Impacts of soil management on root characteristics of switchgrass

One approach to reducing the concentration of atmospheric carbon dioxide, which is a dominant greenhouse gas, is to develop renewable energy sources from biofuel crops. Switchgrass, (Panicum virgatum L.) as an energy crop, can partly mitigate potential global warming by supplementing fossil fuels and sequestering carbon (C). Although switchgrass grown for energy may impact C sequestration via the input of root biomass, information on the impact of soil management on switchgrass root growth is extremely limited. We determined the influence of row spacing, nitrogen (N) rate, switchgrass cultivar, and soil type on switchgrass root characteristics. Roots were mainly distributed in the surface soil (0–15 cm), and were 90.4 and 68.2% of the total in the intrarow and interrow profile, respectively. Nitrogen application altered root N but not C concentration, implying that any increase in C sequestration by switchgrass roots will be due to increased root biomass rather than increased C concentration. Root weight density generally decreased in the interrow with wider row width, and N application generally did not affect root weight density. Root weight density in the Pacolet soil was higher than in the other four soils, and root density was 4.1 times higher in the Pacolet soil than in the Norfolk soil. Root mass in the Pacolet soil (36,327 kg ha⁻¹) was 2.7 times greater than that found in the Norfolk soil (13,204 kg ha⁻¹) within 150 cm of the soil surface. Differences in root characteristics were found among cultivars: root weight density with ‘Cave-in-Rock’ switchgrass was 29.4 and 47.6% higher than ‘Alamo’ and ‘Kanlow’, respectively. Variations in switchgrass root biomass production owing to soil type and cultivar suggest that site and cultivar selection will be important determinants of C sequestration by switchgrass roots. A potential benefit of switchgrass is the reduced loss of nutrients associated with non-point pollution, owing to its deep root system that may extend 330 cm below the soil surface.     

Impact of row spacing, nitrogen rate, and time on carbon partitioning of switchgrass

Cultivation of switchgrass (Panicum virgatum L.) as an energy crop could lower atmospheric carbon dioxide (CO₂) levels by replacing fossil fuel and sequestering carbon (C). Information on the details of C partitioning within the switchgrass–soil system is important in order to quantify how much C is sequestered in switchgrass shoots, roots, and soil. No studies of C partitioning in a switchgrass–soil system under field conditions have been conducted. This study was aimed at determining the impact of agricultural management practices, such as row spacing and nitrogen (N) application rate, on C partitioning within the switchgrass–soil system; changes in C partitioning with time after switchgrass establishment were also considered. The results indicate that C storage in switchgrass shoots was higher with wide than narrow rows, and increased with N application rates. These responses were due to higher yields with wide than narrow rows and higher yields as N application rate increased. Carbon storage in shoots was 14.4% higher with 80-cm than 20-cm row spacing. Annual application of 224 kgNha⁻¹ increased C storage in shoots by 207% and 27% when compared with annual applications of 0 and 112 kgNha⁻¹, respectively. Carbon storage increased by 62% over time from 1995 to 1996 in newly established switchgrass on sandy loam soil in the coastal plain of Alabama. Rate of C increase in roots (72%) was higher than in shoots (49%) between 1995 and 1996. Carbon storage was in order of soil C > root C > shoot C in both 1995 and 1996. The root/shoot ratio of C storage was 2.2. It appears that C partitioning to roots plays an important role in C sequestration by switchgrass.     

