RUDN Biotechnologists developed an effective technology for nutrient biocapture from wastewater

Wastewater pollutes the environment and can cause natural water bodies to bloom. In addition, elements that could find useful applications are thrown away with it. Therefore, special man-made facilities are built to treat wastewater, and biotechnology often comes to the rescue. In this case microorganisms, including microalgae, which can be free-floating or attached to various filters, help decompose pollutants. RUDN biotechnologists proposed a new polymer design for such facilities, which will allow a times more efficient extraction of the necessary elements from wastewater, will be biodegradable and will not damage algae cells.

“Our team was the first c to successfully use cross-linked chitosan polymers to immobilize unicellular algae and make them effectively consume nutrients while at the same time not preventing them from growing and photosynthesizing”, — said Alexei Solovchenko, a PhD in Biology from the Department of Agrobiotechnology, RUDN University.

Chitosan is a substance from crustacean shells and cell walls of zygomycetes fungi. It is a polysaccharide with amino groups and its chemical composition is similar to that of chitin which strengthens its external skeleton arthropods. Chitosan is not water-soluble and therefore can be used to grow algae; does not disintegrate or decompose prematurely.

To make the polymers, long branched molecules with repeating similar links-monomers, it is necessary to cross-link chitosan molecules and glutaraldehyde molecules, a compound used for disinfection, preservation and fixation in dentistry, surgery, and other areas of medicine. The polymer of chitosan and glutaraldehyde was porous and hydrophilic, absorbing water, and did not interfere with algae growth for seven days.

The green microalgae that were bound with this polymer belong to the PPAS 2047 strain of the genus Lobosphaera, patented by the authors of the project.

Chitosan is a polysaccharide with amino groups and its chemical composition is similar to that of chitin that can be found in shellfish crusts and mushroom cell walls. Chitosan is not water-soluble and therefore can be used to grow algae. However, it is biodegradable. Using an original methodology developed in the Kurchatov Institute, it was cross-linked with glutaraldehyde molecules and thus turned into a strong biocompatible polymer. Then, the team grew the IPPAS C-2047 strain of the Lobosphaera incisa algae on it for seven days.

Based on the results of the seven-day long experiment, the team concluded that a complex of microalgae cells and chitosan-based polymer with a total molecular mass of 600 kDa was more effective than that with a molecular mass of 250 kDa. The algae on the filter captured the nutrients more efficiently than those suspended in the wastewater: specifically, they consumed phosphates 16.7 times and nitrates 1.3 times faster.

“Our team has demonstrated that cross-linked chitosan polymers are safe for the environment and effectively support the biocapture of nutrients from wastewater by unicellular algae. When added to a non-toxic medium, the algae biomass could be used as a fertilizer that would gradually release the accumulated nutrients into the soil,” added Alexei Solovchenko.

The results of the study were published in Journal of Water Process Engineering.