Influência da pré-cloração na clarificação de águas para abastecimento utilizando coagulante à base de tanino / Pre-chlorination effects on drinking water treatment using tannin-based coagulant

RESUMO Diferentes técnicas de tratamento de água destinada ao abastecimento público, como a pré-cloração e o uso de coagulantes orgânicos, têm sido relatadas como alternativas econômica, técnica e ambientalmente viáveis. Entretanto, o resultado da interação entre esses processos deve ser estudado para sua aplicação com segurança. Dessa forma, este estudo objetivou avaliar a influência da pré-cloração na clarificação de água para abastecimento público, utilizando coagulante à base de tanino. Os ensaios foram conduzidos em jar test com o uso de Tanfloc SG como coagulante, variando as dosagens de 2,5 a 45,0 mg L−1, e de oxidante hipoclorito de sódio (NaClO) nas concentrações de cloro residual livre (HClO(NaClO)) de 0,8 e 5,0 mg L−1, no tratamento da água do ribeirão João Leite. As dosagens ótimas de coagulante foram determinadas para as seguintes condições de tratamento: adição somente de tanino; tanino e NaClO aplicados simultaneamente; e tanino adicionado após 30 min da pré-cloração. Nessas condições, o pH de coagulação foi analisado de 6,0 a 8,5. Foram avaliados parâmetros como turbidez, cor aparente, pH e HClO(NaClO). A melhor condição de tratamento com pré-cloração foi a adição simultânea de NaClO e coagulante tanino nas dosagens de 0,8 mg L−1 (HClO(NaClO)) e 10,0 mg L−1, respectivamente, com remoção de turbidez de 71,6% e cor aparente de 62,7%. Os resultados demonstraram que a pré-cloração afetou negativamente o processo de tratamento, e para maior concentração de HClO(NaClO) maior foi a dosagem de tanino requerida, sem apresentar aumento significativo nas eficiências de remoção de turbidez e cor aparente.

ABSTRACT Different techniques in the treatment of water intended for public supply such as pre-chlorination and use of organic coagulants have been reported as economic, technical and environmental viable alternatives. However, the result of the interaction between these processes should be studied for their safe application. Thus, this study aimed to evaluate the influence of pre-chlorination on coagulation and flocculation of water for public supply using a tannin-based coagulant. The assays were conducted in Jar Test using Tanfloc SG as a coagulant, varying the dosages from 2.5 to 45.0 mg L−1, and sodium hypochlorite oxidant (NaClO) in the concentrations of free residual chlorine (HClO(NaClO)) of 0.8 and 5.0 mg L−1, in the water treatment of João Leite River. Optimal coagulant dosages were determined for the following treatment conditions: addition of tannin only; tannin and NaClO applied simultaneously; and, tannin added after 30 min of pre-chlorination. Under these conditions, the coagulation pH was analyzed from 6.0 to 8.5. Parameters such as turbidity, apparent color, pH and HClO (NaClO) were evaluated. The best treatment condition with pre-chlorination was the simultaneous addition of NaClO and coagulant at dosages of 0.8 mg L−1(HClO(NaClO)) and 10.0 mg L−1 respectively, with turbidity removal of 71.6% and apparent color of 62.7%. In general, the results showed that pre-chlorination negatively affected the process being that the higher concentration of HClO(NaClO) the higher tannin dosage, without presenting a significant increase in the efficiencies of turbidity and apparent color removal.

