Eletrocoagulação de filtrados de branqueamento de polpa kraft para melhorar sua biotratabilidade

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.A fábrica de polpa kraft branqueada é bem conhecida pelo alto consumo de água dentro dos seus setores sequenciais de fabricação. Como fonte de uma variedade de poluentes orgânicos, os filtrados da unidade de branqueamento são responsáveis pelo maior volume, quantidade de cor e matéria orgânica dos efluentes da fábrica. Além disso, esses filtrados são constituídos por compostos com alta massa molar que levam a uma baixa relação DBO 5 /DQO e, portanto, resistência à degradação biológica. O uso do pré-tratamento branqueamento para por reduzir eletrocoagulação suas cargas dos volumosos orgânicas e filtrados melhorar de sua biodegradabilidade antes do tratamento biológico é uma abordagem para melhorar o tratamento geral de efluentes da fábrica de polpa kraft branqueada. A metodologia da superfície de resposta pode ser usada para o desenvolvimento de modelos para prever os efeitos dos fatores operacionais combinados de eletrocoagulação. Nesse estudo, o objetivo principal foi avaliar o potencial da eletrocoagulação com eletrodos de ferro e alumínio para a melhora da biotratabilidade de filtrados ácido e alcalino de branqueamento de polpa kraft de eucalipto, otimizando as condições operacionais de densidade de corrente, pH e tempo de eletrólise para alcançar as respostas máximas de DBO 5 /DQO dissolvida, por meio da metodologia de superfície de resposta. Os resultados mostram que a eletrocoagulação com eletrodos de ferro e alumínio foi extremamente adequada para remover a matéria orgânica dissolvida recalcitrante dos filtrados de branqueamento ácido e alcalino e, nas condições ideais, a fração biodegradável foi superior a 75% da fração total da matéria orgânica dissolvida remanescente. Os tratamentos envolvendo o eletrodo de alumínio mostraram-se mais eficientes na remoção da cor verdadeira e da atividade estrogênica, enquanto aqueles com ferro apresentaram menor toxicidade à Daphnia similis. Os testes de biodegradabilidade aeróbia mostraram que o tratamento de pelo menos um filtrado com eletrocoagulação é mais vantajoso na remoção de matéria orgânica dissolvida dos filtrados combinados, sob condições aeróbias, do que nenhum tratamento usado em quaisquer dos dois filtrados. A combinação dos dois filtrados tratados separadamente resultou em remoção de 90% do carbono orgânico dissolvido (COD) em cinco dias, enquanto, na mistura dos filtrados no estado bruto, no mesmo período, houve remoção de apenas 30% do COD. Para evitar custos adicionais de ajustes de pH, recomenda-se o tratamento apenas do filtrado alcalino, com eletrodo de alumínio (AlF-Al), para em seguida, o seu envio ao tratamento biológico combinado com o filtrado ácido bruto (AcF). Nessa configuração, é necessário apenas o ajuste inicial de pH do filtrado alcalino, antes ao processo de eletrocoagulação, uma vez que, na situação de mistura e envio à estação de tratamento não é necessário o ajuste. Por fim, os custos de operação dos tratamentos dos filtrados ácido e alcalino com eletrodos de alumínio são mais caros do que com eletrodos de ferro, devido, além dos maiores tempos e densidade de corrente aplicados, ao preço comercial do alumínio ser mais caro. Entretanto, os tratamentos com eletrodos de alumínio se mostraram mais vantajosos na remoção de matéria orgânica recalcitrante. Palavras-chave: Biodegradabilidade. Superfície de Resposta. Toxicidade. Efluentes

Removing Mn, Cu and Fe from Real Wastewaters with Macrophytes: Reviewing the Relationship between Environmental Factors and Plants’ Uptake Capacity

Heavy metal pollution creates environmental health concerns. Among these, iron (Fe), copper (Cu) and manganese (Mn) are commonly found in aquatic environments due to the release of wastewaters. Phytoremediation in hydroponics uses macrophytes to treat contaminated environments, and this is influenced by environmental factors. However, the relationship between these factors and the removal of Fe, Cu and Mn by macrophytes is not known. Therefore, a meta-analysis serves to determine the correlations between environmental factors and the removal of these metals in real wastewater by macrophytes, as well as to identify the role of different aquatic forms of macrophytes in phytoremediation. Emergent macrophytes had higher concentrations of manganese in their tissues, and higher bioconcentrations factor of iron and manganese than floating plants. Regardless of the biotope, higher concentrations of Fe and Cu decreased the ability of plants to bioconcentrate them. The correlations among exposure time, pH, dissolved oxygen, nitrogen, phosphorus, photoperiod and metal phytoremediation by plants were also found. It can be concluded that the emergent macrophytes showed better performance in terms of the removal of Fe, Cu and Mn, and that the significant correlations between environmental factors and removal vary with the type of metal and the environmental factor analyzed

