Cumulative Gas Yield Research Articles

Enhancing biomethanation performance through co-digestion of diverse organic wastes: a comprehensive study on substrate optimization, inoculum selection, and microbial community analysis.

A blend of organic municipal solid waste, slaughterhouse waste, fecal sludge, and landfill leachate was selected in different mixing ratios to formulate the best substrate mixture for biomethanation. Individual substrates were characterized, and the mixing ratio was optimized with the help of a response surface methodology tool to a value of 1:1:1:1 (with a C/N ratio of 28±0.769 and total volatile fatty acid (VFA) concentration of 2500±10.53 mg/L) to improve the overall biomethanation. The optimized blend (C/N ratio: 28.6, VFA: 2538 mg/L) was characterized for physicochemical, biological, and microbial properties and subjected to anaerobic digestion in lab-scale reactors of 1000 mL capacity with and without the addition of inoculum. The biogas yield of individual substrates and blends was ascertained separately. The observed cumulative biogas yield over 21 days from the non-inoculated substrates varied between 142±1.95 mL (24.6±0.3 ml/gVS) and 1974.5±21.72 mL (270.4±3.1 ml/gVS). In comparison, the addition of external inoculation at a 5% rate (w/w) of the substrate uplifted the minimum and maximum cumulative gas yield values to 203±9.9 mL (35.0±1.6 mL/gVS) and 3394±13.4 mL (315.3±1.2 mL/gVS), respectively. The inoculum procured from the Defence Research and Development Organisation (DRDO) was screened in advance, considering factors such as maximizing VFA production and consumption rate, biogas yield, and digestate quality. A similar outcome regarding biogas yield and digestate quality was observed for the equivalent blend. The cumulative gas yield increased from 2673±14.5 mL (373.7±2.2 mL/gVS) to 4284±111.02 mL (391.47±20.02 mL/gVS) over 21 days post-application of a similar dosage of DRDO inoculum. The 16S rRNA genomic analysis revealed that the predominant bacterial population belonged to the phylum Firmicutes, with the majority falling within the orders Clostridiales and Lactobacillales. Ultimately, the study advocates the potential of the blend mentioned above for biomethanation and concomitant enrichment of both biogas yield and digestate quality.

Optimizing Biogas Generation from Blends of Sugarcane Bagasse

Renewable energy has been the alternative source to global energy scarcity which involves renewable resources as more emphasis been put to prospective ways of converting agricultural wastes into energy to meet both the local and global demands.This work analyzed the use of sugarcane bagasse as substrate in biogas production as well as its codigestion with cow dung and chicken droppings. Seven digesters each of 2.5 litres capacity were charged in a ratio of 1:3 solids to liquid for a retention period of 30 days within a temperature range of 25-32 oC was used. Digester A contained 100 % bagasse, B contained 100 % cow dung, C 100 % chicken droppings, D contained 50 % bagasse and 50 % cow dung, E contained 50 % bagasse and 50 % chicken droppings, F contained 70 % bagasse and 30% cow dung and 70 % bagasse and 30 % chicken droppings for digester, G. Proximate and microbial analysis of the spent slurry were carried out. The result shows that sample C has the highest volatile solids and protein content of 56.68 % and 10.01 %. Biogas production was observed to be higher in digester C with cumulative gas yield of 3228.3 cm3 then digester B with 2816.6 cm3 and Digester A had the least gas yield of 681.4 cm3. Lightening test was observed by passage over limewater which result in catching fire except on digester C. Methane and other traces of gases test using gas analyzer shows 61.3 % methane with the least having 46.7 % methane on digester B and C. Pseudomonas spp, Entrobacter aerogenes and Staphylococcus aureus were found to be dominant in almost all the digesters. Further research is required to investigate large volume production and to improve gas storage techniques.

CO2-mediated catalytic upcycling of plastic waste for H2-rich syngas and carbon nanomaterials

