Bioremediation of tannery chromium: A microbial approach

 

Ashish Kumar Gupta*, Deepak Ganjewala, Navodit Goel, Namrata Khurana, Saradindu Ghosh, Abhishek Saxena

Amity Institute of Biotechnology, Amity University Uttar Pradesh, Sector-125, Noida-201 303 (UP), India

 

ABSTRACT:

Chromium is one of the most toxic heavy metals which pose a deadly threat to the environment and living organisms including plants, animals and humans. Wastes from a number of industries are the main sources of chromium release in environment leading to the pollution of air, water and soil. The leather tanning industry is largely responsible for tainting the environment with such a harmful element. This leads to economic loss of the nation because of crop contamination as well as health loss among the consumers of contaminated food. An urgent need of checking the sustenance of chromium in the environment for its healthy preservation has come up as a challenge in the recent times. The conventional existing methods mainly rely upon chemical conversion of the toxic Chromium(VI) into the lesser toxic and stable Chromium(III) by methods such as precipitation, ion exchange, membrane technologies, direct recycling approach etc. However, it has now become inevitable to find out newer, more efficient and eco-friendly techniques to serve this purpose. Bioremediation is an appropriate alternative by using of existing microbes in the ecosystem which are either tolerant to chromium or can convert Cr(VI) into Cr(III). These microbes range from bacteria, fungi, algae and even yeasts in some cases. Apart from these, plants have also demonstrated the accumulation of environmental chromium in their tissues, a phenomenon termed as phytoremediation. In this review, we have tried to cover most of the aspects of chromium bioremediation, studies carried on it till now and its possible application for the future remedy techniques for human and environment welfare.

 

 

INTRODUCTION:

Tanneries are industries where animal hides are converted into leather which is durable and less susceptible to decomposition by the use of tannic acid or mineral salts.  The tanneries provide a lot of leather products that have an important role in human life and for country trade. It is an important source of employment and foreign exchange. India is one of the leading producers of leather and its products. Leather making industries play an important role in the economy of the country.  India serves to be a major exporter of leather products throughout the globe. These industries are a major source of employment for more than 2.5 million people across India¹.

 

Leather production consists of the following processes. These are: 1). Beamhouse process in which salt, dirt and hair are removed. 2).

 

Tanning under which the hide is treated with chemicals to produce leather. Chromium is the most common tanning agent used in the process throughout the world. Conventionally, chromium tanning consists of pickling, tanning and basifying. The main pollutants of the tanning process are chromium, chlorides and sulphates. 3). Post tanning (wet finishing), which includes neutralization, retaining, dying and fat liquoring. The pollutants from the process include chromium, salt, dyestuff residues liquoring agents and vegetable tannins. 4). Finishing in which the leather is given desired properties. The main pollutants produced during finishing are suspended solids and chromium².

 

Tannery effluent and its pollution

The conventional leather tanning technology is highly polluting as it produces large amounts of organic and chemical pollutants. These pollutants are mostly present in the effluent discharged by tanneries and are a serious threat to the environment. Escape of untreated or partially treated tannery effluent can cause serious damage to soil and water bodies.

Table No.1. Presence of different heavy and toxic metals at Ranipet tannery effluent

S. No.	Heavy/ Toxic metals	Symbol	Concentration  average (µg/litre)	Concentration of the  effluent (µg/litre)
1.	Cadmium	Cd	51.1	0.2-401.4
2.	Chromium	Cr	247.2	2.4-1308.6
3.	Copper	Cu	95.5	2.1-535.5
4.	Lead	Pb	467.8	6.4-2,034.4
5.	Nickel	Ni	36.7	1.6-147.0
6.	Zinc	Zn	3,760.4	20.8-1,2718.0

According to a report published by the U.S. EPA⁵ (1996b), the most common metals found at contaminated sites are (in descending order of concentration): lead (Pb), chromium (Cr), arsenic (As), zinc (Zn), cadmium (Cd), copper (Cu), and mercury (Hg).