Simulated biomass,environmental impacts and best management practices for long-term switchgrass systems in a semi-arid region

Long-term information on switchgrass (Panicum virgatum L.) as a biomass energy crop grown on marginally saline soil and the associated impacts on soil carbon (C) and nitrogen (N) dynamics, greenhouse gas (GHG) emissions, and best management practices (BMPs) are limited. In this study, we employed the DAYCENT model, based on a 4-year switchgrass field experiment, to evaluate the long-term biomass yield potential and environmental impacts, and further to develop BMPs for switchgrass in a semi-arid region.The model showed that long-term (14-year) annual mean biomass yields were 9.6 and 5.2 Mg ha⁻¹ for irrigated and rainfed switchgrass systems, respectively. The simulated biomass yields correlated well with field-measured biomass with r² values of 0.99 and 0.89 for irrigated and rainfed systems, respectively. Soil organic carbon (SOC) and soil total nitrogen (STN) accumulated rapidly after switchgrass establishment, with mean accrual rates of 0.99–1.13 Mg C ha⁻¹ yr⁻¹ and 0.04–0.08 Mg N ha⁻¹ yr⁻¹, respectively. Based on the outputs of numerous long-term model simulations with variable irrigation water supplies and N rates, the irrigation regime and N rate with the highest yield to input ratio were chosen as BMPs. The DAYCENT model predicted-BMP was irrigating every 14 days at 70% potential evapotranspiration combined with an N rate of 67 kg ha⁻¹ yr⁻¹. Switchgrass established and produced biomass reasonably well in this semi-arid region; however, appropriate irrigation and N fertilization were needed for optimal biomass yield. Switchgrass had a great potential to sequester C into soils with low N₂O emissions while supplying significant quantities of biomass for biofuel synthesis.     

Soil management impacts on soil carbon sequestration by switchgrass

Increased atmospheric carbon dioxide (CO₂) could have negative impacts on the environment. Producing and creating bioenergy in the form of biofuels and electricity from crops is a practical approach to reducing CO₂ buildup by displacing fossil fuels and sequestering carbon (C). The use of switchgrass (Panicum virgatum L.) as an energy crop can contribute to clean burning fuels, but no studies addressing soil C sequestration as influenced by use of switchgrass as an energy crop have been conducted. Our objective was to determine the effect of different cultural practices on soil C sequestration under switchgrass. Field experiments were designed to provide differences in row spacing, nitrogen (N) rate, switchgrass cultivar, and harvest frequency on a variety of soils. Our results showed that N application, row spacing, harvest frequency, and switchgrass cultivar did not change soil organic C in the short-term (2–3 yr) after switchgrass establishment. However, after 10 yr under switchgrass soil organic C was 45 and 28% higher at depths of 0–15 and 15–30 cm, respectively, compared with fallowed soil in an adjacent area. It appears that several years of switchgrass culture will be required to realize a soil C sequestration benefit.     

Biochar and plant growth promoting rhizobacteria effects on switchgrass (Panicum virgatum cv. Cave-in-Rock) for biomass production in southern Québec depend on soil type and location

Switchgrass (Panicum virgatum L.) is a fast growing native C₄ perennial and a lignocellulosic biomass crop for North America. In combination with biochar, an active plant growth promoting rhizobacterial (PGPR) community can contribute to the long-term sequestration of carbon in soil, fix nitrogen, and enhance the availability of other nutrients to plants. Biochar and PGPR have the potential to improve grass biomass production, but they have not been tested together under high-latitude temperate zone field conditions. Therefore, the objective of this three-year field study was to determine whether there were effects on biomass yield and yield components of switchgrass (cv. Cave-in-Rock) due to a rhizobacterium that was able to mobilize soil phosphorus (Pseudomonas rhodesiae), a bacterial consortium that was able to supply nitrogen (Paenibacillus polymyxa, Rahnella sp., and Serrati sp.), and pine wood chip biochar applied as a soil amendment at 20 Mg ha⁻¹. The incorporation of biochar, or inoculation with the N-fixing consortium, and the combined inoculation of the experimental bacteria had positive effects on switchgrass height. At a loam soil site in Sainte-Anne-de-Bellevue, Québec, when nitrogen fertilizer was not applied, the addition of biochar had a positive effect on stand count (tillers m⁻¹ row). On the sandy soil in Sainte-Anne-de-Bellevue, when biochar was applied with 100 kg N ha⁻¹, biomass yield increased over the control but did not provide additional benefits over plots receiving only 50 kg N ha⁻¹. It remains unclear whether or not the increased C sequestration of this management system justifies increased N fertilizer usage.     

