Technoeconomic analysis of an integrated microalgae photobioreactor, biodiesel and biogas production facility

As fossil fuel prices increase and environmental concerns gain prominence, the development of alternative fuels from biomass has become more important. Biodiesel produced from microalgae is becoming an attractive alternative to share the role of petroleum. Currently it appears that the production of microalgal biodiesel is not economically viable in current environment because it costs more than conventional fuels. Therefore, a new concept is introduced in this article as an option to reduce the total production cost of microalgal biodiesel. The integration of biodiesel production system with methane production via anaerobic digestion is proved in improving the economics and sustainability of overall biodiesel stages. Anaerobic digestion of microalgae produces methane and further be converted to generate electricity. The generated electricity can surrogate the consumption of energy that require in microalgal cultivation, dewatering, extraction and transesterification process. From theoretical calculations, the electricity generated from methane is able to power all of the biodiesel production stages and will substantially reduce the cost of biodiesel production (33% reduction). The carbon emissions of biodiesel production systems are also reduced by approximately 75% when utilizing biogas electricity compared to when the electricity is otherwise purchased from the Victorian grid. The overall findings from this study indicate that the approach of digesting microalgal waste to produce biogas will make the production of biodiesel from algae more viable by reducing the overall cost of production per unit of biodiesel and hence enable biodiesel to be more competitive with existing fuels.     

Optimization of biogas production by anaerobic digestion for sustainable energy development in Zimbabwe

There is increasing international interest in developing low carbon renewable energy technologies. Biomass is increasingly being utilized as an energy source throughout the world. Several modern technologies have been developed that convert biomass to bioenergy. Anaerobic digestion is a mature energy technology for converting biomass to biogas, which is a renewable primary energy source. Biogas is a robust fuel that can be used to supply heat, electricity, process steam and methanol. There are vast biomass resources in Zimbabwe that have good potential for biogas production by anaerobic digestion. However, anaerobic digestion is not being optimally used as a biomass conversion technology in the country. This paper presents an overview of biogas production in Zimbabwe and outlines technical options that can be utilized to optimize biogas production by anaerobic digestion in the country.     

Pretreatment of lignocellulosic biomass for enhanced biogas production

Lignocellulosic biomass is an abundant organic material that can be used for sustainable production of bioenergy and biofuels such as biogas (about 50–75% CH₄ and 25–50% CO₂). Out of all bioconversion technologies for biofuel and bioenergy production, anaerobic digestion (AD) is a most cost-effective bioconversion technology that has been implemented worldwide for commercial production of electricity, heat, and compressed natural gas (CNG) from organic materials. However, the utilization of lignocellulosic biomass for biogas production via anaerobic digestion has not been widely adopted because the complicated structure of the plant cell wall makes it resistant to microbial attack. Pretreatment of recalcitrant lignocellulosic biomass is essential to achieve high biogas yield in the AD process. A number of different pretreatment techniques involving physical, chemical, and biological approaches have been investigated over the past few decades, but there is no report that systematically compares the performance of these pretreatment methods for application on lignocellulosic biomass for biogas production. This paper reviews the methods that have been studied for pretreatment of lignocellulosic biomass for conversion to biogas. It describes the AD process, structural and compositional properties of lignocellulosic biomass, and various pretreatment techniques, including the pretreatment process, parameters, performance, and advantages vs. drawbacks. This paper concludes with the current status and future research perspectives of pretreatment.     

多元原料混合发酵制备沼气技术研究进展

目前,我国沼气的发酵原料主要是禽畜粪便和农作物秸秆,随着厌氧发酵技术的发展,更多种类废弃物也逐步受到人们的关注。有机废弃物沼气化利用在我国生态文明建设中有着重大意义。论文综述了我国生物质资源,如禽畜粪便、农作物秸秆、农产品加工废弃物、市政有机废弃物和能源作物的特性和作为沼气发酵原料的优缺点,比较了这些原料的沼气生产潜力,探讨了混合原料发酵技术及重要的几种沼气发酵外源添加剂。     

Photobiostimulation of anaerobic digestion by laser irradiation and photocatalytic effects of trace metals and nanomaterials on biogas production

