Cumulative Biogas Research Articles

Effect of nanoscale zero-valent iron on sludge anaerobic digestion

Nanoscale zero-valent iron(NZVI) was prepared with a method of reduction in liquid phase by the reaction of FeSO4 and NaBH4, and characterized by SEM. This study investigated the effect of different concentration of NZVI on biogas production and methane content during the anaerobic digestion process at the medium temperature of 35°C. The results indicated that the group with 1000mg/L NZVI maintained ammonia at the level of 600–800mg/L, pH between 6.5-8.0, and improved CODcr degradation rates at 2.91%; this concentration of NZVI produced maximum concentration of VFAs, which can reach 3846mg/L, and strengthen the use of acetic acid. Relative to the control group, the system increased cumulative biogas production of 18.11%, decreased biogas production cycles of three days and increased the methane content by 6.93%.

Comparison of Alkali-Buffering Effects and Co-digestion on High-Solid Anaerobic Digestion of Horticultural Waste

High-solid anaerobic digestion (HSAD) of horticultural waste by adding alkali (ADAA) was optimized in a batch system, and its performance was compared to co-digestion in a semi-continuous system. In the batch system, the process of ADAA was optimized by testing the time point of adding alkali and the type of alkali, both of which had significant influence on HSAD performance. The cumulative biogas yield of poplar leaf was the highest, 156.7 mL/g of volatile solids (VS), when adding CaO on the third day. In comparison to NaOH and Na2CO3, the biogas yield of the ADAA process adjusted with CaO was the highest. When the organic loading rate was 4.0 and 8.0 g of VS L–1 day–1, the co-digestion system would produce 10.30 and 15.28% more methane than ADAA (CaO as alkali), respectively, which was due to the higher nutrients, broader diversity, and better growth of the microorganism in co-digestion of poplar leaf and chicken manure. Microbial community analysis of the seed sludge, co-digestion, and ADAA showed Meth...

Evaluation of biogas production potential of kitchen waste in the presence of spices

Anaerobic digestion (AD) of kitchen waste (KW) for biogas production is a major challenge to all over the world due to significant compositional variations in KW, such as different types and quantities of spices used for preparing food. Spices may affect the AD process owing to their antimicrobial activity. In this paper, the effect of spices (garlic, red chili, cinnamon, coriander, clove, turmeric, cardamom, black pepper) on AD of KW has been investigated. Batch experiments were carried out to determine the maximum biogas production potential, methane production rate and lag phase for biogas production. Analysis of the results revealed different magnitude of inhibition of the AD process of KW in the presence of different spices. Cinnamon, cardamom and clove resulted >85%, black pepper resulted 75%, while coriander, chili, turmeric and garlic resulted 55–70% reduction in cumulative biogas yield. Elemental analysis showed high concentration of heavy metals in the spices, which along with other bioactive components of the spices could be responsible for the inhibitory effect of the spices on biomethanation. Microbial examination of the digestate also showed a decrease in population of fermentative and methanogenic bacteria in the presence of spices.

Experimental and kinetics study for phytoremediation of sugar mill effluent using water lettuce (Pistia stratiotes L.) and its end use for biogas production.

In present study, the performance of phytoremediation by Pistia stratiotes on sugar mill effluent (SME) and its end use for biogas production are investigated. The objectives of the study are to determine the nutrient and pollution reduction efficiency of P. stratiotes from SME and evaluation of its biomass as a feedstock for biogas production. Various concentrations of SME (25, 50, 75, and 100%) were remediated by Pistia stratiotes (initial weight; 150g) outdoor for 60days under batch mode experimental setup. The results showed that P. stratiotes achieved marked reduction in nutrient (TKN, 72.86%; TP, 71.49%) and pollutant load (EC, 25.69%; TDS, 57.26%; BOD, 69.40%; COD, 61.80%; Ca2+, 56.79%; Mg2+, 55.01%; Na+, 42.86%; K+, 54.38%; MPN, 78.13%; SPC, 60.13%) from 75% SME at the end of the experiment. The highest biomass (328.48±2.04g) and chlorophyll content (3.62±3.04mg/g) were also achieved with 75% SME. The dried biomass of P. stratiotes (from 75% SME) was inoculated with cow dung (10% w/v) and diluted with distilled water (1:10). The whole content was used as a substrate for the biogas production within hydraulic retention time (HRT) of 30days at room temperature. Substrate parameters such as pH, TS (%), COD (mg/L), TKN (%), TOC (%), VS (%), and C/N ratio were reduced from 7.85 to 6.0, 66.65 to 28.65%, 12,900 to 2800mg/L, 0.95 to 0.75%, 45.54 to 19.5%, 76.87 to 28.78%, and 47.94 to 26.00, respectively, in 30days of HRT. About 8478.6mL of cumulative biogas production was evaluated by modified Gompertz equation. Thus, the present investigation not only achieved efficient nutrient and pollution reduction from SME but also proved the potential of P. stratiotes for biogas production.

