Sudharsan G, Sarvajith M, Nancharaiah Y V
Biofouling and Biofilm Processes Section, WSCD, Chemistry Group, Bhabha Atomic Research Centre, Kalpakkam, 603102, Tamil Nadu, India.
Biofouling and Biofilm Processes Section, WSCD, Chemistry Group, Bhabha Atomic Research Centre, Kalpakkam, 603102, Tamil Nadu, India; Homi Bhabha National Institute, BARC Training School Complex, Anushakti Nagar, Trombay, Mumbai, 400 094, India.
J Environ Manage. 2023 May 15;334:117482. doi: 10.1016/j.jenvman.2023.117482. Epub 2023 Feb 16.
Microbial transformations play a vital role in Se cycle in the environment and decrease the solubility and toxicity of Se oxyanions by converting to elemental selenium (Se) nanostructures. Aerobic granular sludge (AGS) has attracted interest due to efficient reduction of selenite to biogenic Se (Bio-Se) and retention in bioreactors. Here, selenite removal, biogenesis of Bio-Se and entrapment of Bio-Se by different size groups of aerobic granules were investigated to optimize biological treatment process for Se-laden wastewaters. Furthermore, a bacterial strain showing high selenite tolerance and reduction was isolated and characterized. Removal of selenite and conversion to Bio-Se were achieved by all the size groups of granules ranging from 0.12 mm to 2 mm and above. However, selenite reduction and Bio-Se formation were rapid and more efficient with large aerobic granules (≥0.5 mm). The formed Bio-Se was majorly associated with the large granules, due to better entrapment capabilities. In contrast, the Bio-Se formed by the small granules (≤0.2 mm) was distributed both in the granules and aqueous phase because of ineffective entrapment. Scanning electron microscope and energy dispersive X-ray (SEM-EDX) analysis confirmed formation of Se spheres and association with the granules. Efficient selenite reduction and entrapment of Bio-Se was related to prevalent anoxic/anaerobic zones in the large granules. A bacterial strain showing efficient SeO reduction of up to 15 mM SeO under aerobic conditions was identified as Microbacterium azadirachtae. SEM-EDX analysis confirmed the formation and entrapment of Se nanospheres (size: 100 ± 5 nm) in the extracellular matrix. The cells immobilized in alginate beads showed effective SeO reduction and Bio-Se entrapment. Efficient reduction and immobilization of bio-transformed metalloids by large AGS and AGS-borne bacteria implicates prospective use in bioremediation of metal(loid) oxyanions and bio-recovery.
微生物转化在环境中的硒循环中起着至关重要的作用，通过将硒氧阴离子转化为元素硒（Se）纳米结构来降低其溶解度和毒性。好氧颗粒污泥（AGS）由于能将亚硒酸盐高效还原为生物硒（Bio-Se）并保留在生物反应器中而受到关注。在此，研究了不同粒径组的好氧颗粒对亚硒酸盐的去除、Bio-Se的生物合成以及Bio-Se的截留情况，以优化含硒废水的生物处理工艺。此外，分离并鉴定了一株对亚硒酸盐具有高耐受性和还原能力的细菌菌株。粒径范围从0.12毫米到2毫米及以上的所有颗粒组均实现了亚硒酸盐的去除并转化为Bio-Se。然而，大型好氧颗粒（≥0.5毫米）对亚硒酸盐的还原和Bio-Se的形成更快且更高效。由于具有更好的截留能力，形成的Bio-Se主要与大型颗粒相关。相比之下，小型颗粒（≤0.2毫米）形成的Bio-Se由于截留效果不佳，既分布在颗粒中也分布在水相中。扫描电子显微镜和能量色散X射线（SEM-EDX）分析证实了硒球的形成以及与颗粒的关联。大型颗粒中普遍存在的缺氧/厌氧区域与高效的亚硒酸盐还原和Bio-Se的截留有关。一株在好氧条件下能高效还原高达15 mM亚硒酸盐的细菌菌株被鉴定为印楝微杆菌。SEM-EDX分析证实了细胞外基质中硒纳米球（尺寸：100±5纳米）的形成和截留。固定在海藻酸钠珠中的细胞表现出有效的亚硒酸盐还原和Bio-Se截留。大型AGS及其携带的细菌对生物转化的类金属的高效还原和固定表明其在金属（类金属）氧阴离子的生物修复和生物回收方面具有潜在应用价值。
