Hexavalent chromium detoxification by haloalkaliphilic Nesterenkonia sp strain NRC-Y immobilized in different matrices

Abstract

To develop a bioprocess for Cr(VI) detoxification in industrial effluents, a previously isolated potent Cr(VI) reducing haloalkaliphilic Nesterenkonia sp strain NRC-Y was immobilized and investigated for Cr(VI) detoxification. The immobilization matrices included; natural, modified natural, synthetic, and mixtures of natural and synthetic polymers. Among the tested matrices and immobilization approaches, strain NRC-Y cells encapsulated in 1.5% (w/v) amidated pectin beads exhibited the highest Cr(VI) reduction efficiency (47.02% of initial Cr(VI) concentration 150 mg/L after 20 h) followed by alginate (34.4%), alginate-PVA-chitosan (29.6%), alginate-PVA (25.1%), PVA-PVP (23.2%), and PVA (9.5%). Chromate reductase enzyme was poorly immobilized by covalent binding on the tested materials. Therefore, entrapment in amidated pectin was selected for further investigation and immobilization of both whole cells and partially purified chromate reductase. Operational stability study revealed that the immobilized cells were more efficient and stable than the immobilized chromate reductase, and the free cells. For instance, about 60%, 27.0% and 11.5% of these samples initial activities were retained after four successive batches, respectively. The temperature and pH optima for the immobilized cells were 35°C and 7.0, respectively. The pH and thermal stability of strain NRC-Y cells were significantly enhanced upon immobilization in amidated pectin beads by up to 2.3- and 1.4-fold, respectively. The developed immobilized biocatalyst was applied for Cr(VI) reduction in industrial effluent samples, and it completely reduced Cr(VI) within 4 and 8 h for effluents of initial Cr(VI) concentrations 10 and 30 mg/L, respectively. The developed immobilized biocatalyst is promising and has the potential for large-scale Cr(VI) detoxification application.

Graphical Abstract

Keywords:

• Nesterenkonia sp strain NRC-Y
• chromium
• chromate reductase
• immobilization
• bioremediation

Disclosure statement

The authors have no competing interests to declare that are relevant to the content of this article. All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript. The authors have no financial or proprietary interests in any material discussed in this article. The authors have no relevant financial or non-financial interests to disclose.

Additional information

Funding

This project was supported by National Research Centre (Grant Number E120210), El-Buhouth St., Dokki, Cairo 12311, Egypt.