Kinetic Study of Biogas Recovery from Thermo-chemically Pre-treated Rice Husk

Six simple kinetic models were used to perform comparative investigations of the kinetics of biogas production from thermo-chemically pre-treated rice husk which were heated at 155°C for 4 h prior to soaking in 15% aqueous ammonia for 48 h and finally subjected to anaerobic digestion. The process was operated for 45 days in the mesophilic conditions by comparing the performance of test digesters containing only inoculums, with control operated at similar condition. Kinetic modelling of the biogas production rate and cumulative biogas yield, revealed that thermo-chemical pre-treatment was effective in improving the kinetics of bio-gasification. Comparing linear, exponential and modified exponential models in terms of coefficient R2, it was observed that biogas production rate followed exponential path whereas the cumulative biogas yield exhibited best fitting to the sigmoidal curve for Gompertz relation as compared to that of logistic growth model. Biogas production rate analysed with the Gaussian model revealed better correlation as compared to the linear exponential and modified exponential models where the plots were performed for ascending and descending limbs separately. As, biogas production rate followed exponential path, the Gaussian plot was found to be legible and more accurate.

Anaerobic co-digestion of oil refinery wastewater with bagasse; evaluating and modeling by neural network algorithms and mathematical equations

To survey the anaerobic co-digestion (AcoD) of oil refinery wastewater (ORWW) with sugarcane bagasse (SCB), six different AcoD compositions were evaluated. Results including cumulative biogas production (BGP), bio-methane contents (BMP), and soluble chemical oxygen demand (CODs) removal rate were experimentally obtained. The negligible BGP by ORWW mono-digestion revealed that it could not support any microbial activity. However, increasing the SCB ratio in the AcoD compositions led to increased BGP and BMP contents. By considering the statistical test (LSD0.05) results for the kinetic parameters, the 1:4 ratio treatment was the most favorable AcoD composition. Moreover, the CODs removal rate from 22.34 ± 1.63% for the SCB mono-digestion was improved to 49.67 ± 0.38% for the 2:3 AcoD composition and BMP content from 54.12 ± 0.45% for the SCB mono-digestion was enhanced to 62.69 ± 1.22% for the 1:4 AcoD composition with 20% lower SCB usage. The results computed by applying three mathematical models determined that the modified Gompertz model provided the best fit. Also, implementing artificial neural network algorithms to model the BGP data revealed that the Back Propagation algorithm was the best suited for the experimental BGP data, with 0.6444 and 0.9658 for MSE and R2, respectively.

Determination and evaluation of biogas and methane productions of vegetable and fruit wastes with Hohenheim Batch Test method

