(doi: /ambi-agua.v5.n2)

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ISSN = 1980-993X (Online) www.ambi-agua.net

Edição 13 da Revista Ambiente & Agua - An Interdisciplinary Journal of Applied Science, Taubaté, v. 5, n. 2, p. 1-235, Agosto 2010. (doi:10.4136/ambi-agua.v5.n2)

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COMITÊ EDITORIAL

Editor

Getulio Teixeira Batista

Instituto de Pesquisas Ambientais em Bacias Hidrográficas (IPABHi), Brasil

Editores Associados

Amaury Paulo de Souza

Universidade Federal de Viçosa (UFV), Brasil

Antonio Evaldo Klar

Universidade Estadual Paulista Júlio de Mesquita Filho, UNESP, Brasil

Dar Roberts

Universidade de Stanford; BA pela Universidade da Califórnia, EUA

Hans Raj Gheyi

Universidade Federal de Campina Grande (UFCG), Brasil

Hélio Nóbile Diniz

Instituto Geológico, Secretaria do Meio Ambiente do Estado de São Paulo (IG/SMA), Brasil

João Vianei Soares

Instituto Nacional de Pesquisas Espaciais (INPE), Brasil

Luis A. Bartolucci

Florida International University (FIU), EUA

Marcelo dos Santos Targa

Universidade de Taubaté (UNITAU), Brasil

Nelson Wellausen Dias

Universidade de Taubaté (UNITAU), Brasil

Paul W. Mausel

Indiana State University (ISU), EUA

Paulo Renato Schneider

Universidade Federal de Santa Maria (UFSM), Brasil

Sebastião do Amaral Machado

Universidade Federal do Paraná (UFPR), Brasil

Silvio Jorge Coelho Simões

Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP), Brasil

Yosio Edemir Shimabukuro

Instituto Nacional de Pesquisas Espaciais (INPE), Brasil

Editor da Seção Editorial Nelson Wellausen Dias, PPGCA, UNITAU, Brasil Editora de Texto Maria de Jesus Ferreira Aires, GELP, UNITAU, Brasil Editora de Referência Liliane Castro, Biblioteca ECA/Civil, UNITAU, Brasil Editor de Layout e Suporte Técnico Tiago dos Santos Agostinho, LAGEO, UNITAU, Brasil

Ficha catalográfica elaborada pelo

SIBi – Sistema Integrado de Bibliotecas / UNITAU

Revista Ambiente e Água - An Interdisciplinary Journal of Applied Science / Instituto de Pesquisas Ambientais em Bacias Hidrográficas. Taubaté. v. 5, n. 2 (2006)- Taubaté: IPABHi, 2010.

Quadrimestral ISSN 1980-993X.

1. Ciências ambientais. 2. Recursos hídricos. I. Instituto de Pesquisas Ambientais em Bacias Hidrográficas. III. Título.

CDD - 333.705 CDU - (03)556.18

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ÍNDICE

CAPA

Análises de Componente Principal e de Agrupamento para estudo de ventos para a geração de energia eólica na região do Ceará, Paraíba, Pernambuco e Rio Grande do Norte, Brasil.

Fonte: LIMA, F. J. L.; AMANAJÁS, J. C.; GUEDES, R. V. S.; SILVA, E. M. Análises de Componente Principal e de Agrupamento para estudo de ventos para a geração de energia eólica na região do Ceará, Paraíba, Pernambuco e Rio Grande do Norte, Brasil. Ambi-Agua, Taubaté, v. 5, n. 2, p. 188-201, 2010. (doi:10.4136/ambi-agua.147)

EDITORIAL

Ambiente & Água no contexto dos indicadores de impacto das revistas científicas brasileiras

(doi:10.4136/ambi-agua.131)

Nelson Wellausen Dias; Getulio Teixeira Batista

4

ARTIGOS

Kinetics and mass transfer of atrazine ozonation (doi:10.4136/ambi-agua.132)

Rafaela Cristina Landeiro da Silva; Roberto José de Carvalho; Bruno Abreu Calfa

9 In vitro effects of petroleum refinery wastewater on dehydrogenase activity in marine bacterial

strains (doi:10.4136/ambi-agua.133)

Christopher E. Nwanyanwu; Gideon O. Abu

21

Mathematical modelling of nutrient balance of a goldfish (Carassius auratus Linn.) recirculating aquaculture system (GRAS) (doi:10.4136/ambi-agua.134)

Mohd Tanveer; Sudeep Puthravilakom Sadasivan Nair; Sanjib Moulick; Chanchal Kumar Mukherjee

30

Land cover change and environmental quality assessment using GIS techniques - a case study in Brazilian Southeastern region for the period 1988 - 2003 (doi:10.4136/ambi-agua.135)

Alexandre Marco da Silva

40

Ammonia removal from leachate by photochemical process using H2O2

(doi:10.4136/ambi-agua.136)

Núbia Natália de Brito; José Euclides Stipp Paterniani; Giovani Archanjo Brota; Ronaldo Teixeira Pelegrini

51

Áreas hidrologicamente sensíveis: teoria e aplicação para a bacia do rio Barigui, PR, Brasil

(doi:10.4136/ambi-agua.137)

Cesar Augusto Crovador Siefert; Irani dos Santos

61

Fatores de retardamento e coeficientes de dispersão-difusão de metais pesados em resíduos da construção civil e demolição (doi:10.4136/ambi-agua.138)

Débora Astoni Moreira; Mauro Aparecido Martinez; José Antonio Rodrigues de Souza; Antonio Teixeira de Matos; César Reis; Flávia Mariani Barros

77

Influência da presença de camada de resíduos de construção civil na remoção de metais pesados em percolado recirculado de aterro sanitário (doi:10.4136/ambi-agua.139)

Katia Gonçalves Gutierrez; Antonio Teixeira de Matos; Maike Rossmann

87

Parametrização de modelos de mineralização do nitrogênio orgânico em solo tratado com água residuária da suinocultura (doi:10.4136/ambi-agua.140)

Flávia Mariani Barros; Mauro Aparecido Martinez; Antonio Teixeira de Matos; Júlio César Lima Neves; Demétrius David da Silva

99

Capacidade máxima de adsorção de Cd, Cu, Pb e Zn em resíduos da construção civil

(doi:10.4136/ambi-agua.141)

Débora Astoni Moreira; Mauro Aparecido Martinez; José Antonio Rodrigues de Souza; César Reis; Efraim Lázaro Reis; Flávia Mariani Barros

112

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Sorção de cromo em solos do cerrado goiano, Brasil (doi:10.4136/ambi-agua.143)

Mara Lucia Lemke-de-Castro; Jácomo Divino Borges; Luiz Fernando Coutinho de Oliveira; Cristiane Rodrigues; Cícero Célio de Figueiredo; Welershon José de Castro

133

Crescimento e desenvolvimento de tomateiro fertirrigado com água residuária da suinocultura

(doi:10.4136/ambi-agua.144)

José Antonio Rodrigues de Souza; Débora Astoni Moreira; Daniel Ferreira Coelho

144

Modelagem hidrossedimentológica de bacia hidrográfica na região sudeste do Brasil, utilizando o SWAT (doi:10.4136/ambi-agua.145)

158

Uso da entropia e da análise de agrupamento na avaliação da disponibilidade potencial de recursos hídricos do Nordeste do Brasil (doi:10.4136/ambi-agua.146)

175 Roni Valter de Souza Guedes; Solange S. de Sousa; Francisco de Assis S. de Sousa

Análises de Componente Principal e de Agrupamento para estudo de ventos para a geração de energia eólica na região do Ceará, Paraíba, Pernambuco e Rio Grande do Norte, Brasil

(doi:10.4136/ambi-agua.147)

188

Francisco José Lopes de Lima; Jonathan Castro Amanajás; Roni Valter de Souza Guedes; Emerson Mariano da Silva

