<p>Biodegradable polymer–based hybrid nanocomposite membranes have emerged as sustainable alternatives to conventional non-degradable polymeric membranes that contribute to long-term microplastic pollution. This mini-review highlights the latest advances in natural and synthetic biodegradable polymer systems reinforced with metal/metal-oxide, carbon-based, and bio-derived nanomaterials for environmentally compatible water purification. The incorporation of nanomaterials markedly enhances hydrophilicity, mechanical stability, antifouling resistance, and pollutant removal through synergistic mechanisms such as adsorption, size-exclusion, and photocatalytic degradation. Reported studies consistently demonstrate high removal efficiencies for dyes and heavy metals, in addition to improved permeance and operational stability, underscoring the strong synergistic contribution of polymer–nanofiller interactions. Unlike previous reviews, this work delivers a focused and critical assessment of biodegradable membrane technologies, emphasizing key challenges such as the durability–biodegradability trade-off, fabrication limitations, and the limited adoption of green synthesis routes and life-cycle assessment considerations. From an environmental polymer science perspective, future opportunities toward scalable production, reduced environmental burden, and circular-economy membrane design are discussed, providing sustainability-oriented and polymer-relevant guidance for next-generation water treatment membranes.</p> Graphical abstract <p></p>