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The present study investigates the effect on methane production from waste paper when co-digested with macroalgal biomass. Both feedstocks were previously mechanically pretreated to reduce their particle size. The study was planned according two factors: the feedstock to inoculum (F/I) ratio and the waste paper to macroalgae (WP/MA) ratio. The F/I ratios checked were 0.2, 0.3 and 0.4 and the WP/MA ratios were 0:100, 25:75, 50:50, 75:25 and 100:0. The highest methane yield (386 L kg−1 VSadded) was achieved at an F/I ratio of 0.2 and a WP/MA ratio of 50:50. A biodegradability index of 0.87 obtained in this study indicates complete conversion of feedstock at an optimum C/N ratio of 26. Synergistic effect was found for WP/MA 25:75, 50:50 and 75:25 mixing ratios compared with the substrates mono-digestion.

Supercritical water gasification (SCWG) is a method by which biomass can be converted into a hydrogen-rich gas product. Wet industrial waste streams, which contain both organic and inorganic material, are well suited for treatment by SCWG. In this study, the gasification of two streams of biomass resulting from the pulp and paper industry, black liquor and paper sludge, has been investigated. The purpose is to convert these to useful products, both gaseous and solids, which can be used either in the papermaking process or in external applications. Simple compounds, such as glucose, have been fully gasified in SCWG, but gasification of more complex compounds, such as biomass and waste, have not reached as high conversions. The investigated paper sludge was not easily gasified. Improving gasification results with catalysts is an option and the use of alkali salts for this purpose was studied. The relationship between alkali concentration, temperature, and gasification yields was studied with the addition of KOH, K2CO3, NaOH and black liquor to the paper sludge. Addition of black liquor to the paper sludge resulted in similarly enhancing effects as when the alkali salts were added, which made it possible to raise the dry matter content and gasification yield without expensive additives.

Catalytic co-pyrolysis of biomass and plastics (HDPE (high density polyethylene), PP (polypropylene) and PET (polyethylene terephthalate)) has been performed in a fixed-bed reactor in presence of cobalt based alumina, ceria and ceria-alumina catalysts to analyze the product distribution and selectivity. Catalysts are synthesized using co-precipitation method and characterized by BET (Brunauer-Emmett-Teller) surface area and XRD analysis. The effect of catalytic co-pyrolysis at different temperature with product distribution has been evaluated. The results have clearly shown the synergistic effect between biomass and plastics, the liquid products gradually increases forming with rise in the plastic content in the blend. Gaseous products have yielded most during pyrolysis of blend having biomass/plastics ratio of 5:1 with the presence of 40% Co/30% CeO2/30% Al2O3 catalyst with hydrogen gas production touched its peak of 47 vol%. Catalytic performance enhanced with increase with the cobalt loading, with best performance attributing to 40% Co/30% CeO2/30% Al2O3 catalyst. (C) 2016 Elsevier Ltd. All rights reserved.

The integration of different conversion technologies can strongly contribute to the biomass potential exploitation. To this aim, the use of intermediate pyrolysis biochar is analyzed in this paper as an alternative co-substrate in anaerobic digestion. The specie Ampelodesmos mauritanicus has been specifically chosen in this case for its capacity to tolerate, accumulate and, in some cases, degrade organic and inorganic pollutants. The biochar, produced under intermediate pyrolysis conditions at 450 °C, 500 °C and 550 °C, has been here considered for a biomethane potential assessment. The intermediate pyrolysis process improves the herbaceous bioavailability and promotes the microbial activity by reducing the digestion lag phase. Three reactors, namely B450, B500 and B550, have been considered in this study. Acclimatized cow manure from food wastes digestion has been used as inoculum with 5 g of biochar. The reactors have been continuously monitored for 15 days keeping the temperature fixed at 37 °C. Excluding the inoculum contribution, an accumulated methane production of 465–540.4 ml CH4/g-VS has been measured with an LHV evaluated in the range 25.8–26.9 MJ/kg. The modified Gompertz equation has been then used to describe the influence of biochar production temperature on methane conversion. A lag phase of 1.8, 2.2 and 3.8 days respectively for B450, B500 and B550, has been estimated showing an inverse proportionality to the biochar production temperature. The biomass to biogas energy conversion analysis reveals a reduction in the efficiency with the biochar production temperature increase. This fact is attributed to the steep reduction in volatile solids occurring by increasing the pyrolysis process severity. As a whole, the paper present a novel approach to possibly combine phytoremediation and production of renewable energy by using Ampelodesmos mauritanicus.

Black soldier fly larvae containing high lipids had been considered an novel sustainable feedstock for lipid extraction to biofuels. The insect lipid was extracted with microwave assisted solvent extraction method. The energy consumption of this way was analyzed to determine the feasibility of the lipid extraction process. The comparison of the effects of different extraction conditions (dehydration methods, water content, extraction temperature, extraction time, equipment power, and solute-solvent ratio) on the energy consumption of lipid extraction from the energy insect was investigated systematically. The dewatering of the insect biomass was the most energy consuming step via a dry extraction method in this paper, constituting about 40–80% of the total energy consumption demand. Within the ranges of extraction factors values compared in this analysis, the microwave radiation powder and lipid extraction temperature had a pronounced effect on the total energy consumption in the ranges of investigated parameter. At last, the lipid extraction yield-dependent evolution of energy consumption for different extraction conditions was also investigated. Anyway, the economic and environmental aspects of lipid extraction from the energy insect needed to be further improved for its large scale implementation in the future.

The practice of injecting a coal/biomass blend can alleviate the pressure on carbon emissions and energy of ironmaking blast furnaces (BFs). In this paper, corn stalks treated by hydrothermal carbonization (HTC) are used as raw materials to eliminate the harm of alkali metals in the ash. The overall performance of individual behavior of the hydrochar, coal, and their blends are analyzed over the raceway with special reference to gas flow, temperature, species, and combustion efficiency. The results show that the hydrochar with higher volatile content is faster to devolatilize, showing a higher CO2 content at the nozzle tip, and reaching a higher burnout in the raceway. The addition of hydrochar to coal can improve the overall flow and combustion performance of the blends. The simulated value is higher than the calculated value, indicating the synergistic effect has existed. When the proportion of the hydrochar is 75% in blends, the synergistic effect is most obvious. The model provides an effective tool for the design of coal/biomass blends.

Landfill leachate secreted from the compressed wastes in landfills over time is toxic to natural ecosystem and poses serious health issues for communities and surrounding environment. The dual role of microalgae for leachate remediation and biomass production make them one of the most sustainable renewable systems for leachate quality improvement. Ultra-membrane treated leachate from Istanbul municipal landfill was evaluated in three laboratory scale experimental sets for the growth of indigenous microalgal strains and ammonium nitrogen (NH 4 + -N) removal. Among all the dilutions of leachate 50% showed better microalgal growth curves, but significantly lesser than control nutrient media. NH 4 + -N removal was systematically decreasing with increasing leachate concentration. Highest removal efficiency (100%) was observed in 10% TL (∼50 mg/L NH 4 + -N). Overall quality of TL was improved in terms of NH 4 + -N removal which is considered as one of the most persistant pollutants pertaining to leachate toxicity. The issues discussed in the paper can be a focus point to further improve leachate quality.

