Modified Gompertz Model Research Articles

Effect of inoculums type and optimization of inoculum to substrate ratio on the kinetics of biogas production of fruit and vegetable waste

Annually 5.6 million tonnes of FVW are produced in India. Anaerobic digestion (AD) holds the potential of generating renewable energy from this organic waste. Therefore, an attempt has been made to optimize inoculum to substrate (I/S) ratio via biochemical methane potential (BMP) of FVW using two different types of inoculums viz. anaerobic sludge and a mixture of anaerobic sludge and cow dung in (1:1) ratio. Different (I/S) ratios selected for the study were 0.2, 0.3, 0.4, 0.5, and 0.6. Results indicated that anaerobic sludge (AS) along with cow dung (CD) at a (1:1) ratio performed better than AS alone. The highest cumulative biogas yield was obtained at (I/S) ratio 0.3 for AS+CD (1:1) ratio, which is equivalent to 468.82 ml/g VS. On the other hand, the biogas yield using only AS was found to be 459.49ml /g VS. The highest methane content was obtained as 64% and 61.2%, for inoculums AS+CD and AS, respectively. Performance analysis portrayed volatile solids (VS) reductions of 74% and 68% for (AS+CD) and AS, respectively. The kinetic parameters of AD were studied by the modified Gompertz model (MGM) and the first-order kinetic model. The experimental data fitted well with the MGM model.

Multiscale kinetic modeling for biohydrogen production: A study on membrane bioreactors

Hydrogen can be a capable alternative to fossil fuels due to its carbon-free characteristics, in this content, biological hydrogen production is considered a practical approach because technology is green. Due to parameters affecting biohydrogen production, such as operating conditions, it is crucial to predict the process to see the proper yield. There are several conventional and unconventional models used in biohydrogen production prediction. This paper derived a triple first-order prediction model from a previously presented multi-scale kinetic model polynomial built upon the multi-stage growth hypothesis for bio-hydrogen production prediction. The original model was applied to batch and continuous stirred tank reactor studies for their model evaluation, this study evaluated the newly derived model for studies of membrane bioreactors. Due to their increased production yield, membrane bioreactors are an emerging field in biohydrogen production. Although the previous study was mainly applied for batch dark fermentations consisting of various microorganisms, the results presented in this study indicate that it is also applicable for continuous and photo fermentation systems. The original model results reported significant fitness accuracy among different datasheets compared to conventional models like the modified Gompertz model, considering essential factors impacting biohydrogen production suggested in the original model, this paper investigated eleven case studies of dynamic membrane bioreactors with modeling fitness of 99% for most cases. This study reports even higher fitness accuracy compared to the original model, even with different operating conditions.

A comparison of ultrasonic, ozone, and enzyme pre-treatments on cheese whey degradation for enhancement of anaerobic digestion

Lactose in cheese whey wastewater (CWW) makes it difficult to degrade under normal conditions. The effect of ultra-sonication (US), ozonation and enzymatic hydrolysis on increasing the bioavailability of organic matter in CWW and biogas production were evaluated. The pre-treatment conditions were: specific energy input varied from 2130 to 8773KJ/KgTS for a sonication time of 4.5–18.5 min, Ozone (O3) dosages ranging from 0.03 to 0.045gO3/gTS were applied for 4–16 min, pH (3.8–7.1), temperature (35°C–55°C), enzyme dosage (0.18–0.52%), was operated from 7.75 to 53 min for enzymatic hydrolysis by β-galactosidase. The results of the US reported a maximum sCOD solubilisation of 77.15% after 18.5 min of operation, while the corresponding values for ozonation and enzymatic methods were 64.8% at 16 min and 54.79%, respectively. The organic matter degradation rates evaluated in terms of protein and lactose hydrolysis were 68.78%,46.03%; 47.83%,16.15% and 54.22%,86.2%respectively, for US, ozonation and enzymatic methods. The cumulative methane yield for sonicated, ozonised and enzymatically hydrolysed samples were 412.4 ml/g VS, 361.2 ml/g VS and 432.3mlCH4/gVS, respectively. Regardless of the lower COD solubilisation rates attained, enzymatic pre-treatment showed maximum methane generation compared to US and ozonation. This could be attributable to the increased activity of β-galactosidase in hydrolysing whey lactose. The energy calculations revealed that the pre-conditioning of organic-rich CWW with enzymatic hydrolysis is more effective and efficient, yielding a net energy gain (gross output energy-input energy) of 9166.7 KJ and an energy factor (ratio of output to input energy) of 6.67. The modified Gompertz model well simulated all experimental values.

