This dataset presents the results of hydrothermal carbonization (HTC) performed on residual microalgal biomass obtained after anaerobic digestion. The microalgal biomass, grown in 90% brewery wastewater (WW) and processed for pigment extraction, underwent HTC at three different temperatures (180°C, 210°C, and 240°C) to assess its potential for biochar production and liquid phase valorization. Experimental Details: Hydrothermal Carbonization (HTC): Solid-to-liquid ratio: 1.5 g biomass per 32 mL anaerobically digested effluent. HTC reactors: Small stainless-steel reactors (40 mL capacity) operated in a convection oven (Carbolite AX 30). Reaction conditions: 180°C, 210°C, and 240°C for 3 hours. Cooling method: Submerged in cold water post-reaction. Biochar Recovery: Separation: Filtration using Whatman filter paper. Measurement: Dried biochar mass used to calculate yield. Biochar Characterization: Thermal Stability: Evaluated through Thermogravimetric Analysis (TGA). Elemental Analysis: C, H, N, S measured using a Flash 2000 Elemental Analyzer. Samples processed in duplicate for accuracy. ICP Analysis (ICP-OES; iCap 7000 Series Thermo Scientific, USA): Biochar digested in concentrated HNO₃ and analyzed via ICP for elemental composition. FTIR Spectroscopy (Nicolet, USA): Functional group analysis for potential applications in adsorption and soil amendments. Liquid Phase Characterization: Bio-oil extracted from the aqueous phase using ethyl acetate. Data Analysis: One-way ANOVA in Microsoft Excel was followed by a post hoc Tukey test to compare group means. Data processing:FTIR data was smooshed using available code from "https://github.com/cran/signal/blob/master/R/sgolayfilt.R" The FTIR data were smoothed using the Savitzky-Golay algorithm in RStudio to enhance signal clarity while preserving peak features. The code was already existed in "https://github.com/cran/signal/blob/master/R/sgolayfilt.R"The smoothing process involved the following steps: The raw FTIR data, consisting of wavenumber and intensity values, were imported into RStudio. The Savitzky-Golay filter was applied using the sgolayfilt() function from the signal package. The filter was configured with a polynomial order of 3 and a window size of 201 points, ensuring an odd-length window for accurate filtering. This method effectively reduced noise while retaining the integrity of spectral features, making the data suitable for further analysis. Dataset Includes: Biochar yield and thermal stability data. Elemental composition results (C, H, N, S, and ICP analysis). FTIR spectroscopy results for functional group identification. Wastewater characteristics. Purpose:The dataset aims to evaluate the potential of HTC as a valorization pathway for residual microalgal biomass, supporting sustainable biochar production and the circular bioeconomy.