**1. Introduction**

Extraction of nuclear materials like Uranium from ores generates effluents containing sul‐ phate. Sulphate mostly comes from the sulphuric acid used for extraction of uranium from its ore. Sulphate is also released as a by-product of different anthropogenic activities such as metal smelting, fuel gas scrubbing, molasses fermentation, tanneries, food processing, coal burning, pulp and paper processing and mining activities [1, 2]. Increase in sulphate concentration in ground water causes various adverse effects such as laxative effect, dehydration, and skin problem, and it also imparts an unpleasant taste to water [3]. It is an eye irritant, causing redness upon exposure. It has also been reported that sulphate pollution results in eutrophication of both surface and ground water. It indirectly enhances phosphate-based eutrophication that can inhibit the growth of different plant species. Na2SO4 contamination in the soil can lead to change in freezing temperature by 0.28 °C [4, 5]. The standard level for the presence of sulphate is 250 ppm in drinking water while it is 1000 ppm for waste water. There are different techni‐ ques for sulphate demineralization such as reverse osmosis, distillation, ion exchange for drinking water, while methods involving chemical precipitation using chemicals like barium chloride exist for environmental waste disposal. The chemical method of reduction of sul‐ phate using barium chloride also ensures substantial reduction of heavy metals in the form of precipitates. But for the chemical process to function optimally, it is essential that the concen‐ tration of the chemical is high and that it is thoroughly mixed with the effluent discharged. The mechanical stirring in case of large volumes may not be a feasible option at the industrial scale. Hence, physicochemical techniques have many drawbacks when their efficiency is compared with the cost of implementation of the technology [6].

Bioremediation happens to be an alternative method of treatment. Biological sulphate reduction is a state-of-the-art technology, which has definite advantages over conventional treatments. Sulphate-reducing bacteria (SRB) play an important role in several biochemical processes. Sulphate is taken up by these microbes as a nutrient and reduced to sulphide, which is then incorporated into sulphur-containing amino acids. Thus, they are significant in sulphur transformation [7]. SRB is heterogeneous, morphologically diverse, physiologically unique anaerobic microorganisms that are widespread in anoxic habitats [8, 9], where they use sulphate as a terminal electron acceptor for the degradation of organic compounds, resulting in the production of sulphide. Both oxidation and reduction reactions for the generation of metabolic energy are important. The sulphide thus produced can be oxidized in the presence of high levels of oxygen by chemolithotrophic sulphur bacteria or under anoxic conditions by phototrophic sulphur bacteria, whereas SRB perform the dissimilatory sulphate reduction [10– 12]. In marine sediments, above 50% organic carbon mineralization is carried out by sulphate reduction making the sulphate reducers extremely important for both the sulphur and carbon cycles. However, the use of SRB for bioremediation of waste water has some bottle necks. These include (a) the continuous supply of microbes for sulphate reduction within reasonable time and (b) the survival of the microbes in the environment while maintaining the efficiency of reduction. The literature reported a retention time of 15 days [13], 14 days [14], 10 days [7], 6 days [15], and 1 day [16] while working at laboratory scale with associated problems of clogging, back pressure and need for repeated maintenance. These facts made them non-viable for large-scale applications. Hence, the need of the hour was to develop a microbial solution through which rapid removal of soluble sulphate could be carried out in a sustainable manner. To address this issue, the following points had to be considered: (1) appropriate site selection for enrichment of SRB; (2) appropriate medium selection for the same; and (3) consortium optimization and development of packed bed reactor with optimal design for sustained performance of the system.

**1. Introduction**

18 Nuclear Material Performance

with the cost of implementation of the technology [6].

Extraction of nuclear materials like Uranium from ores generates effluents containing sul‐ phate. Sulphate mostly comes from the sulphuric acid used for extraction of uranium from its ore. Sulphate is also released as a by-product of different anthropogenic activities such as metal smelting, fuel gas scrubbing, molasses fermentation, tanneries, food processing, coal burning, pulp and paper processing and mining activities [1, 2]. Increase in sulphate concentration in ground water causes various adverse effects such as laxative effect, dehydration, and skin problem, and it also imparts an unpleasant taste to water [3]. It is an eye irritant, causing redness upon exposure. It has also been reported that sulphate pollution results in eutrophication of both surface and ground water. It indirectly enhances phosphate-based eutrophication that can inhibit the growth of different plant species. Na2SO4 contamination in the soil can lead to change in freezing temperature by 0.28 °C [4, 5]. The standard level for the presence of sulphate is 250 ppm in drinking water while it is 1000 ppm for waste water. There are different techni‐ ques for sulphate demineralization such as reverse osmosis, distillation, ion exchange for drinking water, while methods involving chemical precipitation using chemicals like barium chloride exist for environmental waste disposal. The chemical method of reduction of sul‐ phate using barium chloride also ensures substantial reduction of heavy metals in the form of precipitates. But for the chemical process to function optimally, it is essential that the concen‐ tration of the chemical is high and that it is thoroughly mixed with the effluent discharged. The mechanical stirring in case of large volumes may not be a feasible option at the industrial scale. Hence, physicochemical techniques have many drawbacks when their efficiency is compared

Bioremediation happens to be an alternative method of treatment. Biological sulphate reduction is a state-of-the-art technology, which has definite advantages over conventional treatments. Sulphate-reducing bacteria (SRB) play an important role in several biochemical processes. Sulphate is taken up by these microbes as a nutrient and reduced to sulphide, which is then incorporated into sulphur-containing amino acids. Thus, they are significant in sulphur transformation [7]. SRB is heterogeneous, morphologically diverse, physiologically unique anaerobic microorganisms that are widespread in anoxic habitats [8, 9], where they use sulphate as a terminal electron acceptor for the degradation of organic compounds, resulting in the production of sulphide. Both oxidation and reduction reactions for the generation of metabolic energy are important. The sulphide thus produced can be oxidized in the presence of high levels of oxygen by chemolithotrophic sulphur bacteria or under anoxic conditions by phototrophic sulphur bacteria, whereas SRB perform the dissimilatory sulphate reduction [10– 12]. In marine sediments, above 50% organic carbon mineralization is carried out by sulphate reduction making the sulphate reducers extremely important for both the sulphur and carbon cycles. However, the use of SRB for bioremediation of waste water has some bottle necks. These include (a) the continuous supply of microbes for sulphate reduction within reasonable time and (b) the survival of the microbes in the environment while maintaining the efficiency of reduction. The literature reported a retention time of 15 days [13], 14 days [14], 10 days [7], 6 days [15], and 1 day [16] while working at laboratory scale with associated problems of clogging, back pressure and need for repeated maintenance. These facts made them non-viable

As an outcome of this study, a consortium was developed using which a packed bed bioreac‐ tor–based process has been drawn up, which is by far the fastest and the most stable sulphate removal system. This invention has been filed as an Indian patent and a PCT [17] to protect the intellectual property associated with this invention. It has immense application for industrial effluent treatment. Although biofilm-based bioreactors have been the point of investigation and application for a long period of time [18–21], little progress has been made in terms of real-life industrial application.
