Mesophilic anaerobic digestion of corn thin stillage: a technical and energetic assessment of the corn‐to‐ethanol industry integrated with anaerobic digestion

BACKGROUND: The purpose of this study was to reduce the VS (volatile solid) and recover energy (methane) from thin stillage through mesophilic anaerobic digestion in corn–ethanol plants. The performance of a continuously stirred tank reactor (CSTR) with different hydraulic retention times (HRTs) was evaluated in this study. RESULTS: The results show no differences in volatile solid (VS) destruction (82–83%) in the reactor with HRTs ranging from 25 to 40 days. The maximum volumetric methane production rate of 1.41 L L^?1 day^?1 was produced at 25‐day HRT, whereas the maximum methane yield of approximately 0.63 L CH₄ g^?1 VS_fed (0.77 L g^?1 VS_removed) was achieved with HRTs between 30 and 40 days. Simulation results using a kinetic model indicate that the reactor needs to be operated for longer than 23 days in order to achieve 80% of maximum methane yield. The techno‐economic potential of a corn–ethanol facility to produce an estimated 57% energy recovery using mesophilic anaerobic digestion has long been overlooked. A corn–ethanol plant integrated with mesophilic anaerobic digestion increases the net energy balance ratio from 1.26 to 1.80. CONCLUSION: Mesophilic anaerobic digestion complements the corn–ethanol business so that the sustainable energy obtained from corn recovery is made more lucrative and renewable. Copyright © 2011 Society of Chemical Industry     

Effects of bioaugmentation by an anaerobic lipolytic bacterium on anaerobic digestion of lipid‐rich waste

The effect of bioaugmentation with an anaerobic lipolytic bacterial strain on the anaerobic digestion of restaurant lipid‐rich waste was studied in batch experiments with a model waste containing 10% lipids (triolein) under two sets of experimental conditions: (A) methanogenic conditions, and (B) initially acidogenic conditions in the presence of only the lipolytic strain biomass (4 days), followed by methanogenic conditions. The bioaugmenting lipolytic strain, Clostridium lundense (DSM 17049^T), was isolated from bovine rumen. The highest lipolytic activity was detected at the beginning of the experiments. A higher methane production rate, 27.7 cm³ CH_4(STP) g^?1 VS_added day^?1 (VS, volatile solids) was observed in experiment A with the presence of the bioaugmenting lipolytic strain under methanogenic conditions. The highest initial oleate concentration, 99% of the total oleate contained in the substrate, was observed in the experiments with the bioaugmenting lipolytic strain under treatment A conditions; the levels of palmitate and stearate were also higher until day 15, indicating that the bioaugmentation strategy improved the hydrolysis of the lipid fraction. In general, the results indicated that degradation of the long chain fatty acids (LCFAs) controlled the digestion process. Copyright © 2006 Society of Chemical Industry     

Statistical optimization of mixture ratio and particle size for dry co-digestion of food waste and manure by response surface methodology

Response surface methodology has been widely applied to optimize the process. However, it was rarely applied to dry digestion. We used central composite design to optimize the anaerobic dry co-digestion of food waste and manure. Mixture ratio and particle size of food waste and manure were selected as independent variables, and target surface response was the methane production yield (MPY). BMP tests were conducted, and MPY was fitted by a secondorder polynomial quadratic model, which was found to be significant with higher coefficient (R²=0.98). As results of F-value analysis, the mixture ratio was found to be more important than particle size. Finally, the optimum conditions of mixture ratio (food waste:manure=5.79: 4.21) corresponding to 15.6 of C/N ratio and particle size 1.12 cm were determined. In addition, 313mL CH4/g VS _added of MPY was anticipated under optimum conditions with 94.4% of desirability.     

