Prospects and Potential of Value Added Products from a Biorefinery
Gangagni Rao Anupoju, Sameena Begum, Sudarshan Juntupally, Vijayalakshmi Arelli, IICT- Hyderabad.
As petrobased feedstocks are finite and diminishing, bio-based renewables are increasing in importance. Biorefineries can produce a variety of products. Biorefineries could become a major contributor to the bio-based economy of the nation, according to the author.
Abstract In the long run fossil based raw-materials will deplete and therefore the shift to renewable based feedstocks need to be expedited [ 1]. This is also required from the perspective of moving towards a low carbon economy. Exploitation of biomass, organic waste materials as renewable feedstock is an attractive possibility. The country could profitably utilize 65% of the waste in producing energy and value-added products. This article describes biorefineries, renewable feedstocks and the multiple products that can be obtained from the biorefineries which could contribute to the bio-based economy of the nation.
Dr A. Gangagni Rao is Chief Scientist at Bioengineering and Environmental Sciences (BEES) Group of Centre for Environmental Engineering & Fossil Fuels (CEEFF) division of CSIR-IICT, Hyderabad. He has about 25 years of research experience in the field of waste management and has his expertise in biomethanation (anaerobic digestion) and biological gas purification. He has developed a novel high rate biomethanation reactor for the treatment of waste and retrofitted numerous biogas plants. He has 50 research publications and 4 patents to his credit.
Sameena Begum (BTech-Chem Engg – Rajiv Gandhi Univ) is currently enrolled for Ph.D in Chemical Engineering at Royal Melbourne Institute of Technology (RMIT), Australia in collaboration with CSIR-IICT, Hyderabad. She is currently pursuing her doctoral studies under the guidance of Dr. A. Gangagni Rao.
Sudharshan Juntupally, post graduate in Microbiology from Jawaharlal Nehru Technological University (JNTU), Hyderabad, is currently pursuing his Ph.Din life sciences under the guidance of Dr. A. Gangagni Rao at Bioengineering and Environmental Sciences Group of CEEFF, CSIRIICT,Hyderabad.
Vijayalakshmi Arelli obtained her Masters degree in Chemical Engineering from Osmania University, Hyderabad. She is currently pursuing her Ph.D under the guidance of Dr. A. GangagniRao at Bioengineering and environmental sciences division of CSIR-IICT, Hyderabad.
What is a Bio-refinery?
The biorefinery is exactly analogous to a petrochemical refinery. The only difference between a bio-refinery and a petroleum refinery is the use of raw materials[ 2]. In the petroleum refinery, crude oil and natural gas is used as raw material whereas in the bio-refinery organic waste and biomass is used as raw material (Fig.1). Among several definitions of biorefinery, the most exhaustive was recently formulated by International Energy Agency (IEA) Bioenergy Task 42. “Bio-refining is the sustainable processing of biomass into a spectrum of marketable products and energy”[ 3]. The bio-refinery is now a recognized approach for transforming renewable raw materials into separate bio-based marketable chemicals and fuels. Biorefineries can produce both the energetic and non-energetic products and can be broadly classified into two main classes such as Energy-Driven Bio-refinery (EDB) systems and Material Driven Bio-refinery (MDB) systems[ 4]. In the EDB, the biomass is primarily exploited for the production of secondary energy carriers such as transportation biofuels, power, heat etc., products as feed material or even can be upgraded to value added biobased products. This kind of EDB is beneficial to optimize economic and ecological performances of the full biomass supply chain. On the other hand, MDB primarily generates bio based products like bio-materials, lubricants, chemicals, food, feed etc. and process residues that can be further processed or used to produce energy for decentralized applications.
Classification of bio-refineries
Bio-refineries can be broadly classified based on the feedstock viz: Agricultural bio-refinery, cereal bio-refinery, oilseed bio-refinery, green bio-refinery, lignocellulosic bio-refinery, forestry bio-refinery and industrial or municipal waste based biorefinery. The availability of the feedstock for the production of various intermediates and marketable products is a crucial factor for the implementation of a biorefinery.
