WASTEWATER STABILIZATION PONDS FECAL COLIFORM REMOVAL EFFICIENCIES

Transcription

1 WASTEWATER STABILIZATION PONDS FECAL COLIFORM REMOVAL EFFICIENCIES Martins de Aguiar Marluce 1, rreira MendonçaAntonio Sérgio 2* 1 Espírito Santo State Secretary for Health 2 Environmental Engineering M.Sc. Program at the deral University of Espírito Santo. Av. São Paulo 1890/104 - Praia da Costa- Vila Velha - ES - CEP 29101/301 BRAZIL. FAX : asergio@npd1.ufes.br ABSTRACT- The main objective of the research was the evaluation of the fecal coliform bacteria (FC) removal efficiencies for waste stabilization ponds (WSP) located in the Great Vitória region, southeast of Brazil. Statistical analysis was applied to data from 5 (five) wastewater treatment systems. Data from long term monitoring were analyzed. Eldorado, Laranjeiras and Maringá systems are composed by anaerobic ponds followed by facultative ponds. Mata da Serra and Barcelona systems present only one facultative pond each. Geometric average FC concentrations for the raw sewage, anaerobic pond and final effluent for all treatment systems were computed. The results showed the lower efficiency obtained by utilizing only one facultative pond. However, Laranjeiras two-pond system, underdesigned and presenting other design problems, showed average efficiencies close to those obtained by one-pond systems. Espírito Santo State and brazilian legislation for freshwater quality indicate the limit for fecal coliforms concentration as NMP/100 ml. The two-pond treatment systems named as Eldorado and Maringá presented average effluents FC concentrations ten times as much this limit. Facultative ponds systems and Laranjeiras twopond system presented concentrations higher than one hundred as much the legislation limit. The water bodies that receive the final effluents from the analyzed WSP systems are very small creeks presenting minimum annual discharges lower than ten times as much the average of the effluent discharges. Hence, in order to satisfy environmental legislation and improve water resources quality it is necessary the construction of effluent polishing ponds or the application of desinfection procedures. Palabras clave: coliforms, waste stabilization ponds, wastewater treatment efficiency INTRODUCTION Wastewater Stabilization Ponds(WSP) are utilized all around the world for wastewater treatment. WSP treatment efficiencies are generally measured by the relationships between treated and raw sewage Biochemical Oxygen Demands(BOD) or cal Coliforms(FC). The main objective of the study was the evaluation of the fecal coliforms removal efficiencies for waste stabilization ponds located in the Great Vitória metropolitan region, in the Espírito Santo State, southeast of Brazil. cal coliforms are well accepted as indicators for fecal pathogenic viruses and bacteria. Coliforms analysis results are utilized for testing the suitability of water for different uses such as human supply, irrigation, bathing, leisure and aquaculture. Human diseases transmitted through water, such as hepatitis and gastroenteritis are common in Brazil and in the Espírito Santo State. Wastewater treatment plants coliforms removal efficiencies are utilized as indicators for their efficiency for pathogenic viruses and bacteria removal. Efficiency analysis for wastewater stabilization ponds must take into account local climatological and geographical conditions. WSP efficiencies depend on biological aspects, such as raw sewage quality and strength. Biological activity is affected by many environment factors such as temperature, wind velocity, sunlight; physical factors, such as ponds geometry, dead zones, stratification, position of inflow and outflow structures; dissolved oxygen concentrations; ph; light absence; algae adsorption, etc. Statistical analysis was applied to data from 5 (five) wastewater treatment systems located in the Great Vitória metropolitan area, that are operated by CESAN (Companhia Espiritossantensse de Saneamento). Data from long term monitoring of the systems (from 1984 to 1994) were analyzed. Eldorado, Laranjeiras and Maringá systems are composed by anaerobic ponds followed by facultative ponds. Mata da Serra and Barcelona systems present only one facultative pond each.