Nowadays, biogas technology applications are gradually increasing worldwide due to the economic and environmental benefits. Many researches and studies related to the determination of the biogas potential of organic waste materials have been carried out in the recent years. Studies to determine the specific methane potential of organic waste materials have a great importance for both design and economical operation of the biogas plants. Energy potential that will be recovered from organic wastes is substantial in Turkey. Thanks to biogas plants gathering vegetable-fruit wastes and other organic wastes are planned to produce significant amount of renewable energy in Turkish markets. Owing to the use of organic wastes, the disposal of waste as well as energy production, soil, water and air pollution in terms of environmental protection are also minimized. On the other hand, the organic wastes produced from plants can also be utilized as fertilizer in vegetable production. In this study, the cumulative biogas and methane production of vegetable and fruit wastes were experimentally determined with HBT (Hohenheim Batch Test) method. Biogas and methane yields of vegetable and fruit wastes were found as 0.54-0.73 Nm3/(kg ODM) and 0.29-0.37 Nm3/(kg ODM), respectively. The highest value of the cumulative specific methane production was tomato wastes (0.37 Nm3/(kg ODM)), and the lowest value was lettuce wastes (0.29 Nm3/(kg ODM)), as well. The average cumulative specific methane production values of mixed vegetable and fruit wastes are determined as 0.34 Nm3/(kg ODM). Keywords: biogas, methane production, Hohenheim Batch Test, vegetable and fruit wastes, renewable energy, Turkey DOI: 10.25165/j.ijabe.20171004.2864 Citation: Aybek A,Ucok S. Determination and evaluation of biogas and methane productions of vegetable and fruit wastes with Hohenheim Batch Test method Int J Agric & Biol Eng, 2017; 10(4): 207–215.

The toxicity effects of ammonia on anaerobic digestion of organic fraction of municipal solid waste

In this research the inhibitory effects of ammonia on the AD of synthetic OFMSW were examined under different total ammonia nitrogen (TAN) concentrations of 2,500, 5,000, 7,500, and 10,000mg/L and at pH levels of 7.5, 8.0 and 8.5 using a factorial experimental design and statistical analysis. Reduction in Cumulative Biogas Production (CBP) at a TAN concentration of 2,500mg/L was close to 10% for all 3 pH levels. For a TAN concentration of 10,000mg/L the percent reduction in CBP was over 80% for all 3 pH levels showing significant inhibition due to ammonia with neglible influence due to change in pH. However, pH played a more significant role for TAN concentrations between the above two levels, as at a TAN concentartion of 7,500mg/L, the percent reduction in CBP increased from 42.2% at a pH of 7.5 to 76.5% at a pH of 8.5. Regression analysis was used to estimate CBP and % reduction (%R) in CBP using a quadratic equation with pH and TAN as independant variables (R2=0.95 and 0.94). Methane produciton per g of COD removed was obsereved to vary from 264mL CH4/g CODd for control reactors at pH 7.5 down to 1mL CH4/g CODd for the reactor at pH of 8.5 which contained 10,000mg/L TAN. Results of gradual ammonia loading also showed that mesophilic bacteria could be adapted to a TAN concentration of up to 5,000mg/L at pH 7.5 through gradual TAN loading. At 10,000mg/L TAN CBP in reactors with gradual TAN loading was more than 1.9–3 times the CBP in reactors with abrupt TAN addition.

Effect of substrate pretreatment on biogas production through anaerobic digestion of food waste

This work presents the effect of autoclave, microwave and ultrasonication pretreatment on anaerobic digestion of food waste co-digested with poultry manure. Four batch reactors with 2 L volume each were used for the study. The reactors were operated with a hydraulic retention time of 30 days and stirred twice a day. The daily biogas production, cumulative biogas production, methane and carbon dioxide composition were measured. The pretreatment of the substrates with autoclave, microwave and ultrasonication caused an increase in cumulative biogas production of approximately 4.67, 6.43 and 10.12% respectively. The degradation efficiency also showed positive result for substrates with pretreatment. The highest cumulative biogas yield was obtained with ultrasonication technique (9926 ml), followed by autoclave, microwave and untreated substrates. The results obtained from the experiments were evaluated to determine the kinetic constants of the process. Modified Gompertz model and Logistic model were used to determine the kinetic parameters of the reaction. The results obtained with the modified Gompertz model was more suitable than the result obtained with the Logistic model for describing the process kinetics.

Copper stressed anaerobic fermentation: biogas properties, process stability, biodegradation and enzyme responses.

