Yeqing Li | China University of Petroleum, Beijing (original) (raw)

Papers by Yeqing Li

BioResources, 2013

The influence of particle size and an alkaline pretreatment on the anaerobic digestion of corn st... more The influence of particle size and an alkaline pretreatment on the anaerobic digestion of corn stover was studied. Four particle sizes, 0.075 to 0.25, 0.25 to 1.0, 1.0 to 5.0, and 5.0 to 20.0 mm, were used. The highest and lowest methane yields were obtained from untreated corn stover at particle sizes of 0.25 to 1.0 and 5.0 to 20.0 mm, respectively. 4% NaOH and 2% Ca(OH) 2 (combined alkaline pretreatment, CAP) were then used together to pretreat corn stover at these two particle sizes, compared with 6% NaOH pretreatment (single alkaline pretreatment, SAP). The cumulative methane yields from particle sizes 0.25 to 1.0 mm after CAP, 0.25 to 1.0 mm after SAP, 5.0 to 20.0 mm after CAP, and 5.0 to 20.0 mm after SAP were 286.9, 287.0, 268.7, and 272.6 mLg -1 VS, respectively. The particle size barely influenced the final cumulative methane yield of alkali-treated corn stover. Moreover, the cumulative methane yield of the corn stover after CAP was comparable with that of the corn stover after the SAP under the same conditions. These results provide us with a promising substitute of NaOH pretreatment for corn stover bioconversion in the future.

Applied Biochemistry and Biotechnology, 2013

In order to investigate the effects of inoculum source and pre-incubation on methane production p... more In order to investigate the effects of inoculum source and pre-incubation on methane production performance of chicken manure (CM) and corn stover (CS), two sets of bio-methane potential tests using non-and pre-incubated inocula (digested sludge from a municipal wastewater treatment plant (DSMW) and digested sludge from a chicken manure treatment plant (DSCM)) were conducted at 37°C. Modified Gompertz and first-order models were used to evaluate the kinetic parameters. The results revealed that DSMW was better than DSCM in digesting organic substrates (CM and CS), since the average ultimate methane yields were 351 mL g −1 volatile solid (VS) added for CM and 300 mL g −1 VS added for CS when DSMW was used as inoculum, and 298 mL g −1 VS added for CM and 218 mL g −1 VS added for CS when DSCM was used as inoculum, respectively. Nevertheless, there was no significant difference (p>0.05) in the ultimate methane yields between non-and pre-incubated inoculum for digesting CM and CS, regardless of the inoculum source. However, when evaluating the kinetic parameters of anaerobic digestion, the correlation coefficient, maximal methane production rate, and hydrolysis rate constant were slightly higher using pre-incubated inoculum as compared to non-incubated inoculum.

Strength of pretreatment to CS ascended in the following order: KOH, SE, and SPPE. SPPE was first... more Strength of pretreatment to CS ascended in the following order: KOH, SE, and SPPE. SPPE was firstly reported to effectively destroy lignocellulosic structure of CS. Methane production of CS was significantly enhanced by 80.0% after SPPE.

Ambient temperature KOH pretreatment over a wide loading range (2-50%) was studied. 20% KOH loadi... more Ambient temperature KOH pretreatment over a wide loading range (2-50%) was studied. 20% KOH loading resulted in the maximum overall reducing sugar and methane yield. The maximum lignin reduction achieved through KOH pretreatment was 54.7%. The maximum specific hydrolysis yield achieved for pretreated wheat straw was 92.3%. KOH pretreatment increased the methane yield of wheat straw by 77.5%.

