Toxicity Assessment of Tanning Effluents Treated via Electrocoagulation and Ozonation Using a Bioassay with Lactuca sativa L.

In this study, the aim is to assess the toxicity of tannery wastewater treated with electrocoagulation and ozonation to determine the suitability of the approach for application, while maintaining the environmental quality of receiving water bodies and/or sewer systems. For this, an electrocoagulation reactor and an ozonation tank were built considering current intensity (I), treatment time (T), and ozone concentration O3 as operating factors. Acute toxicity tests were conducted using Lactuca sativa L. lettuce seeds for the raw sample (MI), sample treated with electrocoagulation (EC), and sample treated with EC and ozonation (EC+OZ). The toxicity parameters assessed in this study were the absolute germination (AG), germination index (GI), and average inhibition concentration (EC50). The electrocoagulation reactor achieved 92% removal efficiency for total suspended solid (TSS) and 10% removal efficiency for chemical oxygen demand (COD) with a current intensity of 7A and a treatment time of 30 min. In addition, the COD was further reduced in the ozonation tank by 18% with an ozone dosage of 10 g/h and a contact time of 30 min. Despite these treatments, EC50 values indicated acute toxicity in all three samples. The ANOVA analysis (p value of 0.05) revealed no significant differences between the GI values for the three samples, suggesting that toxicity did not decrease substantially, despite treatment. This is attributed to the incomplete removal of the pollutant load, expressed as COD, and formation of recalcitrant and toxic compounds during treatment processes. This work demonstrates the importance of including the “toxicity” variable in the assessment of treatments to conduct them in an integral way and preserve the environmental quality of receiving water bodies.