**1. Introduction**

Contamination of water and soil environment due to the release of toxic and hazardous chemicals as a result of industrialization has taken its toll by causing environmental pollu‐ tion. If not treated and managed appropriately, toxic and hazardous pollutants may cause severe detrimental (negative), reversible or irreversible, intangible and incapacitating im‐ pacts on all forms of living cells. Thiocyanate (N≡C─S- ) is one such known hazardous chem‐ ical and an important member of cyanide (CN- ) family. It is a simple inorganic and one carbon (C-1) compound. Despite its toxicity, it is introduced into the environment by natural (principally by biological cyanide detoxification processes) as well as industrial processes (Kelly and Baker, 1990; Wood, 1975). Thiocyanate (SCN- ) has some novel properties. It is lin‐ ear in nature, electronegative polyatomic ion and a good example of pseudohalide; and therefore produced on a grand scale for its use in diverse industrial processes such as dye‐ ing, acrylic fibre production, thiourea production, photo-finishing, herbicide and insecticide production, metal extraction and electroplating industries (Hughes, 1975). SCN- is also known for its applications in soil sterilization and corrosion inhibition (Beekhuis, 1975). Consequently, these industries emanate large volumes of SCN- bearing wastewaters. Apart from SCN- , these effluents might contain other contaminants like heavy metals, cyanide (CN- ), metal-cyanides (MxCN) and metal-thiocyanates (MxSCN). Cyanide has the potential to reacts readily with sulphur to produce SCN- and any industry with cyanide in its waste is a potential source of SCN contamination. Steel manufacturing, metal mining and electro‐ plating units are some examples of such industries.

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All the species of cyanide family (viz. thiocyanate, cyanide and their metal complexes) have potential to interacting with living cells and strong tendencies to connect to proteins and thereby acts as a non-competitive inhibitor (Westley, 1981). This fact necessitate the industries using and/or emanating SCN to adequately detoxify the effluents on priority basis before its discharge in soil and water environment; as it may pose detrimental im‐ plications on aquatic life. Moreover, in water scarce situations such untreated and partial‐ ly treated wastewaters could not be recycled back into the industrial processes. The concentration of SCN arising from all the above mentioned sources is normally in the range of 5 - 110 mg/l (Mudder and Whitlock, 1984). Although many statutory agencies across the world have set the statutory limits for cyanide and heavy metal discharge, till date there are no such prescribed limits set or documented for SCN discharge. Earlier sci‐ entific studies indicate that in general, SCN is approximately 7 to 10 times less toxic then free cyanide species. The US-health service cites 0.01 mg/l as guideline and 0.2 mg/l as the permissible limit for cyanide species. In India, the Central Pollution Control Board (CPCB) had set a Minimum National Standard (MINAS) limit for cyanide as 0.2 mg/l. Therefore, the cyanide bearing effluents generated from industries needs suitable treat‐ ment to bring down the total cyanide levels below 0.2 mg/l. Taking into consideration the mentioned facts, standards for discharge of SCN could readily be deduced to 1 mg/l to be on the safer side. In order to minimize the risk of exposure to the public and aquatic ecosystems, the clean-up of SCN contaminated wastewaters is therefore necessary. Patil and Kulkarni (2008) have reported the environmental sensitivity and safety aspects in mining industries in regard to cyanide. Impact of cyanide species on fresh water fish Cat‐ la catla have also been reported (Prashanth and Patil, 2008).

MxCNs are well documented and have been studied for long time (Dash et al., 2009; Gurbuz, et al., 2004; Karavaiko et al., 2000; Patil and Paknikar, 2000a; Patil and Paknikar, 2000b; Patil and Paknikar, 2001; Patil et al., 2012). Some research papers on biodegradation of SCN-

also been reported (Chaudhari and Kodam, 2010; Hung and Pavlostathis, 1998; Patil, 2008a; Van Zyl et al., 2011). Use of metabolically passive (dead or inactive) microorganisms for the removal and recovery of metal-cyanides and SCN- have also been reported (Gaddi and Patil, 2011; Patil, 2012; Patil and Paknikar, 1999; Thakur and Patil, 2009). Successful efforts to setup large scale bioremediation technology for the treatment of cyanide, metal-cyanide and

from mining effluent have been made on commercial scale (Mudder and Whitlock,

from aqueous industrial wastes using metabolically active

Development of a Bioremediation Technology for the Removal of Thiocyanate from…

process development point of view (Patil, 2006; Patil, 2008a; Patil, 2008b; Patil, 2011; Sorokin

growth substrate (carbon and/or nitrogen source) is poorly understood. Lack of scientific knowledge in this regard may pose problems in the biological treatment systems. The au‐ thor in the present research chapter focuses on the development of a bioremediation tech‐

