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Extraction of metals by bioleaching

Microbial ore leaching consists of the processes involving bacteria, mainly Thiobacillus ferrooxidans, that leads to leaching of metal sulphates from low grade ores containing insoluble metal sulphides.

The metal solubilizing action of bacteria is both direct as well as indirect. In direct conversion, the metal sulphide is itself converted to metal sulphate as follows:

CuS + 2O2                  →                  CuSO4.

T. ferrooxidans

 In contrast to this indirect conversion is based on the reduction of ferric sulphate to ferrous sulphate.

T. ferrooxidans

CuS + Fe2(SO4)3                      →                  CuSO4 + FeSO4 + S↓

T. ferrooxidans also oxidizes sulphur to H2SO4 and converts FeSO4 to Fe2(SO4)3

T. ferrooxidans

S8 + 12O2 + 8H2O                      →                  8H2SO4


T. ferrooxidans

2FeSO4 + H2SO4                     →                  Fe2(SO4)3 + H2


Limitations of Microbial Ore Leaching

  1. The desired metal is recovered as a dilute solution of its salts and not as elemental metal. This makes a recovery process from the solution essential.
  2. The micro-organisms must be kept viable by providing appropriate conditions
  3. It is a relatively slow process.

Merits of Using Microbes for Ore Leaching

  1. It does not require high energy inputs.
  2. It can be applied both on small and large scales.
  3. The process can be used to extract a variety of metals.
  4. The process can be applied in situ. i.e., in the mine itself.
  5. It does not produce toxic or noxious gases as by-products.

 Applications of Microbial Ore Leaching

  1. Extraction of metals from ores. For example, copper as their sulphates.
  2. Partial leaching of mineral concentrates to remove impurities.
  3. Conversion of mineral into a form suitable for processing by other means.


i.            Oil spills
ii.            Paper waste>
iii.            Domestic waste
iv.            Toxic waste
v.            Agricultural waste>
vi.            Sewage treatment. .

Environment consists of the sum of all the factors outside an organism. It consists of both biotic as well as abiotic factor. Any unwanted material present in environment is called waste. Waste may be biological, chemical or physical in nature.

Sources of Wastes and Pollutants

  1. Manufacturing. It includes chemical industry, oil refinery/spill, fertilizer industry wastes. These activities generate a wide variety of wastes depending on the nature of raw materials and products, as well as the design and the operation of the involved processes.
  2. Agriculture and Dairy. These activities produce crop residues, which are biodegradable. Most of the pesticides used are nonbiodegradable. In addition, plastics, copper present in feed additives and wastes arising from use of fossil fuels are recalcitrant to biodegradation.
  3. House Building and Domestic Activities. It generates biodegradable and non-biodegradable wastes. It include stone, asbestos, fly ash, sewage, garbage, plastic, paper, tins and bottles etc.)
  • Treatment of Liquid Wastes

Liquid wastes are treated by either aerobic or anaerobic digestion in large centralized, water reclamation or sewage treatment units.

  • Treatment of Solid Wastes

Solid wastes can be sorted out into biodegradable and non-biodegradable components; the latter may be recycled while the former may be (i) either incinerated or (ii) used for anaerobic digestion.

The entire solid waste is usually dumped into pits, the process is called landfill.

1. Aerobic Reactors or Digesters

Biological treatment of settled sewage may be based on fixed film digester or dispersed growth digester under aerobic conditions.

These are basically of two types:

(i)                 Trickling filter digesters

(ii)               Rotating biological contractors

 (i) Trickling Filter Digester

These reactors are either rectangular or circular and consist of 3 m deep filters made up of 25-100 mm diameter chunks of crushed rock, ceramic bricks. The micro-organisms are present as a layer called biofilm on the surface of filter particles. With time, the biofilm grows thick and
peels off the filter particles; a new biofilm soon forms due to microbial growth. Arrow indicates the direction of waste water flow.


Fig. 53.5. The filter medium is crushed rock or ‘blast furnace slag’ and each filter particle is covered with a slime composed of the micro-organisms forming a biofilm.

 (ii) Rotating Biological Contractors

It consists of set of discs about ‘2-3 m in diameter oriented vertically to the direction of waste water flow. The biofilm is adhered to the disc surface, which keeps on rotating at the speed of 1-2 rpm.


Fig.53.6. Representation of rotating biological contractor: the biofilm is present on the surface of the disc.The waste water flows at right angles to the disc. A series of discs is used in the contractor.

2. Dispersed Growth Digesters

In such processes, the microbial population is dispersed throughout the sewage being treated. The activated sludge process is a typical example; it uses a large aerated vessel for a large scale oxidation of liquid wastes. The micro-organisms are distributed as floes, throughout the waste water being treated.

3. Enzyme Technology

     i.      Biological washing powders or Detergents

ii.    Pectinase in fruit juices.

 (i) Detergents

Detergents represent the largest industrial application of enzymes amounting to 25-30% of the total sales of enzymes. The enzymes used in detergents must be cost-effective, safe to use and be able to perform the task in the presence of anionic and unionic detergents.

Enzymes constitute only 0.4-0.8% crude enzyme by weight. The chief enzymes used are proteases, α-amylase and sometimes cellulose.

