Higher Biomethane Potential Research Articles

Methane production through anaerobic digestion: Participation and digestion characteristics of cellulose, hemicellulose and lignin

Lignocellulosic biomass is the most abundant natural resource with high biomethane potential. However, complex structure of lignocellulosic biomass has hampered the efficient utilization of this bioresource. Previous studies have investigated the overall anaerobic digestion performance of lignocellulosic biomass, but the individual participation of each lignocellulosic component during anaerobic digestion remained unclear. Thus, this study investigated the methane production characteristics of cellulose, hemicellulose, lignin and their mixtures along with the microbial communities involved in anaerobic digestion. The results showed that the biomethane potential of cellulose was higher than that of hemicellulose; however, hemicellulose was hydrolysed more quickly than cellulose, while lignin was very difficult to be digested. The higher concentrations of acetic, n-butyric and n-valeric acids hydrolysed from the hemicellulose resulted in a lower pH and more severe inhibition on methane production than that of cellulose, and the methanogenesis gradually recovered after pH adjustment. The co-digestion of cellulose and hemicellulose increased the methane yield and biodegradability compared to mono-digestions. The addition of lignin to cellulose brought more significant decrease in the methane yield of cellulose than that of hemicellulose. Substrate-related bacteria such as Clostridium sensu stricto, Lutaonella, Cloacibacillus and Christensenella showed higher relative abundance in cellulose digestate, and sugar-fermenting bacteria such as Saccharofermentans, Petrimonas and Levilinea were more rich in the digestate of hemicellulose. Moreover, methanogenic Methanospirillum and Methanothrix likely contributed to the methane production of cellulose, while aciduric methanogens from Methanobrevibacter, Methanomassiliicoccus, Methanobacterium and Methanoculleus contributed to that of hemicellulose. This study provides a deeper understanding of the mechanism in the bioconversion of lignocellulosic biomass during anaerobic digestion.

Strategies for the sustainable management of orange peel waste through anaerobic digestion

The processing of oranges is a major industry worldwide and leads to the production of large amounts of orange peel waste (OPW). Energy production through anaerobic digestion of OPW is a promising option; however, the high content of essential oil, mainly composed of d-limonene, a well-known antioxidant, can cause the inhibition of the biological activity. In this paper, different pretreatment methods were tested (e.g. ensiling, aeration, thermal and alkaline treatments) to optimize the anaerobic digestion of OPW focusing on d-limonene removal. The raw and pretreated substrates were characterized and their biochemical methane production was measured. The results demonstrated the ability of some of the treatments to reduce d-limonene content up to 80%. A relatively high biomethane potential production of OPW (up to about 500 NmL CH4 g−1VS) was measured. The importance of the acclimation of inoculum and the risk connected to the accumulation of inhibiting substances in the reactor is discussed.

A comparison in product‐value potential in four treatment strategies for food waste and faeces – assessing composting, fly larvae composting and anaerobic digestion

AbstractMunicipalities are expected to provide solid waste management, which is funded by tax revenue or/and waste treatment fees. In many low‐ and middle‐income countries, municipalities struggle to provide an adequate level of service, and in these places, the informal sector plays a major role in the collection and treatment of solid waste. In contrast to the plastic and metal fraction, the organic fraction is not managed by the informal sector, primarily because it has low or no financial value and treatment would cost more than the possible revenue. If the organic fraction could be converted to valuable products, the treatment could bear its own cost and this could act as an incentive to collect and treat this fraction. In this study, the potential product value generated through four treatment strategies treating food waste and faeces was compared in a Swedish context: (i) thermophilic composting; (ii) black soldier fly treatment (BSF treatment); (iii) anaerobic digestion (AD); and (iv) BSF treatment followed by AD (BSF + AD). In order to assess the AD strategies, the biomethane potentials of the substrates were assessed. Food waste had the highest biomethane potential, while BSF‐treated faeces had the lowest (417 and 188 NmL g VS−1, respectively). Thermophilic composting yielded the lowest value product (organic fertilizer; 26 € t−1 treated food waste) and BSF treatment + AD the highest total value of products (animal feed, vehicle gas and organic fertilizer; 215 € t−1 treated food waste). The treatment costs were not taken into account here; the total value gives an indication of the cost margin for the different strategies studied. In places with an existing AD plant, BSF treatment + AD strategy is the most economically viable. In places where no such plant exists, BSF treatment is likely to be the most economically favourable treatment.

Biomethanation of Carpet Grass (Axonopus fissifolius)

Axonopus fissifolius commonly called “carpet grass” was subjected to anaerobic digestion for 30 days. Anaerobic digestion was carried out in a batch-fed process at the ambient temperature of 27-290C. Biomethane measurements were obtained by measuring the volume displacement of a saturated filtered calcium hydroxide solution in a transparent calibrated vessel. 42.7g of fresh carpet grass clippings yielded 1.955 L of biomethane. Biomethane potential (BMP) of carpet grass for a 30 day anaerobic digestion was 0.05 m3 CH4 kg-1 TS. The rates of biomethane potentials for the first, second, third, fourth and fifth six-day intervals were 1.5mL g-1 TS (2.81%), 6.4mL g-1 TS (14.58%), 16.1mL g-1 TS (30.18%), 17.74mL g-1 TS (33.25%), and 10.23mL g-1 TS (19.81%) respectively. The total solids, volatile solids and pH of feedstock and digestate were 85.80% and 85.56%, 90.91% and 87.58%, 6.6 (27oC) and 6.9 (27oC) respectively. The relatively high biomethane potential of carpet grass at the ambient temperature presented in this paper depicts anaerobic digestion as a viable means of profitably treating grass waste for both sanitation and generating biomethane especially in the tropics where the ambient temperatures are usually favourable for optimum biomethanation for most part of the year, thus making the process affordable and less cumbersome.DOI http://dx.doi.org/10.5755/j01.erem.66.4.5228

Kinetics Modeling of Anaerobic Fermentative Production of Methane from Kitchen Waste Solid Residual

A series of batch mesophilic anaerobic digesntion were conducted using an automatic methane potential test system (AMPTS) and the kinetics of methane production was also discussed using modified Gompertz equation, Logistic function, First-order kinetics model and Transference function, respectively. The results showed that the kitchen waste solid residual was of high biomethane potential, and the maximum specific methane yield was obtained 585 NmL/g TS at inoculums substrate ratio (ISR) 2:1. All of the four models could appropriately fit the accumulative methane production in steady state (R2>0.95), where the 1st-ordre model and Transference function were relatively much better (R2>0.99) than the other two models. The maximum methane production and maximum methane production rate obtained from the Transference function were 569.32 NmL/g TS and 150.22 NmL/g TS day; the maximum kinetics constant obtained from the 1st-order model was 0.272/day; the lag time (λ) was basically negligible in all the cases. These parameters were quite close to the experimental results.