Dynamic Effect of Operational Regulation on the Mesophilic BioMethanation of Grape Marc

Wine production annually generates an estimated 11 million metric tonnes of grape marc (GM) worldwide. The diversion of this organic waste away from landfill and towards its use in the generation of renewable energy has been investigated. This study aimed to evaluate the effectiveness of operational parameters relating to the treatment regime and inoculum source in the extraction of methane from GM under unmixed anaerobic conditions at 35 °C. The study entailed the recirculation of a previously acclimated sludge (120 days) as downstream inoculum, an increased loading volume (1.3 kg) and a low substrate-to-inoculum ratio (10:3 SIR). The results showed that an incorporation of accessible operational controls can effectively enhance cumulative methane yield (0.145 m3 CH4 kg−1 VS), corresponding to higher amounts of digestible organics converted. The calculated average volumetric methane productivity equalled 0.8802 L CH4 LWork−1 d−1 over 33.6 days whilst moderate pollutant removal (43.50% COD removal efficiency) was achieved. Molecular analyses identified Firmicutes and Bacteroidetes phyla as core organisms for hydrolytic and fermentative stages in trophic relationships with terminal electron acceptors from the methane-producing Methanosarcina genus. Economic projections established that the cost-effective operational enhancements were sustainable for valorisation from grape marc by existing wineries and distilleries.

Biochemical Methane Potential of Swine Slaughter Waste, Swine Slurry, and Its Codigestion Effect

The codigestion of slaughter waste with animal manure can improve its methane yield, and digestion parameters; however, limited studies are available for the effectiveness of anaerobic codigestion using swine slaughter waste (SSW) and swine slurry (SS). Hence, this study was conducted to determine the characteristics of SSW and the effect of anaerobic codigestion with (SS) and explored the potential of CH4 production (Mmax), the lag phase period (λ), and effective digestion time (Teff). SSW contains fat and protein contents of 54% and 30% dry weight within 18.2% of solid matters, whereas SS showed only 6% and 28% within 4.1% of solid matters, respectively. During sole anaerobic digestion, SSW produced a high Mmax (711 Nml CH4/g VSadded) but had a long duration λ (~9 days); whereas SS produced a low Mmax (516 Nml CH4/g VSadded) but had a shorter duration λ (1 day). Codigestion increased the Mmax from 22–84% with no significant Teff compared to sole SS digestion. However, the low Mmax of SS and high Mmax of SSW, resulted in a 7–32% decrease in Mmax at codigestion compared to SSW sole digestion. Codigestion improved the digestion efficiency as it reduced λ (3.3–8.5 days shorter) and Teff (6.5–9.1 days faster) compared to SSW sole digestion. The substrate-to-inoculum ratio of 0.5 was better than 1; the volatile solid and micronutrient availability may be attributed to improved digestion. These results can be used for the better management of SSW and SS for bio-energy production on a large scale.

Bioenergy Production through Mono and Co-Digestion of Tomato Residues

The agro-industry of tomato generates three types of residues: ripe rotten tomato (unfit for consumption) (RT), green (unripe) tomato (GT), and tomato branches including leaves and stems (TB). These materials are commonly wasted or used as feed for livestock. Energy production through anaerobic digestion is an alternative way to manage and simultaneously valorise these materials. Initially, the operating conditions of mono anaerobic digestion were investigated using RT. Thus, a design of experiments based on a two-level fractional factorial design with resolution V was performed to determine the factors that affect biochemical methane potential (BMP). The substrate to inoculum ratio (SIR), total volatile solids concentration (VSt), working volume (WV), presence of nutrients (Nu), and the pre-incubation of the inoculum (Inc) were investigated. The results showed that SIR is the most important factor. The maximum BMP for RT was 297 NmLCH4/gVS with SIR = 0.5; tVS = 20 g/L; WV = 20%; no pre-incubation and the presence of nutrients. Using these optimum operating conditions, co-digestion was investigated through a mixture design approach. The substrates RT and GT presented similar BMP values, whereas TB led to a significantly lower BMP. Indeed, when high concentrations of TB were used, a significant decrease in methane production was observed. Nonetheless, the highest BMP was achieved with a mixture of 63% RT + 20% GT + 17% TB, with a production of 324 NmLCH4/gVS, corresponding to a synergetic co-digestion performance index of about 1.20. In general, although the substrate RT generates the highest BMP, the mixture with GT did not impair the methane yield. Overall, the co-digestion of tomato residues must be conducted with SIR close to 0.5 and the content of tomato branches in the reaction mixture should be kept low (up to 20%).