Kitchen waste as the main component of municipal waste with high-moisture and high-organic has be... more Kitchen waste as the main component of municipal waste with high-moisture and high-organic has become one of the key environmental problems. Anaerobic digestion was considered a most promising alternative for handling this kind of waste for waste reduction and clean energy production. The batch fermentation for kitchen waste from university dinning service with different organic concentrations were conducted with and without pH value adjustment at 35 C. The results showed that maximum organic concentration can reach 25 g/L without pH adjustment, highest biogas yield 938.6 mL/g was achieved at 20 g/L and highest methane yield was 506.44 mL/g at 16 g/L While adding to adjust the pH value, the maximum organic loading can reach 45 g/L with a higher biogas and a methane yield compared with and without adding Ca(OH) 2 The effects of feed to inoculums ratio (three kinds of F/M ratio 0.26, 0.36, and 0.6) on the anaerobic digestion performance were studied. Appropriate inoculum (F/M = 0 36) can improve the digestion efficiency and biogas production.

Anaerobic mono-and co-digestion of kitchen waste (KW), corn stover (CS), and chicken manure (CM) ... more Anaerobic mono-and co-digestion of kitchen waste (KW), corn stover (CS), and chicken manure (CM) under mesophilic (37°C) conditions were conducted in batch mode with the aim of investigating the biomethane potential (BMP), biodegradability, methane production performance, and stability of the process. An initial volatile solid concentration of 3 g VS L −1 with a substrate-to-inoculum (S/I) ratio of 0.5 was first tested, and two S/I ratios of 1.5 and 3.0 were evaluated subsequently. The modified Gompertz equation was used to assist in the interpretation of the conclusions. The results showed that BMP and specific methane yields were 725 and 683 mL g −1 VS added for KW, 470 and 214 mL g −1 VS added for CS, and 617 and 291 mL g −1 VS added for CM, respectively. Therefore, KW had the highest biodegradability of 94% as compared with CS (45%) or CM (47%). For KW mono-and co-digestion with CS, CM, or their mixture, methane production performance was better at an S/I ratio of 1.5 than that of 3.0. For CS, CM, and their mixture, S/I ratios of both 1.5 and 3.0 were suitable. A synergistic effect was found in the co-digestion process, which was mainly attributed to a proper carbon-to-nitrogen ratio and the reduced total volatile fatty acids-to-total alkalinity ratio, thus providing better buffering capacity and supporting more microorganisms for efficient digestion.

Methane production potential, BD, and kinetics of various substrates were compared. Both of eleme... more Methane production potential, BD, and kinetics of various substrates were compared. Both of elemental and organic analysis could be used to calculate the TMY and BD. 15% VS of lignin was a critical point in AD of lignocellulosic and manure wastes.

Solid-state anaerobic digestion (SS-AD) of corn stover (CS) was conducted at mesophilic (37°C) an... more Solid-state anaerobic digestion (SS-AD) of corn stover (CS) was conducted at mesophilic (37°C) and thermophilic (50°C) conditions with/without solid-state NaOH pretreatment. Fourier transform infrared (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to help with the understanding of the changes of the physicochemical structure of pretreated CS. Additionally, thermophilic SS-AD of pretreated CS and chicken manure (CM) was investigated. First-order, Cone, and modified Gompertz models were used to evaluate the methane production. Results showed that solid-state NaOH pretreatment could partly dissolve lignin and hemicelluloses and significantly increase the internal surface area of CS, which could make it more readily biodegradable. At a substrate/inoculum (S/I) ratio of 3, mesophilic SS-AD of CS failed because of the accumulation of organic acids. However, under thermophilic SS-AD conditions, biogas and methane yields of pretreated CS were found to be 386.3 and 194.8 mL g −1 of VS added , respectively, which were 29.4 and 40.1% higher than those of untreated CS. Thermophilic solid-state co-digestion of pretreated CS with CM showed no beneficial effects for enhancing the biogas and methane yields, because of the accumulation of volatile fatty acids and ammonia. Methane production could well be explained by the Cone and modified Gompertz models compared to the first-order model, because higher R 2 values were obtained. On the basis of the results of the Cone model, the first-order rate constant (k) of thermophilic SS-AD of CS and CM decreased from 0.132 to 0.039 day −1 with the increasing portion of CM. Through the modified Gompertz model, a higher lag phase time (λ) and lower maximal methane production rate (μ m ) were found, with the content of CM increasing under thermophilic solid-state co-digestion conditions. These results collectively suggested that thermophilic SS-AD of pretreated CS could be a promising way to produce biogas in the future.

