Thermal Pretreatment Temperature Research Articles

Extraction of protein from excess sludge by thermal pretreatment assisted enzymatic hydrolysis

In this paper, the hydrolysis conditions to extract protein from excess sludge by thermal pretreatment assisted enzymatic were studied. The optimum technological conditions were the sludge moisture content of 95%, thermal pretreatment temperature of 100 °C, heating time of 3h, initial pH of enzymolysis sludge of 11, enzyme dosage of 3000U/g dry sludge, enzymolysis temperature of 55°C and time of 3h. Up to 52.8% of the protein content of the sludge was extracted, and the dehydration performance of the hydrolyzed sludge was 87.46% higher than that of the original sludge. Therefore, thermal pretreatment-assisted enzymolysis can effectively extract protein from excess sludge and improve its dewatering performance.

A novel insight into the influence of thermal pretreatment temperature on the anaerobic digestion performance of floatable oil-recovered food waste: Intrinsic transformation of materials and microbial response

The intrinsic reason determining digestion performance of 100–160 °C preheated food waste after recovering floatable oil (FO-recovered FW) was investigated using two-dimensional correlated infrared spectroscopy, three-dimensional fluorescence spectroscopy and high-throughput 16S rRNA amplicon sequencing. The results indicated that thermal temperature significantly affected CH4 production of FO-recovered FW due to different structural alteration degree of starch, protein, cellulose and lipid components. Fragmentation of starch mainly occurred at 100 °C. The hydrolytic and acidogenic rate of starch was promoted and accordingly induced rapid growth of carbohydrate-fermenting bacteria, which resulted in severe acidification. Protein hydrolysis and cellulose H-bonds cleavage occurring at 120–160 °C accelerated the accessible sites interacting with microbial hydrolytic enzymes, and growth of Cloacimonetes and Syntrophomonas enhanced CH4 production. Non-degradable humic acid-like organics remarkably formed at 160 °C caused a carbon loss and digestion inhibiting/deteriorating. Pretreatment at 120 °C was feasible for promoted methane production based on energy assessment.

The effects of temperature and duration of thermal pretreatment on the solid-state anaerobic digestion of dairy cow manure

Cellulosic substrates such as dairy cow manure often yield low volumes of biogas and low concentrations of methane when digested anaerobically. Thermal pretreatment of dairy cow manure was investigated to determine if pretreatment temperature and duration can be optimized to maximize biogas yield and methane concentration. A central composite rotatable design was used to select combinations of temperature and duration. Based on measured data, statistical models were generated to estimate the biogas yield and methane concentration during digestion. The highest biogas yields were from the untreated samples and samples treated at the center temperature and duration of the statistical model (125 °C, 37.5 min). The model predicted the optimum pretreatment conditions of 140 °C for 30 minutes. Under the conditions of this experiment, temperature and duration had no significant effect on the biogas yield and methane concentration. This lack of significance may indicate that thermal pretreatment may be an unnecessary step in the anaerobic digestion of dairy cow manure, which could reduce capital and operating costs for the industry.

A solid-phase extraction method using acid-modified Transcarpathian clinoptilolite for preconcentration of trace amounts of lead in water samples

The sorption properties of acid-modified Ukrainian Transcarpathian clinoptilolite towards lead aqueous solutions under dynamic conditions have been investigated. The obtained results show that this nanomaterial most effectively sorbs cationic aqua hydroxo complexes of Pb(II) ions. The optimal conditions for the sorption of Pb(II) on the acid-modified Transcarpathian clinoptilolite are as follows: temperature of H-clinoptilolite thermal pre-treatment—600 °C; sorbent grains diameter—0.20–0.31 mm; pH—8.5; flow rate of Pb(II) solution with the concentration of 0.5 µg mL−1 through the sorbent—5 mL min−1. The maximal sorption capacity value of the acid-modified Transcarpathian clinoptilolite towards Pb(II) is equal to 48.79 mg g−1, that is 4.5 times higher than the respective sorption capacity value of the natural form of this zeolite. The best desorbent of Pb(II) from acid-modified clinoptilolite is 1 M KCl (acidified with hydrochloric acid to pH 4.0). This desorbent removes 97% of sorbed Pb(II). The preconcentration method of Pb(II) nanogram amounts in the solid-phase extraction mode during the atomic absorption analysis of natural waters has been proposed. The linearity of the proposed method was evaluated in the range of 0.08–16 ng mL−1 with the detection limit of 0.025 ng mL−1. Due to acceptable recoveries (≥ 96%) and relative standard deviation (RSD) values (1.6–6.6%) from a spiked tap water.