Effects of biogas slurry reflux mode and reflux rate on methane production by mixed anaerobic digestion of corn straw and pig manure

Biogas slurry reflux is a promising method to realize biogas slurry reduction and improve biogas production performance of anaerobic digestion. The purpose of this study was to investigate the effects of reflux mode and reflux ratio on mixed anaerobic digestion of corn straw and pig manure to obtain the best biogas slurry reflux process. The influence of reflux mode and reflux ratio on the internal environment during anaerobic digestion were clarified by kinetic analysis. The results showed that compared with the control group, the degree of substrate hydrolysis in the hydrolysis phase reflux (HPR) and two-phase synergistic reflux (TPSR) treatment groups increased, and the initial concentration and peak value of volatile fatty acids (VFAs) increased by 20.35%–85.81% and 24.72%–74.37%, respectively. The modified Gompertz model fitting results that the three biogas slurry reflux modes all significantly shortened the lag period of anaerobic digestion (17.29%–48.32%) and increased the peak gas production (7.54%–88.07%). And the maximum daily gas production (65.82 mL/(g VS∙d)), methane production (422.86 mL/g VS) and biodegradation rate (83.65%) were obtained under the TPSR mode with reflux ratios of 75% and 100%. This study provides a theoretical basis for the development of biogas slurry reflux technology in the mixed anaerobic digestion of corn straw and pig manure, and realizes the reduction and resource utilization of biogas slurry.

Anaerobic co-digestion of grass and cow manure: kinetic and GHG calculations

Grass is a highly desirable substrate for anaerobic digestion because of its higher biodegradability and biogas/methane yield. In this study, anaerobic co-digestion of grass, cow manure and sludge was studied under mesophilic conditions for 65 days. Experiments were performed on a feed ratio of grass/manure from 5 to 25%, respectively. The maximum cumulative biogas and methane yield was obtained as 331.75 mLbiogas/gVS and 206.64 mLCH4/gVS for 25% ratio. Also, the results of the experiments were tested on the three different kinetics model which are the first order kinetic model, modified Gompertz model and Logistics model. As a result of the study, it was found that by using grass nearly 480 × 106 kWh/year electricity may be produced and 0.5 × 106 tons/year CO2 greenhouse gas emission mitigation may be reached.

Low-temperature phenol-degrading microbial agent: construction and mechanism.

In this study, three cold-tolerant phenol-degrading strains, Pseudomonas veronii Ju-A1 (Ju-A1), Leifsonia naganoensis Ju-A4 (Ju-A4), and Rhodococcus qingshengii Ju-A6 (Ju-A6), were isolated. All three strains can produce cis, cis-muconic acid by ortho-cleavage of catechol at 12℃. Response surface methodology (RSM) was used to optimize the proportional composition of low-temperature phenol-degrading microbiota. Degradation of phenol below 160mgL-1 by low-temperature phenol-degrading microbiota followed first-order degradation kinetics. When the phenol concentration was greater than 200mgL-1, the overall degradation trend was in accordance with the modified Gompertz model. The experiments showed that the microbial agent (three strains of low-temperature phenol-degrading bacteria were fermented separately and constructed in the optimal ratio) could completely degrade 200mgL-1 phenol within 36h. The above construction method is more advantageous in bio-enhanced treatment of actual wastewater. Through the construction of microbial agents to enhance the degradation effect of phenol, it provides a feasible scheme for the biodegradation of phenol wastewater at low temperature and shows good application potential.

Co-digestion of poultry droppings and banana waste for maximizing biogas production in Bangladesh