The main aim of the paper is to analyze the effect of different pretreatment processes (HTC, torrefaction and slow pyrolysis) on the properties of Miscanthus giganteus. In this study, the HTC process was conducted in a Zipperclave Stirred Reactor under following parameters: temperature (180, 200 and 220 °C), pressure (

This study explored the optimization of pretreatment of pineapple peel for biogas generation. Pretreatments were carried out sulfuric acid and alkaline hydrogen peroxide prior to anaerobic digestion while the response surface methodology (RSM) was used for optimization of the pretreatment procedures. The physical, chemical, proximate and structural compositions of the peels were determined prior to and at the end of the pretreatment procedures. The dynamics of microorganisms in the reactors were also evaluated by rapid molecular methods while the Fourier Transform Infra-red (FTIR) spectroscopy was employed in the identification of the chemical changes as a result of pretreatments. The use of H2O2 pretreatment caused enormous lignin solubilization in the pineapple peel. In comparison, biogas production was 67% more in the alkaline pretreated pineapple peel than the biomass treated with acid and also 51% over the untreated samples. The total biogas volume produced from the acidic pretreated, alkaline pretreated, not sifted untreated and sifted untreated samples are 194.2 ± 3.0, 587.5 ± 5.2, 287.8 ± 2.1 and 245.4 ± 3.1 respectively. Thus, the alkaline pretreated experiment used lower retention time to achieve maximum gas production in this study. The use of alkaline H2O2 on lignocelluloses has remained unpopular prior to this study. However, its usage in this study yielded better result than all the conventional treatments in terms of lignin solubilization and improvement in methane yield. Economically, the use of H2O2 for pretreatment is adjudged feasible because the 1504 kWh t−1 TS thermal energy gain obtained from the biogas produced by the alkaline treated peel exceeded the 921 kWh t−1 TS used in the pretreatment. This gives a net thermal energy of 583 kWh t−1 TS. Whereas, the investment into acidic pretreatment of pineapple peel may not be economically justified because the total thermal energy gain of −200 kWh t−1 TS was far lower than the 1236 kWh t−1 TS thermal energy that was consumed during the pretreatment giving a net thermal energy of −1436 kWh t−1 TS. Therefore, the use of mild alkaline pretreatment is advocated in biogas generation from pineapple peel and also for biofertilizer production mostly in localities of mass production.

The main objective of the research was to develop a method of biomass grindability determination (Biomass Grindability Index), which would allow for a clear classification of different types of solid biofuels in terms of their milling properties. The objective of the research included also the assessment of the possibility of adaptation of the existing coal grindability determination methods for evaluation of biomass milling. In the course of research, the biomass grindability determination method was modified to obtain the highest possible reliability of the developed index. The scope of laboratory tests being focused on influence of circumferential speed of test mill beaters, particle size distribution of sample, test time, mass and volume of sample. The results of laboratory and industrial tests have shown that the grindability index based on mean particle sizes of feed and product is unreliable. Grindability of different types of biomass, comminuted in beater mills, can be clearly determined by the index expressed as the ratio of energy consumption during the test to the amount of specified product size fraction. During the study laboratory test results obtained for proposed grindability index were compared to other grindability indices determined for utilized in research types of biomass.

In this work, the liquefaction of coal and biomass with direct liquefaction strategy was explored. The point of liquefaction is both to utilize a greater amount of the current coal and biomass assets all the more productively and to create an alternative liquid fuel to oil. Along these lines, the procedure parameters must be resolved to expand the liquefaction efficiency. In addition, it is proposed to do the liquefaction efficiency, particularly in the reactant conditions, to expand the measure of oil. Process parameters were controlled by utilizing Factorial Experimental Design technique in the liquefaction procedures. The solid/liquid ratio was changed as 1/2-1/4, the catalyst concentration was 2–6%, the temperature was 375–400 °C and the duration was 30–90 min. Starting nitrogen pressure was set at 30 bar, stirring speed was 400 rpm, coal/biomass proportion was settled at 1/1. Tetralin as a solvent and MoO3 as catalyst were utilized. Toward the finish of the liquefaction procedure, the total conversions were computed in view of the acquired non-reactive solid (char). As indicated by the outcomes obtained, the most total conversion (81.9%) was acquired at a solid/liquid proportion of 1/2, a catalyst concentration of 2%, a reaction time of 90 min and a reaction temperature of 400 °C. In light of total conversions and elective liquid fuel (oil) in the given conditions, the solid/liquid ratio should be taken as 1/2, the catalyst concentration is 2%, the reaction time is 30–90 min and the reaction temperature is 400 °C. The lowest reaction time found, in this study, is the innovative solution for reducing co-liquefaction cost preferred.

When using the novel N2 explosive decompression pre-treatment, its effect was investigated in relation to the biomass structure and chemical processes during the treatment process. The results that were gained from this testing were compared to those for the widely-used steam explosion pre-treatment method in order to be able to present the advantages in using each method. Both methods are economically and environmentally attractive since only the pressure and water or steam are used to break down the biomass structure. Two pre-treatment methods were used at different temperatures and samples from various process steps were analysed. The results were used to assess the pre-treatment effect and the chemical changes in the biomass and, finally, mass balances were compiled for the bioethanol process at different process steps. The results show that the highest glucose and ethanol yields were obtained by means of the steam explosion pre-treatment method at a temperature of 200 °C (24.29 g and 12.72 g for 100 g of biomass respectively), and at 175 °C (15.4 g and 9.0 g for 100 g of biomass respectively). At lower temperatures the nitrogen explosion treatment produced better yields.

A heat exchanger and vegetable oil bubbling system was designed and tested for biomass-generated syngas cooling and cleaning. The fully enclosed heat exchanger contained water at 15 °C, with syngas having to travel 35 m3/s. Using canola oil, the bubbler was tested at 70 and 100 mm oil depths and 5 and 10 mm syngas bubble sizes to determine the effect of tar removal. The results showed that tar removal efficiency was significantly affected by oil depth and bubble size; however, the interaction between bubble size and oil depth was not significant. About 60% of tars was removed by the heat exchanger alone and 96% of the remaining tars was removed by the oil bubbler when used in series with the heat exchanger. Overall, tar reduction efficiency of 98.5% was achieved with the heat exchanger plus oil bubbler having oil depth of 100 mm and syngas bubble size of 5 mm. Heat exchanger removed most of the tars by cooling the syngas below its dew point but syngas tars with low dew point was absorbed in the oil bubbler.

