Inoculum To Substrate Ratio Research Articles

In-situ sulphide control in the anaerobic co-digestion of residual biomass from the production of penicillin and cystine

This study was focused on the anaerobic digestion of residual biomass from the production of penicillin and l-cystine. The biogas potential tests of individual substrates and their mixture showed good anaerobic biodegradability. The highest measured specific biogas production was 712 l/kg volatile solids (VS) for penicillin biomass and 676 l/ kg VS for cystine biomass. The biogas potential tests were performed at different inoculum-to-substrate ratios (ISR) and showed that high concentrations of nitrogen and sulphur present in residual biomass have a major impact on the anaerobic processes. The long-term operation of the laboratory anaerobic reactor showed that the mono-digestion of the penicillin biomass was stable at an OLR of 1 kg/(m3.d). When co-digestion of penicillin and cystine biomass at a ratio of 0.9:0.1 (on a VS basis) and at the same OLR was enhanced, the operation of the laboratory model turned unstable. During this phase of the operation, the course of anaerobic processes was affected by ammonia and especially sulphide inhibition. Sulphide inhibition was effectively reduced by direct dosing of FeCl2 (in-situ sulphide control), at a molar iron-to-sulphur ratio of β = 1 (mol Fe/mol S). When suppressing sulphide inhibition, the operation of the laboratory model became stable even at a co-digestion ratio of 0.5:0.5 (VS basis). The results of this work open a new scope for future applications in the anaerobic digestion of waste biomass with high sulfur content, coming from industrial fermentation processes.

Biohydrogen potential assessment of Opuntia spp.: Effect of inoculum-to-substrate ratio and residual biomass evaluation

Opuntia spp. are considered bioenergy crops for contributing against global warming while avoiding water scarcity and declining fertile land problems in their cultivation. Unfortunately, these have been scarcely researched. This work targets to evaluate the biohydrogen potential of three Opuntia varieties (Opuntia ficus-indica var. Milpa Alta, OfiM; O. ficus-indica var. Copena, OfiC; and O. engelmannii, Oeng). Hydrogen production evaluated at three inoculum-to-substrate ratios (ISR) for OfiM and OfiC, showed that the ISR decrease was inversely proportional to the maximum hydrogen cumulative production and the highest hydrogen production rate. Afterwards, hydrogen production using methanol extracted residual biomass was demonstrated feasible but resulted in a reduction in hydrogen production. The best results attained were 438 mL H2 (41 mL H2/g VS) for OfiC at ISR 0.2 The use of Opuntia species for hydrogen production should be further explored to increase its competitive potential and the possibilities of new paths on bioprocesses integration.

Evaluation of the biodegradability of a heat-treated anaerobic inoculum

The citrus industry produces a considerable amount of solid and liquid waste, which are mostly wasted. Anaerobic digestion of sewage sludge is an attractive option as it can produce fuels in the form of methane gas. However, the presence of complex organic compounds and pathogenic microorganisms significantly hinders the effectiveness of this process. The objective of this work is the selection of a source of inoculum free of pathogenic microorganisms by means of a thermal pretreatment and in this way is conducive to the treatment of residual sludge from the Citrus industry. The inoculum was taken from a geomembrane reactor which uses cattle manure as a substrate. 6 biodegradability kinetics were performed, varying the substrate-inoculum ratio, three of them with inoculum without pretreatment and another three with treatment, all under mesophilic conditions. SV parameters, pH, and biogas production were determined.

Influence of the substrate to inoculum ratio on the methane yield from the batch anaerobic digestion of river tamarind (Leucaena leucocephala) and Guinea grass (Panicum maximum)

AbstractThe substrate to inoculum ratio (SIR) is an often overlooked parameter in the determination of the methane potential of a substrate.In this article we highlight the importance of the SIR, in the determination of the biochemical methane potential of two substrates, Guinea grass (Panicum maximum) and river tamarind (Leucaena leucocephala). Additionally, the results of this method not only give the specific methane potential, but also the optimum substrate to inoculum ratio, which is an important parameter for bioreactor start‐up.The specific methane volumes of the two substrates are, 148 mL/gDM and 250 mL/gDM for the river tamarind and Guinea grass, respectively, with optimum substrate to inoculum ratios of 0.055 and 0.035, respectively. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Biogas production from winery wastewater: Effect of the substrate-inoculum ratio on fly ash addition and iron availability

