Solid-state Anaerobic Co-digestion Research Articles

Effect of inoculum and substrate/inoculum ratio on the performance and methanogenic archaeal community structure in solid state anaerobic co-digestion of tomato residues with dairy manure and corn stover

Effects of methanogenic community of inoculum (liquid anaerobic digestion effluent (L-AD effluent), waste activated sludge (WAS), and anaerobic granular sludge (AGS)) and substrate/inoculum ratio (S/I) on reactor performance in solid state anaerobic digestion (SS-AD) were investigated. L-AD effluent, which can provide sufficient microbes and enough buffering capacity to the reactor at an S/I ratio of 6, was found to quickly initiate SS-AD processes. The highest methane production was obtained in reactor inoculated with WAS at an S/I ratio of 2. Higher volatile fatty acids and total ammonia nitrogen concentrations were found when AGS was used as inoculum, which led to a low methane production. Methanosaetaceae, Methanosaetaceae, and Methanosaetaceae together with Methanobacteriaceae were the dominant methanogens in reactors inoculated with L-AD effluent, WAS, and AGS, respectively. These findings suggest among the three inoculum, L-AD effluent is the most effective inoculum for SS-AD of on farm organic waste.

Influence of feedstock-to-inoculum ratio on performance and microbial community succession during solid-state thermophilic anaerobic co-digestion of pig urine and rice straw

This study investigated the effect of the feedstock-to-inoculum (F/I) ratio on performance of the solid-state anaerobic co-digestion of pig urine and rice straw inoculated with a solid digestate, and clarified the microbial community succession. A 44-day biochemical methane potential test at F/I ratios of 0.5, 1, 2 and 3 at 55 °C and a 35-day large-scale batch test at F/I ratios of 0.5 and 3 at 55 °C were conducted to investigate the effects of F/I ratio on anaerobic digestibility and analyze microbial community succession, respectively. The highest cumulative methane yield was 353.7 m3/t VS in the large-scale batch test. Volatile fatty acids did not accumulate at any F/I ratios. The volatile solids reduction rate was highest at a F/I ratio of 0.5. Microbial community structures were similar between F/I ratios of 3 and 0.5, despite differences in digestion performance, suggesting that stable operation can be achieved at these ratios.

Reactor performance and energy analysis of solid state anaerobic co-digestion of dairy manure with corn stover and tomato residues

Anaerobic co-digestion is commonly believed to be benefical for biogas production. However, additional of co-substrates may require additional energy inputs and thus affect the overall energy efficiency of the system. In this study, reactor performance and energy analysis of solid state anaerobic digestion (SS-AD) of tomato residues with dairy manure and corn stover were investigated. Different fractions of tomato residues (0, 20, 40, 60, 80 and 100%, based on volatile solid weight (VS)) were co-digested with dairy manure and corn stover at 15% total solids. Energy analysis based on experimental data was conducted for three scenarios: SS-AD of 100% dairy manure, SS-AD of binary mixture (60% dairy manure and 40% corn stover, VS based), and SS-AD of ternary mixture (36% dairy manure, 24% corn stover, and 40% tomato residues, VS based). For each scenario, the energy requirements for individual process components, including feedstock collection and transportation, feedstock pretreatment, biogas plant operation, digestate processing and handling, and the energy production were examined. Results showed that the addition of 20 and 40% tomato residues increased methane yield compared to that of the dairy manure and corn stover mixture, indicating that the co-digestion could balance nutrients and improve the performance of solid-state anaerobic digestion. The energy required for heating substrates had the dominant effect on the total energy consumption. The highest volatile solids (VS) reduction (57.0%), methane yield (379.1 L/kg VSfeed), and net energy production were achieved with the mixture of 24% corn stover, 36% dairy manure, and 40% tomato residues. Thus, the extra energy input for adding tomato residues for co-digestion could be compensated by the increase of methane yield.

Solid state anaerobic co-digestion of tomato residues with dairy manure and corn stover for biogas production

Solid-state anaerobic co-digestion of tomato residues with dairy manure and corn stover was conducted at 20% total solids under 35°C for 45days. Results showed digestion of mixed tomato residues with dairy manure and corn stover improved methane yields. The highest VS reduction (46.2%) and methane yield (415.4L/kg VSfeed) were achieved with the ternary mixtures of 33% corn stover, 54% dairy manure, and 13% tomato residues, lead to a 0.5–10.2-fold higher than that of individual feedstocks. Inhibition of volatile fatty acids (VFAs) to biogas production occurred when more than 40% tomato residues were added. The results indicated that ternary mixtures diluted the inhibitors that would otherwise cause inhibition in the digestion of tomato residues as a mono-feedstock.