  • Proteases are used to digest away proteins present in blood stains, milk, grass etc. and also in association with dirt ; therefore they help in removal of dirt as well. Only serine proteases are suitable for use in detergents. These enzymes are produced by Bacillus
    and Bacillus amyloliquefaciens. Proteases are packed inside dust-free granules coated with wax materials made from paraffin oil.
  • α-Amylase. It is used to digest away the starch present in association with dirt and stains. They are produced by B. Licheniformis.
  • Celluloses. It is produced by fungi and are used for washing cotton fabrics. The enzyme digests away the small fibres raised from the fabric without damaging the major fibres of the fabric. This restores the fabric to “as new” condition and also removes soil particles by digesting the associated cellulose.
  • Lipases. Which are suitable for detergent use have been identified and are used for digestion of lipids present in stains or dirt.

 (ii) Pectinase in Fruit Juices

The cloudiness of fruit juices and wines is primarily due to the pectins. It exhibits various degrees of methyl esterification and are usually associated with other plant polymers and even cell debris.

The pectins are digested by pecteolytic enzymes prepared from Aspergillus niger.

These enzyme preparations ate mixtures of the following enzyme activities:

i.    polygalacturonase (random digestion of pectin)

ii.    pectin esterase (removal of methyl esters and release of methanol)

iii.   pectin lyase (cleaves pectins into aligosaccharides even without pectin esterase action).

iv.   hemicellulose (a mixture of enzymes degrading hemicellulose).

These enzymes have pH optimum between 4 and 5, optimum temperature below 50°C.



I. Objective Type Questions

Select the most appropriate choice from the options given as (a), (b), (c) and (d) after each question:

1.      All the information needed to make an entire organism is in a molecule called

a)      DNA

b)      a protein

c)      a cell

d)     a gene

2.      What controls inherited traits in an organism such as eye, hair, or skin color?

a)      meiosis

b)      a bacterium

c)      a cell

d)     a gene

3.      Examples of biotechnology in animals include

a)      animal cloning

b)      cancer research

c)      human tissue replacement

d)     all of the above

4.      A transgenic organism is one that

(a)   has genes inserted into it from another organism

(b) has genes created through mitosis

(c) normally occurs in nature

(d) none of the above

5.      Clones are

a)      organisms from which genes are removed

b)      genes that cause the production of twins

c)      genetically identical organisms

d)     organisms which produce a clone protein

6.      Bioreactors are

a)      pieces of machinery that extract genes

b)      organisms engineered to make specific compounds

c)      nuclear power plants that use biotechnology

d)     none of the above

7.      Goals of biotechnology in plants include making plants

a)      stronger

b)      more productive

c)      more nourishing

d)     all of the above

8.      Biotechnology may help some people in developing countries who need

a)      vaccinations and disease prevention

b)      better nutrition

c)      more food

d)     all of the above

9.      In humans, genes control all of the following except

a)      nutrition

b)      eye color

c)      skin color

d)     inherited diseases

10.  Biotechnology can be used in all of the following except

a)      plants

b)      animals

c)      human medicine

d)     replication of cells

11.  The most commonly-used bacterium for gene transfer in plants is

a)      Bacillus thuringiensis

b)      Escherichia coli

c)      Agrobacterium

d)     none of the above

12.  When a gene is transferred into an organism, the organism is called

a)      transgenic

b)      transformed

c)      all of the above

d)     none of the above

13.  What are inserted into a cells’s DNA along with genes of interest to visually identify transgenic character?

a)      marker genes

b)      cultures

c)      clones

d)     bioreactors


II. Fill  in the Blanks

14.  Complete the following sentences by supplying appropriate words:

i.            The production of cheese involves separation of from whey

ii.            A clone consists of ….. of a single individual or cell.

iii.            A/An ….. is used to introduce recombinant DNA into cells.

iv.            Genetic engineering has enabled the production of large number of ….. proteins.

v.            Leaching of copper sulphate from the ores is possible with ….. ferroxidans, bacteria.

vi.            Biomass produced by unicellular organisms is called …..

vii.            The pasteurized milk with known cultures of micro- organisms is referred to as …..

Dough is ….. by bread yeast which ….. the sugars in dough to produce ….. and …..

ix.            Human insulin is a dimer comprising of two claims A and B which are derived from a single polypeptide chin called …..

x.            The micro-organism used for SCP must be of  …..

xi.            Recombinant vaccines contains ….. encoding a protein of a …..

xii.            The process of producing ethanol using cellulose is done by micro-organism …..


III. Discussion Questions

15.  Explain briefly the application of biotechnology in the industries of

i.            Mining

ii.            Medical products

16.  Outline the various steps involved in the cheese production.

17.  What is Genetic Engineering? Explain briefly.

18.  What are Biofuels? Give useful features of biofuels.

19.  Explain the following terms

i.            SCP

ii.            Starter culture

iii.            Brewing

20.  How is Humulin produced? Explain

21.  Give the main steps involved in the process of drug designing.

22.  What is an ideal vaccine and a recombinant vaccine. Clearly different iate between the two.

23.  What is the objective of Gene transfer in animals

24.  Explain briefly the various types of fuels used

25.  Discuss two methods for treatment of solid wastes.



I. Objective Type Question

1.      (a)

2.      (d)

3.      (d)

4.      (a)

5.      (c)

6.      (b)

7.      (d)

8.      (d)

9.      (a)

10.  (d)

11.  (c)

12.  (c)

13.  (a)

II. Fill in the Blanks

        i.            curd

ii.            sexual progeny

iii.            vector

iv.            recombinant

v.            thiobacillus

vi.            single cell protein

vii.            starter culture

leavened, ferments, CO2, alcohol

ix.            preproinsulin

x.            good nutritional valve

xi.            gene, pathogen origen

xii.            Trichoderma reesei