Characterization of fine root system and potential contribution to soil organic carbon of six perennial bioenergy crops

Perennial bioenergy crops provide biomass for renewable energy production, but also sequester atmospheric carbon (C) in the soil. Roots represent one of the most important soil C inputs-root length density (RLD, cm cm⁻³), root diameter and fine root biomass (FRB, Mg ha⁻¹) in the top 1 m of soil were characterized for three woody (poplar, black locust, willow) and three herbaceous (giant reed, miscanthus, switchgrass) perennial crops in the same location. The vertical distribution of FRB and RLD was described by fitting the “beta” (β) model to the experimental data. The herbaceous species had higher β values for FRB and RLD than woody crops, suggesting that the former explore the deeper soil layers with a greater proportion of roots. In particular, 3.7 Mg ha⁻¹, or 43% of the whole root mass, was found below the ploughing soil layer (0.3 m) for the herbaceous species, while only 1.2 Mg ha⁻¹, or 26% of the whole root mass, was allocated by woody crops to the same soil layer. In all the species, the majority of the sampled roots (99.1%) had a diameter lower than 2 mm, and in the first 10 cm of the soil the woody species tended to produce roots with a smaller diameter than those of the herbaceous species. Overall, the herbaceous crops have a higher potential to contribute to C storage in the deep soil layers, while the woody species, have a greater potential to affect soil organic carbon in the top soil layer.     

Switchgrass (Panicum virgatum L.) nutrients use efficiency and uptake characteristics,and biomass yield for solid biofuel production under Mediterranean conditions

Switchgrass produces high amounts of biomass that can be used for solid biofuel production. In this study, the dry biomass yield vs. N–P–K nutrient uptake relations as well as the N-mineralization and the N-fertilization recovery fraction for switchgrass (cv. Alamo) were determined under field conditions for three N-fertilization (0, 80 and 160 kg ha⁻¹) and for two irrigation (0 and 250 mm) levels, in two soils in central Greece with rather different moisture status over the period 2009–2012. It was found that dry biomass yield on the aquic soil may reach 27–30 t ha⁻¹ using supplemental irrigation, and remain at high levels (19–24 t ha⁻¹) without irrigation. In the xeric soil, however, lower biomass yields of 14–15 t ha⁻¹ may be produced with supplemental irrigation. The average N-concentration varies between 0.23% in stems and 1.10% in leaves, showing the very low needs in N. P-content varies between 0.16% in leaves and 0.03% in stems, whereas K-content fluctuates between 0.67% and 0.78%. Linear biomass yield-nutrient uptake relationships were found with high R², pointing to nutrient use efficiencies of 240 and 160 kg kg⁻¹, for N and K respectively. The base N-uptake ranged 70–84 kg ha⁻¹ in the aquic to 60 kg ha⁻¹ or less in the xeric soil. N-recovery fraction was about 30% in the aquic soil and lower in the xeric. Therefore, switchgrass is very promising for biomass production and its introduction in land use systems (especially in aquic soils of similar environments) should be seriously taken into consideration.     

Sub-surface soil carbon changes affects biofuel greenhouse gas emissions

Changes in direct soil organic carbon (SOC) can have a major impact on overall greenhouse gas (GHG) emissions from biofuels when using life-cycle assessment (LCA). Estimated changes in SOC, when accounted for in an LCA, are typically derived from near-surface soil depths (<30 cm). Changes in sub-surface soil depths (>30 cm) could have a large positive or negative impact on overall GHG emissions from biofuels that are not always accounted for. Here, we evaluate how sub-surface SOC changes impact biofuel GHG emissions for corn (Zea mays L.) grain, corn stover, and switchgrass (Panicum virgatum L.) using the (Greenhouse Gases, Regulated Emissions, and Energy Use in the Transportation) GREET model. Biofuel GHG emissions showed as much as a 154% difference between using near-surface SOC stocks changes only or when accounting for both near- and sub-surface SOC stock changes. Differences in GHG emissions highlight the importance of accounting for sub-surface SOC changes especially in bioenergy cropping systems with potential for soil C storage to deeper soil depths.     