Qualidade da água de abastecimento público de Ribeirão Preto em área de abrangência do Aquífero Guarani: determinação de metais e nitrato (doi:10.4136/ambi-agua.148)

202 Sérgio Marcos Sanches; Eny Maria Vieira; Eliana Leão do Prado; Angela Maria Magosso

Takayanagui

Estimativa do fator topográfico da USLE a partir de três algoritmos (doi:10.4136/ambi-agua.149)

217 Paulo Tarso Sanches de Oliveira; Dulce Buchala Bicca Rodrigues; Teodorico Alves Sobrinho; Elói

Panachuki

Comportamento do usuário na valoração contingente e custo de viagem - O caso do Parque das Palmeiras em Chapecó, SC, Brasil (doi:10.4136/ambi-agua.150)

226 Débora Carneiro Leite; Claudio Alcides Jacoski

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ISSN = 1980-993X - doi:10.4136/1980-993X www.ambi-agua.net

E-mail: [email protected] Phone.: +55 (12) 3625-4212

Ambiente & Água in the context of impact indicators of scientific

Brazilian journals

(doi:10.4136/ambi-agua.131)

Nelson Wellausen Dias; Getulio Teixeira Batista

Professors of the Master Degree Program in Environmental Sciences of Taubaté University Estrada Municipal Dr. José Luiz Cembranelli, 5.000; Bairro Itaim; 12.081-010 - Taubaté, SP

E-mail: [email protected]

For quite some time the international scientific community has criticized the use of impact indicators based only on few journals registered at commercially subscribed databases such as the ISI Web of Knowledge (producer of Journal Citation Reports - JCR). Several studies focusing on different subject areas have demonstrated the advantages and disadvantages of assessing the impact of an article, or journal, from commercial and open-access databases, such as Google Scholar (Segen, 1997; Gisvold, 1999; DuBois and Reeb, 2000; Whitehouse, 2002; Baumgartner and Pieters, 2003; Cameron, 2005; Ha et al., 2006; Mingers and Harzing, 2007). Most of the studies found that there was a strong correlation between impact indicators measured by a commercial databases (restricted) and open-access in certain field areas (Science, Health, Biological and Applied Social), while areas usually with lesser coverage by commercial databases (Environment, Humanities, among others) end up having lower impact indicator values based on these commercial databases. Moreover, the number of publications in these last areas has shown a significant expansion recently and, therefore, they end up receiving greater impact scores when evaluated by open-access databases. In these cases the correlation between impact indicators calculated by restricted versus open-access database is significantly lower.

In order to assess the position of the journal Ambiente & Água, with respect to its performance indicators in comparison with other Brazilian scientific journals, categorized by QUALIS-CAPES Interdisciplinary strata A2, B1, B2 and B3, an analysis was developed based on the values of three indicators calculated for the last five years of 58 Brazilian journals (with publications in thematic areas that overlap with those of Ambiente & Água) subdivided into: 11 of stratum A2, 22 in stratum B1, 8 in stratum B2 and 17 in stratum B3. The first indicator used was the h-index proposed by Hirsch (2005) and defined as: "a scientist has index h if h of his/her Np papers have at least h citations each, and the other (Np-h) papers have no more than h citations each". Thus, the h-index provides a value that is a mix of quantity and quality of articles published by a researcher, if quality is measured by citations. According to Bornmann and Daniel (2007) the h-index favors a researcher who publishes a series of articles over time with an above average impact measurement. The same concept is applied to calculate the impact of a scientific journal. The second indicator used was the g-index proposed by Egghead (2006) which is defined as: " [Given a set of articles] ranked in decreasing order of the number of citations that they received, the g-index is the (unique) largest number such that the top g articles received (together) at least g2 citations”. The third indicator used was the AW-index which was proposed based on a note published by Jin (2007) that gave origin to the AWCR indicator that uses a weighted age factor and measures a bundle of articles adjusted for the age of their publication. The AW-index corresponds to the square root of the AWCR that allows a more direct comparison with the h-index (Spiroski and Gogusev, 2008).

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DIAS, N. W.; BATISTA, G. T. Ambiente & Água in the context of impact indicators of scientific Brazilian journals. Ambi-Agua, Taubaté, v. 5, n. 2, p. 4-8, 2010.(doi:10.4136/ambi-agua.131)

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Figure 1 presents the results of the comparative values of the h-index and g-index for the journal Ambiente & Água and 58 other Brazilian scientific journals that were analyzed. It is evident from the figure that there is a high correlation between these indicators, which, numerically, were expressed as 0.99 for stratum A2, 0.90 for stratum B1, 0.99 for stratum B2, and 0.89 for stratum B3. The relative position of Ambiente & Água in all four strata is remarkable. In the A2 graphic Ambiente & Água surpasses three other journals and positions itself in the lower quarter of an imaginary regression line crossing all points. In the B1 stratum this journal moves slightly toward higher impact indicators, but if an imaginary cluster was drawn that surrounds most of the journals in this stratum (with values between 2 and 10 for both indicators), it could be stated that the position of Ambiente & Água would be in the center of this group. In the B2 stratum the relative position of this journal continues to progress toward higher impact values compared to earlier graphics and, again, positions itself ahead of three other journals in this category. In stratum B3 (which is the current rank of Ambiente & Água), it should be noted the relative value of the g-index value of this journal, which is surpassed by only one of the other journal while in the h-index only by three.

Based on the results presented in Figure 1 it is correct to state that Ambiente & Água has shown outstanding performance, in these five years of its brief history, as a scientific publication with significant impact when measured by indicators that use data from open-accessed databases. 0 5 10 15 20 25 30 0 5 10 15 20 H-Index G-Inde x

Interdisciplinar A2 Ambiente & Água

0 5 10 15 20 25 30 35 0 5 10 15 20 H-Index G -I nde x

Ambiente & Água Interdisciplinar B1

0 2 4 6 8 10 12 14 16 18 20 0 5 10 15 H-Index G-Inde x

0 2 4 6 8 10 12 0 2 4 6 8 10 12 H-Index G -I nde x

Interdisciplinar B3 Ambiente & Água

Figure 1. Comparison between h-index and g-index values of the journal Ambiente & Água and 58

Brazilian scientific journals subdivided in the strata A2, B1, B2, and B3 of the Interdisciplinary area of QUALIS-CAPES ranking.

Figure 2 shows the comparative results between the h-index and AW-index of the same journals. The distribution patterns among the four strata are clearly related to the patterns of

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Figure 1. If on the one hand it shows little innovation in terms of new information, on the other it confirms the relative position of the journal Ambiente & Água in relation to the other Brazilian journals analyzed. It is worth emphasizing one aspect observed in stratum B3, where the AW-index value of the journal was passed only by two others, while the h-index shows the same pattern. 0 5 10 15 20 25 30 0 5 10 15 20 H-Index A W -I nde x

Ambiente & Água Interdisciplinar A2

0 5 10 15 20 25 0 2 4 6 8 10 12 14 16 18 20 H-Index A W -I nde x

Interdsiciplinar B1 Ambiente & Água

0 2 4 6 8 10 12 14 16 18 0 5 10 15 H-Index A W -I nde x

0 2 4 6 8 10 12 0 2 4 6 8 10 12 H-Index A W -I nde x

Figura 2. Comparison between h-index and AW-index values of the journal Ambiente & Água and 58

Brazilian scientific journals subdivided in the strata A2, B1, B2, and B3 of the Interdisciplinary area of QUALIS-CAPES ranking.

Figure 3 complements the comparative analysis between the three impact indicators and presents the comparison values between g-index and AW-index. The distribution patterns of values in the charts, although similar to previous ones, show some significant differences. The pattern of stratum B1, for example, is more clearly divided into two clouds (or clusters) of points, one denser with values below 12 in both indicators and other with a more scatter pattern above value 15. But once again the position of Ambiente & Água is toward the center of the denser cloud. In stratum B2, although quite similar to the previous ones, it should be noted that the journal is positioned ahead of four other journals. In the group B3 the relative position of Ambiente & Água is still higher compared with the previous ones, being surpassed by only two other journals in the comparison of these indicators.

