Electrocoagulation of kraft pulp bleaching filtrates to improve biotreatability

• Ano de defesa: 2020
• Autor(a) principal: Coimbra, Eder Carlos Lopes
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa; Engenharia Civil
• Palavras-chave em Português: Biodegradação; Toxicidade; Superfície de resposta (Estatística); Estudos e Caracterização de Efluentes Industriais
• Link de acesso: https://locus.ufv.br//handle/123456789/29824

Bleached kraft pulp mills are well known for high water consumption throughout the production process. Bleaching filtrates, with high color and organic loads, are responsible for the largest volume of total mill wastewater. These filtrates contain many high molecular weight compounds of low biodegradability (BOD 5 /COD ratio). Electrocoagulation as pretreatment of the high-volume bleaching filtrates to lower their organic loads and improve their biodegradability before biological treatment is one approach to improving overall bleached kraft pulp mill effluent treatment. The response surface methodology can be used to develop models to predict effects of the combined electrocoagulation operating factors. In this study, the main objective was to evaluate the potential of electrocoagulation with iron and aluminum electrodes for increasing biological treatability of acid and alkaline eucalypt kraft pulp bleaching filtrates, and to optimize operating conditions (pH, current density and electrolysis time), in order to achieve maximum dissolved BOD 5 /COD ratios. Electrocoagulation with iron and aluminum electrodes was effective for removing recalcitrant dissolved organic matter from acid and alkaline bleaching filtrates and under optimal conditions the biodegradable fraction was always greater than 75% of the total dissolved organic matter after treatment. Electrocoagulation with aluminum electrodes was more efficient in removing true color and estrogenic activity, while filtrates treated with iron electrodes were less toxic to Daphnia similis. Electrocoagulation of at least one filtrate before their combination was more advantageous in removing dissolved organic matter during aerobic biodegradability tests than no pretreatment of either filtrate. Electrocoagulation of both filtrates separately before their combination led to 90% DOC in a five-day biodegradability test, while only 30% DOC removal was achieved in the combined raw filtrates in the same test. Treatment of alkaline filtrate, with aluminum electrodes, followed by combination with raw acid filtrate prior to biological treatment is recommended to reduce additional pH adjustment costs, since only alkaline filtrate needs pH adjustment before electrocoagulation. Finally, electrocoagulation with aluminum electrodes is the more expensive option because of the higher cost of this metal and the higher optimum treatment time and current density. However, electrocoagulation with aluminum electrodes was more efficient in removing recalcitrant organic matter. Keywords: Biodegradability. Response surface. Toxicity. Wastewater.