## 1 Introduction  
As global concerns about sustainable waste management intensify, industries are increasingly looking for innovative solutions to address environmental challenges. In the dairy sector, the management of raw whey--a by-product generated in abundance during the production of cheese and yogurt--is a major environmental challenge [1]. Raw whey, characterized by its high organic load and nutrient content, poses significant challenges for disposal and treatment [2]. Traditional methods of dealing with raw whey, such as land application and direct discharge to water, have been associated with negative environmental impacts, including soil and water pollution, eutrophication of water bodies, and the release of greenhouse gases [3]. According to sustainable indicators within the dairy industry, the valorization of whey is an excellent alternative that offers both economic and environmental benefits [4, 5]. Valorizing whey is therefore essential to meet the requirements of the 2030 Agenda, in particular with regard to SDGs 6, 9, and 12 (drinking water and sanitation; industry, innovation, and infrastructure; responsible consumption and production) [5]. The current raw whey treatment landscape includes a variety of methods, such as anaerobic or aerobic digestion, coagulation-flocculation, oxidation processes, and direct land application [6; 7]. While these approaches have shown promise in addressing certain aspects of raw whey management, they often face challenges in efficiently managing the high nutrient content and organic load. As a result, residual environmental impacts and operational inefficiencies persist, highlighting the need for novel, environmentally friendly solutions that can mitigate the adverse effects of raw whey on ecosystems [6; 8]. There is an urgent need to explore novel, environmentally friendly solutions that effectively mitigate the negative impact of raw whey on ecosystems. This research seeks to bridge this gap by proposing an environmentally sustainable approach to raw whey treatment. Specifically, it is hypothesized that a novel method involving the sequential cultivation of macrophytes and microalgae can effectively reduce the nutrient load and organic pollutants in raw whey. This hypothesis is based on the unique properties of these organisms, which offer potential for developing a cost-effective, efficient, and environmentally friendly treatment method. The coexistence of macrophytes and microalgae in a unified treatment system typically poses challenges for microalgae. In addition to competing with microalgae for nutrients, densely growing floating macrophytes on the surface of the wetlands or tanks drastically reduces light penetration into the water [9], thereby limiting microalgal activity and growth [10]. Concomitant treatment with macrophye could, therefore, lead to the eradication of the microalgal population from the effluent. To address these challenges, the efficacy of a two-stage photobioreactor system was explored, where _Lemma minor_ L. MO23, a macrophyte, is used in the initial step, followed by microalgae (_Chorella_ sp. MC18 and _Scenedesmus_ sp. MJ23-R) in a second stage. _Lemma minor_ presents attributes that make it a promising candidate for treating raw whey [11]: (i) high nutrient uptake efficiency, particularly for nitrogen and phosphorus, along with strong phytoremediation capabilities that aid in degrading organic compounds in wastewater; (ii) rapid growth and low maintenance, which make it both efficient and cost-effective; (iii) genetic diversity, allowing for selection of optimal strains. Similarly, microalgae from the genera _Chlorella_ and _Scenedesmus_ have also proven effective in wastewater remediation [12]. To test our hypothesis, batch culture experiments in flasks were conducted to assess the individual tolerance of the microalgae and the macrophyte to raw whey. Next, a sequencing batch photobioreactor system, utilizing _Lemma minor_ in the initial treatment step and microalgae in the subsequent polishing stage, was operated.