Citric acid-assisted biofilm treatment enabling nutrient recovery and safe discharge of hydroponic wastewater.
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75% confidenceThis MES study investigates Bacteriobiome analysis, Biofilm reactor, COD/N ratio. The research focuses on system optimization and characterization.
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Abstract
Soilless greenhouse cultivation generates large volumes of wastewater with high nutrient concentrations, while effective solutions for its environmentally safe management remain limited. This study compared two strategies for final wastewater treatment. In Variant A, wastewater underwent direct biological treatment in a biofilm reactor, whereas in Variant B, it was first alkalized to pH 8.5 to induce phosphorus precipitation and recovery before biological treatment. Citric acid served as the sole organic carbon source, applied at COD/N ratios of 2, 4, and 6. The study evaluated nitrogen and phosphorus removal efficiency, citric acid utilization, sludge characteristics, and bacteriobiome dynamics. Preliminary alkalization enabled recovery of over 95% of phosphorus and improved denitrification, resulting in effluent nitrogen and phosphorus concentrations below discharge limits. Denitrification was efficient across a wide pH range (2.45-8.97), and citric acid supported complete denitrification despite inhibitory effects of increased alkalinity from nitrate reduction or post-alkalization conditions. The COD/N ratios required for complete denitrification were 3.16 ± 0.16 (Variant A) and 3.14 ± 0.10 (Variant B). Higher COD/N ratios enhanced pollutant removal rates and reduced hydraulic retention time. Alkalization had a stronger impact on bacteriobiome composition than on metabolic activity, with structural transformations proving more critical than changes in microbial abundance. Dominant genera included Castellaniella, Paracoccus, and Trichococcus, depending on treatment variant and COD/N ratio. Overall, the two-stage strategy integrating alkalization with citric acid-driven biological denitrification provides an effective and sustainable solution for managing nutrient-rich wastewater from hydroponic systems.