A two-stage biological system integrating pseudomonas fluorescens and oscillatoria splendida for heavy metal and nutrient removal from municipal wastewater

The increasing wastewater pollution and its potential harmful impacts make it imperative to seek cost-effective and sustainable solutions for wastewater treatment while exploring options for resource recovery from waste. A two-stage biological treatment system was evaluated: (i) aerobic bacteria) Pseudomonas fluorescens (used to remove pollutants from real municipal wastewater and (ii) the cyanobacteria Oscillatoria splendida used to polish the effluent. The wastewater was obtained from the Greater Ramadi Sewerage Project, Iraq, utilizing three independent composite samples (20 L each) collected from the raw wastewater inlet and characterized for pH, EC, TDS, TSS, nutrients, heavy metals, and total bacterial count. The samples were treated under controlled laboratory conditions at the University of Anbar. Stage 1 involved the exposure of wastewater for 6 h to P. fluorescens 1.5 × 10 8 ) CFU/mL) in a serial glass-filter bioreactor containing activated carbon and polyethylene media. For Stage 2, the Stage-1 effluent was diluted to 20%, 40%, and 60% (v/v (using sterilized distilled water, and fed to O. splendida for 15 days (2,500 lux illumination, 16:8 h light/dark) with sampling on Days 0, 5, 10, and 15. In Stage 1, descriptive reductions were observed in COD (81.4%), TDS (62.6%), Ni (75.1%), and Zn (71.7%) across the three independent wastewater samples; however, due to the limited sample size (n = 3 independent composite batches), a paired t-test confirmed statistical significance only for Co 2+ (p = 0.026). Two-way ANOVA performed on the triplicate experimental data (sub-samples within each batch) from Stage 2 revealed that both the dilution ratio and the incubation day significantly affected all measured parameters (p < 0.05) The greatest decreases occurred at) 20%v/v (dilution for most parameters (EC 56.6%, TDS 99.5%, BOD 5 32.3%, Ni 64.9%, Co. 88.3%) and at) 40% v/v (dilution for phosphate (55.5%) and copper (84.5% (The sequential two-stage system yielded higher cumulative removal efficiencies than the P. fluorescens stage alone) e.g., cumulative COD removal ≈ 93% versus 81.4% for Stage 1 alone). This sequential performance suggests a beneficial treatment sequence, though parallel single-treatment) O. splendida -only) controls were not run under identical conditions to statistically define a synergistic effect. The outcomes indicate that this two-stage biological scheme holds potential as a polishing step for municipal wastewater in resource-limited arid areas like Iraq, providing a preliminary rationale for future circular-bioeconomy and biomass-recovery assessments at a pilot scale.