Poultry industry is a promising sector for meeting protein demands in Bangladesh. Poultry droppings generated from farms pose a threat to the environment, but could be one of the best sources of plentiful substrates for anaerobic co-digestion. Poultry droppings mixed with carbon rich banana waste, which is readily available in Bangladesh, can be used for increasing biogas production. Hence, a study was conducted to assess the bio-methane potential from the anaerobic co-digestion of poultry droppings (PD) with raw banana peel (BP), and to find the optimal mixing ratio. The batch study was conducted in an incubator at 35 °C for a retention time of 83 days. The PD and BP were mixed at a ratio of 100:0, 90:10, 70:30, 50:50, 30:70,10:90 and 0:100 to find out the optimum one. Five kinetic models were used to fit the experimental result to determine different kinetic parameters. The highest amount of biogas (347.0 ± 53.6 ml/gVS) and methane (200.1 ± 18.6 ml/gVS) were obtained at 50:50 ratio of PD and BP for the digestion period. The biogas and methane yield at this ratio were 1.68 and 3.12 times higher than the mono-digestion of banana peel, respectively. Biogas production was not significant when compared with mono-digestion of PD, but co-digestion at 50:50 ratio showed maximum usability of banana peel. Furthermore, the results of kinetic modelling showed both the cone model and the modified Gompertz model are best fitted for predicting methane production.

Improvement of Asterarcys quadricellulare biomass solubilization and subsequent biogas production via pretreatment approaches: structural changes and kinetic modeling evaluation.

This study investigated the effect of enzymatic and hydrothermal pretreatment approaches on the solubilization of organic matter, structure, and biogas yield from microalgal biomass. The soluble chemical oxygen demand (sCOD) concentration increased by 1.21-3.30- and 5.54-6.60-fold compared to control by enzymatic and hydrothermal pretreatments respectively. The hydrothermal pretreatment affected the structural changes in the microalgal biomass markedly; nonetheless, increased enzymatic concentration also had a definite effect on it as determined by qualitative approaches like scanning electron microscopy and Fourier transform infrared spectroscopy. Also, the hydrothermal pretreatment (100°C for 30min) resulted in the highest biogas production potential (P) of 765.37 mLg-1 VS at a maximum biogas production rate (Rm) of 22.66 mLg-1day-1 with a very short lag phase (λ) of 0.07days. The biogas production of pretreated microalgal biomass particularly at higher enzyme dose (20%, 24h) and higher hydrothermal pretreatment temperature (120°C, 30min) showed a significant but weak correlation (R = 0.53) with sCOD, thus demonstrating that the less organic matter was used up for the biogas production. The modified Gompertz model explained the anaerobic digestion of microalgal biomass more accurately and had a better fit to the experimental data comparatively because of the low root mean square error (3.259-16.728), residual sum of squares (78.887-177.025), and Akaike's Information Criterion (38.605-62.853).

Effect of Temperature on Co-Anaerobic Digestion of Chicken Manure and Empty Fruit Bunch: A Kinetic Parametric Study

The rapid growth of the Malaysian poultry and palm oil industries has led biomass waste generation in abundance specifically chicken manure and empty fruit bunch (EFB). Anaerobic digestion (AD) is a circular economy-based approach which converts chicken manure and EFB into biogas which can be utilized for heating and power generation. Operating temperature is an imperative consideration for AD hence the objective of the study is to evaluate the effect of different temperature profiles namely, psychrophilic (20 °C), mesophilic (35 °C) and thermophilic (50 °C) on AD of chicken manure and EFB. The kinetic parameters are also evaluated using five kinetic models to enable readers to comprehend the kinetic behaviours of the systems. The volume and composition of biogas is measured every five days for a 50-day retention time. The findings observed that mesophilic condition is the most favourable with cumulative methane, CH4 composition of up to 17.07%, almost two folds that of thermophilic (9.12%) and five folds that of psychrophilic (3.49%). The CH4 generation rate, Rb based on the modified Gompertz model which is deemed the best fit further supports these findings as the Rb under mesophilic condition is significantly higher (0.330 mL/gvs day) compared to psychrophilic (0.088 mL/gvs day) and thermophilic (0.120 mL/gvs day) conditions.

Valorization of brown macroalgae Sargassum plagiophyllum for biogas production under different salinity conditions

This study investigates the biogas production from Sargassum plagiophyllum under different salinity using a semi-continuous reactor. Inoculum preparation was conducted by mixing the two prepared S. plagiophyllum juice (deionized and saline water) with the cow manure using a ratio of 1:1. Once every two days, 5 % of the substrate was replaced with 5 % of fresh macroalgae juice continuously. The results found that cumulative biogas production in deionized water was 3.7 times higher than in saline water after 30 days. It could be attributed to anaerobic bacteria growth inhibited by salt. The maximum cumulative methane and biogas yields in the deionized water digester were 266.18 mL/g-VS and 371.76 mL/g-VS, respectively. The kinetics of the methane production was also determined, and the experimental data fitted well with the modified Gompertz model. These results indicate that S. plagiophyllum, under low salinity conditions, can be developed as a feedstock for biogas production.