Organic waste biorefinery
In the industrial or municipal waste biorefinery, the raw material used is the organic fraction of waste produced from industries and the waste collected at municipalities. The municipal solid waste consists of 51% of organic waste that can be utilized for the generation of various products through a biorefinery approach. The input material, process and output involved in a waste biorefinery is shown in Fig. 2. The most eco-friendly process for deriving various products through a bio-refin-
ery is through anaerobic digestion. Anaerobic digestion is a sequential process consisting of four stages namely, hydrolysis, acidogenesis, acetogenesis and methanogenesis. At each stage of the anaerobic digestion process, multiple intermediates (value added chemicals) and products (biofuels, fertilizer) can be obtained from organic waste as shown in Fig. 2.
Organic waste as a feedstock for biorefinery
Organic waste streams are a sustainable alternative to fossil-based resources as they do not compete directly with food crops. All the waste streams presently have some value, for instance organic fraction of MSW, waste generated in hotels, restaurants, markets, industries etc., is currently being exploited as feedstock for bioenergy (heat and power) production. It is known that a feedstock is defined as any renewable, biological material that can be used directly as a fuel or converted to another form of fuel or energy product. These wastes could effectively be utilized as a feedstock for biorefinery to obtain multiple products at various stages. In addition to these, biomass feedstocks are the plant and algal materials used to derive fuels like ethanol, butanol, biodiesel, and other hydrocarbon fuels. Examples of biomass feedstocks include corn starch, sugarcane juice, crop residues such as corn stover and sugarcane bagasse, purpose-grown grass crops, and woody plants. As the fossil fuel-based resources are depleting day by day, the exponential increase in the variety of waste generation across the globe could be treated as a potential renewable feedstock for biorefinery.
Anaerobic digestion (AD) is a sequence of biological processes for the treatment of waste streams to obtain value added products as described below and shown in Fig. 3 6].
The first step of AD is the hydrolysis of waste material. In this step the hydrolytic bacteria and the inherent enzymes present in the waste breaks down the biopolymers and other organic material to monomers 7]. For example: Hydrolysis of lipid molecules to fatty [ acids, polysaccharides to monosaccharides, proteins to amino acids, nucleic acids to purines and pyrimidines etc as shown in Eq.1.
C H O + 2H O C H O + 2H ..... Eq.1[ 1].
6 10 4 2 6 12 6 2
Acidogenesis is the next step of AD in which acidogenic micro-organisms further break down the hydrolyzed monomers to products such as volatile fatty acids, carbon dioxide, hydrogen etc. Acidogenic organisms convert the monomer molecules into organic acids (lactic, formic, butyric, acetic acids) acetate and carbon dioxide, alcohols and ketones. The products formed during acidogenesis are due to a number of different microbes, e.g., Syntrophobacterwolinii, a propionate decomposer and Sytrophomonoswolfei, a butyrate decomposer. Other acid formers are Clostridium spp., Peptococcusanerobus, Lactobacillus, and Actinomyces[ 8]. In the acidification phase, ethanol type fermentation occurs, in which the main liquid products are ethanol and acetic acid. These acidogenic bacteria produce an acidic environment in the reactor while creating ammonia, H , CO , volatile fatty acids, carbonic acids, al
2 2 cohols, as well as trace amounts of other byproducts 9].
In general, acetogenesis is the formation of acetate, a derivative of acetic acid, from carbon and energy sources by acetogens[ 10]. These microorganisms catabolize many of the products created during acidogenic phase into acetic acid, CO and H . Acetogens break
2 2 down the organic matter where volatile fatty acids are
produced and trace amounts of ethanol. Acidogenesis and acetogenesis leads to the formation of mixture of alcohols including volatile fatty acids (acetic acid, butyric acid and propionic acid). Methanogenesis
The last step of AD process is methanogenesis where the methanogenic bacteria transform acetate, hydrogen, carbon dioxide and formate that are end products of acid fermentation into methane along with CO and traces of H S,
2 2 N , O . Methanogens belong to the archaebacteria,
2 2 which are different from normal bacteria in cell wall composition, cell membranes, coenzyme, and ribosomal RNA sequences composition. Methanogens are sensitive to oxygen and rich in degradable organic compounds. Some of the examples of methanogens include Methanococcus, Methanoculleus, Methanofollis, Methanopyrus, Methanosarcina, Methanosphaera, Methanothermobacter, Methanolaciniapetrolearia, Methanoplanuslimicola, Methanosalsumzhilinae, Methylobacteriumphyllosphaerae, Methanosarcinabarkeri, Methanosarcinavacuolata 11].
