Sludge Biotic Index Research Articles

Combination of Microscopic Tests of the Activated Sludge and Effluent Quality for More Efficient On-Site Treatment

Container on-site wastewater treatment plants are systems of growing interest in the areas where sewer systems cannot be implemented. In this study, container on-site wastewater treatment plant with low-loaded activated sludge has been examined. The aim of the study was: (i) to assess the efficiency of the plant; and (ii) to evaluate the relationship between the condition of activated sludge and selected parameters of effluent quality. Effluent quality has been characterized by the reliability factor (RF) and technological purity index (TPI). Sludge quality assessment covered measurements of volume (Vo), dry matter (DM), sludge index (SI), and the unit oxygen consumption rate (UOCR). Microscopic analysis has been performed to assess the morphological (flocks) and biotic quality (sludge biotic index, SBI) of activated sludge. The research has been completed by an on-site measurement of dissolved oxygen concentration in an activated sludge chamber with 30 s intervals. Results confirmed a significant (p < 0.05) correlation (CC = −0.9277) between biochemical oxygen demand (BOD5) and SBI for the oxygen level in the aeration chamber between 1–2 mg/L. Negative significant correlation (p < 0.05) has also been found between SBI and electrical conductivity (EC) (CC = −0.7478). In the examined case, the optimal EC of the effluent was in the range of 600–800 µS/cm.

The applicability of the Sludge Biotic Index in a facility treating sugar refinery effluents and municipal wastewater.

Protozoans are valuable indicators of the wastewater biological treatment process and are used in a variety of water resource recovery facilities (WRRF). The aim of this study was to determine the applicability of the Sludge Biotic Index (SBI) as an indicator of activated sludge purification efficiency during different influent loadings: municipal wastewater (M) and municipal wastewater combined with industrial wastewater from a sugar refinery (M+S). Despite the higher organic load during the M+S period, purification efficiency was higher for BOD5 , compared with the M period. SBI values were high during both periods, indicating stable sludge, excellent biological activity, and good to very good performance. According to the share of indicator taxa, better conditions of activated sludge were found during the M+S period. Protozoan abundance differed between the two study periods, as well as purification efficiency for some parameters. Certain taxa showed a significant correlation with purification efficiency for specific parameters. Although SBI is a useful tool for estimating activated sludge health, it should be used in combination with additional indicator metrics and/or a species-specific approach. PRACTITIONER POINTS: Activated sludge can have high purification efficiency during the co-treatment of industrial and municipal wastewater. The Sludge Biotic Index is applicable as an indicator of activated sludge condition during the treatment of municipal and sugar refinery wastewaters. A combination of indicators and a species-specific approach can give better estimation of the health of activated sludge.

Microscopic Analysis of Activated Sludge in Industrial Textile Wastewater Treatment Plant

Abstract The relationship between a quality of activated sludge microbiota and wastewater treatment plant (WWTP) operational stability has been defined in the past few decades. However, this dependence is not so clear in the case of industrial wastewater treatment. In this article, a very specific example of industrial textile wastewater treatment plant (ITWTP) is analyzed. Textile effluents are well known as highly contaminated wastewater containing many biodegradable compounds. Microscopic analysis included flocs morphology examination, attempts to evaluate the Sludge Biotic Index (SBI), and identification of dominant filamentous microorganisms. Routine operational control of ITWTP covered pH, temperature, redox potential, dissolved oxygen and COD measurements. The average ecosystem existing in the described ITWTP differed significantly compared to municipal WWTPs. The flocs were smaller and irregular. Filamentous bacteria did not cause foaming although filaments index reached 4. Nostocoida limicola I dominated with significant amounts of type 0041 and type 021N. The evaluation of SBI was impossible as the most of protozoan was in the form of cysts. The overall microbiota diversity correlated with COD removal in activated sludge unit of ITWTP.