The effect of substrate-inoculum ratio and fly ash (FA) concentration on the anaerobic digestion of winery wastewater was studied. Two substrate-inoculum ratios (0.50 and 1 g soluble COD/g VSS) and five fly ash concentrations (25, 50, 75, 100 and 150 mg/L) were tested under mesophilic conditions. The results showed that 0.50 g soluble COD/g VSS was the best substrate-inoculum ratio. Regarding the FA, 100 mg/L improved the specific methane production by 79% compared to the control assay. In comparison, 150 mg/L produced an inhibition of methane production, with a 55% decrease in specific methane production with respect to the control assay. According to the bioavailability study, FA had a similar effect to a system with Fe-EDTA on anaerobic digestion, which could indicate that the Fe present in FA was present in the solution and bioavailable to microorganisms. Therefore, a possible mechanism for the action of FA on anaerobic digestion was proposed. Finally, the kinetic analysis showed that FA improved the maximum specific methane production rate and decreased the lag phase.

Semi-solid anaerobic co-digestion of source-separated fecal slag and food waste: focusing on methane production, ecological risk assessment, and quality evaluation as fertilizer.

Toilet revolution is driven by the urgent need for solutions to improve sanitation and access to high-quality organic fertilizer for rural areas, which is tagged "resource recovery from human waste." This study provides a possible solution via semi-solid anaerobic co-digestion (Aco-D) of source-separated fecal slag (SFS) and food waste (FW) (3:1). A comprehensive investigation of Aco-D at different inoculum/substrate ratios (ISR) was conducted. Results revealed that the reactor with ISR of 1:4 reached the highest methane yield (255.05mL/gVS), which enhanced Methanosaetaceae, Methanomicrobiales, and Syntrophomonas. Additionally, the reactor with low feedstock (ISR of 1:2) showed higher removal efficiency of antibiotics (74.75%). The ecological risk of digestate decreased to an insignificant hazard quotient level, and the contents of nutrients and heavy metals were in line with the standard requirement for fertilizer. This study could serve as an alternative technology to support further research in SFS management and digestate utilization as fertilizer.

The Influence of Biochar Augmentation and Digestion Conditions on the Anaerobic Digestion of Water Hyacinth

The augmentation of biochar (BC) during anaerobic digestion (AD) has been identified as a potential strategy for improving the AD of complex feedstocks. This study evaluates the influence of oak wood biochar 450 °C and fermentation conditions during the AD of the invasive aquatic plant, water hyacinth (WH). Factorial 22 design of experiments (DOE) allowed the evaluation of the effect of the crucial processing conditions, inoculum-to-substrate ratio (ISR) and biochar load. Further optimisation was performed to identify the best processing conditions for the AD of WH, at an ideal ISR of 1. The contour plots suggested that methane yield is favoured at biochar loads of ≤0.5%, whereas the production rate is favoured by increasing biochar loads. However, biochar addition offered no further improvement or significant effect on the digestion of WH. The subsequent AD of WH samples collected from different locations in India and Uganda exhibited variable biochemical methane potential (BMP) yields. BC addition had little effect on BMP performance, and in some cases, it even reduced the BMP. This study concludes that the amendment potential of biochar is influenced by digestion conditions and the substrate, particularly when working with complex substrates.

Effect of inoculum origin and substrate-inoculum ratio to enhance the anaerobic digestion of organic fraction municipal solid waste (OFMSW)

This study evaluated the key role of inoculum in mesophilic anaerobic digestion (AD) of Organic Fraction of Municipal Solid Waste. The effect of two different inocula, the mesophilic digestate of wastewater activated sludge (WAS) and the mesophilic digestate of cow-agriculture sludge (CAS), at three different substrate: inoculum ratios (1:2, 1:1 and 2:1) at three different incubation times (0, 5 and 10 d) were studied in batch feeding reactor for a total of 18 AD configurations. The AD configurations were study through specific biogas and methane productions, first order disintegration kinetics, Gompertz modified study and energy sustainable index. A multi criteria decision aid outranked the 18 AD configurations tested. The study proved that the AD performed with inoculum CAS incubated for 10 d at 2:1 substrate inoculum ratio reached the highest biogas yield and methene content equal to 997.81 NL/kgVS and 70.00% v/v.