To establish a reliable disposal platform of plastic waste, this work developed a novel dual-stage CO2-medaited decomposition-catalysis route by applying multi-functional zeolite-supported bimetallic catalysts. Catalytic upcycling of plastic was first performed in Ar as a reference environment. Bimetallic Fe-Co/ZSM5 catalyst achieved the highest gas yield (53.98 mmol/g), with a H2 proportion of 62.17 vol%. It was evidenced that the Fe-Co alloy had an apparent positive synergistic effect on catalytic cracking and reforming of intermediate volatiles into H2-rich fuel gas and pure carbon nanotubes (CNTs). Regarding CO2-mediated decomposition-catalysis of plastic, there was an apparent synergistic effect between metallic Ni and Fe on gas production so that bimetallic Ni-Fe catalyst gained the maximum cumulative gas yield of 82.33 mmol/g, with a syngas purity of ∼74%. Ni-Fe/ZSM5 also achieved the maximum hydrogen efficiency (87.38%) and CO2-to-CO conversion efficiency (98.62%), implying hydrogen content in plastic and oxygen content in CO2 were essentially converted into gases. Additionally, bimetallic Ni-Fe catalyst revealed the highest carbon production (33.74 wt%), witnessing a synergistic enhancement of 43.45%; specially, approximately 257 mg/g CNTs were anchored on Ni-Fe/ZSM5, with a CNTs purity of over 76%. Overall, this study offers a superb solution in plastic waste valorization and greenhouse gas emission management.

Improved temperature distribution upon varying gas producing channel in gas hydrate reservoir: Insights from the Joule-Thomson effect

The gas production from marine gas hydrate has always been plagued by low productivity; the complex geological environment poses a significant obstacle to its commercialization. Horizontal wells are thus getting increasing attention due to their advantages in facilitating pressure propagation. Here a pre-embedded dual horizontal well was used to probe its effects in the local temperature distribution and gas production behavior. By doubling the number of boreholes, the flow channels of gas were increased enlarging the decomposition zone. Specifically, this was found to raise the reservoir temperature from −1 °C in a single well to approximately 0 °C. The temperature decline was more moderate due to a weakened Joule-Thomson effect. Consequently, almost 90% of the cumulative gas yield was produced before the lowest temperature occurred, compared to ∼30% in the single vertical well case. This indicates that the gas production from a dual well case was proceeding at a relatively higher temperature, potentially benefitting an enhanced gas production efficiency. An enlarged depressurization region was thus suggested in the field test for a controlled temperature decline to make more use of the sensible heat of the reservoir.

Tunable H2/CO syngas production from co-gasification integrated with steam reforming of sewage sludge and agricultural biomass: A experimental study

Biowastes to tunable H2/CO syngas is a promising way to produce clean energy carrier. This study proposed a new concept of improving the production of tunable H2/CO syngas and tar abatement via co-gasification integrated with inline steam reforming (co-GSR) of wheat straw (WS) and sewage sludge (SS) over self-derived gasification/co-gasification carbon materials (G/CGCMs). Binary mixtures with varying WS/SS mass ratios were initially subjected to steam co-gasification, achieving H2-enriched syngas with the tunable H2/CO molar ratio of 1.77 – 3.35. By introducing C[WS] in co-GSR process, the synergistic interactions between binary mixture and C[WS] on the cumulative gas yield, H2 yield, and syngas yield were more predominant by using WS/SS-9/1 as the feedstock, reaching 94.74, 51.53, and 77.99 mmol/g. Moreover, co-GSR of WS/SS-9/1 presented the highest CCE (98.77C%) and CGE (121.63%), suggesting the C content in the binary mixture and C[WS] was almost entirely converted and reformed into gaseous product. Correspondingly, WS/SS-9/1 subjected to co-GSR was also found to gain the lowest tar yield (5.99 g/Nm3). These observations were possibly because the addition of 10% of SS in the blend could not only assure the sufficient C and volatile contents in the blend, but also ensure the sufficient supply of alkali metals and alkaline earth metals (AAEMs) from SS as a catalyst to facilitate catalytic cracking and reforming of intermediate tar from decomposition of 90% of WS. When G/CGCMs were applied in both GSR and co-GSR processes, co-biocarbon C[WS + SS] used in the GSR of SS could garner a higher H2 concentration (57.79vol%) and H2/CO ratio (2.89). In addition, plausible reaction pathways and mechanisms regarding co-GSR of binary WS/SS mixture in the presence of G/CGCMs were discussed and elucidated. Simply put, this study provides a newly sustainable route to produce tunable H2/CO syngas towards a clean and sustainable waste management way.

