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Currently a number of thermal conversion systems are in various stages of development. These include pyrolysis, gassification and hydrogenation.
For direct burning, moisture contents should be less than 30% Advanced fluidized bed incinerators can take biomass of even 55% water. wood and straw is normally used for combustion. Animal wastes sewage sludges, compost sludges which contain upto 75% water can also be used. pyrolysis, liquification and gassification are upgrading processes converting biomass into stable, transportable fuel, solid, liquid, gaseous forms thus produced have similar properties as coal, oil and natural gas. All these processes require feedstock of relatively low water content and operate at a higher temperature. Biological conversion processes, however, can handle feedstock of high water content and operate at a temperature range 25-65°C.
Sources of Biomass
Sources of biomass for fuel conversion included: 1) Land and crops - lignocellulosic material from trees of
Eucalyptus, like maize, cassava and sugar crops like cane and beet.
(2) Aquatic plants - Unicellular algae, multicultural algae, aquatic weeds like water hyacinth, Hydrol etc
(3) Wastes like manure, domestic rubbish, and municipal waste/sewage
(4) Agro-industrial wastes - wood and crop residues like straw, husks, citrus peels, bagasse molasses, willow dust, press mud, paper sludge etc.
Biomass as a source of energy has its advantages and disadvantage which decide whether solar energy - biomass - utilizable energy route can be exploited or not. But as said above, biological conversions are easier than other technologies and if environmental pollution control is simultaneously achieved, then the utilization of biomass for energy has a heavier side in balance. Thus, various agro-industrial wastes as biomass definitely suits the bioconversion processes for energy and chemicals.
Advantages of biomass as a source of energy: (1) Storage is possible;
(2) Transportation possible; (3) It is renewable;
(4) High energy fuels can be obtained; (5) Low capital input required;
(6) Can be developed with present man and material abilities; (7) It is ecologically safe and is inoffensive;
(8) It does not increase CO2 content of the atmosphere.
Disadvantages to be listed are:
(1) Land and water use competition;
(2) Solar energy a source of biomass is diffuse and intermittent; (3) Collecting and storing it is bulky and costly;
(4) Supply uncertainty initially; (5) Costs uncertain;
(6) Fertilizer, soil, water required;
(7) Low conversion efficiency (% solar energy trapped).
Reactors Using Immobilized Cells for Biomethanisation Immobilized cell anaerobic reactors are now used in more numbers for treating industrial waste-water. This is due to their capacity to retain biomass and better performance. Following systems are available in immobilized cell technology with anaerobic conditions:
(a) Up flow anaerobic sludge blanket reactor (UASB). (b) Hybrid reactors. .
(c) Up flow fixed film anaerobic filter. (d) Down now fixed film anaerobic filter. (e) Expanded bed reactor.
(f) Fluidized bed reactor.
It is difficult to compare the above systems as far as superiority is concerned. Low-loading rates or low biogas production do not necessarily reflect poor reactor design. The amount of active biomass decides the loading capacity and subsequent biogas production and also waste-water depollution.
Immobilized cell anaerobic reactors are only able to treat waste- waters with low concentrations of particulate material.
Agro-industrial waste-waters and to a lesser extent, diluted and filtered animal manures can be used as substrates.
The development of stable associations of micro-organisms is required for methanogenesis, Concentration of biomass in the reactor and minimum hydraulic retention time are achieved which result in a smaller reactor volume and reduced investments.
Biogas Production from Food Processing Industries Effluents from food processing industry are most suitable for biogas production. These effluents have a high BOD due to easily biodegradable organic matter that they contain and hence are of immediate concern while releasing into the water bodies. The overall trend of industries to conserve energy and if possible, to generate it from wastes has increased anaerobic digestion of effluents in general.
Milk processing unit’s wastes could be processed to cause 99% reduction in BOD and gas production 0.85m3 kg.l BOD in 6 days’ retention time.
Disposal of whey is the most serious problem for the cheese manufacturing units. One tonne of cheese gives rise to 10 tonnes of whey. Each cubic meter of whey produces
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daily pollution by 600 people. The strength of whey is 32000- 60000 mg BOD 1.1.35% of the costs of cheese manufacturing unit could be recovered from biogas generated from effluents. Biogas produced is 1500 m3/day to 4000 m3/day depending upon whey production. Methane contents of biogas produced are 62%. Biogas produced can be used for boilers or for generating electricity (generators using biogas for electricity generation are available) or after treatment and compression, it can be used for vehicle propulsion or can be sold to other users. For vegetable canning wastes (carrot peelings) with a two stage reactor (liquefaction separated from methanogenesis) 2.4 m3 methane/m3 digester/ day is produced while with a one stage system, only 1.35 m3 methane/ m3 digester/day can be produced.