Biogas generation from the latent energy in biomass is one of the most attractive renewable energy sources. This can be attributed to the environmental friendly nature of the process and its less energy requirements. This article reviews the anaerobic digestion of biomass (livestock manure and crop residues) for biogas and methane production as a source of renewable energy. Furthermore, this study investigates the enhancement of biogas and methane production using light and laser radiations. The laser radiation accelerates bacterial division and growth, where this process is termed as “photobiostimulation.” Additionally, laser radiation photoactivates the inactive enzymes. The results of this literature review showed that the irradiation of methanogenic bacteria with laser sources increased the biogas production by one and a half fold the traditional method of biogas production. The simultaneous irradiation of both nanomaterials and methanogenic bacteria using laser radiation increased the biogas volume by twofolds the biogas volume resulted from the traditional method of biogas production.     

Economic analysis of renewable heat and electricity production by sewage sludge digestion—a case study

In this paper, we assess the total cost of energy recovery from sewage sludge through anaerobic digestion with biogas utilization in combined heat and power (CHP) system. The important advantage of anaerobic digestion process is the production of biogas, which can be used to generate electricity and heat as a source of renewable energy. From this study, it can be retained that the generated thermal energy from the anaerobic digestion process meets the needs of the wastewater treatment plant (WWTP) and guarantees its self‐sufficiency in heat. The surplus of renewable heat produced by CHP is not a primary factor to improve the economic viability of the process. Moreover, the sales of electricity output represent about 76% of the operating costs of anaerobic digestion process. Renewable energy production is not economically viable by its own, without considering the wastewater treatment function and the associated incomes. Nevertheless, sludge digestion helps to reduce the wastewater treatment costs mainly by giving a good source of revenue via electricity production. Copyright © 2014 John Wiley & Sons, Ltd.     

Conjoint effect of microwave irradiation and metal nanoparticles on biogas augmentation from anaerobic digestion of green algae

Pretreatment of biomass is a commonly applied technique for improving its biodegradability; however, such methods are energy intensive, which affects the overall efficiency. This study aims to provide an energy efficient solution by combining microwave (MW) pretreatment of algal biomass (Enteromorpha) and metal nanoparticles (NPs). The MW pretreatment of the biomass was in the form of a slurry (liquid:solid 20:1), while pretreatment time and MW pretreatment power were 6min and 600 W, respectively. Nickel (Ni) and Cobalt (Co) NPs with a concentration of 1 mg/L were used. Batch-wise anaerobic digestion was carried out for a period of 264 h. The results showed that MW pretreatment initiates early hydrolysis of green algae thus reducing lag time. NPs had a positive influence in biogas production at the later stages of anaerobic digestion. The highest total biogas production of 53.60ml/gTS was attained by Co NPs + MW pretreatment whereas maximum biohydrogen of 59.52% (v/v) was produced by Ni NPs + MW pretreatment group. Energy analysis showed that combined utilization of MW pretreatment and metal NPs produced added energy while consuming less input energy than MW pretreatment alone. The kinetic parameters were calculated by using modified Gompertz and Logistic function model for each experimental case.     

Two-stage anaerobic dry digestion of blue mussel and reed

Blue mussels and reeds were explored as a new biomass type in the Kalmar County of Sweden to improve renewable transport fuel production in the form of biogas. Anaerobic digestion of blue mussels and reeds was performed at a laboratory-scale to evaluate biogas production in a two-stage dry digestion system. The two-stage system consisted of a leach bed reactor and an upflow anaerobic sludge blanket (UASB) reactor. The two-stage system was efficient for the digestion of blue mussels, including shells, and a methane yield of 0.33 m³/kg volatile solids (VS) was obtained. The meat fraction of blue mussels was easily solubilised in the leach bed reactor and the soluble organic materials were rapidly converted in the UASB reactor from which 68% of the methane was produced. However, the digestion of mussels including shells gave low production capacity, which may result in a less economically viable biogas process. A low methane potential, 0.22 m³/kg VS, was obtained in the anaerobic two-stage digestion of reeds after 107 days; however, it was comparable to similar types of biomass, such as straw. About 80% of the methane was produced in the leach bed reactor. Hence, only a leach bed reactor (dry digestion) may be needed to digest reed. The two-stage anaerobic digestion of blue mussels and reeds resulted in an energy potential of 16.6 and 10.7 GWh/year, respectively, from the estimated harvest amounts. Two-stage anaerobic digestion of new organic materials such as blue mussels and reeds can be a promising biomass resource as land-based biomass start to be limited and conflict with food resources can be avoided.     

