Effect Of Hydrothermal Pretreatment Research Articles

Effects of Hydrothermal Pretreatment and Anaerobic Digestion of Pig Manure on the Antibiotic Removal and Methane Production.

Whether advanced biological waste treatment technologies, such as hydrothermal pretreatment (HTP) integrated anaerobic digestion (AD), could enhance the removal of different antibiotics remains unclear. This study investigated the outcome of antibiotics and methane productivity during pig manure treatment via HTP, AD, and HTP + AD. Results showed improved removal efficiency of sulfadiazine (SDZ), oxytetracycline (OTC), and enrofloxacin (ENR) with increased HTP temperatures (70, 90, 120, 150, and 170°C). OTC achieved the highest removal efficiency of 86.8% at 170°C because of its high sensitivity to heat treatment. For AD, SDZ exhibited resistance with a removal efficiency of 52.8%. However, OTC and ENR could be removed completely within 30days. When HTP was used prior to AD, OTC and ENR could achieve complete removal. However, residual SDZ levels reduced to 20% and 16% at 150 and 170°C, respectively. The methanogenic potential showed an overall upward trend as the HTP temperature increased. Microbial analysis revealed the antibiotics-induced enrichment of specific microorganisms during AD. Firmicutes were the dominant bacterial phylum, with their abundance positively correlated with the addition of antibiotics. Methanobacterium and Methanosarcina emerged as the dominant archaea that drove methane production during AD. Thus, HTP can be a potential pretreatment before AD to reduce antibiotic-related risks in manure waste handling.

Component Analysis of Corncob After Hydrothermal Treatment

Hydrothermal pretreatment is a green pretreatment technology, which can effectively promote the degradation of biomass without adding any chemical reagent. In this study, hydrothermal pretreatment on improving digestibility of corncobs was investigated and the effect of hydrothermal pretreatment on changes of structure of the corncob lignocellulose was investigated. The composition and amounts of sugar content in hydrolysate and enzymatic hydrolysate were determined. Hydrothermal treatment destroyed the lignocellulose structure of corncob and caused different degrees of degradation. With the increasing temperature of hydrothermal treatment, the degradation of cellulose, hemicellulose and lignin in corncob was detected with increasing the content of reducing sugars in hydrolysate. The hydrolysate of corncob treated by hydrothermal treatment at 190 °C for 60 min mainly included glucose, xylobiose, xylotriose and xylotetraose. The content of glucose, xylobiose, xylotriose and xylotetraose in the hydrolysate of hydrothermal treatment corncob was at level of 0.001 mg • g−1, 16.740 mg • g−1, 4.306 mg • g−1 and 3.164 mg • g−1 respectively. The yield of glucose, xylobiose, xylotriose and xylotetraose in enzymatic hydrolysate were 4.771 mg • g−1, 64.437 mg • g−1, 6.853 mg • g−1 and 1.835 mg • g−1, respectively. The understanding will help to improve the conversion and utilization of corncob as an agriculture residue.

Effect of hydrothermal pre-treatment and development of non-stone chakki atta

Effect of hydrothermal pre-treatment and development of non-stone chakki atta

Pre-Treatment of Separately Collected Biowaste as a Way to Increase Methane Production and Digestate Stability