Pyrolysis of defatted Euglena gracilis was investigated in this study to maximize energy recovery from algal biomass after lipid extraction. Prior to pyrolysis of defatted E. gracilis, the growth rate of E. gracilis was monitored to determine its potential as an initial carbonaceous feedstock for pyrolysis. This study revealed that the cell density of E. gracilis linearly increased for the first 5 days, during which the cell density reached 6.06 ± 0.82 g L−1, demonstrating that defatted E. gracilis is a promising feedstock for pyrolysis. To increase the thermal efficiency of defatted E. gracilis pyrolysis, CO2 was employed as a reactive gas medium. CO levels were increased by 45% following pyrolysis of defatted E. gracilis in a CO2 environment compared to in an N2 environment. Considering that CO is a highly combustible permanent gas, the use of CO2 in pyrolysis may result in the production of more fuel-range gaseous chemicals. Additionally, CO2 utilization increased the gaseous product yield compared to N2-pyrolysis for treating the defatted algal biomass while decreasing tar yield.

This study compares two processes to produce γ-valerolactone from lignocellulosic biomass: Process A is single processing of cellulose by using lignin-derived propyl guaiacol solvent; Process B is simultaneous processing of cellulose and hemicellulose by using γ-valerolactone solvent derived from cellulose and hemicellulose. Large-scale processes that integrate conversion and separation technologies are assembled based on experimental data, and daily GVL productions are 98 tonnes (Process A) and 375 tonnes (Process B). A heat-exchanger network is designed to reduce heating requirements, and the energy efficiencies are 13.3% (Process A) and 37.3% (Process B). Techno-economic assessment is conducted to identify the economic feasibility. The minimum selling price of γ-valerolactone for Process A (US$ 2.36/kg) and Process B (US$ 0.88/kg) are comparable with market price. The difference in the minimum selling prices is mainly caused by effective utilization of the hemicellulose in lignocellulose biomass in Process B. Sensitivity analyses present that changes in key parameters could not reverse the minimum selling price of γ-valerolactone between the two strategies, but the conversion of xylose to value-added chemical in Process A makes this possible. This study shows that development of conversion technologies to effectively utilize the hemicellulose in lignocellulosic biomass is critical to improve process economics.

Microwave hydrothermal liquefaction (MHTL) was introduced to transform watermelon peel to 5-hydroxymethylfurfural (HMF), a top value added chemical from biomass. The key MHTL process parameters of holding temperature, holding time, and liquid-to-solid ratio were optimized by a Box-Behnken design and response surface methodology. The highest HMF yield (3.8%) was obtained with a holding temperature of 135 °C, holding time of 6 min, and liquid-to-solid ratio of 12:1, respectively. The economic evaluation showed that 1.52 kg of HMF could be obtained from 1 t of fresh watermelon peel under the optimum MHTL conditions. It indicates a feasible and environmental friendly waste valorization method.

Liquefaction is a promising technology for the preparation of bio-oil and biochar products from sewage sludge (SS). Co-liquefaction of SS and agricultural/forestry biomass is likely a potential method for obtaining high yield/quality of bio-oil and biochar. In this work, rice straw (RS) and wood sawdust (WS) were selected as representatives of agricultural/forestry biomass and the effects of main process parameters during the co-liquefaction of SS-RS/WS on the yields/properties of bio-oil and biochar were explored in details. The proper reaction temperature, solid-liquid ratio and reaction time for the co-liquefaction of SS-RS/WS were suggested to be 280–300 °C, 0.1 g/mL and 10–30 min, respectively. Potassium/sodium salt (-OH and -CO3) catalysts could efficiently enhanced the co-liquefaction of SS-RS/WS. The introduction of RS/WS into the liquefaction of SS would reduce the contents of nitrogen and sulfur in bio-oil and enhance the formation of phenolic compounds. In addition, co-liquefaction of SS-RS could promote the percentage of lower-boil-point compounds in bio-oil. Although the thermal stability, surface area and pore volume of biochars slightly decreased, the contents of organic matters in biochars were obviously improved, suggesting higher potential in land application.

A novel two-stage gasifier, consisting of a fluidized bed gasifier and a swirl-melting furnace, was proposed and built to gasify biomass with low ash melting temperatures into clean fuel gas. Improvements of the two-stage gasification in gas upgrading, tar removal and ash separation were confirmed by characteristic analysis of gas, tar, ash and slag. Influence of equivalence ratio (ER), oxygen distribution and gasifying agent were assessed for process optimization. Refined gas with a LHV up to 11.1 MJ/Nm3 and a tar content lower than 1 g/Nm3 was produced. Ash was completely vitrified with a high conversion of fixed carbon and volatile, resulting in a cold gas energy fraction of approximately 80%. Increasing ER promoted gas production but limited energy conversion efficiency and gas LHV. Proper oxygen distribution among the two stages was beneficial to decrease energy loss and increase gas quality. Increasing oxygen percentage of gasifying agent enhanced combustible gas content and improved overall gasification efficiency.

Non-edible Jatropha seed used for biodiesel production has increased due to its high-oil contents in kernel and potential to reduce greenhouse gas emission. High demand for biodiesel generates a large volume of waste. In this study, de-oiled Jatropha seed kernel was torrefied at 200 °C, 250 °C and 300 °C, holding time of 15, 30, 45 and 60 min and particle sizes of 0.5–1.0 and 1.0–2.0 mm to produce solid fuel. Torrefaction performance was highly affected by torrefaction temperature compared with holding time. The enhancement factor of HHV increased up to 1.243 after torrefaction at 300 °C and 60 min with particle size of 0.5–1.0 mm. The large particle size reduces the diffusion rate of torrefaction vapour through internal pores, thereby producing high solid yield and low enhancement in HHV. The analysis of torrefaction severity index shows that HHV increase is highly dependent on the weight loss, thereby directly decreasing the total energy in biochar. Scanning electron microscopy image clearly illustrated that the microparticles on the surface were destroyed to increase the porous structure of the biochar with increasing torrefaction temperature. Severe torrefaction with particle size of 0.5–1.0 mm was an effective approach to increase the energy content of biochar.

Rapid depletion of fossil fuel and CO2 mitigation are two major challenges in the modern society. CO2 gasification of carbon-neutral biomass could be an attractive technology to cope up these two emerging problems. Replacing conventional gasifying agent air with CO2 could reduce the fraction of undesired N2 in the gas products because CO2 behaves as inert gasifying agent under low temperature and could be converted to CO at high temperature range. However, most researches on CO2 gasification are limited at the lab-scale level due to the endothermic feature of Boudouard reaction. In this work, a feasibility study of small-scale autothermal gasification using 15% CO2 and 85% air was conducted and compared with traditional air gasification. Prior to that, a lab-scale study of gasification behaviors, under N2, air and CO2 agents, were performed. It was found that using CO2 as gasification oxidant could produce comparable energy (6.67 kJ/g feedstock) to air gasification (7.45 kJ/g feedstock) at equivalent condition (800 °C, 40 min). The pH of biochar obtained under CO2 condition at 800 °C was measured to be 10.63 while the pH of biochar derived by air gasification at the same temperature could reach 12.32. In addition, a small-scale gasification experiment with 15% CO2 addition was successfully conducted in a downdraft autothermal reactor. The results showed CO production was greatly enhanced while CH4 generation was suppressed owing to Boudouard reaction and CO2 dry reforming. Cold gas efficiency and carbon conversion efficiency were both enhanced by 5.8% and 6%, respectively, with CO2 addition. Meanwhile, particulate matters (PM) emitted from both air gasification and 15% CO2 gasification experiments were measured. It was found that under the same equivalence ratio (ER), 75.4% less particle number concentration was emitted during 15% CO2 gasification compared to air gasification.