Physical characteristics of AFEX-pretreated and densified switchgrass,prairie cord grass,and corn stover

The goal of the study was to evaluate and compare the physical properties of control, pretreated and densified corn stover, switchgrass, and prairie cord grass samples. Ammonia Fiber Expansion (AFEX) pretreated switchgrass, corn stover, and prairie cord grass samples were densified by using the comPAKco device developed by Federal Machine Company of Fargo, ND. The densified biomass were referred as “PAKs” in this study. All feedstocks were ground into three different grind size of 2, 4 and 8 mm prior to AFEX pretreatment and the impact of grinding on pellet properties was studied. The results showed that the physical properties of AFEX-PAKed material were not influenced by the initial grind size of the feedstocks. The bulk density of the AFEX-PAKed biomass increased by 1.2–6 fold as compared to untreated and AFEX-pretreated materials. The durability of the AFEX-PAKed materials were between 78.25 and 95.2%, indicating that the AFEX-PAKed biomass can be transported easily. To understand the effect of storage on the physical properties of these materials, samples were stored in the ambient condition (20 ± 2 °C and 70 ± 5% relative humidity) for six months. After storage, thermal properties of the biomass did not change but glass transition temperature decreased. The water absorption index and water solubility index of AFEX-treated and AFEX-PAKed biomass showed mixed trends after storage. Moisture content decreased and durability increased upon storage.     

Soil carbon accrual in particle-size fractions under Miscanthus x. giganteus cultivation

The energy crop Miscanthus x. giganteus is a deep rooting perennial rhizomatous C4 grass with great biomass production, even under temperate German climate conditions. Accordingly we hypothesized that this crop may accumulate great amounts of carbon in soil, particularly in deeper soil layers. We sampled several former C3-derived arable fields that had been cropped with Miscanthus for 0–19 years. We were able to trace the origin and turnover of soil organic C (SOC) on the basis of natural ¹³C/¹²C abundance measurements. The analysis was performed on bulk soil samples and on particle-size fractions that are known to comprise SOC of different availability for decay. Miscanthus-derived C accumulated at a rate of 1800 kg ha⁻¹ y⁻¹ down to a soil depth of 100 cm. Only about 50% of this C accrual occurred in the surface soil (0–10 cm). The C accumulation differed among size fractions. Miscanthus-derived C in the coarse-POM fraction increased rapidly during the first years of Miscanthus cultivation until a steady state was reached after approximately seven years. The stocks of Miscanthus-derived C associated with the clay fraction increased at a rate of 230 kg ha⁻¹ y⁻¹ in 0–5 cm, 45 kg ha⁻¹ y⁻¹ in 20–30 cm and 38 kg ha⁻¹ y⁻¹ in 50–75 cm. The C accumulation rate decreased with increasing soil depth. In particular, Miscanthus-derived C associated with the clay fraction led to increasing SOC stocks, even below the former Ap; that is, below a depth that would respond sensitively to a future land use change.     

Comparative net energy ratio analysis of pellet produced from steam pretreated biomass from agricultural residues and energy crops

A process model was developed to determine the net energy ratio (NER) for the production of pellets from steam pretreated agricultural residue (wheat straw) and energy crops (i.e., switchgrass in this case). The NER is a ratio of the net energy output to the total net energy input from non-renewable energy sources into a system. Scenarios were developed to measure the effects of temperature and level of steam pretreatment on the NER of steam pretreated wheat straw and switchgrass pellets. The NERs for the base case at 6 kg h⁻¹ are 1.76 and 1.37 for steam-pretreated wheat straw and switchgrass-based pellets, respectively. The reason behind the difference is that more energy is required to dry switchgrass pellets than wheat straw pellets. The sensitivity analysis for the model shows that the optimum temperature for steam pretreatment is 160 °C with 50% pretreatment (i.e. 50 % steam treated material is blended with the raw biomass and then pelletised). The uncertainty results for NER for steam pretreated wheat straw and switch grass pellets are 1.62 ± 0.10 and 1.42 ± 0.11, respectively.     

