Biorefinery

A process has been elaborated for one-step low lignin content sugarcane bagasse hemicellulose extraction using alkaline solution of hydrogen peroxide. To maximize the hemicellulose yields several extraction conditions were examined applying the 2 4 factorial design: H 2 O 2 concentration from 2 to 6% (w/v), reaction time from 4 to 16 h, temperature from 20 to 60 • C, and magnesium sulfate absence or presence (0.5%, w/v). This approach allowed selection of conditions for the extraction of low and high lignin content hemicellulose. At midpoint the yield of hemicellulose was 94.5% with more than 88% of lignin removed. Lignin removal is suppressed at low extraction temperatures and in the absence of magnesium sulfate. Hemicellulose in 86% yield with low lignin content (5.9%) was obtained with 6% H 2 O 2 treatment for 4 h and 20 • C. This hemicellulose is much lighter in color than samples obtained at the midpoint condition and was found suitable for subsequent enzymatic hydrolysis.

Development of artificial enzymes designed for industrial plants that could convert carbon dioxide into carbonates, with the ultimate aim of reducing CO2 emissions. Enzymes are biological catalysts that accelerate chemical reactions, such as the conversion of gaseous carbon dioxide (CO2) into carbonates. Carbonates are the basic component of coral reefs, mollusc shells, geological platforms and kidney stones. Although naturally occurring enzymes would be ideal for converting human-generated CO2 emissions into carbonates, they are generally incapable of coping with the extreme conditions of industrial plants. Ernesto and colleagues are now developing artificial enzymes that can withstand the harsh environments of industrial plants while accelerating chemical reactions. His team ultimately aims to create a clean, cheap, practical and socially responsible solution for global warming by reducing CO2 emissions. "We believe that our novel artificial enzymes will be the first tailor-made enzymes for industrial plants to produce carbonates," says Dr Hernandez. So far, Dr Hernandez and his colleagues have built an artificial environment composed of chimney-like equipment, measuring 1.5 metres in height and 15 centimetres in diameter, that mimics the smoke released by power plants. Using the artificial environment, the researchers will ensure that their artificial enzymes can function properly under extreme conditions consisting of hot, corrosive, poisonous and sticky smoke as well as soot and other gases produced by power plants. The team is basing the development of its artificial enzyme on naturally occurring carbonic anhydrase (CA), which accelerates the conversion of CO2 into carbonates. Carbonic anhydrase is capable of turning CO2 molecules into carbonates at a rate of one million molecules per second. However, "the enzyme's CO2 conversion rate slows down dramatically under industrial conditions," Dr Hernandez points out. He and his colleagues are now engineering artificial enzymes based on natural CA, using directed evolution techniques. Their first step involves the creation of a library of diverse genes that encode for carbonic anhydrases. "This library includes sequences of unique forms of carbonic anhydrases recently found near deep-ocean chimneys (hydrothermal vents)," says Dr Hernandez. The team plans to modify and multiply the genes encoding for carbonic anhydrases using a molecular technique called random mutagenesis. The researchers will then place the mutated genes in the artificial environment to see which ones are most effective at converting carbon dioxide into carbonates. The best mutations will then be put through the modification and multiplication processes again. The researchers will repeat the whole process until they have isolated a mutated gene encoding for recombinant carbonic anhydrase that can convert CO2 into carbonates under industrial conditions. With the help of artificial enzymes, CO2-converted carbonates could be used in everything from baking soda and chalk to Portland cement and lime manufacturing.

Biodiesel is a promising liquid fuel that is mainly derived from triglycerides and is utilized in diesel engines directly or after blending with conventional gasoline. Triglycerides comprise fatty acid methyl esters (FAME), which are generated from plant or animal based sources. Biodiesel generated from vegetable oils is expensive than petroleum-based diesel and has concerns with food vs. fuels debate. Therefore, biodiesel from renewable sources such as non-food feedstocks has attained a considerable interest in last two decades. This paper aims to examine the biodiesel generation from the non-food feedstocks available in the Kingdom of Saudi Arabia (KSA) as a source of renewable energy and valueadded products along with and a solution to current waste disposal problems. In KSA, non-food feedstocks such as animal fats, waste cooking oil (WCO), agricultural wastes, sewage sludge, and microalgae are promising sources for biodiesel production. These feedstocks are relatively cheap, easily available, portable, and renewable in nature. A case study of waste to biodiesel refinery is presented for KSA under three different scenarios, including (1) KSA population in 2017, (2) KSA population and pilgrims in 2017, and (3) KSA population and pilgrims by 2030. It was assessed that around 482, 488 and 627 MW of electricity on a continuous basis could be generated every year for scenarios 1, 2 and 3 respectively if using the fat fraction of municipal solid waste in waste to biodiesel refineries in KSA. Similarly, a total net savings of US$ 272, 275.2 and 353.9 million can be achieved from scenarios 1, 2 and 3 respectively. However, there are many challenges in commercializing the waste to biodiesel refinery in KSA such as collection of feedstocks, separation of lipids, products separation, soap formation, preserving products, and adequate regulations.