 

The high amount of salt contained in the effluent can increase soil salinity, reduce its fertility and damage farming in large areas. Tanneries also produce harmful gases, dust and a large amount of solid waste. The technologies used by Indian leather firms are outdated and inefficient. Their environmental performance is poor. They do not use environment-friendly techniques and produce large amounts of effluent with a high load of pollutant. Their limited capacity to treat the effluent and ineffective facilities in most of the cases is also a matter of concern³. A case study (Table 1) conducted at Ranipet, an industrial area of Chennai, TN, India, indicated the presence of different heavy and toxic metals⁴.

 

Application of chromium in tanning

Tanning is the most important step in the leather processing industries. Chrome tanning in the leather industry was introduced in 1858 by Knapp because of which there was a remarkable change in the leather industry. Chromium tanning is more popular than the vegetable tanning and thus the effluent coming out from the production unit is highly loaded with chromium as a contaminant⁶. Basic Chromium sulphate (BCS) is a tanning agent, which is employed by 90% of tanning industries. Due to this, it has been estimated that a concentration as high as 1500 to 3000 ppm of chromium is present in tannery effluents, which is highly toxic to the environment as well as to the living organisms. Release of chromium is damaging the environment and also causing a substantial financial loss. It is estimated that in India alone almost 10 million US dollars worth of chromium is wasted every year. Different forms of toxic waste Chromium have been reported throughout the world. It may be present in several oxidation states like Cr(0) to Cr(VI)^7,8 (Table 2).

Hexavalent chromium

In the industrial wastes chromium is primarily present in the hexavalent form as divalent oxy anions, chromate (CrO₄²) and dichromate (Cr₂O₇^2-). Hexavalent chromium is highly soluble in water and toxic for most organisms due to their strong oxidizing nature⁹.

 

Trivalent chromium

Chromium (III) is present naturally in the environment and it is a highly stable form of chromium. Bioremediation of hexavalent chromium into non toxic form may also increase the Cr(III) concentration in the environment¹⁰. Cr(III) in effluent is primarily less toxic but when this effluent is discharged into the soil, Cr(III) is oxidized to Cr(VI) form and it is very toxic^11,12 .

 

Chromium toxicity

Chromium is one of the heavy metals that occur naturally in earth crust in small quantities associated with other metals. Its atomic weight is 51.996, atomic number is 24, melting point is 1.875^◦ C, boiling point is 2680^◦ C and specific gravity is 7.19. Chromium, as mentioned above, can occur in several oxidation states from Cr(0) to Cr(VI). It may be found naturally in rocks, soil, plants, and animals, including people. It may also occur in combination with other elements as chromium salts, some of which are soluble in water. Cr(III) is most common form of naturally occurring chromium, but it is largely immobile in the environment, mobile with only trace amount unless when the pH is extremely low. Under strong oxidizing conditions, chromium is present in the Cr(VI) state and persists in anionic form as chromate.

 

Table No. 2. Different oxidation states or chemical species of Cr in the environment

 

Most stable state of chromium is trivalent species when pH ranges from 3.5-4.0. At low pH, Cr(III) is bound to organic matter, clays, or oxide minerals; above pH 5, it is of low solubility due to the formation of insoluble Cr(III) hydrous oxides¹³.Cr can be beneficial or toxic to humans, depending upon its oxidation state and concentrations¹⁴.

 

Cr(III) is essential for the proper functioning of living organisms in trace amount. At low concentrations, nutritionally Cr(III) is an important component of a balanced human and animal diet for preventing adverse health effects. At the cellular level Cr(III) might be toxic to organisms because of its tendency to form complexes with nucleic acids, proteins, and organic compounds ¹⁵.