Carbon sequestration in willow (Salix spp.) plantations on former arable land estimated by repeated field sampling and C budget calculation

Short rotation coppice (SRC) plantations are of interest as producers of biomass for fuel, but also as carbon (C) sinks to mitigate CO₂ emissions. Carbon sequestration in biomass and soil was estimated in 5-year-old replicated SRC plantations with willows (Salix spp.) on former arable land at five sites in Sweden. Total standing C stocks, i.e. C stored in woody biomass above- and belowground, fine root standing crop, litter, and soil organic carbon (SOC) were estimated by repeated field sampling and C budget calculation.Overall, the SRC willow plantations represented a C sink after five years. Estimated increase of total standing C stock was 15% on average compared to pre-planting conditions. There was no change in SOC when including all sites. Analyses within sites revealed a decrease in SOC at one site, although the decrease was compensated for by C stored in willow biomass. After removal of stem biomass, C in other plant pools was sufficient to compensate for the SOC decrease. Remaining C in stumps, stool, and coarse roots was estimated at ca 20% of stem C.There was a discrepancy between SOC sequestration rates from soil sampling and C budget calculation, −2.1–1.0 and 0.15–0.45 Mg ha⁻¹ y⁻¹, respectively. Mineralization of old organic material from previous land-use and input to SOC from understory vegetation were not included in the calculations, which may explain part of the differences. The importance of understory litter in C budgets for young plantations was apparent, as it comprised 24–80% of aboveground litter C.     

Size matters? – The diverging influence of cutting length on growth and allometry of two Salicaceae clones

Short rotation coppices (SRC) are often established by inserting cuttings vertically into the soil. Longer cuttings are generally regarded as superior to establish plants on stress-prone sites. However, knowledge about above- and belowground biomass production, plant allometry and root characteristic of clones established through different lengths of cuttings is scarce.The experiment was performed with 2 common SRC clones (Populus clone Max 4, Salix clone Inger) and 2 cutting length (20 cm and 40 cm). Above- and belowground biomass and leaf and root morphology were determined after one growing season. Longer cuttings produce more biomass but have a diverging influence on the shoot:root allocation of both clones. Long cuttings of Populus cl. Max produce more aboveground biomass, mostly leaves, than 20 cm cuttings, while 40 cm Salix cl. Inger cuttings have more fine roots. Leaf and root morphology are only marginally influenced by cutting length.Choosing longer Populus cl. Max cuttings might not be a good strategy when considering SRC establishment on more stress-prone sites, since their larger above-ground biomass will e.g. increase transpirational demand. Because of the lower shoot:root ratio, longer Salix cl. Inger cuttings seem to be more suitable to establish SRC on fields with (partially) restricted water and nutrient supply than shorter cuttings. Thus, planting difficulties and higher costs of longer cuttings may be offset by higher survival and greater aboveground productivity only in some clones. In the future, optimal cutting lengths must be evaluated not only for different environmental conditions but also for different SRC species/clones.     