Agriculture is one of the biggest of Indonesia’s economic sectors, with the area used for agriculture totaling 8.19 million hectares. The usage of agricultural fertilizers is causing significant environmental contamination, with one of the biggest contaminants being excess phosphate. This is because phosphate is one of the most intensely used fertilizers but has the lowest plant absorption rate. Excess phosphate can cause the eutrophication of large bodies of water. One method used to reduce this effect is phytoremediation with Spirodela sp. and Iris pseudacorus L, which can reduce phosphate concentrations from 29.625 mg/l to 0.2 mg/l. By applying the biorefinery concept, in which plant biomasses are used, Spirodela sp. can be utilized to produce duckweed powder with a yield of 20.8% and flavonoids can be extracted from iris plants to produce flavonoid powder with a yield of 20.9%. These byproducts add economic value to the system to generating a gross profit margin of 5.91, thus indicating the profitability of applying the biorefinery concept to phytoremediation.

The alkaline extraction of hemicelluloses from hardwoods prior to pulping, for further conversion to value-added products, seems to be a promising pathway for paper mills to increase profit and improve sustainability. However, the amount of hemi-cellulose extracted will be limited by the requirement to maintain pulp quality and pulp yield in comparison to existing pulping processes. The effects of NaOH concentration, temperature, and time on hemicellulose extraction of Eucalyptus grandis were studied using a statistical experimental design. Extracted wood chips were subjected to kraft pulping to evaluate the effect of the extraction on cooking chemicals, pulp quality, and handsheet paper strengths. The selective xylan recovery (12.4% dry mass) from E. grandis combined with low-cooking, active alkali charge, and less cooking time ad-vantaged the xylan extraction and subsequent modified kraft pulping process under the studied conditions. Pulp viscosity, breaking strength, and tensile index of handsheets were slightly improved.

The degree of polymerization (DP) of cellulose in cellulosic biomass and how it changes during enzymatic
and chemical transformations has remained a fundamental property of interest to numerous researchers. Currently,
with increased interest in cellulosic biofuels, more attention is being focused on determining changes in cellulose
DP before and during pre-treatment, as well as the effect of DP on enzymatic deconstruction of cellulose to glucose.
Different sources of celluloses from woody and non-woody biomass have been isolated and the DP has been frequently
examined as a key parameter contributing to efficient biomass deconstruction. The isolation and derivatization/dissolution of cellulose are crucial steps in determining cellulose DP. This review summarizes approaches to measuring DP developed over the past six decades and highlights opportunities for further  mprovements.

Cheese whey is a type of dairy wastewater that is either discharged directly into the environment or the local sewer, treated with the primary object to meet effluent discharge limits, or used as a resource to produce, for example, biofuels, single cell proteins, animal feed after condensation, sweetener after crystallization of lactose, xanthan gum, glycerol and 2,3 butanediol upon fermentation. This review has been dedicated to the production of biofuels, specifically biogas, from cheese whey. We aim to provide the reader with a brief account of how knowledge in the field of biogas production from cheese whey effluents has evolved, the current status quo, and identify areas that should be addressed in the near future. Based on the review of ca. 100 research papers published over the past 25 years following facts were extracted: A large body of knowledge exists at lab- and pilot-scale. It has been shown that cheese whey wastewater can be used either as a primary or co-substrate for the production of biomethane and biohydrogen. Amongst the reactors studied, high-rate anaerobic digesters can be operated at organic loading rates up to 40 g COD L-1 d-1 with relatively low hydraulic retention times (0.5-10 d). The 1980ies have seen the implementation of the first fully integrated systems in New Zealand and Ireland. It was also concluded that anaerobic treatment of full-strength cheese whey, despite COD removal efficiencies of up to 99%, cannot meet the stringent discharge criteria set forth in most countries thus requiring an aerobic polishing step. As the biogas technology reaches technical maturity and enters the commercial stage in the dairy industry, more data and reliable statistics are needed to evaluate the economical and operational feasibility at the industrial scale, including how we deal with the anaerobic digester effluent. Life cycle and carbon footprint assessments of the overall treatment process are to be carried out before it can be promoted as a technology that can contribute towards sustainable development and a more environmentally friendly agro-industry. Cooperation and promotion should be encouraged among agro-industries, government and national research institutes as well as providers of technology, operators and clients of digestion products. Consequently, decision makers will be able to choose the best technologies and options to promote the digestion products. It should also be recognized that the competition between different processes exploiting cheese whey as a resource will continue due to technological advances.