In this work, the concept of biomass direct (air) gasification was demonstrated in a pilot-scale bubbling fluidized bed and the influence of in-situ application of low-cost catalytic materials on the produced gas characteristics and gasifier performance was analyzed. Three different low-cost catalysts were tested: bottom bed ashes resulting from combustion of residual forest biomass derived from eucalyptus, char particles resulting from wood pellets direct (air) gasification, and synthetic fayalite (Fe2SiO4). Without using catalysts, the produced gas composition was 7.7–16.9%v CO, 3.2–8.3%v H2, 0.5–3.4%v CH4 and 9.5–14.6%v CO2, with 2.4–4.3 MJ/Nm3 lower heating value, specific dry gas production between 1.0 and 1.8 Nm3 dry gas/kg biomass (dry basis), cold gas efficiency between 13.7 and 30.5% and carbon conversion efficiency between 30.7 and 50.9%. With the use of catalysts, the produced gas composition was 14.2–37.6%v CO, 9.5–14.7%v H2, 2.6–3.5%v CH4 and 3.6–14.8%v CO2, with 3.9–6.3 MJ/Nm3 lower heating value, specific dry gas production between 1.4 and 2.0 Nm3 dry gas/kg biomass (dry basis), cold gas efficiency between 38.1 and 66.3% and carbon conversion efficiency between 56.8 and 86.6%. The highest increase in H2 concentration (352% increase) was observed on experiments using wood pellets char as catalyst while the highest increase in CO (305% increase), lower heating value (123% increase), specific dry gas production (62% increase), cold gas efficiency (262% increase) and carbon conversion efficiency (174% increase), was observed on experiments using synthetic Fe2SiO4 as catalyst.

Previous research has shown that alkali addition has operational advantages in entrained flow biomass gasification and allows for capture of up to 90% of the biomass sulfur in the slag phase. The resultant low-sulfur content syngas can create new possibilities for syngas cleaning processes. The aim was to assess the techno-economic performance of biofuel production via gasification of alkali impregnated biomass using a novel gas cleaning system comprised of (i) entrained flow catalytic gasification with in situ sulfur removal, (ii) further sulfur removal using a zinc bed, (iii) tar removal using a carbon filter, and (iv) CO2 reduction with zeolite membranes, in comparison to the expensive acid gas removal system (Rectisol technology). The results show that alkali impregnation increases methanol production allowing for selling prices similar to biofuel production from non-impregnated biomass. It was concluded that the methanol production using the novel cleaning system is comparable to the Rectisol technology in terms of energy efficiency, while showing an economic advantage derived from a methanol selling price reduction of 2–6 €/MWh. The results showed a high level of robustness to changes related to prices and operation. Methanol selling prices could be further reduced by choosing low sulfur content feedstocks.

Microalgal biomass produced from the inexpensive nutrient medium is a potential raw source for manufacturing different essential products covering a broad spectrum of applications. In this study, six separate microalgal strains were isolated from lake freshwater and screened based on their growth and biomass productivity in 10% raw dairy wastewater (DWW). Statistically optimized growth parameters of microalga using CCD-RSM were light intensity 65 μE m−2s−1, pH 7, temperature 35 °C and agitation 150 rpm with maximum dry biomass yield 16.35 ± 0.34 g/L in ultrasonic pre-treated DWW (UPDWW) (75%, v/v). The physicochemical properties of 75% UPDWW were observed pre- and post-algal cultivation and found 94.8% COD removal, indicating the strain's potential phycoremediation. At optimal conditions, hydrolysate of C. sorokiniana NITTS3 biomass yielded 13.67 g/L of bioethanol using selected yeast. The findings of this investigation suggest that C. sorokiniana NITTS3 isolated from freshwater could effectively be used for phycoremediation of DWW with concomitant biomass production as an appropriate feedstock for bioethanol production.

Harvesting of forest residual biomass contributes to regulating wildfires during hot and dry seasons. The collected biomass can be converted into liquid biofuel by pyrolysis. Simple pyrolysis procedures such as slow pyrolysis will allow to dimension and design of mobile pyrolysis units to avoid biomass transportation fees and guarantee efficient management of forest residues. Portuguese forest wastes, particularly biomass from maritime pinus and eucalyptus globulus, were characterized by thermogravimetry and pyrolyzed in a fixed bed reactor, at 698 K, using commercial alkali carbonates and zeolites, bauxite ores, and marble dust as catalysts. Pyrolysis data for mixed biomasses showed the existence of synergy effects. The catalytic pyrolysis experiments led to improved bio-oil quality for all the tested catalysts. The bio-oil produced from pyrolysis with sodium carbonate was the most volatile, since the maximum peak of the volatilization rate is at 390 K, while the bio-oils produced by the remaining catalysts have maximum volatilization at 410 K. Marble dust, a waste from ornamental stones industry, revealed excellent catalytic properties during biomass pyrolysis, allowing an improved bio-oil yield with a decrease in the oxygen-containing functional groups.

Microalgae are considered to be a promising biofuel resource for carbon dioxide fixation in the future. Modeling the growth of microalgae is an effective method to study the growth performance of microalgae, which is also helpful to control the cultivation of microalgae in artificial bioreactor. In continuous culture, dilution rate and influent inorganic nitrogen concentration have shown significant effects on the growth of microalgae. In this paper, the common and overall influences of dilution rate and influent inorganic nitrogen concentration on the microalgae growth have been investigated. Based on numerical simulation, this paper plots the results of total and unit time particulate carbon concentration in 3D figures to expose the varied tendency. It is found that the value of points on the ridge line increases with the dilution rate decreasing and influent inorganic nitrogen concentration increasing for both the total particulate carbon concentration and the particulate carbon concentration per day. The influence of several typical temperatures has been modeled and calculated. The value of biomass productivity will be further increased when the dilution rate is getting closer to 0. This paper will go a step further for the parameters design of continuous culture photo-bioreactor (PBR) for later study.