The effect of copper (added as CuCl2) on the anaerobic co-digestion of Phragmites straw and cow dung was studied in pilot experiments by investigating the biogas properties, process stability, substrate degradation and enzyme activities at different stages of mesophilic fermentation. The results showed that 30 and 100mg/L Cu2+ addition increased the cumulative biogas yields by up to 43.62 and 20.77% respectively, and brought forward the daily biogas yield peak, while 500mg/L Cu2+ addition inhibited biogas production. Meanwhile, the CH4 content in the 30 and 100mg/L Cu2+-added groups was higher than that in the control group. Higher pH values (close to pH 7) and lower oxidation-reduction potential (ORP) values in the Cu2+-added groups after the 8th day indicated better process stability compared to the control group. In the presence of Cu2+, the degradation of volatile fatty acids (VFAs) and other organic molecules (represented by chemical oxygen demand, COD) generated from hydrolysis was enhanced, and the ammonia nitrogen (NH4+-N) concentrations were more stable than in the control group. The contents of lignin and hemicellulose in the substrate declined in the Cu2+-added groups while the cellulose contents did not. Neither the cellulase nor the coenzyme F420 activities could determine the biogas producing efficiency. Taking the whole fermentation process into account, the promoting effect of Cu2+ addition on biogas yields was mainly attributable to better process stability, the enhanced degradation of lignin and hemicellulose, the transformation of intermediates into VFA, and the generation of CH4 from VFA.

EXPERIMENTAL STUDY ON A SOLAR-HEATED BIOGAS DIGESTER USING SHALLOW SOLAR POND IN COLD CLIMATE

In northern Egypt, the ambient temperature almost below 20°C during winter months, which is insufficient for the anaerobic digestion (AD) and affecting negatively the biogas yield, especially for the floating dome digester(Indian model) due to the heat losses through the gas holder. Since the slurry temperature is a crucial factor for the AD rate, this investigation aims to heat a concrete pre-constructed floating dome biogas digester (Family-scale digester) during winter season for enhancing the fermentation rate by utilizing the extracted heat of integrated shallow solar pond (SSP) using dairy cattle dung comparing to a previous work of un-heated digester. The solar-heated digester was evaluated under the same operating conditions of the un-heated digester except the slurry temperature and similar values of both the solar radiation intensity and ambient temperature during 30 days without feeding as a digestion time taking into consideration the slurry temperature, pH, daily, cumulative (m3/month) and specific (m3/kg VS) biogas yield as well as the total net gained energy. The obtained results revealed that, the average slurry temperature of the solar-heated biogas digester system increased by 12.3°C which led to increase the average daily, cumulative and specific biogas yield by about 129 % higher than the un-heated digester with average methane content of 70% and total net gained energy of 553.1 MJ/month.

Biomethanization of the Mixture of Cattle Manure, Pig Manure and Poultry Manure in Co-Digestion with Waste Peels of Pineapple Fruit and Content of Chicken-Gizzard - Part II: Optimization of Process Variables

Background: The indiscriminate discharge of industrial waste, agricultural-biomass waste, waste of municipal, domestic and kitchen waste has negatively impacted on the environment and human health. It is very pertinent to reduce these impacts to the barest minimum through conversion of the waste to useful products. The conversion of these wastes to generate alternative energy to fossil fuel through the technology of anaerobic fermentation is one of the viable and more fascinating options for the management of waste. Objective: To investigate the interactive effect and optimization of process parameters of temperature, total solid content and feed/inoculum ratio on the biomethanization of the mixture of cattle manure, pig manure and poultry manure in co-digestion with waste peels of pineapple fruit and content of chicken-gizzard. Method: Full-factorial central composite design of experiment (RCCD) of the response surface method (RSM) was adopted to assess the possible interactive effects of the process variables and the optimal parameters (i.e. optimization) for biogas/biomethane production in an anaerobic digester. Result: The process variables had a significant (P < 0.05) positive and negative interactive effect on the biomethanization process. A second-order quadratic polynomial regression model which is statistically significant (p < 0.0001) was respectively obtained for cumulative biogas yield (CBY), biomethane content (BC) and hydraulic retention time (HRT). Temperature of 55.2°C; total solid content of 6.25%; and feed/inoculums ratio of 1:2 were found to be the optimum values required to attain a predicted optimum values of 6.261 dm3/g CBY, 71.54% BC within a minimum 8 days of HRT. At this optimum process conditions, the experimental observed maximum CBY, and BC with a minimum HRT were found to be 6.217 dm3/g of slurry, 71.10% and 7 days, respectively. Conclusion: Biogas/biomethane generation through co-substrate anaerobic fermentation of animal waste with waste of fruits constitute a reasonable and applicable renewable energy alternative and this can be optimized through response surface methodology.

