In this article we will discuss about:- 1. Introduction to Biofuels 2. Biofuel Versus Fossil Fuel 3. Classification 4. Advantages and Limitation 5. Future Prospects.
Contents:
- Introduction to Biofuels
- Biofuel Versus Fossil Fuel
- Classification of Biofuels – First, Second, Third and Fourth Generation
- Advantages and Limitation of Biofuels
- Future Prospects of Biofuels
1. Introduction
to Biofuels:
ADVERTISEMENTS:
The continuous growth of plants on our planet exceeds men’s primary energy requirements many times over. Of course, only part of the biomass that grows can actually be supplied for energy use, due to ecological, technical and economic reasons. However, there remains a huge amount of biomass that is very suitable for exploitation. Biomass resources comprise those which are received from agriculture and forestry as well as from agro industry and wood industry. It also includes waste sources from construction and demolition as well as municipal wastes.
The potential biomass available in India seems to be sufficient to support the ambitious renewable energy targets in an environmentally responsible way. Agricultural waste generated after harvesting the crops, waste of forestry and organic waste generated from various sources, such type of waste can be utilised for production of various biofuels like methane, biohydrogen, ethanol, etc. Biomass can be used for generation of heat, power and transport fuels in an environmentally friendly way. Consequently, it is useful for both, i.e., reduction in emission of greenhouse gases and achieve the Indian renewable energy targets.
Recent concerns arise that biofuel production competes with food production. However, in India the production of many agricultural products is more than saturated. In order to guarantee profitable market prices, production limits were introduced and high premiums are paid for some agricultural products and set-aside land.
Therefore the production of biofuels does not compete with food production at the moment. But once the demand for biomass increases, the production of biofuels will not only compete with the food sector, but also with chemical industries and regenerative raw materials.
Useful Features of Biofuels:
ADVERTISEMENTS:
1. Most of biofuels are derived from biomass, which is renewable low cost and locally available and no commitment of foreign exchange.
2. They lead to relatively low CO2 emission then fossil fuels.
3. The substrate is often a waste, including municipal waste use of such materials for biofuel production not only generates more valuable products from low cost substrate but also help in cleaning up the environment.
2. Biofuel Versus Fossil Fuel
:
ADVERTISEMENTS:
Biofuels are not new. In fact, Henry Ford had originally designed his Model T to run on ethanol. There are several factors that decide the balance between biofuel and fossil fuel use around the world. Those factors are cost, availability, and food supply.
All three factors are actually interrelated. Availability of fossil fuels has been of concern almost from day one of their discovery. The cost of fossil fuel is very high due to processing cost as pumping fuel from the ground is a difficult and expensive process, which adds more cost of these fuels. Availability of fossil fuel depends upon our ability to recover fossil fuels from the ground. If availability decreases, the supply will decrease, which will lead to an increase in price.
It was originally thought that biofuels could be produced in almost limitless quantity because they are renewable. Unfortunately, our energy needs far outpace our ability to grown biomass to make biofuels for one simple reason, land area.
There is very limited covered area of land, farming for biofuels will decrease covered area for food product farming. As the population grows, our demands for both energy and food grow. Today, we do not have sufficient land to grow both biofuel and enough food to meet out our needs. The result of this limit has an impact on both the cost of biofuel and the cost of food. For wealthier countries, the cost of food is less of an issue.
ADVERTISEMENTS:
However, for poorer nations, the use of land for biofuels, which drives up the cost of food, can have a tremendous impact. The balance between food and biofuel production can be achieved by using advanced technologies. When this factor is combined with an increased ability to extract oil from the ground using advance technology, the price of fossil fuel is actually lower than that of biofuel for the most part.
3. Classification of Biofuels – First, Second, Third and Fourth Generation
:
The classification of biofuels can be applied to first generation and second generation biofuels. PPO, biodiesel, bioethanol and ETBE are first generation biofuels since the conversion and engine technologies are widely developed and approved in practice. They offer the greatest short-term potentials of biofuels today. Although they differ in properties, technical requirements, economical aspects and potential, they can contribute to guarantee long-term mobility.
The second generation biofuels are not yet commercial available since the conversion technologies require great improvement. This group of biofuels includes, e.g., BTL fuels and ethanol from starch. BTL fuels are a promising option for the future, but will not achieve relevance to the market before 2018.
However, the boundaries first and second generation fuels are fluently and not exactly defined. Currently biogas is shifting from first to second generation biofuel. First biogas stations are built at the moment. Biomethane from biogas can be used in natural gas vehicles without any adjustments.
The third generation biofuel refers to biofuel derived from algal biomass. The diversity of fuel that algae can produce results from two characteristics of the microorganism. First, algae produce an oil that can easily be refined into diesel or even certain components of gasoline. More importantly, however, is a second property in it can be genetically manipulated to produce everything from ethanol and butanol to even gasoline and diesel fuel directly.
Fourth generation biofuels are derived from specially engineered plants or biomass that may have higher energy yields or lower barriers to cellulosic breakdown or are able to be grown on non-agricultural land or bodies of water. In fourth generation production systems, biomass crops are seen as efficient carbon capturing machines that take CO2 out of the atmosphere and store it in their branches, trunks and leaves.
Conversion of Organic Waste in to Biofuels:
At present time automobile industries are also manufacturing pure or hybrid natural gas vehicles as standard models. One of the promising future options for sustainable transport fuels is the subsidisation of natural gas by biomethane. Biogas or biomethane is the most efficient and clean burning biofuel which is available easily today. It can be produced from nearly all types of biomass including wet biomass which is not usable for most other biofuels. Another motivational use of gaseous biofuels for transportation.