To produce a valuable final product from anaerobic digestion (AD), one of the preferred methods of organic recycling, high quality feedstock must be ensured. In this study, separately collected real biowaste (B) was used, consisting of 90% food waste and 10% green waste. The priority issues of AD are both high methane production (MP) and high organics removal efficiency (as organic matter, OM and dissolved organics, and DCOD), which may be improved after pre-treatment. In this study, the effect of hydrothermal pre-treatment (BHT) and enzymatic additives (BE) on MP and organics removal from biowaste in mesophilic (37 °C) conditions was analyzed. To assess the adequacy of pre-treatment application, biowaste without treatment (BWT) was used. Pre-treatment of biowaste prior to AD affected the maximal MP, the removal effectiveness of both OM and DCOD, and the kinetic parameters of these processes. For BWT, the maximal cumulative MP reached 239.40 ± 1.27 NL/kg OM; the kinetic coefficient of MP (kCH4) and the initial MP rate (rCH4) were 0.32 ± 0.02 d−1 and 76.80 ± 1.10 NL/(kg OM·d), respectively. After hydrothermal pre-treatment, the MP of BHT (253.60 ± 1.83 NL/kg OM) was 6.3% higher than BWT. However, the highest MP was found for BE, 268.20 ± 1.37 NL/kg OM; to compare, it increased by 12.1% and 5.5% with BWT and BHT, respectively. However, the kinetic parameters of MP were highest with BHT:kCH4 0.56 ± 0.02 d−1 vs. 0.32 ± 0.02 d−1 (BWT) and 0.34 ± 0.02 d−1 (BE); rCH4 141.80 ± 0.02 NL/(kg OM·d) (BHT) vs. 76.80 ± 1.10 NL/(kg OM·d) (BWT) and 89.80 ± 0.50 NL/(kg OM·d) (BE). The effectiveness of OM removal was highest with BE, similarly to the MP with the use of an enzymatic additive. The kinetics of OM removal (rOM, kOM) were highest with BHT, similarly to the kinetics of MP (rCH4, kCH4). The highest effectiveness of OM and, consequently, its lowest final content obtained with BE means that the organics were used most efficiently, which, in turn, may result in obtaining a more stable digestive system.

Effect of hydrothermal pretreatment on mercury removal performance of modified biochar prepared from corn straw

To further widen the specific surface area and enrich functional groups of biochar for improving the mercury removal performance, this paper compared the difference between wet impregnation and hydrothermal pretreatment to preload ferric chloride on active sites construction of biochar surface. Through systematically evaluating the physicochemical properties of biochar modified by various methods, the mechanism of mercury removal was analyzed. The results indicated that the hydrothermal pretreatment at 180 °C could widen the specific surface area of the precursor benefiting for modifiers adsorption and render the apparent activation energy reduced to 34.11 kJ/mol, causing more intense thermolysis reaction during carbonization. In this way, the specific surface of biochar reached to 282.4 m2/g and a more abundant porous structure was constructed. Additionally, after hydrothermal pretreatment, the proportion of chemisorbed oxygen and CO bonds on the surface of biochar was significantly promoted, facilitating the formation of HgO. The improvement of both physical structure and chemical properties of biochar together increases the mercury removal efficiency to over 90 % under the N2 atmosphere.

Effect of hydrothermal pretreatment and compound microbial agents on compost maturity and gaseous emissions during aerobic composting of kitchen waste

Though aerobic composting is commonly used in kitchen waste (KW) disposal, the high-oil and high-salt characteristics of KW could affect composting efficiency and lead to the land using risk of produced fertilizer. The impact of hydrothermal pretreatment (HTP) and addition of compound microbial agent (CMA) on compost maturity, greenhouse gas (GHGs) emissions and bacterial community during the kitchen waste composting were evaluated in the present work. Results indicated that N2O, CH4 and CO2 emissions from treatment by HTP and CMA addition were reduced by 82.72%, 13.77% and 20.78 %, respectively, comparing with the control (without HTP and without CMA addition). The seed germination index (GI) value of the HTP and CMA addition treatment was 1.03 and had the highest maturity in all treatments. Furthermore, the bacterial community analysis indicated that CMA inoculation could increase the relative abundance of genus Bacillus at the thermophilic stage of composting to accelerate organic biodegradation. This work provided important insight into mitigating GHGs emissions and improving compost quality in kitchen waste composting.

Comparative study on the properties of wood vinegar prepared from the pretreated Chinese fir: Effect of hydrothermal parameters and hydrogen peroxide

