Production of thermostable protease enzyme in wastewater sludge using thermophilic bacterial strains isolated from sludge

Abstract

The volume of sludge produced annually is very high and poses serious disposal problems. The traditional methods of sludge disposal produce secondary pollutants. Therefore, the alternate or suitable solution is reuse of sludge in an ecofriendly approach. Biotechnology is an interesting tool to add value to the processes involved in wastewater and wastewater sludge disposal/reuse. In this context, a study was carried out on thermophilic bacterial strains that produce thermostable proteases. The bacterial strains were first isolated from municipal wastewater sludge. In contrast to the conventional strains used in industries, like Bacillus sp., the new strains were Gram-Negative type. In semi-synthetic medium, a maximal protease activity of 5.25 IU/ml (International Unit per ml) was obtained at a pH of 8.2 and at a temperature of 60 °C, which is higher than the stability temperature of 37 °C for a similar protease obtained from the conventional producer Bacillus licheniformis. Moreover, growth and protease activity of the strains were tested in wastewater sludge. It is expected that the complexity of sludge could stimulate/enhance the protease production and their characteristics. In conclusion, reuse of wastewater sludge will help to reduce their quantity as well as the value-added products produced will replace chemical products used in industries.