capability of ciliated protozoa
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capability of ciliated protozoa

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~) 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



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


BOD 5 E = BOD 5 effluent
SS = suspended solids

SSE = suspended solids effluent
STD = standard deviation

AVG = average
MAX = maximum
MIN = minimum


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


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.


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

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.