EFFECT OF SOLIDS CONCENTRATION AND SUBSTRATE TO INOCULUM RATIO ON METHANE PRODUCTION FROM ORGANIC MUNICIPAL SOLID WASTE

Organic Fraction of Municipal Solid Waste (OFMSW) is usually stored under variable humidity conditions and long periods before processing them in anaerobic digestion plants. Lately, the fermented OFMSW is mixed with recirculated digestate from the same biogas plants, which is used as methanogenic inoculum. Although both the moisture content during the storage of OFMSW and the inoculum concentration in the feed mixture to the anaerobic reactors are determining factors for the process, to our knowledge, no studies have been done about the combined effect of these operational parameters on methane production. Therefore, this study focused on determining how humidity conditions during OFMSW storage and the substrate to inoculum ratio (S/I) in the methanisation stage can be adjusted to improve methane production. OFMSW was stored at 35°C and 10, 20, and 28%TS for 15 days. In the second stage, methanisation of previously fermented OFMSW was allowed at different S/I ratios of 0.5, 1.0, and 1.5. Ethanol and acetic acid accounted for 90% of all products of fermentation. The lowest solids concentration reached the highest fermentation degree. Compared to fresh OFMSW (without storing), methane from fermented OFMSW increased 32% and, the times to reach the maximum methane production decreased between 11 and 40%. For fermented OFMSW, S/I ratio of 1.0 is the best condition to produce methane. ANOVA shows that, independently of solid concentration during storage, the S/I ratio is the main parameter improving methane production and reducing reaction times.

EFFECT OF OPERATING CONDITIONS ON THE PRODUCTION OF VOLATILE FATTY ACIDS FROM ORGANIC WASTES

The five parameters being analyzed are pH, temperature, retention time/organic loading rate, substrate to inoculum ratio, and inhibitors of VFAs. The effect of pH has been shown to produce optimal concentrations of VFAs when outside the optimal range of methanogenesis. Temperature sees different types of VFAs being produced at different concentrations dependant on mesophilic or thermophilic conditions. The organic loading rate (OLR) and retention time (RT) demonstrate similar concepts as longer periods of time allow for more VFAs to be converted from the waste but readily supplying waste to digesters sees higher concentrations produced immediately. The substrate to inoculum ratio (S/I) showed ratios above 1 to be favorable in production as it provided enough inoculum (microorganisms) to convert VFAs effectively. Lastly, the effects of several VFA inhibitors are discussed with regards to their impacts on the anaerobic digestion process and their inhibition of certain VFA’s formation.

EFFECT OF OPERATING CONDITIONS ON THE PRODUCTION OF VOLATILE FATTY ACIDS FROM ORGANIC WASTES

The five parameters being analyzed are pH, temperature, retention time/organic loading rate, substrate to inoculum ratio, and inhibitors of VFAs. The effect of pH has been shown to produce optimal concentrations of VFAs when outside the optimal range of methanogenesis. Temperature sees different types of VFAs being produced at different concentrations dependant on mesophilic or thermophilic conditions. The organic loading rate (OLR) and retention time (RT) demonstrate similar concepts as longer periods of time allow for more VFAs to be converted from the waste but readily supplying waste to digesters sees higher concentrations produced immediately. The substrate to inoculum ratio (S/I) showed ratios above 1 to be favorable in production as it provided enough inoculum (microorganisms) to convert VFAs effectively. Lastly, the effects of several VFA inhibitors are discussed with regards to their impacts on the anaerobic digestion process and their inhibition of certain VFA’s formation.

Co-digestion of Pretreated Chicken – Goat and Untreated Cow Manure at Different Substrate to Inoculums Ratios and Total Solids for Biogas Production

Biogas production can be greatly affected by inoculum addition and total solids. The effect of the substrate to inoculum ratios and total solids of chicken, goat and cow manure on biogas production was studied using a 0.15m3 laboratory-scale batch digester at a constant temperature of 35°C. Feedstocks were mechanically minced to 3 mm effective particle sizes prior to co-digesting with untreated cow manure from a free-range dairy rearing system. Different amounts of cow substrate inoculum were used at ratios of 2:1, 3:1, 4:1, 5:1 and 6:1, while total solid levels between (7.5% and 10.5%) at intervals of 0.5% were used to study their effects on biogas production. Increasing inoculums and total solids resulted in increased biogas production with peaks at a substrate to inoculum ratio of 4:1 (20% inoculum addition) and 9% total solids. Biogas production rates of 0.61 and 0.63m3/m3d were realized respectively. Keywords: Biogas Production, Chicken-Goat-Cow Manure, Substrate to Inoculum Ratios, Total Solids