ADMI color and toxicity reductions in raw textile mill effluent and dye mixtures by TiO2/UV is limited by presence of vat dyes

Full-scale application of heterogeneous photocatalysis for industrial wastewater treatment remains a challenge because of the complex nature of these matrices and the potential to form toxic by-products during treatment. A recent unsuccessful attempt to find adequate conditions for TiO2/UV treatment of a cotton dyeing textile mill led to this study on the treatability of mixtures of the dyes used in the greatest amounts at the mill and therefore most likely to be present in mill effluent. Four reactive and three vat dyes were mixed in different combinations and treated (10 mg/L of each dye, 0.5 mg/L TiO2, pH 4) to evaluate the influence of the different dyes on ADMI color, chemical oxygen demand (COD), and acute toxicity. While ADMI color removal was similar in all dye mixtures, COD removal was higher when vat dyes were absent. When treated individually, vat dyes exhibited greater recalcitrance, with no ADMI color removal and COD removals of less than 30%. Toxicity to Daphnia similis was decreased or eliminated from dye mixtures that exhibited the highest COD removals and corresponded to those in which reactive dyes were partially degraded. For raw textile mill effluent, photocatalysis reduced but did not eliminate treated effluent toxicity (EC50 = 26.8%)

Swine Wastewater Treatment in Constructed Wetland Systems: Hydraulic and Kinetic Modeling

The use of constructed wetland systems (CWS) is presented as an alternative for the treatment of effluents since these have reduced implementation costs and relative ease of operation. The present research was undertaken to evaluate to study the hydrodynamic and the fitting of first-order mathematical kinetic models for the removal of pollutants in CWS. Three CWS were built, using expanded clay as filter support: one cultivated with Polygonum punctatum (CWSw), another cultivated with Chrysopogon zizanioides (CWSV), and a control unit (CWSc). The actual retention time was 3.12 days in the CWSc, whereas, in the CWSw and CWSv, we observed values of 4.14 and 4.11 days, respectively. The dispersion values were high in all CWS. The values of chemical oxygen demand (COD) across the length of the CWS were used to fit the kinetic models that describe the first-order decay of organic matter over the CWS. The models that showed a better fit to the experimental data were the plug-flow with residual concentration, the continuous stirred tank reactor, and Shepherd’s models

Swine Wastewater Treatment in Constructed Wetland Systems: Hydraulic and Kinetic Modeling

The use of constructed wetland systems (CWS) is presented as an alternative for the treatment of effluents since these have reduced implementation costs and relative ease of operation. The present research was undertaken to evaluate to study the hydrodynamic and the fitting of first-order mathematical kinetic models for the removal of pollutants in CWS. Three CWS were built, using expanded clay as filter support: one cultivated with Polygonum punctatum (CWSw), another cultivated with Chrysopogon zizanioides (CWSV), and a control unit (CWSc). The actual retention time was 3.12 days in the CWSc, whereas, in the CWSw and CWSv, we observed values of 4.14 and 4.11 days, respectively. The dispersion values were high in all CWS. The values of chemical oxygen demand (COD) across the length of the CWS were used to fit the kinetic models that describe the first-order decay of organic matter over the CWS. The models that showed a better fit to the experimental data were the plug-flow with residual concentration, the continuous stirred tank reactor, and Shepherd’s models

ADMI color and toxicity reductions in raw textile mill effluent and dye mixtures by TiO2/UV is limited by presence of vat dyes

Full-scale application of heterogeneous photocatalysis for industrial wastewater treatment remains a challenge because of the complex nature of these matrices and the potential to form toxic by-products during treatment. A recent unsuccessful attempt to find adequate conditions for TiO2/UV treatment of a cotton dyeing textile mill led to this study on the treatability of mixtures of the dyes used in the greatest amounts at the mill and therefore most likely to be present in mill effluent. Four reactive and three vat dyes were mixed in different combinations and treated (10 mg/L of each dye, 0.5 mg/L TiO2, pH 4) to evaluate the influence of the different dyes on ADMI color, chemical oxygen demand (COD), and acute toxicity. While ADMI color removal was similar in all dye mixtures, COD removal was higher when vat dyes were absent. When treated individually, vat dyes exhibited greater recalcitrance, with no ADMI color removal and COD removals of less than 30%. Toxicity to Daphnia similis was decreased or eliminated from dye mixtures that exhibited the highest COD removals and corresponded to those in which reactive dyes were partially degraded. For raw textile mill effluent, photocatalysis reduced but did not eliminate treated effluent toxicity (EC50 = 26.8%)