Hydrothermal (HT) pretreatment and hydrothermal oxidative (HO) pretreatment are efficient in upgrading the quality of wood vinegar (WV), while little research pays attention to the systemic comparison between the effects of HT and HO pretreatment on the resulted WV. Therefore, in the present study, the response surface method is adopted first to analyze the effect of HT temperature, solid-to-liquid ratio (S/L), and retention time on the physicochemical properties of WV prepared from Chinese fir (CF). Then, the main compositions (hemicellulose, cellulose, and lignin) of the pretreated CF are quantitatively measured, and the comparative study between the effects of HT pretreatment and HO pretreatment on the yield, density, and compositions of the resulted WV is carried out based on CF composition. The results show that HT temperature is the main parameter that affects the physicochemical properties of the resulted WV. With the increase of HT temperature, the cellulose content of CF samples increases first at 180–230 °C and then decreases at 260–280 °C, the hemicellulose content decreases, and the lignin enriches. The cellulose enrichment gives rise to the increasing WV yield at 180–200 °C and the increasing WV density at 180–230 °C. While the dramatic cellulose decomposition at 230–280 °C results in the decreasing WV yield at 230–280 °C and the decreasing WV density at 260–280 °C. The cellulose is the main component that contributes to the yield and density of WV. Moreover, due to the cellulose enrichment, the contents of the organic compounds, especially the phenols, ketones, and aldehydes, increase dramatically at 180–230 °C, contributing to the lower pH value of the resulted WV. However, HO pretreatment aggravates the decomposition of CF components. During HO pretreatment, the decreases in the hemicellulose content and cellulose content are advanced to 160–200 °C and 180–230 °C respectively, and the lignin content increases. Thus, WV with the comparable yield and density to the unpretreated WV can be prepared at HO pretreatment temperature of 160 °C. Moreover, the pH value of WV decreases significantly after HO pretreatment of 160–200 °C because of the existence of the acid compounds with higher acidity in the resulted WV. Meanwhile, the content of the aldehydes contained in WV prepared from HO pretreated CS increases dramatically.

Effect of Hydrothermal Pretreatment on Anaerobic Digestion of Erythromycin Fermentation Dregs: Biogas Production, Antibiotic Resistance Gene Evolution, and Microbial Community Dynamics

The utilization of erythromycin fermentation dregs (EFD), one kind of solid biowaste, is limited due to the high-level residue of antibiotics. Hydrothermal pretreatment (HT) has great potential to remove residual antibiotics. However, its harmless performance and influence on the EFD anerobic digestion (AD) process remains unclear. In this study, HT was conducted for erythromycin removal before EFD AD with the temperature ranging from 80 to 180°C. Moreover, changes in biogas yield, antibiotic resistance genes (ARGs), and microbial communities in the EFD AD process were compared among different treatments. The results showed that under the optimal hydrothermal temperature of 160°C, more than 85% of erythromycin was eliminated. In addition, HT significantly reduced the ARGs in the EFD AD process and ermT and mefA relative abundance decreased by one order of magnitude. Mobile genetic elements (IntI1 and Tn916/1545) also showed decreased tendency with the hydrothermal temperature elevation. The maximum methane production of 428.3 ml g−1 VS was obtained in the AD system of EFD with hydrothermal treatment at 160°C. It is attributed to the cooperation of hydrolysis and acidogenesis bacteria (e.g., Aminicenantales and Sedimentibacter) and methylotrophic methanogens (Candidatus_Methanofastidiosum and Methanosarcina), and they presented the highest relative abundance in this group. The results indicated that methylated substance reduction was the major methanogenesis route. Hydrothermal technology was of great potential to realize the harmless treatment of EFD and for recycling EFD via AD.

Hydrothermal pretreatment improves humification in co-composting of oil palm fronds and paper mill sludge

The co-composting of oil palm fronds and paper mill sludge may be economical and eco-friendly, yet the complex indigenous configuration of lignocellulose reduces the bioavailability of waste, resulting in the hindrance to the humification process. In this work, oil palm fronds after hydrothermal pretreatment were mixed with paper mill sludge for co-composting, and the effect of hydrothermal pretreatment on the humification process was explored using excitation-emission matrix-parallel factor analysis and 16S rDNA sequencing. The results showed that the duration of thermophilic phase was extended from 13 days to 17 days after hydrothermal pretreatment. During hydrothermal-pretreated composting, the consumption of protein-like substances and the production of humus-like substances increased by 24.7% and 33.9%, respectively, compared with those of control. The degradation of polysaccharide (decreased from 76.5 to 20.0 g/kg) was accelerated and the content of reducing sugar (ranged from 11.5 to 13.5 g/kg) was increased. The key microbial communities (including Bacillaceae, Sphingobacteriaceae, Streptosporangiaceae and Thermonosporaceae) showed obviously stronger activity. Correlation analysis showed that the production of reducing sugar and the activity of key microbial communities were reinforced, and both were favorable for the rapid synthesis of humus. Collectively, this work provides an overview of a regulatory mechanism underlying humus formation during the composting of lignocellulosic wastes.