Exploring the Influence of Thermal Pretreatment on Carbon Paper Electrodes for Vanadium Redox Flow Batteries

Grid-scale energy storage is anticipated to play a critical role in the decarbonization of the electric power sector by enabling the reliable integration of intermittent renewable sources and increasing the efficiency of non-renewable energy processes.1 Redox flow batteries (RFBs) are a promising electrochemical device for such applications due to their independent energy and power scaling and long operational lifetime.2 Aqueous vanadium RFBs (VRBs) have been the most successful chemistry, due to their high power density and recoverable capacity from crossover, but further cost reductions are needed for ubiquitous adoption. Vanadium redox reactions have sluggish kinetics on the carbon electrodes typically employed in VRBs which motivates the implementation of pretreatment strategies to increase electrochemically active surface area and introduce catalytically active functional groups onto the electrode surface.3 While many pretreatments have been successfully demonstrated most studies are empirically-driven.4 Few have focused on systematically correlating changes in electrode structure and surface chemistry to shifts in electrochemical performance. To this end, we utilize a suite of ex-situ characterization techniques, coupled with flow cell testing, to explore structure-performance relations of thermally pretreated carbon paper electrodes. Specifically, we vary thermal pretreatment temperature from 400 °C, a commonly used temperature for VRB electrode treatments3,4, to 500 °C, to quantify changes in the physicochemical properties of the electrode, and link these changes to shifts in VRB performance. We leverage microscopic, spectroscopic, and analytical techniques to determine how microstructural, morphological, and chemical properties of electrodes are impacted by thermal pretreatment. We then evaluate the effect of these properties on flow cell performance using polarization, electrochemical impedance spectroscopy, and cell cycling. We find that many factors contribute to the observed electrode performance, including hydrophilicity, electrochemical surface area, and surface chemistry, and that not all of these factors improve with increasing temperature. Consequently, while the best overall performance is achieved with pretreatment at 475 °C, a 26% increase in maximum power density over the base case of pretreatment at 400 °C, this enhancement is based on a balance of critical properties rather than a maximization of all. Acknowledgements The authors acknowledge the financial support of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the United States Department of Energy. K.V.G acknowledges additional funding from the National Science Foundation Graduate Research Fellowship. A.F.C. acknowledges financial support from the Swiss National Science Foundation (P2EZP2_172183). The authors acknowledge the Center for Nanoscale Systems and the NSF’s National Nanotechnology Infrastructure Network (NNIN) for the use of Nanoscale Analysis facility to collect X-ray photoelectron spectroscopy data. We thank Michael L. Perry and Robert M. Darling for guidance in experimental conditions and critical evaluation of results. References Z. Yang, J. Zhang, M. Kintner-Meyer, X. Lu, D. Choi, J. P. Lemmon, J. Liu, Chem. Rev., 111, 3577–3613 (2011).M. Skyllas-Kazacos, M. H. Chakrabarti, S. A. Hajimolana, F. S. Mjalli, and M. Saleem, J. Electrochem. Soc., 158, R55 (2011).B. Sun and M. Skyllas-Kazacos, Electrochim. Acta, 37, 1253–1260 (1992).M. H. Chakrabarti et al., J. Power Sources, 253, 150–166 (2014). Figure 1

CO2 Capture Performance of Portland Cement‐Based Carbide Slag and the Enhancement of Its CO2 Capture Capacity

AbstractCarbide slag (CS) is a CaO‐based waste with superior CO2 capture capacity. As it is usually recycled in the form of fine powder, the pelletization of CS is indispensable for its practical application. Here, commercial Portland cement (PC) was used as a cheap binder to produce PC‐based carbide slag (PCCS) pellets and to enhance the mechanical strength of CS. The carbonation conversion of CS declined with the addition of PC, but the ability to resist sintering was improved. Prolonging the hydration time (HT) was effective in improving the CO2 capture performance of PCCS. During the thermal pretreatment of CS, the grain size of the CS increased with increasing thermal pretreatment temperature and time, but the mechanical strength of the CS increased.