Using lignocellulosic biomass as an alternative resource for transportation fuel is an attractive prospect due to its abundance and low cost. Conventional pre-treatment methods such as steam explosion or ammonia fibre expansion need technologically complex equipment and high energy input, and they use toxic chemicals in order to achieve high glucose and ethanol yields. In this paper, the freezing pre-treatment of barley straw is investigated as a low energy input and cost-effective alternative pre-treatment method for second generation bioethanol production. In the freezing pre-treatment method, milled biomass mixed with water was frozen in temperatures as low as −18 °C for a certain period of time and was then thawed to room temperature (around 22 °C). The freezing cycles were repeated several times so that the effect of repeated freezing could be studied. In addition, field experiments were carried out by taking samples of barley straw which had been stored outside, both in bales and swathes during a period of time between September and March in two consecutive years (in winter 2014–2015 and 2015–2016). Freezing pre-treatment was followed by enzymatic hydrolysis and fermentation. Glucose and ethanol yields and, additionally, hydrolysis and fermentation efficiencies were used as indicators of pre-treatment efficiency. The highest hydrolysis efficiency figure was 19.42%, which was achieved in laboratory tests where the biomass was frozen and thawed a total of four times. The best result from a field test was 10.28% from straw which had been stored in a swathe and which has been gathered in March. Fermentation yields ranged up to 88.80 g per kilogramme of biomass. Field tests showed that in the bale the temperature never fell below freezing and therefore the pre-treatment was not effective. When in the swathe the straw does freeze through, but the winter in Estonia was too changeable for this method to work effectively.

Facing the global issues of dwindling oil reserves and global warming, the search for alternative green energy source has become a priority. Microalgal biofuels has been regarded as a potential sustainable energy source, due to the high oil yield per area of land, ease of culturing microalgae, zero net carbon emission and reduced competition for arable land. In this paper, five different lipid extraction methods were studied using dry biomass of the microalga Chlamydomonas sp. Folch et al. method gave the highest oil yield of 26.27 wt%. The extracted microalgal oil underwent transesterification process using immobilised lipases. The highest conversion achieved was 72.09% in the following optimized conditions: 0.100 g of immobilised enzymes and solvent to methanol volume ratio of 1:1 with tert-butanol as the organic solvent.

Torrefaction can upgrade the properties of biomass by reducing its oxygen content. In this study, the effects of torrefaction pretreatment on four different lignocellulosic biomass materials at three different temperatures (200 °C, 250 °C, and 300 °C) were studied using a Bosio EUP 6/1200 electric furnace. The results of proximate and ultimate analyses showed that the oxygen content is reduced with a higher torrefaction temperature, while the heating values increased, with 260 °C being the optimal temperature for the process. Among the torrefied products, oak waste wood (OWW, torrefied at 200 °C) had the highest solid yield, 93.2%, while the energy yield was 95.7%, fixed carbon (FC) content 11.8%, volatile matter (VM) content 80.9%, ash content 0.8%, and HHV 19.1 MJ/kg. The TGA/DTG experiments confirmed typical thermal properties for all lignocellulosic biomaterials, while the FTIR and XRD patterns for miscanthus and OWW indicate that the molecular chains of cellulose are broken (damaged) at temperatures higher than 300 °C. Porous ovals were observed at all temperatures in all biomass materials using SEM. SEM images showed that at higher temperatures the ovals started to crack, leading to materials with better grindability than the raw materials. Therefore, we conclude that solid biofuels with properties similar to coal can be produced with torrefaction.

Biomass-derived biochar emerges as a potential green bio-coal candidate for power generation. Microwave-assisted pyrolysis has been proven to be an efficient and economical technique for biomass conversion into biochar. The process can be further improved by utilising susceptor. This research focuses on producing biochar from microwave pyrolysis of empty fruit bunch (EFB) in an alumina susceptor. EFB pellet (PEFB) and EFB short fibre (FEFB) were pyrolysed in a 14L bench scale microwave pyrolyser at temperatures between 200 and 400 °C. The pyrolyser performance (biochar yield, energy efficiency) and biochar properties (proximate analyses, ultimate analyses, calorific value and ash content) were analysed. The results showed that temperature of 300 °C demonstrated the optimised conditions for biochar production. FEFB produced 5.2% higher biochar yield and exhibited better biochar properties compared to PEFB. FEFB-derived biochar (FEFBC) overall characteristics were better than PEFB-derived biochar (PEFBC), with higher heating value (25.19 MJ/kg), fixed carbon (64.52%), volatile matter (13.38%) and carbon content (59.83%). However, FEFBC has high tendency of forming slagging and fouling in the combustor as the ash indexes was >0.34 kg/GJ and RB/A > 1.75.

Biomass structure and reactivity of torrefied products are a matter of great concern to explore the fuel properties, pyrolysis characteristics, and microcosmic appearance, and life cycle assessment (LCA) is of great importance to evaluate the environmental impact of the torrefaction process. This study investigates the properties and microstructure of torrefied rice straw, including fuel properties, pyrolysis kinetics, crystallinity, surface functional group changes, and microscopic appearance. Results show that a good linear distribution appears between the comprehensive pyrolysis index (CPI) and atomic H/C ratio, and CPI and crystallinity index (CrI). Fourier transform infrared spectra depict dehydration, decarboxylation, and decarbonylation occur during the torrefaction process. The scanning electron microscope images illustrated the surface characteristics are closely related to the release of volatiles during the torrefaction process. The solid 13C NMR spectra of raw and torrefied rice straw reflect that the aromaticity will improve with increasing the torrefaction severity. For LCA analysis, the environmental impact of the torrefaction process shows a positive correlation with torrefaction temperature, and the global warming potential is in the range of 0.1469–0.2707 kg CO2 emission. This study is meaningful for the evaluation of fuel properties and torrefaction performance as well as microstructure and reactivity of torrefied rice straw.

The results of the theoretical and experimental studies of the ignition processes of a new class of fuel: bio-water-coal (Bio-WCF) have been presented. The latter has been a water-coal suspension with the addition of 10% leaf or coniferous litter of various tree species, as well as charcoal. It has been established that the addition of biomass to the structure of a water-coal suspension leads to a decrease in the ignition delay time (tign) by 30% under conditions of relatively low oxidizing temperatures. It has been established that when drops of fuel are heated with the addition of charcoal before ignition, dispersion occurs. A mathematical model of the process of ignition of a complex structured bio-water-coal suspension has been developed. According to the results of a numerical simulation, the ignition delay times have been established. A comparative analysis of the theoretical and experimental values of tign has shown their good agreement. Based on the results of the experimental and theoretical studies, the possibility of a significant reduction in the ignition delay time of water-coal suspensions with the introduction of biomass in their structure has been substantiated.

