Whey has applications in food, beverages, personal care products, pharmaceuticals, and the medical sector. However, it remains a massive dairy residue worldwide (160.7 million m³ year⁻¹), with high organic and nutrient loads. About 42% is used for low-value products such as animal feed and fertilizers or is even directly discharged into water streams, leading to ecosystem damage via eutrophication. We reviewed the uses and applications of cheese whey, along with associated environmental impacts and innovative ways to mitigate them using affordable and scalable technologies. Recycling and repurposing whey remain challenges for remote locations and poor communities with limited access to expensive technology. We propose a closed-loop biorefinery strategy to simultaneously mitigate environmental impacts and valorize whey resources. Anaerobic digestion utilizes whey to produce biogas and/or carboxylates. Alternative processes combining anaerobic digestion and low-cost open photobioprocesses can valorize whey and capture organic, nitrogenous, and phosphorous nutrients into microalgal biomass that can be used as food and crop supply or processed into biofuels, pigments, and antioxidants, among other value-added products. The complete valorization of cheese whey also depends on facilitating access to relevant information on whey production, identifying stakeholders, reducing technology gaps among countries, enforcing legislation and compliance, and creating subsidies and fostering partnerships with industries and between countries.

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Milk discovery and processing enabled human settling and thriving in various settings. The discovery of cheese led to the production of whey as dairy by-product. Although it can find application in food, beverages, personal care products, pharmaceuticals and medical treatment, cheese whey is a massive dairying residue world-wide (154 Mm3·y-1) with high organic and nutrient loads. About 42% is used as low-value products as animal feed and fertilisers or even directly discharged in water streams, leading to ecosystem damage by eutrophication. Recycling and repurposing whey remains a challenge for remote locations and poor communities with limited access to expensive technology. Anaerobic digestion is proven and accessible for utilizing whey as substrate to produce biogas and/or carboxylates. Alternative processes combining anaerobic digestion and low-cost open photobioprocesses can foster the valorisation of cheese whey and capture of organics and nitrogen and phosphorus nutrients into a microalgal biomass that can be used as food and crop supply or processed into biofuels, pigments, antioxi-dants, among other value-added products. Awareness should be raised about the economic potential of cheese whey surplus by developing an action plan that (i) identifies stakeholders, (ii) sets goals and achieves solutions, (iii) decreases technology gaps among countries, (iv) enforces legislation and compliance, and (v) creates subsidies and foments partnerships with industries and other countries for the full valorisation of whey. We propose a closed-loop biorefinery implementation strategy to simultaneously mitigate environmental impacts and valorise whey resources.@en