Inoculum To Substrate Ratio Research Articles

Anaerobic co-digestion of poultry slaughterhouse wastes with sewage sludge in batch-mode bioreactors (effect of inoculum-substrate ratio and total solids)

High amounts of organic matter and protein in slaughterhouse wastes make them a viable choice for anaerobic digestion and biogas production. The purpose of this study was to investigate potentials of biogas production from poultry slaughterhouse residues (waste and sludge) in a batch-fed anaerobic co-digestion process. In the first phase of the study, laboratory-scale experiments were conducted using 1-liter reactors at 34 °C with a retention time of 50 days in order to optimize digestion parameters; i.e. inoculum-substrate ratio (ISR) and total solids (TS). Based on these experiments, the ISR of 4 and the TS of 5% were determined as optimal settings for digestion over a retention time of 50 days. The highest biogas and methane yields in these experiments were respectively reported by 0.631 and 0.462 m3/kg-VSadded, achieved with 66% removal of volatile solids (VS). The optimized parameters obtained from the first phase were also used for verification at a larger scale (20 liters), wherein biogas and methane yields were found to be 0.574 and 0.402 m3/kg-VSadded; respectively. Moreover, results showed that optimal anaerobic digestion of slaughterhouse wastes in 20-liter digester could lead to 63% removal of VS and 88% reduction of chemical oxygen demand (COD) over a retention period of 42 days. The findings also indicated that decreasing ISR and increasing TS could bring about reduced pH as well as accumulation of fatty acids and ammonia, which could severely undermine yields of methanogenesis process.

Effect of anaerobic digester inoculum preservation via lyophilization on methane recovery

A robust anaerobic digestion (AD) inoculum is key to a successful digestion process by providing the abundant bacteria needed for converting substrate to useable methane (CH4). While transporting digester contents from one AD to another for digester startup has been the norm, transportation costs are high, and it is not feasible to transport wet inoculum to remote locations. In this study, the impact of preservation of AD inoculum via lyophilization was investigated for the purposes of digester startup and restabilization. The effect of lyophilizing inoculum on CH4 production using food waste as the substrate was tested using biochemical methane potential (BMP) tests under the following conditions: (1) three inoculum sources, (2) two inoculum to substrate ratios (ISR), (3) two cryoprotectants, and (4) two inoculum growth phases. After lyophilization with skim milk, the three inocula produced 144–146 mL CH4/g volatile solids (VS) and 194–225 mL CH4/g VS at a 2:1 and 4:1 ISR, respectively, with 33–57% more CH4 at the 4:1 ISR. Preservation with 10% skim milk exhibited complete recovery of CH4 production, while 10% glycerol and 10% glycerol/skim milk mixture yielded 76% and 4% CH4 recovery, respectively. Inoculum growth phase before preservation (mid-exponential or stationary growth phase) did not significantly affect CH4 recovery. The study indicates that inoculum can be preserved via lyophilization using 10% skim milk as a cryoprotectant and reactivated for food waste digestion. The results provide a systematic quantification of the conditions needed to successfully preserve a mixed AD inoculum.

The effect of ISR on OFMSW during acidogenic fermentation for the production of AD precursor: kinetics and synergies.

Acidogenic fermentation of the organic fraction of municipal solid waste (OFMSW) and its components (food waste, paper waste) was studied in a batch percolator reactor without artificial pH adjustment. The effect of inoculum to substrate ratio on process performance, in terms of pH, hydrolysis and volatile fatty acid (VFA) production, has been investigated. The inoculum to substrate ratio (ISR) was varied from 0 to 0.36 VS/VS and at optimized conditions for fermentation of OFMSW, with ISR 0.23, pH, hydrolysis and acidification yield were 5.5, 625 mg sCOD per g BD VS and 408 mg g−1 BD VS respectively. Due to the uplift of pH from 4 to 5.5 because of addition of ISR, the VFA composition was dominated mostly by butyric, acetic acids and propionic acid. Kinetics regarding rate of hydrolysis and acidification were calculated and reported. A significant synergistic effect was noticed in the acidification and hydrolysis, which were 1.76 and 1.35 fold higher than individual components (paper waste and food waste) of OFMSW, respectively and approximately 70% of biodegradable solid carbon solubilized into the liquid carbon within a short retention time of 78 h.

