Acute Toxicity Assessment of Textile Wastewater Treated with Pinus patula Biochar Using Daphnia pulex

The discharge of textile wastewater (TWW) into the environment releases multiple toxic substances that pose a significant threat to aquatic life. Most studies evaluating wastewater treatment efficiency focus on the removal of parameters, such as chemical oxygen demand (COD), total organic carbon (TOC), dissolved organic carbon (DOC), biochemical oxygen demand (BOD), and colour. One of the processes that has presented high efficiencies in the treatment of TWW is the use of biochar (BC) as an adsorbing material. BC has shown a high ability to remove complex organic substances from water since it is able to decrease the content of COD, TOC, and DOC. However, the toxicity of treated effluents has not been widely studied. In this regard, it is essential to focus not only on the efficiency of treatments in removing organic matter but also on their ability to reduce WW toxicity. This research evaluates the acute toxicity of real TWW treated with Pinus patula BC by using Daphnia pulex as a sentinel species. For this purpose, D. pulex individuals were exposed to TWW and BC-treated TWW for 48 h, with mortality defined as the absence of movement in the limbs and antennas. It was found that although the treatment with P. patula BC for 120 min eliminated 72.8% of the initial DOC under optimal conditions (pH 3 and 13.5 g/L BC dose), the textile effluent remained toxic, inducing 85.7% and 71.4% mortality rates on D. pulex for 100% (v/v) and 50% (v/v) dilutions. Despite the increase in the survival rate of D. pulex individuals due to the protective effect achieved by the constituents contained in the reconstituted 50% (v/v) samples, these findings emphasize the necessity of conducting toxicity studies before considering the discharge of TWW effluents after having been treated.