Bioenergy Potential and Kinetic of Biogas Production in Anaerobic Digestion of Slaughterhouse Effluent

Many studies have investigated the technology of anaerobic digestion for waste treatment and its benefits. However, most of those studies have reported on solid waste. So, there are few articles on the anaerobic digestion of effluent, especially anaerobic digestion of slaughterhouse effluent and its bioenergy potential. The purpose of this study is to evaluate the bioenergy potential in slaughterhouse wastewater treatment. Then, anaerobic digestion (AD) was used in this study to assess the bio-energy potential and kinetics of biogas production during processing. The slaughterhouse wastewater collected was characterized before the experiments using french standard method “AFNOR”. pH, Temperature, turbidity, dissolved oxygen (O_2dis.), oxidation-reduction potential (ORP), Conductivity, Chemical Oxygen Demand (COD), biochemical oxygen demand in five days (BOD₅), total Kjeldahl nitrogen (TKN) and total phosphorus (P_tot) were analyzed and the ratio BOD₅/COD was calculated to evaluate the biodegradability of the biomass. Laboratory-scale anaerobic batch digesters consisting of a 1 L plastic container were used in all the experiments and the biogas produced in the digesters was measured daily by the water displacement method. The wastewater produced by slaughterhouses is biodegradable with a ratio between biological oxygen demand and chemical oxygen demand (BOD₅/COD) > 0.5. An effective AD design shows that over 90% of organic matter was removed when inoculation and the carbon/nitrogen (C/N) ratio were adjusted. The cumulative volume of biogas increased from 415 mL to 2,150 mL as the substrate/inoculum (S/I) ratio has decreased from 2.028 to 0.337 and increased from 1,140 mL to 5,250 mL as the C/N ratio increased from 6 to 22. The biogas produced has a high calorific value, as the methane content is 74%. Among the three kinetic models used to describe biogas production, a modified Gompertz model was found to be the best with R² between 0.983 and 0.993. This study points out energy potential of slaughterhouse wastewater and its benefit as it is managed efficiently.

Recycling cinder in efficient methane production from wheat straw via solid-state anaerobic digestion (SS-AD)

Solid-state anaerobic digestion (SS-AD) has received widespread attention due to its high methane productivity and organic loading, as well as its almost nonexistent wastewater emission. However, local acidification of the reaction system resulted in low material transfer efficiency due to low free water content leading to low energy conversion efficiency. Cinder is a byproduct of the coal chemical industry that has the potential to enhance the SS-AD performance due to its porous structure, electrocatalytic activity, and high trace elements concentration. The effect of cinder addition on SS-AD of wheat straw at 35 °C was studied herein. The cumulative methane of 2.5%, 5.0%, and 10.0% cinder groups were 41.25, 33.34, 28.94, and 26.68 mL/g VS, respectively, which increased 54.61%, 24.96%, and 8.47% compared to control (CK), with 2.5% cinder obtained the highest methane production. Cinder considerably enhanced volatile fatty acids conversion, particularly the propionic acid. The modified Gompertz model was used to predict the methane production potential and found to be able to accurately fit the characteristics of gas production. The maximum methane production of three test groups (2.5%, 5.0%, and 10.0%) was predicted to increase by 53.28%, 26.60%, and 11.56%, respectively, compared to CK. Cinder greatly enhanced the abundance of Methanosarcina, Fibrobacteres, and Spirochaetoma, which contributed to the switch from hydrogenophilic to acetylated methanogenesis. The prediction of the abundance of enzymes associated with microbial metabolism verified that cinder contributed to the greatest abundance of enzymes working in the hydrolysis phase, including peptidases, pyruvate metabolism, and genes encoding methane metabolism. Based on the concept of circular economy, this study presents a significant reference for synergistic and efficient disposal of industrial and agricultural wastes with high-value utilization.

Effects of Magnetic Biochar Addition on Mesophilic Anaerobic Digestion of Sewage Sludge.

