Lagoon effluents often contain nutrients that exceed the permissible discharge limits set by the National Pollutant Discharge Elimination System (NPDES), contributing to eutrophication, algal blooms, and disruption of aquatic ecosystems. This study evaluates the performance of a novel iron-dosed up-flow anaerobic sludge blanket (UASB) bioreactor for treating lagoon effluents. The bioreactor was first inoculated with anaerobic sludge from a municipal wastewater treatment plant and fed with a synthetic influent designed to replicate lagoon effluent characteristics (BOD₅: 30 mg/L, TSS: 30 mg/L, NO3-N: 10 mg/L, NH3-N: 3 mg/L, TP: 3 mg/L) and a ferric chloride solution for biomass enrichment. Following acclimatization, monitoring and chemical analyses were conducted to assess the treatment efficacy of the UASB. Redox potential measurements confirmed anoxic conditions (-50 to -200 mV) inside the reactor, and the hydraulic retention time (HRT) was calculated to be approximately 9 hours. The results show that denitrification was the main nitrate removal pathway, while phosphate precipitation occurred via iron-phosphate (vivianite) precipitation. Measurements of total iron and ferrous indicated active microbial iron uptake and the presence of iron-reducing bacteria within the reactor. Total suspended solids (TSS) and volatile suspended solids (VSS) were measured to assess sludge distribution within the UASB. Microscopic analysis revealed that the sludge predominantly consisted of small sludge flocs (100 – 150 µm). Sludge characterization using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) showed a heterogeneous distribution of the sludge materials, with the upper layers enriched in organic matter and the lower layers rich in inorganic constituents such as iron and phosphorus. Depth-specific sludge sampling was used for microbial community analysis through DNA extraction, qPCR, sequencing, and metagenomic profiling. Overall, the iron-dosed UASB bioreactor demonstrated effective nutrient removal and sludge stratification, offering a cost-effective and sustainable approach to lagoon effluent management.