Bioconversion of wheat straw to energy via anaerobic co-digestion with cattle manure in batch-mode bioreactors (Experimental investigation and kinetic modeling)

Rising concerns about environmental issues including pollution control, waste management and energy demands have drawn the world’s attention to the merits of renewable energy sources. In this regard, the anaerobic digestion of organic wastes for the purpose of bioenergy production is of particular importance. This study investigated the potential for biogas production from the co-digestion of a lignocellulosic biomass (wheat straw) with cattle manure after physical and chemical pretreatment at two Total Solids (TS) levels of 3% and 6% and three Inoculum-to-Substrate Ratios (ISRs) of 1, 2 and 4 (based on volatile solids). The materials were loaded into single-stage 1-liter digesters in batch mode under mesophilic conditions (35 °C) for 125 days. The best anaerobic digestion performance was observed in the treatment with 3%TS and ISR1, where the biogas and methane production yields were 0.510 and 0.307 m3/kg-VSadded, respectively. At both TS levels, biogas production increased with the increase in the Volatile Solids (VS) content of wheat straw and the decrease in ISR. This can be due to easier access of microorganisms to the organic matter and better microorganism-substrate balance, which ultimately result in improved digestion performance. The kinetic modeling results showed that the modified Gompertz model and the logistic function model had the highest level of consistency with the experimental results for TS3% and TS6%, respectively. The first-order kinetic model failed to provide a good estimate of biogas production from the co-digestion of wheat straw with cattle manure, irrespective of the TS level.

Novel application of pyrolytic carbon generated from waste tires: Hydrolytic and methanogenic performance promotion in vinegar residue anaerobic digestion

Random disposal of waste tires and vinegar residues is deleterious to the environment; these materials can be sufficiently treated using pyrolysis and anaerobic digestion, respectively. In this study, pyrolytic carbon was used to enhance the performance of the anaerobic digestion of vinegar residues, which is a much more economic method comparing with dosing commercial-level carbon based materials. The conductivity of pyrolytic carbon at 1000 °C is much higher than that of commercial activated carbon. At a dosage of 10 g per 29 g of vinegar residues, the maximum volatile fatty acid production was 4225.4 mg COD/L in the reactor (effective volume of 400 mL) with inoculum to substrate ratio (ISR) of 1:1, representing an increase of 50.3% from that of the control reactor. A sufficient dosage is necessary to improve methane yield. The maximum methane yield was obtained at a pyrolytic carbon dosage, obtained at 1000 °C, of 12 g per 29 g of vinegar residues. The results indicated that the differences in the microbial communities of the control and experimental reactors correlated with the performance; however, the deep microbial mechanism of pyrolytic carbon boosting anaerobic digestion performance must be explored in further studies.

Biomethane Production from Anaerobic Co-Digestion of Selected Organic Fraction of Municipal Solid Waste (OFMSW) with Sewage Sludge: Effect of the Inoculum to Substrate Ratio (ISR) and Mixture Composition on Process Performances.

The aim of this study was to evaluate the effect of the inoculum to substrate ratio (ISR) and the mixture ratio between organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS) on the methane production potential achievable from anaerobic co-digestion (AcoD). Biochemical Methane Potential (BMP) assays at mesophilic temperature were used to determine the best AcoD configuration for maximizing methane yield and production rate, as well as to address possible synergistic effects. The maximum methane yield was observed at ISR of 1 and 60% OFMSW: 40% SS as co-digestion mixture, whereas the highest methane production rate was achieved at ISR of 2 with the same mixture ratio (207 mL/gVS/d). Synergistic effects were highlighted in the mixtures having OFMSW below 60%, determining an increase of approximately 40% in methane production than the OFMSW and SS digestion as a sole substrate. The experimental data demonstrated that co-digestion of OFMSW and SS resulted in an increase in the productivity of methane than anaerobic digestion using the sole substrates, producing higher yields or production rates while depending on the ISR and the mixture ratio.

Biochemical Methane Potential and Kinetic Parameters of Goat Manure at Various Inoculum to Substrate Ratios

Anaerobic digestion is a proven technology for managing manure while harvesting natural gas and digestate as a biofertilizer. The biochemical methane potential (BMP), biodegradability, and kinetic parameters of goat manure (GM) were investigated at different inoculum to substrate ratios (ISRs). The cumulative biomethane yields at the ISRs of 0.0, 0.3, 0.5, 0.8, 1.1, 1.3, and 2.6 were 191.7, 214.3, 214.9, 225.9, 222.1, 222.8, and 229.9 mL gvs−1, respectively. The biomethane yield at all ISRs was significantly higher than control (0 ISR). Above the ISR of 0.0, the biomethane yield was similar among all ISRs. The biodegradability of GM at the ISRs of 0.3, 0.5, 0.8, 1.1, 1.3, and 2.6 varied between 73.3% and 78.7% and was statistically similar. In total, 90% of the yield was observed in 31 and 32 days in control and all other ISRs, respectively. The modified Gompertz equation fitted very well (R2 = 0.99) to the BMP of GM but predicted the lag phase (λ) of 3.2–5.2 days against observed 8–10 days among control and other ISRs.