Biochemical methane potential (BMP) of solid organic substrates: evaluation of anaerobic biodegradability using data from an international interlaboratory study

BACKGROUND: This paper describes results obtained for different participating research groups in an interlaboratory study related to biochemical methane potential (BMP). In this research work, all experimental conditions influencing the test such as inoculum, substrate characteristics and experimental conditions were investigated. The study was performed using four substrates: three positive control substrates (starch, cellulose and gelatine), and one raw biomass material (mung bean) at two different inoculum to substrate ratios (ISR). RESULTS: The average methane yields for starch, cellulose, gelatine and mung bean at ISR of 2 and 1 were 350 ± 33, 350 ± 29, 380 ± 42, 370 ± 36 and 370 ± 35 mL CH₄ g^?1 VS_added, respectively. The percentages of biotransformation of these substrates into methane were 85 ± 8, 85 ± 7, 88 ± 9, 85 ± 8 and 85 ± 8%, respectively. On the other hand, the first‐order rate constants obtained from the experimental data were 0.24 ± 0.14, 0.23 ± 0.15, 0.27 ± 0.13, 0.31 ± 0.17 and 0.23 ± 0.13 d^?1, respectively. CONCLUSION: The influence of inocula and experimental factors was nearly insignificant with respect to the extents of the anaerobic biodegradation, while the rates differed significantly according to the experimental approaches. Copyright © 2011 Society of Chemical Industry     

Effects of chemical and thermochemical pretreatments on sunflower oil cake in biochemical methane potential assays

BACKGROUND: The effects of chemical and thermochemical pretreatments on the composition and anaerobic biodegradability of sunflower oil cake were studied to compare these pretreatments and to assess their effectiveness. Four reagents (lime, sodium hydroxide, sulphuric acid, and sodium bicarbonate) at concentrations of 25% (w/w) of dry weight of substrate and 20 g L^?1 substrate concentration were used for the chemical pretreatment for 4 h. The same conditions were used for thermochemical pretreatment with heating at 75°C. After the pretreatments, the solid and liquid fractions were separated and subjected to biochemical methane potential tests. RESULTS: The methane yields of the solid fraction obtained with lime, sodium hydroxide, sulphuric acid and bicarbonate were 130±9, 54±4, 61±6 and 88±7 mL CH₄ g^‐1COD_added, respectively, and after thermochemical pretreatment were 26±2, 84±7, 74±7, and 77±6 mL CH₄ g^‐1COD_added, respectively. The methane yields for liquids were 152±13, 2±0, 0±0, 249±19 mL CH₄ g^‐1COD_added, for the chemical pre‐treatment, respectively, and after the thermochemical pretreatment were 273±13, 58±5, 0±0 and 145±12 mL CH₄ g^‐1COD_added, respectively. CONCLUSION: Only the solid fraction obtained after the chemical pretreatment with lime gave a methane yield higher (130 mL CH₄ g^‐1COD_added) than the obtained for the untreated solid material (114 mL CH₄ g^‐1COD_add). No thermochemical pretreatment enhanced the methane yield of the solid or liquid fractions of the untreated material. © 2012 Society of Chemical Industry     

Straw bed priming enhances the methane yield and speeds up the start‐up of single‐stage,high‐solids anaerobic reactors treating plant biomass

A simple and potentially inexpensive implementation of a high‐solids reactor is a single‐stage, stratified bed reactor, in which the bed is made up of the plant biomass fed into the system. In the present study, the stratified bed was started up for a period of four weeks by either direct feeding of sugar beet leaves at four different feeding rates, or by introducing a straw bed primer which was batch digested without feeding. During weeks five to six both systems were fed with sugar beet leaves at such a rate that the total amount of beet leaves added at the end of week six was the same in each of the four corresponding pairs of straw and ‘no‐straw’ reactors. Straw bed priming enhanced the methane yield of the sugar beet leaves, with 0.33–0.37 m³ kg^?1 VS_added (volatile solids) accumulated at average solid retention times as short as 11–25 days, while the ‘no‐straw’ reactors had lower yields at longer average solid retention times. The levels and speciation of the organic acids suggested that both the rate and extent of the anaerobic digestion of the sugar beet leaves added in the straw reactors were improved. At the highest loading rate, the straw reactor failed, while the ‘no‐straw’ reactor did not. It is hypothesised that the microbial biomass was better established in the straw reactors than in the ‘no‐straw’ reactors. Copyright © 2006 Society of Chemical Industry     