Improving fermentative hydrogen and methane production from an algal bloom through hydrothermal/steam acid pretreatment

Algal blooms can be harvested as renewable biomass waste for gaseous biofuel production. However, the rigid cell structure of raw algae may hinder efficient microbial conversion for production of biohydrogen and biomethane. To improve the energy conversion efficiency, biomass from an algal bloom in Dianchi Lake was subjected to a hydrothermal/steam acid pretreatment prior to sequential dark hydrogen fermentation and anaerobic digestion. Results from X-ray diffraction and Fourier transform infrared spectroscopy suggest that hydrothermal acid pretreatment leads to stronger damage of the amorphous structure (including hemicellulose and amorphous cellulose) due to the acid pretreatment, as evidenced by the higher crystallinity index. Scanning electron microscopy analysis showed that smaller fragments (∼5 mm) and wider cell gaps (∼1 μm) on algal cell surfaces occurred after pretreatment. In comparison to steam acid pretreatment, hydrothermal acid pretreatment resulted in a maximum energy conversion efficiency of 44.1% as well as production of 24.96 mL H₂/g total volatile solids (TVS) and 299.88 mL CH₄/g TVS.     

Biogas generation potential by anaerobic digestion for sustainable energy development in India

The potential of biogas generation from anaerobic digestion of different waste biomass in India has been studied. Renewable energy from biomass is one of the most efficient and effective options among the various other alternative sources of energy currently available. The anaerobic digestion of biomass requires less capital investment and per unit production cost as compared to other renewable energy sources such as hydro, solar and wind. Further, renewable energy from biomass is available as a domestic resource in the rural areas, which is not subject to world price fluctuations or the supply uncertainties as of imported and conventional fuels. In India, energy demand from various sectors is increased substantially and the energy supply is not in pace with the demand which resulted in a deficit of 11,436 MW which is equivalent to 12.6% of peak demand in 2006. The total installed capacity of bioenergy generation till 2007 from solid biomass and waste to energy is about 1227 MW against a potential of 25,700 MW. The bioenergy potential from municipal solid waste, crop residue and agricultural waste, wastewater sludge, animal manure, industrial waste which includes distilleries, dairy plants, pulp and paper, poultry, slaughter houses, sugar industries is estimated. The total potential of biogas from all the above sources excluding wastewater has been estimated to be 40,734 Mm³/year.     

Hydrogen production by the thermophilic eubacterium Thermotoga neapolitana from storage polysaccharides of the CO2-fixing diatom Thalassiosira weissflogii

Planktic diatoms are the largest primary producers in marine and freshwater habitats. Their dry biomass accumulates up to 50% of lipids and contains water-soluble β-1,3-glucans as major storage products. Because of the world-wide abundance of these photosynthetic protists, β-1,3-glucans may rival cellulose as the polysaccharide with the highest annual production on Earth. Here we show the feasibility of a simple and efficient process leading to bio-hydrogen by dark fermentation of microalgal biomass with the thermophilic bacterium Thermotoga neapolitana. Production of the biogas on minimum medium supplemented only with the extract of the diatom Thalassiosira weissflogii proved that algal biomass per se can serve as substrate for sustaining the biotechnological process with no requirement of any pretreatment and external integration of other nutrients. At the same time, lipids unused for the anaerobic production of the biogas, can be employed for production of bio-diesel, thus considerably increasing the economic potential of these renewable feedstocks.     