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7 0 5 10 15 20 25 30 0 5 10 15 20 25 30 G-Index A W -I nde x

Interdisciplinar A2 Ambiente & Água

0 5 10 15 20 25 0 10 20 30 40 G-Index AW -I n d e x

0 2 4 6 8 10 12 14 16 18 0 5 10 15 20 G-Index AW-I n d e x

Interdsiciplinar B2 Ambiente & Água

0 2 4 6 8 10 12 0 2 4 6 8 10 12 G-Index AW-In d e x

Figure 3. Comparison between g-index and AW-index values of the journal Ambiente & Água and

58 Brazilian scientific journals subdivided in the strata A2, B1, B2, and B3 of the Interdisciplinary area of QUALIS-CAPES ranking.

In this exercise, developed to obtain impact values of various Brazilian scientific journals in international open-access databases, not only it could be demonstrated the role that the journal Ambiente & Água withholds in the national scientific community (and even international if considered the information published in previous editorials), but also witnesses the degree of efficiency, transparency, and simplicity of the indicators used.

The Editorial Board of the journal Ambiente & Água stands in favor of using indicators that are transparent, simple, and free of charge in the process of assessing the impact of published articles and scientific Brazilian journals.

REFERERENCES

BAUMGARTNER, H.; PIETERS, R. The structural influence of marketing journals: a citation analysis of the discipline and its subareas over time. Journal of Marketing, v. 67, 123-39, 2003.

BORNMANN, L.; DANIEL, H. D. What do we know about the h index? Journal of the

American Society for Information Science and Technology, v. 58, p. 1381-1385,

2007.

CAMERON, B. D. Trends in the usage of ISI Bibliometric Data: uses, abuses, and implication.

Portal: Libraries and the Academy,v. 5, p. 105-125, 2005.

DUBOIS, F. L.; REEB, D. Ranking the international business journals. Journal of

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EGGHE, L. Theory and practice of the g-index. Scientometrics, v. 69, p. 131-152, 2006. GISVOLD, S. E. Citation analysis and journal impact factors – is the tail wagging the dog?

Acta Anaesthesiol Scand, v. 43, p. 971-973, 1999.

HA, T. C.; TAN, S. B.; SOO, K. C. The journal impact factor: too much of an impact? Annals

Academy of Medicine, v. 35, 911-916, 2006.

HIRSCH J. E. An index to quantify an individual's scientific research output. Proceedings of

the National Academy of Sciences, v.102, p.16569–16572, 2005.

JIN B. The AR-index: complementing the h-index. ISSI Newsletter, v. 3, n. 1, p. 6, 2007. MCGARTY, C. The citation impact factor in social psychology: a bad statistic that encourages

bad science. Current Research in Social Psychology, v. 5, p. 1-16, 2000.

MINGERS, J. HARZING, A.W. K. Ranking journals in Business and Management: A statistical analysis of the Harzing Dataset. European Journal of Information Systems, v. 16, p. 303-316, 2007.

SEGLEN, P.O. Why the impact factor of journals should not be used for evaluating research.

British Medical Journal, v. 314, p. 497-502, 1997.

SPIROSKI, M.; GOGUSEV, J. Macedonian medical journals have very limited scientific influence. Macedonian Journal of Medical Sciences, v. 1, n. 2, p. 10-16, 2008.

WHITEHOUSE, G. H. Impact factors: facts and myths. European Radiology, v. 12, p. 715-717, 2002.

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Revista Ambiente & Água - An Interdisciplinary Journal of Applied Science: v. 5, n. 2, 2010.

ISSN = 1980-993X – doi:10.4136/1980-993X www.ambi-agua.net

E-mail: [email protected] Tel.: (12) 3625-4212

Kinetics and mass transfer of atrazine ozonation

(doi:10.4136/ambi-agua.132)

Rafaela Cristina Landeiro da Silva1; Roberto José de Carvalho2; Bruno Abreu Calfa3

Departamento de Engenharia de Materiais - PUC-Rio

E-mail: [email protected]; [email protected]; [email protected]

ABSTRACT

The kinetics of the atrazine oxidation in aqueous solution by ozone was studied under different initial pH conditions and in the presence of a hydroxyl radical scavenger at pH 2.8. It was verified that the process took place mainly through radical reaction, even in acid medium. Therefore, a relatively high value of 26.4 L/(mol.s) for the rate constant of the direct reaction between molecular ozone and atrazine was found. After 10 minutes of oxidation, the degradation of the herbicide was more effective for pH 10.30 than for pHs 6.25 and 2.80. The mass transfer of ozone from the gas phase to the liquid phase was strongly affected by the oxygen flowrate and to a lesser extent by the stirring speed.

Keywords: atrazine; ozonation; kinetics; mass transfer.

Cinética e transferência de massa da ozonização da atrazina

RESUMO

A cinética da oxidação da atrazina em solução aquosa por ozônio foi estudada sob diferentes condições de pH inicial e na presença de um sequestrador do radical hidroxila em pH 2,8. Verificou-se que o processo ocorreu principalmente através da reação com o radical, mesmo em meio ácido. Portanto, um valor relativamente elevado de 26,4 L/(mol.s) para a constante cinética da reação direta entre o ozônio molecular e atrazina foi encontrado. Após 10 minutos de oxidação, a degradação do herbicida foi mais efetiva para pH 10,30 do que para pHs 6,25 e 2,80. A transferência de massa do ozônio da fase gasosa para a fase líquida foi fortemente afetada pela vazão de oxigênio e, em menor medida, pela velocidade de agitação.

Palavras-chave: atrazina; ozonização; cinética; transferência de massa.

1. INTRODUCTION

The growing demand for agricultural products has driven the use of large amounts of pesticides to prevent or combat pests and ensure higher productivity (Sanches et al., 2003). Due to their indiscriminate use, pesticides have been detected in surface and groundwaters throughout the world. Thus, it is necessary to develop technologies that promote the degradation of these pollutants. A promising alternative is the application of an oxidative process using ozone as the oxidizing agent (ozonation).

Among the pesticides systematically monitored in the water bodies, atrazine (2-chloro-4-ethylamino-6-isopropylamine-s-triazine) emerges as the most frequent and abundant (Sousa, 2002). Atrazine is a selective herbicide used in the control of weeds, especially in crops of maize, sugar cane and sorghum (Sanches et al., 2003). Studies have indicated that atrazine is resistant to biological degradation (Adams and Randtke, 1992). Therefore, several authors have studied different methods for degradation of this herbicide. The processes for water treatment include: i) physical processes such as adsorption and extraction; ii) biological processes; iii) chemical processes such as chlorination and advanced oxidation. In general,

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SILVA, R. C. L.; CARVALHO, R. J.; CALFA, B. A. Kinetics and mass transfer of atrazine ozonation. Ambi-Agua, Taubaté, v. 5, n. 2, p. 9-20, 2010. (doi:10.4136/ambi-agua.132)

adsorption and extraction are cost effective and easy to perform. However, they only allow the transfer of the pollutant to another phase, not promoting its degradation to a less harmful species (Belhateche, 1995).

A promising way to enable degradation of an undesired chemical species is to apply oxidative treatments employing various agents such as ozone (O3), hydrogen peroxide (H2O2),

UV (Meunier et al., 2006), combinations of oxidizing agents such as O3/H2O2, O3/UV, or the

use of Fenton reagent and photo-Fenton system (Huston and Pignatello, 1999).

Ozone is an excellent oxidizing agent and has become attractive for the treatment of drinking water and wastewater, due to its low generation cost and high oxidizing potential (E0 = 2.07 V). It can promote the degradation of various organic pollutants in a short time (Kunz et al., 1999). The use of ozonation as a technique for wastewater treatment is still very limited in emerging countries like Brazil, because it requires a large amount of investments. However, in several developed countries the ozonation technology is widely used in water purification, especially for the production of drinking water.