Anaerobic Biogas Production Using Microalgae Chlorella sp. as Biomass Co-digested by Cow Manure and Cow Rumen Fluid as Inoculum.

World’s demand for energy is steadily increasing following population increase, on the other hand reserves for fossil and coal energy are limited. Therefore research for renewable sources of energy is important. Biogas produced from renewable source could be one of the answer for future energy production. Researches regarding biogas production utilizing microalgae biomass such as Chlorella sp. have received much attention. In this study, co-digestion of Chlorella sp. “CD01” isolated from Cideng/Krukut River using cow rumen fluid and cow manure as inoculum were used to enhance biogas production. Our experiment used a simple non-stirred batch anaerobic bioreactor that was carried out for 29 days. Biogas volume, COD value, and microorganism were the parameters in this study. Our result showed that Chlorella sp. “CD01” and rumen fluid alone could not produce biogas. Co-digestion of Chlorella sp. “CD01” substrate and rumen fluid inoculum produced 314.5 mL biogas with yield of 43.23 mL/gTS. Co-digestion of Chlorella sp. “CD01” substrate and manure inoculum produced 1758 mL biogas with yield of 98.96 mL/gTS. The best substrate inoculum ratio (S/X) in this study was 0.33 based on cumulative biogas production. Attempts for isolating anaerobic culture from each reactor had been done using methanogenic selective media. Two methanogens isolates were morphologically characterized.

Biohydrogen Production from Food Waste: Influence of the Inoculum-To-Substrate Ratio

In this study, the influence of the inoculum-to-substrate ratio (ISR) on dark fermentative hydrogen production from food waste (FW) was evaluated. ISR values ranging from 0.05 to 0.25 g VSinoculum/g VSsubstrate were investigated by performing batch tests at T = 39 °C and pH = 6.5, the latter being the optimal value identified based on a previous study. The ISR was found to affect the fermentation process, clearly showing that an adequate ISR is essential in order to optimise the process kinetics and the H2 yield. An ISR of 0.14 proved to optimum, leading to a maximum H2 yield of 88.8 L H2/kg VSFW and a maximum production rate of 10.8 L H2/kg VSFW∙h. The analysis of the fermentation products indicated that the observed highest H2 production mostly derived from the typical acetate/butyrate-type fermentation.

Improvement of biohydrogen production by optimization of pretreatment method and substrate to inoculum ratio from microalgal biomass and digested sludge

Abstract Biohydrogen from microalgal biomass has shown particular advantage due to its high growth rate and high bioenergy production. As a representative of microalgae, Chlorella vulgaris was chosen as substrate along with digested sludge (DS) as inoculum in this research. In order to improve the hydrolysis of algal biomass and enhance biohydrogen production, pretreatment methods like acid and thermal pretreatment were employed. Thermal pretreatment showed better results than acid pretreatment of microalgal biomass. 100 °C for 60 min was identified as the optimum condition for the thermal pretreatment of C. vulgaris by response surface methodology (RSM) analysis. Experiments were also carried out to identify the optimum substrate to inoculum ratio (SIR) for the process. SIR of 8 generated the highest hydrogen yield of 190.90 mL H2/g-VS. Moreover, the overall energy balance of the process was evaluated and the results showed a positive energy balance of 1790.13 kJ/kg. The results indicated that optimization of pretreatment methods and substrate to inoculum ratio was effective in enhancing biohydrogen production from microalgal biomass and digested sludge.

