Effect of feed to microbe ratios on anaerobic digestion of Chinese cabbage waste under mesophilic and thermophilic conditions: biogas potential and kinetic study

The Valorization of Wastes and Byproducts from Cruciferous Vegetables: A Review on the Potential Utilization of Cabbage, Cauliflower, and Broccoli Byproducts

The management of vegetable waste and byproducts is a global challenge in the agricultural industry. As a commonly consumed vegetable crop, cruciferous vegetables marked higher amounts of wastage during their supply chain processes, with a significant contribution from cabbage, cauliflower, and broccoli. Therefore, the sustainable and resource-efficient utilization of discarded materials is crucial. This review explores potential applications of cruciferous vegetable waste and byproducts, spotlighting cabbage, cauliflower, and broccoli in food, medicinal, and other industries. Their significance of being utilized in value-added applications is addressed, emphasizing important biomolecules, technologies involved in the valorization process, and future aspects of practical applications. Cabbage, cauliflower, and broccoli generate waste and low-processing byproducts, including leaves, stems, stalks, and rot. Most of them contain high-value biomolecules, including bioactive proteins and phytochemicals, glucosinolates, flavonoids, anthocyanins, carotenoids, and tocopherols. Interestingly, isothiocyanates, derived from glucosinolates, exhibit strong anti-inflammatory and anticancer activity through various interactions with cellular molecules and the modulation of key signaling pathways in cells. Therefore, these cruciferous-based residues can be valorized efficiently through various innovative extraction and biotransformation techniques, as well as employing different biorefinery approaches. This not only minimizes environmental impact but also contributes to the development of high-value-added products for food, medicinal, and other related industries.

Optimization of biomethane production from sweet sorghum bagasse using artificial neural networks combined with particle swarm algorithm

In the face of international movement away from fossil fuels caused pollution menace, many research labs are rushing towards next big breakthrough via effective biorefinery development employing non-edible agro-residues as feedstock. This work aims to evaluate and optimize the methane potential of underutilized full strength sweet sorghum bagasse (SSB) via anaerobic digestion (AD). Biochemical methane potential assays are set up for SSB AD under mesophilic and thermophilic conditions at four substrate-o-inoculum ratios (SIR) 3, 5, 7, and 9 with pH 6.5, 7.5, and 8.5 and with 80, 90, and 100 rpm mixing speed over 50 days. SIR 5 produced the highest cumulative biomethane yield of 4.25 L methane g-1 VS with a shorter lag time of 7.5 days and technical digestion time of 24 days. The influence of physio-chemical parameters on AD process dynamics is supported with 16s rRNA metagenomic sequencing. Based on complete experimental data sets, two artificial neural network (ANN) models are developed to identify the relevant significance of process parameters and to predict bagasse methane potential. Further, the developed ANN model is integrated with particle swarm optimization algorithm to create ideal AD process operating conditions which maximize the target variable, biomethane. The trained and cross-validated ANN-PSO model showed good-fit-accuracy with R2 > 0.995 and demonstrated satisfactory performance in the biomethane yield prediction from AD of non-edible agri-residues.

Characterization of kitchen and municipal organic waste for biogas production: Effect of parameters

Globally, the production of municipal solid waste is rising annually because of consumerism and the urbanization process. In the past few years, different researchers have explored strategies for generating biogas from various organic wastes. In this study, kitchen waste and municipal solid waste were characterized by several physical-chemical parameters. Ten of these substrates were mono-digested for biogas production in batch reactors where cabbage showed a 96.36 ± 1.73% volatile solid and biogas yield of 800 ± 8.8 mL within 10 days, while cooked rice had an 83.00 ± 1.49% volatile solid, and a biogas yield of 2821 ± 31.03 mL within 28 days. The CN ratio for cabbage and cooked rice waste was 13.9 and 30.9 respectively, whereas their pH values were 6.2 and 7.2. Based on the characterization and biogas yields attained, cooked rice waste could be mono-digested for biogas production and no published work showed a high yield as the current study while the other substrates require co-digestion to improve the biogas yield.