The ozonation of atrazine in water has been studied by different authors (Adams et al., 1990; Yao and Haag, 1991; Adams and Randtke, 1992; Xiong and Graham, 1992; Beltrán et al., 1994, Acero et al., 2000) to identify the main by-products formed and determine the kinetic rate constant of the overall reaction between ozone and this herbicide. However, the reported results show a great discrepancy in the values found for this parameter.

In this work, the kinetics of the ozonation of soluble atrazine was studied at different pHs and in the presence of a hydroxyl radicals scavenger. A kinetic equation is proposed representing the oxidation of atrazine by molecular ozone. The mass transfer of ozone from the gas phase to the liquid phase was also investigated by evaluating the influence of several experimental parameters such as the inlet gas flow and the solution stirring speed.

2. MATERIALS AND METHODS

2.1. Chemicals

Oxygen gas (99.5%) was used for ozone generation. Atrazine degradation tests were performed using commercial atrazine (Gesaprim 500) purchased from Sigma Aldrich Química Brasil Ltda. Mixtures of methanol (HPLC grade) and water (distilled-deionized) were used as the mobile phase in HPLC experiments. Solutions of sodium hydroxide (0.01 mol/L) and sulfuric acid (0.06 mol/L), purchased from Vetec Química Fina Ltda., were used to adjust the initial pHs. All stock solutions were prepared with distilled-deionized water. All chemicals were used as received without further purification.

2.2. Equipments

All experiments were performed in a cylindrical glass reactor (32 cm high and 4 cm internal diameter). The ozone was produced by an Ozontechik generator with a throughput of 80 mg/h. The experimental setup is shown in Figure 1. Atrazine concentration was measured by HPLC (Perkin Elmer Series 200, USA) equipped with an UV/VIS absorption detector. Quantification of ozone in solution was performed in a model Spec 20MV spectrophotometer. The efficiency of atrazine ozonation was evaluated by determining the total organic carbon in a TOC analyzer (Shimadzu, Japan).

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Figure 1. Atrazine ozonation setup.

2.3. Procedures

To prevent loss of material due to the agitation of the system during the injection of gas and to ensure better efficiency of the system, only 75% of the total reactor volume was used. The ozone was fed at the base of the reactor which was fitted with a porous bubble diffuser to improve mass transfer from the gas to the liquid phase. The excess of ozone was collected and washed in a KI solution to be quantified by iodometry.

For each of the experiments, a pre-determined volume of distilled and deionized water was saturated with a continuous ozone flow for 20 minutes. Solutions of sulfuric acid (0.06 mol/L) or sodium hydroxide (0.01 mol/L) were added to the ozone solution to adjust the pH. The reaction was set off by adding 10 mL of a 0.3 mg/mL atrazine solution (Gesaprim 500) to the saturated ozone solution resulting in a final volume of 300 mL.

Ozonation tests were conducted with the objective of determining the effect of pH and contact time on the rate of atrazine degradation. The values of pH utilized were 2.8, 6.3 and 10.3. To obtain the rate constant of the reaction between ozone and atrazine, 0.01 mol/L of t-butanol was added in the aqueous medium at pH 2.8 in order to slow the reaction rate.

Samples with approximately 4 mL were collected at different times and residual atrazine was immediately analyzed in a Perkin Elmer Series 200 HPLC equipped with a UV/VIS detector. A Microsolb C18 column (150 mm length x 4.6 mm internal diameter, particle size 5 nm) was used and an isocratic elution with mobile phase composed by a 65% in volume methanol solution at a flowrate of 0.5 mL/min was performed for the separation of atrazine. The solvents were previously filtered in Millipore membrane filters and degassed offline in an ultrasound bath. The samples were filtered through 0.2 μm pore membranes before the analysis. The volume injected was 20 µL. The wavelength used was 222 nm selected from the absorption spectrum of a standard atrazine solution with a concentration of 10 mg/L.

The identification of atrazine in the samples was done by comparing its retention time with that of the standard solution. The calibration curve used for determining the atrazine concentrations was constructed using five concentrations of an atrazine standard with a purity of 95.4%: 1.0; 2.5; 5.0; 7.5 and 10.0 mg/L. For each standard concentration, three injections were made. Atrazine concentration was determined by interpolation in the calibration curve using simple linear regression.

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Atrazine degradation was evaluated by measuring the concentration of total organic carbon (TOC) according to the method described by Eaton et al. (1998). 20 mL samples were collected at the end of each ozonation test and analyzed.

Experiments for determining the mass transfer capacity coefficient were performed at pH 2.8. Aliquots of approximately 6 mL were taken throughout ozonation for the purpose of quantifying the ozone in solution using a colorimetric method with indigo as described by Eaton et al. (1998). Table 1 summarizes the conditions adopted in each of the tests.

Table 1. Test conditions for calculation of the mass

transfer capacity coefficient.

O2 flowrate (L/h) Stirrer rotational speed

0 100 12 155 0 100 21 155

3. RESULTS AND DISCUSSION

3.1. Effect of Initial pH

The effect of pH on the concentration of dissolved ozone is presented in Figure 2. The concentration increases in the first minutes until it reaches a stationary value. As in Sotelo et al. (1989), it is observed that the concentration of dissolved ozone decreases with increasing pH due to the higher concentration of OH- ions in basic medium, since these ions promote the decomposition of ozone. Higher concentrations of ozone are obtained in acid medium due to the lower concentrations of OH- ions available to decompose the ozone molecule.

The effect of initial pH on the efficiency of atrazine ozonation is shown in Figure 3. When the initial pH of the solution increased from 2.8 to 6.3, there was a 24% increase in the degradation of atrazine after 10 minutes of ozonation. In this same time of treatment, 97% degradation was obtained when the initial pH of the solution was increased to 10.3, which corresponded to an increase of approximately 47% when compared to the results obtained in acid medium. In acid medium, the ozone tends to react by the direct mechanism (oxidation by O3). At such condition, the degradation is usually less efficient. In basic medium, the ozone

reacts with hydroxyl ions leading to formation of radical species, particularly hydroxyl radicals (.OH). Due to the non-selective nature of hydroxyl radicals, the indirect mechanism (oxidation by .OH) is generally more efficient to degrade organic compounds.

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0 10 20 30 40 50 60 70 80 0 0.5 1 1.5 2 2.5 3 3.5 time (min) C o nc e n tr a ti o n o f di s s o lv ed oz on e (m g/ L) pH 2,8 pH 6,3 pH 10,3

Figure 2. Effect of pH on dissolved ozone concentration (O2 flowrate: 12 L/h;

stirrer rotational speed: 100 rpm).

Figure 3. Effect of pH on atrazine degradation.

3.2. Atrazine Mineralization

Examining the total organic carbon content (TOC), there were mineralization rates of approximately 20% (pH = 2.8 and pH = 6.3) and 60% (pH = 10.3) in 10 minutes of ozonation. Despite the greater efficiency in the degradation of atrazine at pH 6.3 (80%) than at pH 2.8 (65%), removal of TOC is the same in both cases. This result can be explained by the

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generation of by-products of atrazine ozonation. The by-products generated by exposure of atrazine to ozone for 10 minutes are illustrated in Figures 4 to 6 for a wavelength of 222 nm.

Figure 4. Chromatogram for atrazine ozonation at pH 2.8 after 10 minutes.

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Figure 6. Chromatogram for atrazine ozonation at pH 10.3 after 10 minutes.

3.3. Atrazine Ozonation Kinetics

The degradation of atrazine by direct ozonation is a complex process where both the oxidation of atrazine and the decomposition of dissolved ozone may take place due to its instability in aqueous media containing OH- anions. Atrazine is degraded through reaction with molecular ozone and .OH radicals due to decomposition of dissolved ozone, according to Equations 1 and 2. Atrazine + O3

⎯

⎯→

3 O k Products 1 [1] Atrazine + .OH

⎯

k.

