Volumetric Methane Yield Research Articles

Anaerobic Co-Digestion to Enhance Waste Management Sustainability at Yosemite National Park

This study evaluated the co-digestion of domestic wastewater solids (WWS) and food waste (FW) at the bench-scale for Yosemite National Park, California, which operates a 1900 m3/d wastewater treatment plant in El Portal, California. A 35-day biochemical methane potential test was performed on varying amounts of FW as a percentage of total waste (WWS plus FW) on a volatile solids basis (%FW). Specific methane yield and volumetric methane yield increased substantially with increasing %FW. A higher %FW was also associated with slower degradation kinetics but higher methane content in biogas. The 75 %FW treatment had relatively rapid kinetics, a high cumulative specific methane yield (453 mL CH4/g VS), and an elevated methane content in biogas, and is suggested as an upper limit %FW mixture for full-scale co-digestion. This, coincidently, is near the estimated ratio of WWS and FW production at the Park (70 %FW). Co-digesting the Park’s feedstock of FW with WWS in existing anaerobic digestion facilities could increase methane production five-fold. Combusting this methane in a combined heat and power system would produce about twice the energy needed to heat anaerobic digestors and power the treatment plant.

Biomethanation of syngas at high CO concentration in a continuous mode

Syngas from pyrolysis/gasification process is a mixture of CO, CO2 and H2, which could be converted to CH4, so called syngas biomethanation. Its development is obstructed due to the low productivity and CO inhibition. The aim of this study was to demonstrate the feasibility of using syngas as the only carbon source containing high CO concentration (40%) for biomethanation. Lab-scale thermophilic bioreactor inoculated with anaerobic sludge was operated continuously for over 900 h and the shift of microbial structure were investigated. Results showed that thermophilic condition was suitable for syngas biomethanation and the microbes could adapt to high CO concentration. Higher processing capacity of 12.6 m3/m3/d was found and volumetric methane yield of 2.97 m3/m3/d was observed. These findings could strengthen the theoretical basis of syngas biomethanation and support its industrialization in the future.

Continuous anaerobic digestion of zucchini stem after pretreatment

Anaerobic digestion (AD) is a widely used technology for converting organic wastes into biomethane with the advantages of clean energy production and few environmental impacts. Zucchini stem (ZS), the main waste produced from zucchini cultivation, is a potential feedstock for AD due to its high moisture and organic contents. This study investigated the methane production performance and system stability of ZS in continuous AD mode with the increase of organic loading rate (OLR). Moreover, to improve the methane production efficiency, KOH, NaOH, and alkaline hydrogen peroxide (AHP) pretreatments were also performed. The results showed that raw ZS gave a daily methane yield (DMY) of 182.1 mL g VS − 1 d −1 and volumetric methane yield (VMY) of 0.546 L L −1 d −1 at an OLR of 3.0 g VS L −1 d −1 . At the same OLR, 2% KOH-pretreated ZS significantly enhanced the DMY to 236.0 mL g VS − 1 d −1 and the VMY to 0.708 L L −1 d −1 , with a biodegradability (B d ) of 56.3%, which was 29.7% higher than that of raw ZS. However, NaOH- and AHP-pretreated ZS could not achieve stable methane generation at an OLR of 2.0 g VS L −1 d −1 . This study forms a foundation for future industrial applications of ZS; the investigated approach not only utilizes this waste efficiently and reduces its environmental pollution but also produces renewable biomethane energy and may improve the energy structure in rural areas. • Continuous anaerobic digestion (AD) of pretreated zucchini stem (ZS) was explored. • 2% KOH pretreated ZS performed stably and efficiently continuous AD system. • The highest volumetric methane yield was 0.708 L L -1 d -1 after 2% KOH pretreatment.

Dry Anaerobic Digestion of Chicken Manure: A Review

Providing anaerobic digestion is a prospective technology for utilizing organic waste, however, for waste with a high content of nitrogen such as manure, dilution is necessary to decrease the ammonia inhibition effect which leads to the production of a huge effluent amount which is difficult to use. Dry anaerobic digestion has some advantages such as reduced reactor volume, higher volumetric methane yield, lower energy consumption for heating, less wastewater production, and lower logistic costs for fertilizers. These factors generate interest in using it for treatment of even high-nitrogen substrates. The purpose of this work was to analyze different dry anaerobic digestion technologies, the features of dry anaerobic digestion, laboratory studies on chicken manure dry anaerobic digestion, and methods of reducing inhibitors’ effects. Nowadays, there are no dry anaerobic industrial plants working on chicken manure. However, studies on dry anaerobic digestion of chicken manure have proven the possibility of methane production under fermentation of chicken manure with high total solids content, but the process has been described as being unstable. Co-fermentation, ammonium/ammonia removal, and adaptation of the microbial consortium have been used to decrease the effect of ammonia inhibition. A prospective way for ammonia concentration control is absorption using a non-volatile sorbent located in the reactor. It decreases ammonia content during wet anaerobic digestion by 33% and it is characterized by having a positive economic effect. Therefore, dry anaerobic fermentation of chicken manure is possible, but there is still no efficient way to provide it. The results of this article should be helpful in the selection of anaerobic digestion technology for treating chicken manure.

