The secrets of activated sludge – a discovery by researchers from the Jagiellonian University in Krakow

Activated sludge, which plays a key role in the biological treatment of wastewater, still holds many secrets. It was discovered that a significant role in this process is played by rotifers. More specifically, the Lecaneinermis rotifiers (microorganisms that naturally occur in activated sludge).

The bacteria found in activated sludge decompose and mineralise the contaminants present in wastewater. Uncontrolled growth of some of them, namely filamentous bacteria, causes foaming and swelling of activated sludge.  This is one of the most serious operational problems faced by every wastewater treatment plant — not only in Poland, but also worldwide. High concentrations of filamentous bacteria result in high costs for treatment plants, reducing their efficiency, and the preventive measures applied so far have a negative impact on the environment.

When sediment swells

If uncontrollable growth of filamentous bacteria occurs, which is often the case, sludge begins to foam and swell, leading to operational and technological problems in treatment plants. This results in improper sludge recirculation and difficulties in maintaining its proper concentration in the aeration chambers. The microbiological composition is disturbed. First of all, this leads to a decrease in the efficiency of the treatment plant, additional difficulties in separating treated sewage, and a deterioration in the quality of its discharge. In severe cases, the treatment plant must suspend its operation and replace the activated sludge, or at least a part of it, with new sludge, and dispose of the defective sludge, which in turn means incurring additional, significant costs and performing burdensome procedures.

How “chemistry” works

Tackling this phenomenon mainly involves the use of expensive aluminium-based chemicals with very low pH. They only act temporarily, minimising the “effects” but not combating the “cause” underlying the whole problem. Furthermore, their disadvantages also include the necessity to introduce technological changes in treatment plants, relatively high application costs, increased sludge weight, and, above all, adverse environmental impact. Operators are accustomed to this method because it is faster and works almost immediately.

Lecane inermis

Two researchers from the Jagiellonian University in Krakow: dr hab. Agnieszka Pajdak-Stós and dr hab. Edyta Fiałkowska developed a biological method to reduce swelling in activated sludge. It can counteract excessive filamentous bacteria growth in wastewater treatment plants.

The technology can be used in treatment plants with inflow of various types of wastewater. This is due to the exceptionally high resistance of rotifers to adverse environmental conditions, acquired thanks to a patented method of culturing these microorganisms, which has been refined over many years and patented. An important feature of the presented technology is that it does not require technological changes in the treatment plant itself, which is often the case when new chemical solutions are introduced. Rotifers also act as bioindicators.

Recently, the developed technology is being successfully implemented in several wastewater treatment plants.

Fight against microplastics

Preliminary studies further indicate that Lecane inermis rotifers have the ability not only to limit sediment swelling, but also to aggregate microplastic particles (average size 1 µm). These are very small particles (<5 mm) formed as a result of mechanical, chemical or photochemical decomposition of plastic, and also produced as additives to chemicals and cosmetics. They currently constitute a very serious problem for the natural environment.

Applause for the researchers from Jagiellonian University!