Evaluation of biogas production from different biomass wastes with/without hydrothermal pretreatment

Municipal biomass waste is regarded as new available energy source, although it could cause serious environmental pollution. Generally, biogas recovery by anaerobic digestion was seen as an ideal way to treat biomass waste. Different types of biomass waste have different biogas production potential. In this paper, cow manure, pig manure, municipal sewage sludge, fruit/vegetable waste, and food waste were chosen as typical municipal biomass waste. In addition, hydrothermal pretreatment was used to accelerate digestion and increase biogas production. Biochemical methane potential (BMP) test was used to evaluate biogas production for raw biomass and hydrothermal treated waste. Raw materials of fruit/vegetable and food waste show higher methane production than that of cow manure, pig manure, and municipal sewage sludge. After hydrothermal pretreatment at typical condition (170 °C at 1 h), the biogas production of pig manure, cow manure, fruit/vegetable waste, and municipal sewage sludge increased by 7.8, 13.3, 18.5, and 67.8% respectively. While, for treated food waste, the biogas decrease by 3.4%. The methane yield of pig manure, fruit/vegetable waste, and municipal sewage sludge increased by 14.6, 16.1, and 65.8%, respectively. While, for treated cow manure and food waste, the methane decrease by 6.9% and 7.5%.     

尿素预处理对玉米秸秆厌氧发酵产沼气特性影响及动力学分析

针对玉米秸秆厌氧发酵产沼气过程中难降解问题,选用尿素对玉米秸秆进行预处理,并进行批次厌氧发酵产沼气试验研究。结果表明:经过45 d厌氧发酵,累积产气量最高为757.83 mL/g VS,最低为588.64 mL/g VS,厌氧发酵进行到25 d时达到45 d累积产气量的85%。分析联合预处理对累积沼气产气量影响得出,尿素质量浓度、预处理时间和玉米秸秆粒径3个因素对累积沼气产气量的影响程度是:玉米秸秆粒径>尿素质量浓度>预处理时间。通过2种动力学模型分析产气规律,对比模型的检验参数,得出Cone模型拟合预处理玉米秸秆厌氧发酵产气规律的适合度较高。     

Modeling & optimization of renewable hydrogen production from biomass via anaerobic digestion & dry reformation

There is a growing interest in the usage of hydrogen as an environmentally cleaner form of energy for end users. However, hydrogen does not occur naturally and needs to be produced through energy intensive processes, such as steam reformation. In order to be truly renewable, hydrogen must be produced through processes that do not lead to direct or indirect carbon dioxide emissions. Dry reformation of methane is a route that consumes carbon dioxide to produce hydrogen. This work describes the production of hydrogen from biomass via anaerobic digestion of waste biomass and dry reformation of biogas. This process consumes carbon dioxide instead of releasing it and uses only renewable feed materials for hydrogen production. An end-to-end simulation of this process is developed primarily using Aspen HYSYS® and consists of steady state models for anaerobic digestion of biomass, dry reformation of biogas in a fixed-bed catalytic reactor containing Ni–Co/Al₂O₃ catalyst, and a custom-model for hydrogen separation using a hollow fibre membrane separator. A mixture-process variable design is used to simultaneously optimize feed composition and process conditions for the process. It is identified that if biogas containing 52 mol% methane, 38 mol% carbon dioxide, and 10 mol% water (or steam) is used for hydrogen production by dry reformation at a temperature of 837.5 °C and a pressure of 101.3 kPa; optimal values of 89.9% methane conversion, 99.99% carbon dioxide conversion and hydrogen selectivity 1.21 can be obtained.     

Bio-fuels from Agricutural Residues

Abstract

Bio-fuels, such as bio-oil, bio-char, and bio-gas, can be obtained from agricultural residues. Agricultural residues are potential renewable energy resources such as biogas from anaerobic digestion, bio-oil from pyrolysis, and bio-char from carbonization and slow pyrolysis processes. Pyrolysis process of agricultural residues are the most common and convenient methods for conversion into bio-oil and bio-char. When the pyrolysis temperature increased, the bio-char yield decreased. The bio-char yield increased with increasing particle size of the sample. The yield of bio-oil from pyrolysis of the samples increased with temperature. Anaerobic biogas production is an effective process for conversion of a broad variety of agricultural biomass to methane to substitute natural gas and medium calorific value gases.     