Towards an eDNA metabarcode-based performance indicator for full-scale municipal wastewater treatment plants

Knowledge-driven management for wastewater treatment plant (WWTP) performance becomes increasingly important considering the globally growing production of wastewater and the rising demand of clean water supply. Even though the potential of microbial organisms (bacteria and protists) as bioindicators for WWTP performance is well known, it is far from being fully exploited for routine monitoring programs. Therefore, we here used massive sequencing of environmental (e)DNA metabarcodes from bacterial (V3-V4 region of the SSU rRNA gene) and eukaryote (V9 region of the SSU rRNA gene) communities in 21 activated sludge samples obtained from full-scale municipal WWTPs in Germany. Microbial community patterns were compared to standard WWTP operating parameters and two traditionally used WWTP performance indicators (Sludge Biotic Index and Sludge Index). Both indices showed low concordance and hardly correlated with chemical WWTP performance parameters nor did they correlate with microbial community structures. In contrast, microbial community profiles significantly correlated with WWTP performance parameters and operating conditions of the plants under study. Therefore, eDNA metabarcode profiles of whole microbial communities indicate the performance of WWTP and can provide useful information for management strategies. We here suggest a strategy for the development of an eDNA metabarcode based bioindicator system, which can be implemented in future standard monitoring programs for WWTP performance and effluent quality.

Discharge quality from municipal wastewater treatment plants and the Sludge Biotic Index for activated sludge: integrative assessment

Abstract Wastewater treatment plants (WWTPs) are scrutinized by Environmental Authorities particularly regarding the compliance to discharge limit values fixed by national and local regulations. An integrated approach is necessary to achieve the objectives established with Directive 2000/60/EC (WFD) considering the ecological status of the receiving water body and the quality of the discharge. Specifically, documentary, technical, management and analytical controls should be developed. Moreover, integrative information on the behaviour of the activated sludge in the aeration tank can be useful for plant managers as well as for the regulating Authorities. The study presents the experience concerning WWTP regulation considering the analytic assessment of the discharge as well the monitoring of the Sludge Biotic Index (SBI) for activated sludge. Data from monitoring during the period 2008–14 on SBI values and chemical and microbiological data on the discharges of a sample of 35 WWTPs in the province of Venice (north-east Italy, Veneto region) are presented and discussed. Together with chemical and microbiological analysis, the SBI appears to be a highly useful index for the integrative assessment of plant functionality, in particular when monitoring and identifying critical situations that can determine the exceedance of discharge limit values. The SBI method, in an integrated control approach, can be used for small and medium sized WWTPs that only treat domestic wastewaters. In a case by case assessment this may even substitute part of the analytical monitoring carried out in the WWTPs' control process.

Comparison of the Results from Microscopic Tests Concerning the Quality of Activated Sludge and Effluent

Physicochemical studies on wastewater quality and microscopic analyses of activated sludge are necessary to properly evaluate the condition of activated sludge. The aim of this study was to evaluate the application of the sludge biotic index to determine when a change in treatment quality is short-lived, caused by, e.g., a change in influent quality or quantity, and when it indicates adverse changes in the biocenosis of activated sludge, which would very likely result in the lower efficiency of wastewater treatment in the near future. The objects of the study were two identical parallel running small wastewater treatment plants. The following indicators of contamination were analyzed: the chemical oxygen demand (COD), biochemical oxygen demand (BOD5), and total suspended solids (TSS). The authors additionally carried out a microscopic analysis. The study confirmed a correlation between the sludge biotic index and the removal efficiency of COD and BOD5; however, no correlation was found between the sludge biotic index and the removal efficiency of total suspended solids. The presence of metazoan microorganisms coincided in time with a good effluent treatment efficiency. When their quantity declined, a decrease in the efficiency of wastewater treatment was also observed.

Bioindicator value of flagellates in urban wastewater treatment using membrane bioreactors

Two experimental submerged membrane bioreactors (MBR) at the industrial scale with different membranes (microfiltration and ultrafiltration) were used to analyse the influence of the small flagellates on the lack of significance of the sludge biotic index (SBI). Also, with these systems, flagellates were analysed as bioindicators in the activated sludge of MBRs. Both facilities were operated in parallel with a pre-denitrification system for a period of nearly two years and fed with real pretreated urban wastewater. During the experimental period, the sludge-retention time in the facilities was from 16.5 to 36.5 days, the organic loading ranged between 1.8 Kg COD/d m3 and 0.14 Kg COD/d m3, and the temperature of the activated sludge was between 32.8 and 12.8 °C. Under these conditions, the concentrations of total solids in the activated sludge reached 21.6 and 0.3 g/L, and the ratio of food:microrganims (F:M) remained stable at around 0.1 Kg BOD5/Kg VSS day, while the trans-membrane pressure (TMP) followed an increasing trend. Both facilities presented a high capacity for organic matter elimination and complete nitrification. The small flagellates were present throughout the experimental period in the activated sludge and showed no significant bioindicator role in the MBR systems which limited the application of SBI. Of the large flagellates studied, only Peranema sp. could be considered to be a bioindicator of MBR systems, indicating the effectiveness of denitrification for systems with complete nitrification and correlating with the time course of the TMP.