⎯→

⎯

OH Products 2 [2]

Thus, the rate of degradation in the ozonation process may be described by Equation 3.

OH A OH O A O A C. C k. C C k dt dC 3 3 + = − [3]

where CA is the atrazine concentration, t is the reaction time, k is the rate constant for O₃

reaction 1, k._OH is the rate constant for Equation 2 and C._OH is the concentration of hydroxyl radicals and

3

O

C is the concentration of dissolved ozone.

However, the rate of ozone decomposition depends on the pH value. In acid media, the rate of decomposition is very small and the contribution of Equation 2 can be neglected. Based on this fact, this work considers only the degradation of atrazine by direct ozonation, Equation 1, since the experiments were performed at pH 2.8 and in the presence of t-butanol. The t-butanol decreases the action of hydroxyl radicals reacting rapidly with it. The rate constant for this reaction is 7.3 x108 L/(mol.s) (Hoigné and Bader, 1983).

Neglecting the reactions of intermediate products or by-products of ozonation, the atrazine degradation rate is simplified to:

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3 3 A O O A C C k dt dC = − [4]

According to Beltrán et al. (1994), the concentration of ozone reaches a maximum and stationary value in the ozonation process. If Equation 4 is applied for a reaction time equal to or greater than that required for the ozone concentration reach its saturation value, COsat₃ , then

the ozonation of atrazine follows a pseudo-first order kinetics:

O A A C ' k dt dC 3 = − [5] where: _O _O _Osat 3 3 3 k C ' k = [6]

The solution of Equation 5 is given by:

t k Ao A O e C C = − ' 3 _[7] where: CAo is the initial concentration of atrazine.

The variation of atrazine concentration with time for the experimental conditions indicated is presented in Figure 7. As seen in this figure, a good fit was obtained between the experimental concentrations and the concentrations predicted by Equation 7 (correlation coefficient 0.987).

The rate constant for the degradation of atrazine by molecular ozone was evaluated as 26.4 L/(mol.s). Different values for the rate constant of the direct ozonation reaction were determined by other authors. Some results are listed in Table 2.

The difference between the rate constant obtained in this work and the values found in the literature may be imputed to the different experimental conditions used, especially the pH which is directly related to the concentration of hydroxyl radicals generated by the decomposition of ozone.

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Table 2. Rate constants for the direct reaction between ozone and atrazine presented in the

literature.

pH Rate constant,

k

O₃ (L/(mol.s))

OH sequestrant

concentration Reference

7.5a 12.24 cabonate, 10-4 mol/L Xiong and Graham (1992) 2a 2.25 t-butanol, 0.01 mol/L Xiong and Graham (1992) 4.1 b 6 t-butanol, 0.01 mol/L Yao and Haag (1991)

7 6 t-butanol, 0.02 mol/L Acero et al. (2000) 2 4.5 t-butanol, 0.05 mol/L Beltrán et al. (1994)

5b 73c -- Adams et al. (1990)

7b 146c -- Adams et al. (1990)

9b 617c -- Adams et al. (1990)

7d 125c -- Adams and Randtke (1992)

2.8 26.4 t-butanol, 0.01 mol/L this study

a

batch competitive ozonation with MCPA (2-methyl-4-chlorophenoxyacetic acid) as reference. bbatch ozonation. creported as total rate constant. dContinuous ozonation.

3.4. Mass Transfer of Ozone

The kinetics of the ozonation process is usually controlled by mass transfer of ozone from the gas phase to the liquid phase. Several models have been proposed to describe this transfer. Generally these models postulate that the concentration of ozone in both phases is homogeneous except in a thin layer around the gas-liquid interface.

The mass transfer capacity coefficient, kLa, is determined from the mass balance in the

liquid phase given by the following equation:

(

)

3 3 3 O O O sat O L O C k C C a k dt dC 3 3 = − − [8]

The experimental runs were conducted at room temperature and pH 2.8 with the purpose of minimizing ozone decomposition and thus eliminate

3

O

k in Equation 8. Under these conditions this equation can be integrated to:

C C

[

exp

(

kLat

)

]

sat

O

O₃ = ₃ 1− − [9]

The variation of the dissolved ozone concentration with time for three stirring speeds (0 rpm, 100 rpm and 155 rpm) is presented in Figure 8 for an O2 flowrate of 12 L/h and in

Figure 9 for an O2 flowrate of 21 L/h. It may be observed in these figures that with increasing

stirring speed the dissolved ozone concentration reaches its maximum value in a shorter time. The values of _Osat

3

C , kLa and R2 for different O2 flowrates and stirring speeds presented in

Table 3 were obtained by fitting the data shown in Figure 8 and 9 with Equation 9. They are similar to those reported by Kunz et al. (1999) and Beltrán et al. (2000) and suggest a high mass transfer rate in the reactor. They also indicate that the gas flowrate and especially the stirring speed affect the mass transfer of ozone from the gas phase to the liquid phase.

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0 5 10 15 20 25 30 35 40 0 0.5 1 1.5 2 2.5 3 3.5 time (min) C o nc e n tr a ti o n o f di s s o lv ed oz on e (m g/ L) 0 rpm 100 rpm 155 rpm

Figure 8. Variation of dissolved ozone concentration with time for an O2 flowrate

of 12 L/h, pH = 2.8. 0 5 10 15 20 25 30 35 40 0 0.5 1 1.5 2 2.5 time (min) C o nc ent ra ti on of di s s o lv e d oz on e (m g/ L ) 0 rpm 100 rpm 155 rpm

Figure 9. Variation of dissolved ozone concentration with time for an O2 flowrate

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Table 3. Mass transfer capacity coefficients, kLa (min-1), for different stirring speed and oxygen

flow rates. O2 flowrate (12 L/h) O2 flowrate (21 L/h) 0 rpm 100 rpm 155 rpm 0 rpm 100 rpm 155 rpm sat O₃ C 2.722 3.023 3.016 1.589 1.607 1.650 a kL 0.1477 0.1662 0.2810 0.3512 0.4571 0.6472 R2 0.9728 0.9887 0.9481 0.9076 0.8206 0.8961

4. CONCLUSIONS

The pH had a pronounced effect on the concentration of dissolved ozone and determines the predominant oxidant (O3 or .OH) for the reaction with atrazine. The process is carried out

mainly through radical reaction, even in acid medium.

The rate constant of the direct reaction between molecular ozone and atrazine was 26.4 L/(mol.s).

The degradation of atrazine was more effective at pH 10.3 than at pHs 6.3 and 2.8.

The rate constant for the atrazine ozonation reaction determined in this work was relatively high when compared to the values found in the literature. This may have been caused by the different experimental conditions used, especially the pH which is directly related to the concentration of hydroxyl radicals generated by the decomposition of ozone set off by the OH- anions.

The transfer of ozone from the gas phase to the liquid phase was strongly affected by the oxygen flowrate and to a lesser extent by the stirring speed.

5. ACKNOWLEDGEMENTS

The authors are grateful to CNPq for supporting this research. Rafaela Cristina Landeiro da Silva thanks CNPq and FAPERJ for granting a M.Sc. scholarship.

6. REFERENCES

ACERO, J. L.; STEMMLER, K.; Von GUNTEN, U. Degradation kinetics of atrazine and its degradation products with ozone and OH radicals: a predictive tool for drinking water treatment. Environmental Science and Technology, Washington, v. 34, n. 4, p. 591-597, 2000.

ADAMS, C. D.; RANDTKE, S. J.; THURMAN, M. E.; HULSEY, R. A. Occurrence and treatment of atrazine and its degradation products in drinking water. In : American Water Works Association Annual Conference, Cincinati, 1990. Proceedings… AWWA: Denver, 1990. p. 871-894.

ADAMS, C. D.; RANDTKE, S. J. Ozonation byproducts of atrazine in synthetic and natural waters. Environmental Science and Technology, Washington, v. 26, n. 11, p. 2218-2227, 1992.

