Anaerobic Mono- and Co-digestion of Mechanically Pretreated

Article pubs.acs.org/EF

Anaerobic Mono- and Co-digestion of Mechanically Pretreated Meadow Grass for Biogas Production Panagiotis Tsapekos, Panagiotis G. Kougias, and Irini Angelidaki* Department of Environmental Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark ABSTRACT: Biomass from permanent grasslands and meadows can be exploited for biogas production, because this substrate is abundant and does not compete with food production. In the present study, the biogas productivity of meadow grass silage, harvested in two different seasons (early and late cut), was investigated. The grass silage was mechanically pretreated with different methods to increase its biodegradability. It was found that the early cut of non-treated meadow grass silage led to higher methane production [294 mL of CH4/g of volatile solids (VS)] compared to the corresponding non-treated meadow grass silage from the late cut (282 mL of CH4/g of VS). Moreover, it was found that the application of two mesh grating plates, as the pretreatment method, greatly enhanced the methane production in early and late cut silage in a range of 15 and 17%, respectively, compared to the non-treated grass silage. The methane productivity from pretreated meadow grass silage, harvested at fall (late cut), was further examined in a co-digestion process with three different types of livestock manure (mink, poultry, and cattle). The silage was co-digested with manure in five different manure/silage mixing ratios in terms of organic matter. The results showed that the optimum silage concentration in the co-digestion mixture with manure, for the highest methane yield, was strongly dependent upon the chemical composition of the manure. More specifically, the ammonia concentration of manure and the C/N ratio of the co-digestion mixture were found to be the key parameters for an improved biomethanation process.

■

hemicellulose and lignin.11 Taken together, the biodegradability of meadow grass is greatly influenced by the stage of vegetation, and as a consequence, the harvesting period can affect the methane production. Several studies have pointed out that the advancing stage of vegetation has an adverse impact on the biodegradability of different lignocellulosic substrates.12,13 On the contrary, AD of ryegrass presented higher methane yields related to the increased age of the plant.14 Therefore, it is still unclear how the harvesting time effects the degradability of meadow grass. Meadow grass is a seasonal feedstock, and therefore, efficient storage and preservation is needed to continuously supply the biogas plant with biomass. Ensiling is a widely known method to preserve biomass over the world.15,16 Moreover, it has been previously shown that the methane yield of lignocellulosic biomass can be preserved significantly during ensiling and efficiently be used for energy production.16 It is well-known that the anaerobic digestion of lignocellulosic materials, such as meadow grass, is difficult because of the complicated polymer of lignin. Thus, pretreatment of the feedstock is required to optimize the biomass conversion process by increasing the anaerobic biodegradability of biomass. In the cited literature, several pretreatment methods have been investigated and are classified as mechanical, physicochemical, chemical, and biological.17 Mechanical pretreatment methods are widely used for fibrous biomasses. Promising results were previously found in our previous study, in which different mechanical pretreatment methods were applied on meadow

INTRODUCTION Biogas can be produced by a vast variety of organic substrates, through the anaerobic digestion (AD) process. In Denmark, most of the biogas plants are co-digesting different types of agro-industrial wastes together with manure. The use of manure for biogas production is well-established in Denmark, which has a huge animal industry, and as a consequence, 40 million tons of manure are produced each year.1 In addition, the Danish Green Growth strategy set an aim of 50% livestock manure exploitation for biogas production by 2020.2 Nevertheless, it is widely accepted that manure has a low methane yield,3 and therefore, co-digestion is applied to obtain a more economical and feasible process.4 Co-digestion gives the possibility to optimize the biogas yield and to avoid potential process imbalance, by an appropriate combination of specific biomasses. The ideal co-substrate should have a high methane yield, be plentiful, and not adversely influence the biogas process. Moreover, it should not compete with food production, because the global demand for food is increased as a result of the increasing worldwide population. Accordingly, food and bioenergy production are competing for land usage.5 Therefore, meadow grass is a potentially suitable feedstock for biogas production because it is abundant in set-aside land and does not conflict with food production.6 The exploitation of agricultural biomasses for methane production has been increased during the last few years.7,8 However, biogas production from agricultural biomasses varies highly throughout the year, because the chemical composition of such lignocellulosic substrates changes at different stages of vegetation. The methane yield of fibrous biomass is highly influenced by cellulose, hemicellulose, and lignin contents.9 It has been shown that increasing concentrations of lignin lead to lower productivity rates in anaerobic bioprocesses.10 Moreover, the increasing plant maturity leads to a higher content of © XXXX American Chemical Society

