Nutrient removal from hydroponic wastewater by a microbial consortium and a culture of Paracercomonas saepenatans

The potential of microbial processes for removal of major nutrients (e.g., N, P) and inorganic cations (e.g., Ca²⁺, Mg²⁺, and Fe²⁺) from hydroponic systems was investigated. Microbial consortium- and axenic culture-based experiments were conducted in a waste nutrient solution (WNS). A microbial consortium grown in the WNS and selected microalgae species of Paracercomonas saepenatans were inoculated in two different synthetic media (Bold's Basal Medium (BBM) and synthetic WNS) in batch systems, and the microbial growth characteristics and the rate and extent of nutrient removal were determined for each system. No toxicity or growth inhibition was observed during microbial growth in either media. Both the waste-nutrient-grown microbial consortium and Paracercomonas saepenatans can be grown effectively in BBM and WNS, and both remove most ions from both media (e.g., >99% removal of NO₃ ⁻ and 41–100% removal of PO₄ ³⁻) within 16 days. Significant nutrient removal was observed during the growth phase of the microbial communities (4–10 days period), indicating major nutrient utilization for microbial growth as well as chemical mineral precipitation. Furthermore, MINEQL + 4.6 modeling showed higher PO₄ ³⁻ removal in WNS during microbial growth (compared to BBM) due to precipitation of phosphate minerals (e.g., hydroxyapatite, vivianite). The dominant microbial species in both systems were also identified. DNA sequencing showed that Vorticella (58%) and Scenedesmus (33%) in WNS and Scenedesmus (89%) in BBM were the predominant species. This study demonstrates the potential application of microbial consortium (predominantly algae and protozoan)-based treatment techniques for hydroponic systems.