Biomethanization of Cattle Manure, Pig Manure and Poultry Manure Mixture in Co-digestion with Waste of Pineapple Fruit and Content of Chicken-Gizzard- Part I: Kinetic and Thermodynamic Modelling Studies

Background:The increased energy consumption from fossil fuels with its attendant gas emissions and environmental problems has provided the impetus to exploit new energy source that are renewable and environmentally-friendly.Objective:This work focused on the investigation and evaluation of the single or individual effects of feed-inoculum ratio, temperature, and agitation speed (i.e.operating variables) on biomethanization of the mixture of cattle manure, pig manure and poultry manure (mixed animal wastes) co-digested with pineapple fruit waste and content of chicken-gizzard (inoculum) as well as to model the kinetics of biomethanization at these different operating variables and to determine the thermodynamic properties of the biomethanization process.Method:The biomethanization experiments were carried out in anaerobic biodigesters at operating variables of feed/inoculums ratio that ranged from 1:1 to 3:1, temperature from 25 to 60°C, and agitation speed from 30 - 70 rpm using one factor at a time (OFAT) method. The biodigesters were incubated for 70 days retention time.Result:The feed/inoculum ratio, temperature and agitation speed had positive impact on cumulative biogas yield, biomethane content and start-up time of biomethanization. The cumulative biogas yield and biomethane content achieved with agitation speed of 30 to 70 rpm was respectively higher than the biogas yield and biomethane content attained without agitation. Minimum cumulative biogas yield and biomethane content was respectively obtained with feed/inoculum ratio of 1:1, temperature of 25°C and agitation speed of 70 rpm; while maximum cumulative biogas yield with its biomethane content was attained with feed/inoculum ratios of 1:3 and 3:1, temperature of 60°C and agitation speed of 30 rpm, respectively. Modified Gompertz and Exponential Rise to Maximum kinetic models fitted very well to the data and thus showed better correlation of cumulative biogas production. The thermodynamic parameters of Gibbs free energy, enthalpy, entropy change and activation energy of biomethanization were estimated and evaluated, and was found that the biomethanization process was thermodynamically feasible, spontaneous and endothermic in nature suggesting hydrogenotrophic methanogenesis pathway. The activation energy of the biomethanization process was found to be 3.324 kJ/ mol. The specific heat capacity at constant volume and constant pressure, specific internal energy and specific enthalpy of the biogas and biomethane content increased with increase in temperature.Conclusion:Biogas/biomethane production from the biomethanization of mixed animal wastes co-digested with fruit waste and inoculum is a feasible, viable and sustainable renewable energy option that can be simulated by kinetic models and influenced by operating variables.

The impact of pretreatment and inoculum to substrate ratio on methane potential of organic wastes from various origins

Biochemical methane potentials (BMP) of two different substrates from macroalgae (MA) and market place wastes (MPW) were investigated using anaerobic granulated sludge from food industry with different ratios of substrate to inoculum (S/X). The substrates were used as MA only, MPW only, MA–MPW mixture, pretreated MA, and pretreated MA–MPW mixture. Research involved investigation of the effects of parameters such as temperature (35, 45, and 55 °C), substrate to inoculum ratio (S/X = 0.5, 2.0, 4.0, and 6.0 as g VSsubstrate/g VSinoculum), and the type of pretreatment (by microwave, thermal, and ultrasonic) on BMP. BMP assays were performed for all substrates. The highest cumulative biogas production (and BMP) were obtained for MA only at an S/X ratio of 4.0 g VS/g VS as 357 Lbiogas/kg VS (197 L CH4/kg VS) and 33 Lbiogas/kg VS (17 L CH4/kg VS), respectively, at 35 and 55 °C. For pretreated substrates, the highest cumulative biogas production and BMP were observed as 287 Lbiogas/kg VS and 146 L CH4/kg VS using pretreated macroalgae at 35 °C. Results suggested that MA only and MA–MPW mixtures are suitable substrates for biogas production. It is also concluded that any type of pretreatment has adverse effects on biogas and methane productions.