Methane production from citrus wastes: process development and cost estimation

BACKGROUND: Because of its extreme toxicity for microorganisms, the limonene content of citrus wastes (CWs) has been a major obstacle to the conversion of CWs to biofuels. The main objective of this study was to develop a new process for the utilization of CWs that can be economically feasible when the supply of CW is low. RESULTS: Steam explosion pre‐treatment was applied to improve the anaerobic digestibility of CWs, resulting in a decrease of initial limonene concentration by 94.3%. A methane potential of 0.537 ± 0.001 m³ kg^?1 VS (volatile solids) was obtained during the following batch digestion of treated CWs, corresponding to an increase of 426% compared with that of the untreated samples. Long‐term effects of the treatment were further investigated by a semi‐continuous co‐digestion process. A methane production of 0.555 ± 0.0159 m³ CH₄ kg^?1 VS day^?1 was achieved when treated CWs (corresponding to 30% of the VS load) were co‐digested with municipal solid waste. CONCLUSION: The process developed can easily be applied to an existing biogas plant. The equipment cost for this process is estimated to be one million USD when utilizing 10 000 tons CWs year^?1. 8.4 L limonene and 107.4 m³ methane can be produced per ton of fresh citrus wastes in this manner. Copyright © 2011 Society of Chemical Industry     

Assessment of solid retention time of a temperature phased anaerobic digestion system on performance and final sludge characteristics

BACKGROUND: This paper describes the results obtained during the thermophilic/mesophilic temperature phased anaerobic digestion (TPAD) of sewage sludge on a pilot scale. The aim of this research study was not only to optimize the anaerobic digestion process, but also to obtain a digested sludge suitable for agricultural applications according to the legal requirements. RESULTS: Four TPAD assays were carried out: 5/15, 3/15, 3/12 and 3/9 (days/days of solid retention time) with a specific methane production (expressed as LCH₄ g^?1 VS_destroyed) of 0.77, 0.83, 0.66 and 0.20, respectively. TPAD 3/15 and 3/12 reached pathogen concentrations of less than 1000 MPN g^?1 TS (faecal colifoms) and 3 MPN per 4 g TS (Salmonella spp.); therefore, these digested sludges can be considered Class A biosolids, according to the US Environmental Protection Agency. Concentrations of heavy metals rose after the anaerobic digestion of mixed sludge, but the final values were always below the limits required by legal regulations. CONCLUSION: TPAD 3/15 is the best option in terms of organic matter removal, CH₄ generation, and process stability. TPAD 3/12 obtained the best final dewaterability and pathogen reduction and in general, showed much better results than those obtained by anaerobic mesophilic control (15 days of SRT). Copyright © 2012 Society of Chemical Industry     

The effect of organic loading rate on the anaerobic digestion of two‐phase olive mill solid residue derived from fruits with low ripening index