Waste-waters from manufacture of wheat gluten, starch from flour contain proteins, carbohydrates, mixture of amino acids, hemicellulose, pentose gums, suspended starch granules etc., and COD is 10000-25000 mg I-I with a loading rate of 2.6 kg COD/m2/day. Methane yield is 0.33 m3 per kg of COD. Methane content in the biogas is 65% and BOD reduction achieved is 95%. Size of the plant is 1000 m3.
In citric acid production from molasses using Aspergillus niger for fermentation 18-20 tonnes of wastes-water is produced for every 1 tonne of citric acid produced. COD of this waste-water is 30000 - 50000 mg per liter. Biogas can be produced from it and COD reduction achieved in the treatment.
From the Fruit pulp and apple juice the united states produces 1.5 million tones of pomance every year and that requires 10 million for the disposal. The Cornell University, N.Y., U.S. has developed an anaerobic process for the treatment of pomance and returns in the form of gas expected are 10-30 dollars per wet tonne of pomace.
In citrus processing industries peels can be used for anaerobic fermentation. But first oil is removed from them since it is inhibitory to microbes 0.5 m3 biogas can be produced per 1kg total solids.
Wastes from bean leaching, pear and potato peeling can be used for biogas production with anaerobic contact process or UASB as the bioreactor.
Table: Industrial Anaerobic Treatment Plants Waste Reactor Type Molasses CSTR
Starch CSTR/USAB
Sugar beet CSTR
Potato UASB
Dairy UASB
Yeast production Filter Papemill UASB
Table : Biogas Potential of Food Processing Wastes
Substrate Biogas l/Kg
Organic fraction municipal solid waste 450 Vegetable processing waste 600 Brewer’s and grains 500 Distillery wastes(fruits) 550 Slaughter house waste 450
Pressed grape skin 400
Mown grass 600-700
Fats from skimmined tanks 1000
In India M/S Ashok organics treat their distillery wastes to generate biogas. With a residence time of 8-10 days pH of digester 7.2 and temperature around 48-52°C, 40 to 50 M3 biogas is generated for M3 effluent that is treated. BOD reduction achieved is 80-85%. The Sakthi Sugars Ltd. uses French and Italian technology and carries on in fixed fIlm reactor biomethanisation to achieve 90% BOD reduction or 65- 70% COD reduction and biogas production. Each tonne of COD reduced produces 530 m3 biogas.
Upflow anaerobic filter and gas collection system can be used for soluble carbohydrate wastes for example for soft drink bottling industry, as a pre-treatment process. COD can be substantially reduced, and methane is produced. Filter operating at 41 hour HRT can remove 85-90% of soluble COD.
Anaerobic fluidized bed biofilm reactor has been used for acid whey, soft drink bottling waste-water, whey permeate molasses, municipal wastes etc. COD removal efficiency is >90%, load rate is 35 kg/m3/day and 332I methane produced per kg COD removed.
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Biogas production from poultry manure of large farms is ecologically and economically effective technology. 40% COD reduction takes place with 1m3 biogas produced for every 1 kg of degraded organic matter with 15-40 days retention time. It removes aggressive odour, reduces number of pathogens, and converts organic nitrogen to ammonia.
Agricultural firm ‘Ogre’ in the USSR uses l00m3 bioreactor with pig slurry for fermentation. Biogas production is 0.5 m3/kg dry organic matter/day. It contains 65% methane. Yields are 2.6 m3/mJ sludge/day There is another 50 m3 bioreactor at agrofirm ‘Uzvara’ in the USSR which produces 15-20 m3 biogas/m3 brown juice with 70-80% COD reduction. Biogas production is a convenient way of agricultural wastes disposal for more than one reasons. Substrate detoxification, deodorization, inactivation of pathogens, dehelminthization Occur along with biogas production and fertilizer or humus forming substance as a byproduct.
Rapid production’ of methane from chicken manure by microbes immobilized on ceramic and placed in continuous plug flow reactor is feasible and has been operated for 9 months continuous. A carrier with porosity between 2-35.!J. pore diameter is better.
Piggery wastes produce maximum biogas when compared with other animal wastes and it is observed that 60% of organic substances could be converted into gas from the pig manure. Sheep manure, silkworm waste produced less gas, may be due to more nitrogen content of these wastes.