Co-gasification is considered as a useful technique for post-treatment of anaerobic digestion residues. The present study has dealt with the efficiency parameter of 24 kWe downdraft biomass gasifier with 50% mixture ratio of wood chips + corn cobs and 50% ratio of sugarcane bagasse + coconut shells. The performance of the gasification process was assessed with respect to biomass ratios on gasification efficiencies, reactor thermal profiles and equivalence ratio on specific yield of syngas composition and tar contents. Trials were conducted at a temperature range of 650–950 °C using equivalence ratios from 0.15 to 0.30. The biomass feeding rate was maintained between 35 and 40 kg/h. The total volume of gas obtained from co-gasification of wood chips + corn cobs was low (75.6 m3) than the mixture of sugarcane bagasse + coconut shells (94.33 m3) of gas at 5% moisture content. The average yield of syngas produced from the mixture of 1 kg wood chips + corn cobs and sugarcane bagasse + coconut shells were 2.52 and 3.14 m3, respectively. These results have shown that the mixture of wood chips + corn cobs produced almost 4238.6 mg/m3 tar impurities compared with the co-gasification sugarcane bagasse + coconut shells that produced 3767 mg/m3 with LHV of 3.8 MJ/Nm3 and 4.56 MJ/Nm3 at 5% moisture content respectively. This research concluded that co-gasification of sugarcane bagasse + coconut shells were found to be a suitable feedstock mixture for gasification and utilization of syngas for power generation depends on tar production, the flowrate of syngas, and performance in a downdraft gasifier.

The article presents the results of the experimental studies of the processes of removing moisture from fairly typical and widespread forest combustible materials, and woodworking waste under conditions of their thermal preparation for combustion. Based on the results of the experiments, the main regularities of the drying processes of woody biomass under conditions of radiation-convective heating have been established. The integral characteristics (characteristic times) of the drying process of forest biomass under typical (for this technology) heating conditions have been determined. The experiments were carried out on equipment that provides a low level of error (less than 3.3%) for determining the main characteristics of the biomass dehydration process. The values of the mass rates of moisture removal (Weva) of four promising (for modern and future power engineering) and fairly common types of biomass have been established in the ambient temperature range from 333 to 393 K, which corresponds to the operating modes of the drying equipment of power plants. According to the results of the experiments, it was shown that at relatively moderate ambient temperatures (333≤ Tg ≤ 353 K), the type of wood has a rather significant effect on the characteristics and conditions of the dehumidification process. At the same time, the process of drying wood chips is much faster compared to other types of biomass. As the ambient temperature rises (at 373≤Tg ≤ 393 K), the influence of the type of biomass decreases. As a result of the experiments, a physical model of the process of removing moisture from the bulk layer of biomass was formulated. According to the results of the experiments, it was found that before burning forest biomass in boilers of thermal power plants, it is most advantageous to carry out drying in conditions of relatively moderate (at 333≤Tg ≤ 353 K) ambient temperatures. The studies carried out provide grounds for justifying the use of forest combustible material as fuel (or one of the components of the fuel mixture) at thermal power plants currently operating on coal.

This study investigated the influence of torrefaction (300 °C) on the combustion performances of blends of biomass-plastic wastes (Mango branches (MBr), newspaper (Np), LDPE) using thermogravimetric analysis. The torrefied waste blends were co-combusted with coal at a blending ratio of 25 and 50 wt. % to identify possible interactions between the fuels’ components. Synergistic behaviours were noted during combustion of the torrefied MBr-Np blend and the comprehensive combustion index, Dc was 29 % higher than the predicted value. Interestingly, synergistic interactions were perceived during co-combustion of the different wastes with coal. The measured burnout temperatures (TBO) of all torrefied waste-coal blends were lowered by 6–15 %, compared to their predicted values, especially for MBr-Np-coal blends. Synergistic interactions during torrefaction of MBr-Np not only improved the combustion reactivity of the resulting char but also enhanced coal combustion in the blend compared to combustion of torrefied biomass-LDPE-coal blends. It was concluded that synergies during co-combustion of waste char with coal were governed by the waste type, its composition and the interactions that prevailed during torrefaction of the wastes.

Due to its abundance, biomass is widely used in many engineering applications such as gasification process. Using biomass as a raw material for H2-rich syngas production can not only reduce greenhouse gas emissions but also promote renewable energy utilization. In this study, a multi-stage model for H2-rich syngas production from biomass gasification was developed and studied using Aspen Plus simulator. The model is divided into four sub-models including drying sub-model, devolatilization sub-model, tar cracking sub model and gasification sub model. Performance of biomass gasifier was evaluated by predicting the gas yield, lower heating value of produced syngas, carbon conversion efficiency and cold gas efficiency. The maximum H2 content of 14.9 vol% was achived when S/B and reaction temperature were 1.0 and 1123 K, respectively. The highest CCE of 67.8 % and CGE of 37.9 % were also achieved at 1123 K. An increase in S/B from 0 to 0.5 led to a lower tar yield, which was from 133.557 g/Nm3 to 127.193 g/Nm3, and then leveled off as loading increased further from 0.5 to 1.0. The results also showed that during high S/B conditions, the gas-phase chemistry is dominated by water-gas shift (WGS) and Boudouard reactions.

The augmented concerns towards greenhouse emissions have stimulated the innovative technologies to reduce the carbon footprints and lessen the usage of fossil fuel by replacing them with biomass. Wheat straw is a biowaste and has a great potential for energy-production. However, the inorganic contents in the wheat straw cause operational problems such as low heat transfer and ash-deposition in combustion chamber leading to high maintenance requirements. Demineralization of wheat straw with various basic and acidic leaching reagents (NaOH, HCl, HNO3) was investigated in this study. The concentrations of leachants was varied from 0.6, 0.4 and 0.2M to study their effect on physical, chemical, thermal and kinetic behavior of the biomass. The 0.6 M HCl solution reduced the maximum ash content up to 92.71 % and raised the heating value to 3.98 % than raw wheat straw. The kinetic study of the samples treated with 0.6M HCl demonstrated the superior ignition and the activation-energy than other samples. On other hand NaOH damaged the structure of the wheat straw and had adverse effects on their physical and chemical properties. The results of the current study suggested that HCl treated wheat straw can provide a cost effective and eco-friendly solution for energy generation.

To achieve reductions in CO2 emissions, replacing fossil fuels with biomass in thermal power generation is becoming increasingly prevalent. In general, the fuel nature and combustion characteristics of biomass are distinct from those of fossil fuels. Biomass is typically subjected to torrefaction to improve its grindability, hydrophobicity, and heating value (HV). However, the pretreatment process is accompanied by fuel property alteration and an energy penalty. This is strongly associated with the operating envelope and combustion stability of biochar cofiring with coal. Therefore, in this study, the Taguchi method was used to calculate the optimal torrefaction parameters for maximum energy yield and HV. Thermogravimetric and fuel characteristic analyses were performed to examine the pyrolysis features and combustion behavior of the studied fuels. In addition, a blend of 50% Miscanthus biochar and 50% Australia coal was produced and pressed into pellets. The pellets were placed into a free-drop furnace to observe their combustion behavior. The results demonstrated that the ignition temperature and burnout temperature of the blended fuels could be effectively reduced, and that their fuel conversion rates and combustion characteristic index could be enhanced. The results can be applied to coal cofiring in large-scale boilers in the future.