Coupling biomass gasification and inline co-steam reforming: Synergistic effect on promotion of hydrogen production and tar removal

Biomass to green H2 is a promising strategy to achieve clean energy. This study proposed a novel concept of enhancing H2 production and tar removal via biomass gasification coupled with inline co-steam reforming (BGCSR) process. Varying gasification/pyrolysis biochar materials (G/PCMs) were applied assisted-reforming agents and co-reactants at the steam reforming stage in the BGCSR process. First, four representative biomass categories (wheat straw, microalgae, sewage sludge, and cow manure) were subjected to BGCSR process. Microalgae presented the more positive synergistic effect on H2 production and tar reduction. It was noticed that microalgae subjected to BGCSR in the presence of G/PCMs showed the comparable H2 concentration (over 56 vol%). The highest cumulative gas yield (104.17 mmol/g) and H2 yield (59.55 mmol/g) were manifested in the presence of C[F900], with the highest synergistic effect of 16.02% and 19.74%, respectively. C[F900] also presented the most significant synergistic effect (13.81%) on tar elimination. There outcomes were in relation to the properties of G/PCMs, e.g., elemental compositions, inherent alkali and alkaline earth metals (AAEMs), and surface functional groups. In addition, reaction mechanism regarding BGCSR was elucidated. Overall, this study provided a novel and effective way to valorize biomass into H2-enriched gas whilst minimizing tar formation.

Torrefaction/carbonization-enhanced gasification-steam reforming of biomass for promoting hydrogen-enriched syngas production and tar elimination over gasification biochars

Biomass to H2-enriched syngas is a very promising route to produce clean energy. This work proposed a new concept of promoting H2-enriched syngas production and tar elimination through torrefaction/carbonization-enhanced gasification-steam reforming (T/CEGSR) of wheat straw (WS) over its gasification biochar materials (GCMs). WS torrefied at 280 °C (WS-280) subjected to gasification-steam reforming (GSR) over C-control presented the maximum gas yields and H2/CO molar ratio (1.72). By introducing C[10 %O2] for GSR of WS-280, the maximum cumulative gas yield (112.10 mmol/greactants), H2 yield (59.91 mmol/greactants), and syngas yield (94.10 mmol/greactants) were achieved. Furthermore, C[10 %O2] were superior to C-control, C[Ar] and C[CO2] in light of carbon conversion efficiency, cold gas efficiency, and tar yield, reaching 97.45C%, 118.40 %, and 3.36 g/Nm3, respectively. Simply put, this study provides a newly sustainable and promising route by combining biomass torrefaction/carbonization with GSR using gasification biochar for enhancing H2-enriched syngas production while reducing tar formation.

Steam Gasification of Torrefied/Carbonized Wheat Straw for H2-Enriched Syngas Production and Tar Reduction.

Torrefaction/carbonization integrated with steam gasification of agricultural biomass for gas production and tar reduction was not investigated. The aim of this study was to evaluate the influence of the torrefaction/carbonization severity on H2-enriched syngas production and tar reduction during steam gasification of wheat straw (WS). The torrefaction/carbonization experiments were initially performed at 220–500 °C to examine the effect of pretreated temperature on the fuel properties of torrefied/carbonized WS. Then, the gasification temperature (700–900 °C) was optimized at 900 °C in terms of gas formation behaviors. Afterward, steam gasification of raw and torrefied/carbonized WS feedstocks was conducted. WS carbonized at 500 °C (WS-500) possessed the highest H2 concentration (54.21 vol%) and syngas purity (85.59%), while the maximum H2/CO molar ratio (1.83), high carbon conversion efficiency (90.33 C%) and cold gas efficiency (109.24%) were observed for WS torrefied at 280 °C. Notably, the cumulative gas yield, H2 yield, and syngas yield respectively reached 102.68 mmol/g, 55.66 mmol/g, and 87.89 mmol/g from steam gasification of WS-500. In addition, the carbonized WS feedstocks, especially WS-500, revealed a lower tar content. Simply put, integrating torrefaction/carbonization with steam gasification provided a novel and effective route to manufacture H2-enriched syngas with extremely low tar content from agricultural biomass.

Relationship between Different Anaerobic Digestion Parameters in a Pig-dung Aided Water Hyacinth Digestion Process