Co-digestion and model simulations of source separated municipal organic waste with cattle manure under batch and continuously stirred tank reactors

This study investigates the co-digestion of source separated municipal organic waste (SSMOW), pretreated using a biopulper, and cattle manure both in batch and continuous stirred tank reactors. The optimum co-digestion feeding mixture was consisted of 90% SSMOW and 10% cattle manure on organic matter basis, yielding 443 mLCH4/gVS. The high performance of the co-digestion was explained by the fact that the efficient pulping pretreatment boosted the methane production from SSMOW and that the added livestock slurry provided the buffer capacity to avoid inhibition occurred by intermediates’ accumulation. Moreover, batch assays focused on the effect of inoculum to substrate ratio (ISR) were performed. Results showed that the reduction of ISR had slight impact on extending the lag phase, without affecting the rest kinetic parameters. The efficiency of the co-digestion process in continuously fed reactor was comparable with the results obtained from the batch assay (i.e. <95% of the maximum expected value). Finally, the outputs from an applied mathematical model were in good agreement with the experimental data obtained from the continuous reactor operation, demonstrating that the BioModel can serve as a reliable tool to predict the process performance under real-scale conditions.

Anaerobic digestion of food waste: Correlation of kinetic parameters with operational conditions and process performance

The correlations between kinetic parameters and both operational conditions and process performance during the anaerobic digestion of food waste were investigated. Substrate concentration (SC), biomass concentration (BC), and substrate–inoculum ratio (S/I) were selected as the operational conditions, while first-order and modified Gompertz models were introduced to evaluate digestion kinetics. The results indicated that no significant correlations between both hydrolysis and methanogenesis kinetic parameters (k and Rm) relative to the operational conditions and process parameters could be determined; however, k/Rm′ was observed to significantly correlate with these parameters. Specifically, substrate load (both SC and S/I) positively influenced k/Rm′ via its impact on volatile fatty acid (VFA) and pH, while BC reduced k/Rm′ by increasing the alkalinity of the system. Moreover, k/Rm′ was negatively correlated with process efficiency. The methane recovery rate exceeded 90% when 1.55<k/Rm′<3.13, but decreased by 50% when k/Rm′>4.64 (p=0.05). These findings provide a scientific foundation for predicting the behavior of anaerobic systems and optimizing the digestion process.

Valorisation of the liquid fraction from hydrothermal carbonisation of sewage sludge by anaerobic digestion

AbstractBACKGROUNDThe mesophilic anaerobic digestion of the liquid fraction from hydrothermal carbonisation (208°C, 1 h) of dehydrated sewage sludge has been studied. Two initial inoculum concentrations (IC) (10 and 25 g COD L‐1) and four inoculum to substrate ratios (ISR) (2, 1, 0.5 and 0.4 on a COD basis) have been selected to analyse their influence on the evolution of the anaerobic digestion process.RESULTSThe substrate is characterised by a high COD (95.5 g L‐1) and TKN (8.7 g N L‐1) values. High inoculum concentration (25 g COD L‐1) and/or low ISR (≤ 0.5) inhibited methanogenesis due to the high ammonia nitrogen (1.4 g TAN L‐1) and VFA (&gt;4 g COD L‐1) released. For the inhibited samples final COD removals lower than 15% and IA/TA ratios higher than 0.3 were found. The greatest methane yield (177±5 mL CH4 STP g‐1 CODadded) was achieved at 25 g COD L‐1 of IC and at an ISR of 2.CONCLUSIONDuring anaerobic digestion of the liquid fraction from the hydrothermal carbonisation of sewage sludge, the IC and ISR must be adequately selected for proper operation of the process and successful valorisation. According to the results, working at an ISR ≥ 1 is recommended. © 2017 Society of Chemical Industry

A parametric response surface study of fermentative hydrogen production from cheese whey