2 MATERIAL AND METHODS Statistical analysis was applied to data originated from long term monitoring ( ) for 5 (five) wastewater treatment systems located in the Great Vitória metropolitan area, Espírito Santo State, southeast of Brazil, that are operated by CESAN (Companhia Espiritossantensse de Saneamento). The selected systems treat sanitary sewage originated from residential districts located in Serra municipal district. Eldorado, Laranjeiras and Maringá systems are composed by anaerobic ponds followed by facultative ponds. Mata da Serra and Barcelona systems present only one facultative pond each. The main geometric characteristics for the analyzed wastewater stabilization ponds are presented on Table 1. Table 1 - Wastewater Stabilization Ponds Geometric Characteristics SYSTEM TYPE AVERAGE AREA(sq.m.) V(cu.m.) DEPTH (m) Barcelona Facultative ,715 43,501 Mata da Serra Facultative ,712 6,340 Eldorado Anaerobic ,020 1,978 Eldorado Facultative ,000 23,750 Laranjeiras Anaerobic ,447 8,762 Laranjeiras Facultative ,226 7,057 Maringá Anaerobic ,096 2,213 Maringá Facultative ,946 6,669 The number of houses and population that contribute with sewage for the different systems are shown on Table 2. Table 2 - Number of houses and population that contributes for the systems SYSTEM HOUSES POPULATION Barcelona 3,663 15,750 Mata da Serra 721 3,100 Eldorado 1,860 7,998 Laranjeiras 7,000 31,000 Maringá 465 2,000 Serra municipal district is geographically located on the south latitude and west longitude Table 3 presents the main climatological characteristics for the region.

3 Table 3 - Climatological data (1994) MONTH TEMPERATURE ( C) HUMIDITY (%) CLOUDINESS ( 0-10) TOTAL RAINFALL (mm) JAN FEV MAR ABR MAI JUN JUL AGO SET OUT NOV DEZ Espírito Santo Company for Sanitary Works (CESAN) monitors sewage inflow and outflow physico-chemical and bacteriological water quality parameters for the ponds that compose the five treatment systems. Samples are collected and analyzed once or twice a month. During this study ph, Dissolved Oxygen(D.O.) and Biochemical Oxygen Demand(B.O.D), besides fecal coliforms, parameters, estimated from simple samples, were statistically analyzed. The number of samples and sampling periods for each system are shown on Table 4. Table 4 - Sampling period an number of samples SYSTEM Sampling Period Total Samples Barcelona Mata da Serra Eldorado Laranjeiras Maringá Systems inflow and outflow sewage discharges were measured by using Parshall flumes and triangular weirs. Table 5 shows the average inflow discharges and detention times for the treatment systems during Since inflows from anaerobic to facultative ponds, intermediary flows, were not measured by CESAN, it was assumed, as an approximation, for the filling of this table, that all the sewage that enters the anaerobic ponds reaches the facultative ponds (neither infiltration nor evaporation losses). Table 5 - Average discharges and detention times SYSTEM TYPE DISCHARGE (l/s) DETENTION TIMES (days) Barcelona Facultative Mata da Serra Facultative Eldorado Anaerobic Eldorado Facultative Laranjeiras Anaerobic Laranjeiras Facultative Maringá Anaerobic Maringá Facultative

4 RESULTS Tables 6 and 7 show the average values for ph, Biochemical Oxygen Demand, Dissolved Oxygen and cal Coliforms, for the five systems analyzed, during the monitoring period., and represent Raw sewage, Anaerobic pond effluent and Facultative pond effluent. N represents the total number of samples analyzed. Table 6 - Average ph and Biochemical Oxygen Demand (mg/l) parameters for the monitoring period SYSTEM N ph ph ph B.O.D. B.O.D. B.O.D. Barcelona Mata da Serra Eldorado Laranjeiras Maringá Table 7 - Average Dissolved Oxygen (mg/l) and cal Coliforms(NMP/100 ml) parameters for the monitoring period SYSTEM N D.O. D.O. D.O. C.F. C.F. C.F. Barcelona x x 10 5 Mata da Serra x x 10 5 Eldorado x x x 10 4 Laranjeiras x x x 10 5 Maringá x x x 10 3 From Table 7, Barcelona treatment system geometric average fecal coliforms concentrations for raw sewage and facultative pond effluents were 1.3x10 8 and 7.8 x10 5 NMP/100 ml. For Mata da Serra system the corresponding concentrations were 6.5x10 7 and 4.0x10 5. Geometric average fecal coliforms concentrations for the raw sewage, anaerobic pond and final effluent for Eldorado treatment system were 7.3x10 7, 4.6x10 6, and 1.1x10 4 NMP/100 ml. For Laranjeiras system the corresponding values were 5.0x10 7, 2,5x10 6 and 4.4x10 5. For Maringá system, the corresponding values were 5,8x10 7, 1,7x10 6 and 7,5x10 3 NMP/100 ml. Table 8 shows the average fecal coliforms removal efficiencies (%) for the anaerobic ponds (Ap) and facultative ponds (Fp) that compose the five wastewater treatment systems analyzed. Table 8 - Average FC removal efficiencies SYSTEM N Removal Efficiency Anaerobic Pond Removal Efficiency Facultative Pond Removal Efficiency System Barcelona Mata da Serra Eldorado Laranjeiras Maringá

