Synergistic role of Trichormus variabilis and zeolites in three-layer culturing system for modulating the wastewater effluent community

Due to their nitrogen-fixing capabilities, cyanobacteria hold significant potential for wastewater bioremediation through nutrient removal and modulation of the microbial community. The current study explored these traits using the cyanobacterium Trichormus variabilis strain AICB 1382 in combination with natural zeolites to treat municipal wastewater effluent. A combination of colorimetric, gravimetric, and 16 S/18S rDNA amplicon sequencing analyses was used to evaluate nutrient removal rates, biomass yield, and microbial community structure. The zeolites-AICB 1382 pair features (i.e. gradual release of nutrients by zeolites and vertical distribution of the cyanobacterium) enabled the stratification of the culturing system into three layers with distinct morphology and microbial populations. Results showed efficient removal of nitrate (up to 91.8%), ammonium (up to 97%), and phosphate (up to 99.2%), with enhanced biomass yields in zeolite-enriched cultures. T. variabilis reduced the diversity of the prokaryotic and eukaryotic community, lowering the presence of multidrug-resistant bacteria, whereas zeolites promoted the development of AICB 1382 and increased microbial diversity. The three-layer culturing system offers a promising solution for nutrient reclamation, biomass production, and pathogen reduction, with potential for scale-up as a semi-continuous, self-sustaining method that facilitates biomass harvesting while ensuring environmental safety for agricultural reuse or discharge into urban rivers.