Hydrothermal Pretreatment of Wheat Straw—Evaluating the Effect of Substrate Disintegration on the Digestibility in Anaerobic Digestion

The increasing demand for renewable energy sources and demand-oriented electricity provision makes anaerobic digestion (AD) one of the most promising technologies. In addition to energy crops, the use of lignocellulosic residual and waste materials from agriculture is becoming increasingly important. However, AD of such feedstocks is often associated with difficulties due to the high content of lignocellulose and its microbial persistence. In the present work, the effect of hydrothermal pretreatment (HTP) on the digestibility of wheat straw is investigated and evaluated. Under different HTP temperatures (160–180 °C) and retention times (15–45 min), a significant increase in biomethane potential (BMP) can be observed in all cases. The highest BMP (309.64 mL CH4 g−1 volatile solid (VS) is achieved after pretreatment at 160 °C for 45 min, which corresponds to an increase of 19% of untreated wheat straw. The results of a multiple linear regression model show that the solubilization of organic materials is influenced by temperature and time. Furthermore, using two different first-order kinetic models, an enhancement of AD rate during hydrolysis due to pretreatment is observed. However, the increasing intensity of pretreatment conditions is accompanied by a decreasing trend in the conversion of intermediates to methane.

Effect of hydrothermal and hydrothermal oxidation pretreatment on the physicochemical properties of biofuel pellet

The effects of hydrothermal pretreatment with and without H2O2 addition on the properties of the resulted biofuel pellets prepared from cotton stalk (CS) and Chinese fir wood sawdust (WS) were mainly studied in the paper. Based on the changes of three main components (hemicellulose, cellulose and lignin) of biomass during the pretreatment process, the relaxation density, compressive strength, heating values (HVs), and combustion characteristics of the resulted pellets were analyzed to evaluate the feasibility of the utilization as biofuel pellets. The results indicate that the hydrothermal pretreatments with and without H2O2 addition are beneficial to the quality of the resulted biofuel pellets. Particularly, the hydrothermal pretreatment with H2O2 addition, namely the hydrothermal oxidation pretreatment can significantly alleviate the pretreatment severity of the high-strength biofuel pellet preparation. H2O2 addition promotes the decomposition of hemicellulose and cellulose during the pretreatment. Compared with CS, WS is more sensitive to the pretreatment, especially hydrothermal oxidation pretreatment. The crystallinity index and the cellulose content of the biomass sample both increase firstly and then decrease with the increasing pretreatment temperature. In the study, the pretreatment temperature for the biofuel pellets with the best mechanical properties is 230 °C for the hydrothermal process and 200 °C for the hydrothermal oxidation process, respectively. The HVs of the resulted biofuel pellet increases with the increasing pretreatment intensity and the suitable pretreatment can improve the combustion characteristics of the resulted biomass. The mechanical properties of the pretreated biofuel pellets were positively correlated with the crystallinity and the content of the cellulose. HVs of WS pellets is higher than CS pellets, with the better mechanical properties. The cellulose is more favorable for the improvement of the combustion properties of the biomass sample than the hemicellulose and lignin. In addition, HVs and the compressive strength of all the biofuel pellets prepared from the pretreated biomasses meet the Sweden Standard (SS18 7120) and the Ministry of Agriculture of China standard (NY/T1878–2010), respectively.

Effect of hydrothermal pretreatment on two-stage anaerobic digestion of food waste and Enteromorpha: Digestion performance, bioenergy efficiency, and microbial community dynamics

The effects of hydrothermal pretreatment (HTP) on the performance, bioenergy efficiency, and microbial community dynamics of two-stage anaerobic digestion (AD) of food waste (FW) and Enteromorpha were analyzed. The results showed that hydrogen production and total volatile fatty acids (VFAs) concentration in the dark fermentation (DF) stage and cumulative biomethane yield in the methanogenic stage exhibited an increasing trend in response to increasing HTP temperature. The highest hydrogen and biomethane yields of 62.7 ± 0.3 and 590.6 ± 8.0 mL·gVS−1 were obtained at HTP temperature of 140 °C, which were 242.6% and 11.8% higher than those in two-stage AD with untreated substrates (designated as RTCK), respectively. Simultaneously, bioenergy generation yield (BGY) of 21.18 ± 0.44–24.21 ± 0.32 kJ·gVS−1 in two-stage AD achieved bioenergy conversion efficiency (BCE) of 71.69–80.37% and process energy efficiency (PEE) of 22.31–39.01%, which showed 14.27–16.91% and 24.83–31.15% improvement compared to one-stage AD, respectively. HTP significantly altered the bacterial communities, resulting in the enrichment of butyric- and acetic-type fermentation bacteria and the inhibition of propionate-type fermentation bacteria. This study demonstrated that HTP could improve the performance and achieve a higher BGY in two-stage AD.

