The algae turf scrubber (ATS) is an excellent system for nutrient removal in wastewater or water bodies. The purpose of this study was to evaluate the production of periphytic biomass in an ATS system installed in a freshwater reservoir and to recognize biomass composition. Mid-infrared spectroscopic analysis was carried out to identify the main composition and variability of biomass using multivariate analysis. The composition was studied for potentiality to use the periphytic biomass for the industry. As a result, the system produced a dry weight of 4.46 g m−2 day−1 of periphytic biomass. It was determined that the biomass contained 43.71% carbon, 6.03% nitrogen, and 2.87% phosphorus. Protein, lipid, and carbohydrate contents were 19.27%, 5.90%, and 65.9%, respectively. Carbohydrate and protein values indicated that the periphytic biomass has a potential for biofuel, fertilizer, and animal feed, and other products; due to the carbohydrate content, application for fermentative products is relevant.