Batch factorial experiments were performed on cheese whey+wastewater sludge mixtures to evaluate the influence of pH and the inoculum-to-substrate ratio (ISR) on fermentative H2 production and build a related predictive model. ISR and pH affected H2 potential and rate, and the fermentation pathways. The specific H2 yield varied from 61 (ISR=0, pH=7.0) to 371L H2/kg TOCwhey (ISR=1.44gVS/g TOC, pH=5.5). The process duration range was 5.3 (ISR=1.44gVS/g TOC, pH=7.5) − 183h (ISR=0, pH=5.5). The metabolic products included mainly acetate and butyrate followed by ethanol, while propionate was only observed once H2 production had significantly decreased. The multiple metabolic products suggested that the process was governed by several fermentation pathways, presumably overlapping and mutually competing, reducing the conversion yield into H2 compared to that expected with clostridial fermentation.

Factors affecting on hythane bio-generation via anaerobic digestion of mono-ethylene glycol contaminated wastewater: Inoculum-to-substrate ratio, nitrogen-to-phosphorus ratio and pH

This study aims to assess the effect of inoculum-to-substrate ratio (ISR) and nitrogen-to-phosphorus balance on hythane production from thermophilic anaerobic decomposition of mono-ethylene glycol (MEG) contaminated wastewater. ISRs ranging from 2.65 to 13.23gVSS/gCOD were employed, whereas the tested N/P ratios varied from 4.6 to 8.5. Maximum methane and hydrogen yields (MY and HY) of 151.86±10.8 and 22.27±1.1mL/gCODinitial were achieved at ISRs of 5.29 and 3.78gVSS/gCOD, respectively. HY increased 1.45-fold by decreasing N/P from 8.5 to 4.6, while MY improved 1.6-fold by increasing N/P from 4.6 to 5.5. Methane production was strongly influenced by initial NH4-N, compared to initial PO4-P. Optimal HY of 47.55mL/gCODinitial was achieved at pH 5.0 and ISR of 3.78gVSS/gCOD using thermal-treated sludge. Three-dimensional regression model was applied for the combined effect of initial MEG, NH4-N and PO4-P on hythane production. Potential economic benefits of hythane production from MEG contaminated wastewater were assessed.

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Abstract The quantity and quality of inoculum used in the Anaerobic Digestion (AD), impact seriously on the biodegradability and the amount of methane produced. This research evaluated the effect of the source of inoculum municipal wastewater treatment plant (WWTP) on the production of methane as a source of renewable energy AD from Municipal Biowaste (MB), analyzing the Substrate-Inoculum (S/I) ratio and the buffering capacity of the inoculum as key aspects. The experiments were performed on a laboratory scale by testing Biochemical Methane Potential (BMP) in the mesophilic range with a retention time of solids (RTS) 21 days; two inoculums from UASB reactors and the other of an anaerobic sludge digester. The S/I ratios ranged between 0.5 and 12gVSsubstrate gVS-1 inoculum. Although it was found that there were no statistically signifcant differences between the inoculum (p>0.05), the inoculum from the anaerobic digester presented a better performance because of its greater capacity buffer. The S/I ratio showed statistically signifcant differences (p 70mLCH4 gVS-1 substrate ) hydrolysis rates (from 0,15 to 0,21d-1) and phases of lethargy (2,7-9,3d). Keywords: biowaste; renewable energy, hydrolysis, anaerobic sludge, methane, substrate-inoculum ratio.

Substrate-inoculum Ratio Optimization upon the Biogas Production from Peels of Eggplant and Cassava by Biomethanization

Substrate-inoculum Ratio Optimization upon the Biogas Production from Peels of Eggplant and Cassava by Biomethanization

Batch anaerobic digestion of simulated Bangladeshi food waste: methane production at different inoculum-to-substrate ratios and kinetic analysis