This study is aimed at assessing the relationship between different anaerobic digestion parameters (biogas quality, retention time, pH, temperature, biogas pressure, volume of biogas produced and cumulative volume of gas produced) in a Pig-dung (PD) aided Water Hyacinth (WH) digestion process in order to maximize biogas yield in terms of quantity and quality. 25 - litre capacity plastic prototype digesters were used in the study and eleven (11) mix ratios of PD and WH were prepared namely: 10 WH: 0 PD, 9 WH: 2 PD, 8 WH: 2 PD, 7 WH: 3 PD, 6 WH: 4 PD, 5 WH: 5 PD, 4 WH: 6 PD, 3 WH: 7 PD, 2 WH: 8 PD, 1 WH: 9 PD and 0 WH: 10 PD. The digestion process was evaluated for a retention period of 40 days. A bivariate Pearson correlation analysis was carried out to examine the relationship between the quality of gas produced and other variables. The results revealed that daily gas production yields greatly improved in the co-digestion runs with mix 3 WH: 7 PD recording the highest maximum daily yield of 9.5 L with a cumulative gas volume of 140 L. For this mix, the methane content of the gas produced increased from 5.8% on day 4 to 69.2% on day 20. The least quantity and quality of gas was produced by mix 10 WH: 0 PD with a maximum daily yield 2.34 L and a cumulative gas yield of 32.18 L. The digestion of all the mixes occurred within a mesophilic temperature range of 28.2 to 31.4 0C and an increase in temperature within the digestion resulted in an increase in the quality of gas produced. The gas pressure ranged from 1 bar to 3.324 bars with an increase in gas pressure leading to a corresponding increase in volume of gas produced. The pH of the substrates ranged from 6.1 to 8.4 with the values low at the start of the digestion process and gradually increasing to its maximum at the end of the digestion process. The results revealed a very strong, positive and significant association between the quality of the biogas produced and other digestion parameters.

Scalable decomposition-catalysis of disposable COVID-19 face mask over self-assembly metal-doping carbocatalysts for tunable value-added products

This study explored a scalable decomposition-catalysis route to effectively valorize disposable COVID-19 face mask into tunable value-added products. The metal-doping carbonaceous catalysts (M/Cs) were successfully synthesized through a single-step energy-efficient thermal process. The modest decomposition-catalysis of face mask over Zn/C gave rise to a relatively high yield (73.52%) of liquid oil with 99% of selectivity toward jet fuel range (C8 – C16) hydrocarbons. Besides, the scalable decomposition-catalysis of face mask over Ni(50)/C at 800 ℃ was observed to thoroughly transform face mask into gas with the cumulative gas yield of 967 NmL/gmask, involving 49.90 vol% of H2 and 40.90 vol% of CH4. Moreover, a dense, entangled growth of carbon nanotubes were formed on the surface of M/Cs. In brief, this study developed a scalable and promising route by using M/Cs for the valorization of COVID-19 face mask into hydrocarbon fuel or coupling harvest of H2-enriched fuel gas and carbon nanotubes.

COMPARATIVE STUDY OF BIOGAS PRODUCTION BOTH FROM PLANTAIN PEELS AND ROTTEN ONION BLENDED WITH POULTRY DROPPINGS

A comparative study was carried out on biogas production potential of plantain peels and rotten onion blended with poultry droppings. Three digesters labeled A, B and C were fabricated with Digester A fed with a mixture of rotten onion and poultry droppings (OP) in a ratio 1:1, Digester B fed with a mixture of plantain peels and poultry droppings (PP) also in the same ratio but Digester C fed in a ratio 1:2:1 of rotten onion, plantain peels and poultry droppings (OPP). The rate of production over a retention period of 40 days was measured using a digital weighing balance to measure the weight of gas retained in each of the circular rubber tube connected to each digester. The effect of the variation in average daily temperature on biogas yield of each feedstock was also analyzed. The co-digestion of rotten onion, plantain peels and poultry droppings yielded most with value of 705.5 g compared to either of plantain peels and rotten onion blended with poultry droppings which has cumulative gas yield of 348.1 g and 199.9 g respectively. It can be concluded that the blending of poultry droppings with agricultural wastes will greatly improve biogas yield.

Long-term numerical simulation of a joint production of gas hydrate and underlying shallow gas through dual horizontal wells in the South China Sea

Recent field tests to recover natural gas from marine gas hydrate reservoirs in Japan and China have exhibited worldwide attention to this strategic energy form; significant challenges still remain in improving the accumulative gas yield for a better economic efficiency. According to the geological survey in marine hydrate reservoirs, there exists a concomitant free gas layer underlying the gas hydrate reservoir. Consequently, here we propose a new scheme to jointly produce the gases from hydrate layer and its underlying shallow gas layer. It was found that a dual horizontal well deployment respectively in the corresponding two layers could contribute to a 4.1 times cumulative gas yield comparing that of a single vertical well scenario. This implies a remarkable enhancement of gas productivity via making full use of the gases in the shallow gas layer. Notably, a potential risk of interlayer failure could occur upon the great interbedded pressure difference (maximum 10.7 MPa) arising from the varying behavior of pressure propagation in the layers. This can be effectively alleviated by separately controlling the depressurization scheme in different layers; a mild step-wise depressurization was suggested in the more permeable shallow gas layer while the hydrate layer with a lower permeability should experience a sharper pressure drop. This was found beneficial reducing the interbedded pressure difference by about 70% without intervening the gas production. An energy return on investment (EROI) analysis showed a promising positive energy harvest of our optimized layer-dependent pressure scheme. It could be therefore a potential method to be applied in the field tests in the South China Sea to improve the economic efficiency without disturbing the reservoir stability.