 

Information regarding health depleting effects of Chromium(VI) or Chromium(III) exposure in humans is mainly available from case report of acute accidental or intentional ingestion, acute dermal exposure, and from occupational case reports. Occupational exposure to Cr(III) are associated with respiratory and nasal, cardiovascular, gastrointestinal haematological, hepatic renal and dermal effects. An inhalation exposure to a sample of Cr(III) sulphate is known to develop coughing, wheezing, and decreased forced expiratory volume¹⁶. It may also lead to chronic tonsillitis, chronic pharyngitis and atrophy of larynx¹⁷. Cr(III) at increased concentrations can interfere with several metabolic processes because of its high capability to form coordinate compounds with various other existing organic compounds resulting in the inhibition of several metalloenzyme systems¹⁴ (Figure 1). In contrast, hexavalent Cr is a highly toxic carcinogen and may be a lethal threat to animals and humans if ingested in large doses.

 

Figure 1. Effects of Chromium on human body

 

Chromium removal by Conventional methods

Removal of chromium present in tannery effluent is important for environment and economics. The methods for chromium removal from tannery effluent include chemical reduction followed by precipitation of chromium as chromium hydroxide (Cr(OH)₃), ion exchange, membrane technologies, direct recycling approach, which involves filtration of the waste liquor followed by chemical replacement. Adsorptions of chromium by several types of adsorbents such as activated carbon, bone charcoal and waste activated sludge¹⁸ have also been reported. Electro coagulation has often been considered efficient for removal of chromium species from liquid wastes by using aluminium ¹⁹ or iron²⁰ .

 

Bioremediation

Bioremediation is a process whereby organic wastes are biologically degraded under controlled conditions to a harmless state, or to levels below concentration limits established by regulatory authorities²¹ which are not lethal and thus harmless. In the process of bioremediation, living organisms, primarily microorganisms are used to degrade the environmental contaminants into less toxic forms. It employs the use of naturally occurring bacteria and fungi or plants to degrade or detoxify substances which are otherwise hazardous to human health and/or the environment.

 

Advantages of bioremediation

Ø  Bioremediation is a natural and widely acceptable waste treatment process for contaminated material such as soil. Microbes which are able to degrade the contaminants are usually present in waste and usually give an innocuous state of products.

Ø  In most of the cases, bioremediation is useful for complete destruction of a wide variety of contaminants. By this process largely, hazardous compounds can be transformed into harmless products. This eliminates future liability associated with treatment and disposal of contaminated material.

Ø  Bioremediation can often be carried out on site, often without causing a major disruption of normal activities. This also eliminates the need to transport quantities of waste off site and the potential threats to human health and the environment that can arise during transportation. Thus, this technology provides a convenient and safer alternative to the prevalent chemical methods of toxic compound removal.

Ø  Bioremediation can prove less expensive than other technologies that are used for clean-up of hazardous waste because it doesn’t involve the use of sophisticated instruments or skilled labors for handling them, which are a necessity in other conventional methods and thus are responsible for high cost of detoxification. Thus, bioremediation is a cost-effective technique.

Ø  In bioremediation, the already known capabilities of microbes such as algae, fungi, and bacteria are employed for the removal of heavy metals from industrial effluents.

Ø  The remediation of Cr(VI) leads to its conversion into a stable, less soluble and very less toxic form i.e. Cr(III). Reduction of potentially toxic Cr(VI) to Cr(III) is thus a useful process for remediation of Cr(VI) affected environments²² .

 

Microbes in Chromium(VI) bioremoval

The following table lists the different microorganisms and mechanisms employed for removal of toxic Cr from environment.

 

Table No. 3. List of important microorganism and type of mechanism for Cr(VI) conversion

