Acute ecotoxicity on Daphnia magna to evaluate effluent samples of Kraft pulp mill treated by UV/H2O2 process

Abstract The pulp and paper industry is one of world’s largest water consumers, generating high volumes of effluents. The Kraft process produces effluents with high BOD, COD, suspended solids, lignin and a myriad of potentially toxic compounds, which require treatment before discharge into the aquatic environment. Advanced oxidation processes, such as UV/H2O2, have been applied as treatment alternatives because they can destroy many compounds before they mineralize. However, when the oxidation process is incomplete, occurs could be produced by products with high toxicity. This study evaluated the acute toxicity on Daphnia magna of two effluent samples of Kraft pulp mill (KE1 and KE2) treated by UV/H2O2 process. The effects of the pH variation and oxidant concentration on the removal of DOC, total UV-vis spectral area and apparent color were considered to adjust the experiments’ conditions with diluted effluent KE1. Both samples were treated at pH 4.0 and 70 mg L-1 of H2O2 for 40 min, achieving removals of up to 69.4% in apparent color, 73.7% of phenolic compounds and 68.9% of lignin compounds. When the reaction was applied in undiluted effluent samples, the acute toxicity for Daphnia magna decreased for KE1 after 780 min of treatment, whereas KE2 became four times more toxic. The data showed that although the treatment had been efficient considering physics and chemicals parameters, it is necessary follow the oxidative processes with ecotoxicological bioassays to guarantee their safety, since different effluents of the Kraft pulp mill could present different levels of organic compound mineralization.

摘要 制浆造纸工业是全球最大的用水行业之一，会产生大量废水。硫酸盐制浆法（Kraft process）所产生的废水含有高浓度生化需氧量（Biochemical Oxygen Demand, BOD）、化学需氧量（Chemical Oxygen Demand, COD）、悬浮固体、木质素以及多种潜在有毒化合物，这类废水在排入水生环境前必须经过处理。高级氧化工艺（Advanced Oxidation Processes）如紫外/过氧化氢（UV/H₂O₂）已被用作废水处理的替代方案，因为它们可在多数有机化合物完全矿化前将其降解。然而，若氧化过程不完全，则可能生成高毒性副产物。本研究评估了经紫外/过氧化氢工艺处理的两处硫酸盐制浆厂废水样品（KE1与KE2）对大型溞（Daphnia magna）的急性毒性。以稀释后的KE1废水为研究对象，本实验考察了pH值变化与氧化剂浓度对溶解性有机碳（Dissolved Organic Carbon, DOC）、总紫外-可见光谱面积及表观色度去除效果的影响，以此优化实验条件。两处样品均在pH=4.0、过氧化氢投加量为70 mg·L⁻¹的条件下处理40 min，最终表观色度去除率可达69.4%，酚类化合物去除率达73.7%，木质素类化合物去除率达68.9%。当对未稀释的废水样品进行处理时，KE1样品对大型溞的急性毒性在处理780 min后有所降低，而KE2样品的毒性则升高至原来的4倍。研究数据表明，尽管该处理工艺在物理与化学参数层面表现高效，但仍需配套开展生态毒理学生物测试以跟进氧化过程，确保废水排放的安全性，因为不同硫酸盐制浆厂的废水可能呈现出不同程度的有机化合物矿化水平。