EFFECT OF UREA ADDITION ON BIOGAS PRODUCTION FROM THE CO-DIGESTION OF RICE STRAW AND PIGGERY DUNG

The anaerobic co-digestion of Rice straw (RS) and Piggery dung (PD) at initial Total Solid (TS) loading of 10% was studied. This paper has investigated the effect of supplementing this co-digestion of RS and CD at with urea with an objective of reducing pH as well as improving biogas yield. These experiments were also carried out at different substrate mixing ratios of RS-CD 1:1 and RS-CD 1:2. The anaerobic digestion was carried out in a digester designed and fabricated locally with retention time of between 40 days and 60 days. Results show that addition of 1g of urea improved the maximum Biogas Yield of RS-PD 1:1 by 17.7% and RS-PD 1:2 by 23.4%. Further experiments with 0.5g, 1.5g and 2g of urea added to a co-digestion of RS-CD 1:1 produced a Cumulative Gas Yield of 75 L/Kg, 85.2 L/Kg and 76 L/Kg respectively. Experiments also showed that increasing urea concentration also leads to an increased methane content of the biogas produced.

Biogas Production Using Cow Dung and Sawdust

An investigation of the biogas generation capacity of sawdust and its mixture with cow dung in the ratio (1:2) was conducted. The experiment was performed in a 30-litre digester containing water, cow dung, and sawdust in a 3:1:2 ratio. Mineral elements such as Boric acid, NiSo4, and CoSo4 were added as micronutrients to improve methanogenic activity. The setup was allowed to undergo anaerobic digestion and monitored for a retention period of 20 days at temperatures ranging from 0 ℃ to 37 ℃ and pH levels ranging from 4.3 to 5.4. The results showed that the combination of sawdust and cow dung had a cumulative gas yield of 20.9g after 20 days with a significant increase noticed with increasing temperature. According to the study, sawdust that is either burned off or tossed away creating problems for the environment would be an excellent fuel for biogas generation. It also indicated that mixing sawdust with cow dung will offer continuous gas flammability throughout the digestion phase of the waste. The theory of waste to energy is supported by the generation of biogas from sawdust for improved sustainable development. Keywords— Anaerobic Digestion, Biogas, Cow dung, Digester, Sawdust

Anaerobic Co-Digestion of Oil Sludge with Corn Stover for Efficient Biogas Production

The feasibility of anaerobic co-digestion for the utilization of oil sludge was verified using corn stover, to assess the influence of different raw material ratios and inoculum volumes on the properties of the generated gas. The anaerobic co-digestion method is a novel treatment technology, which may help to solve the problem of pollution by hazardous waste oil sand from the oil exploitation and smelting process. Results showed that single-oil sludge was not suitable for gas production as a digestive substrate due to the lack of organic materials and possible hazardous materials. With the increase in the quality of exogenous organic matter (corn stover), the cumulative gas production volume was proportional to the amount of corn stover material added. It was established that when the mass ratio of corn stover to oil sludge was 4:1, the gas production performance was optimal, with a cumulative gas yield of 1222.5 mL using an inoculum volume of 30 mL. The results of this study provide a fundamental parameter baseline for the treatment of oil sludge and the improvement of gas production efficiency.