5 cal coliforms average removal efficiencies for Eldorado, Laranjeiras and Maringá wastewater treatment systems were , and %. For Mata da Serra and Barcelona systems, presenting only facultative ponds, the average removal efficiencies were and %. DISCUSSION Wastewater stabilization ponds systems fecal coliforms removal efficiencies depend on several factors, including raw sewage quality, organic load, temperature, wind velocity, sunlight, ponds geometric form, inflow and outflow structures position, ph, starvation, absence of light phenomenon and algae adsorption (Parhad and Rao, 1974; Middlebrooks et al Silva e itosa, 1984; Curtis and Mara, 1994; Frederik and Lloyd, 1995; e Oragui et al., 1995). Distances between the waste stabilization ponds are lower than 10 miles. Hence, the climatological conditions for all the analyzed systems are very close. Sewage that reaches all the systems comes from low income blue-collar residential districts. Barcelona and Mata da Serra systems, presenting only one facultative pond, presented average final effluent fecal coliforms concentrations 7.8 x 10 5 and 3.9 x 10 5 NMP/100 ml, corresponding to and % average removal efficiencies. Eldorado and Maringá systems, composed by one anaerobic and one facultative pond in series, presented lower final effluent fecal coliforms concentrations ( 1.1 x 10 4 and 7.5 x 10 3 NMP/100 ml) and higher fecal coliforms removal efficiencies ( and %). These results showed the lower efficiency obtained by utilizing only a facultative pond in comparison with the use of two-pond systems. Larger total detention times for the two-pond systems (46.9 and 69 days for Eldorado and Maringá systems, comparing with 25.6 and 26.9 for Barcelona and Mata da Serra systems) contributed for their best performance. However, Laranjeiras wastewater treatment system results, similar to those presented by the one-pond systems indicate that it is not enough to have more than one pond in order to obtain higher fecal coliforms removal efficiencies. Among the factors that contributed for the weak performance of this system are the underdesign (measured sewage discharges were more than three times the design discharge), low detention time, 4.6 days and ponds geometric form (close to a square). Pearson(1987), indicate that the larger the relationship between the length and width for the pond, the higher the fecal coliform removal efficiency. Average effluent fecal coliforms concentrations for Eldorado and Maringá wastewater treatment systems were ten times as much the corresponding to Laranjeiras and two pond systems. Espírito Santo State and brazilian legislation (SEMA/MHU, 1986) for freshwater quality indicate the limit for fecal coliforms concentration as NMP/100 ml. Eldorado and Maringá two-pond treatment systems presented average effluents fecal coliforms concentrations ten times as much this limit. Laranjeiras and facultative ponds systems presented concentrations higher than one hundred as much this legislation concentration limit. Average ph parameters for the final effluents from Eldorado and Maringá systems were higher than 8( 8.7 and 8.4, respectively), while the averages for the other systems (lower fecal coliforms removal efficiencies) were lower than 8. Average final effluents dissolved oxygen concentrations for Eldorado and Maringá systems reached values higher than the saturation concentration(9.4 and 9.1, respectively). For Laranjeiras system, the average final effluents dissolved oxygen concentration was 6.8, while the averages for the one facultative pond systems were below 6 (5.6 for Mata da Serra and 1.8 for Barcelona).