A study of the effect of organic loading rate on the performance of anaerobic digestion of two‐phase olive mill solid residue (OMSR) was carried out in a laboratory‐scale completely stirred tank reactor. The reactor was operated at an influent substrate concentration of 162 g chemical oxygen demand (COD) dm^?3. The organic loading rate (OLR) varied between 0.8 and 11.0 g COD dm^?3 d^?1. COD removal efficiency decreased from 97.0% to 82.6% when the OLR increased from 0.8 to 8.3 g COD dm^?3 d^?1. It was found that OLRs higher than 9.2 g COD dm^?3 d^?1 favoured process failure, decreasing pH, COD removal efficiency and methane production rates (Q_M). Empirical equations described the effect of OLR on the process stability and the effect of soluble organic matter concentration on the total volatile fatty acids (TVFA)/total alkalinity (TAlk) ratio (ρ). The results obtained demonstrated that rates of substrate uptake were correlated with concentration of biodegradable COD, through an equation of the Michaelis–Menten type. The kinetic equation obtained was used to simulate the anaerobic digestion process of this residue and to obtain the theoretical COD degradation rates in the reactor. The small deviations obtained (equal to or lower than 10%) between values calculated through the model and experimental values suggest that the proposed model predicts the behaviour of the reactor accurately. Copyright © 2007 Society of Chemical Industry     

Synthesis and biological activity of phthalimide‐based polymers containing 5‐fluorouracil

The attachment of anticancer agents to polymers is a promising approach towards reducing the toxic side‐effects and retaining the potent antitumour activity of these agents. A new tetrahydrophthalimido monomer containing 5‐fluorouracil (ETPFU) and its homopolymer and copolymers with acrylic acid (AA) and with vinyl acetate (VAc) have been synthesized and spectroscopically characterized. The ETPFU contents in poly(ETPFU‐co‐AA) and poly(ETPFU‐co‐VAc) obtained by elemental analysis were 21 mol% and 20 mol%, respectively. The average molecular weights of the polymers determined by gel permeation chromatography were as follows: M_n = 8900 g mol^?1, M_w = 13 300 g mol^?1, M_w/M_n = 1.5 for poly(ETPFU); M_n = 13 500 g mol^?1, M_w = 16 600 g mol^?1, M_w/M_n = 1.2 for poly(ETPFU‐co‐AA); M_n = 8300 g mol^?1, M_w = 11 600 g mol^?1, M_w/M_n = 1.4 poly(ETPFU‐co‐VAc). The in vitro cytotoxicity of the compounds against FM3A and U937 cancer cell lines increased in the following order: ETPFU > 5‐FU > poly(ETPFU) > poly(ETPFU‐co‐AA) > poly(ETPFU‐co‐VAc). The in vivo antitumour activities of all the polymers in Balb/C mice bearing the sarcoma 180 tumour cell line were greater than those of 5‐FU and monomer at the highest dose (800 mg kg^?1). © 2002 Society of Chemical Industry     

Synthesis and biological activity of medium range molecular weight polymers containing exo‐3,6‐epoxy‐1,2,3,6‐tetrahydrophthalimidocaproic acid

A new monomer, exo‐3,6‐epoxy‐1,2,3,6‐tetrahydrophthalimidocaproic acid (ETCA), was prepared by reaction of maleimidocaproic acid and furan. The homopolymer of ETCA and its copolymers with acrylic acid (AA) or with vinyl acetate (VAc) were obtained by photopolymerizations using 2,2‐dimethoxy‐2‐phenylacetophenone as an initiator at 25 °C. The synthesized ETCA and its polymers were identified by FTIR, ¹H NMR and ¹³C NMR spectroscopies. The apparent average molecular weights and polydispersity indices determined by gel permeation chromatography (GPC) were as follows: M_n = 9600 g mol^?1, M_w = 9800 g mol^?1, M_w/M_n = 1.1 for poly(ETCA); M_n = 14 300 g mol^?1, M_w = 16 200 g mol^?1, M_w/M_n = 1.2 for poly(ETCA‐co‐AA); M_n = 17 900 g mol^?1, M_w = 18 300 g mol^?1, M_w/M_n = 1.1 for poly(ETCA‐co‐VAc). The in vitro cytotoxicity of the synthesized compounds against mouse mammary carcinoma and human histiocytic lymphoma cancer cell lines decreased in the following order: 5‐fluorouracil (5‐FU) ≥ ETCA > polymers. The in vivo antitumour activity of the polymers against Balb/C mice bearing sarcoma 180 tumour cells was greater than that of 5‐FU at all doses tested. © 2001 Society of Chemical Industry     