Anomalies and genetic mechanism of ethane carbon isotope in the Ordovician carbonate reservoirs in the Jingbian gas field, Ordos Basin, China

The Ordos Basin is one of the most petroliferous basins in China, and the cumulative gas yield of the Jingbian gas field was 91.36 × 109 m3, accounting for nearly 30% of total gas production in the Ordos Basin. The ethane carbon isotopic value of gases in the Ordovician carbonate reservoirs in the Jingbian gas field is abnormally depleted (δ13C1 > δ13C2 < δ13C3), which has directly led to the controversy over the source and genetic types of natural gas in the Jingbian gas field. To find out the genetic mechanism of anomalies of ethane carbon isotope, components and carbon isotopic values of natural gas in the Jingbian gas field were measured. On this basis, natural gas components and stable carbon isotopic values of the Wushenqi and Jingbian gas field were comprehensively measured and compared. The results show that higher thermal maturity leads to further cracking of the oil generated earlier and the residual kerogen. These secondary cracked gases mixed with the early generated gases lead to the anomalies of ethane carbon isotope. When thermal maturity reaches a critical value, it will have different effect on carbon isotopic values of methane and ethane. The carbon isotopic value of methane will continue to increase; however, that of the ethane will gradually decrease, which will eventually lead to the anomalies of ethane carbon isotope. Migration fractionation will also lead to the abnormally depleted of carbon isotopic values of ethane.

Steam Gasification of Biochar Derived from the Pyrolysis of Chrome‐Tanned Leather Shavings

AbstractChromium‐treated leather shavings are generated in large quantities by the leather industry. The biochar gasification from leather shavings leads to two main products, a hydrogen‐rich syngas and a chromium‐rich ash. Syngas has found different applications such as electricity generation and chemical manufacturing. The remaining ash potentially can be utilized, e.g., in stainless‐steel production processes. The thermochemical conversion of biochar from chromium‐tanned leather shavings via steam gasification was investigated. The cumulative gas yield and cumulative H2 yield were determined as well as the total chromium as Cr2O3 in the remaining ash.

Biogas Production from the Co-Digestion of Cornstalks with Cow Dung and Poultry Droppings

The Anaerobic digestion of Corn Stalk (CS) with Cow Dung (CD) and Poultry Droppings (PD) was investigated. Batch mono-digestion and Co-digestion experiments were performed with initial total solid loading of 37.5%. The main objective of this work was to investigate the biogas yield at different CS to CD ratios and CS to PD ratios. Results show that the highest Cumulative Gas Yield (CGY) of 6833 mL/g of biomass was achieved in 21 days for CS-CD ratio of 2:1. Similarly high CGY of 6107 mL/g, 6100 mL/g and 5333 mL/g were obtained for CS-PD ratio of 2:1, CS-CD ratio of 1:1 and CS-PD ratio of 1:1 respectively. It is concluded that co-digestion of Cow dung or poultry droppings is beneficial for improving bio-digestibility and Biogas yield from corn stalk. The results of this work provide useful information to improve the efficiency of co-digestion of CS with CD and PD under anaerobic conditions.

Anaerobic digestion and agricultural application of organic wastes

The anaerobically digestion and agricultural application of organic wastes was conducted using food wastes and cow dung. Twenty kilograms each of the feed stocks was added into two 30 liters-capacity batch digesters. The anaerobic digestion was carried out within a temperature range of 25 – 31O C for a retention time of 51days. The results showed a cumulative gas yield of 5.0 bars for food waste and no gas production for cow dung within the retention time. Bacteria such as Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Proteus vulgaris and Clostridium sp were isolated. Fungi isolated included Aspergillus niger, Aspergillus nidulan, Trichophyton rubrum and Epidermophyton flocossum. The non-dispersive infrared (NDIR) analysis of the biogas produced confirmed that the gas consisted of CH4, CO2 and H2. Statistical analysis revealed there was no significant correlation between temperature and biogas produced from the organic wastes (r= 0.177, p = 0.483).The organic wastes from the biogas production process stimulated maize growth when compared to control (soil without organic waste) and indicated maximum height. The study therefore reveals that food waste as potential substrates for biogas production has a moderate bio-fertilizer potential for improving plant growth and yield when added to soil.

Enhanced Biogas Production in the Duckweed Anaerobic Digestion Process

In order to enhance biogas production in the anaerobic digestion of duckweed, and duckweed with excess sludge as single and mixed substrates, the effects of hot alkali pretreatment and variation of the ratio of substrate to inoculum were investigated. The results showed that the delayed stage of anaerobic gas generation could be shortened when the two substrates were mixed during methane production, to give a cumulative gas yield of 2963 mL, which was 11% higher than the calculated value for the complementary substrate. The methane content was 57%, which was 13% higher than that from the duckweed group and 9% higher than from the excess sludge group. Furthermore, the methane yield was improved by 8% after the duckweed was pretreated with hot alkali. When the substrate to inoculum ratio was 1:1, the maximum biogas production of 3309 mL was achieved, with a methane yield of 1883 mL which, respectively, increases of 151 mL and 304 mL compared with the worst group (1:2.5).