Hydrogel granules used for wastewater treatment

Researchers from Lithuania’s Kaunas University of Technology (KTU) have developed an innovative method for cleaning contaminated water. Hydrogel granules made from polyvinyl alcohol function as a biological carrier for microorganism cultures, which decompose pollutants in wastewater. The researchers say their treatment works up to five times faster than conventional methods.

According to a 2020 European Commission report, 95% of wastewater in the EU is collected and 88% is biologically treated; however, over 6% is not sufficiently well treated to meet secondary biological treatment standards. KTU researcher Judita Švaikauskaitė said the increasing number of micropollutants in waste and surface water poses challenges to wastewater treatment plant engineers around the world.

“Water quality in the European Union is being closely monitored and analysed,” Švaikauskaitė said. “The wastewater treatment companies need to update their methods with up-to-date technologies. Ozonation and other oxidation methods, biological treatment and membrane filtration are the advanced technologies used to remove pollutants from water. Also, to improve the efficiency of biological treatment various biological carriers are used.”

Hydrogel granules, designed by environmental scientists at KTU, are made from polyvinyl alcohol (PVA). Sized 3–4 mm in diameter, a granule has a porous structure made of macropores of up to 20 µm — an appropriate size to immobilise microorganisms — and can serve as a biological carrier. The use of PVA hydrogel granules in biological wastewater treatment technologies can increase the removal efficiency of pollutants up to five times compared to conventional activated sludge treatment.

“Inside the pores of the granules, cultures of microorganisms that decompose pollutants in wastewater can live,” Švaikauskaitė said. “The network of pores in the PVA hydrogel granules ensures a constant supply of oxygen and nutrients to the bacteria inside the granules, thus creating a highly durable and efficient biological wastewater treatment system.”

PVA hydrogel granules are mechanically stable and therefore suitable for long-term use. The bacteria play a significant role in this process — they use ammonia, phosphate, organic compounds and other dangerous chemical substances as nutrient and energy sources. A wide spectrum of bacteria can be immobilised inside a gel granule. PVA hydrogel granules demonstrate great absorption capacities for organic micropollutants and pharmaceuticals.

“PVA hydrogel granules not only increase the efficiency of the biological wastewater treatment system but also have excellent sorption properties in removing residues of pharmaceutical substances and other micropollutants from wastewater,” Švaikauskaitė said.

The environmentally friendly solution was created by Švaikauskaitė together with researchers Inga Urniežaite and Vytautas Abromaitis. Their invention was recently presented at the KTU innovation fair Technorama, where it beat more than 70 other ideas for new technologies and scientific innovations to take out the highest prize.

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