Microfauna community during pulp and paper wastewater treatment in a UNOX system

This study characterized the microfauna community during treatment of pulp and paper wastewater in a UNOX system aerated with pure oxygen, and with a high organic loading rate (0.4±0.06kg BOD/kg MLSSday), low sludge retention time (3.73±0.33 day), and high oxygen concentration (≤20mg O2/L) in comparison to municipal treatment systems. In the aeration tank, temperatures were high, averaging 35.7°C (March–May), then 38.9°C (June–August). Effluent quality was acceptable: 180±22mg COD/L, 7.2±2.1mg BOD5/L, and 33±5mg TSS/L. At 35.7°C, 5 taxa were identified in the activated sludge: small flagellates (flagellates <20μm), attached ciliates (Vorticella infusionum, Vorticella octava), crawling ciliates (Chilodonella uncinata) and free-swimming ciliates (Sathrophilus muscorum). During this period, the SBI (Sludge Biotic Index) was 6–7, corresponding to Quality Class II. At 38.9°C, two taxa co-dominated (Vorticella infusionum, Sathrophilus muscorum). When Vorticella infusionum dominated, the SBI was 5 or 7 (Quality Class III/II); when Sathrophilus muscorum dominated, the SBI was 0 (Quality Class IV). Slight changes in the abundance of two opposing Madoni keygroups impeded proper classification of activated sludge. However, effluent quality remained the same, showing that these indicators of activated sludge quality do not always reflect effluent quality.

Protozoa and Filamentous Bacteria in the First Biological Monitoring Activity of Wastewater Treatment Plants (WWTPs) in La Spezia district (Italy)

Protozoa and filamentous bacteria identification in Mixed Liquor (ML) allowed to obtain detailed information about the performance of five Wastewater Treatment Plants (WWTPs), placed in La Spezia’s District. Microfauna analysis showed the prevalence of testate amoebas (Euglypha spp. prevalent), rotifers and attached ciliate Epistylis plicatis. Low organic load, high sludge-age and high concentration of dissolved oxygen (DO) were well correlated to the growth of Vorticella campanula and Vaginicola sp. Testate amoebas (Euglypha sp. and Arcella sp.) were the most representative group in WWTPs treating also olive mills effluents. Sludge Biotic Index (SBI) showed, for the investigated plants, an optimal to good depuration efficiency (I and II class quality) but it seemed not adequately responsive when olive mills wastewater (rich in phenols) was mixed with the municipal one. Further investigations should be conducted to explain this result. Filamentous bacteria analysis revealed a higher sensitivity of microorganisms to both influent chemical characteristics and WWTPs operational parameters. In most part of the WWTPs, dysfunctions due to the proliferation of filamentous bacteria were detected. In all WWTPs subjected to foaming, the morphotype Nocardia Amarae Like Organisms (NALO), associated with Type 1851 and 0041, was identified as responsible of the foaming. Type 0092 caused a bulking episode in La Spezia WWTP. Haliscomenobacter hydrossis prevailed in the Mixed Liquor (ML) of a plant treating also olive mills wastewater, while Type 0803, 0675 and 1701 were abundant in plants receiving wastewater produced by meat-processing industries. On the whole, filamentous bacteria community analysis represented a more sensitive tool to characterize the activated sludge plant performances in light of providing an adequate management.

Effect of the presence ofActinomycetesin the activated sludge on the quality of the treated wastewater

The aim of the study was to determine the effect of the Actinomycetes proliferation in the activated sludge on the quality of the treated wastewater and the sewage receiver. The river which is the sewage receiver flows near the wastewater treatment plant. The study was performed on the wastewater (raw and treated) and on the river water samples (collected before and after wastewater discharge). The analysis of the research results, such as the content of total organic carbon (TOC), total phosphorus and oxygen consumption in the examined samples, permit the conclusion that the presence of relatively large population of the Actinomycetes in sewage sludge has a negative impact on the quality of the sewage receiver. Determining the effect of the Actinomycetes in the activated sludge on the wastewater treatment process involved the application of specific analyses, such as Sludge Biotic Index (SBI) and the identification of filamentous bacteria in the activated sludge. The analysis of studies indicates that the presence of the Actinomycetes in the activated sludge adversely affects the efficiency of the wastewater treatment process.

