Solid-state Anaerobic Co-digestion Research Articles

Evaluating the Environmental Impacts of Pretreatment and Nanoparticles in Solid-State Anaerobic Digestion Using Life Cycle Assessment

AbstractThe yield of green energy from solid-state anaerobic co-digestion (SSAD) has recently been enhanced by incorporating innovative pretreatment methods and nanoparticles. However, the environmental consequences of employing new processes have not been fully examined. In this study, the environmental impacts of three high-methane-yielding scenarios including SSAD of corn stover blended with dairy manure (DM) denoted as (SYM1), calcium hydroxide-pretreated corn stover (CpCS) blended with DM (SYM2), and the CpCS blended with DM and nanoparticles (SYM3) were assessed and compared the baselines of solid-state and semi-solid-state anaerobic digestion using a life cycle assessment (LCA) approach. The approach investigated the best management practices that would result in high methane yield and low environmental impact. Results of the life cycle assessment indicate the inclusion of calcium hydroxide and nanoparticle has minimal negative environmental impact. There was an environmental gain in GWP when corn stover was co-digestion with DM (SYM1) relative to DM mono-digestions (baselines) and the carbon footprint of SYM1 was less by more than 85% compared to SYM2 and SYM3. However, the large volume of untreated corn stover harnessed for SYM1 scenario resulted in over 75% fossil fuel depletion compared to the other scenarios. The surplus methane from the SYM3 (at least twofold of other scenarios and baselines) in conjunction with being the least with the environmental implication makes the scenario the most attractive option for on-farm practice capable of harnessing the growing organic waste volume. These outcomes can guide trade-off between pretreatment and nanoparticle application to reduce solid-state anaerobic digestion’s negative environmental impact.

Optimising organic composition of feedstock to improve microbial dynamics and symbiosis to advance solid-state anaerobic co-digestion of sewage sludge and organic waste

This study provided new insight to the underlying mechanisms, by which organic compositions, including protein, fat, degradable carbohydrates and lignocellulose, regulate the performance of solid-state anaerobic digestion (SSAD) for synergistic treatment of organic wastes. Results show that the feedstock with a balanced composition of protein, fat, degradable carbohydrates and lignocellulose could maintain SSAD homeostasis to enhance methane (CH4) production by 14–487%. On the other hand, organic waste with a high content of degradable carbohydrates and fat at 39 and 14%, respectively, showed an initially high CH4 production at the beginning but a lower overall CH4 production. This was because of the accumulation of volatile fatty acids (VFAs) and ammonium nitrogen (NH4+-N) at up to 17.3 and 7227.7 mg·L−1, respectively, leading to anaerobic activity inhibition. Microbial dynamic and modular network analyses indicated that the balanced feedstock secured stepwise biodegradation of different organic substances to reduce the relative abundance of hydrolytic bacteria (e.g. Rikenellaceae_RC9_gut_group and Tepidimicrobium), thus alleviating VFAs and NH4+-N stresses. In particular, fat in the balanced feedstock could not only enrich the phylum Firmicutes for macromolecular biodegradation and genes for VFAs production, but also inhibit relative oxidizers (e.g. Synergistes and Acinetobacter) to facilitate propionate and acetate production to strengthen acetotrophic methanogenesis for effective CH4 yield. Results in this study show that a balanced organic composition could regulate microbial dynamics and symbiosis to advance SSAD homeostasis and methanation in synergistic organic waste treatment.

