## 3 Use of Microbial Agents in Remediation System
### Bacterial Cultures in Submerged Fermentations  
The capability of some bacteria to decolourise and metabolise dyes is known, and therefore the use of remediation technology using these microbes has attracted the interest of many researchers for the biological-treatment of textile wastewater. A group of researchers [3] have studied microbiological decolourisation of dyes from textile industries and reported on its benefits and limitations. Other group [4] reviewed the mechanisms of degradation of dyes used by diverse groups of microorganisms, including anaerobic bacteria consortia. The employment of bacteria for their ability to carry out dye decolourisation has been studied in detail [2; 3; 4]. The research work has revealed the isolation of a variety of microorganisms capable of decolourising a wide range of synthetic dyes. Microbial degradation and decolourisation of dyes is beneficial, being a chemical-free method for the removal of these chemicals from the water sources. A practical and simple biological process using bacteria for the decolourisation of coloured wastewater obtained from a textile company has been studied by [PERSON] et al. [16; 17; 18]. Few aerobic and anaerobic microbes were isolated, showing their capability to decolourise dyes present in textile effluent samples, after prolonged enrichment-culturing of samples collected from textile industry. The decolourisation of some dyes of the effluent and of a solution made in a lab with a mixture of dyes was only observed under anaerobic conditions, suggesting that the chromophoric bonds in the dye structure were broken by bacteria. The five anaerobic bacterial isolates (named as PDC 1 to 5) capable of complete decolourisation of some dyes in individual-dye solutions were further examined in liquid fermentation under anaerobic conditions. One bacterial isolate was capable of decolourising Remazol-Red (diazo dye), Cibacron-red (reactive dye), and Remazol-Golden Yellow (azo dye) completely within one day (24-30 h) of the fermentation process. It also decolourised a reactive dye, Cibacron-Orange, and a diazo dye, Remazol Navy Blue, within 48 h; Remazol-Blue was decolourised within 54 h.  
The researchers have reported that the decolourisation of these dyes was permanent with no revert or change in the colour of the medium on exposure to oxygen. However, a phthalocyanine dye, Remazol-Turquoise Blue, was first completely decolourised but its original colour partially reversed after the exposure of the fermented medium to air. The possible applications of these bacterial isolates in decolourisation and treatment of textile dye effluent have been discussed in a few publications [16; 17; 18]. A microbial consortium named as PDW, isolated from dye-contaminated soil samples collected from a textile company, was studied in detail [17]. This consortium was found capable of the fast decolourisation of commercial textile dyes in a process performed under anaerobic conditions. Decolourisation was affected by the presence of another carbon source in the medium containing textile dyes. This bacterial consortium was found efficient in dye decolourisation when growing in dye-solutions supplemented with low-cost and readily available industrial byproducts used as carbon sources, including lactose-whey, distillery-waste, and starch. PDW reduced colour from textile plant effluent up to 76% in 3 days [17]. Bacterial culture was grown in simulated effluent (mixture of nine dyes, total concentration of dyes 0.5 g/L or 500 mg/L), and with individual dye components at the same concentration of 0.5 g/L, separately. Bacteria could grow at 0.5 g/L dye concentration, which is a very dark coloured solution compared to dye concentration in water bodies after the disposal of actual dye effluent. So if bacteria could remove 76% of colour at 0.5 g or 500 mg/L dye solutions, these could be applied to much-diluted solution of dyes (0.1, 0.2 g/L) for a higher percentage of dye removal, fulfilling the environmental regulations.