BELHATECHE, D. H. Choose appropriate wastewater treatment technologies. Chemical

Engineering Progress, New York, v. 91, n. 8, p. 32-51, 1995.

BELTRÁN, F. J.; GARCÍA-ARAYA, J. F.; ACEDO, B. Advanced oxidation of atrazine in water – I. Ozonation. Water Research, London, v. 28, n. 10, p. 2153-2164, 1994. BELTRÁN, F. J.; GONZÁLEZ, M.; ACEDO, B.; RIVAS, F. J. Kinetic modelling of aqueous

atrazine ozonation processes in a continuous flow bubble contactor. Journal of

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EATON, A. D.; CLESCERI, L. S.; GREENBERG, A. E. Standard methods for the examination of water and wastewater. 20. ed. Washington: American Public Health Association: 1998. 1 v.

HOIGNÉ, J.; BADER, H. Rate constants of reactions of ozone with organic and inorganic compounds in water – I: Non-dissociating organic compounds. Water Research, London, v. 17, n. 2, p. 173–183, 1983. HUSTON, P. L.; PIGNATELLO, J. J. Degradation of selected pesticide active ingredients and commercial formulations in water by the photo-assisted Fenton reaction. Water Research, London, v. 33, n. 5, p. 1238–1246, 1999.

KUNZ, A.; FREIRE, R. S.; ROHWEDDER, J. J. R.; DURAN, N.; MANSILLA, H.; RODRIGUEZ, J. Construção e otimização de um sistema para produção e aplicação de ozônio em escala de laboratório. Química Nova, São Paulo, v. 22, n. 3, p. 425-428, 1999.

SANCHES, S. M.; SILVA, C. H. T. P.; CAMPOS, S. X.; VIEIRA, E. M. Pesticidas e seus respectivos riscos associados à contaminação da água. Pesticidas: Revista de

Ecotoxicologia e Meio Ambiente, Curitiba, v. 13, p. 53-58, 2003.

MEUNIER, L.; CANONICA, S.; Von GUNTEN, U. Implications of sequential use of UV and ozone for drinking water quality. Water Research, London, v. 40, n. 9, p. 1864–1876, 2006.

SOTELO, J. L.; BELTRÁN, F. J.; BENITEZ, F. J.; BELTRÁN-HEREDIA, J. Henry’s law constant for the ozone-water system. Water Research, London, v. 23, n. 10, p.1239-1246, 1989.

SOUSA, I. J. Pesticidas: que estratégia de avaliação na água destinada ao consumo humano. Lisboa: Associação Portuguesa de Distribuição e Drenagem de Água – Comissão Especializada de Qualidade da Água, 2002.

XIONG, F.; GRAHAM N. J. D. Rate constants for herbicide degradation by ozone. Ozone:

Science and Engineering, London, v. 14, n. 4, p. 283-301, 1992.

YAO C. C. D.; HAAG W. R. Rate constants for direct reactions of ozone with several drinking water contaminants. Water Research, London, v. 25, n. 7, p. 761-773, 1991.

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Revista Ambiente & Água - An Interdisciplinary Journal of Applied Science: v. 5, n. 2, 2010.

ISSN = 1980-993X – doi:10.4136/1980-993X www.ambi-agua.net

E-mail: [email protected] Tel.: (12) 3625-4212

In vitro effects of petroleum refinery wastewater on dehydrogenase

activity in marine bacterial strains

(doi:10.4136/ambi-agua.133)

Christopher E. Nwanyanwu1; Gideon O. Abu2

1

Department of Microbiology, Federal University of Technology, P.M.B.1526, Owerri, Imo State, Nigeria E-mail: [email protected]

2

Department of Microbiology, University of Port Harcourt, P.M.B.5323, Port Harcourt, Rivers State, Nigeria E-mail: [email protected]

ABSTRACT

Toxicity of oil refinery effluent on four bacteria strains isolated from refinery effluent impacted river water sample was assessed via dehydrogenase assay. Pure cultures of the bacterial strains were exposed to various effluent concentrations [12.5 – 100% (v/v)] in a nutrient broth amended with glucose and TTC. The response of the bacterial strains to refinery effluent is concentration-dependent. At 12.5% (v/v), the effluent stimulated dehydrogenase activity in Streptococcus sp. RW3 and Pseudomonas sp. RW4. In all strains, dehydrogenase activity was progressively inhibited at concentrations greater than 12.5% (v/v). The IC50 ranges from 25.46 ± 4.75 to 31.30 ± 2.63% (v/v). The result of the in

vitro study indicated that the bacterial strains are sensitive to oil refinery raw wastewater stress. Therefore, the improperly treated effluent when discharged would pose serious threat to the metabolism of the bacterial strains in natural environments.

Keywords: Refinery effluent; toxicity; marine bacteria; dehydrogenase.

Efeitos in vitro de efluentes de refinaria de petróleo em atividade de

desidrogenase de cepas de bactérias marinhas

RESUMO

A toxicidade de efluentes de refinaria de petróleo em quatro linhagens de bactérias isoladas de amostras de água que sofreram influência de efluente de rio refinaria foi avaliada por meio de ensaio de desidrogenase. Culturas puras das estirpes bacterianas foram expostas a diferentes concentrações de efluentes [12,5-100% (v/v) em uma amostra de nutrientes alterada com glicose e TTC. A resposta das cepas bacterianas a efluentes de refinaria é dependente da concentração. A atividade de desidrogenase de efluentes com concentração de 12,5% (v/v) foi estimulada em culturas de Streptococcus sp. RW3 e Pseudomonas sp. RW4. Em todas as estirpes, a atividade de desidrogenase foi progressivamente inibida em concentrações superiores a 12,5% (v/v). O IC50 variou de 25,46 ± 4,75-31,30 ± 2,63% (v/v). O resultado do estudo in vitro indicou que as bactérias são sensíveis ao stress de efluente bruto de refinaria de petróleo. Portanto, a descarga de efluentes com tratamento inadequado representa uma ameaça grave para o metabolismo das bactérias em ambientes naturais.

Palavras-chave: Toxicidade de efluente de refinaria; bactérias marinhas; desidrogenase.

1. INTRODUCTION

Water as resource for life on earth, has several unique properties that help make it such a necessary part of the environment. For example, the entire essential functions within living cells are maintained by water. Water ecosystems are as varied as their individual sites because

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NWANYANWU, C. E.; ABU, G. O. In vitro effects of petroleum refinery wastewater on dehydrogenase activity in marine bacterial strains. Ambi-Agua, Taubaté, v. 5, n. 2, p. 21-29, 2010. (doi:10.4136/ambi-agua.133)

they are influenced not only by characteristic local climate, soil, resident communities but also by the surrounding terrestrial ecosystem. As man advances in technology and industry, large amounts of water are used for industrial activities and consequently significant volumes of wastewaters are generated. Based on the type of industry, various levels of pollutants are deliberately released and discharged into the environment directly. Among these industries that discharge their effluents into the aquatic environments are the petroleum oil refineries. As not all refineries have the same processes, the effluents that are produced will have different chemical compositions depending on the type of treatment they received (Wake, 2005; Hernandez et al., 1998; Lehtinen, 1986). Wastewaters released by oil refineries contain large amounts of toxic derivatives such as oil and grease, phenols, sulphides, cyanides, suspended solids, nitrogen compounds as well as heavy metals such as iron, nickel, copper, selenium, zinc, molybdenum, etc. (Burks, 1982). Due to the ineffectiveness of purification systems, wastewaters from the refineries may become seriously dangerous, leading to the accumulation of toxic products in the receiving water bodies with potentially serious consequences on the ecosystem (Otokunefor and Obiukwu, 2005). Thus the discharge of these effluents containing persistent chemicals into a receiving waterbody may result in the long term effects to aquatic biota (Tisler et al., 1999). The toxicity of oil refinery effluents to aquatic organisms has being reported in many literatures. Toxicity of petroleum refinery depends on a number of factors which include quantity, volume and variability of discharge. The different components of the effluents may have varying effects and toxicity (Saha and Konar, 1985). Aruldoss and Viraraghavan (1998) reported the toxicity of refinery wastewater to luminescent bacteria (Photobacterium phosphoreum) using microtox in the bioassay. This is based on monitoring changes in natural light emissions from the organism. Toxicity and end point was measured as the effective concentration of a test sample that can cause 50% decrease in light out (IC50) after 30min of contact time.