Substrate-to-inoculum ratio drives solid-state anaerobic digestion of unamended grape marc and cheese whey

Inoculation dose is a key operational parameter for the solid-state anaerobic digestion (SS-AD) of lignocellulosic biomass, maximum methane recovery, and stable digester performance. The novelty of this study was the co-digestion of unamended full-strength grape marc and cheese whey for peak methane extraction at variable inoculation levels. An acclimatised digestate from a preceding anaerobic treatment was used as a downstream inoculum. The impact of inoculum size (wet weight) was evaluated at 0/10, 5/5, 7/3 and 9/1 substrate-to-inoculum (S/I) ratios, corresponding to an initial concentration of 20-30% total solids (TS) in digesters over 58 days at 45°C. The optimal 7/3 S/I produced the highest cumulative methane yield, 6.45 L CH4 kg-1 VS, coinciding with the lowest initial salinity at 11%; the highest volumetric methane productivity rate of 0.289±0.044 L CH4 LWork-1 d-1; the highest average COD/N ratio of 9.88; the highest final pH of 9.13, and a maximum 15.07% elemental carbon removal; for a lag time of 9.4 days. This study identified an optimal inoculation dose and opens up an avenue for the direct co-digestion of grape marc and cheese whey without requirements for substrate pretreatment, thus improving the overall bioenergy profile of the winery and dairy joint resource recovery operations.

Methane production by anaerobic co-digestion of mixed agricultural waste: cabbage and cauliflower

Anaerobic co-digestion of residual cabbage and cauliflower mixed at a ratio 1:1 (w/w) was investigated in two continuously stirred tank reactors under mesophilic conditions to ensure stability and enhanced methane generation. The experiments, including start-up, inoculum acclimatisation and treatment of the waste mixture, were carried out over a 65-day period. The characterisation results showed that the residual mixture contained a high proportion of total Kjeldahl nitrogen (around 37 g N/kg dry weight). The maximum value of methanogenic yield potential was found to be 250 L_STP/kg VS (volatile solid) added, at STP conditions (0°C, 1 atm), by loading organic substrate at a concentration of 1 g VS/L, while its biodegradability was 60%. However, instability of the biomethanisation process was observed after 17 days, which might be a consequence of the high concentration of nitrogen in the reactors. The evaluation of the kinetics of the valorisation process revealed that the waste mixture studied can easily be biodegraded through anaerobic co-digestion.

High-Solid Anaerobic Digestion: Reviewing Strategies for Increasing Reactor Performance

High-solid and solid-state anaerobic digestion are technologies capable of achieving high reactor productivity. The high organic load admissible for this type of configuration makes these technologies an ideal ally in the conversion of waste into bioenergy. However, there are still several factors associated with these technologies that result in low performance. The economic model based on a linear approach is unsustainable, and changes leading to the development of a low-carbon model with a high degree of circularity are necessary. Digestion technology may represent a key driver leading these changes but it is undeniable that the profitability of these plants needs to be increased. In the present review, the digestion process under high-solid-content configurations is analyzed and the different strategies for increasing reactor productivity that have been studied in recent years are described. Percolating reactor configurations and the use of low-cost adsorbents, nanoparticles and micro-aeration seem the most suitable approaches to increase volumetric production and reduce initial capital investment costs.

Effect of different vegetable wastes on the performance of volatile fatty acids production by anaerobic fermentation

Volatile fatty acids (VFAs) are intermediates of anaerobic fermentation with high value and wide range of usage. VFA production from vegetable wastes (VW) is an effective way to dispose of wastes and recover resources. The organic matter composition of the substrate influences VFA yield and distribution, which is related to the separation and purification of the downstream steps and the application of the product. Hence, potato peels, carrots, celery, and Chinese cabbage were selected to investigate the effect of VW types on the performance of the VFA production in a batch anaerobic fermentation reactor with continuous stirring at 37 °C, total solid (TS) of 4.5%. A VFA yield of 452 mg COD/g VS_feed (chemical oxygen demand (COD); volatile solids (VS)) was achieved from potato peels, which was 40.1%, 21.5%, and 124.9% higher than that of carrots, celery, and Chinese cabbage, respectively. The rapid acidification of carrots caused a sharp decline in pH and led to inhibition of VFA production. The acidification of celery started slowly, and the yield of hexanoic acid increased rapidly in the later stage of fermentation. The VFA yield of Chinese cabbage was inhibited due to the low initial pH, but the ethanol concentration reached 7577.04 mg COD/L. According to the VFA profile, the fermentation of potato peels, carrots, celery, and Chinese cabbage can be classified as propionate-type, butyrate-type, mixed-acid type, and ethanol-acetate type metabolic pathway, respectively. The results of this study suggest that a suitable combination of vegetable waste types is important for selective VFA production.