Special Issue: 2nd International Scientific Conference Biogas Science Received: December 15, 2014 Revised: February 19, 2015

A

DOI: 10.1021/ef5027949 Energy Fuels XXXX, XXX, XXX−XXX

Article

Energy & Fuels Table 1. Characteristics of Examined Inoculuma

grass silage and the methane yields were increased by approximately 25%.18 Therefore, mechanical pretreatment is a promising and easily applicable method to achieve higher methane yields. Despite the many advantages of grass silage for biogas production, this substrate is not commonly used as the exclusive influent feedstock in full-scale biogas plants. The high solids content (more than 15%) of grass silage is a major limitation that leads to technical issues in biogas plant facilities.19 Similarly, process disturbances have been reported in cases where livestock manure was digested alone because of ammonia toxicity.20 A common solution to overcome the aforementioned drawbacks is the application of co-digestion using ammonia-rich manure substrates (e.g., swine manure) together with agricultural biomasses with a high carbon content.21,22 In this context, the combination of substrates with dissimilar chemical composition can lead to a more effective digestion, as the C/N ratio of the mixture is improved. It has been previously suggested that grass silage could be potential feedstock for co-digestion with livestock manure in anaerobic biogas reactors to enhance the methane production.23 This study is the continuation of the work following our preliminary investigation on the influence of mechanical pretreatments on the meadow grass biodegradability.18 In the present study, we investigate the effect of the harvesting period on meadow grass biodegradability and further examine the impact of mechanical pretreatments related to the decrease of the tissue length of the plant. Additionally, pretreated meadow grass silage was co-digested together with livestock manure to determine the most efficient mixing ratio that results in the highest methane yield. Poultry and mink manure as ammoniarich substrates and cattle manure as primary feedstock in Danish full-scale biogas plants were selected as livestock waste. The results from the present study could be useful for improving the efficiency of the biogas process and, thus, helping to improve the economy of the biogas plant.

■

a

parameter

value

total solids (TS) (g/kg) volatile solids (VS) (g/kg) total Kjeldahl nitrogen (TKN) (g/kg) ammonium nitrogen (NH4 N) (g/kg) pH biochemical methane yield (mL of CH4/g of VS) total volatile fatty acids (VFA) acetate (mg/L) propionate (mg/L) isobutyrate (mg/L) butyrate (mg/L) isovalerate (mg/L) valerate (mg/L) n-hexanoate (mg/L)

24.1 ± 0.1 14.9 ± 0.3 4.6 ± 0.2 3.8 ± 0.1 8.7 26.2 ± 2.4 67.8 ± 15.5 23.8 ± 3.9 2.0 ± 0.3 1.0 ± 0.1 0.8 ± 1.2 5.2 ± 0.3 34.4 ± 10.5 0.6 ± 0.8

The symbol ± designates standard deviation.

Table 2. Characteristics of Examined Meadow Grass Silagesa characteristic TS (%, w/w) VS (% TS) cellulose (% TS) hemicellulose (% TS) Klason lignin (% TS) pH TKN (g/kg) NH4 N (g/kg) protein (g/kg) C/N a