BioResources, 2013

The influence of particle size and an alkaline pretreatment on the anaerobic digestion of corn st... more The influence of particle size and an alkaline pretreatment on the anaerobic digestion of corn stover was studied. Four particle sizes, 0.075 to 0.25, 0.25 to 1.0, 1.0 to 5.0, and 5.0 to 20.0 mm, were used. The highest and lowest methane yields were obtained from untreated corn stover at particle sizes of 0.25 to 1.0 and 5.0 to 20.0 mm, respectively. 4% NaOH and 2% Ca(OH) 2 (combined alkaline pretreatment, CAP) were then used together to pretreat corn stover at these two particle sizes, compared with 6% NaOH pretreatment (single alkaline pretreatment, SAP). The cumulative methane yields from particle sizes 0.25 to 1.0 mm after CAP, 0.25 to 1.0 mm after SAP, 5.0 to 20.0 mm after CAP, and 5.0 to 20.0 mm after SAP were 286.9, 287.0, 268.7, and 272.6 mLg -1 VS, respectively. The particle size barely influenced the final cumulative methane yield of alkali-treated corn stover. Moreover, the cumulative methane yield of the corn stover after CAP was comparable with that of the corn stover after the SAP under the same conditions. These results provide us with a promising substitute of NaOH pretreatment for corn stover bioconversion in the future.

Applied Biochemistry and Biotechnology, 2013

In order to investigate the effects of inoculum source and pre-incubation on methane production p... more In order to investigate the effects of inoculum source and pre-incubation on methane production performance of chicken manure (CM) and corn stover (CS), two sets of bio-methane potential tests using non-and pre-incubated inocula (digested sludge from a municipal wastewater treatment plant (DSMW) and digested sludge from a chicken manure treatment plant (DSCM)) were conducted at 37°C. Modified Gompertz and first-order models were used to evaluate the kinetic parameters. The results revealed that DSMW was better than DSCM in digesting organic substrates (CM and CS), since the average ultimate methane yields were 351 mL g −1 volatile solid (VS) added for CM and 300 mL g −1 VS added for CS when DSMW was used as inoculum, and 298 mL g −1 VS added for CM and 218 mL g −1 VS added for CS when DSCM was used as inoculum, respectively. Nevertheless, there was no significant difference (p>0.05) in the ultimate methane yields between non-and pre-incubated inoculum for digesting CM and CS, regardless of the inoculum source. However, when evaluating the kinetic parameters of anaerobic digestion, the correlation coefficient, maximal methane production rate, and hydrolysis rate constant were slightly higher using pre-incubated inoculum as compared to non-incubated inoculum.

Strength of pretreatment to CS ascended in the following order: KOH, SE, and SPPE. SPPE was first... more Strength of pretreatment to CS ascended in the following order: KOH, SE, and SPPE. SPPE was firstly reported to effectively destroy lignocellulosic structure of CS. Methane production of CS was significantly enhanced by 80.0% after SPPE.

Ambient temperature KOH pretreatment over a wide loading range (2-50%) was studied. 20% KOH loadi... more Ambient temperature KOH pretreatment over a wide loading range (2-50%) was studied. 20% KOH loading resulted in the maximum overall reducing sugar and methane yield. The maximum lignin reduction achieved through KOH pretreatment was 54.7%. The maximum specific hydrolysis yield achieved for pretreated wheat straw was 92.3%. KOH pretreatment increased the methane yield of wheat straw by 77.5%.

Kitchen waste as the main component of municipal waste with high-moisture and high-organic has be... more Kitchen waste as the main component of municipal waste with high-moisture and high-organic has become one of the key environmental problems. Anaerobic digestion was considered a most promising alternative for handling this kind of waste for waste reduction and clean energy production. The batch fermentation for kitchen waste from university dinning service with different organic concentrations were conducted with and without pH value adjustment at 35 C. The results showed that maximum organic concentration can reach 25 g/L without pH adjustment, highest biogas yield 938.6 mL/g was achieved at 20 g/L and highest methane yield was 506.44 mL/g at 16 g/L While adding to adjust the pH value, the maximum organic loading can reach 45 g/L with a higher biogas and a methane yield compared with and without adding Ca(OH) 2 The effects of feed to inoculums ratio (three kinds of F/M ratio 0.26, 0.36, and 0.6) on the anaerobic digestion performance were studied. Appropriate inoculum (F/M = 0 36) can improve the digestion efficiency and biogas production.