As a low-cost additive to anaerobic digestion (AD), magnetic biochar (MBC) can act as an electron conductor to promote electron transfer to enhance biogas production performance in the AD process of sewage sludge and has thus attracted much attention in research and industrial applications. In the present work, Camellia oleifera shell (COS) was used to produce MBC as an additive for mesophilic AD of sewage sludge, in order to explore the effect of MBC on the mesophilic AD process and its enhancement mechanism. Analysis by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectrometry (FTIR), and X-ray diffraction (XRD) further confirmed that biochar was successfully magnetized. The yield of biogas from sewage sludge was enhanced by 14.68-39.24% with the addition of MBC, and the removal efficiency of total solid (TS), volatile solids (VS), and soluble chemical oxygen demand (sCOD) were 28.99-46.13%, 32.22-48.62%, and 84.18-86.71%, respectively. According to the Modified Gompertz Model and Cone Model, the optimum dosage of MBC was 20 mg/g TS. The maximum methane production rate (Rm) was 15.58% higher than that of the control reactor, while the lag-phase (λ) was 43.78% shorter than the control group. The concentration of soluble Fe2+ and Fe3+ were also detected in this study to analyze the function of MBC for improving biogas production performance from sewage sludge. The biogas production was increased when soluble Fe3+ was reduced to soluble Fe2+. Overall, the MBC was beneficial to the resource utilization of COS and showed a good prospect for improving mesophilic AD performance.

Effects of Pretreatment with a Ball Mill on Methane Yield of Horse Manure

Lignocellulosic biomass is an abundant organic material, which can be utilised in biogas plants for sustainable production of biogas. Since these substrates usually have high lignin contents and consist of rather elongated particles, a special pretreatment is required for an economical and process-stable utilisation in the biogas plant. The mechanical pretreatment of horse manure was carried out with the prototype of a ball mill at different speeds. The aim of ball milling is to comminute the substrate and disintegrate the lignocellulosic bond. Mechanical pretreatment in the ball mill resulted in a significant increase in specific methane yield of more than 37% in anaerobic batch digestion (up to 243 LCH4 kgVS−1) of horse manure. The kinetics of the methane gas formation process was analysed by a modified Gompertz model fitting and showed a higher methane production potential and maximum daily methane production rate as well as a lower duration of the lag phase after pretreatment at 6 rpm. This was further confirmed by sieve analyses, which showed a significant reduction of particle size compared to the untreated variant. Thus, the use of the ball mill increases the specific methane yield and improves the fermentation of lignocellulosic substrates such as horse manure.Graphical

Sustainable Use of CO2 and Wastewater from Mushroom Farm for Chlorella vulgaris Cultivation: Experimental and Kinetic Studies on Algal Growth and Pollutant Removal

The potential use of carbon dioxide (CO2) and wastewater released from a mushroom farm for the cultivation of Chlorella vulgaris microalga was investigated in this study. For this purpose, a microcontroller-based aided CO2 capture and mixing prototype was constructed for the cultivation of C. vulgaris under varying concentrations of mushroom farm wastewater (0 as control, 50 and 100%). The results showed that the constructed prototype was helpful to maintain desirable CO2 levels (6000 ppm) in the mushroom cultivation chamber with constant CO2 supply to algal culture, i.e., 0.6% at an airflow rate of 50 mL/min. After 16 days of algal cultivation, it was observed that the maximum significant (p < 0.05) algal biomass production of 2.550 ± 0.073 mg/L was recorded in 50% wastewater concentration followed by 100% and control. Also, the maximum removal of selected mushroom farm wastewater pollutants, such as total dissolved solids (84.00 ± 1.37%), biochemical oxygen demand (90.17 ± 2.42%), chemical oxygen demand (91.53 ± 0.97%), total nitrogen (86.27 ± 1.60%) and total phosphorus (94.19 ± 2.33%), was achieved in 50% concentration of wastewater treatment with maximum first-order rate constant (k) values. In addition, the algal growth kinetics results showed that the logistic model fit best compared to the modified Gompertz model, based on selected validation tools, such as experimental vs. predicted values, coefficient of determination (R2 > 0.9938), model efficiency (ME > 0.98) and root mean square error (RMSE < 0.03). The post-harvest characterization of algal biomass revealed that the proximate, biochemical, ultimate elements (carbon, oxygen and nitrogen) and structural properties were significantly higher in 50% treatment than those in 100% and control treatments. Therefore, the findings of this study are novel and provide significant insight into the synergistic use of CO2 and wastewater produced by mushroom farms for algal cultivation and biological wastewater treatment.