我国生物燃气高效制备技术进展

本文从发酵原料拓展、预处理和厌氧消化工艺等三个方面对我国生物燃气高效制备领域的最新研究成果进行了介绍与评述。重点介绍了高固体浓度、固态、两相、混合发酵等4种高效厌氧消化工艺;鉴于我国正处于生物燃气产业化发展初期,从生物燃气高效制备技术方面对今后的研究重点给出建议。     

Evaluation of marine algae as a source of biogas in a two-stage anaerobic reactor system

The marine algae are considered an important biomass source; however, their utilization as energy source is still low around the world. The technical feasibility of marine algae utilization as a source of renewable energy was studied to laboratory scale. The anaerobic digestion of Macrocystis pyrifera, Durvillea antarctica and their blend 1:1 (w/w) was evaluated in a two-phase anaerobic digestion system, which consisted of an anaerobic sequencing batch reactor (ASBR) and an upflow anaerobic filter (UAF). The results show that 70% of the total biogas produced in the system was generated in the UAF, and both algae species have similar biogas productions of 180.4(±1.5) mL g⁻¹ dry algae d⁻¹, with a methane concentration around 65%. The same methane content was observed in biogas yield of algae blend; however, a lower biogas yield was obtained. In conclusion, either algae species or their blend can be utilized to produce methane gas in a two-phase digestion system.     

Anaerobic digestion of microalgae residues resulting from the biodiesel production process

The recovery of methane from post transesterified microalgae residues has the potential to improve the renewability of the ‘microalgae biomass to biodiesel’ conversion process as well as reduce its cost and environmental impact. This paper deals with the anaerobic digestion of microalgae biomass residues (post transesterification) using semi-continuously fed reactors. The influence of substrate loading concentrations and hydraulic retention times on the specific methane yield of the anaerobically digested microalgae residues was investigated. The co-digestion of the microalgae residues with glycerol as well as the influence of temperature was also examined. It was found that the hydraulic retention period was the most significant variable affecting methane production from the residues, with periods (>5 days) corresponding to higher energy recovery. The methane yield was also improved by a reduction in the substrate loading rates, with an optimum substrate carbon to nitrogen ratio of 12.44 seen to be required for the digestion process.     

Net energy analysis of the production of biodiesel and biogas from the microalgae: Haematococcus pluvialis and Nannochloropsis

Microalgae have been proposed as possible alternative feedstocks for the production of biodiesel because of their high photosynthetic efficiency. The high energy input required for microalgal culture and oil extraction may negate this advantage, however. There is a need to determine whether microalgal biodiesel can deliver more energy than is required to produce it. In this work, net energy analysis was done on systems to produce biodiesel and biogas from two microalgae: Haematococcus pluvialis and Nannochloropsis. Even with very optimistic assumptions regarding the performance of processing units, the results show a large energy deficit for both systems, due mainly to the energy required to culture and dry the microalgae or to disrupt the cell. Some energy savings may be realized from eliminating the fertilizer by the use of wastewater or, in the case of H. pluvialis, recycling some of the algal biomass to eliminate the need for a photobioreactor, but these are insufficient to completely eliminate the deficit. Recommendations are made to develop wet extraction and transesterification technology to make microalgal biodiesel systems viable from an energy standpoint.     

Potential evolution of Turkish agricultural residues as bio-gas,bio-char and bio-oil sources

A study has been conducted to evaluate the potential power production from the pyrolysis for bio-oil and bio-char, and anaerobic digestion (for bio-gas), of agricultural residues in Turkey. Agricultural residues are potential renewable energy resources such as bio-gas from anaerobic digestion, bio-oil from pyrolysis, and bio-char from carbonization and slow pyrolysis processes. Anaerobic bio-gas production is an effective process for conversion of a broad variety of agricultural biomass to methane to substitute natural gas and medium calorific value gases. When the pyrolysis temperature increased the bio-char yield decreased. The bio-char yield increased with increasing particle size of the sample. Thermochemical conversion processes of biomass are the most common and convenient methods for conversion into energy. Among the processes of energy production from biomass, pyrolysis is the most popular thermal conversion process.