Bio-reserves inventory-improving substrate management for anaerobic waste treatment in a fast-growing Indian urban city, Chennai

India is one among the Asia's newly industrialized countries, in which urban centres generate large amount of municipal solid wastes due to the rapid urbanization. To demonstrate urban waste potentials for biogas production by anaerobic digestion, a comprehensive analysis on the availability of organic waste hotspots and its biogas potential for the exemplary case of Chennai, India, was undertaken. The identified hotspots and their biogas potential were plotted with Geographical Information System as thematic maps. The results of biogas potential tests revealed strong variations in the biogas potentials of individual waste streams from 240.2 to 514.2 mL_N/g oDM (organic dry matter) with oDM reduction in the range of 36.4-61.5 wt.-%. Major waste generation hotspots were identified from the surveyed urban bio-reserves and the biogas potentials within an effective area of 5 km radius surrounding the hotspot were estimated. It was found that the biogas potential of individual hotspots ranged between 38.0-5938.7 m³/day. Further results revealed that the biogas potential during anaerobic co-digestion, by considering nearby bio-reserves in the effective areas of major hotspots, with and without residential organic waste, ranged between 4110.4-18-106.1 m³/day and 253.2-5969.5 m³/day, originating from 144.0-620.0 tons and 3.1-170.5 tons, respectively. Despite variations in the composition of the wastes, the Carbon/Nitrogen ratio, oDM reduction, biogas production and substrate availability were improved during co-digestion of nearby bio-reserves within the major hotspots, thereby improving the prevailing barriers in substrate management during anaerobic digestion of wastes.

Comparison of mesophilic and thermophilic methane production potential of acids rich and high-strength landfill leachate at different initial organic loadings and food to inoculum ratios

Landfill leachate (LL), which can contaminate both ground and surface water is a major global environmental issue. The aim of the present study was to investigate the biomethane potential (BMP) of a high-strength LL with low pH (5.0), high solids concentration (16%), and high organic matter (170 g/L of chemical oxygen demand (COD); 55 g/L of volatile fatty acids (VFA)) with ammonia nitrogen (NH₃-N) (17 g/L). We investigated the BMP of LL at four different initial organic loadings (IOL) of 170 g/L, 85 g/L, 42.5 g/L and 21 g/L of COD and Food to inoculum (F/I) ratios of 0.5; 1; 2 and 3 at mesophilic (35 ± 2 °C) and thermophilic temperatures (55 ± 2 °C). We found that the highest cumulative CH₄ could be obtained at an IOL of 42.5 g/L of COD regardless of the F/I ratio and temperature. The highest methane content results in biogas at an IOL of 42.5 g/L were 72% and 74% at mesophilic and thermophilic temperatures respectively. About 80-100% of cumulative methane was produced within 15 days in thermophilic reactors, and 40-72% in mesophilic reactors. The kinetic study revealed a fourfold reduction of lag phase in thermophilic compared to mesophilic reactors. The methane yield and organic matter removal rate increased as the concentration of IOL in LL decreased from 170 g/L to 21 g/L regardless of temperature. There exists an inverse correlation between IOL and organic matter removal efficiency. About 80% COD reduction was obtained at mesophilic temperature, and 90% at thermophilic temperature, at an IOL of 42.5 g/L and 21 g/L of COD. The modified Gompertz model showed a good fit to the experimental data, with R² > 0.98 in all cases. Overall, the findings of this study conclude that treatment of acids rich and high-strength LL both at mesophilic and thermophilic temperature is feasible at an optimum IOL of 42.5 g/L of COD. However, treatment of LL at thermophilic temperature outperformed compared to mesophilic over the digestion time.