Mesophilic and Thermophilic Anaerobic Digestion of Model Kitchen Waste with Variation of Fat Content

Anaerobic digestion of model kitchen waste (MKW) produced on basis of real kitchen waste (KW) is studied in batch tests. The impact of fat content of three MKWs (14.7 %, 23 %, and 27.2 % rapeseed oil content) on the biogas production at mesophilic and thermophilic conditions and two loadings is examined. The loading of 5 g_VSL⁻¹ leads to fast degradation under both temperature modes and the volume of biogas produced is only weakly correlated to the oil content. For the loading of 25 g_VSL⁻¹ a strong retardation of biogas production, high concentration of volatile fatty acids and no correlation of oil content is observed.     

Restriction of linoleic acid inhibition of methanization of piggery wastewater and enhancement of its mineralization by adding calcium ions

BACKGROUND: Linoleic acid, which is a major derivative generated from hydrolysis of vegetable oils, is often found at high concentration in food processing and kitchen wastes. This fatty acid could be introduced into an anaerobic system treating piggery wastewater via co‐digestion strategy. In this study, the effect of CaCl₂ on the inhibitory behavior of linoleic acid in the anaerobic digestion of piggery wastewater was investigated. RESULTS: Linoleic acid exerted strong inhibitory effects on methanization of piggery wastewater with IC₅₀ of 376 mg L^?1 and 568 mg L^?1 for ISR (inoculum substrate ratio) 0.38 and 2.0, respectively. Among tested cations (Na⁺, Mg²⁺, Ca²⁺, Al³⁺ and Fe³⁺), only Ca²⁺ effectively reversed linoleic acid inhibition. In addition, it was found that CaCl₂ restricted linoleic acid inhibition only when it was added before or immediately after linoleic acid addition. Without CaCl₂, linoleic acid was stoichiometrically transformed to oleic acid, which persisted for a prolonged period. In the presence of CaCl₂, however, linoleic acid was completely converted to methane without accumulation of oleic acid. It was also found that oleic acid was self‐inhibitory to its oxidation to acetate, and CaCl₂ removed this inhibition. CONCLUSION: From these findings, it was concluded that calcium ion not only mitigated linoleic acid inhibition in the anaerobic digestion of piggery wastewater, but also enhanced its mineralization to methane. Copyright © 2010 Society of Chemical Industry     

Algorithms for calculating methane and nitrous oxide emissions from manure management

Biogenic emissions of methane (CH₄) and nitrous oxide (N₂O) from animal manure are stimulated by the degradation of volatile solids (VS) which serves as an energy source and a sink for atmospheric oxygen. Algorithms are presented which link carbon and nitrogen turnover in a dynamic prediction of CH₄ and N₂O emissions during handling and use of liquid manure (slurry). A sub-model for CH₄ emissions during storage relates CH₄ emissions to VS, temperature and storage time, and estimates the reduction in VS. A second sub-model estimates N₂O emissions from field-applied slurry as a function of VS, slurry N and soil water potential, but emissions are estimated using emission factors. The model indicated that daily flushing of slurry from cattle houses would reduce total annual CH₄ + N₂O emissions by 35% (CO₂ eq.), and that cooling of pig slurry in-house would reduce total annual CH₄ + N₂O emissions by 21% (CO₂ eq.). Anaerobic digestion of slurry and organic waste produces CH₄ at the expense of VS. Accordingly, the model predicted a 90% reduction of CH₄ emissions from outside stores with digested slurry, and a >50% reduction of N₂O emissions after spring application of digested as opposed to untreated slurry. The sensitivity of the model towards storage temperature and soil water potential was examined. This study indicates that simple algorithms to account for ambient climatic conditions may significantly improve the prediction of CH₄ and N₂O emissions from animal manure.     

