Specific Methane Yield Research Articles

Optimal conditions for high solid co-digestion of organic fraction of municipal solid wastes in a leach-bed reactor

Anaerobic co-digestion of organic fraction of municipal solid waste with solid content greater than 20% and chicken manure was investigated using leach-bed reactors in the framework of Middle East and North African countries. The objectives of the experiments were to determine the optimal ratio of organic fraction, chicken manure and solid inoculum, to compare temperature conditions and usage of liquid inoculum or water in percolation process. The highest specific methane yield (SMY) (236 LN ∙ kg−1 VS) was received in the reactors with 20/80 organic fraction/solid inoculum ratio under thermophilic conditions with liquid inoculum percolation. Under the same conditions but mesophilic temperature, SMY dropped by 12%. Replacing liquid inoculum by water led to 172 LN ∙ kg−1 VS. Addition of chicken manure to the substrate mixture positively influences a start-up phase and keeps pH in optimal range 6.5–8, despite the high ammonia concentration.

Enhancement of methanogenic performance by gasification biochar on anaerobic digestion

This work evaluates the performance of different biochar-amended anaerobic digestion systems. The Fourier Transform Infrared analysis showed that more ordered aromatic groups formed and the aromatization degree increased with the rise of gasification temperature. The biochar produced at 900 °C still showed an excellent ability to maintain the stability of anaerobic digestion performance, where the specific methane yield content steadily reached 742 mL CH4/g ethanol. Besides, the enzymatic activity test indicated an improved performance with the addition of biochar obtained at gasification temperature. The relationship between the microbial community and metabolism pathways result are signified due to the direct interspecies electron transfer among Pseudomonas or Candidatus cloacimonas and Methanosaeta via biochar. These links have promoted the methane metabolism pathway of acetate decarboxylation. Therefore, the current study helps better understand the influence of surface functional groups of biochar at different temperatures on anaerobic digestion performance.

Comparative assessment of pre- and inter-stage hydrothermal treatment of municipal sludge for increased methane production.

Hydrothermal treatment (HT) is a promising technology to enhance anaerobic digestion (AD) of municipal sludge. However, the capacity of pre- and inter-stage HT (i.e., HT-AD and AD-HT-AD, respectively) to enhance the digestibility of municipal sludge has not been sufficiently explored. This study compared the efficacy of pre- and inter-stage HT performed from 90 to 185°C to enhance methane production from a mixture of primary sludge and waste activated sludge using mesophilic (35°C) biochemical methane potential tests. In both configurations, sludge solubilization increased with HT temperature. HT-AD, and to a greater extent AD-HT-AD, increased the release of ammonium nitrogen. Even though HT at 185°C dramatically increased sludge solubilization, the overall specific methane yield with HT at 185°C was lower than or comparable to that at lower HT temperatures in the HT-AD and AD-HT-AD configurations, respectively. Up to 155°C HT, the overall specific methane yield with the HT-AD configuration was higher by 4.9%-8.3% compared to the AD-HT-AD configuration. However, when the HT energy was considered, compared to the control (i.e., AD of sludge without HT), the net energy gain (ΔE) decreased as the HT temperature increased, becoming negative at an HT of 185°C. The AD-HT-AD configuration resulted in a higher overall volatile solids destruction (by 8.1 to 20.1%). In conclusion, for municipal sludge with a relatively high ultimate digestibility, as was the case in this study, HT-AD is preferable as it has a smaller footprint and is easier to operate than the AD-HT-AD configuration. However, given the significantly higher volatile solids destruction in the AD-HT-AD configuration, compared to the HT-AD configuration, AD-HT-AD may be more beneficial considering post-AD sludge handling processes. PRACTITIONER POINTS: Hydrothermal treatment (HT) increased the rate and extent of methane production from municipal sludge mixture. 155°C was the optimal temperature for either pre- or inter-stage HT to increase biogas production. Pre- and inter-stage HT resulted in comparable ultimate methane production. Pre-stage HT is preferable to inter-stage HT (smaller footprint, easier to operate). AD-HT-AD resulted in significantly higher volatile solids destruction compared to the HT-AD configuration.