Solid-state anaerobic co-digestion of food waste, rice straw, and rice husk supplemented with cattle digesta under thermophilic conditions

Solid-state anaerobic co-digestion of food waste, rice straw, and rice husk supplemented with cattle digesta under thermophilic conditions

Transport and retention modeling of the liquid phase through a stratified porous leach-bed. Application for solid-state anaerobic co-digestion of cattle manure and roadside grass

The recirculation flow inside the leach-bed during solid-state anaerobic co-digestion of layered cattle manure and roadside grass was characterized using three different methods on lab scale reactors. Tracing experiments and method of moments were used to characterize percolation flow properties with different leach-bed compositions and a new criterion was proposed to quantitatively evaluate the ratio between preferential pathways and dead volumes for each experiment. The impact of recirculation flow on leach-bed complexity for different moments of SS-AD and substrate layering was characterized using steady-state reactor modeling and the impact of recirculation flow on microporosity and macroporosity evolutions all along SS-AD was determined using modeling of hydrodispersive parameters. It appeared that layering and time could significantly impact percolation flow and leach-bed complexity, until 36 % of residence time variation and 110 % of leach-bed complexity. Moreover, layering could impose a different percolation flow for each layer and cause a preferential pathways disruption.

Assessment of a full-scale solid-state anaerobic co-digestion: A multi-component substrate analysis by using ORWARE

Long-term sustainable biogas production requires different raw material alternatives, especially when reducing the most desirable organic substrate, food waste, which has been set as a goal in the 2030 Agenda. In Sweden, horse manure (HM) is generated in large quantities, and due to its physical and chemical characteristics, it has the potential to be used as a raw material to produce biogas through anaerobic digestion (AD). In order to investigate the challenges that HM digestion can impose in terms of methane yield and/or digestate quality, the modified ORganic WAste REsearch (ORWARE) AD model was applied. The aim was to study the effects of different substrates and combinations of these on the AD process during a full-scale solid-state (SS)-AD. In this sense, the model allows for the analysis of the digestion process of multicomponent substrates at the element level. The simulation results suggested that the replacement of green waste (GW) by HM with wood chips as bedding material gave the best improvement in terms of energy turnover; the liquid fraction of the digestate of this mixture of substrates presented the highest concentration in all the nutrients analyzed, specifically in total carbon-biological and phosphorus. The nutrient concentrations in the digestate from the aforementioned scenario are in line with the SPCR120 certification.

Effectiveness of layered inoculation in solid-state anaerobic co-digestion of pig manure and corn straw: Focus on macro-, micro-, and genetic-levels

Layered inoculation can achieve rapid start-up and promote methanation performance of anaerobic digesters. Daily specific methane yield (SMY) rapidly increased to 2.93 mL/g VS/d during 0–13 days, and cumulative SMY reached 212 mL/g VS in the solid-state anaerobic co-digestion (SS-AcoD) of pig manure and corn straw. Data were collected at macro-, micro-, and genetic-levels of each substrate layer. The results showed that layered inoculation could improve volatile fatty acids utilization and prevent adverse effects of high total ammonium nitrogen concentrations. Layered inoculation accelerated hydrolysis, acidification, and methanogenesis of substrates, as evidenced by the efficient inoculation of Bacteroidetes, Anaerolineales, Methanosphaerula, and Methanothrix, which were primarily from inocula. The various stages of SS-AcoD were synergistically initiated during the first 13 days, and acetoclastic pathway was boosted. These results further explain why layered inoculation is an efficient method for improving methanation performance of SS-AcoD and achieving efficient utilization of organic solid waste.

Effectiveness of Layered Inoculation in Solid-State Anaerobic Co-Digestion of Pig Manure and Corn Straw: Focus on Macro-, Micro-, and Genetic-Levels

Effectiveness of Layered Inoculation in Solid-State Anaerobic Co-Digestion of Pig Manure and Corn Straw: Focus on Macro-, Micro-, and Genetic-Levels

Methane yield optimization using mix response design and bootstrapping: application to solid-state anaerobic co-digestion process of cattle manure and damp grass

Optimization of solid-state anaerobic digestion on cattle manure and damp grass were performed simultaneously and combined to a bootstrapping tool to significantly decrease the number of experiments for a methane yield optimization. 15 batch reactors at lab scale were launched two times respecting a mix surface response methodology. A numerical method called Bootstrapping was used to verify results significance. Results have shown a significant influence with a p-value between 10−8 and 10−11: the optimal parameter values depend on the substrate composition with a maximal p-value of 5.60.10−2. The methane yield reached 156.19 NL · kgVS−1 for a mixture of cattle manure and damp grass, and 142.92 NL · kgVS−1 for cattle manure only. The bootstrapping were validated with a standard error lower than 3% in comparison with ANOVA method, which confirms that the mix surface response methodology combined to bootstrapping is an innovative and efficient way to optimize solid-state anaerobic digestion process.