ABSTRACT According to Food and Agricultural Organization (FAO), one third of food produced globally for human consumption is lost along the food supply chain. In many countries food waste are currently landfilled or incinerated together with other combustible municipal wastes for possible recovery of energy. However, these two approaches are facing more and more economic and environmental stresses. Due to its organic- and nutrient-rich composition, theoretically food waste can be utilized as a useful resource for production of biofuel through various fermentation processes. So far, valorization of food waste has attracted increasing interest, with biogas, hydrogen, ethanol and biodiesel as final products. Therefore, this review aims to examine the state-of-the-art of food waste fermentation technologies for renewable energy generation.

ABSTRACT According to Food and Agricultural Organization (FAO), one-third of food produced globally for human consumption (nearly 1.3 billion tonnes) is lost along the food supply chain. In many countries food waste is currently landfilled or incinerated together with other combustible municipal wastes for possible recovery of energy. However, these two options are facing more and more economic and environmental stresses. Due to its organic- and nutrient-rich nature, theoretically food waste can be converted to valuable products (e.g. bio-products such as methane, hydrogen, ethanol, enzymes, organic acids, chemicals and fuels) through various fermentation processes. Such conversion of food waste is potentially more profitable than its conversion to animal feed or transportation fuel. Food waste valorisation has therefore gained interest, with value added bio-products such as methane, hydrogen, ethanol, enzymes, organic acids, chemicals, and fuels. Therefore, the aim of this review is to provide information on the food waste situation with emphasis on Asia–Pacific countries and the state of the art food waste processing technologies to produce enzymes.

Around the world, significant able steps are being taken to move from today’s fossil-based economy to a more sustainable economy based on biomass. A key factor in the realization of a successful bio-based economy will be the development of biorefinery systems allowing highly efficient and cost-effective processing of biological feedstocks to a range of bio-based products, and successful integration into existing infrastructure.
The recent climb in oil prices and consumer demand for environmentally friendly products has now opened new windows of opportunity for bio-based chemicals and polymers. Industry is increasingly viewing chemical and polymer production from renewable resources as an attractive area for investment. Within the bio-based economy and the operation of a biorefinery, there are significant opportunities for the development of bio-based
building blocks (chemicals and polymers) and materials (fiber products, starch derivatives, etc.). In many cases this happens in conjunction with the production of bioenergy or biofuels. The production of bio-based products
could generate US$10–15 billion of revenue for the global chemical industry. The economic production of biofuels is often a challenge. The co-production of chemicals, materials food and feed can generate the necessary added value. This paper highlights all bio-based chemicals with immediate potential as biorefinery ‘value added products’. The selected products are either demonstrating strong market growth or have significant industry
investment in development and demonstration programs. The full IEA Bioenergy Task 42 report is available from http://www.iea-bioenergy.task42-biorefineries.com.

Spent coffee ground (SCG) is the main residue generated during the production of instant coffee by thermal water extraction from roasted coffee beans. This waste is composed mainly of polysaccharides such as cellulose and galactomannans that are not solubilised during the extraction process, thus remaining as unextractable, insoluble solids. In this context, the application of an enzyme cocktail (mannanase, endoglucanase, exoglucanase, xylanase and pectinase) with more than one component that acts synergistically with each other is regarded as a promising strategy to solubilise/hydrolyse remaining solids, either to increase the soluble solids yield of instant coffee or for use as raw material in the production of bioethanol and food additives (mannitol). Wild fungi were isolated from both SCG and coffee beans and screened for enzyme production. The enzymes produced from the selected wild fungi and recombinant fungi were then evaluated for enzymatic hydrolysis of SCG, in comparison to commercial enzyme preparations. Out of the enzymes evaluated on SCG, the application of mannanase enzymes gave better yields than when only cellulase or xylanase was utilised for hydrolysis. The recombinant mannanase (Man1) provided the highest increments in soluble solids yield (17 %), even when compared with commercial preparations at the same protein concentration (0.5 mg/g SCG). The combination of Man1 with other enzyme activities revealed an additive effect on the hydrolysis yield, but not synergistic interaction, suggesting that the highest soluble solid yields was mainly due to the hydrolysis action of mannanase.