Raw Material for Biogas Production:
The raw material for the production of biomethane is biogas, which can be processed from various feedstock sources. For biogas production much more different feedstock sources can be used than for common liquid biofuels. For instance biodiesel can be only made from plant materials containing certain amounts of oil.
In contrast, biogas is produced from nearly all types of organic materials including vegetable and animal feedstocks. The origin of the feedstock can vary, ranging from livestock waste, manure, harvest surplus, to vegetable oil residues. Dedicated energy crops are becoming more and more practice as feedstock source for biogas production.
Recently, wastewater sludge, municipal solid wastes and organic wastes from households have been introduced as feedstock. Another feedstock source is the collection of biogas from landfill sites.
The main advantage of biogas production is the ability to use so-called ‘wet biomass’ as feedstock source. Wet biomass is not used for the production of other biofuels such as bio-hydrogen, biodiesel. The examples of wet biomass are sewage sludge, manure from dairy and poultry farms as well as residues from food processing industries. All of these are characterised by moisture contents of more than 60-70%.
The waste materials is not only utilised for biogas production, it also creates some additional benefits. Thus, it contributes to reduce animal wastes, odours and green house effects. The digestion or hydrolysis process effectively eliminates environmental hazards, such as over production of liquid manure. Thus biogas production is an excellent way for livestock farmers to comply with increasing governmental regulations of animal waste.
Sources of Biomass:
1. Land crops.
2. Aquatic plants.
3. Wastes – manure, domestic, rubbish, municipal waste sewage.
4. Agro industry waste – wood and crop residue like straw, bagasse, molasses, press mud, paper sludge.
Wastes which can be used for biogas production at various level:
1. Village, farm level: Agricultural waste/vegetable wastes.
2. House hold level: Animal waste/domestic garbage.
3. City level: Municipal garbage/sewage.
4. Industry level: Industrial effluents/solid wastes of dairy/distillery, brewery, food processing units, and chemical industries.
Biomethane Production:
The production of biomethane includes two steps. Firstly, biogas has to be produced from feedstock sources. Secondly, the biogas has to be further processed and cleaned in order to receive biomethane which is suitable for transport applications.
Digestion Process:
Biogas is produced by means of anaerobic digestion. Organic matter is broken down by microbiological activity and in the absence of air. Symbiotic microorganisms plays different roles at different stages of the digestion process during the break down complex organic materials. These micro-organisms are categorised in to four basic types. Hydrolytic bacteria break down complex organic wastes into sugars and amino acids.
Fermentative bacteria then convert those products into organic acids. Acidogenic micro-organisms convert the produced organic acids into hydrogen, carbon dioxide and acetate. At last, the methanogenic bacteria produce biogas (CH4) from acetic acid, hydrogen and carbon dioxide.
Since these bacteria are sensitive to temperature, this has to be considered in the digestion process. In order to promote bacterial activity, temperatures of at least 20°C are required. It has been observed that higher temperatures reduces processing time and reduce the required volume of the reactor tank by 25% to 40%.
Regarding the temperature, bacteria of anaerobic digestion can be divided into psychrophile (25°C), mesophile (32-38°C) and termophile (42-55°C) bacteria. The process temperature depends on the type feedstock used and type of bioreactor/digester used. Thus, digesters have to be heated in colder climates in order to encourage the bacteria to carry out their function.
Digestion time duration ranges from a couple of weeks to a couple of months depending on feedstock, type of bioreactor used in the process and on the reactor temperature also.
Micro-Organism Used for Anaerobic Digestion to Produce Biogas:
Anaerobic digestion to biogas production involves three groups of organism.
1. Hydrolysis of Organic Materials:
Fermentative bacteria convert complex organic material into organic acids, alcohols, esters, sugars, CO2.
2. Acetogenesis:
This group is dependent on first and contains hydrogen and acid producing bacteria.
3. Methanogenesis:
Methanogenesis bacteria convert acetate and H2 into biogas which is mixture of CH4 and CO2, e.g., Mefhanosarcinci barkeri, Methanobacterium omelionskii.
Biogas (CH4) production torn wastes is given more and more importance because it couples degradation of waste to energy production and not energy consumption. Reactions of various designs and size ranging from 2000-20000 m3 capacity are in use worldwide.
Soluble organic matter here is suitable and loads of 25-30 kg COD m-3d-1 are handled. Each 1 kg COD yield 350 litre of methane.
Effluents rich in carbohydrates are rich in methane production but those with high fat and protein contents are still rich. That is the reason why wastes from the food processing units find more potential in biogas production.
Type of Digester:
Biogas production is the digestion of feedstock by common technology in specially designed digesters. These must be strong enough to withstand the buildup of pressure and must provide anaerobic conditions for the bacteria inside. In this process anaerobic digester systems can reduce fecal coliform bacteria in manure by more than 99%.
Further, the ability of the digester to produce and capture methane from the manure reduces the amount of methane that otherwise would enter the atmosphere. Methane gas in the atmosphere is a contributor to global climate change.
Today, there are many different technologies and digester types available. Generally, the size of biogas plants can vary from a small household system to large commercial plants of several thousand cubic meters. Digester size also influences logistics and vice versa.