Enhanced solubilization of solid organics and methane production by anaerobic digestion of swine manure under nano-bubble water addition

Nano-bubble water (NBW) refers to water with a large number of nanoscale particle bubbles. The aim of this work was to study the mechanism of NBW addition into the anaerobic digestion (AD) of swine manure (SM). The results showed that the cumulative methane production from the NBW added reactor was 192-225 mL/g-VS and 19-39% higher than the control group (without NBW addition). Based on the analysis of soluble organics, NBW addition not only accelerated hydrolysis rates of proteins and carbohydrates, but also enhanced the production of VFAs. Moreover, mechanism analysis reveals that NBW with higher spin-spin relaxation time and absolute value of zeta potential might promote enzyme activity and the hydrolysis of organic solids. Simultaneously, the electron transport system activity of the methanogenic communities and electric conductivity were enhanced by NBW addition. This work implies that NBW addition is promising for enhancing AD for enhancement of methane production.

A Review on Anaerobic Digestion of Lignocellulosic Wastes: Pretreatments and Operational Conditions

Anaerobic digestion (AD) has become extremely popular in the last years to treat and valorize organic wastes both at laboratory and industrial scales, for a wide range of highly produced organic wastes: municipal wastes, wastewater sludge, manure, agrowastes, food industry residuals, etc. Although the principles of AD are well known, it is very important to highlight that knowing the biochemical composition of waste is crucial in order to know its anaerobic biodegradability, which makes an AD process economically feasible. In this paper, we review the main principles of AD, moving to the specific features of lignocellulosic wastes, especially regarding the pretreatments that can enhance the biogas production of such wastes. The main point to consider is that lignocellulosic wastes are present in any organic wastes, and sometimes are the major fraction. Therefore, improving their AD could cause a boost in the development in this technology. The conclusions are that there is no unique strategy to improve the anaerobic biodegradability of lignocellulosic wastes, but pretreatments and codigestion both have an important role on this issue.

Effects of Salt on Anaerobic Digestion of Food Waste with Different Component Characteristics and Fermentation Concentrations

Effects of salt on anaerobic digestion are dosage-dependent. As salt is a widely used condiment in food processing, effects of salt are bound to be considered when food waste is digested. In this study, salt addition effects (0, 2, 4, 6, 9, 12 g∙L−1) on biogas and methane yields and kinetics of biogas production were researched. Meanwhile, component characteristics (food waste featured in carbohydrate, protein and fat, respectively) and fermentation concentrations (5 and 8 gVS∙L−1) were also taken into consideration. Results showed that 2–4 g∙L−1 salt addition was the optimal addition dosage for AD systems as they not only have the maximum biogas and methane yields, but also the maximum vs. removal in most cases. Also, according to the results of a modified Gompertz model, which is used to predict biogas and methane production rates, suitable salt addition can accelerate biogas production, improving the maximum biogas production rate (Rmax). Factorial design (2 × 2) proved that interaction of salt and fermentation concentrations was significant for food waste featured with carbohydrate and with protein (p <0.05). High salt addition and fermentation concentration can break the AD system when the feeding material was food waste featured with carbohydrate, but for food waste featured with protein, interaction of fermentation concentrations and salt addition can alleviate inhibition degrees.