meadow grass silage, early cut 46.6 91.4 23.0 15.5

± ± ± ±

meadow grass silage, late cut

0.7 0.4 1.1 0.7

51.6 90.5 22.6 20.2

± ± ± ±

1.5 0.5 1.3 0.4

15.2 ± 2.5

29.6 ± 2.1

4.24 13.6 ± 0.6 1.7 ± 0.1 72.3 ± 3.9 32.0 ± 3.5

4.52 19.0 ± 0.4 2.0 ± 0.1 108.3 ± 0.7 23.2 ± 0.2


Table 3. Characteristics of Examined Manurea

MATERIALS AND METHODS

Characterization of the Inoculum. The thermophilic inoculum (53 °C) used in the experiments was obtained from Snertinge biogas plant, Denmark. The digestate was stored in a thermophilic incubator for 10 days before usage to diminish its biogas production. The chemical composition of the inoculum is presented in Table 1. Each analysis was performed in triplicate. Characterization of the Meadow Grass Silages. Meadow grass was harvested from a field located in Lintrup (South Jutland, Denmark) in two different time periods: (a) June 10, 2014, early harvest, and (b) October 1, 2013, late harvest. The harvested grasses were spread out on the field to dry for 48 h. The grasses were collected afterward and stored in airtight plastic bags, at room temperature and in the absence of light for 2 months to complete the ensiling process. The characteristics of meadow grass silages are presented in Table 2. Data are the means of triplicates along with their standard deviations. Characterization of the Used Manure. Poultry, mink, and cattle manure were obtained from livestock farms in Denmark and kept refrigerated at 4 °C before use. The characteristics of mink, poultry, and cattle manure are presented in Table 3. Each analysis was performed in triplicate. Pretreatment of Meadow Grass Silage. In the present study, three different mechanical pretreatment methods were tested, in which the meadow grass silage was (a) macerated with two rough mesh grating plates, (b) macerated with two rough mesh grating plates, and afterward, the grass was cut at 5.0 cm length, and (c) macerated with two rough mesh grating plates, and afterward, the grass was cut at 1.5

a

parameter

mink manure

poultry manure

cattle manure

TS (%, w/w) VS (% TS) cellulose (% TS) hemicellulose (% TS) pH TKN (g/kg) NH4 N (g/kg) protein (g/kg) C/N VFA acetate (g/L) propionate (g/L) isobutyrate (g/L) butyrate (g/L) isovalerate (g/L) valerate (g/L) n-hexanoate (g/L)

1.4 ± 0.1 62.5 ± 0.9 2.0 ± 0.3 1.3 ± 0.3 7.1 3.7 ± 0.1 3.1 ± 0.1 4.1 ± 0.2 9.6 ± 0.1 5.9 ± 0.3 4.1 ± 0.2 0.9 ± 0.1 0.2 ± 0.0 0.4 ± 0.0 0.3 ± 0.0 0.1 ± 0.0 0.0 ± 0.0

9.2 ± 0.2 66.0 ± 0.4 12.1 ± 0.9 9.8 ± 0.8 6.3 5.0 ± 0.2 2.7 ± 0.1 14.4 ± 0.9 6.3 ± 0.1 8.7 ± 0.3 6.5 ± 0.3 1.4 ± 0.0 0.1 ± 0.0 0.6 ± 0.0 0.1 ± 0.0 0.0 ± 0.0 0.0 ± 0.0

5.3 ± 0.4 75.4 ± 0.3 12.5 ± 1.6 9.3 ± 1.1 6.9 3.4 ± 0.1 2.1 ± 0.1 8.1 ± 0.2 12.4 ± 0.1 7.2 ± 0.2 4.6 ± 0.0 1.5 ± 0.1 0.2 ± 0.0 0.7 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 0.0 ± 0.0


cm length. The selection of the rough mesh grating plates as a maceration tool was based on the results obtained from our previous study.18 During pretreatment, a certain amount of meadow grass silage (1.4 kg) was placed in between the metal plates. Subsequently, the upper plate was moving along the longitudinal surface to shred and cut B