A combination of ammonia stripping and low temperature thermal pre-treatment improves anaerobic post-digestion of the supernatant from organic fraction of municipal solid waste treatment

Municipal Solid Waste is mostly composed of organic material which is often treated in anaerobic reactors in waste treatment plants. In most cases, the obtained digestate undergoes a solid/liquid separation step, producing a liquid fraction (known as anaerobic supernatant) rich in ammonium nitrogen that has to be further treated in order to meet discharge standards. The objective of the present work was to evaluate the feasibility of anaerobic post-digestion (37 °C) of a supernatant rich in carbon and nitrogen from a municipal waste treatment plant. In order to increase the efficiency of the process, a combined pre-treatment consisting of a low-temperature thermal process (75 °C) and ammonia stripping (1.3 Lair Lsupernatant−1 min−1) was applied. The effects of pre-treatment contact time (4 and 8 h) and the hydraulic retention time (HRT) in the anaerobic reactor (20–40 d) were studied. Supernatant pre-treatment with 8-h contact time caused 13% organic matter solubilisation, thus improving methanisation by 18% when the HRT was 40 d. At the same time, ammonia stripping allowed to maintain ammonia concentration in the digester below inhibitory values (less than 100 mg N-NH3 L−1) enabling therefore high methanogenic activity (>0.23 g COD g−1 VS d−1). The final effluent characteristics (low total ammonia nitrogen and aerobically biodegradable organic matter levels) would permit implementing subsequent less energy intensive and more environmental-friendly technologies (such as partial nitritation/anammox) to comply with discharge limits.

Enhancement of biogas production from sewage sludge in a wastewater treatment plant: Evaluation of pretreatment techniques and co-digestion under mesophilic and thermophilic conditions

Boosting biomethane production makes it possible to offset the required energy in a wastewater treatment plant. In this research, using batch biomethane potential assays, various techniques including pretreatment, co-digestion, and digestion temperature rise were evaluated to increase the methane productivity of municipal sewage sludge (SS). Between thermal and sonication pretreatment methods, thermal pretreatment was shown to be more efficient and there was no need to pretreat SS for more than 0.5 h. Thermophilic digestion of SS led to 160.8% rise in the methane productivity, compared to mesophilic digestion. The most suitable co-substrate for co-digestion with SS was food waste (FW). FW and SS had little negative synergistic effect, however higher FW concentration caused to higher specific methane yield. Thermal pretreatment was not effective on FW. To evaluate the techniques, a combined cooling, heat and power plant was suggested. The energy recovery balance was positive for all the techniques, but co-digestion was not successful to reduce the levelized cost of energy (LCOE). Unlike co-digestion, thermal pretreatment and digestion temperature rise decreased the LCOE. The thermophilic digestion of SS, pretreated at 90 °C for 0.5 h, resulted in the lowest amount of LCOE by 43.70% reduction, compared to the mesophilic single digestion of non-treated SS.

Effect of thermal pretreatment on chemical composition, physical structure and biogas production kinetics of wheat straw

Hard lignocellulosic structure of wheat straw is the main hindrance in its anaerobic digestion. Thus, a laboratory scale batch experiment was conducted to study the effect of thermal pretreatment on anaerobic digestion of wheat straw. For this purpose, different thermal pretreatment temperatures of 120, 140, 160 and 180 °C were studied and the results were compared with raw wheat straw. Significant differences in biogas production were observed at temperature higher than 160 °C. Highest biogas yield of 615 Nml/gVS and volatile solids reduction of 69% was observed from wheat straw pretreated at 180 °C. Wheat straw pretreated at 180 °C showed 53% higher biogas yield as compared to untreated. Further, FTIR analysis revealed change in chemical bonds of lignocellulosic structure of wheat straw. Modified Gompertz model was best fitted on biogas production data and predicted shorter lag phase time and higher biogas production as the pretreatment temperature increased. Overall, change in lignocellulosic structure and increase in cellulose content were the main reason in enhancing biogas production.

Evaluation of thermal pretreatment and digestion temperature rise in a biogas fueled combined cooling, heat, and power system using exergo-economic analysis

