## 1 Introduction  
One of the primary wastes from landfills is leachate [1]. Landfill leachate is one of the most complex liquid wastes to treat due to its high content of recalcitrant organic compounds, salts, high concentration of ammonia nitrogen, nitrates, phosphates, and dissolved metals [2]. To date, there are different technologies (physical, chemical, and even biological) available for the treatment of this type of waste [3]. However, their low efficiency in reducing the pollutant capacity of this type of liquid waste and their low economic sustainability have led researchers worldwide to explore new technologies [4].  
Microalgae and cyanobacteria are highly diverse photosynthetic microorganisms found in diverse aquatic environments [5]. They are considered one of the novel biotechnological sources of different metabolites such as lipids, carotenoids, proteins, carbohydrates, bioplastics, auxins, mycosporine-like amino acids (MAA), and others [6]. One of the most exciting applications of algae is the removal of nutrients from polluted waters, or phytoremediation [7, 8, 9, 10, 11, 12, 13]. Phytoremediation using microalgae is not new since the first studies were carried out in San Obispo (California) by [PERSON]'s group in the mid-1950s. By employing this principle, it is possible to valorize certain effluents while reducing their impact and producing biomass with metabolites of industrial interest [14, 15].  
According to a SCOPUS search with the keywords \"Landfill AND Leachate AND alga\", during the last 22 years, about 102 scientific papers have been published (Figure 1a), especially in countries like China, United States, Brazil, and others (Figure 1b), which is few compared to other types of wastewaters treated with microalgae. The latter demonstrates the growing interest in searching for strains resistant to landfill leachates.  
The application of algae and cyanobacteria to remove contaminants possesses limitations, such as the high energy input required for the harvesting of biomass [16; 17; 18; 19] and the selection of the proper strain capable of withstanding the toxicity of leachate. Due to the unique chemical composition of this type of waste, a strain (or several strains) with high-growth capacity has not been isolated so far [20]. During the last few years, strains from different genera of microalgae and cyanobacteria such as _Chlamydomonas_ sp. [21; 22], _Chlorella_ sp. [1; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33], _Desmodesmus_ sp. [23; 34], _Picochlororum_ sp. [35], _Scenedesmus_ sp. [23; 24; 28; 29; 34], _Stigeoconium_ sp. [23], _Tetradesmus_ sp. [26], _Microcyts_ sp. [23], _Oscillatoria_ sp. [23; 28]; and even a consortium of microalgae [20] have been studied. Table 1 shows that the most reported concentration of leachate is 10% \(v/v\)[20; 22; 23; 28; 29; 30; 33]; however, some authors claim that higher concentrations of leachate (from 20%, up to undiluted leachate) can also be used by algae and cyanobacteria [24; 26; 32; 36]. In a different approach, [PERSON] et al. [37] demonstrated that a microalgae-bacteria consortium (_Scenedesmus_ sp. and _Paneibacillus_ sp.) can effectively grow in a media with 20% \(v/v\) of leachate, thus removing toxic elements  
Figure 1: Evolution of the number of publications from 2000 to 2022 on the treatment of landfill leachate using microalgal biotechnology (**a**), and their countries of origin (**b**).  
such as heavy metals and organic compounds. The objective of this study was to evaluate the viability of two strains of thermo-tolerant algae to grow in landfill leachate and their synthesis of usable metabolites such as carbohydrates and lipids, offering an alternative for the reduction of the hazardous potential of landfill leachate and the production of high value-added metabolites.