Rotifers – the allies from the invisible world

Print Friendly Version of this pagePrint Get a PDF version of this webpagePDF





Biological wastewater treatment methods are commonly used, effective ways to deal with the problem of liquid waste. However, they are not free from flaws. Scientists from the Jagiellonian University are working to eliminate one of these issues, so-called sludge bulking.

The demand for clean water and, as a consequence, the amount of wastewater produced is growing year after year. It is becoming a serious threat for the natural environment and the challenge for those responsible for water purification. Modern wastewater treatment plants are technologically complex, automated industrial facilities that treat wastewater until it reaches a state when it is not harmful for the environment anymore. These processes utilize various equipment, technologies and methods, but biological methods still remain the most commonly used, the most effective and the most environmentally friendly. These methods are based on the elimination and mineralization of organic and biogenic contaminants (mainly nitrogen and phosphorus compounds) in the course of aerobic and anaerobic processes with the participation of various microorganisms.

Place of action

In a typical wastewater treatment plant, biological decomposition takes place in chambers or bioreactors containing activated sludge, which are the essential element of the whole technological process. Activated sludge is a complex collection of various bacteria and microscopic organisms inhabiting organic and inorganic particles aggregated in the form of so-called flocks, freely floating and mixing in the aerated bioreactor. Contaminants flowing in constantly with the wastewater provide nutrients for bacteria and enable them to grow intensely. On the other hand, protozoa, including the first of all ciliated protozoa, amoebas and flagellates, as well as small metazoans such as nematodes, rotifers, oligochaeta or water bears (Latin: Tardigrada) maintain the high density of bacteria in the phase of high biological activity by feeding on the bacteria and mechanically crumbling the flock. All bacteria and microorganisms in the activated sludge live in close interdependence and remain in an easily disturbed balance.

Flock of activated sludge full of filamentous bacteria. FISH method


Filamentous bacteria, Type 0092, Microthrix parvicella, and other common types are usually present in the flocks and, in small amounts, in the activated sludge. As the result of various disturbances, the quantity of filamentous bacteria may increase rapidly and the bacteria may disseminate outside the flock. Such a situation causes a serious disturbance in the biological treatment processes, and excessive growth of filamentous bacteria leads to the phenomenon of sludge bulking, which eventually affects the functioning of the whole wastewater treatment plant. An excessive amount of filamentous bacteria has an adverse effect on all living elements of the activated sludge biocenosis, leading, in turn, to a dramatic decrease in the performance of the wastewater treatment plant, technical problems, insufficient elimination of contaminants and a threat for the environment and surface waters. Nowadays, commonly used methods of preventing a mass occurrence of filamentous bacteria consist in the construction of additional chambers, also known as "selectors," and integrating them with the technological system of the wastewater treatment plant or in adding chemical agents directly into the chamber containing activated sludge. Some of the most popular agents include metal salts (aluminum, iron or copper), as well as other coagulating compounds (influencing the aggregation of particles), which, through their activity, improve sedimentation (settling of particles) of filamentous bacteria and thus eliminate the effects of their mass occurrence. Unfortunately, the chemicals often kill other groups of beneficial microorganisms and protozoa. What is more, they are not without harm to the environment.

Innovative solution

Research conducted within the project entitled "Control of the bulking of activated sludge using rotifers (Rotifera)" by the Aquatic Microbial Ecology group at the Institute of Environmental Sciences of the Jagiellonian University resulted in the discovery of a biological method of controlling the population of filamentous bacteria with use of rotifers (Latin: Rotifera). Rotifers are microscopic multicellular organisms that commonly (but not excessively) occur in activated sludge and any naturally aquatic environment. In the course of analysis of the activated sludge samples from wastewater treatment plants from various regions of Poland, the scientists from the Jagiellonian University isolated strains of rotifers, Lecane inermis, which are capable of eating the most common filamentous bacteria. Further research has proven that large quantities of rotifers cultured in a laboratory and then introduced into the sludge threatened by bulking, effectively eliminate filamentous bacteria and prevent adverse phenomena. Moreover, rotifers are resistant to most contaminants that are present in wastewater and they can be artificially introduced even to sludge in which they did not occur previously. Promising results of research give us hope to develop methods and incubators that will enable mass cultures of rotifers and their commercialization for the purposes of limiting and/or controlling the population of filamentous bacteria directly in wastewater treatment plants.

The above-described biological method to limit activated sludge bulking has been patented in Poland and internationally. Moreover, it was awarded a gold medal at the 17th Moscow International Salon of Inventions and Innovation Technologies, ARCHIMEDES 2014. The ongoing research is extremely important from the practical point of view, as it addresses the current problems and needs of wastewater treatment plants and provides them with a new method to fight filamentous bacteria that is an alternative to the chemical methods currently used.

Research team: Aquatic Microbial Ecology Group, Institute of Environmental Sciences, Jagiellonian University in Kraków: Janusz Fyda, PhD; Agnieszka Pajdak-Stós, PhD; Edyta Fiałkowska, PhD; Mateusz Sobczyk, MA; Wioleta Kocerba-Soroka, MA The University of Warmia and Masuria, Olsztyn, Poland: Adam Drzewicki, PhD; Ewa Kowalska, MA

Project Implementation Unit Adjustment Water and Sewage Management in the Municipality Czechowice-Heirs: Małgorzata Pławecka, MA
The University of Barcelona, Spain: Humbert Salvadó-Cabré, PhD
Schmalhausen Institute of Zoology of the National Academy of Sciences of Ukraine, Kyiv, Ukraine: Roman Babko, PhD