Biological CH4 production from H2/CO2 streams: Influence of trace metals concentration on the hydrogenotrophic process

Hydrogenotrophic methanogens require trace metals to perform their metabolic activity, the implementation of gas-phase bioreactors targeting methane production from CO2 and H2 streams will therefore require the addition of these trace metals. In the present study, a kinetic study was performed in batch experiments testing six concentration levels of iron, zinc, molybdenum, cobalt, and nickel, which are cofactors of the enzymes involved in the hydrogenotrophic methane production. The occurrence of acetoclastic methanogenesis or homoacetogenesis were ruled in the present kinetic characterization. The predominant archaea of the culture belonged to the Methanolinea and Methanobacterium genera, with relative abundances of 67.16% and 28.15%, respectively, considering the total archaeal community identified. A mineral salt medium (MSM) with basal trace metals concentration denominated as MSM-1X was used as the reference culture medium in the kinetic studies. Then, 0X, 0.5X, 2X, 10X and 20X concentrations relative the MSM-1X were tested. Experimental CH4 production data were fitted to the modified Gompertz model, yielding 96–99% correlation coefficients. Optimum concentrations of 1.479, 0.063, 0.011, 0.032, and 0.061 mg gVSS−1 of Fe, Zn, Mo, Co, and Ni, respectively, were found. The Haldane-Andrews kinetic model showed that MSM provided with trace metals concentrations 10 and 20 times higher compared with the basal MSM-1X led to an inhibited performance in terms of (i) the duration of the lag phase, (ii) the maximum methane production rate, and (iii) the maximum volume of methane produced.

A novel aerobic denitrifying phosphate-accumulating bacterium efficiently removes phthalic acid ester, total nitrogen and phosphate from municipal wastewater

Simultaneous removal of nitrogen, phosphate and emerging pollutants are critical for safe reuse of wastewater, but research in this field is limited. In the present study, a novel aerobic denitrifying phosphate-accumulating bacterial strain RL-GZ01 was found to be able to utilize phthalic acid esters (PAEs) as carbon resource for cell growth. Based on 16S rRNA gene analysis, physiological and biochemical characterization, and genome-based average nucleotide identity calculation, RL-GZ01 was identified as Rhodococcus pyridinivorans. Strain RL-GZ01 showed high DEHP degradation in alkaline conditions and good tolerance of salinity and organic solvents. The degradation of DEHP by RL-GZ01 fitted well with a modified Gompertz model (R2 = 0.9985). Metabolic intermediates of DEHP were identified via UHPLC-MS/MS analysis and the catabolic pathway was proposed thereafter. Genes and gene clusters contributed to the utilization of DEHP were analyzed through genomic analysis. Analysis of KEGG nitrogen metabolism pathway indicated that nitrate and nitrite were further transformed into ammonium which was further used for the biosynthesis of l-glutamine and L-glutamate. Strain RL-GZ01 was further identified as a denitrifying phosphate accumulating organism which can accumulate phosphate by generating polyphosphate. Finally, strain RL-GZ01 was applied to municipal wastewater treatment for simultaneous removal of nitrogen, phosphate and DEHP. The removal percentages of DEHP (5 mg/L), TN (71.2 mg/L), NH4+-N (70.9 mg/L), PO43−-P (10.89 mg/L) and COD (622.4 mg/L) by strain RL-GZ01 were 89.94 %, 64.45 %, 64.94 %, 76.30 % and 63.23 % within 84 h, respectively. These demonstrated the capability of strain RL-GZ01 for the biological treatment of wastewater containing PAEs.

The effect of silage additive on the kinetics of biogas production from lignocellulosic perennial crops