Solid-state anaerobic co-digestion of organic fraction of municipal waste and sawdust: impact of co-digestion ratio, inoculum-to-substrate ratio, and total solids.

Municipal solid waste contains mainly organic wastes that can be a good source for anaerobic digestion. Solid-state anaerobic digestion is an affordable and suitable technique to mitigate the organic fraction of municipal solid waste (OFMSW). However, as the organic loading of OFMSW is high, co-digestion with other materials can improve the system's performance. This study aimed to investigate the performance of the co-digestion of OFMSW and sawdust and study the parameters affecting its performance. Based on the experiments, the optimum sawdust/OFMSW ratio was achieved 1:2 with the methane production of 0.3L/g VS. In addition, the inoculum-to-substrate ration (I/S) was investigated at 1:4, 1:2, 1:1, 2:1 ratios. The best result was obtained at 2:1 ratio with a total methane yield of 0.28 L/g VS. The results also indicated that I/S ratios less than 1:1 led to fatty acid accumulation and acidic pH condition. The effect of total solids content on the co-digestion process was also examined in this study. According to the results, as the total solids increased, the biomethane yield decreased while the biogas content increased.

Efficacy of magnetite (Fe3O4) nanoparticles for enhancing solid-state anaerobic co-digestion: Focus on reactor performance and retention time

The influence of magnetite nanoparticle (nFe3O4) concentrations (20, 50, and 75 mg/L) on reactor performance and retention time was investigated for the first time in an initially upset solid-state anaerobic batch (SSAB) reactor. nFe3O4 mitigated acidification threat, enhanced reactor stability, ensured rapid volatile fatty acids bioconversion, and modified microbial community. The impacts reduced retention time by 27 days relative to the control. Of the nFe3O4 concentrations, 20 mg/L had the highest hemicellulose degradation (93%) and methane yield (191.2 L/kg VS) with no threat to anaerobic microbes. Besides, existing kinetic models, novel models equally well-described methane yield with low root mean square errors (RMSE) < 1.2 and high coefficients of determination (R2) > 98%, therefore could be used for downstream applications. This study provides useful information on the impact of nFe3O4 on reactor stability and reactor performance in an initially upset SSAB reactor.

Solid-state anaerobic co-digestion of food waste and cardboard in a pilot-scale auto-fed continuous stirred tank reactor system

Abstract Increasing volume of Food waste (FW) and cardboard (CB) which are the two major fractions of municipal solid waste increases environmental concerns. This study evaluated the performance of a pilot-scale auto-fed continuous stirred tank reactor (CSTR) system for the solid-state anaerobic co-digestion (ACoD) of acetic acid rich food waste (FW) and cardboard (CB). The objective to co-digest acids rich FW and CB originates from the fact that acetic acid can act as a pre-treatment agent. Can the frequency of feeding and feeding pattern assists the system to withstand an organic loading rate >4 g volatile solids (VS)/(L.d) without addition of any pH boosting chemicals? Four mixing ratios of 100:0, 80:20, 60:40, 50:50 (v/v %) of FW and CB on biogas yield and process stability at an OLR > 4 g VS/(L.d) at a hydraulic residence time (HRT) of 40 d was investigated. Results revealed that the reactor R1 operated with FW:CB in the ratio of 100:0 achieved 76% biodegradability (the ratio of experimental to theoretical methane yield) while it was 39%, 32% and 22% for FW:CB ratios of 80:20, 60:40 and 50:50, respectively. This study concludes that exposing the CB to acetic acid-rich FW assisted the disintegration and depolymerization of CB without any pre-treatment step. Micro-feeding the reactor on an hourly basis assisted to overcome the susceptible failure of the system. The outcomes of this study provides new insight into the potential of implementing decentralized AD units for the treatment of FW and CB at source, which not only diverts waste from landfills but creates a revenue model through bioenergy generation and digestate sales.

