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

Aguilar-Ascón Edwar, Marrufo-Saldaña Liliana, Barra-Hinojosa Julio Alexis

Journal of Ecological Engineering

2024

Vol. 25, nr 9

316--327

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.

Combining Effluent Treatment Methods to Remove Ammonia Nitrogen from Tannery Wastewater

Aguilar-Ascón Edwar, Marrufo-Saldaña Liliana, Barra-Hinojosa Julio Alexis

Ecological Engineering & Environmental Technology

2024

Vol. 25, iss. 12

371--386

This study assessed the removal efficiency of ammonia nitrogen from tannery wastewater by combining electrocoagulation, ozonation, and ion exchange technologies. For this purpose, an electrocoagulation reactor equipped with aluminum electrodes, an ozonation tank, and a filtration system with zeolite were employed. The electrocoagulation treatment applied the response surface methodology with a 3k factorial design with the following two factors: current intensity (I) ranging from 3 to 7A, and treatment time (t) from 10 to 30 min; the removal percentage of total suspended solids (TSS) is set as a response variable. Results indicate that the treatment time and current intensity were significant for the removal of total suspended solids TSS, at a confidence level of p < 0,05. Under these conditions, a TSS, removal efficiency of 98% was achieved. Through the electrocoagulation process, the chemical oxygen demand (COD) was reduced by 58%, while in the ozonation tank, an additional 23% of COD was removed. The filtration stage demonstrated that 13X HP zeolite can exchange ions with the ammonia nitrogen from tannery wastewater, wherein a 39% removal efficiency is reached at equilibrium. Thus, the integration of various treatment methods is a viable alternative to reduce wastewater from the tannery industry. The novelty of this research lies in the integration of three methods for treating tannery wastewater. The results show that the combination of these treatments provides a more effective solution for removing the pollutant load, especially nitrogen, compared to the use of individual treatment methods alone. The study opens new perspectives for optimizing multi-stage treatment processes.