Ciliates in Activated Sludge

An atlas of Ciliated Protozoa commonly found in aerobic sewage-treatment processes. An aid to monitor treatment-plant performance
by Colin R. Curds, Alan Warren, Humbert Salvadó Cabré & Dave Roberts.


Ciliated protozoa (ciliates) are an important component of the microbial community in aerobic biological wastewater-treatment plants with about 175 species reported. They commonly number 50 million cells per litre in the mixed liquor of the activated-sludge process where their major role is the removal of dispersed bacteria by predation. It has long been known that ciliates can be used as reliable indicators of effluent quality in biological aerobic sewage-treatment processes. The advantage of using ciliates as bioindicators is that of speed, with an accurate prediction of effluent quality being available within an hour or two of sampling. Ciliates are rarely used on site in this way, however, mainly because of the difficulty that non-specialists have in identifying them. The main aim of this project is to produce a multimedia, user-friendly guide that can be used by specialists and non-specialists alike for both training and routine monitoring.

Amphileptus pleurosigma, 4k

Above: Amphileptus pleurosigma, a free-swimming ciliate. Scale bar = 50 micrometres.

If the video files below do not work, check your Quick Time Plug-in. The image quality of these clips has been reduced by compression necessary for the Web.

Download Video clip Amphileptus claparedei (2 Mb)
Showing typical swimming activity, several peripherally-located contractile vacuoles and two ovoid macronuclei.

Download Video clip Euplotes moebiusi (1.6 Mb)
(1) Dorso-ventral view of stationary cell, showing pattern of cirri on ventral surface; (2) lateral view of moving cell, showing typical crawling activity on floc.

Download Video clipCarchesium polypinum (2.5 Mb)
Low magnification - showing that separate branches of the colony can contract independently of one another. Higher magnification - showing; 1, zooids (mature adult cells) on end of stalks, and 2, developing telotroch (larval stage) with its extra row of cilia near the posterior end of the cell which it uses for locomotion.


Data used to compile the Guide

In order to mitigate the problem of recognising organisms observed in fresh samples under the microscope, photographs and/or video clips in vivo are provided in addition to descriptions and line diagrams. There are video clips for the 75 or so species most commonly encountered and/or which are of the greatest indicator value. These digitised images are included in order to show key behavioural patterns, eg swimming, feeding etc. Taxonomic descriptions are presented in a way that emphasises the differences between the species known to occur in wastewater treatment, rather than emphasising the features of systematic importance.

Euplotes aediculatus, 5k

Above: Euplotes aediculatus, a crawling ciliate. Scale bar = 50 micrometres.

How the Guide works

Samples are identified by date and location within the sewage-treatment plant and a profile of ciliate diversity is built using the system. The key is essentially pictorial and multi-entry, meaning that users can skip questions that they cannot answer with confidence. Once an identification is reached, the user can review all data associated with the species and confirm or decline the identification for accumulation into the sample profile. There are numerous short-cuts that can be taken for more experienced users. Species are quantified on a scale of abundance (eg few, several, many) rather than counted.

Carchesium  polypinum, 5k
Above: Carchesium polypinum, an attached ciliate. Scale bar = 50 micrometres.

The sample profile is then used in conjunction with ecological data, saprobic indices etc, obtained from the literature in order to calculate an effluent-quality index. Once the ciliate analysis of a particular sample is complete, an automated function will provide a prediction of effluent quality as defined by the biochemical oxygen demand (BOD).

Results accumulated from the user's wastewater-treatment plant may be used to improve the accuracy of local effluent predictions and data may be shared internationally over the Internet via a central server. The profiles themselves can be compared along the length of a process-track (eg an RBC reactor or an activated-sludge channel) which can serve as an indicator of hydraulic performance to detect problems such as short-circuiting or inadequate mixing. The fact that the results of the analysis should be available within an hour or two of sampling will enable remedial action to be taken with minimum delay.


The guide is now available without charge. You can download the software from here, but you have to be registered on the site to do so.

Note that the Terms and Conditions for use of the software are available here.

Project co-ordinators

David McL Roberts (The Natural History Museum, UK )
Alan Warren (The Natural History Museum, UK)
Colin R Curds (The Natural History Museum, UK)
Humbert Salvado (Department of Animal Biology, University of Barcelona, Spain)

Sat, 2008-03-01 13:25 -- dmr
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith