Valorization of Second Cheese Whey Through Microalgae-Based Treatments: Advantages, Limits, and Opportunities

Abstract

The dairy sector produces considerable amounts of nutrient-rich effluents, which are frequently undervalued as simple by-products or waste. In particular, Second Cheese Whey (SCW), also known as scotta, exhausted whey, or deproteinized whey, represents the liquid fraction from ricotta cheese production. Despite its abundance and high organic and saline content, SCW is often improperly discharged into terrestrial and aquatic ecosystems, causing both environmental impact and resource waste. The available purification methods are expensive for dairy companies, and, at best, SCW is reused as feed or fertilizer. In recent years, increasing awareness of sustainability and circular economy principles has increased interest in the valorization of SCW. Biological treatment of SCW using microalgae represents an attractive strategy, as it simultaneously reduces the organic load and converts waste into algal biomass. This biomass can be further valorized as a source of proteins, pigments, and bioactive compounds with industrial relevance, supporting applications in food, nutraceuticals, biofuels, and cosmetics. This review, starting from analyzing the characteristics, production volumes, and environmental issues associated with SCW, focused on the potential of microalgae application for their valorization. In addition, the broader regulatory and sustainability aspects related to biomass utilization and treated SCW are considered, highlighting both the promises and limitations of microalgae-based strategies by integrating technological prospects with policy considerations.

Keywords: biomass production; biotechnological approaches; circular economy; compound recovery; dairy wastewater; sustainable processes.

Figure 1

Cheese-making process and related outputs. The figure summarizes the cheese-making process from milk to final dairy products (in yellow), including cheese and fresh whey cheese. It also illustrates the generation of dairy wastewater streams (in green), such as CW, SCW, and cleaning-in-place (CIP) water.

Figure 2

Estimated volumes of second cheese whey (SCW) generated per country. Values were obtained from ricotta export data (www.tridge.com, accessed on 1 August 2025).

Figure 3

The three main metabolic pathways of microalgal trophic growth: photoautotrophic (light and inorganic carbon), mixotrophic (light with both inorganic and organic carbon), and heterotrophic (organic carbon in the absence of light).

Figure 4

Biorefinery concept of SCW valorization through microalgae cultivation. The process enables SCW bioremediation and the production of biomass, which can be directed to various applications, including biofuels, food and feed, and nutraceuticals.