The irradiation of rumen fluid (RF) with laser source was hypothesized to enhance the anaerobic process and accelerate the manure digestion, which increases the biogas and methane production. The photobiostimulating effects of laser irradiation on biogas and methane production were investigated by irradiating the RF for 0.5, 1 and 2 h with 532 nm laser source compared with 1 h incandescent light, non-irradiated RF and the control. The highest significant values of the biogas and methane production were found to be 583 ml Biogas g−1 VS and 367.9 ml CH4 g−1 VS when RF was irradiated for 0.5 h with 532 nm laser source (p

In this study, municipal solid waste was gasified with switchgrass, i.e., co-gasification, using a commercial-scale downdraft gasifier to produce power. The experiments were performed using a commercial-scale 100 kg/h downdraft gasifier at co-gasification ratios of 0, 20 and 40%. The hot and cold gas efficiencies, syngas compositions, heating value and yield, gasifier temperatures and tar content were measured and analyzed. The results indicate that co-gasification of up to 40% MSW performed satisfactorily. The heating values of syngas were 6.2, 6.5 and 6.7 MJ/Nm3 for co-gasification ratios of 0, 20 and 40%, respectively. The cold and hot gas efficiencies were 60.1, 51.1 and 60.0% and 65.0, 55.2 and 64.4% for co-gasification ratios of 0, 20 and 40%, respectively.

In this study, a novel attempt has been made to generate energy-efficient biomethane from marine macroalgae (Chaetomorpha antennina) by coupling thermochemical liquefaction with a disperser (thermo-chemo disperser (TCD) liquefaction). A temperature of (80 °C), pH 11 and disperser g-force of 1613 g were considered optimal parameters for effective solubilization and energy-efficient methane generation. This combinative liquefaction considerably reduced the treatment time and specific energy from 60 to 15 min and 6294 to 800 kJ/kg TS. The highest volatile fatty acids (VFA) accumulation of 890 mg/L was recorded in TCD compared to a thermo disperser (TD) (750 mg/L) and disperser (D) (322 mg/L) during anaerobic fermentation. TCD enhances the methane production potential of macroalgal biomass and a higher methane production of 215 mL/g VS was achieved for TCD compared to TD (149 mL/g VS) and D samples (100 mL/g VS), respectively. Cost analysis confirmed the field applicability of TCD liquefaction with a net profit of 90 USD/ton of marine macroalgae. A high energy ratio of 1.5 was achieved with the proposed mode of pretreatment (TCD) compared to TD (0.95) and D (0.28) pretreatment. Therefore, C. antennina is considered a suitable feedstock for methane generation.

A synergistic scheme of co-gasification of wet sewage sludge and torrefied biomass was proposed in order to get the hydrogen-rich syngas, which could avoid the dual energy input for drying of wet sewage sludge and steam generation. Co-gasification behavior of wet sewage sludge and torrefied biomass was evaluated by using a general non-stoichiometric thermodynamic equilibrium model developed based upon the Gibbs free energy minimization. The tenary plot of C H O system was used to evaluate the theoretical carbon formation performance at thermodynamic equilibrium state. The effects of mixing ratio and torrefaction severity on carbon conversion ratio, compositions of dry syngas, and H2 yield were also addressed. High mixing ratio of wet sewage sludge and high gasification temperature were required for the high carbon conversion ratio. The gasification temperature of 1100 K was a favorable level for the H2 yield and energy input. The optimal mixing ratio range of wet sewage sludge for low and middle temperatures torrefied biomass samples was between 30% and 40%, while that for high temperature ones was approximately 55%. This work could provide a feasible technical route and basic data for the resource and energy utilization of sewage sludge and biomass.

Primary energy sources have limited deposits and their exploitation has a negative impact on the environment. Biofuels production is an efficient and profitable method of environmentally-friendly energy production in terms of economic reasons. In recent years use of renewable energy sources (RES) in the Polish energy balance can be noticed. The main sector in which can be observed a dynamic growth is the biomass market, with the solid biofuel market in particular. The aim of this research was to perform an economic and energy analysis of briquettes and pellets production. The obtained results of economic analyzes have shown that the individual production of solid biofuels from digestate is more profitable than using sawdust as a substrate. The costs of producing solid biofuels from solid fraction of digested pulp, as well as their calorific value, make the discussed substrate to be used to produce energy. The calorific value of the solid biofuel produced from the digested pulp solid fraction (DSF) can be compared to the calorific value of biofuel generated from sawdust. The digested pulp can be considered as an alternative to the sawdust in the production of solid biofuels.

The environmental load of continuous bioenergy production from palm oil (Elaeis guineensis) included with a proposed 10 ha of microalgae production system were assessed to be implemented in Indonesia. Material and energy balances, greenhouse gas (GHG) emission, nutrient requirement and also water scarcity during bioenergy production cycle were evaluated. The integrated system was developed for 60 tons h−1 of fresh fruit bunch (FFB) processing capacity of a conventional mill. Aggregate of energy-profit ratio from the proposed system was 5.20, which indicates a positive balance. The total water footprint for each palm oil and microalgae cultivation was 3.18 and 2.85 m3 kg−1 of biodiesel production, respectively. Microalgae mix-culture has the potential to treat organic compounds from palm oil mill effluent (POME) and combined with flue gases from biomass and biogas power plant as the alternative nutrient sources contributed to net-reduction of GHG emission for 158.8 tons ha−1 of microalgae culture, annually. The integrated system produced 26,471 tons of biodiesel that included 223 tons from microalgae and contribute to 39.90% of total GHG emission reduction from diesel fuel substitute. Additional co-product of 520.33 tons year−1 of animal feed from defatted biomass also possible to be produced and have potential for environmental benefits.

For scaling up a lab-designed process of fluidized bed fast pyrolysis, a design concept and techno-economic analysis were both conducted in this study, including system development, experimental investigations and process evaluation. Rice husk was chosen as the feedstock based on its availability in Taiwan. The product distributions were studied with varying temperature, carrier gas flow rate and biomass feeding. The results showed that the optimal experimental conditions for obtaining the maximum bio-oil yield were at the temperature between 400 °C and 450 °C, the flow rate of 45 L/min and biomass feeding of 21.3 g per inject time. The analysis through GC-MS indicated that the major components of bio-oil contain n-hexadecanoic acid, octadecaoic acid, 9-octadecenoic acid and decanoic acid. The element and property analyses of bio-oil demonstrated that the bio-oil has high oxygen content and low heating value. The analyses of GC-MS/FID and GC-TCD showed that the major components of noncondensable gas are CO, CO2, H2, CH4 and N2. The design concepts and experimental conditions were plugged into a process model and the techno-economic analyses were conducted according to the local data. The minimum bio-oil selling price was calculated as $0.55/liter for the plant size of 1000 tonnes/day.