Effects of sorghum biomass quality on ensilability and methane yield

AbstractSorghum is currently being introduced in the temperate regions of Europe. It is characterized by good digestibility and high biomass yields, which make it a useful crop for anaerobic digestion. In this study, six commercial sorghum varieties comprising four different cultivars of Sorghum bicolor L. Moench and two interspecific sorghum hybrids (Sorghum sudanense L. × S. bicolor L. Moench) were harvested on two different dates during the years 2016 and 2017 at two diverse soil‐climate sites in Germany. The fresh harvested material and silages were analyzed to examine the ensilability of the different varieties with contrasting maturity characteristics. Subsequently, methane production experiments were performed to determine the specific methane yield (SMY) of the samples. The sorghum fresh matter (FM) varied among the sorghum types, including the parameters total solids (TS; 22.69%–46.93%FM), water‐soluble carbohydrates (2.68%–11.38%TS), and nitrates (0%–0.35%TS). The excellent ensiling ability of all the sorghum types analyzed was confirmed by evaluating the fermentation profile (pH range of 3.7–4.6; dominant presence of lactic acid [LA]; acetic acid [AA] in the range of 0.70%–2.38%TS; insignificant amount of butyric acid). The SMY ranged between 231.25 and 321.31 Ln kg−1 VS and tended to decrease with the increasing harvest time and maturity. LA and AA were positively correlated with the SMY, while the neutral detergent fiber content was negatively correlated with it. The SMY—a key parameter reflecting the crop biomass quality for biogas production—was slightly higher for S. bicolor than for the sorghum hybrids. However, the results of this study confirmed that if the final purpose is biomethanation, the ensilability of different sorghum types imposes no restriction. Furthermore, different sorghum types offer a wide harvest window, which can be useful for cropping schemes, ensiling, and methane production.

Food waste treatment through anaerobic co-digestion: Effects of mixing intensity on the thermohydraulic performance and methane production of a liquid recirculation digester

This paper investigates the thermohydraulic performance and methane production of a Liquid recirculation Mesophilic Digester with Submerged solid waste (LMDS) under different mixing strategies. A combination of food waste and cow dung was used as a substrate in the co-digestion experiments. After 24 days of digestion, we reported a higher specific methane yield (301.84 Nm3 CH4 tvs−1) when gentle mixing was adopted, compared to intense mixing (221.32 Nm3 CH4 tvs−1). As for the unmixed co-digestion, it produced the lowest methane yield (112.88 Nm3 CH4 tvs−1). Furthermore, the thermal study showed that the gentle mixing caused less heat loss from the LMDS (20.90 kWh) compared to the intense mixing (40.21 kWh). Moreover, CFD results showed that intense mixing caused a higher pumping energy consumption (through increasing pressure drop) without inducing a significant improvement in the mixing inside the LMDS. Additionally, the liquid flow fields, force distribution, and percolation of the submerged waste were qualitatively evaluated for the considered mixing strategies. Based on these findings, we presented several recommendations aimed at reducing thermal and hydraulic energy losses while guaranteeing optimal methane production in LMDS digesters.

Co-digestive performance of food waste and hydrothermal pretreated corn cob

Anaerobic co-digestion of lignocellulosic biomass and food waste (FW) has been extensively applied. However, whether hydrothermal pretreatment (HTP) of lignocellulosic biomass can enhance the performance in co-digestion deserves further investigation. In this study, corn cob (CC) was adopted as a typical lignocellulosic biomass for co-digestion with FW at different VS ratios of 1:3 (S1–S4) and 1:6 (S5–S8), attempting to evaluate the effect of HTP of CC at different temperature gradients (125, 150 and 175 °C) on the co-digestion performance. The emphasis was placed on hydrolysis, acidification and methanogenesis for different feedstock conditions. Results illustrated that the HTP had a certain destroying effect on the lignocellulose structure in CC and the crystallinity of cellulose decreased, significantly facilitating its co-digestion with FW. For FW/CC co-digestion at the VS ratio of 1:3, the S3 group (CC was pretreated at 150 °C) reached the maximum cumulative biogas yield (CBY) of 4660 mL and the maximum specific methane yield (SMY) of 316.9 mL/g·VS. Moreover, at 1:6, S7 group (pretreated at 150 °C) exhibited the optimal CBY of 4100 mL while achieving the SMY of 277.6 mL/g·VS among the digesters, indicating that the co-digestion of pretreated CC and FW could achieve higher methane production, and 150 °C refers to the optimal pretreatment temperature. Moreover, the peak values of the accumulated VFAs in digesters S1–S4 (2000–3000 mg/L) is higher than that in digesters S5–S8 (800–1500 mg/L). As suggested from microbial community and diversity date, the HTP expedited the enrichment of system hydrolyzing and acidogenic bacteria. These results are significant and provide certain guidance for optimizing the co-digestion of FW and CC in actual engineering.