Anaerobic mono-and co-digestion of kitchen waste (KW), corn stover (CS), and chicken manure (CM) ... more Anaerobic mono-and co-digestion of kitchen waste (KW), corn stover (CS), and chicken manure (CM) under mesophilic (37°C) conditions were conducted in batch mode with the aim of investigating the biomethane potential (BMP), biodegradability, methane production performance, and stability of the process. An initial volatile solid concentration of 3 g VS L −1 with a substrate-to-inoculum (S/I) ratio of 0.5 was first tested, and two S/I ratios of 1.5 and 3.0 were evaluated subsequently. The modified Gompertz equation was used to assist in the interpretation of the conclusions. The results showed that BMP and specific methane yields were 725 and 683 mL g −1 VS added for KW, 470 and 214 mL g −1 VS added for CS, and 617 and 291 mL g −1 VS added for CM, respectively. Therefore, KW had the highest biodegradability of 94% as compared with CS (45%) or CM (47%). For KW mono-and co-digestion with CS, CM, or their mixture, methane production performance was better at an S/I ratio of 1.5 than that of 3.0. For CS, CM, and their mixture, S/I ratios of both 1.5 and 3.0 were suitable. A synergistic effect was found in the co-digestion process, which was mainly attributed to a proper carbon-to-nitrogen ratio and the reduced total volatile fatty acids-to-total alkalinity ratio, thus providing better buffering capacity and supporting more microorganisms for efficient digestion.

Methane production potential, BD, and kinetics of various substrates were compared. Both of eleme... more Methane production potential, BD, and kinetics of various substrates were compared. Both of elemental and organic analysis could be used to calculate the TMY and BD. 15% VS of lignin was a critical point in AD of lignocellulosic and manure wastes.

Solid-state anaerobic digestion (SS-AD) of corn stover (CS) was conducted at mesophilic (37°C) an... more Solid-state anaerobic digestion (SS-AD) of corn stover (CS) was conducted at mesophilic (37°C) and thermophilic (50°C) conditions with/without solid-state NaOH pretreatment. Fourier transform infrared (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to help with the understanding of the changes of the physicochemical structure of pretreated CS. Additionally, thermophilic SS-AD of pretreated CS and chicken manure (CM) was investigated. First-order, Cone, and modified Gompertz models were used to evaluate the methane production. Results showed that solid-state NaOH pretreatment could partly dissolve lignin and hemicelluloses and significantly increase the internal surface area of CS, which could make it more readily biodegradable. At a substrate/inoculum (S/I) ratio of 3, mesophilic SS-AD of CS failed because of the accumulation of organic acids. However, under thermophilic SS-AD conditions, biogas and methane yields of pretreated CS were found to be 386.3 and 194.8 mL g −1 of VS added , respectively, which were 29.4 and 40.1% higher than those of untreated CS. Thermophilic solid-state co-digestion of pretreated CS with CM showed no beneficial effects for enhancing the biogas and methane yields, because of the accumulation of volatile fatty acids and ammonia. Methane production could well be explained by the Cone and modified Gompertz models compared to the first-order model, because higher R 2 values were obtained. On the basis of the results of the Cone model, the first-order rate constant (k) of thermophilic SS-AD of CS and CM decreased from 0.132 to 0.039 day −1 with the increasing portion of CM. Through the modified Gompertz model, a higher lag phase time (λ) and lower maximal methane production rate (μ m ) were found, with the content of CM increasing under thermophilic solid-state co-digestion conditions. These results collectively suggested that thermophilic SS-AD of pretreated CS could be a promising way to produce biogas in the future.