This study investigates the anaerobic biodegradation characteristics of a simulated Bangladeshi food waste. Biochemical methane potential experiments carried out in 500 mL batch digesters showed the methane yields of cooked meat, cooked fish, boiled rice, vegetable and mixed food waste (MFW) to be 541, 402, 319, 274 and 484 ml CH4/gVS, respectively. The biodegradability of 87%, 83%, 75%, 76% and 82% were obtained for cooked meat, cooked fish, boiled rice, vegetable and MFW, respectively. At mesophilic temperature (35°C), a maximum of 484.41 ml CH4/g VS was observed at an inoculum to substrate ratio (ISR) of 1 followed by 280, 166, 194 and 43 mL CH4/g VS at ISRs 10, 2, 0.1 and 0.05, respectively. The modified Gompertz model utilised for estimating the kinetic parameters of methane production revealed the maximum methane production rate as 16.02 ml CH2/g VS.d at an ISR of 1 with lag phase of 3.8 days.

Response surface design to study the influence of inoculum, particle size and inoculum to substrate ratio on the methane production from Ulex sp.

Ulex europaeus is one of the world worst invaders vegetal species and its suitability for biogas production is significant. The effect of three factors affecting the Biochemical Methane Potential (BMP, expressed as volume of CH4 per mass of volatile solids of waste) and the biodegradability rate (k, expressed in volume of CH4 per mass of VS and time) of U. europaeus was assessed by a Central Composite Face Centred Design. The BMP varied from 153 L kg−1 to 308 L kg−1. Inoculum to substrate ratio (ISR) and the type of inoculum had high influence on the final results. k varied from 14 L kg−1 d−1 to 49 L kg−1 d−1. The conditions that simultaneously maximized the BMP and k were an inoculum consisting in 55% (v) of granular sludge and 45 % (v) of suspended sludge from a sludge digester, an ISR of 4 g g−1, and a particle size of 1.9 mm. Considering the average biomass production in shrub land areas, the potential energy production from U. europaeus is estimated in (36.9 ± 19.3) GJ ha−1 yr−1. For example, in Europe, a maximum energy supply of 7 EJ yr−1 could be achieved from potentially harvestable shrub land areas.

The impact of inoculum source, inoculum to substrate ratio and sample preservation on methane potential from different substrates

Batch experiments were conducted to evaluate the impact of inoculum sources, inoculum to substrate (IS) ratio and storage conditions on the potential and production rate of methane (CH4) from different substrates: wheat straw, whole crop maize, cattle manure, grass and cellulose.The results of the test with four inocula and four substrates indicated that inoculum source could have a significant impact on both CH4 potential (BMP) and the kinetics parameters of different substrates. The two inocula showing the highest BMP and production rates in each period were those coming from a feeding with more than 70% of animal manure under thermophilic conditions. The impact of the IS ratio in the range 0.25–2.5, in terms of g volatile solids (VS) substrate/g VS inoculum, depended on substrate type. Maize silage was more affected to changes in the IS ratio than wheat straw. The optimal IS ratio range for maize was 1.0–1.5, however, a wider IS range can be used in wheat straw (0.5–2.5). The impact of freezing and drying depended on biomass type. Freezing, drying and ensiling of grass increased the CH4 yield compared to fresh grass. Drying of maize had no impact while freezing reduced the CH4 potential. Drying and freezing had no impact on straw.

Effects of substrate concentration on methane potential and degradation kinetics in batch anaerobic digestion

In this study, two experiments were conducted to evaluate the impact of substrate concentrations on methane potential and degradation kinetics of substrate. The biochemical methane potential (BMP) tests in Experiment I were performed at a constant inoculum to substrate ratio (ISR), whereas, different ISRs were applied in Experiment II. Results obtained from Experiment I revealed that methane potential of substrate increased at a saturating trend with higher substrate concentrations, and could differ by up to 30% between the lowest and highest investigated concentrations. The results of Experiment II verified the results of Experiment I, and further showed that this trend also occurs when the substrate concentration is regulated with ISRs. In contrast, substrate concentration had no significant impact on the degradation kinetics. It was concluded that dilutions should be avoided when the substrate concentration is lower than 10gVS/L in order to avoid underestimations of methane potential from BMP test.