The aim of the study was to assess the effect of silage additive containing heterofermentative lactic acid bacteria (LAB) strain of Lactobacillus buchneri species on ensiling quality, as well as methane yield and the kinetics of biogas production from ensiled perennial energy grasses: Miscanthus × giganteus (miscanthus), Spartina pectinata (cordgrass), Panicum virgatum (switchgrass) and Andropogon gerardii (big bluestem). The listed plants are not commonly used for biogas production, their susceptibility to ensiling is also little known, hence the need to investigate their suitability for these processes. Effective methods for increasing the biogas yield from biomass are still demand, hence the research on the use of LAB for this purpose. After harvesting the grasses were cut and ensiled in barrels with and without (controls) the usage of commercial silage inoculant containing Lactobacillus buchneri LN40177. After 90 days of ensiling obtained silages were analysed in order to compare their chemical composition: organic acids content, the loss of dry matter, the differences in particular fibres composition. The silages were then subjected to methane fermentation using OxiTop® sensors and exposed to air in order to check their aerobic stability. The silages prepared with LAB additive had higher concentration of acetic acid than the control silages prepared without LAB addition, which contributed to increased aerobic stability but had no effect on the methane yield of miscanthus, switchgrass and big bluestem. Using the microbial inoculant during ensiling had beneficial effect in terms of reducing the duration of biogas production process from obtained silages: lag phase was shortened, daily biogas production rate was increased and 90% of biogas was produced in a shorter period of time compared to the control silages from investigated grasses. The modified Gompertz model well reflected the kinetics of biogas production process.

Optimization of Cobalt Nanoparticles for Biogas Enhancement from Green Algae Using Response Surface Methodology

Organic matter may be converted to energy through various methods, but the most preferable one is the Anaerobic Digestion (AD), specifically for biogas production. In sustainable bioenergy production, it can undoubtedly be called one of the most widely used methods from the various feedstock. Over the past years, algae waste has become an increasingly acute environmental problem but luckily it can be used as feedstock to produce bioenergy. In order to improve the energy productivity of green algae, this study is focused on the introduction of cobalt (Co) nanoparticles (NPs) in the AD process. The concentration of Co NPs was optimized using response surface methodology (RSM). Mesophilic temperature range (25–45 °C), initial pH (5–9) and Co NPs dosage (0.5–2 mg/L) were selected as the independent variables for RSM. The results indicated that at optimized values (Co NPs concentration = 1 mg/L, initial pH = 7, and digestion temperature = 35 °C) produced the highest biogas yield of 298 ml. An experiment was carried out at optimized conditions to explore the effect on biogas production. The results showed that Co NPs had a positive influence on biogas yield. The low concentrations achieved higher biogas production as compared to higher ones. A maximum biogas yield of 678 mL is achieved by Co NPs (1 mg/L). AD performance was further evaluated by the modified Gompertz model. Different kinetic parameters were calculated. The values of the performance indicators confirmed that the mathematical model fitted well with experimental data.

Promoting the Circular Economy on an Island: Anaerobic Co-Digestion of Local Organic Substrates as a Possible Renewable Energy Source

The local waste co-digestion is an interesting option to tackle in reduced and isolated areas like the islands. The islands have limited territory and scarce fuel production. Moreover, organic waste can create serious environmental problems in soil, water and air. Anaerobic co-digestion (AcoD) is a technology fulfilling the concept of waste-to-energy (WtE) based on local resources. The valorisation of organic waste through AcoD on an island would prevent environmental impacts, while being a source of renewable energy. In this study, cow manure (outdoor and indoor), pig slurry, bird manure, kitchen waste, sewage sludge and oily lacteous waste produced on Island Terceira (Portugal) were tested in mesophilic -35 °C- Biochemical Methane Potential (BMP) co-digestion assays. The goals were to analyse the recalcitrant and high potential produced waste and to estimate the energetic supply source on the island. The cow manure and pig slurry were used as inocula and specific methanogenic activities (SMAs) were carried out. The results showed that both substrates have a significant methanogenic activity-SMA 0.11 g-COD/(g-VSS.d) and 0.085 g-COD/(g-VSS.d), respectively. All the studied combinations were feasible in AcoD, showing TS removals in the range of 19-37%; COD removals in the range 67-78% and specific methane yields from 0.14 to 0.22 L/gCOD removed, but some differences were found. The modified Gompertz model fitted the AcoD assays (R2 0.982-0.998). The maximum biogas production rate, Rmax. was highest in the AcoD of Cow+Pig+Oily and in the Cow+Pig+Sludge with 0.017 and 0.014 L/g-VSadded.day, respectively, and the lowest in Cow+Pig+Bird with 0.010 L/g-VSadded. In our AcoD studies, the bird manure limited the performance of the process, since it was recalcitrant to anaerobic degradation. On the other hand, the oily lacteous waste showed a great potential in the anaerobic digestion. The estimated biogas production, from the best-studied condition, could cover the 11.4% of the energy supply of the inhabitants. These preliminary results would prevent the environmental impact of organic waste on the island and promote the use of local waste in a circular economy scenario.