Application of Pseudomonas aeruginosa N.R 22 bacteria is introduced as an alternative effort to
convert the present condition of oily wastewater to useful unsaturated Free Fatty Acid. However,
concerns arise when it comes to the microbial growth of bacteria, affecting the lipase production.
Our research suggests that nitrogen compost which composes of Empty Fruit Bunch (EFB) and
animal waste would provide the best nitrogen fertilizer to help Pseudomonas Aeruginosa. EFB
provides a high value of micronutrient of N which helps the improvement of soil acidity as well as
electrical conductivity. Addition of animal waste yields additional advantages to the soil, hence
offsetting the amount of nutrients required. The feedstock chosen is will undergo series of process
flow such as screening, grinding, granulate and cooling to give the best nitrogen fertilizer. Due to
it’s high organic carbon and nitrogen carbon, growth of Pseudomonas aeruginosa is expected to
increase once the extraction of FFA is done. It is concern that different type of animal waste will
produce different Carbon to Nitrogen (C:N) ratio. Study of different sources of nitrogen sources
such as peptone, yeast extract and beef extract gives an agarose activity of 0.112, 0.09836 and
0.082 U. ml-1.

Microalgae are recognized as one of the most powerful biotechnology platforms for many value added products including biofuels, bioactive compounds, animal and aquaculture feed etc. However, large scale production of microalgal biomass poses challenges due to the requirements of large amounts of water and nutrients for cultivation. Using wastewater for microalgal cultivation has emerged as a potential cost effective strategy for large scale microalgal biomass production. This approach also offers an efficient means to remove nutrients and metals from wastewater making wastewater treatment sustainable and energy efficient. Therefore, much research has been conducted in the recent years on utilizing various wastewater streams for microalgae cultivation. This review identifies and discusses the opportunities and challenges of different wastewater streams for microalgal cultivation. Many alternative routes for microalgal cultivation have been proposed to tackle some of the challenges that occur during microalgal cultivation in wastewater such as nutrient deficiency, substrate inhibition, toxicity etc. Scope and challenges of microalgal biomass grown on wastewater for various applications are also discussed along with the biorefinery approach.

The growing volume of municipal solid waste (MSW) generated worldwide often undergoes open dumping, landfilling, or uncontrolled burning, releasing massive pollutants and pathogens into the soil, water, and air. On the other hand, MSW can be used as a valuable feedstock in biological and thermochemical conversion processes to produce bioenergy carriers, biofuels, and biochemicals in line with the United Nations’ Sustainable Development Goals (SDGs). Valorizing MSW using advanced technologies is highly energy-intensive and chemical-consuming. Therefore, robust and holistic sustainability assessment tools should be considered in the design, construction, and operation phases of MSW treatment technologies. Exergy-based methods are promising tools for achieving SDGs due to their capability to locate, quantify, and comprehend the thermodynamic inefficiencies, cost losses, and environmental impacts of waste treatment systems. Therefore, the present review paper aims to comprehensively summarize and critically discuss the use of exergetic indicators for the sustainability assessment of MSW treatment systems. Generally, consolidating thermochemical processes (mainly incineration and gasification) with material recycling methods (plastic waste recovery), heat and power plants (steam turbine cycle and organic Rankine cycle), modern power technologies (fuel cells), and carbon capture and sequestration processes could improve the exergetic performance of MSW treatment systems. Typically, the overall exergy efficiency values of integrated MSW treatment systems based on the incineration and gasification processes were found to be in the ranges of 17–40% and 22–56%, respectively. The syngas production through the plasma gasification process could be a highly favorable waste disposal technique due to its low residues and rapid conversion rate; however, it suffers from relatively low exergy efficiency resulting from its high torch power consumption. The overall exergy efficiency values of integrated anaerobic digestion-based MSW processing systems (34–73%) were generally higher than those based on the thermochemical processes. Exergy destruction and exergy efficiency were the most popular exergetic indicators used for decision-making in most published works. However, exergoeconomic and exergoenvironmental indices have rarely been used in the published literature to make decisions on the sustainability of waste treatment pathways. Future studies need to focus on developing and realizing integrated waste biorefinery systems using advanced exergy, exergoeconomic, and exergoenvironmental methods.