Effect of a static magnetic field on activated sludge community

ABSTRACTThe aim of this study was to determine the effect of a static magnetic field (SMF) on the composition of activated sludge biocenosis. The experiment was carried out in two parallel bench scale Sequencing Batch Reactors (SBRs). Both SBRs were treated with dairy wastewater. The activated sludge in the first SBR was exposed to an SMF via the induction of a 0.6 T magnetic field generated by four magnetic liquid activators. The second reactor (control reactor) was operated at the same operational parameters but the activated sludge was not exposed to the SMF. The mean length of the bacterium Eikelboom Type 0092 was lower in the SMF-exposed reactor than in the control reactor. Different activated sludge morphologies in SBRs were reflected in the values of the sludge volume index and sludge biotic index calculated on the basis of the microfauna composition.

Suitability of Sludge Biotic Index (SBI), Sludge Index (SI) and filamentous bacteria analysis for assessing activated sludge process performance: the case of piggery slaughterhouse wastewater.

Piggery slaughterhouse wastewater poses serious issues in terms of disposal feasibility and environmental impact, due to its huge organic load and variability. It is commonly treated by means of activated sludge processes, whose performance, in case of municipal wastewater, can be monitored by means of specific analyses, such as Sludge Biotic Index (SBI), Sludge Index (SI) and floc and filamentous bacteria observation. Therefore, this paper was aimed at assessing the applicability of these techniques to piggery slaughterhouse sewage. A plant located in Northern Italy was monitored for 1year. Physical, chemical and operation parameters were measured; the activated sludge community (ciliates, flagellates, amoebae and small metazoa) was analysed for calculating SBI and SI. Floc and filamentous bacteria were examined and described accordingly with internationally adopted criteria. The results showed the full applicability of the studied techniques for optimizing the operation of a piggery slaughterhouse wastewater treatment plant.

Adaptation of microbial communities in activated sludge to 1-decyl-3-methylimidazolium bromide.

The effects of 1-decyl-3-methylimidazolium bromide on activated sludge process and microbial composition were investigated. Ionic liquid (IL) was dosed continuously to the laboratory activated sludge system at an influent concentration from 1 to 20 mg l(-1) for about 1 month. As compared to the control test, mean values of degree of chemical oxygen demand removal and degree of biochemical oxygen demand removal were almost remaining constant at a high level, equaling 92.6% and 98.1%, respectively. In addition, no influence of IL on size and shape of flocs was observed. The values of the sludge biotic index indicate that sludge exposed on IL was stable and very well colonized with good biological activity. Increases in Proteobacteria (mainly Variovorax sp., Vogesella sp., Hydrogenophaga sp.), Bacteroidetes (mainly Lewinella sp., Haliscomenobacter sp., Runella sp.) and Nitrospirae were detected in sludge adapted to IL compared to the control system. The results showed that activated sludge can adapt to IL present in wastewater.

Effect of drilling mud addition on activated sludge and processes in sequencing batch reactors

Laboratory-scale sequencing batch reactors (SBR) with activated sludge were used for co-treatment of drilling mud and municipal wastewater. The influence of two doses of drilling mud, 1% (SBR2) and 3% (SBR3) of total added wastewater volume, on wastewater treatment efficiency and community of eukaryotes in activated sludge was examined. Addition of drilling mud significantly decreased the efficiency of TSS removal in SBR2 and SBR3 (from 97% in control bioreactor SBR1 to 75% and 49%, respectively), COD removal (from 93% to 57% and 48%, respectively) and N-NH4+ removal (from 93% to 56% and 48%, respectively). Values of TSS concentration in outflow from SBR2 and SBR3 greatly exceeded the limit value appointed for the wastewater discharged into the environment. Drilling mud addition led to decrease in population and diversity of eukaryotes’ groups in activated sludge, which was reflected by changes in sludge biotic index (SBI). It amounted to 10 in all the SBRs at the beginning of the experiment, and in SBR1, it remained at this same high level throughout. After 1% addition of drilling mud, a slight decrease in SBI (to 8) was observed, but 3% addition lowered the SBI to 4, reflecting serious deterioration of activated sludge quality.