Effect of hydrothermal pretreatment on deashing and pyrolysis characteristics of bamboo shoot shells

Bamboo shoot shells (BSS) were treated at hydrothermal temperatures of 160 °C, 180 °C, and 200 °C with residence times of 6 h, 8 h, and 10 h. The variation of ash-forming elements and the influence of deashing behavior on fuel and pyrolysis characteristics of BSS hydrochars were originally investigated during hydrothermal pretreatment (HTP) process. The results showed that HTP decreased 53.82–64.00% of BSS ash because 95.2–96.5% of K, 61.3–82.1% of Mg, 22.0–39.2% of Al, 23.7–51.8% of Fe, and 28.8–43.6% of Ca were removed. This improved fusion characteristics of BSS ash and reduced the risk of deposition, slagging and scaling. With increase in hydrothermal temperatures and residence times, the contents of fixed carbon, C, and high heating value of BSS hydrochars increased, while the contents of volatiles and O decreased. HTP shifted pyrolysis process of BSS to high temperature zone, and increased their activation energy and the amount of all gaseous products, including CO groups, C–O–C groups, alkyls, H2O, and CO. In conclusion, HTP is helpful for BSS to be used as feedstocks of bioenergy and biomaterials due to decrease of ash contents and improvement of thermal stability.

Effect of hydrothermal pretreatment on sugarcane bagasse to enhance the production of hydrogen and organic acids

Effect of hydrothermal pretreatment on sugarcane bagasse to enhance the production of hydrogen and organic acids

Effect of hydrothermal pretreatment on sugarcane bagasse to enhance the production of hydrogen and organic acids

Effect of hydrothermal pretreatment on sugarcane bagasse to enhance the production of hydrogen and organic acids

Upgrading the wood vinegar prepared from the pyrolysis of biomass wastes by hydrothermal pretreatment

Hydrothermal pretreatment (HT) is an effective method to upgrade biochar pellets, while little attention is paid to wood vinegar (WV), the byproduct of biochar pellets production. Therefore, Chinese fir sawdust (FS) and cotton stalk (CS) were hydrothermally pretreated first at 180–280 °C and then pyrolyzed at 350 °C in the study. The effect of hydrothermal pretreatment on the properties of biomass was evaluated by the Van Soest method and thermogravimetric method. The yield, pH, density, and composition of WV were analyzed. The results showed that hemicellulose and cellulose were completely decomposed at HT temperatures of 230 °C and 280 °C respectively. The removal of hemicellulose and the enrichment of cellulose and lignin in the samples pretreated before 230 °C result in a higher density and lower pH of WV, while the yield only increases before 200 °C. Compared with CS samples, the higher content and reactivity of cellulose, especially amorphous cellulose, and lignin in FS samples results in the higher yield of the organic compounds in FSWV. With HT temperature increasing to 230 °C, the content and yield of acids in FSWV/CSWV shows a declining trend, and the content and yield of phenols, ketones, and aldehydes increase. HT pretreatment below 230 °C can upgrade WV.

Effect of hydrothermal pretreatment on pyrolyzed sludge biochars for tetracycline adsorption

In this research, two biochars derived from activated sludge (wastewater treatment plant) are prepared by two different preparation processes for the comparative studies of tetracycline (TC) adsorption. One is the two-stage process, including hydrothermal pretreatment and subsequent high-temperature pyrolysis (HSBC-600), while the other is the direct pyrolysis method (PSBC-600). Various technologies are employed to characterize physicochemical properties and structural features of the two biochars. The results indicate that hydrothermal pretreatment can increase the specific surface area (133.4 and 114.6 m2/g for HSBC-600 and PSBC-600) and pore volume (0.237 and 0.159 cm3/g for HSBC-600 and PSBC-600) of biochar. At 298 K, the qmax on HSBC-600 and PSBC-600 achieves 116.9 and 89.3 mg/g, respectively. It is noted that the Freundlich isotherm and pseudo-second-order kinetic equations better describe the adsorption behavior, indicating that the adsorption of TC onto HSBC-600 and PSBC-600 is the multi-layer adsorption and involves chemical adsorption. The thermodynamic parameters reveal that the adsorption process is spontaneous and endothermic, causing an increase in the degree of disorder. All adsorption mechanisms may be consisted of pore filling, electrostatic force, hydrogen bond, and π-π interaction. The higher adsorption capacity of HSBC-600 could be attributed to the more adsorption sites provided from high specific surface area and pore volume, in which π-π interaction plays a major role.