Effects of soil texture on germination and survival of non-toxic Jatropha curcas seeds

Toxic oil seeds of Jatropha curcas have been widely propagated in tropical and subtropical regions for biofuel production. However, very little is known about the non-toxic seeds of J. curcas and their germination. This paper describes the germination and survival of non-toxic J. curcas seeds over two consecutive years. Non-toxic seeds native from southeastern Mexico (600–800 mg weight) were sown in three soils with different texture (sandy; sandy-loam and clay-loam) in order to assess germination, speed of germination and survival rates of the emerged seedlings. Sandy soil had the lowest organic matter (OM) content with 1.68 g-kg⁻¹ of dry soil, followed by sandy-loam soil (39 g-kg⁻¹) and clay-loam soil with the highest OM (72.63 g-kg⁻¹). The highest germination rate was obtained in sandy-loam (76%), followed by sandy (75%) and clay-loam soil (24%). The highest survival rates were obtained in sandy (99%) and sandy-loam (99%) soils followed by clay-loam soil (87%). The highest average speed of germination index was recorded in sandy (155), followed by sandy-loam (125) and clay-loam soil (23). It can be concluded that sandy and sandy-loam soil textures, with bigger pore size and low organic matter content, were the more suitable substrates to germinate non-toxic J. curcas seeds; clay loam as substrate was not suitable for non-toxic J. curcas seeds due to the low germination rate and speed.     

Grasses for biofuels: A low water-use alternative for cold desert agriculture?

In arid regions, reductions in the amount of available agricultural water are fueling interest in alternative, low water-use crops. Perennial grasses have potential as low water-use biofuel crops. However, little is known about which perennial grasses can produce high quantity, high quality yields with low irrigation on formerly high-input agricultural fields in arid regions. We monitored biomass production, weed resistance, rooting depth, and root architecture of nine perennial grasses under multiple irrigation treatments in western Nevada. Under a low irrigation treatment (71 ± 9 cm irrigation water annually), cool-season grasses produced more biomass and were more weed-resistant than warm-season grasses. With additional irrigation (120 ± 12 cm water annually), warm- and cool-season grasses had similar biomass production, but cool-season species remained more weed-resistant. Among species within each grass type, we observed high variability in performance. Two cool-season species (Elytrigia elongata and Leymus cinereus) and one warm-season species (Bothriochloa ischaemum) performed better than the other tested species. Root depth was not correlated with biomass production, but species with deeper roots had fewer weeds. Abundance of fine roots (but not large roots) was correlated with increased biomass and fewer weeds. Both L. cinereus and E. elongata had deep root systems dominated by fine roots, while B. ischaemum had many fine roots in shallow soil but few roots in deeper soil. Cool-season grasses (particularly E. elongata, L. cinereus, and other species with abundant fine roots) may be worthy of further attention as potential biofuel crops for cold desert agriculture.     

The recovery over several seasons of 15N-labelled fertilizer applied to Miscanthus×giganteus ranging from 1 to 3 years old

In a field experiment 60 kg N ha⁻¹ of ¹⁵N-labelled fertilizer was applied to Miscanthus×giganteus planted 1, 2 or 3 years previously. Plots were destructively sampled at senescence 1, 2 or 3 years after labelled N was applied with aerial biomass harvested in intervening years. The objective was to quantify N uptake and distribution within the plant, labelled N remaining in the soil (0–50 cm) and overall losses. We report results for the 2nd and 3rd years and compare them to 1st year data previously published. Total biomass more than doubled over 2 years of growth but N concentration did not change. More labelled N was recovered by 3-year-old plants (65%) than by 2-year-old plants (55%) or 1-year-old plants (38%). Between 19% and 26% was found in the soil (0–50 cm) and more than 85% of this N was in topsoil (0–23 cm). Total recovery in plant and soil was 60–71% for 1-year-old plants, 76–81% for 2-year-old plants and 84% for 3-year-old plants. Overall losses (18–24%) from 2- and 3-year-old plants are similar to those from arable and permanent grass crops on the same soil type given similar amounts of N. Labelled (and unlabelled) N stored in rhizomes will take several years to decline because of transfers between rhizomes and shoots. Similarly, labelled N remaining in soil will decline slowly over many years; any N mineralized in subsequent years will be subject to plant uptake and/or loss.     