Comparison of the Reactor Performance of Alkaline-Pretreated Corn Stover Co-digested with Dairy Manure Under Solid-State

Solid-state anaerobic digestion is a promising path to optimize green energy generation from waste management. This mesophilic study investigated the performance of sodium hydroxide (4%NaOH), ammonium hydroxide (2%NH4OH, and 4%NH4OH), and calcium hydroxide (8%Ca(OH)2) pretreated corn stover (Cs) co-digested with dairy manure (Dm) to achieve 4%NaCsDm, 2%AqCsDm, 4%AqCsDm, and 8%CaCsDm treatments. Results showed that 8%CaCsDm had shortened detention time (79 days) and increased methane yield (178 L/kg VS) in comparison with other treatments. In addition, propionic acid concentration in treatment 4%NaCsDm was elevated beyond a safe threshold (> 0.9 g/L) for methanogens, which is unlike the significant bioconversion that occurred for other treatments. Though, free ammonia concentration for 2%AqCsDm and 4%AqCsDm pre-digestates were within the safe limit (< 53 mg/L) relative to other treatments, 8%CaCsDm sufficiently reduced the initial inhibitory concentration to a safe threshold at the cessation of the experiment. Additionally, 8%CaCsDm treatment had the highest VFA bioconversion rate (80%). Therefore, this study demonstrated that 8%CaCsDm treatment could effectively improve reactor performance in solid-state anaerobic co-digestion.

Pilot Scale Solid State Anaerobic Co-digestion of Dairy Manure and Milking Parlor Wastewater

A pilot scale solid-state anaerobic co-digestion study was conducted to elucidate the feasibility of anaerobic digestion as an effective treatment method for dairy manure (DM) and milking parlor wastewater (MPW), and it focusing mainly on the stability of anaerobic digestion process and methane production potential. Dairy manure and milking parlor wastewater were co-digested (1/0.48, w/w) in 11m3 volume reactor for 63days at the mesophilic condition (36°C). In addition, pH, volatile fatty acids and ammonia were periodically analyzed to monitor anaerobic digestion inhibitions. The results showed that the co-digestion of DM and MPW was successfully performed without any inhibition caused by ammonia and volatile fatty acids accumulation. The potential methane production (P) from a modified Gompertz model was about 130.5 mL g-VS-1, and approximately 80% of the methane production was obtained during the 40 days digestion test and the lag phase was 14 days. The pilot scale SSAD (solid-state anaerobic digestion) system showed about 1.3-fold higher methane production than lab-scale system. The results of solid-state anaerobic co-digestion of bedded pack barn dairy manure and milking parlor wastewater using pilot-scale anaerobic digester can be used as a reference for the design of farm-scale anaerobic digester. The pilot scale SSAD system showed about 1.3-fold higher methane production than lab-scale system. The potential methane production (P) was about 130.5 mL g-VS-1, and approximately 80% of the methane production was obtained during the 40 days digestion test and the lag phase was 14 days.

Biogas Production from Corn Stover by Solid-State Anaerobic Co-digestion of Food Waste

Biogas has become an alternative fuel to reduce the lack of fossil fuel. Biogas can be produced from organic wastes such as corn stover. Corn stover is a typical lignocellulosic biomass and contains a total solid (TS) content higher of 15%. Biogas production was conducted by solid-state anaerobic digestion with addition co-digestion of food waste. Co-digestion is useful to help the digestion of corn stover. The purposes of this study were to investigate the effect of the percentage of food waste, volatile solid (VS) reduction, and kinetic model on biogas production from corn stover. Results showed that food waste had a significant effect on biogas yield (p &lt; 0.05). The highest biogas yield of 584.49 mL g-1 VS-1 and the highest VS reduction of 40% was obtained at food waste of 20%. The kinetic model of biogas production from corn stover and food waste followed the first-order kinetic model.