Perspectives on variabilities in biomethane potential test parameters and outcomes: A review of studies published between 2007 and 2018

Biomethane Potential (BMP) test continues to be a useful and inexpensive assay to estimate the digestibility and maximum methane production of various organic substrates in anaerobic digestion or co-digestion processes. Despite its usefulness and several published efforts toward standardizing it, the BMP test still do not follow a universally accepted standard protocol. This makes the comparison of results among studies quite challenging. In this context, this paper analyzes 78 peer-reviewed BMP studies published between 2007 and 2018 that used the BMP test primarily to assess methane potential of commonly digested substrates, such as food waste, wastewater sludge and manure. We focused on the similarities and differences in the methodologies used and, where possible, the results obtained from these studies were compared and discussed. It was observed that many studies do not provide adequate information on salient aspects of the BMP methodology, and results are sometimes reported in different units of measurements. The inoculum to substrate ratio (ISR), substrate concentration and/or load should be clearly indicated in future studies, and positive controls should be included to validate BMP results. It is recommended that more studies assess the impact of nutrient addition, potential effects of continuous and intermittent mixing and mixing intensities and the influence of reactor size and headspace volume on BMP results.

A comparative study of biogasification of wheat straw, sugarcane bagasse and pressmud

A study to compare biogas production potentials of wheat straw, sugarcane bagasse and pressmud was conducted at pH 8.0, temperature 40 °C and substrate concentration 20 g/L. Raw substrates were thermogravimetrically and Fourier-transform infrared spectroscopically characterised. TGA showed the weight loss of samples attributable to moisture, hemicellulose, cellulose and lignin losses. FTIR analysis indicated functional groups characteristics of hemicellulose, cellulose and lignin. Biogas production was the maximum between 10th and 25th day for all the tests. WS with 10% inoculum showed the highest cumulative biogas production of 370 mL/g followed by the SB (316 mL/g) and PM (211 mL/g) counterparts. The corresponding values with 5% inoculum were 303 mL/g (WS), 244 mL/g (SB) and 152 mL/g (PM). The inoculum volume also positively affected the cumulative biogas production (22.1, 29.5 and 38.8% respectively). The higher volatile fatty acids as observed in case of WS which further facilitated higher biogas production could be due to its maximum volatile solids content (88.9%) and water swelling capacity (7.37). A consistently increasing trend in the methane content (varying between 54 and 61%) in all the tests was observed till the 20th day. The biogas (7.7-21.7 mL/g) and the methane (35-42%) contents showed a decreasing trend thereafter, the lowest being observed during the 35-40-day period.

Influence of chemical composition on biochemical methane potential of fruit and vegetable waste

This study investigates the influence of chemical composition on the biochemical methane potential (BMP) of twelve different batches of fruit and vegetable waste (FVW) with different compositions collected over one year. BMP ranged from 288 to 516L_NCH₄kgVS^-1, with significant statistical differences between means, which was explained by variations in the chemical composition over time. BMP was most strongly correlated to lipid content and high calorific values. Multiple linear regression was performed to develop statistical models to more rapidly predict methane potential. Models were analysed that considered chemical compounds and that considered only high calorific value as a single parameter. The best BMP prediction was obtained using the statistical model that included lipid, protein, cellulose, lignin, and high calorific value (HCV), with R² of 92.5%; lignin was negatively correlated to methane production. Because HCV and lipids are strongly correlated, and because HCV can be determined more rapidly than overall chemical composition, HCV may be useful for predicting BMP.

Enhanced methane production by semi-continuous mesophilic co-digestion of potato waste and cabbage waste: Performance and microbial characteristics analysis

Anaerobic granular sludge was used as an inoculum for co-digestion of potato waste (PW) and cabbage waste (CW) in batch and semi-continuous modes at 37±1°C for enhanced methane generation. Batch test results indicated that an equal proportion (1:1) by volatile solid was the optimal mixing ratio for co-digestion of PW and CW. Semi-continuous co-digestion process results showed that the stepwise increasing of the organic loading rates from 1.0 to 5.0kgVS/m³·d improved the methane yield from 224 to 360mL/g-VS. And the highest value was respectively 18.4% and 24.1% higher as compared to the mon-digestion of PW and CW. Further investigation with high-throughput sequencing analysis revealed that the enhanced methane generation was attributed to the partial shift from archaeal Methanosaeta to Methanosarcina and Methanobacterium, and from bacterial Firmicutes to Bacteroidetes and Proteobacteria. The volatile fatty acids concentration accounted for the modification of microbial communities.