Bio-oil derived from fast pyrolysis of lignocellulosic materials is among the most complex and inexpensive raw oils that can be produced today. Although commercial or demonstration scale fast pyrolysis units can readily produce this oil, the pyrolysis industry has not grown to significant commercial impact due to the lack of bio-oil market pull. This paper is a review of the challenges and opportunities for bio-oil upgrading and refining. Pyrolysis oil consists of six major fractions (water 15−30 wt %, light oxygenates 8−26 wt %, monophenols 2−7 wt %, water insoluble oligomers derived from lignin 15−25 wt %, and water-soluble molecules 10−30 wt %). The composition of water-soluble oligomers is relatively poorly studied. In the 1880s, bio-oil refining (formally known as wood distillation) targeted the separation and commercialization of C1−C4 light oxygenated compounds to produce methanol, acetic acid, and acetone with the commercialization of the lignin derived water insoluble fraction for preserving wooden sailing vessels against rot. More recently, the company Ensyn extracted and commercialized condensed natural smoke as a food additive. Most research efforts in the last 20 years have focused on the two-step hydrotreatment concept for the production of transportation fuels. In spite of major progress, this concept remains at the demonstration scale. In this review, the opportunities and progress to separate bio-oil fractions and chemicals, mainly acetic acid (HAc), hydroxyacetaldehyde (HHA), acetol, and levoglucosan, and convert them into value added coproducts are thoroughly discussed. In spite of the large number of separation schemes and products tested, very few of them have been tested as part of fully integrated bio-oil refinery concepts. The synthesis and techno-economic and environmental evaluation of novel integrated bio-oil refinery concepts is likely to become a subject of intense research activity in the coming years.

Anthropogenic greenhouse gas (GHG) emissions are changing our Earth’s climate very rapidly and causing global warming phenomenon. There is a scientific, social, and political consensus that 20% of global GHG emissions are due to the transport sector that is also blamed for increasing oil demand worldwide. The growth in the transportation sector is estimated to increase by 1.3% per year until 2030. The increase in GHG emissions and high demand for fuel in the transport sector can be reduced significantly by replacing fossil fuels with liquid biofuels, which are derived from plant materials and appear to be carbon-neutral, renewable, and capable of cultivation under harsh environments. The plant materials used in producing liquid biofuels are also a potential source of value-added products such as feed, materials and chemicals, in addition to biofuels. This chapter reviews the current trends in liquid biofuel systems on a global platform and criteria for sustainability pertaining to liquid biofuels. The three types of sustainability criteria for liquid biofuels, including economic sustainability, environmental sustainability, and social sustainability are discussed in detail.