Impact of corn stover particle size and C/N ratio on reactor performance in solid-state anaerobic co-digestion with dairy manure

ABSTRACTGreen energy generation from agricultural waste has the potential to minimize dependency on fossil and reduce the resultant environmental impact of this fuel provided anaerobic reactor performance is optimized. Hence, the interactive impact of carbon to nitrogen (C/N) ratio, particle size, and co-digestion of dairy manure (DM) and corn stover (CS) on solid-state anaerobic digester (SSAD) performance was investigated with four treatments (DMCS24S, DMCS24L, DMCS28L, and DMCS32L) in this solid-state study. Novel scanning electron microscope (SEM) image analysis utilized to describe the corn stover using ImageJ indicated that corn stover of particle size 0.18–0.42 mm had lower rough surface texture relative to the 0.42–0.84 mm size. This observation not only influenced the ingestate degradation, the bioconversion rate was negatively affected by 0.18–0.42 mm particle size of corn stover. Notably, increase in C/N ratio led to decrease in total ammonia nitrogen (TAN) and alkalinity concentration (Alk), hence, treatments with the lowest C/N ratio had better reactor performance in terms of suitable process parameters such as Alk, pH, ORP, and TAN. Furthermore, DMCS24L treatment had the highest methane yield (106 mL/g VS) and net methane energy (2.92 MJ/kg). Interestingly, modified Gompertz model gave the best kinetic description of the methane production. This SSAD mesophilic study suggests that corn stover, with particle size of 0.42–0.84 mm, co-digested with dairy manure under a C/N ratio of 24 has the potential to enhance methane yield and optimize reactor performance.Implications: The utilization of agricultural waste for bioenergy generation through solid-state anaerobic digestion could be enhanced through the interactive impact of substrate particle size, carbon-to-nitrogen (C/N) ratio and co-digestion, which has not been previously studied. These ternary factors significantly improved reactor performance and enhanced methane yield when corn stover of 0.42–0.84 mm particle size was co-digested with dairy manure to achieve a C/N ratio of 24.

Modeling and optimization of biomethane production from solid-state anaerobic co-digestion of organic fraction municipal solid waste and other co-substrates

ABSTRACT One of the simplest methods for increasing productivity in biogas production is co-digestion. Co-digestion leads to more biogas yield as well as more nutrient bioavailability. This study reports the modeling and optimization of biomethane potential tests from different combinations of organic fraction of municipal solid wastes (OFMSW), cow manure (CM), and municipal sewage sludge (MSS) in solid-state. The simplex-centroid mixture design (SCMD) and artificial neural network (ANN) models were validated with a high correlation to the real data (R2 = 0.99). Experimental results indicated that the maximum amount of CH4 production of 436 mL CH4/g VS occurs at the identical weight percent of the three substances (33.33%). The maximum methane yield was found to be 445.9 mL CH4/g VS as obtained by the genetic algorithm (GA) optimization process, while 448.5 mL CH4/g VS (448.5 ± 3.05) of methane was produced experimentally. Therefore, integration of the SCMD and ANN model with the GA optimization is useful in the prediction of biomethane production. This research is the first in providing the best combination of co-treating and co-utilizing OFMSW with CM and MSS in the solid-state for biowaste management.

Methane production by co-digestion of poultry manure and lignocellulosic biomass: Kinetic and energy assessment

Six typical Brazilian lignocellulosic biomasses (rice straw, corn cob, peanut shell, sawdust, coffee husk and sugarcane bagasse) were evaluated for methane production by solid-state anaerobic co-digestion with poultry manure. The results showed the highest methane production was obtained with corn cob and poultry manure (126.02 Nm3 CH4. ton residue−1) using a food to inoculum ratio of 0.5, which lowered volatile fatty acids accumulation. In this condition, the thermal energy production (1.73 MJ.kg live chicken−1) would be able to replace 53.2% of the energy with firewood in poultry farming. The high hemicellulose and low lignin content in corn cob seem to explain the biomethanation of such biomass, and this agrees with the microbial analysis which revealed the predominance of bacteria related to plant polysaccharides hydrolysis and carbohydrate conversion in the inoculum. The methane production was best modelled by Groot’s multi-stage model, and the microbial adaptation to lignin might explain this.