Value added productsfrom a biorefinery
Volatile fatty acids
Volatile fatty acids (VFA) are short chain fatty acids consistingof fewer (2–8) carbon atoms that can be separated through distillation at atmospheric pressure. Currently the existing method to produce VFA at commercial scale is by chemical route 13]. However,
VFA could also be generated through biological route using a specially prepared microbial culture through acidogenic AD approach. VFAs has wide variety of applications as they are the precursors for production of hydrogen and biogas, the can be used in the production of alcohols through hydrogenation. In addition to these, VFAs can be exploited for bioplastics and biofuels production 14]. In the recent past, generation of VFA
[ from various organic feedstocks such as food waste 15],
[ press mud[ organic fraction of municipal solid waste
(OFMSW), dairy waste water etc., was reported. A fullscale plant to produce VFA through thermal-alkaline pre-treatment and alkaline fermentation of sewage sludge has been built and operated in China. The average concentration of VFA was found to be ranging between 3 – 7 g/L with acetic acid being the dominant product 17].
Bio-hydrogen production by conversion of organic waste through a biorefinery approach is a promising strategy to valorize the waste as well as increase the demand for implementation of bio-refineries. Hydrogen is considered as one of the clean renewable energy carriers for future, as the production of hydrogen can be feasible in many ways. At present, hydrogen is mostly produced by thermochemical processes such as steam reforming of natural gas and coal gasification etc 17]. However, due to the
[ depletion of fossil fuel reserves as well as environmental concerns such as greenhouse gas emission, exploration of other sustainable methods of hydrogen production is becoming inevitable. Thus, biological hydrogen production from organic waste material has gained significant importance[ 18]. A two-stage (acidogenic followed by methanogenic) pilot-scale plant was designed, manufactured and installed at the experimental farm of the University of Milano for the generation of hydrogen in first stage and methane in second stage. This plant is operated using a biomass mixture of livestock effluents mixed with sugar/starch-rich residues (rotten fruits and potatoes and expired fruit juices), a feedstock mixture based on waste biomasses directly available in the rural area where the plant is installed. A typical hydrogen and methane specific productivity of 2.2 and 0.5 Nm3/m3 reactor per day, in the first and second stage of the plant respectively 18].
The first four alcohols in the order of carbon content are methanol, ethanol, propanol, and butanol, are of greatest interest for fuel use as their chemical properties make them useful in internal combustion engines 19]. These alcohols can be produced through biologi[ cal and chemical methods. The biological methods of alcohol production include yeast fermentation and acidogenic phase of AD. The intermediates produced during AD of waste material can be converted to alcohols through hydrogenation process by the application of reduction catalysts. In Brazil and the United States, fuel ethanol is produced by fermentation of corn glucose in the US or sucrose in Brazil which are the largest ethanol producers in the world but this can also be
 prepared from agro-residues according to the agro-
nomic-based economy of the country. There are some potential methods for low cost ethanol production by using agricultural wastes 21]. Wheat straw is one of the
[ most abundant agricultural wastes, which has been extensively studied 22]. MSW is the lowest cost feedstock
[ for the generation of cellulosic bioethanol. It has been reported that > 80 billion litres of MSW paper derived cellulosic bioethanol can be produced worldwide 23].
A plant for the generation of bioethanol from lignocellulosic biomass is being demonstrated at India Glycols in Kashipur, India 27].