Co-digestion of spent mushroom substrate and corn stover for methane production via solid-state anaerobic digestion

Performance of batch solid-state anaerobic co-digestion of spent mushroom substrates (SMS) and corn stover (CS) was investigated. Digestion with SMS alone (SMS/CS = 100:0) resulted in excessive volatile fatty acids (VFAs) accumulation and low methane yields during the start-up phase. Co-digestion of SMS and CS significantly enhanced digesting performance. Compared to the digesters with 100% SMS, the start-up phase of the digesters with SMS/CS = 75:25 was shortened from 11 days to 4 days, and the methane yield increased by 40%. It was also observed that the peak of daily biogas yields showed up earlier in the co-digestion reactors than in the digesters with SMS alone. A similar phenomenon happened to the methane content curves. The VFAs and pH were shown to be important driving factors for determining the population of methanogenic communities (methanosaeta and methanobacteriaceae), which were obtained by using the Fluorescent in situ Hybridization method. The changes of the methanogenic communities, in return, affected the methane production in digesters. This study showed that co-digesting SMS with CS is a feasible method to handle mushroom wastes and produce bioenergy.

Solid-state anaerobic co-digestion of spent mushroom substrate with yard trimmings and wheat straw for biogas production

Spent mushroom substrate (SMS) is a biomass waste generated from mushroom production. About 5kg of SMS is generated for every kg of mushroom produced. In this study, solid state anaerobic digestion (SS-AD) of SMS, wheat straw, yard trimmings, and their mixtures was investigated at different feedstock to effluent ratios. SMS was found to be highly degradable, which resulted in inhibition of SS-AD due to volatile fatty acid (VFA) accumulation and a decrease in pH. This issue was addressed by co-digestion of SMS with either yard trimmings or wheat straw. SS-AD of SMS/yard trimmings achieved a cumulative methane yield of 194L/kg VS, which was 16 and 2 times higher than that from SMS and yard trimmings, respectively. SS-AD of SMS/wheat straw obtained a cumulative methane yield of 269L/kg VS, which was 23 times as high as that from SMS and comparable to that from wheat straw.

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.

Solid state anaerobic co-digestion of yard waste and food waste for biogas production

Food and yard wastes are available year round at low cost and have the potential to complement each other for SS-AD. The goal of this study was to determine optimal feedstock/effluent (F/E) and food waste/yard waste mixing ratios for optimal biogas production. Co-digestion of yard and food waste was carried out at F/E ratios of 1, 2, and 3. For each F/E ratio, food waste percentages of 0%, 10%, and 20%, based on dry volatile solids, were evaluated. Results showed increased methane yields and volumetric productivities as the percentage of food waste was increased to 10% and 20% of the substrate at F/E ratios of 2 and 1, respectively. This study showed that co-digestion of food waste with yard waste at specific ratios can improve digester operating characteristics and end performance metrics over SS-AD of yard waste alone.

Influence of mixing proportion on the solid-state anaerobic co-digestion of distiller's grains and food waste

The solid-state anaerobic co-digestion (AC) of distiller's grains (DG) and food waste (FW) for biogas production was investigated. The effects of different DG/FW (TS) ratios (10/1, 8/1, 6/1, 4/1, 1/0, and 0/1) were examined. Co-digestion with the above DG/FW ratios was found to be superior to that of mono-digestion. The AC of DG and FW had a good synergistic effect of the lower range of propionate/acetate ratio and VFA/alkalinity ratio. No methane was produced when the propionate/acetate ratio was >0.1 ± 0.01, but this inhibition was reversible. When the propionate/acetate ratio was <0.08 ± 0.01, methane production began to recover. When the volatile fatty acids (VFA)/alkalinity ratios were <0.9 ± 0.05, the AC of the influents successfully proceeded in a stable manner. However, when the VFA/alkalinity and propionate/acetate ratios were >1.25 ± 0.21 and 0.1 ± 0.01, respectively, the AC system reached an acidification crisis and failed. Therefore, the propionate/acetate and VFA/alkalinity ratios may be used as important indices for controlling anaerobic digestion (AD).

Study on Solid-State Anaerobic Co-Digestion with Distiller’s Grains and Food Waste for Methane Production

Solid-state anaerobic digestion (SSAD) of distiller’s grains (DG) and kitchen waste (KW) for biogas was investigated. Six DG to KW ratios of 10/1, 8/1, 6/1, 4/1, 1/0, and 0/1 was used. The results showed that in 48 digestion days the co-digestion with DG to KW ratio of 8:1 obtained the highest methane yield of 159.74mL/gTS, TS and VS reductions of 58.7% and 71.8%, hemicellulase, cellulose and lignin reductions of 46.7%, 45.4% and 4.0%. Compared to mono-digestions of DG or KW, co-digestion of DG and FW had a good synergistic effect. It indicated that SSAD of cellulosic-based waste and food waste could be one of the options for efficient biogas production and waste treatment