For instance, for larger scale digesters feedstock has to be collected from individual farms and transported to central digester facilities. However, independent from the type of digester, they are often built near the source of the feedstock, and several are often used together to provide a continuous gas supply.
Batch Type:
The digester used for biogas production is filled at once and after completion of production process the whole system is emptied.
Continuously Expanding Type:
Firstly, the digester is filled up to 1/3, then it is continuously filled until it is full and finally the digester is emptied.
Continuously Flow Type:
The digester is initially filled completely, then the feedstock is continuously added and digested material is continuously removed.
Pug Flow Type:
The feedstock is added regularly at one end and overflows the other end.
Contact Type:
This is a continuous type, but a support medium is provided for the bacteria.
Reactors Used:
1. Upflow Anaerobic Sludge Blanket reactor (UASB).
2. Upflow fixed film anaerobic filter.
3. Down flow film anaerobic filter.
4. Expanded bed reactor.
5. Fluidised bed reactor.
6. CSTR.
Biogas Purification:
The digestion of organic matter results the production of biogas, a combination of methane and carbon dioxide, typically in the ratio of 6:4 (55-80% methane). In addition, there are small quantities of hydrogen sulphide and other trace gases. Since only the methane is usable as transport fuel, methane has to be separated from CO2 and the remaining components of biogas.
The final product is biomethane, which has methane content between 95 and 100%. Therefore it is very similar to natural gas and suitable for all natural gas applications.
Biomethane can be also produced by gasification. Nevertheless, it has to be recognised that the process of biomass gasification is distinctly different form that of biogas production. Gasification is the process by which solid biomass materials are broken down using heat to produce a combustible gas, commonly known as producer gas.
Factors Affecting Methane Formation:
1. Slurry:
Proper solubilisation of organic material. (The ratio between solid and water should be 1:1 when it is house hold type).
2. Seeding:
In the beginning, seeding of slurry with small amount of sludge of another digester is taken to activate the digester as active microorganisms are present in that sludge.
3. pH:
For the production of sufficient amount of methane, optimum pH of digester should be maintained between pH 6-8 as the acetic medium lowers down methane formation.
Properties and Use of Biomethane:
The simplest hydrocarbon, methane, is a gas at Standard Temperature and Pressure (STP). Its chemical formula is CH4. Further, methane is a combustible and odourless gas. It is also a greenhouse gas with a global warming potential of 23 in 100 years. That means that each kg of methane warms the earth 23 times as much as the same mass of CO2 when averaged over 100 years.
After the digestion and purification process of biomass, biomethane is obtained. In contrast to neat NH4, biomethane also has small amounts of other compounds than NH4. Nevertheless, the methane content of biomethane is 95-100%. For fuel purposes it can be concluded, that the higher the methane content the higher is the fuel quality. Biomethane from biogas is chemically identical with natural gas and therefore does not differ in parameters.
Bioethanol:
Ethanol can be produced from any biological feedstock that contains appreciable amounts of sugar or materials that can be converted into sugar such as starch or cellulose. Different feedstock sources can be used for ethanol production. They can be divided into sugary, starchy and cellulosic feedstock.
Two examples of feedstock for ethanol production are sugar beets and sugar cane which contain high percentages of sugar. Sugars can be easily fermented. For example, Brazil developed a successful fuel ethanol programme from sugarcane. In Europe, sugar beets are used for ethanol production.
Currently, ethanol imports from Brazil are entering the European fuel market. Corn, wheat, barley, rye and other cereals are typical feedstocks containing starch in their kernels. Starch can relatively easily be converted into sugar and then into ethanol. In the USA and Europe, ethanol is manufactured mainly from maize and grain.
At the moment substantial capacities for the manufacture of ethanol are being created in Germany. Other starchy crops that can also be used for bioethanol production are sorghum grains, cassava and potatoes. Recent research includes bioethanol production from potatoes and waste potatoes from food processing industry.
Since ethanol from sugar and starch bearing plants is readily available today, these feedstock types are also called first-generation feedstocks. First generation feedstocks are characterised by the fact that only parts of the plants (starch, sugar, oil) are used for biofuel production. Different feed stock for ethanol production is shown in Fig. 11.4.
Contrary to this, next-generation feedstock types provide the opportunity to use nearly the whole plant for biofuel production and not only parts of the plants (grains, tubes, stalks). The advanced technologies are necessary for the use of second generation fuels. Various types of feedstock is available for producing ethanol from biomass that having large amounts of cellulose and hemiceflulose.
Cellulose and hemicellulose can be converted to sugar by the hydrolysis process, but conversion of starch is more difficult. Considered cellulosic biomass are agricultural wastes (including those resulting from conventional ethanol production), forest residues, municipal solid wastes (MSW), wastes from pulp/paper processes and energy crops.
Cellulosic agricultural wastes for ethanol production include crop residues such as wheat straw, corn stover (leaves, stalks and cobs), rice straw and bagasse (sugar cane waste). Forestry wastes include logging residues as well as wood which is not used and thus left in the forest. MSW contains high percentages of cellulosic materials, such as paper and cardboard.
In contrast to cellulosic waste materials, dedicated energy crops, which are grown specifically for ethanol production, include fast-growing trees (poplars), shrubs (willow), and grasses (switch grass). The cellulosic components of these materials range between 30% and 70%.
This new concept of utilising cellulosic feedstock for bioethanol production is not yet applicable on the large scale, but is currently subject to intensive research. The large-scale production of agricultural ethanol requires substantial amounts of cultivable land with fertile soils and water (except for wastes).