Microorganisms are vital for the efficient functioning of any ecosystem; hence factors that affect their metabolism, composition and abundance are of great concern. Monitoring microbial responses has been recommended as an early warning indicator of ecosystem stress as microbes respond promptly to environmental perturbations (Nweke et al., 2007; Griffiths, 1983). Measurement of microbial enzyme activity is used in the assessment of ecotoxicological impacts of environmental substrates. In this regard, dehydrogenase activity has been widely used. The dehydrogenase assay is an effective primary test for assessing the potential toxicity of chemicals to microbial activities (Ghaly and Mahmoud, 2006; Griebe et al., 1997). In this assessment, dehydrogenase activity (DHA) is measured using the reduction of 2, 3, 5-triphenyltetrazolium chloride (TTC) to triphenylformazan (TPF). Determination of their ability to reduce TTC to the formazan product after exposure to test compounds, compared to the control situation, enables the relative toxicity of the chemicals to be assessed. This study was aimed at assessing the in vitro effects of petroleum refinery wastewater on the dehydrogenase activity in bacterial species isolated from refinery effluent impacted Okrika River water in Port Harcourt, Nigeria.

2. MATERIALS AND METHODS

2.1. Characterization of petroleum oil refinery wastewater

Composite mechanically (gravity separation that include API separators and tank separation) and physicochemically (addition of additives, flocculation, sedimentation and filtration) pretreated petroleum oil refinery wastewater was collected at the inlet to the biological treatment unit (Rotary biodisk) at the Port Harcourt oil refinery complex using 5 litres polyethylene containers. The containers were rinsed several times with the effluent

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6h of collection. Phenol concentration, pH, COD, BOD, THC, cations (Pb3+ and Cu2+) and anions (PO42+ and Cl-) in wastewater samples were determined according to standard methods

(APHA, 1998).

2.2. Bacterial strains and culture conditions

The bacterial strains used in these studies were isolated from water samples collected from oil refinery effluent-impacted Okrika river water samples located in Port Harcourt, Nigeria.

The isolates - Citrobacter sp. RW1, Staphylococcus sp. RW2, Streptococcus sp. RW3, Pseudomonas sp. RW4 were purified on nutrient agar (Fluka) plates and characterizations were done using standard microbiological methods. Identifications to the genus level followed the schemes of Holt et al. (1994). The isolates were maintained and sub-cultured once in every month in a basal minimal medium containing (per liter): ammonium chloride 10 g, ammonium nitrate 4.0 g, K2HPO4 0.2 g, KH2PO4 0.8 g, MgSO4 0.1 g; phenol as the sole

carbon and energy source. The pH was adjusted to 8.0 using phosphate buffers.

The bacterial strains were grown to mid exponential phase in nutrient broth (Lab M) on a rotary incubator (Stuart, ST150SA, UK, 150 rpm) at room temperature (28 ± 2oC). The cells were harvested by centrifugation at 8000 rpm for 10 min. Harvested cells were washed twice in deionised distilled water and suspended in the same deionized distilled water. The re-suspended cells were standardized in a spectrophotometer to an optical density of 0.90 at 540 nm. The dry weight of the standardized cells was determined by drying 15 ml of the cell suspension to constant weight in an oven (Gallenkamp, England) at 110oC. The standardized cell suspensions were used as inoculum in the dehydrogenase activity assay.

2.3. Dehydrogenase activity assay

Dehydrogenase assay method as described by Nweke et al. (2007) was employed with little modification. Briefly, dehydrogenase activity was determined using TTC (BDH England) as the artificial electron acceptor, which was reduced to the red-coloured triphenyl formazan (TPF). The assay was done in 3.5 ml volumes of nutrient broth-glucose-TTC medium supplemented with varying concentrations [0 – 100 % (v/v)] of oil refinery wastewater in separate 20 ml screw-capped test tubes. Aliquots (0.2 ml) of the bacterial suspensions were inoculated into triplicate glass tubes containing 2.5 ml of nutrient broth-glucose medium amended with graded concentrations of oil refinery wastewater that was diluted with 0.7ml deionized distilled water and preincubated on a rotary incubator (150 rpm) at room temperature (28 ± 2oC) for 60 min. Thereafter, 0.1 ml of 0.1 % (v/v) TTC in deionised distilled water were added to each tube to obtain final effluent concentrations of 0, 12.5, 25, 50, 75, 100% (v/v) in different test tubes. The final concentrations of nutrient broth, glucose and TTC in the medium were 2, 2 and 0.267 mg/ml, respectively. The controls consisted of the isolates and the media without wastewater. The reaction mixtures were further incubated statically at room temperature (28 ± 2oC) for 6h. The TPF produced was extracted in 4 ml of amyl alcohol and determined spectrophotometrically at 445 nm (λmax). The amount of formazan produced was determined from a standard dose-response curve [0 - 20 μg/ml TPF (Sigma) in amyl alcohol; y = 0.0484x; R2 = 0.9958]. Dehydrogenase activity was expressed as milligrams of TPF formed per mg dry weight of cell biomass per hour. Inhibition of dehydrogenase activity in the isolates by wastewater was calculated relative to the control. The percentage inhibitions for bacterial strains were linearized against the concentrations of the refinery wastewater using gamma parameter (Ґ) [Ґ = % Inhibition / (100 - %Inhibition)] (Tarkpea et al., 1986). The toxicity threshold concentrations (IC50) which is an inhibitory concentration of toxicant required to reduce 50% of the dehydrogenase activity were then determined from the linear regression plots.

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2.4. Statistical analysis

Data obtained from the study were analyzed by the use of two-way analysis of variance (ANOVA) and values for P < 0.05 were considered statistically significant.

3. RESULTS AND DISCUSSION

The results of the chemical characterization of the oil refinery wastewater sample are shown in Table 1. The Wastewater sample had elevated levels of organic compounds as indicated by the concentrations of COD BOD, THC and phenol as all measured values exceed the FEPA permissible limit values (Table 1). The bacterial strains were able to reduce TTC to its formazan and so were used to assess toxicity of refinery wastewater through the dehydrogenase assay.

The dehydrogenase activity (DHA) varied among the bacterial strains (Table 2). The

Gram-negative strains of Pseudomonas sp. and Citrobacter sp. have higher rate of dehydrogenase Table 1. Characteristics of petroleum oil refinery wastewater.

Parameter/unit Refinery wastewater FEPA wastewater limitations Guideline (1991) pH 7.64 6.0 – 9.0 THC (mg/l) 17.5 10.0 TDS (mg/l) 950 2000.0 BOD (mg/l) 32.0 10.0 COD (mg/l) 112 40.0 Phenol (mg/l) 71.2 0.05 Phosphate (mg/l) 0.22 5.0 Chloride (mg/l) 44.0 600.0 Lead (mg/l) <0.01 0.5 Copper (mg/l) <0.01 1.0

Table 2. Uninhibited dehydrogenase activities in the isolates.

Bacterial Strain Dehydrogenase activity

(µg Formazan/mg cell dry weight/h)

Citrobacter sp. RW1 0.452 ± 0.011

Staphylococcus sp. RW2 0.433 ± 0.012

Streptococcus sp. RW3 0.448 ± 0.012

Pseudomonas sp. RW4 0.467 ± 0.011

activity than the Gram-positive strains of Staphylococcus sp. and Streptococcus sp. This is in agreement with Nweke et al. (2007) and Nwogu et al. (2007) in which the Gram-negative organisms (Pseudomonas species isolated from the environment and human sources respectively) had higher dehydrogenase activity than gram-positive organisms. Earlier report (Alisi et al., 2008) is however at variance with this observation. These variations may be due to differences in bacterial physiology, including cell wall components or dehydrogenase systems, since different microorganisms have been reported to have different dehydrogenase systems (Praveen-Kumar, 2003).