Article

Energy & Fuels the biomass. A cut chopper was used to decrease the grass length to 5 and 1.5 cm. Experimental Setup. Two sets of batch assays were conducted to evaluate the methane production of the examined biomasses, according to the standard protocol for determination of the biochemical methane yield.24 The experimental sets were carried out at thermophilic conditions (54 ± 1 °C). The total and working volume of the batch reactors were 547 and 200 mL, respectively, and the initial organic load of each reactor was 2 g of volatile solids (VS)/L. The reactors were manually shaken once per day to mix the substrates and to avoid the creation of dead zones in the reactors. All examined treatments were performed in triplicates. The first batch assay aimed to evaluate the efficiency of the mechanical pretreatments and to investigate the influence of the harvesting period on the anaerobic biodegradability of meadow grass silage. In this batch test, the grass was anaerobically digested as a single substrate (mono-digestion experiment). According to the results, the harvesting period and pretreatment method that allowed us to achieve the highest statistically significant methane yield was selected for further investigation in a second batch assay (co-digestion experiment). This batch test examined the anaerobic co-digestion of pretreated grass together with poultry, mink, or cattle manure in different mixing ratios. Therefore, the manure contribution, as a percentage of total volatile solids added (VSadded), in the examined treatments was 100, 80, 60, 40, and 20%. Table 4 summarizes the experimental design for the codigestion experiments.

Structural carbohydrates and Klason lignin were determined by strong acid hydrolysis according to the National Renewable Energy Laboratory (NREL) analytical methods.27 Sugars were determined by a Hewlett-Packard Agilent 1100 chromatographer with a BioRadAminex HPX-78H column (dimensions of 300.0 × 7.8 mm) at pH 3.0 with 4 mM H2SO4 as an eluent, at a flow rate of 0.6 mL/min. A vario MACRO cube, CHNOS elemental analyzer, Hanau, Germany, was used to define the C/N ratio of the substrates. Each measurement was conducted in triplicate. Statistical Analysis. Data analysis was performed with the software Graphpad Prism, version 5 (Graphpad Software, Inc., San Diego, CA). Statistical analysis comprised of descriptive statistics, and mean values and standard deviations were calculated. Comparisons of the means were carried out using one-way analysis of variance (ANOVA), and they were evaluated for significant differences (p < 0.05) among the achieved methane yields.

■

RESULTS AND DISCUSSION Effect of the Harvesting Period and Mechanical Pretreatments on Methane Production from Meadow Grass Silage. As mentioned above, two different harvesting periods and three different pretreatment methods focusing on the minimization of the plant length of meadow grass silage were examined to define the most promising combination for viable biogas enhancement. According to the obtained results, it was shown that the advancing maturity of meadow grass silage leads to an increased content of hemicellulose and lignin. More specifically, the concentrations of hemicellulose and lignin were found to be 4.7 and 14.4% higher, respectively, in the grass that was harvested during the late season (Table 2). It has been previously reported that the increasing stage of vegetation is a crucial parameter for increased contents of lignin and hemicellulose.11,28 The results from the present work validate that the increasing stage of vegetation increases the hardly biodegradable components, which would potentially decrease the biodigestibility of the substrate under anaerobic conditions. However, the concentration of cellulose was not affected by the plant maturity, because grasses obtained by both early and late harvesting periods had an almost equal cellulose content (23%). As a consequence, the harvesting period could be correlated with lower energy yields because of the higher concentration of lignin in cases of late harvesting but is rather independent with the content of the easily degradable organic fraction of grass. Previous research showed that the decrease of the particle size of agricultural substrates can have a positive impact on biogas production.29 Concerning the examined meadow grass silage, the harvesting period did not have any significant effect on the grass length (Figure 1). Late-stage harvesting resulted only in 3% higher distribution for grass length lower than 10 cm in comparison to early harvest. The methane yields of untreated meadow grass silage validate the hypothesis that the biogas productivity of feedstock harvested at the late stage would be lower compared to the early harvest. The methane yields of early and late harvests were 294 and 282 mL of CH4/g of VS, respectively. According to statistical analysis, it was found that the difference in the methane yields did not differ significantly. The slightly decreased methane yield (4%) can be ascribed to the increasing lignin content. The results from the present study are in accordance with the values of methane yields found in the literature for grass silage digestion.23 Mechanical pretreatment using mesh grating plates enhanced the methane production in both harvesting periods (Table 5).