%Dry Matter Biogas Produced Cattle dung 17 14,615 cc/21/6 month Sheep manure 34.5 125700cc/21/6 months Piggery wastes 57
Poultry wastes 57 184 72 cc/21/6/months Water hyacinth 13.4 45 lit/kg dry matter/2month Soyabean waste 17
Earlier agricultural wastes, animal wastes, food industry wastes were primarily thought suitable for biogas production. But the range of possible wastes for biogas generation is continuously increasing.
Jute caddis, the unspinnable short fibres deposited by jute mill looms can generate biogas when fermented. Jute caddis is lignocellulosic waste. India produces 0.28 million quintals of this material and is used as boiler fuel or wasted and causes pollution. The Calcutta based Jute Technological Research Laboratory (ITRL) has produced biogas using 2.5% of this material, in 20 days. If alkali-treated caddis are used instead of raw caddis, the same is possible in 15 days. The remaining slurry after biogas production is rich in N,P,K nutrients and is
comparable to the farm yard manure. Alkali treatment of caddis helps solubilization of lignocellulosic material. hence time of fermentation is reduced.
In such examples. the question is not as to how widely such sources can be used for biogas production but the suggestion is wastes (causing pollution) from whatever source can be disposed of for generating energy while simultaneously reducing environmental hazards. .
Similarly, the textile industry in India generates willow dust which is one of the solid cellulosic waste material produced during the processing operations. 30000-33000 tonnes of willow dust is generated per year by the textile industries in India. Composting, direct burning and anaerobic digestion for biogas production are the .three alternatives available for the disposal of willow dust. Biogas production from willow dust was first demonstrated by Cotton Technological Research Laboratory (CTRL), Bombay. Willow dust
contains celluloses, hemicelluloses and C:N ratio is 25:1. Plant producing 17m3 biogas from 100kg willow dust in 30 days is operating satisfactorily. A large scale trial was taken by the Apollo Mills, Bombay. With the help of 6 digestors, 12 tonnes of willow dust were digested per month. 350 m3 biogas was obtained in each digester handling 2 tonnes of willow dust with 90 days retention period. Slurry obtained after digestion serves as good manure With a modified process requiring less water (H2OP to substrate ratio 1.5:1), 250 m3 biogas can be obtained from 1 tonne of willow dust in 60 day.
Anaerobic digestion by the BiotimR System in Malaysia is the 1st full-scale application for rubber factory effluents. These effluents have high sulfates and ammonical nitrogen which are inhibitory to digestion. Smell problem in the ponding system and high operation cost in oxidation ditch hence alternate anaerobic system is set up. Loading rate is 18.5 kg COD/m3 day. Hydraulic Residence Time(HR1) is I and 1.85 days respectively in BCR (Biological Conditioning Reactor) and MOR (Methane Upflow Reactor).
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Hydrogen Gas Production
Hydrogen gas is a perfect renewable fuel. It is produced by sun. Raw materials used for the production can be water which is abundant. 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. It is the cost factor which has prevented hydrogen from becoming a common fuel.
Coupling of solar energy for H2 production using stabilized photo synthetic components and enzyme hydrogenase is the system. The enzyme responsible for making hydrogen gas (joining two hydrogen ions and two electrons to form a molecule of gas) is hydrogenase. This enzymes so far has been extracted from 15 species of bacteria and algae. Attempts to commercialize it are on.
Clostridium butyricum when supplied with sugars produces hydrogen but the system is unstable. After a while, bacteria stop making hydrogen. Japanese biotechnologists have immobilized Cl. butyricum and these cells produce gas for a month instead of a few hours when fed with wastewater containing sugar from a alcohol factory. Anaerobic packed bed reactor and agar entrapment is used for the purpose.
Rhodopseudomonas palustris has been grown in anaerobic bioreactor. Plat~ of agar immobilized organisms are used. The system is easy to operate and build 0.78 lit of production from sugar refinery wastes and 2.2 l/lit H2 from straw paper mill effluent is reported. Current 13-15 mA was generated for 20 days.
Rhodopseudomonas rubrum gives H, production from waste. water containing organic acids (acetic, propionic, butyric). Organisms can be irnmobilised with alginate. .
Rhodospirillum molischianum gives 2.6 1/lit of H, production when. straw papermill waste-water is used. H2 produced can’ be used for fuel cell and current generation of 0.5 - 0.6 A or 0.16 - 0.18 V for 6 hours could be produced.
Scientists at NEERI have identified the photosynthetic bacteria that use solar energy to generate H2 from waste-waters from ice creams and butter factories. With this technology, H2
production is coupled with removal of pollutants. The gas can be used along with others to form enriched fuel or in edible oil industry for hydrogenation of vegetable and animal fats. The gas has immense potential for use as a chemical feedstock in the production of NH3, methanol or other chemicals. NEERI proposes to set up a plant to process 20m3 of whey waste to produce to m3.
