One of the main limitations of commercial production of algae is the cost of cultivation, largely attributed to the cost of the nutrients; hence, finding cheap alternative substrates has been a significant line of research in this field. The dairy industry produces large amounts of wastewater that might be used as a cost-effective nutrient alternative, containing lactose as a main carbon source, as well as other essential nutrients like nitrogen and phosphate. Nevertheless, just a few algal species of commercial value can grow on any organic carbon sources, and even less are able to utilize lactose. In this work we have identified a Parachlorella kessleri strain capable of utilizing lactose for growth, and have characterized its ability to accumulate metabolites of commercial interest under heterotrophic growth conditions. P. kessleri was capable to utilize lactose from dairy wastewater, and to accumulate several amino acids, dicarboxylic acids, such as tartaric acid and succinic acid, and triacylglycerols in heterotrophic conditions. These metabolites have applications in the food, feed, and pharmaceutical industries, and in the green chemical industry for the production of bio-based green polymers and biofuels. The significance of these findings for future product development is discussed.