Alleviating nutrient imbalance of low carbon-to-nitrogen ratio food waste in anaerobic digestion by controlling the inoculum-to-substrate ratio

Food waste (FW) characterized by a low carbon/nitrogen (C/N) ratio ranging between 6 and 19 was used to investigate the feasibility and mechanism of maneuvering inoculum-to-substrate ratio (ISR) to alleviate the metabolic imbalance caused by imbalanced nutrients in the AD process, through biochemical methane potential tests and methanogenic pathway analysis. The maximum methane yield of 0.4 L/g of volatile solid (VS) was obtained at a C/N ratio of 11 and an ISR of 10:3. Increasing ISR from 1:2 to 10:3 promoted methane production by ∼20% via an enhancement in acetoclastic methanogenesis and the hydrolysis of carbohydrates and proteins. At lower ISR < 1, hydrogenotrophic methanogenic and syntrophic bacteria dominated, and methane production decreased by ∼ 20% due to the energy disadvantages of syntrophic methanogenesis. Efficient digestion of FW with low C/N ratio FW could be achieved by using metabolic pathways to regulate it and increasing ISR from 1:1 to 10:3.

Influence of augmentation of biochar during anaerobic co-digestion of Chlorella vulgaris and cellulose

The anaerobic co-digestion (AcoD) of microalgae is a prospective option for generating biomethane from renewable sources. This study investigates the effects of inoculum-to-substrate ratio (ISR), C/N ratio and biochar (BC) load on the AcoD of Chlorella vulgaris and cellulose. An initial augmentation of BC at ISR 0.5–0.9 and C/N ratio 10–30 offered a pH buffering effect and resulted in biomethane yields of 233–241 mL CH4/g VS, corresponding to 1.8–4.6 times the controls. BC addition ameliorated significantly AcoD, supporting the digestate stability at less favourable conditions. The effect of the process variables was further studied with a 23 factorial design and response optimisation. Under the design conditions, the variables had less influence over methane production. Higher ISRs and C/N ratios favoured AcoD, whereas increasing amounts of BC reduced biomethane yield but enhanced production rate. The factorial design highlighted the importance of BC-load on AcoD, establishing an optimum of 0.58 % (w/v).

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 zero-valent iron addition on the biogas fermentation of food waste after anaerobic preservation

To solve the problem of acidification during high-load anaerobic digestion of food waste, the effects of adding Fe0 on acidified fermentation system were investigated. Four adding Fe0 groups and four control groups were set under different inoculum-to-substrate ratios (ISRs) of 1.00, 0.80, 0.65, and 0.50. Results showed that adding Fe0 significantly increased methane production, except for the over-acidification group under ISR= 0.5. As for the control groups, the pH of system decreased to below 5.8 with the decrease of ISR, which led to the instability of the system and the stop of gas production. Compared with the control groups, pH recovered faster and the concentration of volatile fatty acids was lower with Fe0 addition under the same ISR. Moreover, in the Fe0 group under ISR= 0.65, the pH recovery effect was the most obvious and microbial-community analysis showed that the relative abundance of Clostridium increased by 14.9%. As a result, the best recovery effect was obtained by adding Fe0 under ISR= 0.65, and the cumulative CH4 yield increased by 77.3% compared with the control group. Therefore, adding Fe0 to the acidified fermentation system can effectively alleviate acidification and thus increase methane production when ISR > 0.5.