Monitoring switchgrass composition to optimize harvesting periods for bioenergy and value-added products

Switchgrass (Panicum virgatum) is a perennial grass that has emerged as an ideal candidate for production of biofuel and value-added co-products. One of the primary requirements for the successful manufacturing of these switchgrass-derived bioproducts is to produce a consistent feedstock with reliable and adequate amounts of the substrate constituent needed. For example, the biofuels industry requires a fast-growing energy crop with higher cellulose content and lower inhibitors found in secondary constituents. Other industries would profit from higher lignin content for products such as carbon fibers, or higher water and ethanol-soluble extracts containing compounds of interest. Two switchgrass field plots in eastern Tennessee were monitored over a period of six months, including before and after traditional harvesting times for the biorefinery. Characterization of the biomass and its constituents, such as water and ethanol extracts, cellulose, hemicelluloses, lignin, and ash, was performed to examine chemical changes in switchgrass that occurred prior to, during, and after traditional harvesting times used in a biorefinery setting. Total carbohydrate (65.6–66.7 wt%) and lignin (21.7–23.2 wt%) content was found to peak in January. Extractives content was at a maximum in early harvests at 15.9–16.6 wt% and decreased to 5.5–5.8 wt% in February. An inverse relationship exists between the extractives and lignin content (R² = 0.94). Nonstructural soluble sugars peaked in early October with 5.1 wt% of the switchgrass composition. Remobilization efficiencies of K, Mg, P, and Fe increased with time, indicating conservation of soil nutrients if harvests were completed in late winter.     

Harvest storage and handling of round and square bales of giant reed and switchgrass: An economic and technical evaluation

This study evaluated an innovative collection system for biomass based on single-pass harvesting to reduce handling and storage costs. Trials were conducted on two herbaceous perennials: giant reed (Arundo donax L.) and switchgrass (Panicum virgatum L.). A technical and economic evaluation compared two single-pass harvesting systems in which the biomass was cut-shredded-baled in the same operation. The two systems were composed of a Nobili biotriturator (for biomass shredding and windrowing) front-mounted on a 4-wheel-drive tractor and two types of balers: a KUHN VB2160 round baler and a KUHN LSB 1290 large square baler. Costs of harvesting, handling, storage and delivery to the conversion plant were evaluated. Three distances of delivering were considered (0–20; 20–40; 40–60 km). It was estimated that the harvesting system could produce round bales of switchgrass and giant reed stored in-field under a plastic tarp at a cost of 22.3 € Mg⁻¹ and 23.3 € Mg⁻¹ dry and square bales at 26.0 € Mg⁻¹ and 21.7 € Mg⁻¹ for switchgrass and giant reed respectively. The costs of harvesting, handling, in-field storage and delivery to the conversion plant amounted to 43.7 € Mg⁻¹ and 45.7 € Mg⁻¹ dry for round bales and 43.1 € Mg⁻¹ dry and 34.9 € Mg⁻¹ for square bales of switchgrass and giant reed for delivery distances of less than 20 km.     

Co-hydrothermal gasification of microbial sludge and algae Kappaphycus alvarezii for bio-hydrogen production: Study on aqueous phase reforming

In this study, wastewater obtained from a sewage treatment plant was treated successively by using microbial consortium and macroalgae Kappaphycus alvarezii to generate microbial sludge and algal biomass. The production of green fuel was carried out via co-gasification of microbial sludge and macroalgae Kappaphycus alvarezii for a duration of 60 min, feedstock to solvent ratio (5 to 20 g of feedstock in 200 mL), sludge to algae ratio (ranging from 1:1 to 3:1) and temperature (300–400 °C) respectively. Maximum bio-hydrogen yield was 36.1% and methane yield was 38.4% at a temperature of 360 °C at a feedstock to solvent ratio of 15:200 g/mL and sludge to algae ratio of 2:1 individually. The liquid by product of co-gasification process was later subjected to photocatalytic reforming, resulted in an enhanced hydrogen composition of 61.25%.