Combined effect of crude fat content and initial substrate concentration on batch anaerobic digestion characteristics of food waste

The mesophilic anaerobic digestion (AD) characteristics of food waste (FW) with different crude fat (CF) contents and four initial substrate concentrations (4, 6, 8, and 10gVS/L) were investigated. The maximum methane yields of FW with CF contents of 15%, 20%, 25%, 30%, and 35% were 565.0, 580.2, 606.0, 630.2 and 573.0mLCH₄/gVS_added, respectively. An acidification trend with a drop in pH (<6.80) and increase in the volatile fatty acids/total inorganic carbon (VFAs/TIC) ratio (>0.4) were found for CF contents of 30% (10gVS/L) and 35% (8 and 10gVS/L). A 35% CF content in FW led to decrease in the first-order degradation constant of approximately by 40%. The modified Gompertz model showed that the lag phase (λ) was prolonged from 0.4 to 7.1days when the CF content in FW and initial substrate concentration were increased to 35% and 10gVS/L.

Characterization of food waste-recycling wastewater as biogas feedstock

A set of experiments was carried out to characterize food waste-recycling wastewater (FRW) and to investigate annual and seasonal variations in composition, which is related to the process operation in different seasons. Year-round samplings (n=31) showed that FRW contained high chemical oxygen demand (COD; 148.7±30.5g/L) with carbohydrate (15.6%), protein (19.9%), lipid (41.6%), ethanol (14.0%), and volatile fatty acids (VFAs; 4.2%) as major constituents. FRW was partly (62%) solubilized, possibly due to partial fermentation of organics including carbohydrate. Biodegradable portions of carbohydrate and protein were estimated from acidogenesis test by first-order kinetics: 72.9±4.6% and 37.7±0.3%, respectively. A maximum of 50% of the initial organics were converted to three major VFAs, which were acetate, propionate, and butyrate. The methane potential was estimated as 0.562L CH4/g VSfeed, accounting for 90.0% of the theoretical maximum estimated by elemental analysis.

Sequential parametric optimization of methane production from different sources of forest raw material

The increase in environmental problems and the shortage of fossil fuels have led to the need for action in the development of sustainable and renewable fuels. Methane is produced through anaerobic digestion of organic materials and is a biofuel with very promising characteristics. The success in using methane as a biofuel has resulted in the operation of several commercial-scale plants and the need to exploit novel materials to be used. Forest biomass can serve as an excellent candidate for use as raw material for anaerobic digestion. During this work, both hardwood and softwood species-which are representative of the forests of Sweden-were used for the production of methane. Initially, when untreated forest materials were used for the anaerobic digestion, the yields obtained were very low, even with the addition of enzymes, reaching a maximum of only 40 mL CH4/g VS when birch was used. When hydrothermal pretreatment was applied, the enzymatic digestibility improved up to 6.7 times relative to that without pretreatment, and the yield of methane reached up to 254 mL CH4/g VS. Then the effect of chemical/enzymatic detoxification was examined, where laccase treatment improved the methane yield from the more harshly pretreated materials while it had no effect on the more mildly pretreated material. Finally, addition of cellulolytic enzymes during the digestion improved the methane yields from spruce and pine, whereas for birch separate saccharification was more beneficial. To achieve high yields in spruce 30 filter paper units (FPU)/g was necessary, whereas 15 FPU/g was enough when pine and birch were used. During this work, the highest methane yields obtained from pine and birch were 179.9 mL CH4/g VS and 304.8 mL CH4/g VS, respectively. For mildly and severely pretreated spruce, the methane yields reached 259.4 mL CH4/g VS and 276.3 mL CH4/g VS, respectively. We have shown that forest material can serve as raw material for efficient production of methane. The initially low yields from the untreated materials were significantly improved by the introduction of a hydrothermal pretreatment. Moreover, enzymatic detoxification was beneficial, but mainly for severely pretreated materials. Finally, enzymatic saccharification increased the methane yields even further.