Sugar Beet:
Sugar beet (Beta vulgaris L.) belongs to the subfamily of the Chenopodiaceae and to the Family of the Amaranthaceae. Its roots contain a high concentration of sucrose and therefore it is grown commercially for sugar production. The three largest sugar beet producers worldwide are the European Union, the United States, and Russia.
Only Europe and Ukraine are significant exporters of sugar from beet. Ukraine and Russia have the largest cultivated area, but the largest producers by volume are France and Germany. Despite from the food industry, sugar beet molasses is a valuable feedstock for bioethanol.
Sugar beet is a hardy biennial plant that can be grown commercially in a wide variety of temperate climates. During growth it produces a large (1-2 kg) storage root whose dry mass is 15-20% sucrose by weight. This sucrose and the other nutrients in the root are consumed to produce the plant’s flowers and seeds if it is not harvested in the first year.
In commercial beet production, the root is harvested in the first growing season, when the root is at its maximum size. Beets are planted from small seeds. In most temperate climates, beets are planted in spring and harvested in autumn. A minimum growing season of 100 days can produce commercially viable sugar beet crops. In warmer climates, sugar beets can be cultivated as winter crop, being planted in the autumn and harvested in the spring.
Sugar Cane:
Sugar cane (Saccharum sp.) is a genus of 37 species of tall grasses and belongs to the family of the Poaceae and is native to warm temperate to tropical regions. The species of sugarcane are interbreed, and the esteemed commercial cultivars are complex hybrids. Sugarcane is a grass originally found in tropical region of Southeast Asia.
The plants have stout, jointed fibrous stalks which are 2 to 6 meters tall and rich in a sugar bearing sap. Today about 107 countries grow sugar cane whereas Brazil is the world leading producer. Sugar cane is the most significant crop for biofuel production today, supplying more than 40 % of all fuel ethanol.
Besides the production of bioethanol, sugar cane is also used for the production of alimentary sugar, molasses, and rum. In a sugar mill the harvested sugarcane is washed, chopped, and shredded by revolving knives. The shredded cane is repeatedly mixed with water and crushed between rollers.
The collected juice contains 10-15% sucrose. The remaining fibrous solids, also called bagasse, can be used as co-product to generate process heat. It makes a sugar mill more than self-sufficient in energy. The surplus bagasse can be used for animal feed, in paper manufacture, or burned to generate electricity for the local power grid.
The juice from sugar cane is further processed, refined, fermented and distilled for bioethanol production.
Starch Crops:
Cereals:
Cereal crops are grasses which are cultivated originally for their edible grains or seeds (actually a fruit called a caryopsis). Worldwide cereal grains are grown in greater quantities and provide more food energy to the human race than any other type of crop. The most planted cereal crops are corn (maize), wheat and rice, which account for more than 80% of all grain production worldwide.
Although each species has its specific characteristics, the cultivation of cereal crops is similar. In general, they are annual plants and consequently one planting yields one harvest. Nevertheless, in Europe, all cereals can be divided into cool-season and warm-season types.
Recently bioethanol is produced by using waste potatoes which are a co- product of the food industry.
Cellulosic Feedstock:
Primary cellulosic wastes are produced during production and harvesting of food crops such as, e.g., straw, corn stalks and leaves. Also residues from forestry such as, e.g., wood thinning from commercial forestry belong to primary cellulosic wastes. These types of biomass are typically available in the field or forest and must be collected to be available for further use.
Thereby attention has to be paid as there are long-term economic and environmental concerns associated with the removal of large quantities of residues from cropland. Removing residues can reduce soil quality, promote erosion, and reduce soil carbon, which in turn lowers crop productivity and profitability.
But, depending on the soil type, some level of removal can be also beneficial. Establishment and communication of research-based guidelines is necessary to ensure that removal of residue biomass is done in a sustainable manner.
Secondary cellulosic wastes are generated during the production of food products and biomass materials. This biomass include nut shells, sugar cane bagasse, and saw dust, and are typically available at, e.g., industries for food and beverage production as well as at saw and paper mills.
Tertiary cellulosic wastes become available after a biomass-derived commodity has been used. A large variety of different waste fractions is part of this category- Organic part of Municipal Solid Waste (MSW), waste and demolition wood, sludge, paper, etc.
Lipid Derived Biofuel:
Biodiesel:
Properties of Biodiesel:
The properties of biodiesel like viscosity and ignition properties are similar to the properties of fossil diesel.
Although the energy content per litre of biodiesel is about 5 to 12% lower than that of diesel fuel, biodiesel has several advantages. For example the cetane number and lubricating effect of biodiesel, important in avoiding wear to the engine, are significantly higher. Therefore the fuel economy of biodiesel approaches that of diesel.
Additionally, the alcohol component of biodiesel contains oxygen, which helps to complete the combustion of the fuel. The effects are reduced air pollutants such as particulates, carbon monoxide, and hydrocarbons. Since biodiesel contains practically no sulphur in it and can be helpful for reducing the emissions of sulphur oxides.
Biodiesel is sensitive to cold weather and may require special anti-freezing precautions, similar to those taken with standard diesel. Therefore winter compatibility is achieved by mixing additives, allowing the use down to minus 20°C. Another problem is that biodiesel readily oxidises. Thus long-term storage may cause problems, but additives can enhance stability.