Biomass and methane yield of giant reed (Arundo donaxL.) as affected by single and double annual harvest

AbstractThe replacement of silage maize with giant reed as energy crop has been proposed as a mean for reducing the need of irrigation water as well as monetary and environmental costs of cultivation. Little is known about giant reed response to within‐season harvesting, and its effect on the methane production in anaerobic digestion. The effect of three harvest schedules on yield, biomass composition and methane production of giant reed was evaluated at one site of the Po Valley, northern Italy, for three consecutive years. In a completely randomized block design with four replicates the treatments applied annually were: (i) double harvest 1: first cut at the end of June + second cut at the beginning of October (DH1); (ii) double harvest 2: first cut at the end of July + second cut at the beginning of October (DH2); (iii) single harvest at the beginning of October (SH). The crop stand was established in the year 2015 and treatments were repeatedly applied in the years 2016, 2017 and 2018. The SH treatment determined the highest average annual dry matter (DM) yield (59.0 Mg DM ha−1). The DM yield for treatments with double harvest was significantly lower, that is, −30% for DH1 and −15% for DH2. In terms of specific methane yield there was little advantage in harvesting biomass twice during the growing season. The average specific methane yield varied substantially between years (i.e. from 144 to 233 ml CH4 g−1 VS), and in every year the values tended to decrease with the ageing of harvested biomass. Methane yield per hectare, however, was driven by DM yield, thus SH also determined the highest average value (9110 m3 CH4‐STP ha−1). In conclusion, the single annual harvest at the end of the growing season is an ideal strategy for maximizing methane production from giant reed.

Эффективность анаэробной переработки органических отходов в биофильтрах с использованием кондуктивного носителя

Additional anaerobic treatment of the liquid fraction of the methantenk’s effluent to the content of organic substances that ensure subsequent effective processing under aerobic conditions can be carried out in a biofilter. Processing makes it possible to obtain an additional amount of biogas, reduce the volume of sludge residues. To accelerate the processes of wastewater treatment and optimize the processes of anaerobic processing of wastewater, the use of conductive carriers of inorganic biomass is promising. (Research purpose) The research purpose is in studying the effect of conductive biomass carriers on the efficiency of anaerobic processing of organic waste in biofilters. (Materials and methods) The liquid fraction of the effluent obtained as a result of the gravitational separation of the effluent of the methantenk was used as a substrate for the biofilter. The article describes experimental studies on a test bench that includes two identical bioreactors, in one of which there was placed a biomaterial carrier made of carbon tissue. The article presents a technological scheme and an experimental installation for anaerobic post-treatment of the liquid effluent fraction. (Results and discussion) In the course of experimental studies for 25 days, they showed high stability of the operation of the developed and manufactured experimental installation. In the recycled effluent of a bioreactor with a conductive carrier, the organic substances of the effluent are more fully processed into biogas. The specific (in terms of unit volume of the bioreactor) yields of biogas and methane increased by 14.0 and 22.5 percent; the specific methane yield per gram of raw and decomposed organic matter increased by 22.2 and 7.3 percent. (Conclusions) The use of a biofilter in combination with the immobilization of microorganisms on a conductive carrier allowed to increase the efficiency of fermentation of organic waste by 6 percent, increase the specific yields of biogas and methane, and reduce the volume of sludge residues.

Improved anaerobic digestion of swine manure by simultaneous ammonia recovery using gas-permeable membranes

In feedstocks containing high ammonia (NH3) concentration, removal of the NH3 during the anaerobic digestion (AD) process can improve AD process performance. In the present study, the effect of NH3 removal using gas-permeable membrane (GPM) technology on AD process performance and biogas production was investigated using swine manure feedstock. Batch and semi-continuous AD experiments were carried out under mesophilic conditions. In the reactor with NH3 recovery, total ammonia nitrogen (TAN) concentration was reduced 28% in batch experiments and 23% on average in the semicontinuous experiment compared with the reactor without NH3 recovery. Free ammonia (FA) concentrations were also decreased by 23% and 4% on average in batch and semicontinuous experiments, respectively. These reductions in TAN and FA by GPM system positively impacted both the quality and quantity of the biogas produced by AD of swine manure. Specifically, the specific methane yield increased 9% in the batch experiment and 17% on average in the semicontinuous experiment. Furthermore, higher percentages of methane in biogas were obtained during AD retrofitted with GPM system, 24% increase in the batch experiment and 11% on average in the semicontinuous experiment (range 8.3-13.6%). Simultaneously, a uniform TAN recovery rate of 6.7 g N TAN per m2 of membrane and per day was obtained for the 205 days of semicontinuous operation; ammonia nitrogen was recovered in the form of ammonium sulphate solution. Therefore, the AD-GPM configuration produces beneficial results on biogas quantity and quality while recovering ammonia nitrogen in form of ammonium sulphate.