Influence of ionic liquid composition on the stability of polyvinyl chloride‐based ionic liquid inclusion membranes in aqueous solution

Membrane technology has gained significant importance with the incorporation of ionic liquids into their structure. This work shows the influence of ionic liquid composition on the stability of PVC‐based polymer ionic liquid inclusion membranes (PILIMs) in aqueous solution. Among the ILs investigated, those membranes which contain between 20 and 30%_w/w of the least soluble, [OMIM⁺][PF₆^?] and [OMIM⁺][Ntf₂^?], exhibit losses of IL lower than 10%. For both ILs, the amount immobilized was maximum for the membranes with 30%_w/w of IL (0.0838 and 0.0832 g, respectively). On the contrary, the ionic liquid loss increases as its solubility in water increase, reaching 99.52% when PILIMs are prepared with 70%_w/w of [OMIM⁺][BF₄^?]. The results demonstrate that the stability of PILIMs depends on the solubility of the IL in the surrounding phase and the specific interaction between the IL and the polymeric support for PVC‐to‐IL ratios higher than 30%_w/w. © 2016 American Institute of Chemical Engineers AIChE J, 63: 770–780, 2017     

Osmoprotectants enhance methane production from the anaerobic digestion of food wastes containing a high content of salt

BACKGROUND: Treatment and disposal of Korean food waste encounter technical difficulties due to a high‐salt problem. In order to increase methane production from food waste by using osmoprotectants, which are known to overcome osmotic stresses in many plants and other organisms, osmoprotectants including glycine betaine, choline, carnitine and trehalose were added to salt‐containing food wastes for anaerobic digestion. RESULTS: For NaCl‐amended food wastes containing 10 and 35 g L^?1 NaCl, glycine betaine and choline increased methane production by about twofold compared to food waste without any osmoprotectants. For non‐washed food waste containing 11.6 g L^?1 NaCl, glycine betaine increased methane production by about sixfold. Among these osmoprotectants, glycine betaine was the most effective for increasing methane productivity in anaerobic digestion of food waste with salinity. Analysis of glycine betaine in cell extracts using high‐performance liquid chromatography showed that glycine betaine accumulated in the cells of anaerobic sludge. CONCLUSION: Osmoprotectants significantly enhanced methanization of high‐salt food wastes by alleviating the salt‐induced physiological stresses in microorganisms. The application of osmoprotectants provided an effective substitute for other conventional methods to reduce inhibitory effects of high salt, such as dilution and co‐digestion. Copyright © 2008 Society of Chemical Industry     

Preparation and characterization of modified poly(m‐phenylene terephthalamide) and its fiber

Modified poly(m ‐phenylene terephthalamide) (co ‐PMTA₃ ) was prepared by polycondensation of m ‐phenylenediamine, 4,4′‐diaminodiphenylsulfone and terephthaloyl dichloride with an initial feed mole ratio of 3:1:4 in N ,N ′‐dimethylacetamide (DMAc ). The co ‐PMTA₃ was dissolved in DMAc and then spun into fiber via wet spinning. The properties of co ‐PMTA₃ pulp and fiber were investigated using ¹H NMR spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, X‐ray diffraction, sonic velocity meter measurements and thermomechanical analysis. The results indicate that co ‐PMTA₃ has excellent heat resistance with a softening temperature of 323.6 °C. The co ‐PMTA₃ fiber has high strength with a breaking strength of 4.7 cN dtex^?1 and a knot tenacity of 2.2 cN dtex^?1. © 2017 Society of Chemical Industry     

Lipase‐catalyzed esterification of cinnamic acid and oleyl alcohol in organic solvent media

