anode surface area). Upon introduction of an exogenous electricigenic E. cloacae culture in the whey, the tCOD removal efficiency dropped to 5% while cb was the highest (3.7%) with maximum power density of 16.7 ± 1.8 W/m 2 . However, a combination of E. cloacae and unsterilized/unamended whey gave 1.1 W/m 2 , cb of 0.5% and 22.1% tCOD removal. The results confirmed the ability of whey to be used as a fuel in the anodic chamber to drive electricity generation in an MFC system with its partial remediation, but absence of synergism between E. cloacae and the electricigens is inherent to whey.