Performance Comparison of Single and Two-Phase Biogas Digesters Treating Dairy Cattle Manure at Tropical Ambient Temperature

The biodegradation process of organic waste in anaerobic digestion can be in a single or two-phase bio-reactor. This study examined the effect of different biogas digester configurations (single and two-phase) on methane production of dairy cattle manure (DCM) at tropical ambient temperature. Three identical reactors were used in this study (R1, R2, and R3). The two-phase digesters consisted of reactors R1 and R2. R1 had a 2.1 L working volume and 3 d hydraulic retention time (HRT), while R2 had 5.25 L working volume and 22 d HRT (R1 and R2 had a 25 d HRT). The digested slurry of R1 was used to feed R2. R3 served as the single-phase digester and had 5.25 L working volume and 25 d HRT. Methane production were 14.31, 132.82, and 146 L/kg VS for R1, R2, and R3, respectively. The results showed that there was no positive effect of the application of a two-phase digester configuration on the specific methane yield of DCM per kg volatile solids added than that in the single-reactor. Methane production was detected in the first reactor of the two-phase digester configuration and the total methane production of the two-phase digester was found to be 29.98% higher (p<0.05) than that of the single reactor in terms of digester volume (0.41 VS 0.31 L/L/d). Both digester configurations performed well, indicated by a stable methane production and low volatile fatty acids and total ammonia concentrations. The two-phase bio-digester configuration can significantly increase methane production in terms of digester volume.

A method for shifting of cattle dung based biogas digester for enhanced anaerobic co-digestion of cattle dung with leaf litter of neem

In India, many biogas plants process cattle dung (CD). At the same time, an excessive amount of litter of leaves is swept and burnt. The paper investigates small-scale integration of leaf litter of neem (LLN) to the operational CD-based biogas plant under mesophilic conditions. The introduction of LLN at the volatile solid ratio of 1:4 (LLN:CD) respectively increased daily biogas production, specific methane yield, and the resultant electrical energy by 13.11, 15.26, and 15.02% and reduced the proportion of CO2 by 5.85%. However, because of the energy required to pulverize the LLN in CD-LLN–based, the net percentage increase of the electrical energy dropped to 13.59%. CD-LLN–based reactor also produced 56.34% higher electrical energy per organic substrate added and performed well by 15.0% in terms of CO2 emission compared to CD-based. Digester performance was seriously unaffected during the transition stage. The study highlights another way of managing LLN and shifting anaerobic reactors from one feedstock to another.

Biotechnology of co-fermentation of sugar by-products with typical agricultural substrates

Anaerobic digestion (AD) is a promising option for the environmentally friendly recycling of agricultural by-products. However, overloading of the digester with sugar, starch or protein might cause inhibition of the anaerobic processes. The aim of the present project was to investigate the influence of sugar beet by products on biogas yield from a typical mixture of energy crops and animal manure. The investigated substrates have been: cattle slurry, maize, sorghum and grass silage, sugar beet pulp e (SBP) and sugar beet tail silage (SBT). The difference between untreated SBT to processed SBP. All substrates were digested in 1 l eudiometer-batch digesters at 37.5°C during 28 to 38 days. The specific methane yield of mixtures and various substrates exanimated. The experiments showed that edition of sugar beet by product to energy crop and slurry mixture results in high methane yield even the achieved methane yield of the mixture was lower the expected.

Urea-assisted ensiling process of wilted maize stover for profitable biomethane production

Low contents of water-soluble carbohydrates and/or low indigenous microbial activity in wilted maize stover (WMS) usually hinder the establishment of the ensiling process, thereby resulting in a low biogas production because of high loss of dry matter (DM). To enhance the biological activity and substrate biodegradability, this study applied the synergistic regulation of sucrose (carbon source) and increasing levels of urea (nitrogen source) during the ensiling process of WMS. Compared with the application of only sucrose, a higher organic acid content (lactic acid (85 g/kg-DM) and acetic acid (14 g/kg-DM)) and higher degradation ratios for lignocellulose (hemicellulose (28%), cellulose (22%), and lignin (17%)) were observed with urea applications of 1.7% (DM) and 3.9% (DM), respectively. This was caused by the enhanced activities of the hetero-fermenter (Weissella) and cellulolytic bacteria (Cellulosimicrobium). A simultaneous addition of urea and sucrose during the ensiling of WMS increased the specific methane yield by 11.2%–21.1% in comparison to raw WMS. Moreover, an economic cost estimation revealed that this approach could be an effective storage strategy for the efficient production of methane when employing a 1.7% (DM) urea application.