The esterification of cinnamic acid (CA) and oleyl alcohol (OA) in organic solvent media by immobilized lipase Novozym 435 was optimized in terms of selected parameters, including the logarithm of the 1‐octanol/water partition coefficient of the organic solvent (log P, 0.29–4.5), initial water activity (a_w, 0.05–0.75), agitation speed (0–200 rpm), temperature (35–65 °C) and ratio of substrates (CA/OA, 1.0:0.5–1.0:6.0). The results showed that the more hydrophobic solvent mixtures and lower initial a_w values resulted in a higher enzymatic activity and bioconversion yield. The most appropriate solvent medium and initial a_w value was the mixture of iso‐octane/2‐butanone (85:15, v/v) and 0.05, respectively. The results also showed that an agitation speed of 150 rpm and a reaction temperature of 55 °C were optimal for the reaction system. The activation energy (E_a) of the esterification reaction was calculated as 43.6 kJ mol^?1. The optimal ratio of CA to OA was 1.0:6.0, with the absence of any inhibition by OA. Using the optimized conditions, the maximum enzymatic activity was 390.3 nmol g^?1 min^?1, with a bioconversion yield of 100% after 12 days of reaction. In addition, the electrospray ionization‐mass spectroscopy analysis confirmed that the major end product of the esterification reaction was oleyl cinnamate. Copyright © 2005 Society of Chemical Industry     

Toughening of cyanate ester resin by N‐phenylmaleimide–N‐(p‐hydroxy)phenyl‐maleimide–styrene terpolymers and their hybrid modifiers

N‐Phenylmaleimide–N‐(p‐hydroxy)phenylmaleimide–styrene terpolymer (HPMS), carrying reactive p‐hydroxyphenyl groups, was prepared and used to improve the toughness of cyanate ester resins. Hybrid modifiers composed of N‐phenylmaleimide–styrene copolymer (PMS) and HPMS were also examined for further improvement in toughness. Balanced properties of the modified resins were obtained by using the hybrid modifiers. The morphology of the modified resins depends on HPMS structure, molecular weight and content, and hybrid modifier compositions. The most effective modification of the cyanate ester resin was attained because of the co‐continuous phase structure of the modified resin. Inclusion of the modifier composed of 10 wt% PMS (M_w 136 000 g mol^?1) and 2.5 wt% HPMS (hydroxyphenyl unit 3 mol%, M_w 15 500 g mol^?1) led to 135% increase in the fracture toughness (K_IC) for the modified resin with a slight loss of flexural strength and retention of flexural modulus and glass transition temperature, compared with the values for the unmodified resin. Furthermore, the effect of the curing conditions on the mechanical and thermal properties of the modified resins was examined. The toughening mechanism is discussed in terms of the morphological and dynamic viscoelastic behaviour of the modified cyanate ester resin system. © 2001 Society of Chemical Industry     

Improving conversion of Spartina alterniflora into biogas by co-digestion with cow feces

Anaerobic mono-digestion of Spartina alterniflora (S. alterniflora) at initial volatile solid loading (VSL) of 4.0%, 6.0% and 8.0% as well as co-digestion of S. alterniflora and cow feces at cow feces proportions from 12.5% to 87.5% of volatile solid (VS) were investigated. A maximum methane yield of 0.19 L CH₄/g VS_added from mono-digestion of S. alterniflora was obtained at initial VSL of 6.0% and the average methane content was 63.29%. Furthermore, co-digestion of S. alterniflora and cow feces in varying proportions was investigated at constant initial VSL of 7.0%. The addition of cow feces decreased the carbon-to-nitrogen (C/N) ratio from 21.82 to 14.19 in the feedstock. Co-digestion improved the biodegradability of S. alterniflora, and thus increased the methane yield by 7.09-44.26%, leading to a lower volatile fatty acid (VFA) concentration of less than 800 mg/L (only about one third of S. alterniflora digested alone ) in the solution and higher pH value in comparison to S. alterniflora digested alone. Although the VFA concentration was lower than S. alterniflora digested alone, the biogas yield was increased and the biogas yield peak was advanced for about 15 days.