Rhodopseudomonas gelatinosa produced more from organic acid
than from sugars like glucose, sucrose, lactose 50 ml of H2 is produced per gram of total organic carbon used. Technology comprises initial pretreatment of Whey waste which involves neutralisation pasteurisation. Preheated waste is then transferred to bioreactor containing anaerobic photosynthetic bacteria Japan’s Fermentation Research Institute and Agency of Industrial Science and Technology have jointly developed a system to efficiency produce H2 gas. Bacteria used for the system is Rhodobacter sphyroid (photosynthetic bacteria).
H2 gas has 3 times calorific value per unit weight of petroleum and it does not generate CO2 (a green house effect gas) or other air pollutants. Energy conversion can be increased almost 20%.
Table H2 Production from Waste-water
Source of waste water Organisms Alcohol factory Cl. butyricum Refinery Rhodopsedomonas palustris Straw paper mill Rhodospirillum molischianum W.W. containing organic acid
Icecrem and butter factories Rhodopseudomonas rubrum
1. Exercise: AARTI ,an institute involved in the development of sustainable technology for rural development has
developed a mini bio gas plant that can be operated on domestic waste. Find out more about it and write a report. 2. Exercise: what do you know about biodiesel? Write a
report.
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Learning Objectives
In this lecture, you will learn•
What are biohazards?•
Product & worker safety•
Aerosol generation & managementIntroduction
Biotechnology, and especially fermentation technology appears to be a very safe science compared to its other sister branches in terms of the hazards and risks associated. Unfortunately, it is not always so. As a matter of fact, the hazards posed during fermentation technology could actually be more dangerous than most other branches of science.
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Why fermentation technology is hazardous and what are the hazards associated with it?There are three distinct types of hazards associated with fermentation technology.
1. Safety to the workers 2. Safety to the product and 3. Safety to the environment
We will see these hazards one by one. Probably the most important safety hazard by fermentations is posed to the workers who work in the fermentation industry. The various aerosols that are released during the fermentation operations pose the major hazard to the workers. These aerosols affect the workers by three portal of entry.
1. Inhalation 2. Ingestion 3. Skin contact
Of these three, inhalation is most dangerous.
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Why?An average industrial worker, who works for eight hours in a shift, inhales about ten cubic meter of air. Considering that the level of aerosols is only one part in one hundred million, then the worker inhales about 0.1 mg of aerosol. This is a very large dose and is more than sufficient to cause airborne infection and/or allergic reactions in the workers. Interestingly, it is the portal of entry that decides the extent of hazard posed by the aerosol.
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How?Let’s take the example of an organism Francisella tularensis. This organism, if inhaled causes pulmonary disorders. If ingested, the same organism causes typhoidal diseases and if it comes in contact with the skin, it causes infection of bubonic form. Thus, the route of entry of an aerosol, generated during the fermentation process, decides its degree of hazard to the
workers. Similarly, the size of the aerosol particles decides the portal of entry.
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How?Let’s see what makes an aerosol dangerous. First is the duration for which the aerosol can remain airborne. Lighter aerosols can remain freely suspended in the air for longer durations of time, and hence, are more hazardous. Similarly smaller aerosols can penetrate deep into the respiratory tract and are able to cause more serious infections. The size of aerosol also decides the ease with which the aerosol can be removed and the survival and infectivity of the organism involved. In a nutshell, smaller and lighter aerosols are more potent in causing infections and allergic symptoms amongst the workers.
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How are aerosol generated?Handling of microbial suspensions, fermented broth in this case, results in the release of aerosol in the air. Large aerosols are generated when low energy operations are performed. Smaller and hence more dangerous aerosols are generated during high energy operations like cell disruption, centrifugation,
lyophilization etc. which are common during downstream processing. Spray factor is an indicator of aerosol generation by a particular operation.
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What is spray factor?The spray factor is defined as the number of viable organisms released in the air per minute divided by the number of viable organisms being handled per minute. The spray factor is an indicator of aerial contamination levels by common industrial operations.
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What are the major industrial operations that generate maximum number of aerosols?Four major operations associated with industrial fermentation have been identified as potent aerosol formers.
1. Breakdown of bacteriological factors. 2. Failure in antifoam system.
3. Failure in culture transfer pipe work. 4. Explosive breakage of fermentor.
Of these four reasons failure in antifoam systems is considered to be the most dangerous.
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Why do you think it would be so? Use the space below to justify your answer.•
·How do we take care of these aerosols?Aerosols generated during industrial fermentations can be taken care of by two basic techniques.