Biodiesel also has some properties similar to solvents. Therefore it can attack plastic and rubber components such as seals and fuel lines. This causes problems in vehicles which have not been approved or which are filled with biodiesel for the first time after a long mileage with fossil diesel.
In this case biodiesel acts like a detergent additive, loosening and dissolving sediments in storage tanks. Residues of the fossil fuel are released, causing the filter to become blocked. It is therefore advisable to change the fuel filter after several tank fillings with biodiesel.
Conventional diesel engines operate readily with up to 100% biodiesel fuel, but using blends above 20% may require modest costs in order to replace some rubber hoses that are sensitive to the solvent character of biodiesel.
Raw Material for Biodiesel Production:
The choice for a dedicated feedstock is predetermined by agricultural, geographical and climatic conditions. But it also has to be considered, that different feedstock types are characterised by different properties. For instance, the oil saturation and the fatty acid content of different oilseed species vary considerably.
Biodiesel from highly saturated oils is characterised by superior oxidative stability and high cetane number, but performs poorly at low temperatures. The major seeds are from sunflower, peanut, sorghum, rapeseed, ricinus, sorghum, jatropha, etc.
Rapeseed:
Rape (Brassica napus L. ssp. oleifera), also known as canola or colza, belongs to the family of the Brassicacea and is closely related to other oil seed crops such as mustard species (Brassica nigra, Sinapis alba) and Gold-of-pleasure (Camelia sativa).
Rape is cultivated and sowed either in autumn (biennial) or in spring (annual). The plant has a long taproot and the stem can grow up to 1.5 m. The seeds are enclosed in pointed pots. Winter rape in Europe is harvested at the end of July with yields of 3 T/ha. Summer rape ripens in September and yields 2.1 T/ha.
Palm Oil:
The oil palm (Elaeis guineensis) is one of the two palm trees (besides coconut palm) that are used for oil production, mainly in South Asian countries. The two largest producers are Malaysia and Indonesia, where palm oil production has grown rapidly over the last decade. Nigeria has the second largest planted area and high potentials are expected in Brazil. While most palm oil is used for food purposes, the demand for palm biodiesel is expected to increase rapidly, particularly in Asia.
Fuel Production:
Today, mainly oil from plant sources which are exclusively harvested for biofuel production (oil crops) is used for biodiesel processing. Here our concentration is firstly on biofuel production from seed oil crops. The amount of fuel production from microalgae, animal fats and waste oils is only small, although the potential is expected to be very high.
The harvest of oil crops depends on the plant species and the technique available. Taking rape as an example, the harvest is conducted by using a combine harvester. The seeds are either transported directly to the oil mill or stored first. The first process step of biofuel production then is the oil extraction which can be done by several means.
Oil Extraction:
The oil extraction of the feedstock is the first process step of biodiesel processing.
Regarding the scale of production and the infrastructure, there are two fundamental production process types for vegetable oils:
1. Industrial:
Centralised production by refining in large industrial plants.
2. Small Scale Pressing:
Decentralised cold pressing directly on farms or in co-operatives.
In small scale cold pressing facilities, the cleaned oil seeds are exclusively mechanically pressed at maximum temperatures of 40°C. Suspended solids are removed by filtration or sedimentation. As a co-product, the press cake is left with a remaining oil content of usually over 10%, which is used as a protein-rich fodder.
Due to higher production costs, the decentralised oil production by farmers is not widely applied today, although the chance of additional income for farmers is given. Furthermore, the co-product could be directly used for feeding the animals.
The common way in oil extraction is the treatment of feedstock in centralised industrial large scale plants. First, the feedstock has to be pre-treated. For better illustration purposes, the processing of rape oil is used here as an example for oil extraction.
Within the pre-treatment the rape seeds have to be dried first, but only if it will be stored more for than ten days. In this case, the typical water content of rape seeds, which is about 15%, has to be reduced to 9%. Subsequently, the rape seeds are cleaned. Additionally, other seeds that are larger in size, such as sunflower seeds, have to be peeled.
When pressing rape seeds, the press cake is left as co-product. It still contains the remaining 25% of the total rape seed oil content and therefore is further treated. First, the press cake has to be crushed so that the added solvent, which is usually hexane, can extract the oil at temperatures of up to 80°C. The results of this process step are a mixture of oil with hexane, also called miscella, and the so called extraction grist. The solvent is separated from both compounds and recycled to the process.
After these process steps, the oil has more undesired components as in cold pressing. They are removed by refining. The end product is oil designated as fully refined in edible oil quality.
Transesterification:
The molecular structure of lipid molecules are changed in the chemical process of transesterification during biodiesel production. Thereby the physical properties change. Although even refined Pure Plant Oil (PPO) can be used in refitted diesel engines, biodiesel, which is created by a transesterification step, has several advantages.
One advantage is the lower viscosity of biodiesel when compared to PPO. Increased viscosity adversely affects fuel injection duration, pressure, and atomisation of diesel engines. Biodiesel is very similar to fossil diesel and thus can be consumed in common diesel engines which are refitted with only small efforts.
Transesterification, also known as alcoholysis, it is the process in which the refined oil molecule is ‘breakdown’. The glycerin is removed for manufacturing of glycerin soap and methyl-or ethyl esters for biodiesel. Organic fats and oils are triglycerides which are three hydrocarbon chains connected by glycerol. The bonds are broken by hydrolysing them to form free fatty acids.