In a municipal wastewater treatment plant, the anaerobic digesters are able to support the whole or a portion of the required fuel to offset the energy demand. Also, by implementing some techniques on municipal sewage sludge, leading to biomethane productivity enhancement, it is possible to generate surplus power. In this work, using batch biomethane potential assays, thermal pretreatment at 70 °C & 90 °C for the durations of 0.5 h, 1 h, 2 h, 3 h, and 4 h, and digestion temperature rise from the mesophilic to the thermophilic conditions have been studied to boost the biomethane productivity of the sewage sludge. Also a combined cooling, heat, and power generating plant was suggested to evaluate the techniques thermo-economically. It was shown that, compared to the non-treated mesophilic digestion of the sewage sludge, thermal pretreatment at 70 °C and 90 °C for 0.5 h, and thermophilic digestion were able to raise the biomethane productivity by 13.63%, 59.82%, and 160.8%, respectively. In this regard, the thermodynamic and the thermo- economic model of the plant was developed. The energy analysis of the system revealed that not only the studied methods, but also the mesophilic digestion of the non-treated sewage sludge result in a positive energy recovery balance in the plant. The exergo-economic analysis indicated that the major origin of cost in the system is the anaerobic digester. Implementing thermal pretreatment at 90 °C for 30 min and digestion temperature rise led to decrease in the required volume of the digester, and subsequently, in the total system cost rate. Additionally, all the applied techniques provided more fuel compared to the non-treated mesophilic case, and consequently they could reduce the levelized cost of energy in the plant. Among the studied techniques, the most effective one was digestion temperature rise which decreased the total cost rate and the levelized cost of energy by 30.31% and 41.29%, respectively.

Impact of Thermal Pretreatment Temperatures on Woody Biomass Chemical Composition, Physical Properties and Microstructure

Thermal pretreatment of biomass by torrefaction and low temperature pyrolysis has the potential for generating high quality and more suitable fuels. To utilize a model to describe the complex and dynamic changes taking place during these two treatments for process design, optimization and scale-up, detailed data is needed on the property evolution during treatment of well-defined individual biomass particles. The objectives of this study are to investigate the influence of thermal pretreatment temperatures on wood biomass biochemical compositions, physical properties and microstructure. Wild cherry wood was selected as a model biomass and prepared for this study. The well-defined wood particle samples were consecutively heated at 220, 260, 300, 350, 450 and 550 °C for 0.5 h under nitrogen. Untreated and treated samples were characterized for biochemical composition changes (cellulose, hemicellulose, and lignin) by thermogravimetric analyzer (TGA), physical properties (color, dimensions, weight, density and grindablity), chemical property (proximate analysis and heating value) and microstructural changes by scanning electron microscopy (SEM). Hemicellulose was mostly decomposed in the samples treated at 260 and 300 °C and resulted in the cell walls weakening resulting in improved grindability. The dimensions of the wood were reduced in all directions and shrinkage increased with increased treatment temperature and weight loss. With increased treatment temperature, losses of weight and volume increased and bulk density decreased. The low temperature pyrolyzed wood samples improved solid fuel property with high fuel ratio, which are close to lignite/bituminous coal. Morphology of the wood remained intact through the treatment range but the cell walls were thinner. These results will improve the understanding of the property changes of the biomass during pretreatment and will help to develop models for process simulation and potential application of the treated biomass.

The effect of the thermal pretreatment on the performance of ZnO/Cr2O3 catalysts applied in high-temperature methanol synthesis

Co-precipitated ZnO/Cr2O3 catalyst precursors were thermally pretreated in synthetic air (calcination), N2 (pyrolysis) and 10% H2 diluted in N2 (reduction) at temperatures in the range from 320°C to 600°C and then applied in methanol synthesis from CO and H2 at 260–300°C and 60bar. The X-ray diffraction patterns showed that increasing temperatures used in the thermal pretreatment lead to sintering of both the resulting non-stoichiometric Zn-Cr spinel and ZnO phases. However, reduced and pyrolyzed catalysts exhibit a much slower increase in particle size of the Zn-Cr spinel phase compared with the calcined catalyst. Correspondingly, at the same temperature of thermal pretreatment the specific surface areas of the catalyst follow the trend reduced catalyst>pyrolyzed catalyst>calcined catalyst. Chromate species were found to be present in the calcined catalyst, while their amount decreased with increasing calcination temperature. Infrared spectroscopy and temperature-programmed reduction confirmed the existence of carbonate species in the catalysts reduced or pyrolyzed below 500°C. NH3 temperature-programmed desorption showed that the calcined catalysts exhibit more acid sites due to the existence of chromate species. The reduced and pyrolyzed catalysts demonstrate significantly improved performance in high-temperature methanol synthesis compared with the calcined catalysts, and the maximum methanol productivity was achieved subsequent to reduction at 500°C. It is suggested that the thermal pretreatment in reducing or inert atmosphere favors the formation of oxygen vacancies, which are considered to be the active sites for the hydrogenation of CO.