Effect of Methylisothiazolinone on Biological Treatment: Efficiency of SBRs and Bioindicative Studies

Methylisothiazolinone (MIT) is widely used as biocide in hair and skin care products and in high concentrations, more than 150 mg/L, in cooling towers in the paper mill and refinery industry. This product has been recognized as a potent contact allergen and is discharged to the wastewater treatment plants (WWTP) from industrial processes or domestic usages. However, the role of MIT in biological treatment has not been characterized, and therefore, the effect of MIT on the composition and performance of activated sludge has been analyzed. For this purpose, a sequential batch reactor was fed with a synthetic solution containing 5 mg/L of MIT. Addition of MIT had shown no significant effect on organic matter metabolization (dissolved organic carbon [DOC] removal remained constant at 80–90%). On the contrary, a loss of efficiency in the nitrification process occurred (ammonium removal decreased from 90% to 20% per cycle throughout the experiment), first affecting the nitrite oxidizing bacteria and, after around 40 cycles, also the ammonium-oxidizing bacteria disappeared, as shown by fluorescence in situ hybridization analysis. Bioindicative studies based on counts of protozoa and sludge biotic index indicated that, at the end of the process, a stable and well-colonized protozoa community was obtained. Finally, respirometric tests indicated some acclimatization of the heterotrophic bacteria to MIT, as shown by shorter lag periods when the sludge was previously fed with MIT. The role of MIT in biological treatment has been characterized to increase the knowledge about this pollutant effects on activated sludge to improve WWTP performance.

Relationship between protozoan and metazoan communities and operation and performance parameters in a textile sewage activated sludge system

The present study aims at investigating the possibility of assessing performance and depuration conditions of an activated sludge wastewater treatment plant through an exploration of the microfauna. The plant, receiving textile industrial (70%) and domestic (30%) sewage, consists of a two-step biological depurating plant, with activated sludge followed by a percolating system. A total of 35 samples were analyzed during five months, and 30 taxa of protozoa and small metazoa were found. Epistylis rotans, Vorticella microstoma, Aspidisca cicada and Arcella sp. were the most frequent protozoa identified. Several significant correlations between biological, physical–chemical and operational parameters were determined, but no significant correlations could be established between biological parameters and removal efficiencies. The Sludge Biotic Index (SBI) reflected the overall state of the community but only presented statistically significant correlations with the influent total suspended solids (TSS), total suspended solids in mixed-liquor (MLTSS) and dissolved oxygen (DO). The determination of key groups and taxa along with general community parameters showed to have potential value as indicators of the depuration conditions. Despite the impossibility of correlating biological parameters and the removal efficiencies, the present study attests the value of the microfauna to assess the operation of the activated sludge systems even in the case of non-conventional plants and/or plants receiving industrial sewage.

Implementation of the sludge biotic index in a petrochemical WWTP in Brazil: improving operational control with traditional methods

Microbiological analysis of activated sludge is an important tool for monitoring wastewater treatment plants (WWTP). The utilization of the sludge biotic index (SBI) provides helpful information in examining the quality of biological treatment process and has been tested for several different systems. Although its utilization has been increasing, it is still not widespread, especially in Brazil. Also, its applicability has been considered limited for some particular systems. Thus, it becomes important to evaluate the relations among operational and biological parameters of each WWTP in order to characterize the system and its variations. In this work, microscopic analysis were performed once a week for 1year (n=54) and the results were compared to the physicochemical, operational parameters and efficiency of the plant along the period. The four seasons were comprised and analyzed, as we cannot neglect the influence of environmental changes in this subtropical region. Not only had we found a strong influence of the evaluated parameters on the structure of the biological community but there is also a good correspondence of SBI with the performance of the WWTP. More importantly, including microscopic analysis in the operational routine made it possible to notice even the slightest changes in the biological community that were not enough to diminish the SBI classification of the sludge, but were satisfactorily informative to show in advance to operators when to take corrective actions about an increase of COD and BOD in the influent and when it was necessary to discard the exceeding sludge.