These fatty acids are then mixed or reacted with methanol or ethanol forming methyl or ethyl fatty acid esters (monocarbon acid esters). The mixture separates and settles out leaving the glycerin on the bottom and the biodiesel (methyl, ethyl ester) on the top.
Now the separation of these two substances has to be conducted completely and quickly to avoid a reversed reaction. These transesterification reactions are often catalysed by the addition of an acid or base. The chemical transesterification reaction is shown in Fig. 11.7.
For the transesterification process, mainly the alcohols methanol and ethanol are used. Theoretically transesterification can be also processed with higher or secondary alcohols. Transesterification with methanol, also called methanolysis, is the most commonly method for biodiesel production.
Methanol is characterised by its lower prices and its higher reactivity as compared to other alcohols. This reaction can happen by heating a mixture of 80-90 per cent oil, 10-20 per cent methanol, and small amounts of a catalyst. For the reaction it is necessary to mix all ingredients well, as the solubility of methanol in vegetable oil is relatively low. The received biodiesel after methanolysis is Fatty Acid Methyl Ester (FAME).
Biohydrogen:
Biohydrogen gas is a perfect renewable fuel hydrogen when burnt does not cause any pollution but regenerates water. Hydrogen production process operates at a normal temperature. No toxic materials are produced in the process. Biohydrogen can be made directly from biomass in presence of sunlight, or it can be produced by splitting of water molecule into its constituent components of hydrogen and oxygen.
Some microbial strains like Rhodopseudomonas bacterial produces biohydrogen. Algae is also another source of production. Through recent technologies biohydrogen is produced from a variety of energy sources, stored for later use, piped to where it is used and then converted cleanly into heat and electricity.
Hydrogen is the most efficient source of energy. Now a days hydrogen production is being done by steam reforming natural gas, but the natural gas is already a good energy source or fuel. Natural gas is rapidly becoming dangerous and more expensive. As natural gas is a fossil fuel, so it will generate greenhouse gases whenever biohydrogen does not cause any type of pollution.
Very high energy is liberated during the combustion of biohydrogen. The major challenge is to increase the production efficiency of biohydrogen, so new technology is needed to increase production, store and transport it. The fuel cell technology is still in early development, it is needing improvements in efficiency and durability.
Micro-Organisms:
1. Anaerobic bacteria.
2. Photosynthetic algae, e.g., Clostridium butyricum, enterobacter aerogenes, Rhodopseudomonas palustirs, Rhodopseudomonas rubrum, Rhodobacter sphyroid.
Substrate (Raw Material):
Wastewater, food waste, vegetable waste, other organic wastes.
Bio-Hydrogen Production Mechanisms:
It can be possible by two routes:
1. Anaerobic fermentation.
2. Photolysis of water.
Anaerobic Bacterial Mechanism of Bio-Hydrogen Production:
An anaerobic bacteria oxidise the substrate by reducing NAD+ to NADH. But for continued substrate oxidation, it is essential to remove NADH which is transferred to H+ions to produce gas; there by regenerating NAD+, the reaction is catalysed by enzyme ‘Hydrogenase’ as shown below-
‘Hydrogenase’ enzyme that has been extracted from 15 species of bacterial and algae. Japanese biotechnologists have immobilised Clostridium butyricum and these cells produce H2 gas for a month when feel with wastewater containing sugar from a alcohol industry. Anaerobic packed bed reactor and agar entrapment used for the purpose.
R. palustris has been grown in anaerobic bioreactor. Plants of agar immobilised organism are used. The system is easy to operate and build 0.78 L/L of H2 production from sugar refinery and 2.2 L/L H2 from straw paper mill effluent is reported. R. gelatinosa produced more H2 from organic acid than from sugars like glucose, sucrose, lactose, 50 ml of H2 is produced per gram of total organic carbon used.
Japans fermentation Research Institute and agency of industrial science and technology have jointly developed a system to efficiently produce the H2 gas. Bacteria used for the system is Rhodobactor sphyroid (photosynthetic bacteria). H2 gas has 3 times more calorific value per unit weight of petroleum and it does not generate CO2 or other air pollutants. Energy conversion can be increased up to 20%.
Photosynthetic Pathway (Algae):
Some algae also produce H2. Photosynthetic apparatus splits water molecule into H2 and O2. The photosystem-I produces then reduced ferredoxin. Ferredoxin then oxidised and protein (H+) act as electron acceptors to produced H2. The efficiency of H2 production is reasonable at low light intensities.
Upon a dark anaerobic incubation of the algae and the ensuing induction of the hydrogenase, electrons for the photosynthetic apparatus are derived upon a catabolism of endogenous substrate and the attendant oxidative carbon metabolism in the green algae.
Electrons substrate catabolism feed into the photosynthetic electron transport chain between the two photosystems, PS-I and PS-II. Light absorption by Photosystem-I and the ensuing electron transport elevates the redox potential of these electrons to the redox equivalent of ferredoxin and the hydrogenase, thus permitting the generation of molecular H2.
4. Advantages and Limitation of Biofuels
:
Advantages of Biofuels:
The advantages of biofuels are given below:
1. Cost:
As well as new technologies are being developed the prices of biofuels are falling which have the potential to be significantly much less expensive than fossil fuels. In fact, bioethanol is already less costly than diesel and gasoline. Although it is absolutely true that the worldwide demand for fuels is increasing exponentially. So the alternative source of biofuels/bioenergy have to be developed and searched because we have a limited stock of fossil fuel as it is decreasing very rapidly.