6 CONCLUSION All the analyzed systems presented average fecal coliforms removal efficiencies lower than 99.9 %. One facultative pond systems presented the lowest average fecal coliform bacteria removal efficiencies (below 98.5%). Underdesign and poor facultative pond geometric form contributed to the very weak performance for the two-pond Laranjeiras system (removal efficiency also below 98.5%). Systems that produced effluents presenting ph average values larger than 9.0 also presented the largest fecal coliforms removal efficiencies. The water bodies that receive the final effluents from the analyzed wastewater treatment systems are very small creeks presenting minimum annual discharges lower than ten times as much the average of the effluent discharges. Hence, in order to satisfy environmental legislation it is necessary the construction of effluent polishing ponds or the application of desinfection procedures for reducing the concentration of fecal coliform bacteria that reach the water bodies even for the Eldorado and Maringá systems that presented the highest removal efficiencies. Addition of anaerobic ponds to the Barcelona and Mata da Serra systems and the design of a new wastewater treatment system for Laranjeiras is also recommended. BIBLIOGRAPHY CURTIS, T.P. and MARA, D.D (1994) The Effect of Sunlight on Mechanism for the Die-off of cal Coliform Bacteria in Waste Stabilization Ponds. University of Leeds. Research Monograph n 1. pp4-17. FREDERICK, G.L. and Lloyd, B.J. (1995) An Evaluation of Retention Time and Short-Circuiting in Waste Stabilization Ponds using Serratia Marcescens Bacteriaphage as a Tracer. Cayman Islands, 3rd IAWQ, International Conference on Waste Stabilization Ponds Technology and Applications. 27th-31st March 1995, João Pessoa, Paraíba, Brazil. MARA, D.D. et al. (1992) Waste Stabilization Ponds. A Design manual for Eastern Africa. Lagoon Technology Intern. Leeds- England. pp MIDDLEBROOKS J.E. et al. (1982) Wastewater Stabilization Lagoon Design, Performance and Upgrading. Macmillan Publishing Co. Inc. New York. pp 21-37, ORAGUI J.I. et al. (1995) Pathogen Removal Kinetics in a Tropical Experimental Waste Stabilization Pond in Relation to Organic Loading, Retention Time and Pond Geometry, 3 rd IAWQ International Conference on Stabilization Ponds Technology and Applications 27th-31st March 1995, João Pessoa, Paraíba, Brazil. PARHAD, N.M. and RAO, N.N (1974) Effect of ph on Survival of Escherichi coli. Journal of the Water Pollution Control deration, 46, PEARSON, H.U. et al. (1987) Physiochemical Parameters Influencing cal Bacteria Survival in Wastewater Stabilization Ponds. Water Science and Technology, 19, SEMA/MHU (1986) Resolução CONAMA 20/86. Classificação das águas doces, salobras e salinas do território nacional. SILVA, S.A. e FEITOSA, N.B. (1983) Influência do Tempo de Detenção na Eficiência de Lagoas Facultativas Secundárias tratando Esgotos Domésticos no Nordeste do Brasil. EXTRABES - Campina Grande, Paraíba, Brasil.

7 CURRICULUM VITAE AUTHORS : Marluce Martins de Aguiar 1 and Antonio Sérgio rreira Mendonça 2 1 -Civil and Sanitary Engineer (deral University of Espírito Santo ), -Public Health Engineering Specialization (ENSP-FIOCRUZ-1982), -Environmental Engineering Graduate Student, -Espírito Santo State Secretary Health Engineer 2 -Civil Engineer (deral Univ. of Espírito Santo ), -M.Sc. in Water Resources Engineering (deral Univ. of Rio de Janeiro - COPPE ) -Ph.D. in Water Resources Engineering (Colorado State University - USA ), -Associate Professor at the Hydraulics and Sanitary Engineering at the deral University of Espírito Santo. - Environmental Engineering M.Sc. Program Coordinator at the deral University of Espírito Santo. - Environmental Engineering Specialization Program Coordinator at the deral University of Espírito Santo.