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Bioremediation is traditionally carried out using ‘free’ bacterial cells; however, in recent years, utilization of ‘immobilized’ bacterial cells has gained attention as a promising technique due to multifarious benefits. This review collates a vast amount of existing literature on the myriad contaminants treated using immobilized bacteria. We also discuss various mechanistic aspects of using immobilized cells for environmental remediation applications, with special attention on cells encapsulated in hydrogels and their implementation in detoxifying harmful contaminants and environmental cleanup. We examine different methods/techniques for immobilizing viable bacterial cells in various supporting matrices, use of single- and multi-species bacterial communities, various growth substrates, and factors affecting the remediation process including mass transfer, kinetic processes and bioreactor configurations used in pilot and field-scale applications. The advantages and limitations associated with the use of immobilized bacteria in a bioreactor for contaminated water treatment are also discussed. From a sustainable futures perspective, resource recovery and retrieval of value-added products along with bioremediation could be an added benefit of the immobilized cell-based treatment system, making it a more cost-effective and viable treatment strategy as well as one that is amenable to the principles of circular economy.

Bacterial strain Bacillus pseudomycoides, isolated from domestic wastewater was used to decolorize azo dye Acid Black 24. Response Surface Methodology based on Box- Behnken model was used to optimize the conditions for maximum dye decolorization. High regression coefficient values (adjusted R2 = 0.9317 and predicted R2 = 0.8343) confirmed that the predicted values are in compliance with the experimental values implying the appropriateness of the employed polynomial regression model. The adequacy of the model was validated by different descriptive statistics viz. lack of fit, adequate precision, F and p values. 96.79% of dye decolorization was achieved at pH 7, temperature 37 °C and 40 mg L−1 dye concentration. The activities of oxido-reductive enzymes like lignin peroxidase, laccase and azoreductase were found to be induced during the dye decolorization process. The biodegradation of the dye was assessed by HPLC, FTIR and UV spectroscopy. Genotoxicity and phytotoxicity studies substantiated the nontoxic nature of the degraded dye.