Biomethanation macrodynamics of vegetable residues pretreated by low-frequency microwave irradiation

The effects of microwave irradiation on the digestibility and biogas production of cauliflower (Brassica oleracea var. botrytis) and cabbage (Brassica oleracea var. capitata) leaves were investigated using biochemical methane potential (BMP) assays. Cow dung was utilised as inoculum. Different microwave powers (87.5, 175 and 350W) were applied in a first set of runs for 15min. The second set consisted of 20, 25 and 30min irradiation at 350W. Based on ANOVA analysis (α=0.05), biogas production was significantly higher for the irradiated substrates compared to controls. The peak biogas production was 700ml for 36days HRT for 350W/25min. Peak COD, SCOD, volatile and total solids removals were 54.84%, 39.08%, 34.60% and 71.96%, respectively. Phosphate and total nitrogen increased significantly. Cumulative biogas production data fitted the modified Gompertz equation well. The highest biogas yield was 0.271L/g VSremoved at a 350W microwave irradiation for 30min.

Optimal ratio for anaerobic co-digestion of poultry droppings and lignocellulosic-rich substrates for enhanced biogas production

The poultry industry is a progressive and prospective agro-based sector in Bangladesh. Poultry droppings (PD) make an excellent and abundant raw material for anaerobic co-digestion (AD) because of its high nitrogen content. Two sets of comparative assays were conducted on the anaerobic co-digestion of PD with two lignocellulosic co-substrates (LCSs), namely wheat straw (WS) and meadow grass (MG), under five different mixing ratios to optimize substrate composition and C:N ratio for enhanced biogas production. All digesters were run simultaneously under a mesophilic temperature of 35±1°C with an identical volatile solids (VS) concentration. The results showed that the co-digestion of PD with LCSs was significantly higher in terms of biogas yield and bio-methane potential (BMP) than those obtained by mono-digestion of PD and LCSs. Co-digestion of PD and MG produced a higher cumulative biogas production, biogas yield and BMP than from respectively PD and WS. The highest methane contents found were 330.1 and 340.1Nlkg−1 VS after digestion for 90days at a mixing ratio of, respectively, 70:30 (PD:WS) with a C:N ratio of 32.02 and a mixing ratio of 50:50 (PD:MG) with a C:N ratio of 31.52. The increases were 1.14 and 1.13 times those of the LCSs alone, respectively. Predicted optimum ratio for PD:LCSs and C:N ratios, maximum BMP and percentage volatile solids destruction (PVSD) were calculated by using software MINITAB-17 according to the best fit regression models for co-digestion of PD with LCSs.

Effect of alkaline microwaving pretreatment on anaerobic digestion and biogas production of swine manure

Microwave assisted with alkaline (MW-A) condition was applied in the pretreatment of swine manure, and the effect of the pretreatment on anaerobic treatment and biogas production was evaluated in this study. The two main microwaving (MW) parameters, microwaving power and reaction time, were optimized for the pretreatment. Response surface methodology (RSM) was used to investigate the effect of alkaline microwaving process for manure pretreatment at various values of pH and energy input. Results showed that the manure disintegration degree was maximized of 63.91% at energy input of 54 J/g and pH of 12.0, and variance analysis indicated that pH value played a more important role in the pretreatment than in energy input. Anaerobic digestion results demonstrated that MW-A pretreatment not only significantly increased cumulative biogas production, but also shortened the duration for a stable biogas production rate. Therefore, the alkaline microwaving pretreatment could become an alternative process for effective treatment of swine manure.