SUMMARY
Around the world significant steps are being taken to move from today’s fossil based economy to a more sustainable economy based on biomass. The transition to a bio-based economy has multiple drivers:
• the need to develop an environmentally, economically and socially sustainable global economy,
• the anticipation that oil, gas, coal and phosphorus will reach peak production in the not too distant future and that prices will climb,
• the desire of many countries to reduce an over dependency on fossil fuel imports, so the need for countries to diversify their energy sources,
• the global issue of climate change and the need to reduce atmospheric greenhouse gas (GHG) emissions, and
• the need to stimulate regional and rural development.
One of the key institutions to accommodate this transition is the IEA Bioenergy Implementation Agreement. Within IEA Bioenergy, Task 42 specifically focuses on Biorefineries; e.g. the co-production of fuels, chemicals, (combined heat &) power and materials from biomass. A key factor in the realisation of a successful bio-based economy will be the development of biorefinery systems allowing highly efficient and cost effective processing of biological feedstocks to a range of bio-based products, and successful integration into existing infrastructure.
Although global bio-based chemical and polymer production is estimated to be around 50 million tonnes, the historic low price of fossil feedstocks together with optimized production processes has restricted commercial production of bio-based products. The recent climb in oil prices and consumer demand for environmentally friendly products has now opened new windows of opportunity for bio-based chemicals and polymers. Industry is increasingly viewing chemical and polymer production from renewable resources as an attractive area for investment. Within the bio-based economy and the operation of a biorefinery there are significant opportunities for the development of bio-based building blocks (chemicals and polymers) and materials (fibre products, starch derivatives, etc). In many cases this happens in conjunction with the production of bioenergy or biofuels. The production of bio-based products could generate US$ 10-15 billion of revenue for the global chemical industry.
Within IEA Bioenergy Task 42 “Biorefinery” a biorefinery classification method for biorefinery systems was developed. This classification approach relies on four main features which are able to classify and describe a biorefinery system:
1. Platforms (e.g. core intermediates such as C5 -C6 carbohydrates, syngas, lignin, pyrolytic liquid)
2. Products (e.g. energy carriers, chemicals and material products)
3. Feedstock (i.e. biomass, from dedicated production or residues from forestry, agriculture, aquaculture and other industry and domestic sources)
4. Processes (e.g. thermochemical, chemical, biochemical and mechanical processes)
The platforms are the most important feature in this classification approach: they are key intermediates between raw materials and final products, and can be used to link different biorefinery concepts and target markets.
The platforms range from single carbon molecules such as biogas and syngas to a mixed 5 and 6 carbon carbohydrates stream derived from hemicelluloses, 6 carbon carbohydrates derived from starch, sucrose (sugar) or cellulose, lignin, oils (plant-based or algal), organic solutions from grasses and pyrolytic liquids. These primary platforms can be converted to wide range of marketable products using mixtures of thermal, biological and chemical processes. In this report a direct link is made between the different platforms and the resulting bio-based chemicals.
The economic production of biofuels is often a challenge. The co-production of chemicals, materials food and feed can generate the necessary added value. This report highlights all bio-based chemicals with immediate potential as biorefinery ‘value added products’. The selected products are either demonstrating strong market growth or have significant industry investment in development and demonstration programmes. The report introduces companies actively developing bio-based chemicals and polymers and provides Information on potential greenhouse gas emissions savings and how the co-production of bio-based chemicals with biofuels can influence the economics of biofuels production.

The increasing demand for biofuels has encouraged the researchers and policy makers worldwide to find sustainable biofuel production systems in accordance with the regional conditions and needs. The sustainability of a biofuel production system includes energy and greenhouse gas (GHG) saving along with environmental and social acceptability. Life cycle assessment (LCA) is an internationally recognized tool for determining the sustainability of biofuels. LCA includes goal and scope, life cycle inventory, life cycle impact assessment, and interpretation as major steps. LCA results vary significantly, if there are any variations in performing these steps. For instance, biofuel producing feedstocks have different environmental values that lead to different GHG emission savings and energy balances. Similarly, land-use and land-use changes may overestimate biofuel sustainability. This study aims to examine various biofuel production systems for their GHG savings and energy balances, relative to conventional fossil fuels with an ambition to address the challenges and to offer future directions for LCA based biofuel studies. Environmental and social acceptability of biofuel production is the key factor in developing biofuel support policies. Higher GHG emission saving and energy balance of biofuel can be achieved, if biomass yield is high, and ecologically sustainable biomass or non-food biomass is converted into biofuel and used efficiently.

Grass is ubiquitous in Ireland and temperature northern Europe. It is a low input perennial crop; farmers are well versed in its production and storage (ensiling). Anaerobic digestion is a well understood technology. However the level of comfort with the technology can mask the difficulties associated with digestion of high solid content feedstocks especially grass silage. It is not simply a matter of using a digester designed for slurry or for Maize to produce biogas from grass silage. Grass is a lignocellulosic feedstock which is fibrous; it can readily cause difficulties with moving parts (wrapping around mixers); it also has a tendency to float. This thesis has an ambition of establishing the ideal digester configuration for production of biogas from grass. Extensive analysis of the literature is undertaken on the optimal production of grass silage and the associated biodigester configurations. As a result of this analysis two different digester systems were designed, fabricated, commissioned and operated for over a year. The first system was a two stage wet continuous system commonly referred to as a Continuously Stirred Tank Reactor (SCTR). The second was a two stage, two phase system employing Sequentially Fed Leach Beds complete with an Upflow Anaerobic Sludge Blanket (SLBR-UASB). These were operated on the same grass silage cut from the same field at the same time. Small biomethane potential (BMP) assays were also evaluated for the same grass silage.
The results indicated that the CSTR system produced 451 L CH4 kg-1 VS added at a retention time of 50 days while effecting a 90% destruction in volatile dry solids. The SLBR-UASB produced 341 L CH4 kg-1 VS added effecting a 75% reduction in volatile solids at a retention time of 30 days. The BMP assays generated results in the range 350 to 493 L CH4 kg-1 VS added.
This thesis concludes that a disparity exists in the BMP tests used in the industry. It is suggested that the larger BMP (2L with a 1.5 L working volume) gives a good upper limit on methane production. The micro BMP (100 ml) gave a relatively low result. The CSTR when designed specifically for grass silage is shown to be extremely effective in methane production. The SLBR-UASB has significant potential to allow for lower retention times with good levels of methane production. This technology has more potential for research and improvement especially in enzymatic hydrolysis and for use of digestate in added value products.