Table 4. Experimental Setup of Batch Co-digestion Experiments mix composition (% of VSadded) feed components

trial number

Feed A mink manure and pretreated meadow M1 grass silage M2 M3 M4 M5 Feed B poultry manure and pretreated P1 meadow grass silage P2 P3 P4 P5 Feed C cattle manure and pretreated meadow C1 grass silage C2 C3 C4 C5

manure

grass silage

C/N

100 80 60 40 20

0 20 40 60 80

9.6 12.6 15.7 18.7 21.8

100 80 60 40 20

0 20 40 60 80

6.3 10.0 13.7 17.4 21.1

100 80 60 40 20

0 20 40 60 80

12.4 14.9 17.4 19.9 22.3

Analytical Methods. Total solids (TS), VS, pH, total Kjeldahl nitrogen (TKN), and total ammonia were calculated according to Standard methods.25 The pH of each substrate was measured by a PHM 92 LAB pH-meter. The methane content in batch assays and volatile fatty acids (VFA) composition in the manure and inoculum were measured according to the study by Kougias et al.26 Methane production in the glass reactors was measured by a gas chromatograph (Shimadzu GC-8A, Tokyo, Japan) equipped with a glass column (2 m, 5 mm outer diameter, and 2.6 mm inner diameter) packed with Porapak Q 80/100 mesh (Supelco, Bellefonte, PA) and a flame ionization detector (FID). The injection and detection temperatures were at 110 and 160 °C, respectively. The VFA content was analyzed by a gas chromatograph (Shimadzu GC-2010, Kyoto, Japan) with a FID. C


Article

Energy & Fuels

Co-digestion of pretreated meadow grass silage, harvested at the late cutting period, together with mink, poultry, or cattle manure as co-substrates was investigated in batch assays. Five different mixing ratios in terms of organic content were selected to define the most optimal ratio, with respect to the methane production. Table 6 summarizes the methane production yields achieved at all different combinations. Table 6. Practical Methane Yields of Pretreated Meadow Grass Silage Co-digestion with Mink, Poultry, and Cattle Manure trial number

methane yield (mL of CH4/g of VS)

M1 M2 M3 M4 M5 P1 P2 P3 P4 P5 C1 C2 C3 C4 C5

239 252 265 290 348 438 496 538 516 494 324 383 441 449 425

Figure 1. Length distribution of meadow grass silage for two different harvesting periods.

Table 5. Methane Yield of Early and Late Harvested Meadow Grass Silage methane yield (mL of CH4/g of VS) untreated mesh−mesh mesh−mesh 5 cm mesh−mesh 1.5 cm untreated mesh−mesh mesh−mesh 5 cm mesh−mesh 1.5 cm

Early Harvest 294 338 350 359 Late Harvest 282 329 339 340

biogas enhancement (%)

15 19 22 a

17 20 21

percentage of CH4 enhancement over manure yield (%)

statistical significance

5 11 21 45

nsa ns ns b

13 23 18 13

ns b c ns

18 36 38 31

ns c c ns

ns = not significant. bp < 0.01. cp < 0.05.

Mink manure showed statistically lower methane production, 239 mL of CH4/g of VS (Figure 2a and Table 6), compared to poultry and cattle manure. In this set of batch assays, the addition of 80% by meadow grass silage (M5) was the most promising mixing ratio. M5 produced 348 mL of CH4/g of VS, which was statistically significant, compared to other mink manure to meadow grass silage ratios. It was found that, by increasing the concentration of lignocellulosic biomass, the methane production in this set of batch assays was gradually increased. This could be explained by the high ammonia concentration (3.1 g/L) in mink manure, which was decreased by the addition of meadow grass. Consequently, the ammonia toxicity was reduced, and better biomethanation efficiency was achieved. Hydrolysis of complex polymers is known to be the rate-limiting step for the anaerobic degradation of lignocellulosic substrates.30 Lignocellulosic substrates need a large digestion period to be degraded.31 Thus, when the proportion of meadow grass silage was increased in the batch reactors, the digestion process was slower and the full biomethanation of these substrates took a longer time. More specifically, in the treatment that no silage was added (M1), more than 95% of the achieved methane yield was recorded during the first 9 days of the anaerobic digestion process. In contrast, the feedstock of M5 needed approximately 20 days to be fully degraded. Furthermore, the graphs that illustrate the cumulative methane production reveal that the degradation of mink manure occurred in a shorter time period compared to poultry and cattle manure, when digested without the addition of grass silage (Figure 2). Moreover, no lag phase was observed. This could be due the lower VFA concentration in mink manure compared to poultry and cattle manure (Table 3). It has been

