capability of ciliated protozoa
Disciplina:Qualidade da Água Residuária2 materiais • 46 seguidores
~) Pergamon 0043-1354(94)00258-4 Wat. Res. Vol. 29, No. 4, pp. 1041-1050, 1995 Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0043-1354/95 $9.50 + 0.00 CAPABILITY OF CILIATED PROTOZOA AS INDICATORS OF EFFLUENT QUALITY IN ACTIVATED SLUDGE PLANTS H. SALVADO*, M. P. GRACIA and J. M. AMIGO Departament de Biologia Animal, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain (First received April 1994; accepted in revised form September 1994) A~tract--The aim of this study is to determine the relationship between the ciliate populations density and effluent quality in activated sludge plants. A total of 231 samples taken at three activated sludge plants were analyzed over a three year period. Seven physico-chemical parameters were examined and protozoa (in particular ciliate protozoa) and small metazoa were counted by means of optical microscopy. Effluent quality was determined from BOD 5 and suspended solids concentration. For data analysis the species were classified in ranges in terms of abundance. Mean and standard deviation of effluents BOD s and SS were calculated for each range. It was found that as the abundance of each species population increased, both BOD s and suspended solids from effluents tended to a particular range of values (the optimal range) whereas the standard deviation diminished. Thus the higher the ciliate species population density, the better the capability of the species as an indicator, which is something reflected in the standard deviation. This capability of ciliated protozoa to act as indicators of effluent quality will also be limited by the 6ther factors influencing the presence of species. It was observed that the correlation coefficients between ciliates and effluent quality depend on the range of physico-chemical values studied, i.e. whether they are superior or inferior to the "optimal range". The values of each species' BOD 5 optimal range varied from 4 mg/1 to 18 ppm, suggesting that ciliates are good indicators between 4 and 18 ppm in activated sludge plants. In all cases observed, less common species such as Acineta tuberosa, Euplotes sp. and Zoothamnium sp. were indicators of high effluent quality. By contrast, the species that reach the highest densities and are the most common, such as Uronema nigricans, Vorticella microstoma and Opercularia coarctata, indicated lower effluent quality. Key words--ciliate protozoa, activated sludge, indicator species, effluent quality NOMENCLATURE BOD 5 E = BOD 5 effluent SS = suspended solids SSE = suspended solids effluent STD = standard deviation AVG = average MAX = maximum MIN = minimum INTRODUCTION The importance of ciliated protozoa in wastewater treatment involving activated sludge has often been described. Their effectiveness in the purifying process is due to the fact that they feed off dispersed bacteria, thus eliminating them (see Curds et al., 1968). The presence of ciliate protozoa reflects an increase in effluent quality (Curds, 1982a, 1993) and can also be taken as indicators of effluent quality (BOD) (Curds and Cockburn, 1970; Sartory, 1976; Al-shahwani and Horan, 1991). They are also useful as indicators of *Author to whom all correspondence should be addressed. parameters other than effluent quality in the purifying process. The type of structure of the ciliate protozoa community can characterize various types of biologi- cal treatment (Madoni and Ghetti, 1981), sludge loading (Curds and Cockburn, 1970), organic loading rate (Salvad6 and Gracia, 1993), mean cellular reten- tion time (MCRT) (Salvad6, 1994) and biological quality of the sludge (Madoni, 1994). It has often been observed that the relation be- tween various physico-chemical parameters and a particular species does not follow a linear model. For example, in the relation between the abundance of a certain organism and pH (a parameter not included in this study) an optimal range is observed; above and below this range either the species' density diminishes or the species disappears altogether. However, stat- istical analyses used to relate physico-chemical par- ameters and organisms are generally based on linear models, by means of either bivariant or multivariant analysis. Consequently, when the relationship be- tween a parameter and a particlar species is studied, if the range of study of the parameter is above or below the values of the optimal range, it is easy to see 1041 1042 H. Salvad6 et al. that for the same species good correlation coefficients will be found with positive or negative values. The aim of this study was to examine the relation between the densities of the different species of ciliate protozoa that colonize activated sludge and effluent quality, by analyzing a wide range of BOD 5 and suspended solids values. MATERIALS AND METHODS Sampling Three activated sludge plants in the vicinity of Barcelona were sampled over a three-year period. Each sampling (165 at Plant A, 30 at Plant B and 36 at Plant C) included one sample from the primary settling tank, one from the sec- ondary settling tank and one from the aeration tank. Primary and secondary settling tank samples were inte- grated for 24 h and collected (approx. 0.51) every hour. Sludge samples were taken from the aeration tank. The characteristics of each plant are outlined in Table 1. Physical and chemical parameters from effluent were measured on three separate occasions for each microorgan- ism sample: two days before, one day before and on the same day as the microorganism sample. Physical and chemical monitoring BODs, suspended solids (SS), volatile suspended solids and dissolved oxygen concentration in the aeration tank were measured in accordance with APHA (1989). Hydraulic retention time was calculated as the ratio of aeration tank volume to flow rate. Identification and quantification of microorganisms Microorganism counting was carried out using 500 ml portions of mixed liquor from the aeration tank. Ciliates were counted immediately in the plant laboratory. The number of organisms for each taxon was counted under an optical microscope at x 100 magnification in four 50pl subsamples taken with an automatic micropipette. Small flagellates and gymnoamoebae were counted using × 400 magnification. Ciliate species were identified in accordance with Kahl (1930 35), Curds (1982b), Curds et al. (1983), Guhl (1979), Foissner et al. (1991, 1992), Foissner and Schiffman (1974), Augustin et al. (1987), Perez-Uz (1993), using special techniques: Protargol (Tuffrau, 1967), pyridi- nated ammonic silver carbonate (Fern~indez-Galiano, 1976) and silver nitrate (Klein, 1928). Non-ciliated protozoa and small metazoa were identified following Baldwin and Chan- dler (1966), Kudo (1966) and Lee et al. (1985). Filamentous microorganisms were quantified according to Salvad6 (1990). Data analysis Two parameters for effluent quality control were selected for data analysis: BOD 5 and suspended solids. A table, in which physical-chemical data were grouped according to different ranges of density corresponding to each species of ciliates found, was elaborated. Against each range of density the mean and standard deviation of BOD 5 E and SSE were calculated. In analyzing these data we should bear in mind that effluent quality is found for a particular ciliate species' density and not the other way round. The correlation coefficients for each group classified according to abundance is given for each species, BODsE and SSE, using the logarithmic transformation (x = Log(x + 1)). Data table, described above, was used in order to select the best sampling day for further statistical analysis.