Anaerobic co-digestion of forage radish and dairy manure in complete mix digesters

Pilot-scale digesters (850 L) were used to quantify CH4 and H2S production when using forage radish cover crops as a co-digestion feedstock in dairy manure-based digesters. During two trials, triplicate mixed digesters were operated in batch mode with manure-only or radish+manure (27% and 13% radish by wet weight in Trial 1 and 2, respectively). Co-digestion increased CH4 production by 11% and 39% in Trial 1 and 2, respectively. As H2S production rapidly declined in the radish+manure digesters, CH4 production increased reaching high levels of CH4 (⩾67%) in the biogas. Over time, radish co-digestion lowered the H2S concentration in the biogas (0.20%) beyond that of manure-only digestion (0.34-0.40%), although cumulative H2S production in the radish+manure digesters was higher than manure-only. Extrapolated to a farm-scale (200 cows) continuous mixed digester, co-digesting with radish could generate 3150 m(3) CH4/month, providing a farmer additional revenue up to $3125/month in electricity sales.

Anaerobic co-digestion of kitchen waste and fruit/vegetable waste: lab-scale and pilot-scale studies

The anaerobic digestion performances of kitchen waste (KW) and fruit/vegetable waste (FVW) were investigated for establishing engineering digestion system. The study was conducted from lab-scale to pilot-scale, including batch, single-phase and two-phase experiments. The lab-scale experimental results showed that the ratio of FVW to KW at 5:8 presented higher methane productivity (0.725 L CH4/g VS), and thereby was recommended. Two-phase digestion appeared to have higher treatment capacity and better buffer ability for high organic loading rate (OLR) (up to 5.0 g(VS) L(-1) d(-1)), compared with the low OLR of 3.5 g(VS) L(-1) d(-1) for single-phase system. For two-phase digestion, the pilot-scale system showed similar performances to those of lab-scale one, except slightly lower maximum OLR of 4.5 g(VS) L(-1) d(-1) was allowed. The pilot-scale system proved to be profitable with a net profit of 10.173$/ton as higher OLR (⩾ 3.0 g(VS) L(-1) d(-1)) was used.

Anaerobic digestion of Chinese cabbage waste silage with swine manure for biogas production: batch and continuous study

The aim of this study was to investigate the potential for anaerobic co-digestion of Chinese cabbage waste silage (CCWS) with swine manure (SM). Batch and continuous experiments were carried out under mesophilic anaerobic conditions (36-38°C). The batch test evaluated the effect of CCWS co-digestion with SM (SM: CCWS=100:0; 25:75; 33:67; 0:100, % volatile solids (VS) basis). The continuous test evaluated the performance of a single stage completely stirred tank reactor with SM alone and with a mixture of SM and CCWS. Batch test results showed no significant difference in biogas yield up to 25-33% of CCWS; however, biogas yield was significantly decreased when CCWS contents in feed increased to 67% and 100%. When testing continuous digestion, the biogas yield at organic loading rate (OLR) of 2.0 g VSL⁻¹ d⁻¹ increased by 17% with a mixture of SM and CCWS (SM:CCWS=75:25) (423 mL g⁻¹ VS) than with SM alone (361 mL g⁻¹ VS). The continuous anaerobic digestion process (biogas production, pH, total volatile fatty acids (TVFA) and TVFA/total alkalinity ratios) was stable when co-digesting SM and CCWS (75:25) at OLR of 2.0 g VSL⁻¹ d⁻¹ and hydraulic retention time of 20 days under mesophilic conditions.

Evaluation of dried sweet sorghum stalks as raw material for methane production

The potential of utilizing dried sweet sorghum stalks as raw material for anaerobic digestion has been evaluated. Two different treatments were tested, a mild thermal and an enzymatic, alone or in combination. Thermal pretreatment was found to decrease the methane yields, whereas one-step enzymatic treatment resulted in a significant increase of 15.1% comparing to the untreated sweet sorghum. Subsequently, in order to increase the total methane production, the combined effect of enzyme load and I/S on methane yields from sweet sorghum was evaluated by employing response surface methodology. The obtained model showed that the maximum methane yield that could be achieved is 296 mL CH₄/g VS at I/S ratio of 0.35 with the addition of 11.12 FPU/g sweet sorghum.