In addition to producing bioenergy and molecules with high added value, microalgae have been recognized as an efficient microorganism for wastewater treatment. However, a major obstacle preventing its widespread use is the high energy cost of pretreatment, cultivation and downstream processes. Different types of wastewaters have been tested as culture mediums for microalgal biorefinery system. This review gives a summary of the most used microalgae strains for wastewater treatment, as well as information on the physical and chemical characteristics of domestic, agricultural, and industrial wastewaters. It also discusses wastewater pretreatment techniques, nutrient uptake and removal, biomass production and biomolecules productivities. There is also discussion on how microalgae remove contaminants from wastewater. Additionally, the problems and restrictions of microalgae-based wastewater treatment are explored, and recommendations are made for additional study and advancement. This literature review demonstrates that microalgae monoculture systems have proven to be beneficial as an innovative wastewater treatment technology, due to its high efficiencies in pollutant removals and biomolecule production; however, the upstream and downstream treatment pose a limit to industrialize the process. Until now, there has been no conventional design of the wastewater treatment process using microalgae in the biorefinery system, which constitutes a huge gap to assess a real life cycle assessment (LCA) and techno economic analysis (TEA).

Phycoremediation of wastewater with microalgae is a viable option and is considered a process for cleaning up toxic waste using microalgae or macroalgae. Most water is modified by its use and must be treated before discharge. Given this situation, and following the example of other researchers around the world, our study focuses on the filtration method and combines it with the microalgae method to treat domestic wastewater. The aim of our work is to study the effects of using the microalgae system in combination with the decontamination and filtration system to reduce the nutrient content of domestic wastewater. The coupling of the two methods produced very significant results. However, the removal efficiencies for the filtered effluent increased to 86.34%, 100%, and 91.12% for COD, ammonia, and phosphate, respectively. The algae treatment offers an ecologically safe and less expensive system for nutrient removal and eliminates the need for tertiary treatment, which refers to the filtered treatment effluent, allowing us to conclude that the Chlorella vulgaris species has a very interesting influence on dissolved oxygen and that it had a very remarkable effect on COD, with a maximum reduction that reached 80%. The results obtained show that the phosphate content of the treated wastewater was significantly reduced during the cultivation period. In time, a decrease in solids was observed within the microalgae treatment system, influenced by the use of two different types of microalgae and the incorporation of the filtration system, which is based on the use of biosorption of methylene blue by biomass. The parameters analyzed in this study are hydrogen potential (pH), ammonia (NH₃), phosphate ion (PO₄³⁻), chemical oxygen demand (COD), electrical conductivity (EC), total solids (TS), total dissolved solids (TDS), total suspended solids (TSS), nitrates, and dissolved oxygen (DO).