Comparison of methane production performance of vinegar residue under liquid‐ and solid‐state conditions

AbstractVinegar residue (VR), a major by‐product in the vinegar brewing process, is generated at least three million tons annually in China. Currently major part of the disposal of VR is fulfilled by landfill and incineration, however, serious environment pollution along with such processes is a challenging issue. Anaerobic digestion (AD) can provide benefits of environment and renewable methane generation, which seems to be a reasonable alternative to traditional treatment. Noticeably, total solids (TS) is an important influential parameter to AD performance. Therefore, VR was evaluated for methane production and associated kinetic characteristics during the liquid‐state AD (LS‐AD) and solid‐state AD (SS‐AD) in this study. The results indicated that the highest specific methane yield of 194.8 mL gVS−1 and volumetric methane yield of 9.4 Lmethane Lreactor volume−1 were achieved in LS‐AD (TS = 10%) and SS‐AD (TS = 20%), respectively. The kinetic analysis showed a higher specific methane production rate for LS‐AD than SS‐AD, while volumetric methane production rate presented a reverse trend. This study provides useful guidance for the sustainable utilization of VR while contributes to environmental protection and alleviates the dependence on fossil fuels.

Influence of operation conditions on methane production from swine wastewater treated by a self-agitation anaerobic reactor

This study aimed to evaluate both the feasibility of using ambient temperatures (15, 20 and 25 °C) in a self-agitated anaerobic baffled reactor (SaABR) fed with swine wastewater, and the impact of decreasing the hydraulic retention time (HRT) down to 3 days. The highest specific methane yield (0.61 ± 0.14 L/gVSin) and organics conversation efficiency (66% on TCOD basis) were attained by elevating temperature from 15 to 25 °C under an HRT of 10 days. Even though the highest volumetric methane yield (0.85 ± 0.17 L/L/day) was registered during a 3-day HRT, the specific methane yield was lower as a result of volatile fatty acids accumulations (up to 790 ± 39 mg/L). The dominant bacterium was Clostridium sensu stricto while Methanosaeta was the dominant archaea throughout all the conditions, indicating strong acetoclastic methanogenic activity under ambient temperatures. These results demonstrate that using ambient temperatures and short HRTs is a promising strategy to successfully treat wastewater with decreasing energetics entries. This can, thereby, increase the treatment capacity and enhance the methane yield during the anaerobic digestion process.

Comparison of varying operating parameters on heavy metals ecological risk during anaerobic co-digestion of chicken manure and corn stover

In this study, the potential ecological risk of heavy metals (Mn, Zn, Cu, Ni, As, Cd, Pb, Cr) accumulation from anaerobic co-digestion of chicken manure (CM) and corn stover (CS) was evaluated by comparing different initial substrate concentrations, digestion temperatures, and mixture ratios. Results showed that the highest volumetric methane yield of 20.3±1.4L/L reactor was achieved with a CS:CM ratio of 3:1 (on volatile solid basis) in mesophilic solid state anaerobic digestion (SS-AD). Although co-digestion increased the concentrations of all tested heavy metals and the direct toxicity of some heavy metals, the potential ecological risk index indicated that the digestates were all classified as low ecological risk. The biogasification and risk variation of heavy metals were affected by the operating parameters. These results are significant and should be taken into consideration when optimizing co-digestion of animal manure and crop residues during full-scale projects.

Composition and biogas yield of a novel source segregation system for pig excreta

The performance of a novel source segregation method for pig excreta (a V-shaped conveyor belt underneath the slatted pen floor) was compared to conventional separation methods for pig slurry (screw press, centrifugation, flocculation with/without centrifugation). For the source segregation system, a larger amount of organic matter accumulated in the solid fraction (96%) than for conventional separation systems (34–93%). Also the dry matter content, nutrient content (total N and P), and methane production of this solid was higher than for the other systems. Furthermore the volumetric methane yield was much higher than for the solid fraction from the other separation systems (1.6 vs 0.8–1.0 m 3 [CH 4 ]·m −3 [reactor]·day −1 for a CSTR). Due to the high methane yield, digestion of the solid from source segregation is expected to require a considerable smaller reactor than for slurry digestion, which would increase the economic feasibility of mono-digestion systems for animal manure.