2. Raw Materials:
Biofuels can be produced from a wide range of raw materials including agricultural waste, domestic waste, food industry waste, meat industry waste and other by-products of different industries. This will be helpful for managing the waste material, utilisation and recycling of waste for biofuel production.
3. Renewable:
Biofuels can be produced from waste or very cheap raw materials. The production time and cost is much lower. The process of fossil fuels formation takes a very long time.
4. Feature Security:
Biofuels can be produced easily worldwide. The dependency on foreign nations can be reduced for fossil fuels by producing biofuels locally. Country like India imports approximately 80% fossils fuels from other countries. It has been observed the cost of fossil fuels are increasing very high rate. So biofuels not only make a nation independent for energy requirement but it is also very helpful to build a nation prosperous by saving currency spent for fossil fuels purchasing.
5. Economic Boostup:
Biofuels can be produced locally at very low cost. The production of biofuels will definitely reduce the dependency of a country on other country for fossil fuels. It will save currency which is spending for fossil fuels purchasing, that currency now, will be utilise for other developmental work and will be helpful for boostup the economy of any nation.
6. Lower Carbon Emissions:
Environmental pollution is another big challenge to all of us. On of the major causes of air pollution is highly consumption of fossil fuels which cannot be reduced. Biofuels are eco-friendly fuels it produce significantly less carbon output and fewer toxins, making them a safer option to preserve atmospheric quality and lower air pollution.
Disadvantages of Biofuels:
There are some following disadvantages of biofuels production and utilisation:
1. Energy Yield:
Although biofuels have a lower energy output than traditional fossil fuels, so biofuels are required in greater quantities for producing the same energy level. This has been noticed by energy analysts that biofuels are not worth the work to convert them to ethanol rather than bioenergy or electricity.
2. Carbon Emissions:
Some of researchers have been studied to analyse the carbon footprint of biofuels, while they are being cleaner to burn, during the process to producing the biofuels. The production processes of biofuels production, cultivation of crops have hefty carbon emissions. In addition, pretreatment of raw materials and during the production of biofuels (e.g., CH4) also promotes large amount of carbon emissions.
3. High Cost:
In some cases biofuels production and purification cost may be higher (e.g., biodiesel).
4. Food Prices:
As some biofuels like ethanol can be produced by grains as raw materials, this may cause for increase of demand for food crops such as corn, due to higher demand the rates may increase of staple food crops.
5. Food Shortages:
The area of agricultural land is shrinking day by day, in such case our first priority should be to make available food to our peoples. In such case the production of biofuels from food grains may lead to shortage of food materials.
6. Water Use:
Huge amount of water is consumed during irrigation of biofuel crops as well as in manufacturing process of biofuels.
5. Future Prospects
of Biofuels:
Economy of Biofuels:
In the whole life cycle of biofuels, the relatively high production costs still remain a critical barrier to commercial development, although continuing improvements are achieved. The technologies for pure plant oil (non-edible oil) extraction, purification and conversion to biodiesel have been developed.
The competitiveness of biofuels will increase as prices for crude oil and other fossil sources increase and overstep a critical threshold. Subsidies can be both agricultural aids and market incentives for the biofuel itself. Also tax exemptions have considerable impacts on end-user costs for biofuels.
For first generation biofuels, the feedstock is a major component of overall costs. As crop prices are highly volatile, the overall production costs of biofuels vary. The production scale of biofuels has significant impact on cost. It is more important for ethanol processing than for production of pure plant oil and biodiesel.
This advantage for lipid derived fuels is especially important for small scale agricultural producers and SME’s. Some country like Brazil, Germany, etc., have established industrial plants for biofuels or bioenergy production. Generally biofuels are expected to have large socio-economic impacts, especially for local actors.
Biofuel production opens new market opportunities for agricultural products and thus new income options for farmers. In the future agriculture will not only play a role in food production, but also in energy provision. The increased feedstock production is expected to strongly contribute to the multi-functionality of the agricultural sector. Nevertheless it is difficult to assess the real dimension of additional employment and impact on local economy in the biomass sector.
Second generation fuels are not yet produced on commercial scale. Due to high production costs, they are not competitive at the moment, but as technology improves, they may become an important role in biofuel provision. The great advantage of these fuels is the vast range of feedstock that can be used for biofuel production, as well as the reduced feedstock (e.g., cellulose crops) costs.
After overall process and technologies used for biofuels production we are able to conclude that there are a lot of advantage of biofuels over fossil fuels, but direct cost comparisons may be difficult. Negative externalities associated with fossil fuels tend to be poorly quantified, such as military expenditures and costs for health and environment.
Biofuels have the potential to help environment clean and green due not emission of greenhouse gases and decrease the air pollution, production and management of biofuels will create millions of jobs worldwide.
Additionally biofuels decrease dependency from crude oil imports. Consequently biofuels are a more socially and environmentally desirable liquid fuel, a fact that is often neglected in direct-cost calculations. So biofuels are the potential fuels which have no competitiveness with fossil fuels. Biofuels are sustainable energy source so it may actually provide long-term economic benefits to market, eco-friendly environment.
Economical and Social Aspect of Waste Treatment:
The economic feasibility of using anaerobic treatment process for production of biogas from wastes are:
1. It is dependent on various factors such as availability of a domestic source of energy.
2. Cost of imported fuel.
3. Uses and actual benefits from biogas production, the public and private costs associated with the development and utilisation of biogas production, the public and private costs associated with the development and utilisation of biogas.
