Progress in wastewater treatment, separation and purification technologies: mechanisms, benefits, challenges,...

Escalating global demand for clean water, compounded by increasing contamination from untreated wastewater effluents, has intensified the need for advanced wastewater treatment, separation, and purification technologies. Wastewater treatment is indispensable for safeguarding ecosystem integrity, protecting public health, and enabling sustainable resource recovery. This critical review systematically synthesises and evaluates over 50 established wastewater separation, treatment, and purification technologies, enriched with pictorial illustrations that elucidate their operational principles and mechanisms. Comparative analysis highlights their benefits, limitations, efficiencies, energy consumption, and sustainability. Emphasis is placed on integrated or hybrid systems, strategically combining nature-based solutions, such as constructed wetlands, with advanced technologies, including membrane separations and advanced oxidation processes (AOPs). These synergies demonstrate significant potential to enhance contaminant removal, improve environmental sustainability, and accelerate circular resource recovery. Treatment performance is evaluated against the removal of excess nutrients, persistent pollutants, heavy metals, emerging contaminants, and pathogens. While nature-based systems offer low-energy operation, biodiversity enhancement, and ecosystem services, advanced technologies deliver superior purification efficiency but remain constrained by high operational costs, intensive energy demands, and skilled operators. Persistent challenges underscore the need for cost-effective, energy-efficient designs supported by robust monitoring and maintenance frameworks. Prospects emphasise integrating intelligent monitoring and control systems employing artificial intelligence (AI), machine learning (ML), the Internet of Things (IoT), and predictive analytics. Coupled with renewable energy adoption and green chemistry innovations, these advancements are poised to deliver more efficient, sustainable, and resilient treatment solutions aligned with circular economy principles, thereby addressing pressing imperatives of ecosystem protection, water security, and sustainable development.