Reaproveitamento de sabugo de milho para potencial remoção de formulação comercial de glifosato em fase aquosa pela técnica de adsorção / Corn cob reuse in the adsorption of a commercial formulation of glyphosate

RESUMO Neste estudo, foi produzido biocarvão de sabugo de milho ativado com ácido fosfórico (BCA) para potencial remoção do herbicida glifosato — GLF (formulação comercial) em meio aquoso. O BCA foi caracterizado por análises de difração de raios X, espectroscopia de infravermelho, adsorção e dessorção de N2, microscopia eletrônica de varredura e determinação do potencial de carga zero. O efeito do pH inicial e da massa de adsorvente também foi avaliado. Os resultados cinéticos de adsorção foram ajustados aos modelos de pseudoprimeira e pseudossegunda ordem. A natureza do processo foi estudada por meio dos modelos de isoterma de Langmuir e Freundlich, e os parâmetros termodinâmicos calculados para as temperaturas de 23, 43 e 63°C. Os resultados obtidos demonstraram que a adsorção de GLF no BCA foi dependente da temperatura, da massa de adsorvente e do pH do meio, com a melhor condição de ensaio caracterizada por 63°C, 0,25 g de BCA e pH = 7, resultando em boa eficiência de remoção (62,67%), porém com baixa capacidade de adsorção (2,67 mg.g−1). A cinética de adsorção foi representada pelo modelo de pseudossegunda ordem e considerada rápida, sendo necessários 15 min para atingir 98% da capacidade máxima de adsorção. Os dados da isoterma foram bem descritos pelo modelo de Freundlich. Por fim, o estudo termodinâmico revela que a adsorção de GLF é de natureza endotérmica (∆Hº > 0) e endergônica (∆Gº > 0). Os resultados apresentados confirmam que o BCA de sabugo de milho é um adsorvente capaz de remover GLF (formulação comercial) do meio aquoso.

ABSTRACT In this study a biochar was produced from corn cob (BCA), which was activated with phosphoric acid to verify its potential for removal of herbicide glyphosate (GLF) (commercial formula) in aqueous media. BCA was characterized by X-ray diffraction spectroscopy, infrared spectroscopy, sorption and desorption of N2, scanning electron microscope, and zero charge potential. Kinetic results of adsorption were adjusted to pseudo-first and pseudo-second order reactions. The adsorption process was studied to verify if it followed Freundlich and Langmuir isotherms, and the thermodynamic parameter was calculated for 23 oC, 43 cC and 63 oC. The results showed that adsorption of GLF on BCA depended on temperature, adsorbent mass, and pH. The best results were obtained for the temperature of 63 oC with 0.25 g de GLF and pH = 7.0, conditions that presented 62.3% of GLF removal and low adsorption capacity (2.67 mg. g−1). That was probably due to the porous nature of BCA and co-adsorption of other constituents that were present in the commercial formula of GLF. The adsorption kinetics was represented by the model of pseudo-second order and considered fast, taking 15 min to reach 98% of the maximum adsorption capacity. The isotherm data were well represented by the Freundlich model. Finally, the thermodynamic study demonstrated that the adsorption of GLF is of endothermic nature (ΔHº > 0) and endergonic (ΔGº > 0). The results confirmed that BCA from corn cob is an adsorbent capable of removing GLF (commercial formula) from aqueous media. However, the endothermic nature of the process can compromise its performance in water treatment processes.

Influência do etanol como cosubstrato na biorremediação de água contaminada com formulação comercial à base de glifosato / Influence of ethanol as a co-substrate on bioremediation of water contaminated with glyphosate-based comercial formulation

RESUMO O presente trabalho objetivou avaliar a eficiência e a cinética de degradação de formulação comercial à base de glifosato em amostras de água, previamente contaminadas, via processo aeróbio, utilizando etanol como cosubstrato no processo. Utilizou-se um reator aeróbio com capacidade volumétrica de 1 L, operado em sistema de batelada sequencial com ciclos de 24 horas e biomassa em suspensão. Foram testadas quatro fases sob diferentes condições nutricionais: 1 sem a presença do etanol e outras 3 com relação etanol:glifosato de 7,8:1, 27,5:1 e 18,3:1. Quando o sistema operou sem a presença de etanol, a eficiência de remoção do glifosato foi de 18%, a qual aumentou para 78% ao se adicionar etanol na relação 7,8:1. No entanto, ao aumentar a concentração de etanol nas demais fases, não foram observadas melhoras na eficiência de remoção devido, provavelmente, à preferência dos organismos pelo uso do etanol como fonte de carbono em relação ao glifosato. Com relação aos ensaios cinéticos, os resultados foram ajustados ao modelo de degradação de pseudoprimeira ordem, considerando o residual de glifosato. A fase 3, com relação etanol:glifosato 27,5:1, foi a que apresentou maior valor da constante cinética aparente, k = 0,01746.min-1. Os resultados obtidos neste estudo indicam que a utilização de etanol como cosubstrato pode ser uma alternativa para a descontaminação de águas contaminadas com glifosato.