Production of lactic acid from thermal pretreated food waste through the fermentation of waste activated sludge: Effects of substrate and thermal pretreatment temperature

Valorization of organic-rich waste stream to lactic acid by the mixed microbial consortium has attracted tremendous research interests in recent years. In this study, thermal pretreatment was involved in co-fermentation of food waste (FW) and waste activated sludge (WAS) to enhance lactic acid production. First, sole FW was observed as the most suitable substrate employing thermal pretreatment for the generation of lactic acid. The fermentation time for reaching the maximal plateau was significantly shortened at a corresponding thermal pretreatment temperature. The mechanism study found that the enhancement of lactic acid yield was in accordance with the acceleration of solubilization and hydrolysis. Furthermore, the physicochemical characteristics of fermentative substrate and surface morphology of the fermentation mixture varied with the pretreatment temperatures. Further investigations of microbial community structure also revealed that the proportions of key microorganisms such as Bacillus and Lactobacillus were changed by the thermal pretreatment.

Pretreatment effect on the properties of the Cr–Mg catalyst for the gas-phase hydrofluorination of perchloroethylene into pentafluoroethane

The effect of the temperature of thermal pretreatment of the precursors of the Cr–Mg catalyst on its physicochemical properties (specific surface area and elemental composition) and catalytic properties has been experimentally investigated. The dehydration of the precursor takes place up to a temperature of ~500°С, making it possible to tune the catalyst composition by varying the heat-treatment temperature. The samples prepared from precursors with various compositions differ in their specific surface area and catalytic activity. The highest activity is shown by the catalyst prepared by heat treatment of the precursor at 330°С.

Effect of low temperature of thermal pretreatment on anaerobic digestion of textile dyeing sludge

The minimization and methane production of textile dyeing sludge (TDS) can be simultaneously attained via anaerobic digestion (AD). However, the possible toxicity and complex recalcitrant organic matters involved in limited the hydrolysis of TDS. Therefore, the low-temperature of thermal pretreatment (LTTP) lasting for 1h at temperatures from 60 to 100°C was employed to accelerate the hydrolysis and subsequent methane generation of TDS. The results showed that LTTP with temperatures higher than 70°C obviously improve the AD performance of TDS. Highest accumulative methane production was achieved for 100°C pretreated TDS and from thermal analysis point of view it was due to the disintegration of some recalcitrant macromolecules in TDS. Nevertheless, 90°C pretreated TDS did not perform favorable methane yield as expected, attributing to the inhibited acetogenesis as well as the hindered methanogenesis which was simultaneously competed by dye reducer for electrons.

Pretreatment of a primary and secondary sludge blend at different thermal hydrolysis temperatures: Impacts on anaerobic digestion, dewatering and filtrate characteristics

A study was performed to evaluate the effect of thermal hydrolysis pretreatment (THP) temperature on subsequent digestion performance and operation, as well as downstream parameters such as dewatering and cake quality. A blend of primary and secondary solids from the Blue Plains treatment plant in Washington, DC was dewatered to about 16% total solids (TS), and thermally hydrolyzed at five different temperatures 130, 140, 150, 160, 170 °C. The thermally hydrolyzed solids were then fed to five separate, 10 L laboratory digesters using the same feed concentration, 10.5% TS and a solids retention time (SRT) of 15 days. The digesters were operated over a six month period to achieve steady state conditions. The higher thermal hydrolysis temperatures generally improved the solids reduction and methane yields by about 5–6% over the temperature range. The increased temperature reduced viscosity of the solids and increased the cake solids after dewatering. The dissolved organic nitrogen and UV absorbance generally increased at the higher THP temperatures. Overall, operating at a higher temperature improved performance with a tradeoff of higher dissolved organic nitrogen and UV adsorbing materials in the return liquor.

Modified ADM1 for high-rate anaerobic co-digestion of thermally pre-treated brewery surplus yeast wastewater.

Co-digestion of surplus yeast with brewery wastewater is a potentially economical method for recovering energy, in the form of biogas, from this difficult to dispose of by-product. In this work a modified version of the ADM1 (Anaerobic Digestion Model No. 1) was calibrated for an anaerobic digester fed with thermally pre-treated brewery yeast surplus wastewater. The model could predict changes to reactor methane production and reduction of biodegradable matter when fed with both pre-treated and untreated yeast surplus wastewater at varying loading rates. Model calibration focused on low temperature thermal pre-treatment as experiments into a combined thermal-alkaline pre-treatment did not show any significant improvements. A low temperature pre-treatment of 60 °C for 30 minutes was sufficient for yeast inactivation and allowed for stable and more efficient operation of the high-rate anaerobic digester over a period of 232 days. The low temperature and time for pre-treatment also reduced the evaporation of easily biodegradable residual ethanol present in the influent, while still maintaining a low level of suspended matter. Inline measurements of gas composition, production and effluent chemical oxygen demand were sufficient for reliable model calibration of these same outputs. More detailed characterization of influent and effluent is required if organic acid concentrations for pH control are needed.