A novel integrated single-stage anaerobic co-digestion and oxidation ditch-membrane bioreactor system for food waste management and building wastewater recycling

This study is to develop a novel integrated single-stage anaerobic co-digestion and oxidation ditch membrane bioreactor (SAC/OD-MBR) for food waste and building wastewater recycling. The co-digestion of food waste (FW) from a canteen with waste sludge (WS) from OD-MBR was performed with the proportion of FW:WS at 10:1 by weight. The liquid digestate from the co-digestion process was further co-treated with building wastewater in the OD-MBR system for water reuse purpose. Maximum methane content of 65.2% in biogas as well as average specific methane yield of 0.24 gCH4/gVS could be obtained with anaerobic co-digestion of food waste and waste sludge from OD-MBR with HRT of 24 h and horizontal flow velocity of 0.3 m/s. The observed main methanogen species in this co-digestion process were Methanoculleus bourgensis and Methanoculleus palmolei. For co-treatment of liquid digestate and building wastewater with the OD-MBR, it was found that HRT of 24 h and horizontal flow velocity of 0.3 m/s could achieve highest COD and nitrogen removal efficiencies. HRT can be considered as a main key parameter to promote nitrification activity inside the OD-MBR system. Moreover, treated effluent from the SAC/OD-MBR could comply with the water reuse standard for garden and landscape application in the university campus. Furthermore, the techno-economic analysis indicates that this proposed system has a high potential of total cost savings and other indirect benefits. Therefore, the prototype SAC/OD-MBR can be an alternative system for food waste management and wastewater recycling for building application.

Study on interchangeability of seed based feedstocks for biogas production in multi-feeding mode

Biogas is an excellent renewable fuel providing gas for clean energy applications and fertilizers for organic farming. In the present study, seeds from four tree species of Acacia nilotica , Albizia lebbeck , Prosopis juliflora , and Leucaena leucocephala have been utilized for biogas production as alternative feedstocks. They have been investigated in a mixed-feeding mode in a single digester to tackle the feedstock availability and seasonality challenges. The investigations were conducted in a 300 ​L anaerobic digester for 120 days under daily feeding mode. The average specific biogas yield and specific methane yield was found to be 0.425 ​m 3 /kg of volatile solids and 0.228 ​m 3 /kg of volatile solids, respectively. The average volumetric methane content in biogas was 54.7%. This paper presents a unique study on anaerobic digestion of selected seeds in a mixed-feeding mode to provide broad opportunities for their efficient and sustainable utilization. • Interchangeability of tree species seeds explored for 120 days in the mixed-feeding mode for biogas production. • Anaerobic digestion parameters for the utilization of these seeds are investigated in detail. • An amount of 3.0–3.5 ​kg of seeds is required to produce one cubic metre of biogas. • Specific biogas yield of 0.425 ​m 3 /kg VS with methane of 54.7% and TVSMRE as 46.0% were found.

Anaerobic Digestion of aqueous Jatropha seed oil extraction residues and phorbol ester degradation

Aqueous Jatropha Oil Extraction Residue (AJOR) is a byproduct from a novel technique for Jatropha seed oil extraction. Its potential for biogas production, its effects on process stability and the reduction of toxic phorbol esters were investigated. AJOR had a total solid and volatile solid content of 24.3% and 92% and contained 35.5% of crude protein and 17.5% of crude fat, based on total solids. The specific methane yield was measured with the Hohenheim Biogas Yield Test at 406 LCH4 kg−1VS. In continuous digestion, 405 LCH4 kg−1VS was reached, but was accompanied by an excessive volatile organic acids to total inorganic carbon ratio at an organic loading rate of 2.64 kgVS m−3 d−1. After a reduction of the organic loading rate to 1.7 kgVS m−3 d−1, the specific methane yield amounted to 440 LCH4 kg−1VS and the fermentation process became stabilized. Phorbol esters per FM decreased by 97–98%.