The examined pretreatment method may manage to disrupt the heterogeneous structure of biomass in a high level and increase the biodigestibility of the substrate. The second pretreatment method, in which the grasses were cut at 5.0 cm length, increased the methane production in a higher level compared to the first pretreatment, in both harvesting periods. Specifically, the enhancement on early and late harvest meadow grass was 19 and 20% higher than the untreated samples, respectively. The methane yields were further increased by the third pretreatment method, in which the grasses were cut at 1.5 cm length. It can be concluded that the size reduction had a positive effect on meadow grass silage biodegradability (Table 5), although the methane yields among the examined pretreatments did not differ statistically significantly. It should be noted that the highest methane yield (359 mL of CH4/g of VS) was achieved in the early harvested and pretreated meadow grass silage with the minimum plant length (i.e., 1.5 cm). Moreover, it was found that the biogas enhancement was almost equal by comparing the different harvesting periods using the same pretreatment method. Because of the fact that the size reduction did not enhance statistically significantly the methane production compared to the treatment with mesh grating plates, the pretreatment methods that decreased the plant length were not further examined. Therefore, for the codigestion experiments, it was decided to use the mechanically pretreated meadow grass silage with the mesh grating plates that was harvested at the late season. Methane Production from Co-digestion of Manure Together with Meadow Grass at Different Mixing Ratios. D


Article

Energy & Fuels

(poultry manure, no grass silage) as the methane yield was enhance by 23 and 18%, respectively. These results are in accordance with previous findings, which concluded that poultry manure has a good buffer capacity but low C/N ratio, and therefore, their co-digestion with lignocellulosic substrates could lead to better AD performance.31 The methane yield of cattle manure was 324 mL of CH4/g of VS (Figure 2c and Table 6). The highly achieved methane yield can be ascribed to the fact that the manure was sieved before usage. Therefore, a significant amount of lignocellulosic material (e.g., barley) that is normally present in the manure as a result of the cattle feed was removed. It was proven that manure containing smaller sizes of lignocellulosic fibers can lead to higher methane production.34 The addition of meadow grass silage as a co-substrate positively affected the digestion process. The highest methane production, equal to 449 mL of CH4/g of VS, was achieved by adding 60% grass silage in cattle manure (C1). The methane yield of this mixing ratio was found to be 38% higher compared to the corresponding methane yield of cattle manure. On the basis of the statistical analysis, the addition of 40 and 60% significantly enhanced the methane yield. The results of our study are in accordance with similar experiments in the cited literature, investigating the codigestion of cattle manure together with lignocellulosic substrates. Lehtomäki et al., who investigated the co-digestion of cattle manure with grass silage in continuous mode experiments found that the highest methane production was achieved in the level of 30% grass contribution in the feedstock composition.35 In another research, Seppälä et al., who studied the co-digestion of maize with cattle manure, suggested the addition of 60 and 40% of maize as the most efficient mixing ratios for biogas production.36 To summarize the results from all of the co-digestion tests, it was observed that the optimum manure/meadow grass silage ratio differs for each animal waste, depending upon the chemical composition of manure. However, the co-digestion process had a clear positive impact in methane production, not allowing process imbalances or inhibitory effects to occur, especially in the treatments in which ammonia-rich livestock wastes were used. This was due to the fact that meadow grass silage is a relatively richer carbon source and, therefore, can improve the nutrient balance in the co-substrate mixture. Finally, it was found that the addition of 80% grass silage in mink manure and 40−60% in poultry or cattle manure were the optimum mixing ratios to achieve the highest methane production.