4. Technology used to generate biogas.
All these parameters have to be taken into account while a analysing the cost effectiveness of such as project.
An interesting cost benefit analysis and comparison has been reported on the production of 230000 T of nitrogen fertiliser annually using chemical technology and alternate biogas technology. This analysis has been done for biogas produced using cattle dung as raw material.
Thus, this quantity of dung can produce more than 100 million m3 biogas per day, having an energy equivalent of 560 million kwh or kerosene equivalent of 30000 T.
The potentiality of cattle dungs as one the best feedstocks for the production of biogas and biofertiliser in India. Further the large scale utilisation of dung in biogas plant would simultaneously produce gaseous fuel and organic manure, which in turn, will reduce the country’s dependence on fossil fuels as the main source of energy and on naphtha as a fertiliser.
People in the rural sector depend mostly on wood, straw, leaves, dung cakes, etc., as their main source of energy. These fuel materials are mostly burnt in primitive ovens, with minimum fuel efficiency. That means, per unit of useful energy, fuel consumption is very large. Others disadvantages are the trees are cut to be used as fuel and thereby cause deforestation.
These problems and effects are being directed at seeking alternative source of energy for the rural population. The alternative energy sources for the rural, sector can be categorised as directly solar and indirectly solar.
Although biomass can be burnt directly as fuel, it is not advisable to do so for two reason. First, all types of biomass have food fertiliser value, which the village people can directly use for their land. Therefore, these materials should not be wasted by burning them as fuel second, biomass is low grade fuel.
If burnt directly, only about 10% of its energy content is utilised, and the remaining gets waste. An appropriate technology for the rural community will be one which extract high grade fuel value from biomass and also ensure that it does not lose its fertiliser.
Concepts:
Biomass is abundantly available in villages. If all kinds of cellulosic wastes material (or biomass) available in a village are collected together and treated in a common ferment or, the gas produced from such a plant may be sufficient to cater to the energy needs of the entire village. There is another reason in favour of community biogas plants. Lack of private toilets in rural areas, which forces people in the villages to develop the unhealthy habit of going to the field to relive themselves.
A suitably designed and conveniently located community biogas plant can solve the aforementioned problems and will have the following advantages:
1. Land Economy:
A community biogas plant occupies a much smaller area of land.
2. Toilet Facility:
Community toilets can be constructed and attached to biogas plant. This will improve the hygiene condition of the village on one hand and allow for the utilisation of the waste material for production of gas and fertiliser on the other hand.
3. Maintenance Problem:
The smooth operation of a gas plant depends on its proper maintenance. It will be less troublesome and more economical to maintain a single large unit than a large number of small units.
Various factors their need to be considered while deciding the size of a community biogas plant.
Size:
Size of a biogas plant depends on various factors.
1. Nature and quantity of biomass available in a village, purpose of utilisation of biogas.
2. Necessity of single unit or more than one in village.
The number of biogas units may be selected after considering the problem related to the collection of biomass.
Retention Time:
Another important factor that influences the size of community gas plant is the retention time.
The destruction of the pathogenic bacteria present in the biomass fed into the digester should be one of the prime concerns in dividing the retention time.
Economic Analysis of Family Size Biogas Plant:
The economic analysis of any venture involves expenditure and statements. To evaluate the cost benefit viability of any viability of any project, the total investment incurred in the venture and the annual earnings therefore are to be necessarily considered.
Social Aspect of Waste Treatment:
Ethical issues involved in environmental biotechnology- Ethics is the science of morals as found in human conduct or behaviour and is related to the study of moral principles of human behaviour in a society.
Many individuals feels that nature and environment exist for the benefit of human being alone. Therefore they indiscriminately use plants, animals, and other environmental resources to meet their selfish purposes.
However there is also a parallel attitude which demands that nature be considered a sacred creation and that it must be respected and not tampered with mean that human beings should not manipulated nature.
1. Impact of biotechnology on human health and safety and on the environment.
2. The extent of undesirable intrusion into the natural order.
3. Issues of right justice and the economics of biotechnology application.
The specific issues of concern about the development and application of biotechnology include damage to the environment, injury to human health, food safety and socio-economics. There is a growing concern about the destruction of the aesthetic value of nature and the survival of wild animals and plants being put at stake by destroying their natural habitat. It becomes our moral obligation to take care of and preserve nature.
Intellectual Propriety Right (IPR) is an ethical issues that a society observes to insure that an inventor is protected from unfair use of his/her invention by any unauthorised person. This ethical principle is supported by law. Copy right trademarks, patents, etc. Come under IPR. Music paintings, software, literature work, customary protection of published data in the area of biotechnology, etc., are covered under copy right.
Biogas Scheme – Scope for Rural Employment:
Biogas plant can be considered as the starting point of advancing rural development. Biogas plants can bring many positive changes both at the family and society levels.
A few considerations are:
1. Waste and dung pits, which are breeding grounds for flies and insect, can be eliminated.
2. Hygiene conditions can be improved by building toilets, which may be connected to the biogas plants.
3. Immediate ready-to-use hearth for cooking can be provided doing away with the troublesome smoky kitchens.
4. From the fermented decomposed sludge, organic manure of very high grade in obtained, which can be used for enhancing the fertility of the soil.
In villages most families do not have sufficient cattle heads to operate their our biogas plants. In this context community biogas plant will prove to be beneficial, especially to the weaker sections of the rural population.