Evaluation of locally-available agricultural and industrial waste materials as effective carriers for bacterial inocula in freshwater bioremediation

The pollution of freshwater is a pressing global environmental concern, necessitating effective management strategies for polluted aquatic environments. Bioremediation has emerged as a highly promising environmentally friendly approach. However, the selection of suitable candidates capable of effectively degrading or removing pollutants remains a challenging task. The introduction of live candidates, particularly bacteria, into natural environments also poses its own set of difficulties. To address these challenges, immobilizing bacteria within carrier materials has emerged as a leading option. In this study, we meticulously assessed the suitability of four locally-available and low-cost agricultural and industrial waste materials as carriers to transport bacteria into water bodies. The selection criteria encompassed bacteria immobilization capacity, viability, and the resulting water quality after treatment. In order to facilitate comparison, the widely-used sodium alginate was included as a benchmark, and Escherichia coli was employed as the model bacterial inoculum. Our findings revealed that alkaline pre-treatment of corn husk, rice husk, rice straw, and sugarcane bagasse significantly enhanced the bacteria immobilization capacity of these materials. Notably, the viability of bacteria in carrier materials, including sodium alginate, exhibited remarkable resilience, with a count of 107 CFU/g material even after 49 days of storage at room temperature. Moreover, upon determining the quality parameters of the receiving water, the introduction of rice husk and sodium alginate materials demonstrated no significant adverse impact. The quality parameters were well within the acceptable range defined by the World Health Organization standards for drinking water and the Sri Lankan ambient water quality standards for various purposes. Based on the overall performance evaluation, we advocate for the application of rice husk and sodium alginate as superior carriers for delivering bacterial inocula to aquatic environments, particularly in polluted water bodies targeted for bioremediation efforts. Nonetheless, we recommend the collection of carrier materials only after the establishment of bio inoculum in the receiving water, as a precautionary measure to minimize any potential impact on the chemical oxygen demand of the water.