The global population growth and the westernization of cultures causes an increase in animal-based protein demand. Current agriculture will not be adequate to meet this demand in a sustainable manner. A more efficient protein production is needed utilizing less resources like fertilizers, water and energy. This can be achieved by a microbial protein production approach. Through the use of microorganisms, feed or food can be decoupled from land use, minimizing water use whilst increasing nutrient uptake. However, a feedstock still needs to be supplied. Nevertheless, due the versatility of microorganisms, a broad spectrum of feedstocks can be used, even industrial side streams can be exploited. One of these streams is cheese whey containing high value compounds such as lactose, minerals and vitamins. However, one vital component is missing to improve the protein production specifically nitrogen. This limiting factor can be provided by the agriculture side streams producing biogas and nitrogen rich digestate. To that end, we will study three possible protein production approaches valorizing both side streams. In a first part we will screen different microorganisms and their ability to grow in the salt concentrated whey environment. Secondly, the three protein production routes will be optimized and evaluated in regards of environmental impact and economic feasibility. Finally, the proposed route will be validated on lab-scale in regard to side stream valorization.