The effects of the different concentrations of the effluent on the bacterial isolates with respect to inhibition and dehydrogenase activity are shown in Figures 1 and 2. The responses of the bacterial dehydrogenase activities to the refinery effluent are concentration-dependent and vary among the organisms. For Citrobacter sp. RW1 and Staphylococcus sp. RW2,

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Figure 1. Effluent inhibition of dehydrogenase activity in Citrobacter sp.

RW1 (A), Staphylococcus sp. RW2 (B), Streptococcus sp. RW3(C),

Pseudomonas sp.RW4 (D).

(> 0% = Inhibition; < 0% = Stimulation).

Figure 2. TTC reduction activity in response to different concentration of the

refinery effluent by Citrobacter sp. RW1 (A), Staphylococcus sp. RW2 (B),

Streptococcus sp. RW3 (C), Pseudomonas sp. RW4 (D). Mean ± standard deviation

(n=3) are indicated by bars. Some standard deviations are within data point. Effluent concentration %( v/v) RW 1 0 20 40 60 80 100 12.5 25 50 75 100 RW 2 0 20 40 60 80 100 12.5 25 50 75 100 RW 4 -20 0 20 40 60 80 100 12,5 25 50 75 100 Inhi b iti o n (%) A B C D RW 4 -20 0 20 40 60 80 100 12.5 25 50 75 100 RW1 0 0.1 0.2 0.3 0.4 0.5 0 22 44 66 88 110 RW 2 0 0.1 0.2 0.3 0.4 0.5 0 22 44 66 88 110 RW 3 0 0.11 0.22 0.33 0.44 0.55 0 22 44 66 88 110 RW 4 0 0.11 0.22 0.33 0.44 0.55 0 22 44 66 88 110 Dehydrogenase activity

(µg Formazan/mg cell dry weight/h)

Effluent Concentration %( v/v) A

C

B

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Figure 3. Correlation of effluent concentrations with dehydrogenase

activity (DHA) in response to effluent toxicity by Citrobacter sp. RW1 (A), Staphylococcus sp. RW2 (B), Streptococcus sp. RW3 (C),

Pseudomonas sp. RW4 (D).

Figure 4. Gamma (Ґ) parameter values of Citrobacter sp. RW1 (A),

Staphylococcus sp. RW2 (B), Streptococcus sp. RW3 (C), Pseudomonas sp.

RW4 (D) in response to refinery effluent [0 – 100%(v/v)].

dehydrogenase activity reduced with increasing concentrations of effluent (Figure 2). On the contrary, for Streptococcus sp. RW3 and Pseudomonas sp. RW4, dehydrogenase activities were stimulated at 12.5% (v/v) and thereafter progressive inhibition was also observed at concentrations above 12.5% (v/v). The stimulation of Streptococcus sp. RW3 and Pseudomonas sp. RW4 observed at lower concentration of effluent is attributable to the use of phenols and other inorganic pollutants within the effluents by these bacteria. The inhibition of

A R2_{= 0.9748} -1.5 -1.2 -0.9 -0.6 -0.3 0 0 25 50 75 100 B R2 = 0 .9 9 3 3 -2 -1 .6 -1 .2 -0 .8 -0 .4 0 0 2 5 5 0 7 5 1 0 0 C R2_{= 0 .9 4 4 5} -1 .4 -1 .2 -1 -0 .8 -0 .6 -0 .4 -0 .2 0 0 2 5 5 0 7 5 1 0 0 D R2 = 0 .9 6 7 8 -1 .4 -1 .2 -1 -0 .8 -0 .6 -0 .4 -0 .2 0 0 2 5 5 0 7 5 1 0 0 Lo g10 DH Effluent concentration %( v/v) A y = 0.0684x - 0.9905 R2 = 0.9948 0 2 4 6 8 0 20 40 60 80 100 120 B y = 0.6016x - 15.655 R2 = 0.7079 0 14 28 42 56 70 0 24 48 72 96 120 C y = 0.0666x - 1.0661 R2_{= 0.9622} -2 -1 0 1 2 3 4 5 6 7 0 20 40 60 80 100 120 D y = 0.102x - 1.8622 R2 = 0.9849 -4 -2 0 2 4 6 8 10 12 0 20 40 60 80 100 120 Ґ – Parameter values Effluent concentration %( v/v)

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industrial effluents at high concentrations (Tisler et al., 1999; Fountoulakis et al., 2002). Results presented in Figure 1 showed that at lower effluent concentrations [≤ 25.0% (v/v)], Streptococcus sp. RW3 had higher percentage inhibition than other organisms. This implies that Streptococcus sp. RW3 was more sensitive to refinery effluent stress than the other bacterial strains studied. Comparatively, at higher concentrations [≥ 50.0%( v/v)], Pseudomonas sp. RW4 was more tolerant to the refinery effluent than the other bacteria. Different sensitivities of microbes to refinery effluent toxicity could be related to the long-term exposure to toxic components of the effluent by the organism.

Table 3. Threshold inhibitory concentrations of petroleum refinery

wastewater against the bacterial strains.

Bacterial strain Inhibitory concentration (IC50) % (v/v)

Citrobacter sp. RW1 29.25 ± 1.13

Staphylococcus sp. RW2 25.46 ± 4.75

Streptococcus sp. RW3 31.30 ± 2.63

Pseudomonas sp. RW4 31.30 ± 1.71

Table 4. R2 values of linear regression plots of transformation data of dehydrogenase activity

of the bacterial strains.

R2 - values Regression plot Log

dehydrogenase Inhibition (%) Ґ - parameter Citrobacter sp. RW1 0.9748 0.955 0.9948 Staphylococcus sp. RW2 0.9933 0.940 0.7079 Streptococcus sp. RW3 0.9445 0.8025 0.9622 Pseudomonas sp. RW4 0.9678 0.9630 0.9498

The gram-negative Pseudomonas sp. RW4 seems to tolerate the toxicity of the effluent more than the gram-positive Staphylococcus sp. RW2. The evidence is seen from the threshold inhibitory concentration data (Table 3). Dehydrogenase activity correlates with effluent concentration as shown in Figure 3. The higher R2 values (0.9445 ≤ R2 ≤ 0.9933) indicate that the concentration was a strong determinant of dehydrogenase activity in the isolates. Thus, the effluent at high concentration exerted serious stress on the organisms. The logarithmic plot of the dehydrogenase activity (Figure 3) and the gamma parameter model (Figure 4) gave good linearization of the dose response data for the bacterial isolates. The high R2 values for the linear regression plots of Log DHA and gamma parameter (Table 4) lays credence to the linear relationship. Gamma parameter models had higher R2 values than the % inhibition plots (Table 4) and hence the linear regression models were used to assess the threshold inhibitory concentration of the effluent on the organism.

The 2-way analysis of variance shows that the dehydrogenase activity and its percentage inhibition varied significantly (P < 0.05) with bacteria strain and effluent concentration. The result of this in vitro study indicated that oil refinery effluent exerts toxic effect against the tested organisms and positive Staphylococcus sp. was more responsive than the Gram-negative Pseudomonas sp.

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4. CONCLUSIONS

In all strains, dehydrogenase activity was progressively inhibited at concentrations greater than 12.5% (v/v). The IC50 ranges from 25.46 ± 4.75 to 31.30 ± 2.63% (v/v). The

result of the in vitro study indicated that the bacterial strains are sensitive to oil refinery raw wastewater stress. Therefore, the improperly treated effluent when discharged would pose serious threat to the metabolism of the bacterial strains in natural environments.

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