Characterization of the treatment units and their microbial communities in a waste stabilization pond system treating wastewater from an industrial complex located in Northeastern Brazil

The Multifactory Wastewater Treatment Plant (MF-WWTP) in Recife, Brazil, receives effluents from 15 different industries as well as domestic waste and, unlike other facilities, has never undergone sludge removal over 20 years of operation. It allowed the establishment of a highly adapted microbial community and a high level of waste removal. This study investigated its physicochemical characteristics and how the microbial composition may contribute to its efficiency. The results indicated a COD and BOD removal of 84%, primarily occurring in Pond 1 (P1, anaerobic), while Pond 3 (P3, aerobic with high algal activity) aided in heavy metal removal. Despite this efficiency, toxicity persisted in the final effluent, evidenced by mitotic index values (9.20–11.44% vs. 6.79% control) and chromosomal alterations (1.49–2.20%), which could be a result of toxin-producing algae in P3. The microbial analysis identified Fervidobacterium as the dominant bacterial genus up to 38% of relative abundance, alongside methanogenic archaea ( Methanolinea and Methanosaeta ), suggesting their importance for the organic substrate conversion and degradation of industrial pollutants. Additionally, the cyanobacteria Cyclotella and the microalgae Planktothrix were highly abundant in P3 (10 mm³.L ^-1 and 9 mm³.L ^-1 , respectively), which might have contributed to the treatment system but also to potential toxin production in the final effluent. These findings suggest that the combination of anaerobic, microaerobic, and aerobic ponds, along with additional polishing units, can be a viable approach for industrial wastewater treatment. Furthermore, both the sludge and final effluent from MF-WWTP could serve as valuable inoculum sources for other treatment units dealing with complex industrial contaminants, aiding in establishing resilient microbial communities for optimized wastewater treatment.