Effect of Harvesting Age and Size Reduction in the Performance of Anaerobic Digestion of Pennisetum Grass

In the rural zones of Latin American and Caribbean developing countries, the poorest households rely on traditional fuels such as firewood to meet their daily cooking needs. Many of those countries are located near the equator, where they have a tropical climate and grass is one of the most common biomass crops. The aim of this study was to evaluate the effect of harvesting age (30, 44, and 57 days) in the performance of anaerobic digestion of King Grass (Pennisetum purpureum cv. King Grass) grown under tropical climate conditions. Three reduction methods of crop size were also compared. Results showed that 44-day harvesting age presented the greater specific methane yield (347.8 mLCH4 g−1VS) and area-specific methane yield (9773 m3CH4 ha−1 y−1). The machine chopped method (1–3 cm for stems and 1–10 cm for leaves) was the reduction method that maximized the methane production. From those results, the calculated area required for grass cultivation to provide the cooking energy to a typical family in the Colombian rural zones is 154 m2.

Comparison of methane production performance of vinegar residue under liquid‐ and solid‐state conditions

AbstractVinegar residue (VR), a major by‐product in the vinegar brewing process, is generated at least three million tons annually in China. Currently major part of the disposal of VR is fulfilled by landfill and incineration, however, serious environment pollution along with such processes is a challenging issue. Anaerobic digestion (AD) can provide benefits of environment and renewable methane generation, which seems to be a reasonable alternative to traditional treatment. Noticeably, total solids (TS) is an important influential parameter to AD performance. Therefore, VR was evaluated for methane production and associated kinetic characteristics during the liquid‐state AD (LS‐AD) and solid‐state AD (SS‐AD) in this study. The results indicated that the highest specific methane yield of 194.8 mL gVS−1 and volumetric methane yield of 9.4 Lmethane Lreactor volume−1 were achieved in LS‐AD (TS = 10%) and SS‐AD (TS = 20%), respectively. The kinetic analysis showed a higher specific methane production rate for LS‐AD than SS‐AD, while volumetric methane production rate presented a reverse trend. This study provides useful guidance for the sustainable utilization of VR while contributes to environmental protection and alleviates the dependence on fossil fuels.

Effect of Mixture Ratio of Food Waste and Vetiver Grass on Biogas Production

The objectives of this research were to study the optimum percentage ratios of food waste and vetiver grass (Vetiveria zizaniodes (L.) Nash) for biogas production and process stability in anaerobic digestion system. The nine mixture ratios of food waste (FM) and vetiver grass (VG) were 100:0, 80:20, 75:25, 66.67:33.33, 50:50, 33.33:66.67, 25:75, 20:80 and 0:100. The biogas production was subjected to anaerobic batch with working volume of 1.8 L and had digestion time 60 d at 35 ± 2 °C. High specific methane yield of 0.30 L g-1 VS removed was obtained from the fermentation at ratio of FW:VG at 80:20 with C/N ratio of 28.20. The specific methane yield of the single digestion of food waste (100:0) and single digestion of vetiver grass (0:100) were only 0.18 and 0.11 L g-1 VS removed, respectively. It was found that the cumulative methane production of FW: VG ratio of 80:20 was increased 34.89 % and 96.93 % compared to single substrate of food waste and vetiver grass, respectively. The results also showed the highest COD, VS and TS removal with a percentage ratio of FW: VG at 80:20, while the single vetiver grass digestion was the lowest COD, VS and TS removal. VFAs/Total alkalinity ratio of all ratio of food waste to vetiver at digestion time 40 d remained in 0.0895±0.0007 to 0.1944±0.0027 were steadied for this digester. It can be concluded that co-digestion of food waste and vetiver improve the biogas yield and degradation efficiency.

Valorization of apple pomaces for biofuel production: A biorefinery approach

This study is aimed at assessing the potential of apple pomace (AP) as a substrate for biofuel production following a biorefinery approach. Two different APs, from juice and cider production were evaluated. First, bioethanol generation was performed and its fermentation residues, together with available biobutanol fermentation residues, were studied for biogas production. Moreover, co-digestion of AP and swine manure was investigated following a factorial design. Twelve different bacterial and yeast strains were compared for bioethanol production, obtaining bioethanol concentrations about 50 g L−1 by different strains of Kluyveromyces marxianus, K. lactis, Lachancea thermotolerans and Saccharomyces cerevisiae, with yields of 0.371–0.444 g g−1. Specific methane yields of the fermentation residues of bioethanol and biobutanol production were 463 and 290 mL CH4 g −1VS added, respectively. Methane yield for the co-digestion of AP and swine manure was 596 mL CH4 g−1VS added, with an AP percentage of 14.6% and a substrate concentration of 9.38 g VS L−1.