Advanced reactor designs and technologies for wastewater purification: Bioprocesses and nanotechnology for nutrient and energy sustainability

The growing impact of anthropogenic activities, including urbanization, agriculture and industrial expansion, has intensified water and environmental pollution, and wastewater treatment has evolved beyond pollutant removal toward the recovery of nutrients, energy and high-value materials. This work is a critical review supported by a systematic search and selection procedure: Scopus, Web of Science Core Collection and Google Scholar were searched for English-language records published between January 2015 and March 2026, using Boolean combinations of technology, treatment-performance and resource-recovery terms (final search 28 March 2026). Of 1142 records identified, 318 were assessed at full text and 102 studies met the predefined inclusion criteria and were synthesised, with evidence weighted by reactor scale and matrix realism so that results obtained with synthetic solutions are never presented as full-scale performance. Technologies are compared only on normalised criteria, and a system boundary is stated for every energy value. Three comparative findings emerge. First, biological systems achieve the highest carbon-removal performance at the lowest specific energy demand, but they eliminate nitrogen mainly as N 2 , which prevents pollution without retaining nitrogen in a reusable material pathway. Second, physicochemical and nanomaterial-based systems achieve the highest selectivity and product purity, but their net energy benefit is frequently negative once oxidant, photon and sorbent-regeneration inputs are accounted for. Third, hybrid configurations improve removal efficiency and reduce footprint, but they transfer the cost from energy to operational complexity and control requirements. The review provides process engineers and decision-makers with comparative criteria for technology selection and identifies explicitly where the current evidence base is insufficient to support claims of net energy gain, low lifecycle impact or economic feasibility. The technologies discussed are relevant to SDG 6, SDG 9 and SDG 12; however, the reviewed literature does not quantify the contribution of any individual technology to these goals, and no claim of measurable progress towards them is made in this work.