Aerobic treatment of dairy wastewater in an industrial three-reactor plant: Effect of aeration regime on performances and on protozoan and bacterial communities

An industrial three-reactor plant treating 45 m3 d−1 of dairy wastewater was monitored to investigate the effect of different aeration regimes on performance efficiency and to find relationships with bacterial and protozoan communities in the activated sludge. During the study, the plant was maintained at six different “on/off” cycles of the blower (45/15, 15/15, 15/45, 30/30, 30/45 and 30/60 min), providing between 30.2 and 90.6 kg O2 d−1, and the main chemical/biochemical parameters (COD, BOD, NH4+, NO2−, NO3−, PO43−, etc.) were determined. When at least 45.4 kg O2 d−1 (30/45) were provided, COD removal efficiencies were always in the range 88–94% but decreased to about 70% under aeration regimes 15/45 and 30/60. Ammonium ion degradation performance was compromised only in the lowest aeration regime (15/45). Total number of protozoa and their species richness, and bacterial viable counts and denaturing gradient gel electrophoresis (DGGE) profiles were used to characterize the microbiota of the activated sludge. Cell abundances and community structures of protozoa and bacteria were very similar in the three aerated reactors but changed with the aeration regimes. In particular, the 15/45 and 30/60 regimes led to low protozoan diversity with prevalence of flagellates of the genus Trepomonas at the expense of the mobile and sessile forms and, thus, to a less efficient activated sludge as indicated by Sludge Biotic Index values (3 and 4.5 for the two regimes, respectively). The structure of the bacterial community strongly changed when the aeration regimes varied, as indicated by the low similarity values between the DGGE profiles. On the contrary, number of viable bacteria and values of the biodiversity index remained stable throughout the whole experimentation. Taken together, the results of the present study clearly indicate that aeration regime variations strongly influence the structure of both protozoan and bacterial communities and, above all, that a high biodiversity among protozoan populations in the activated sludge is prerequisite for high performances in dairy wastewater treatment.

Analysis of the usefulness of biological parameters for the control of activated sludge wastewater treatment plants in an interlaboratory study context

The quality of the sludge in Wastewater Treatment Plants (WWTPs) depends on the suitable colonization of the flocs by microorganisms. Due to the functional importance of these biological constituents, several biological or biological-related parameters have been commonly used for the control of depuration efficiency. According to national and international water regulation recommendations, interlaboratory studies have a great relevance to determine which parameters are more reliable for their extensive application in routine control. However, these studies are also very useful to demonstrate consistency in results from multiple laboratories and to develop reliable and reproducible methodologies which might be necessary for protocol validation and also for accreditation issues to meet regulatory environmental requirements. The main purpose of this work was to assess the results obtained in consecutive interlaboratory assays in order to determine the concordance degree in the application of biological parameters by participating laboratories. Following the international recommendations about these studies, a common working protocol was proposed. Statistical tests indicated that Sludge Index and several routine physical-chemical analyses [V30, Mixed Liquor Suspended Solids (MLSS), Mixed Liquor Volatile Solids (MLVS) and Sludge Volumetric Index (SVI)] show low variability and therefore are suitable tools for laboratory control. Shannon Index and Sludge Biotic Index also presented low variability although a more precise protocol would be necessary, in particular the methodology to count small flagellates. The abundance and identification of protist species showed low concordance among laboratories and three factors were responsible for the low reliability of data: population density, size and morphological distinguishable characters of the specimens.

Limitation of Sludge Biotic Index application for control of a wastewater treatment plant working with shock organic and ammonium loadings

This study aimed to determine the relationship between activated sludge microfauna, the sludge biotic index (SBI) and the effluent quality of a full-scale municipal wastewater treatment plant (WWTP) working with shock organic and ammonium loadings caused by periodic wastewater delivery from septic tanks. Irrespective of high/low effluent quality in terms of COD, BOD5, ammonium and suspended solids, high SBI values (8–10), which correspond to the first quality class of sludge, were observed. High SBI values were connected with abundant taxonomic composition and the domination of crawling ciliates with shelled amoebae and attached ciliates. High SBI values, even at a low effluent quality, limit the usefulness of the index for monitoring the status of an activated sludge system and the effluent quality in municipal WWTP-treated wastewater from septic tanks. It was shown that a more sensitive indicator of effluent quality was a change in the abundance of attached ciliates with a narrow peristome (Vorticella infusionum and Opercularia coarctata), small flagellates and crawling ciliates (Acineria uncinata) feeding on flagellates.