Figure 2. Methane development plotted against time for batch reactors co-digesting pretreated meadow grass silage together with (a) mink (M), (b) poultry (P), and (c) cattle (C) manure in different mixture compositions. The numbers 1−5 following the M, P, and C symbols represent the manure contribution in terms of VS in the feed, which was 100, 80, 60, 40, and 20%, respectively.

previously reported that high concentrations of VFA can disrupt the process stability and cause imbalances.32 Nevertheless, even though there was a lag phase during the digestion of poultry and cattle manure, the whole process was not seriously inhibited and the methane production was markedly increased after the initial lag phase. Possible adaptation could potentially prevent the process upsets. In the treatments in which poultry manure was used, it was found that the addition of grass silage up to 40% of the total organic content led to increasing methane production. Further addition of grass silage led to a gradual decrease of the methane yield (Table 6). The accumulated methane production for P2− P5 treatments was 496, 538, 516, and 494 mL of CH4/g of VS, respectively (Figure 2b and Table 6). Additionally, the methane yield of poultry manure (438 mL of CH4/g of VS) was found to be higher compared to the corresponding methane yield of mink or cattle manure (Figure 2b and Table 6). The results of the present study are in accordance with other researchers, who determined the methane yield of poultry manure in a range of 103−548 mL of CH4/g of VS.33 On the basis of the statistical analysis, the addition of 40 and 60% meadow grass silage in poultry manure showed a significant difference compared to P1

■

CONCLUSION This study showed that the mechanical pretreatment using mesh grating plates had a positive impact on the biodegradability of meadow grass silage, increasing the methane yield by 17% compared to untreated silage. Moreover, it was shown that the harvesting period is a crucial parameter for the exploitation of lignocellulosic biomasses for biogas production. The harvesting period could be correlated with lower energy yields because of the higher concentration of lignin in cases of late harvesting but is rather independent with the content of the easily degradable organic fraction of grass. Finally, co-digestion of meadow grass silage with mink, poultry, or cattle manure positively affected the methane production, because grass silage is a relatively richer carbon source and, therefore, can improve the nutrient balance in the co-substrate mixture. Nevertheless, the optimum silage/manure mixing ratio, which results in a E


Article

Energy & Fuels

(25) American Public Health Association (APHA). Standard Methods for the Examination of Water and Wastewater; APHA: Washington, D.C., 2005. (26) Kougias, P. G.; Boe, K.; Tsapekos, P.; Angelidaki, I. Bioresour. Technol. 2014, 153, 198−205. (27) Sluiter, A.; Hames, B.; Ruiz, R.; Scarlata, C.; Sluiter, J.; Templeton, D.; Crocker, D. Determination of Structural Carbohydrates and Lignin in Biomass; National Renewable Energy Laboratory (NREL): Golden, CO, 2011. (28) Prochnow, A.; Heiermann, M.; Plöchl, M.; Linke, B.; Idler, C.; Amon, T.; Hobbs, P. J. Bioresour. Technol. 2009, 100, 4931−4944. (29) Hills, D. J.; Nakano, K. Agric. Wastes 1984, 10, 285−295. (30) Wang, H.; Lehtomäki, A.; Tolvanen, K.; Puhakka, J.; Rintala, J. Bioresour. Technol. 2009, 100, 2311−2315. (31) Li, Y.; Zhang, R.; Liu, X.; Chen, C.; Xiao, X.; Feng, L.; He, Y.; Liu, G. Energy Fuels 2013, 27, 2085−2091. (32) Boe, K.; Batstone, D. J.; Angelidaki, I. Biotechnol. Bioeng. 2007, 96, 712−721. (33) Nasir, I. M.; Mohd Ghazi, T. I.; Omar, R. Eng. Life Sci. 2012, 12, 258−269. (34) Angelidaki, I.; Ahring, B. K. Water Sci. Technol. 2000, 41, 189− 194. (35) Lehtomäki, A.; Huttunen, S.; Rintala, J. A. Resour., Conserv. Recycl. 2007, 51, 591−609. (36) Seppälä, M.; Pyykkönen, V.; Väisänen, A.; Rintala, J. Fuel 2013, 107, 209−216.

higher methane yield, is strongly dependent upon the chemical composition of the manure substrate.