Herein, we report on a combined process that incorporates hydrothermal liquefaction (HTL) and supercritical water gasification (SCWG) to improve energy recovered from algal biomass. Eight algal biomasses, including four microalgae and four macroalgae with a large difference in biochemical compositions, were screened for this dual process. The algal biomass feedstocks significantly affected the carbon and energy distribution in the product fractions (crude bio-oil, solid, gas, and water-soluble products). 62.50–71.34% energy of microalgae and 6.03–41.06% energy of macroalgae could be recovered as crude bio-oil. 11.86–21.55% carbon of the microalgae and 8.01–15.82% carbon of the macroalgae was distributed in the HTL process water in form of water soluble products after the HTL process. 14.3–33.7% energy of microalgae and 30.18–36.34% energy of macroalgae was retained in the HTL process water. SCWG could convert the organics in the HTL process water into fuel gases consisting mainly of H2 and CH4. 54–91% carbon of the HTL process water was transformed into the fuel gases, which correspond 5.53–18.30% energy of the algal biomass. Thus, this work shows that the integration of HTL and SCWG could improve energy recovery from algal biomass relative to the HTL process alone.

The economic feasibility of a facility producing jet fuel range cycloalkanes, hydrogen and biochar via microwave-assisted catalytic pyrolysis integrated with mild hydrogenation was evaluated by modeling a 1000 metric dry tonne feedstock/day using ASPEN PLUS®. The effects of hydrogenation solvent, heat integration, and coproducing H2 or syngas were investigated in different analysis scenarios. The results indicated that the production of jet fuel could reach 47882.74 Gallon/day, with 9.58 Metric tonne/day biochar and 28200 kg/day H2 as coproducts. The lowest minimum selling price of 3.78 $/Gallon was obtained when using n-hexane as the hydrogenation solvent and coproducing H2 with heat integration. The sale of H2 offset the high production cost, resulting in a significant decrease in the minimum selling price. Sensitivity analysis indicated that the production process was greatly sensitive to total capital investment, internal rate of return, market prices of feedstock and H2.

Torrefaction improves energy density, grindability, and hydrophobicity of raw biomass for gasification and combustion. While literature focuses on single biomass torrefaction, industrial production is likely to be from biomass mixtures. To address this knowledge gap, we torrefied three raw biomasses (pistachio nutshells, feed corn stover, cherry pits) at 250 °C, as “pure” biomasses and in multiple component mixtures to understand if synergistic interactions during torrefaction impact oxidation behavior of resulting solid fuels. The combustion enthalpies of blended biomasses were well predicted by an additive function, whereby a blend's property was the mass-weighted average of each biomass' torrefied property. However, synergistic effects that enhanced devolatilization when biomasses were comingled during torrefaction led to systemically lower volatile matter contents and higher surface areas of resulting solid fuels. This synergistic behavior continues in terms of activation energy of oxidation of the torrefied samples. Co-torrefaction of biomass may lead to a solid fuel with predictable heat content, but synergistic effects lead to oxidation of blended streams at different rates and activation energies, with blends often having lower reactivities and higher activation energies than an “additive” prediction of pure fuel components. This is attributed to enhanced devolatilization among biomasses, leading to more condensed carbonaceous solids.

An algal biorefinery approach is today's need for commercialization of microalgal biodiesel production. In the present study, an indoor photobioreactor with Chlorella minutissima was evaluated to upgrade biogas produced from anaerobic digestion of cow dung. The potential of C. minutissima was assessed in two different growth media viz. BG 11 and wastewater. The significant CO2 absorption reported by C. minutissima was in the range of 75–85.4% at 1296 μmol m−2s−1 of light intensity and 0.33 vol per volume per minute (vvm) gas flows. The present study demonstrated that there is an increase in methane content from 63.5 to 86.4% in the effluent biogas. The highest biomass productivity was observed at 1296 μmol m−2 s−1 light intensity with the same gas flow and the productivity of 0.18 gL−1 and 2.2 gL−1 in the BG11 medium and wastewater respectively. Further, we reported that total lipid content based on dry biomass of C. minutissima were 22.4% and 26% in the BG11 medium and wastewater, respectively. The gross calorific value of treated biogas was also higher (8.15 kWh m−3 and 8.63 kWh m−3) in both BG11 and wastewater, respectively.

Lignite is one of common applied fossil fuels worldwide, and solid wastes like biomass as well as sewage sludge are promising alternatives of fossil fuels. The isothermal combustion performances of lignite/solid wastes (eucalyptus bark and sewage sludge) briquettes between 500 °C and 800 °C in a bench-scale fixed bed furnace were examined based on a macro-thermogravimetric analysis approach. Compared with untreated samples, the average combustion rates of lignite and sewage sludge with the microwave treatment decreased, while those for treated eucalyptus bark increased. The drying, devolatilization and char combustion processes overlapped in the isothermal combustion for all samples. The treated lignite had a high aromatic hydrocarbon, while both the treated sewage sludge and eucalyptus bark had high hydroxyl and methyl group (CH3). After the microwave pretreatment, the fuel rank of lignite was prompted, while that for eucalyptus bark and sewage sludge degraded. Through the microwave pretreatment, the activation energies of lignite, sewage sludge, and eucalyptus bark grew from 15.45 to 21.20 kJ mol−1, 18.23–20.77 kJ mol−1, and 13.27–14.22 kJ mol−1. The study can provide some basic data for the energy utilization of lignite and solid wastes.

Fertilizer assisted optimum culture medium was formulated to enhance the productivity of Dunaliella tertiolecta productivity for biofuel feedstock by selecting the appropriate environmental and nutrient parameters involving 100% CO2. The influences of NPK-fertilizer, NaCl and NaOH loading along with light intensity were investigated to maximize algae-biomass growth, lipid productivity and CO2 sequestration. Five-level and four-factor response surface method (RSM) was used for optimization. The optimum algal cultivation based on RSM technique was compared with simple genetic algorithm (SGA) technique and standard artificial seawater (ASW) based f/2 culture medium. Significant improvement in algae-biomass growth and lipid productivity was obtained along with the enhancement of CO2 sequestration using RSM- and SGA-oriented culture medium over standard ASW-based f/2 medium. Several multi-objective optimization problems involving conflicting objectives (algae-biomass growth, lipid productivity, CO2 sequestration and cultivation cost) were formulated and solved using the elitist non-dominated sorting genetic algorithm. The non-dominated Pareto-optimal solutions were obtained for all multi-objective optimization problem studied. The effects of fertilizer, NaCl and NaOH loading, light intensity and their interacting effects on algae-biomass growth, lipid productivity and CO2 sequestration were revealed successfully. Finally, volumetric mass transfer coefficient of CO2 was determined to link the operating variables with algae-biomass growth while cultivation.