The production of grass biomethane is an integrated process which involves numerous stages with numerous permutations. The grass grown can be of numerous species, it can involve numerous cuts. The lignocellulosic content of grass increases with maturity of grass; the first cut offers more methane potential than the later cuts. Water soluble carbohydrates (WSC) are higher (and as such methane potential is higher) for grass cut in the afternoon as opposed to the morning. The method of ensiling has a significant effect on the dry solids content of the grass silage. Pit or clamp silage in southern Germany and Austria has a solids content of about 40%; warm dry summers allow wilting of the grass before ensiling. In temperate oceanic climates like Ireland, pit silage has a solids content of about 21% while bale silage has a solids content of 32%.  Biogas production is related to mass of volatile solids rather than mass of silage; typically one ton of volatile solid produces 300m3 of methane. The dry solids content of the silage has a significant impact on the biodigester configuration. Silage with a high solids content would lend itself to a two stage process; a leach bed where volatile solids are converted to a leachate high in chemical oxygen demand (COD), followed by an Upflow Anaerobic Sludge Blanket where the COD can be converted efficiently to CH4. Alternative configurations include for wet continuous processes such as the ubiquitous Continuously Stirred Tank Reactor; this necessitates significant dilution of the feed-stock to effect a solids content of 12%. Various pre-treatment methods may be employed especially if the hydrolytic step is separated from the methanogenic step. Size reduction, thermal and enzymatic methodologies are used. Good digester design is to seek to emulate the cow, thus rumen fluid offers great potential for hydrolysis.

The current world population of 7.2 billion is projected to reach up to 8.2 billion in 2025 with current annual growth rate of 1%. The Asia, Middle East, Africa and Latin America are the places, where most of this growth will occur due to rapidly growing industries and urbanization. As a consequence, the generation rate of municipal solid waste (MSW) will increase from 1.2 to 1.5 kg per capita per day in next 15 years. Globally, around 2.4 billion tons of MSW is generated every year that will reach up to 2.6 billion tons by 2025. Similarly, the energy demand will increase significantly in developing countries, especially in Asia with an increase of 46-58% at annual rate of 3.7% till 2025. Fossil fuels are the most relied source at the moment to meet the world's energy demands. The intensive and solely utilization of fossil resources are not only depleting our natural reserves but also causing global climate change. The municipal waste can be a cheap and valuable source of renewable energy, recycled materials, value-added products (VAP) and revenue, if properly and wisely managed. The possibilities for converting waste-to-energy (WTE) are plentiful and can include a wide range of waste sources, conversion technologies, and infrastructure and end-use applications. Several WTE technologies such as pyrolysis, anaerobic digestion (AD), incineration, transesterification, gasification, refused derived fuel (RDF) and plasma arc gasification are being utilized to generate energy and VAP in the form of electricity, transportation fuels, heat, fertilizer, animal feed, and useful materials and chemicals. However, there are certain limitations with each WTE technology, as an individual technology cannot achieve zero waste concept and competes with other renewable-energy sources like wind, solar, and geothermal. A conceptual and technological solution to these limitations is to integrate appropriate WTE technologies based on the country/or region specific waste characterization and available infrastructure, labor skill requirements, and end-use applications under a biorefinery concept. Such waste-based biorefinery should integrate several WTE technologies to produce multiple fuels and VAP from different waste sources, including agriculture, forestry, industry and municipal waste. This paper aims to assess the value of waste-based biorefinery in developing countries as a solution to waste-related environmental and human health problems with additional bonus of renewable energy and VAP.