Safe-by-design algal extracellular polymeric substances-based zeolite/ZnO bio-nanocomposite for the removal of bisphenol-A

The existence of endocrine disrupting chemical (EDCs), like bisphenol-A (BPA), creates a huge challenge for conventional wastewater treatment plants. The current study aimed to develop a hybrid adsorption-photocatalytic material for efficient BPA removal under UV-A irradiation. The characterization of the bio-nanocomposite was performed using FE-SEM, EDX, FTIR, UV–Vis spectrophotometry and total organic carbon (TOC). Batch experiments were performed to evaluate the effects of concentration, catalyst dosage, pH and an optimal bio-nanocomposite was developed. The optimized zeolite:ZnO:EPS ratio of 1:1:0.5 achieved the highest BPA removal under UV-A irradiation. Reactive oxygen species (ROS) scavenging experiments identified superoxide radicals as the dominant oxidative species. Among the scavengers, p-benzoquinone was seen to reduce efficiency, along with isopropanol and sodium azide. In addition, degradation kinetics were determined to be pseudo-first-order kinetics. The TOC analysis further confirmed approximately 96% mineralization of BPA after UV-A irradiation. In addition, the bio-nanocomposite showed 54.74% effectiveness on its 6th cycle of usage. In real water matrices under optimized conditions, the bio-nanocomposite showed 82.9%, 79.4% and 78.4% removal efficiencies for tap water, seawater and lake water, respectively. For the biosafety assessments, Scenedesmus obliquus and Allium sativum were used as model organisms. The results indicate that the presence of EPS reduced oxidative stress and improved biological compatibility.