Olive mill solid waste biorefinery: High-temperature thermal pre-treatment for phenol recovery and biomethanization

Circular bioeconomy has become a major issue for sustainable development in recent years. In the agricultural sector, circular economy focuses on the valorization and the pollution footprint reduction of organic waste. Due to the high volume generated and its high polluting potential, it is necessary to develop an economical and environmentally-friendly sustainable treatment of Olive Mill Solid Waste (OMSW). In the present study, a high-temperature thermal pre-treatment carried out at 170 °C for 60 min and a subsequent phenol extraction were proposed for OMSW valorization. A further anaerobic digestion step was proposed for the stabilization and energy recovery of pre-treated OMSW, with the necessity to study the effect of the inhibitory metabolites generated during the thermal pre-treatment in order to assess the viability of the process. Thermal pre-treatment induced organic matter solubilization and phenol generation with respect to untreated OMSW, with increases of 26.3% and 60.4%, respectively. Phenol extraction allowed the recovery of 1600 mg of hydroxytyrosol per 1 kg of OMSW. Thermal pre-treatment resulted in an improvement in the liquid fraction of both methane yield and methane production rate compared to untreated OMSW up to 16.9% and 6.9%, respectively. Further extraction of phenols produced a more significant enhancement of both methane yield and methane production rate in the de-phenolized liquid fraction compared to untreated OMSW, reaching improvements of 44.1% and 103%, respectively. The proposed economic assessment showed that the combination of high temperature thermal pre-treatment, phenol recovery and the subsequent biomethanization of the substrates was the most attractive treatment option. The economical suitability of the proposed biorefinery concept is favorable for a phenol extract price higher than 67.0 €/kg, 87% lower than the referenced actual price of 520 €/kg.

Low-temperature thermal pre-treatment of municipal wastewater sludge: Process optimization and effects on solubilization and anaerobic degradation

The present study examines the relationship between the degree of solubilization and biodegradability of wastewater sludge in anaerobic digestion as a result of low-temperature thermal pre-treatment. The main effect of thermal pre-treatment is the disintegration of cell membranes and thus solubilization of organic compounds. There is an established correlation between chemical oxygen demand (COD) solubilization and temperature of thermal pre-treatment, but results of thermal pre-treatment in terms of biodegradability are not well understood. Aiming to determine the impact of low temperature treatments on biogas production, the thermal pre-treatment process was first optimized based on an experimental design study on waste activated sludge in batch mode. The optimum temperature, reaction time and pH of the process were determined to be 80 °C, 5 h and pH 10, respectively. All three factors had a strong individual effect (p < 0.001), with a significant interaction effect for temp. pH2 (p = 0.002). Thermal pre-treatments, carried out on seven different municipal wastewater sludges at the above optimum operating conditions, produced increased COD solubilization of 18.3 ± 7.5% and VSS reduction of 27.7 ± 12.3% compared to the untreated sludges. The solubilization of proteins was significantly higher than carbohydrates. Methane produced in biochemical methane potential (BMP) tests, indicated initial higher rates (p = 0.0013) for the thermally treated samples (khyd up to 5 times higher), although the ultimate methane yields were not significantly affected by the treatment.

Biomethane potential of food waste: modeling the effects of mild thermal pretreatment and digestion temperature

ABSTRACTIn order to enhance anaerobic biodegradability of food waste (FW), thermal pretreatment was applied. The effectiveness in terms of biodegradability extent and process rate improvement was investigated. To this aim, Biomethane Potential tests were carried out under mesophilic and thermophilic conditions. The IWA anaerobic digestion Model 1 (ADM1), a powerful tool for modeling the anaerobic digestion (AD) of different substrates, was implemented to predict the methane production. Disintegration constant (k_dis) and maximum acetate uptake rate (km_ac) were identified as the most sensitive parameters and were calibrated over the observed methane production. Pretreatment improvement was more evident in enhancing parameters related to the process rate, such as solubilization extent (+153%) and disintegration constant (+18%), rather than increasing substrate biodegradability. Thermophilic conditions proved to be effective in speeding up the whole AD process, since all the kinetics were significantly improved (disintegration rate increased up to fivefold). Furthermore, it was demonstrated that, after k_dis and km_ac calibration, default thermophilic ADM1 parameters can be suitable to model FW digestion.