Influence of variable feeding on mesophilic and thermophilic co-digestion of Laminaria digitata and cattle manure

In this study the effect of various feeding ratios on mesophilic (∼35°C) and thermophilic (∼50°C) co-digestion of brown algae Laminaria digitata and cattle manure was investigated. Algae input of 15% VS caused no influence on specific methane yield from mesophilic co-digester while deteriorated the process parameters such as the development of propionic acid in total volatile fatty acids (tVFA) pattern of the thermophilic co-digester. The accumulation of tVFA continued for the latter reactor as the feeding ratio of algae enhanced to 24% VS, but the specific methane yield improved dramatically. Same rise in feeding once again showed no improvement in specific methane yield from mesophilic co-digester even though the other process parameters stabilized or, enriched such as the gain in average volumetric methane yield. For the last feeding ratio at 41% VS algae, specific methane yield from mesophilic co-digester slightly increased which however was not still comparable with the ultimate methane yield from the cattle manure alone. The thermophilic co-digestion on the other hand yielded maximum specific methane, together with the improvement in different process characteristics, as the feeding of algae maximized at the final stage. The trend of methane production from this reactor nevertheless was sharply downward towards the end of the experiment suggesting that the optimum feeding ratio has already been achieved for the present experimental conditions.

Solid-state anaerobic co-digestion of hay and soybean processing waste for biogas production

Co-digestion of soybean processing waste (SPW) and hay in solid-state anaerobic digestion (SS-AD) for biogas production was investigated. Effects of the SPW to hay ratio, feedstock to effluent (inoculum) ratio, premixing of effluent with feedstock, and leachate recirculation on biogas production via SS-AD were studied. The highest methane yield of 258 L/kg VS was obtained with a SPW/hay ratio of 75:25 and feedstock/effluent (F/E) ratio of 3, which was 148% and 50% higher than that of 100% SPW and 100% hay, respectively. Increasing the F/E ratio from 1 to 5 decreased methane yield, however the highest volumetric methane yield (16.2L/L reactor) was obtained at an F/E of 3. There was no significant difference in methane yields between premixing 50% and 100% of the effluent. Leachate recirculation significantly accelerated the SS-AD start-up process when effluent was not completely premixed.

Effect of increasing the organic loading rate on the co-digestion and mono-digestion of cattle slurry and maize

Co-digestion of cattle slurry and maize has been shown to have benefits for both, improving the biogas yield of the slurry and stability of digestion of the maize. The effect of increasing the total loading rate from 3 to 6 g VS l(-1) day(-1) on the co-digestion of cattle slurry and maize, mixed at equal volatile solids volumes, was investigated in laboratory-scale continuously stirred digesters. These were compared with similar digesters evaluating the increase of 1.5 to 3 g VS l(-1) day(-1) loading rates of slurry and maize digested separately. Compared with mono-digestion of the substrates, where the digestion of maize failed at loading rates greater than 2.5 g VS l(-1) day(-1), the co-digestion of cattle slurry and maize was feasible at all the loading rates tested with an increase in the volumetric methane yield occurring with loading rate. Even at the lowest rate of loading, the addition of equal amounts of volatile solids of maize to slurry leads to an increase in volumetric methane yield of 219%.

Methane productivity of manure, straw and solid fractions of manure

The methane productivity of manure in terms of volatile solids (VS), volume and livestock production was determined. The theoretical methane productivity is higher in pig (516 l kg −1 VS ) and sow (530 l kg −1 VS ) manure than in dairy cattle manure (469 l kg −1 VS ) , while the ultimate methane yield in terms of VS is considerably higher in pig (356 l kg −1 VS ) and sow manure (275 l kg −1 VS ) than in dairy cattle manure (148 l kg −1 VS ) . Methane productivity based on livestock units (LU) shows the lowest methane productivity for sows (165 m 3 CH 4 LU −1 ) , while the other animal categories are in the same range (282– 301 m 3 CH 4 LU −1 ). Pre-treatment of manure by separation is a way of making fractions of the manure that have a higher gas potential per volume. Theoretical methane potential and biodegradability of three types of fractions deriving from manure separation were tested. The volumetric methane yield of straw was found to be higher than the yield from total manure and the solid fractions of manure, due to the higher VS content, and hence the use of straw as bedding material will increase the volumetric as well as the livestock-based methane productivity.

Kinetics of rice straw methane fermentation

The kinetics of anaerobic fermentation of rice straw to methane were studied. Rice straw was the only carbon source at influent volatile solid concentrations of 18.9 and 37.8 g/l. Semicontinous runs were carried out at 37°C in laboratory scale perfectly mixed reactors. The Contois' kinetic model constants were calculated from the experimental data. Arefrac tory coefficient was measured (R=0.374) to account for the nonbiodegradable portion of the organic matter of rice straw and incorporated into the kinetic equations. The predicted values of effluent substrate concentration, volumetric methane yield, volumetric methane production rate, and biodegradable conversion efficiency fit well with those measured experi mentally.