The effect of hydrothermal pretreatment on the structure and fast pyrolysis behaviors of ShengLi lignite

The structure and composition of coal determine its fast pyrolysis characteristics, and the study of the relationship between them can play an important role in the efficient and clean utilization of coal. So, in this work, hydrothermal pretreatment was used to artificially change the structure and composition of ShengLi (SL) lignite, which was used to investigate the influence of structural changes on pyrolysis. The physicochemical structure and composition of samples were characterized by X-ray diffraction, specific surface area and porosity analyzer, solid-state 13C nuclear magnetic resonance, Fourier transform infrared spectroscopy, and elemental analyzer. Pyrolysis experiments were carried out in a powder-particle fluidized bed reactor, and the distribution and composition of the pyrolysis products were analyzed. The gasification activity of char was investigated by thermogravimetric analysis with a CO2 atmosphere. The results show that hydrothermal pretreatment (HTP) can destroy the cross-linking structure of SL lignite, and affect its aromaticity, pore structure, functional group, and carbon structure to change the distribution and composition of pyrolysis products of SL lignite, especially the composition of tar. Finally, the structure–activity relationship between the structure, composition, and pyrolysis characteristics of coal was comprehensively studied.

Effects of hydrothermal pretreatment and bamboo hydrochar addition on anaerobic digestion of tofu residue for biogas production

The effect of hydrothermal pretreatment (HTP) of tofu residue (TR) and co-digestion of TR with hydrochar (HC) and a liquid fraction (LF) of hydrothermal pretreatment on biogas production was studied. The highest biogas and methane yield observed with the pretreated TR at HTP temperature of 140 °C reached 288 and 207 L/Kg VS, 24 and 37% above than the raw TR (control), respectively, and the highest content of methane 72%. Adding 4 g/L of HC (produced at 200 °C) enhanced the methane and biogas yield by 18 and 19% compared to untreated TR, respectively. It was found that HTP at temperature 140 °C and additive HC-200 (4 g/L) was the most efficient for biogas production from tofu residue and significantly reduced the digestion time needed from 20 to 10–13 days to reach 95% of biogas yield, which may result in substantial economic benefits.

Effects of Hydrothermal Pretreatment and Hydrochar Addition on the Performance of Pig Carcass Anaerobic Digestion.

Proper disposal and utilization of dead pig carcasses are problems of public concern. The combination of hydrothermal pretreatment (HTP) and anaerobic digestion is a promising method to treat these wastes, provided that digestion inhibition is reduced. For this reason, the aim of this work was to investigate the optimal HTP temperature (140–180°C) for biogas production during anaerobic digestion of dead pigs in batch systems. In addition, the effects of hydrochar addition (6 g/L) on anaerobic digestion of pork products after HTP in continuous stirred tank reactors (CSTR) were determined. According to the results, 90% of lipids and 10% of proteins present in the pork were decomposed by HTP. In addition, the highest chemical oxygen demand (COD) concentration in liquid products (LP) reached 192.6 g/L, and it was obtained after 170°C HTP. The biogas potential from the solid residue (SR) and LP was up to 478 mL/g-VS and 398 mL/g-COD, respectively. A temperature of 170°C was suitable for pork HTP, which promoted the practical biogas yield because of the synergistic effect between proteins and lipids. Ammonia inhibition was reduced by the addition of hydrochar to the CSTR during co-digestion of SR and LP, maximum ammonia concentration tolerated by methanogens increased from 2.68 to 3.38 g/L. This improved total biogas yield and degradation rate of substrates, reaching values of 28.62 and 36.06%, respectively. The acetate content in volatile fatty acids (VFA) may be used as an index that reflects the degree of methanogenesis of the system. The results of the present work may also provide guidance for the digestion of feedstock with high protein and lipid content.