ABSTRACT This study aimed to evaluate the efficiency and degradation kinetics of commercial glyphosate formulation in previously contaminated water samples via aerobic process using ethanol as a co-substrate. An aerobic reactor with 1L volumetric capacity operated in sequential batch system with 24-hour cycles and suspended biomass was used. Four different nutritional conditions were tested: one with no ethanol addition; and three others with ethanol: glyphosate ratios of 7.8:1, 27.5:1 and 18.3:1. Operating with no ethanol addition, the efficiency of glyphosate removal was 18% and increased to 78% when ethanol was added to the system in a 7.8:1 ratio. However, when glyphosate concentration was further increased in the next phases, it did not result in higher removal efficiency, probably due to the preference of organisms for ethanol use as a carbon source over glyphosate. The results of the kinetic tests adjusted to first-order degradation models considering residual glyphosate. Phase 3 with 27.5:1 ethanol/glyphosate ratio showed the highest apparent kinetic constant value, k = 0.01746. The results of this study suggest that using ethanol as a co-substrate can be an alternative for decontamination of glyphosate contaminated waters.

Use of Adsorbent Biochar from Pequi (Caryocar Brasiliense) Husks for the Removal of Commercial Formulation of Glyphosate from Aqueous Media

Abstract This study evaluated the capacity of adsorbent biochar derived from pequi husks to remove glyphosate (commercial formulation) in aqueous medium under three pH conditions (5.5, 7.0 and 8.0). This biochar presented a mean yield of 33.1% ± 2.66% and a high amount of surface particles of small dimensions endowing it with high surface area. The results showed that removal is proportional to pH increase in the range of 5.5 to 8.0. Adsorption assays performed at pH 7 and 8 fitted better to the Langmuir pseudo-first order kinetics model with fast adsorption in the first 15 to 30 minutes. The results for the acidic pH range fit none of the adopted models satisfactorily. The results obtained suggest that adsorbent can be used as an efficient and inexpensive alternative for the adsorption of glyphosate present in commercial formulations from aqueous matrices.

Denitrification coupled with methane anoxic oxidation and microbial community involved identification

In this work, the biological denitrification associated with anoxic oxidation of methane and the microbial diversity involved were studied. Kinetic tests for nitrate (NO3-) and nitrite (NO2-) removal and methane uptake were carried out in 100 mL batch reactors incubated in a shaker (40 rpm) at 30 ºC. Denitrificant/methanotrophic biomass was taken from a laboratory scale reactor fed with synthetic nitrified substrates (40 mgN L-1 of NO3- and subsequently NO2-) and methane as carbon source. Results obtained from nitrate removal followed a first order reaction, presenting a kinetic apparent constant (kNO3)) of 0.0577±0.0057d-1. Two notable points of the denitrification rate (0.12gNO3--N g-1 AVS d-1 and 0.07gNO3--N g-1 AVS d-1) were observed in the beginning and on the seventh day of operation. When nitrite was added as an electron acceptor, denitrification rates were improved, presenting an apparent kinetic constant (kNO2) of 0.0722±0.0044d-1, a maximum denitrification rate of 0.6gNO2--N g-1AVS d-1, and minimum denitrification rate of 0.1gNO2--N g-1AVS d-1 at the beginning and end of the test, respectively. Endogenous material supporting denitrification and methane concentration dissolved in the substrate was discarded from the control experiments in the absence of methane and seed, respectively. Methylomonas sp. was identified in the reactors fed with nitrate and nitrite as well as uncultured bacterium.