Optimization of biochemical sulfide potential (BSP) assay for anaerobic biodegradability assessment

The anaerobic biodegradability assessment (biodegradation extent and kinetics) of organic wastes is critical for optimum design and evaluating treatment efficiencies for anaerobic treatment technologies. The biochemical sulfide potential (BSP) assay has previously demonstrated the advantages of its time efficiency and measurement accuracy for biologically assessing substrate degradability, while its application is limited by undefined operational parameters. In this study, the BSP assay was further optimized through a systematic investigation of a critical parameter, inoculum-to-substrate ratio (ISR), and the applicable kinetic model to unravel the potential use of BSP assays for anaerobic waste treatment. Under two series of experimental scenarios, the common ISR ranges of 0.5–4.0 (based on the traditional BMP assay) and extreme ISRs (as low as 0.1) were studied, in which the advantage of a BSP assay on extreme ISRs was highlighted. Meanwhile, the underlying cause and mechanism for biodegradability discrepancies under different ISRs (0.1–6.0) were further investigated. The extracellular polymeric substance (EPS) characterization of residual organics and the two-substrate first-order hydrolysis model analyses revealed that the hydrolysis process of slowly-biodegradable organics fraction was hindered under improper ISR conditions. Furthermore, the Cone model was evaluated as more appropriate for biodegradation kinetics analysis in BSP assays among the five common kinetic models (i.e., Exponential, Fitzhugh, Cone, Transference, and modified Gompertz models). Overall, the results provide fundamental guidance on designing consistent BSP assays and put a step forward in standardizing the BSP assay for anaerobic biodegradability assessments.

Parametric optimization of the dark fermentation process for enhanced biohydrogen production from the organic fraction of municipal solid waste using Taguchi method

In this work, the Taguchi method was used to optimize the dark fermentative H2 production from the organic fraction of municipal solid waste (OFMSW). The experiments were planned using the L16 orthogonal array design with each trial conducted at different levels of substrate concentration, inoculum-to-substrate ratio (ISR), and temperature. Based on the results, the optimal setting of the process parameters was the substrate concentration of 6 g-VS/L, ISR 0.5, and temperature of 55 °C. Furthermore, substrate concentration was the most important parameter affecting bio-H2 production among the three process parameters considered. Finally, a confirmation experiment under optimal conditions yielded 62.5 mL H2/g-VSadded, which was higher than all the bio-H2 yield values obtained in the other conditions tested in this study. The measured and predicted bio-H2 yields in the verification test were also very close to each other, confirming the reliability of the Taguchi method in optimizing the bio-H2 production process.

Biochemical Methane Potential of Cork Boiling Wastewater at Different Inoculum to Substrate Ratios

The present study evaluates the digestion of cork boiling wastewater (CBW) through a biochemical methane potential (BMP) test. BMP assays were carried out with a working volume of 600 mL at a constant mesophilic temperature (35 °C). The experiment bottles contained CBW and inoculum (digested sludge from a wastewater treatment plant (WWTP)), with a ratio of inoculum/substrate (Ino/CBW) of 1:1 and 2:1 on the basis of volatile solids (VSs); the codigestion with food waste (FW) had a ratio of 2/0.7:0.3 (Ino/CBW:FW) and the codigestion with cow manure (CM) had a ratio of 2/0.5:0.5 (Ino/CBW:CM). Biogas and methane production was proportional to the inoculum substrate ratio (ISR) used. BMP tests have proved to be valuable for inferring the adequacy of anaerobic digestion to treat wastewater from the cork industry. The results indicate that the biomethane potential of CBWs for Ino/CBW ratios 1:1 and 2:1 is very low compared to other organic substrates. For the codigestion tests, the test with the Ino/CBW:CM ratio of 2/0.7:0.3 showed better biomethane yields, being in the expected values. This demonstrated that it is possible to perform the anaerobic digestion (AD) of CBW using a cosubstrate to increase biogas production and biomethane and to improve the quality of the final digestate.

The effect of mono- and multiple fermentation parameters on volatile fatty acids (VFAs) production from chicken manure via anaerobic digestion

Although the high nitrogen content of chicken manure (CM) poses major challenges for methane production through anaerobic digestion, on the bright side, it has a great potential for production of value-added intermediate products, such as volatile fatty acids (VFAs). However, in order to enhance VFAs yield, methane formation should be substantially suppressed. In the current research, individual and multiple effects of initial pH, heat-shock pretreatment, chemical methanogens inhibitor and the inoculum to substrate ratio (ISR) on optimization VFAs fermentation from CM were evaluated via batch assays. In this regard, the highest net VFAs yield, 0.53 g-VFA/g-VS, was achieved at conditions with heat-shocked inoculum and CM at ISR 1:6 and pH uncontrolled. Acetate dominated the VFAs mixture, accounting for up to 75% of total. Increased inoculum content enhanced the bioconversion efficiency to 78% at ISR 1:3. The study results suggest that alkalinity is a key promoter of VFAs production from CM.