■

AUTHOR INFORMATION

Corresponding Author

*Telephone: +45-4525-1429. Fax: +45-4593-2850. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank Hector Garcia for technical assistance. This work was funded by the Danish Agency of Energy under the Energy Technology Development and Demonstration Program (EUDP) “New Technology for an Efficient Utilization of Meadow Grass in Biogas Reactor”.

■

REFERENCES

(1) Biswas, R.; Ahring, B. K.; Uellendahl, H. Water Sci. Technol. 2012, 66, 1751−1758. (2) Danish Goverment. Grøn Vækst; Danish Goverment: Copenhagen, Denmark, 2009. (3) Seppälä, M.; Paavola, T.; Lehtomäki, A.; Rintala, J. Bioresour. Technol. 2009, 100, 2952−2958. (4) Raven, R. P. J. M.; Gregersen, K. H. Renewable Sustainable Energy Rev. 2007, 11, 116−132. (5) Johansson, D. J.; Azar, C. Clim. Change 2007, 82, 267−291. (6) Triolo, J. M.; Pedersen, L.; Qu, H.; Sommer, S. G. Bioresour. Technol. 2012, 125, 226−232. (7) Raju, C. S.; Ward, A. J.; Nielsen, L.; Møller, H. B. Bioresour. Technol. 2011, 102, 7835−7839. (8) Kandel, T. P.; Sutaryo, S.; Møller, H. B.; Jørgensen, U.; Lærke, P. E. Bioresour. Technol. 2013, 130, 659−666. (9) Lissens, G.; Thomsen, A. B.; De Baere, L.; Verstraete, W.; Ahring, B. K. Environ. Sci. Technol. 2004, 38, 3418−3424. (10) Zeng, Y.; Zhao, S.; Yang, S.; Ding, S.-Y. Curr. Opin. Biotechnol. 2014, 27, 38−45. (11) Sharma, H. S. S.; Lyons, G.; McRoberts, C. Chem. Eng. Res. Des. 2011, 89, 2309−2321. (12) Bruni, E.; Jensen, A. P.; Pedersen, E. S.; Angelidaki, I. Appl. Energy 2010, 87, 2212−2217. (13) Gunnarsson, I.; Svensson, S.; Johansson, E.; Karakashev, D.; Angelidaki, I. Ind. Crops Prod. 2014, 56, 231−240. (14) Pouech, P.; Fruteau, H.; Bewa, H. Proceedings of the 10th European Conference Biomass for Energy and Industry; Würzburg, Germany, June 8−11, 1998; p 165. (15) Dussadee, N.; Reansuwan, K.; Ramaraj, R. Bioresour. Technol. 2014, 155, 438−441. (16) Pakarinen, O.; Lehtomäki, A.; Rissanen, S.; Rintala, J. Bioresour. Technol. 2008, 99, 7074−7082. (17) Monlau, F.; Barakat, A.; Steyer, J. P.; Carrere, H. Bioresour. Technol. 2012, 120, 241−247. (18) Tsapekos, P.; Kougias, P. G.; Angelidaki, I. Bioresour. Technol. 2015, 182, 329−335. (19) Vavilin, V. A.; Rytov, S. V.; Lokshina, L. Y.; Pavlostathis, S. G.; Barlaz, M. A. Biotechnol. Bioeng. 2003, 81, 66−73. (20) Hansen, K. H.; Angelidaki, I.; Ahring, B. K. Water Res. 1999, 33, 1805−1810. (21) Kougias, P. G.; Kotsopoulos T.A, M. G. G. Fresenius Environ. Bull. 2010, 19, 1682−1686. (22) Kougias, P. G.; Kotsopoulos, T. A.; Martzopoulos, G. G. Renewable Energ 2014, 69, 202−207. (23) Nizami, A.-S.; Korres, N. E.; Murphy, J. D. Environ. Sci. Technol. 2009, 43, 8496−8508. (24) Angelidaki, I.; Alves, M.; Bolzonella, D.; Borzacconi, L.; Campos, J. L.; Guwy, A. J.; Kalyuzhnyi, S.; Jenicek, P.; van Lier, J. B. Water Sci. Technol. 2009, 59, 927. F


Anaerobic Mono- and Co-digestion of Mechanically Pretreated

Recommend Documents