The effects of cathodic micro-voltage combined with hydrothermal pretreatment on methane fermentation of lignocellulose substrate

The methane fermentation study assisted with cathodic micro-voltage was carried out to investigate the electric field effects on the fermentation of hydrothermally pretreated lignocellulose substrate. It was illustrated that a 0.25V cathode voltage and hydrothermal pretreatment could improve the biogas production, biogas quality and lignocellulose degradation ratio significantly. The cumulative biogas productions in the fermentation of hydrothermally pretreated cow dungs at 50°C, 150°C and 200°C with a 0.25V cathode voltage were observed in a total of 6640mL, 9218mL and 9456mL respectively over a detention time of 33 days. In comparison with the fermentation pretreated at 200°C without any voltage, nearly doubled of cumulative biogas production was obtained in the process of cathode-assisted fermentation. It was also observed that the daily methane content greater than or equal to 70% in the biogas generated with cathode voltage were clearly greater than that without voltages. Furthermore, the fermentation applied with a 0.25V cathode voltage had resulted into significant increases of 12.64% and 9.44% in lignin and cellulose degradation ratio relative to voltage free fermentation. And in the process of fermentation applied with cathode voltage, the final lignocellulose degradation ratio increased with the hydrothermal pretreatment temperature. Thus, the hydrothermal pretreatment and assisting fermentation with low cathode voltage can effectively promote the lignocellulose degradation. All results revealed that cathodic micro-voltage combined with hydrothermal pretreatment can remarkably improve the fermentation of lignocellulosic materials, indicating that a more effective fermentation technology can be developed by applying with cathodic micro-voltage.

Comparison of Different Pretreatments of Rice Straw Substrate to Improve Biogas Production

Chemical and biological pretreatments (with NaOH, HCl, CO(NH2)2 and cellulase) were used to pretreat rice straw at ambient temperature (about 20 °C) to improve its biodegradability and increase anaerobic biogas production. The NaOH and CO(NH2)2 pretreatments reduced the percentage contents of hemicellulose and lignin. The HCl pretreatment mainly dissolved the hemicellulose and resulted in decreases of 12.5–7.1% of the hemicellulose. The percentage content of cellulose showed a dramatic decrease, from 38.3 to 10.9%, after the cellulase pretreatment. Compared with untreated rice straw substrate, the total biogas yield ratios were 3.38–5.91, 1.63–2.99, 1.93–5.22 and 3.62–6.45, with a hydraulic retention time of 30 days, under NaOH, HCl, CO(NH2)2 and cellulose pretreatments, respectively. The highest yields of biogas and methane were obtained from 40 U/g total solids (TS) cellulase-pretreated rice straw (20.433 and 9.918 L respectively). Biogas production yields of volatile solids (VS) were 123.7, 273.8, 318.5, 353.5 mL/g for control, 6% CO(NH2)2-, NaOH- and 40 U/g TS cellulase-pretreated rice straw substrate, respectively. Compared to untreated rice straw substreates, cumulative biogas production yields increased 16–103, 25–122% for NaoH- and cellulase-pretreated rice straw substrate, respectively. The results suggested that the highest removal efficiencies of TS and VS were obtained from 6% NaOH-pretreated (53.80 and 36.80%), 6% CO(NH2)2-pretreated (54.90 and 36.10%) and 40 U/g TS cellulase-pretreated (51.30 and 37.30%) rice straw substrate. In short, NaOH, HCl, CO(NH2)2 and cellulase pretreatment was suitable to enhance the biogas production. However, to choose the optimal treatment, the energy requirements relative to the energy gain as extra biogas production have to be taken into account, as well as the costs of chemicals or enzymes.

Effective bio-pretreatment of sawdust waste with a novel microbial consortium for enhanced biomethanation

Anaerobic digestion (AD) is considered an efficient cost-effective technology for sustainable biogas production from lignocellulosic wastes. A novel lignocellulosic degradation microbial consortium (LCDC) was isolated from rotten sawdust, and further used for sawdust pretreatment prior to AD. Results showed that pretreatment of sawdust for 10days led to significant reduction in cellulose, hemicelluloses, and lignin contents by 37.5%, 39.6%, and 56.7%, respectively, with respect to the control. In addition, the pretreatment enhanced cumulative biogas yield, which reached its maximum value of 312.0Lkg−1VS after 28days of AD (25.6% higher than the corresponding control). Moreover, the maximum significant cumulative methane yield was recorded after 28days of AD of the pretreated sawdust (155.2Lkg−1VS), which represented 72.6% higher than the corresponding control. Significantly higher biomethane yield from sawdust pretreated with LCDC confirms that this process is more economical than the previous reports.