Potassium SCN- (KSCN) was obtained from Qualigens, Mumbai, India. SCN- assay was car‐ ried out spectrophotometrically (Spectronic, Model-20D, India) using ferric nitrate method at 460 nm as described in Standard Methods (APHA-AWWA-WEF, 1998). Digital pH meter (Elico, Model Ll-120, India) was employed to determine pH of solutions. Bacterial popula‐ tion from culture media, activated sludge and soil were determined microscopically (Met‐ zer, India, METZ-778A) using Neubauer's chamber (Fein-Optik, Blankenburg, GDR) and by total viable count (TVC). Analytical grade chemicals were used for all experiments. Re‐ agents were prepared in glass distilled water and stored under refrigerated conditions

Enrichment culture and growth of mixed bacterial community (bacterial consortium) was carried out using M-9 minimal salts medium (MSM) (Patil and Paknikar, 2000a). One litre of medium contained Na2HPO4.2H2O - 3.0 g; KH2PO4 - 1.5 g; NaCl - 0.25 g; distilled water - 1000 ml and 1 ml/l trace metal solution (Bauchop and Elsden, 1960; Millar, 1972). The medi‐ um pH was adjusted to 7.5 using 1 M NaOH/HCl. Glucose (10 mM) was added as the sole

organisms were set-up in aerobic and unsterilized conditions using activated sludge (ob‐ tained from secondary treatment of sewage treatment plant) and garden soil. Both the

as the sole source of nitrogen. Enrichment culture for the isolation of SCN-

 **degrading bacterial consortium**

(50 mg/l) was supplemented to the enrichment medium

degrading micro‐

1984). However, there are very few reports on the microbial SCN-

et al., 2001; Stratford et al., 1994). Moreover, utilization of SCN-

SCN-

nology for the removal of SCN-

**2. Materials and methods**

**2.1. Analyses, chemicals and glassware**

**2.2. Enrichment and isolation of SCN-**

source of carbon and energy. SCN-

microorganisms.

(8-10°C).

have

33

degradation from the

by microbes as a suitable

http://dx.doi.org/10.5772/56975

Numerous technologies are currently employed to detoxify SCN- bearing effluents; and the most widely being used is direct alkaline chlorination or addition of hypochlorite. However, this method produces large aggregates of chemical sludge, which does not have any further utilization and is environmentally hazardous to handle (Lanza and Bertazzoli, 2002). As per Indian regulations, such hazardous chemical sludge is transited from the industrial location to a specially designed Treatment, Storage and Disposal Facility (TSDF) thereby increasing the overall energy consumption, transportation cost and air pollution. Secondly, chlorina‐ tion also fails to bring the concentration of SCN- (and other CN species) within the statutory limits especially when heavy metals are present in the effluents. Thirdly, chlorination in‐ creases the total dissolved solids (TDS) content of the treated wastewaters, which makes it unfit for further use. Other physico-chemical processes like hydrogen peroxide oxidation, ozone oxidation, electrolytic decomposition, etc. are highly expensive and are rarely used for the treatment of SCN- . Thus, there is a pressing need for the development of an alterna‐ tive treatment process capable of achieving high degradation efficiency at low cost.

Bioremediation (biological treatment system) using metabolically active (live) microorgan‐ ism is one such effective alternative for the detoxification of toxic chemical wastes. This process has immense potential of treating variety of pollutants (both toxic and non-toxic); has several advantages over conventional methods and therefore being explored by the re‐ searchers world-wide. Microorganisms capable of utilizing C-1 compounds like CN and MxCNs are well documented and have been studied for long time (Dash et al., 2009; Gurbuz, et al., 2004; Karavaiko et al., 2000; Patil and Paknikar, 2000a; Patil and Paknikar, 2000b; Patil and Paknikar, 2001; Patil et al., 2012). Some research papers on biodegradation of SCN have also been reported (Chaudhari and Kodam, 2010; Hung and Pavlostathis, 1998; Patil, 2008a; Van Zyl et al., 2011). Use of metabolically passive (dead or inactive) microorganisms for the removal and recovery of metal-cyanides and SCN- have also been reported (Gaddi and Patil, 2011; Patil, 2012; Patil and Paknikar, 1999; Thakur and Patil, 2009). Successful efforts to setup large scale bioremediation technology for the treatment of cyanide, metal-cyanide and SCN from mining effluent have been made on commercial scale (Mudder and Whitlock, 1984). However, there are very few reports on the microbial SCN degradation from the process development point of view (Patil, 2006; Patil, 2008a; Patil, 2008b; Patil, 2011; Sorokin et al., 2001; Stratford et al., 1994). Moreover, utilization of SCN by microbes as a suitable growth substrate (carbon and/or nitrogen source) is poorly understood. Lack of scientific knowledge in this regard may pose problems in the biological treatment systems. The au‐ thor in the present research chapter focuses on the development of a bioremediation tech‐ nology for the removal of SCN from aqueous industrial wastes using metabolically active microorganisms.