No.	Microorganism	Mechanism	References
1	Brevibacterium casei	Bioremediation	Verma and Singh 201323
2	Bacillus cereus	Bioremoval	Zhao et al. 201124
3	KI and SL14	Reduction	Mahmood et al. 201225
4	Trichosporon cutaneum R57	Bioremoval	Bajgai et al. 201226
5	Stenotrophomonas maltophilia, Staphylococcus gallinarum, Pantoea sp. and Aeromonas sp.	Detoxification	Alam and Ahmad 201227
6	Serratia sp.	Biosorption	Srivastava and Thakur 201228
7	Ochrobactrum intermedium	Detoxification	Batool et al. 201229
8	Cellulosimicrobium cellulans KUCr3	Bioremediation	Chatterjee et al. 201130
9	Bacillus spp. strain FM1	Reduction	Masood and Malik 201131
10	Staphylococcus aureus and Pediococcus pentosaceus	Reduction	Ilias et al., 201132
11	Bacillus cereus	Bioremediation	Tripathi et al., 201133
12	Bacillus brevis	Reduction	Verma et al., 200934
13	Spirulina fusiformis	Bioaccumulation	Pandi et al. 200935
14	Trichoderma inhamatum	Bioremediation	Morales-Barrera and Cristiani-Urbina, 200836
15	NBRIP-1, NBRIP-2, NBRIP-3 and NBRIP-4	Bioaccumulation	Shukla et al. 200737
16	Acidithiobacillus ferrooxidans and A. thiooxidans	Reduction	Cabrera et al. 200738
17	Aspergillus spp.	Bioremoval	Srivastava and Thakur 200639
18	Lentinus edodes	Biosorbent	Chen et al. 200640
19	Bacillus cereus S-6 , Ochrobactrum intermedium CrT- 1, Oscillatoria sp. and Synechocystis sp.	Bioremediation	Faisal et al. 200541
20	Pseudomonas sp., Mycobacterium sp., Shewanella sp., E.coli, Desulfovibrio sp., Enterobacter sp., Bacillus sp	periplasmic biosorption, bioaccumulation and biotransformation	Camargo et al. 200342
21	Arthrobacter sp	Bioremediation	Megharaj et al. 200343
22	Pseudomonas aeruginosa A2Chr	Reduction	Ganguli and Tripathi 200244
23	Bacillus circulans  and Bacillus megaterium	Bioaccumulation	Srinath et al. 200245
24	A. niger	Biotoleration	Dursun et al., 200246

 

Bioremoval of chromium(III)

Bioremoval, a technique which use the biological systems for the removal of metal ions such as chromium from polluted waters like effluents ⁴⁷. Bioremoval of both trivalent and hexavalent chromium by Seaweeds has been noted by Kratochvil et al. ⁴⁸(1998). Bioremoval action in form of biosorption of Cr(III) has been investigated by some bacterial strains isolated from  Ramsar warm springs, Iran.  Removal of Cr(III) species from liquid streams by a hydrophobic bacteria strain, Rhodococcus opacus has been observed by Calfa and Torem⁴⁹ (2008), proving it to be highly efficient in Cr(III) removal. Later in 2010, Gupta and Kumar⁵⁰ investigated role of indigenous tannery effluents microbes in trivalent chromium bioremoval in Ranipet, a hub of leather industries. The metabolic response of plants to exogenous supply and bioaccumulation of trivalent chromium was investigated by Yu et al. (2007)⁵¹. The total amount of Cr accumulated in plant biomass of hybrid willows was found to be variable in response to Cr (III) supply.

 

Authors Approach

Adaptation for better uptake

Adaptation process can make an efficient strain for better removal of Cr(III). In adaptation process isolated tolerant strains were subjected to Cr exposure from a low concentration to higher concentration for a specific time period under sterile conditions. These adapted strains had higher efficacy in terms of their ability of chromium uptake and subsequent removal from the tannery waste. Uptake for Cr(III) was observed to be highly dependent on the pH of the solution⁵² .At pH ≤ 4, it showed an efficient uptake of Cr(III) while at higher pH values the same was not observed possibly due to the precipitation of chromium.

 

ACKNOWLEDGEMENT:

Corresponding author of this article is grateful to Dr. Ashok Kumar Chauhan, Founder President and Atul Chauhan, Chancellor, Amity University, Uttar Pradesh, Noida, India for providing necessary facilities and support.

 

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Received on 30.09.2013       Modified on 24.10.2013

Accepted on 28.10.2013      © RJPT All right reserved