Biogas Production from Oil Palm Empty Fruit Bunches and Palm Oil Decanter Cake using Solid-State Anaerobic co-Digestion

Oil palm empty fruit bunches (EFB) and palm oil decanter cake (DC) were used to investigate biogas production by using solid-state anaerobic co-digestion (SS-AcoD) with 15% total solid (TS) content. Solid state anaerobic digestion (SS-AD) using substrate to inoculum (S:I) ratio of 3:1, methane yields of 353.0 mL-CH4/g-VS and 101.5 mL-CH4/g-VS were respectively achieved from mono-digestion of EFB without oil palm ash (OPA) addition and of DC with 10% OPA addition under mesophilic conditions 35 °C. By adding 5% OPA to SS-AD using 3:1 S:I ratio under thermophilic conditions (55 °C), mono-digestion of EFB and DC provided methane yields of 365.0 and 160.3 mL-CH4/g-VS, respectively. Furthermore, SS-AcoD of EFB:DC at 1:1 mixing ratio (volatile solid, VS basis), corresponding to carbon to nitrogen (C:N) ratio of 32, gathering with S:I ratio of 3:1 and 5% ash addition, synergistic effect is observed together with similar methane yields of 414.4 and 399.3 mL-CH4/g-VS, achieved under 35 °C and 55 °C, respectively. According to first order kinetic analysis under synergistic condition, methane production rate from thermophilic operation is 5 times higher than that from mesophilic operation. Therefore, SS-AcoD could be potentially beneficial to generate biogas from EFB and DC.

Anaerobic co-digestion of food waste with pretreated yard waste: A comparative study of methane production, kinetic modeling and energy balance

Abstract Solid state anaerobic digestion of food waste (FW) with yard waste (YW) appears to be an efficient technique for bioenergy production. However, the reluctant nature of YW and nutrient imbalance due to high C/N ratio are the two major obstacles for maximum methane production. In this study to improve the methane production potential, YW was thermally pretreated to reduce its recalcitrance nature and then the pretreated YW was co-digested with FW to balance nutrient for anaerobic co-digestion. Moreover, optimization of F/M (Food/Microorganism) ratios (1.0, 1.5, 2.0 and 2.5) for solid state anaerobic co-digestion was also considered. The highest methane production of 431 mL/gVSadded was observed for co-digestion of FW with microwave pretreated YW at the F/M ratio of 1.5. Energy balance of the pretreatment technique was conducted and the highest net energy gain 3.98 kJ/gVS (= output energy of 14.04 kJ/gVS - input energy of 10.05 kJ/g VS) obtained at the F/M ratio of 1.0.

Anaerobic cultivation of waste activated sludge to inoculate solid state anaerobic co-digestion of agricultural wastes: Effects of different cultivated periods

This study investigated effects of waste activated sludge (WAS) after anaerobic cultivation as inoculum on solid-state anaerobic digestion (SSAD) of agricultural wastes. WAS was anaerobically cultivated for 0, 20 and 50 days and then used as inoculum for co-digestion at substrate/inoculum (S/I) ratios of 2 and 4, respectively. Results showed that treatments inoculated with cultivated WAS exhibited better buffering capability. The highest cumulative methane production (218 L/kg VS) was achieved when inoculating WAS after 50 days of cultivation at the S/I ratio of 2. Fresh WAS without any anaerobic cultivation as inoculum led to digestion instability with significant acidification and limited biogas production, particularly at the S/I ratio of 4. Microbial analysis deciphered that Methanosarcina was the dominant archaea in all treatments and its relative abundance increased with the extension of WAS cultivation time. Hence, WAS after prolonged anaerobic cultivation could be a favorable inoculum for SSAD of agricultural wastes.