Effect of ethanol pre-fermentation and inoculum-to-substrate ratio on methane yield from food waste and distillers’ grains

Abstract Anaerobic digestion of food waste and distillers’ grains with ethanol pre-fermentation (EP) at different inoculum-to-substrate ratios (ISRs) was investigated. With EP, the highest methane yield of 581.2 mL/g-VS was observed at ISR 2.5, with the methane yields of ISR 1.0 and ISR 0.4 being 41.8% and 71.7% lower. At the same ISR, the methane yield without EP (control group) was 143.2 mL/g-VS, 57.7% lower than that with EP. EP effectively alleviated inhibition by acidification, greatly reduced the duration of the lag phase, and markedly stimulated the growth of methanogens, compared with that of the control group. Thermodynamics analysis of various acidogenic fermentation patterns suggested that directing the acidogenic phase towards ethanol, instead of towards volatile fatty acids, allocates more potentially available energy for methanogens. Thus, EP prior to anaerobic digestion is a suitable way to stabilize an anaerobic digestion system even at a low ISR.

Effect of inoculum to substrate ratio on the performance of modified anaerobic inclining-baffled reactor treating recycled paper mill effluent

Three start-up techniques were investigated to evaluate the suitability of the bench-scale modified anaerobic inclining-baffled reactor (MAI-BR) for the treatment of recycled paper mill effluent (RPME) and to achieve an improved understanding of the inoculum to substrate ratio (ISR). The ISR ratios used were 3.53, 1.17, and 10.63 g volatile suspended solids (VSS)/g chemical oxygen demand (COD) for the first, second, and third start-ups, respectively. On a 30-d duration, the first start-up succeeded in removing 72% of the COD with an effluent pH of 6.2 and a methane production of 0.076 L/d. The second start-up was considered unfavorable after 16 d because of low methane production and effluent pH level. The third start-up with a 21-d duration was the best because of its 87% COD removal, 6.82 effluent pH, and 0.164 L/d methane production. The effluent volatile fatty acid (VFA)/alkalinity ratios were concurrently varied as 0.56, 0.45, and 0.034 for the first, second, and third start-ups, respectively. Subsequently, the VSS/TSS ratio of 0.78–0.86 formed in the reactor was sufficient to control biomass washout. The third start-up demonstrated that an ISR of more than 10 g VSS/g COD is an important factor that leads to a successful and efficient start-up operation. The batch feeding rate must be as low as 0.1 g COD/L d. Furthermore, the VFA/alkalinity ratio of the third start-up was excellent. The bench-scale unique design of the MAI-BR showed good performance in the RPME treatment within a period of less than one month.

High rate psychrophilic anaerobic digestion of high solids (35%) dairy manure in sequence batch reactor

Zero liquid discharge is increasingly adopted as an objective for waste treatment process. The objective of this study was to increase the feed total solids (TS) and the organic loading rate (OLR) fed to a novel psychrophilic (20°C) dry anaerobic digestion (PDAD). Duplicate laboratory-scale bioreactors were fed cow feces and wheat straw (35% TS in feed) at OLR of 6.0g TCOD kg−1 inoculum d−1 during long-term operation (147days consisting of 7 successive cycles).An overall average specific methane yield (SMY) of 151.8±7.9NL CH4 kg−1 VS fed with an averaged volatile solids removal of 42.4±4.3% were obtained at a volatile solids-based inoculum-to-substrate ratio (ISR) of 2.13±0.2. The operation was stable as indicated by biogas and VFAs profiles and the results were reproducible in successive cycles; a maximum SMY of 163.3±5.7NL CH4 kg−1 VS fed was obtained. Hydrolysis was the reaction limiting step. High rate PDAD of 35% TS dairy manure is possible in sequential batch reactor within 21days treatment cycle length.