Bio-methane produced by anaerobic digestion of organic waste is an alternative gas source to that of the natural gas. Bio-methane offers enormous potential as an alternative source of energy, especially to fossil fuels. Even though its usability is known for quite some time, production of bio-methane started only in the recent years because of the rising prices of natural gas and high electricity prices other fossil fuels as well as the threat of global climate change. Chemically, it is identical to natural gas which is stored deep in the ground and is also produced from dead animal and plant material. However, there are several important differences between bio-methane and fossil fuel derived methane even though both are produced from organic matter. Methane is about 20 times more potent greenhouse gas than carbon dioxide if released into the atmosphere[ 24]. Furthermore, its use for power generation produces heat and emits carbon dioxide and some other gases but despite that biomethane has several environmental benefits which make it a green source of energy. Organic waste material from which bio-methane is produced would release the gas into the atmosphere if the waste is simply left to decompose naturally, while other gases that are produced during the decomposition process such as nitrous dioxide for instance further contribute to the greenhouse effect. It was reported by Kuruti et al., 2017 that a fullscale biogas plant based on Anaerobic Gas lift Reactor Technology installed at Bellary for the treatment of 1000 kg/day of food waste (cooked and uncooked food waste) yielded about 150 m3/day of biogas with 65% methane and 200 kg/day of digestate. Biogas could be purified to make Bio-CNG which is equivalent to CNG (compressed natural gas). Few plants are working in India to make Bio-CNG from Press mud and agri
 culture waste 26].
Digestate is a nutrient-rich substance produced by AD that can be used as a fertilizer.However, the nutri- ents are significantly more available in digestate than in raw slurry i.e. it is easier for plants to make use of the nutrients present in the digestate. The residue after the AD of organic waste i.e. digestate could be exploited as fertilizer in liquid or solid form depending on the requirement. This helps in the reduction of using chemical fertilizers. The digestate that would be obtained from AD of different substrates is not similar. The Nitrogen, phosphorous and potassium content differs. Some typical values of nutrients present in the digestate are:
• Nitrogen: 2.3 - 4.2 kg/ton
• Phosphorous: 0.2 - 1.5 kg/ton
• Potassium: 1.3 - 5.2 kg/ton
Bio-refinery: An approach to improve bio-based economy
Bio-refineries enable the effective reuse of waste materials as renewable feedstock for materials and energy recovery. Resource-efficient use of bio-based resources also reduces waste and pollution. Broad range of end products can be produced from biorefineries and they can create production systems that dramatically reduce the input needed as well as waste and support new bio-based industries and the ‘greening’ of traditional industries. A bio-based economy has the potential to contribute significantly to the reduction in CO emissions as well as meet the energy and
2 economic goals. For example, the separate collection of bio-waste and its treatment through anaerobic digestion in a bio-refinery serves as applied climate protection as there is a concomitant production of valueadded chemicals, bioenergy and a solution to waste disposal issue. Shifting towards a bio-based economy creates new business opportunities in the agricultural, forestry and industrial sectors etc. By supporting new bio-based industries and the ‘greening’ of traditional industries, a bio-based economy will change. A socially and environmentally beneficial bio-based economy already exists to some extent, but their efforts need to be put to implement and flourish the bio-refineries to avail multiple benefits.
A successful biorefinery will fulfill two strategic goals i.e. replacing non-renewable raw materials such as fossil fuels with renewable organic material such as biomass, organic waste etc., and provides economic incentive to support a robust bio-refining industry (an economic goal, met by the production of high value chemicals). Meeting the energy crisis by the generation
of biofuels and reaching the set economic goal would be met by the production of the high value-added chemicals through the implementation of bio-refineries.
The authors are thankful to the Government of India; Council for Scientific and Industrial research (CSIR), for funding the projects. The authors are also grateful to the Director-Indian Institute of Chemical Technology (IICT) for his encouragement in carrying out this work.
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Fig.2 Organic waste biorefinery 
Fig. 1 Petroleum refinery v/s Biorefinery