A Step Forward in Biocapture from Wastewater

Biotechnologists from RUDN University in collaboration with Lomonosov MSU and Kurchatov Institute have made an important contribution to the technology of phosphate and nitrate biocapture from wastewater using Lobosphaera algae fixed on the filters. Biomass obtained in the course of this process can be used as a fertilizer. The results of the study were published in the Journal of Water Process Engineering.

Phosphates and nitrates find their way into wastewater with industrial and household waste, especially detergents. Normally, both substances are parts of phosphorus and nitrogen chemical cycles. However, when these cycles are disturbed by human activity, the growing amounts of phosphates and nitrates cannot be processed by water ecosystems. As a result, these substances turn from useful nutrients to harmful pollutants. To manage the pollutants, wastewater is currently treated with special equipment and microorganisms, including microalgae, that consume phosphates and nitrates.

In order to recapture the valuable elements and reduce their polluting effects, the biotechnologists have recently developed a biopolymer filter upon which useful microalgae can be placed. The polymer is chitosan-based, safe for the algae, biodegradable, and able to capture chemical elements from wastewater more effectively than its existing analogs.

Chitosan polymers make algae consume nutrients

“Our team was the first 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 polysaccharide with amino groups and its chemical composition is similar to that of chitin, 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, chitosan 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 experiment, the team concluded that a complex of microalgae cells and chitosan-based polymer with a total molecular mass of 600 kDa was effective. 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.

Used chitosan biofilters can be repurposed as fertilizers. With time, chitosan degrades without causing any harm to the environment, while the algae acts as a source of accumulated phosphates and nitrates for the plants.

“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,” said Dr. Solovchenko.