METAL REMOVAL FROM ACIDIC ZINC-PLATING EFFLUENTS USING THE INVASIVE MACROALGA RUGULOPTERYX OKAMURAE

The invasive brown macroalga Rugulopteryx okamurae has produced substantial ecological and socioeconomic impacts on coastal ecosystems, particularly along the Algarve coast and the Mediterranean shores of Spain, where its massive accumulation has disrupted local habitats and affected fisheries and tourism. This study evaluated its potential as a bioremediation agent for metal removal from a zinc-plating effluent, as its high abundance makes it a promising material for environmental remediation. The effluent, collected at a zinc galvanizing plant, exhibits very low pH (<2) and high Fe and Zn concentrations. Dry biomass of R. okamurae collected on the Algarve coast was pre-washed, milled, and sieved. Batch assays were carried out for 5 h under orbital agitation using both the original effluent and a 50% dilution. Each assay used 3 g of biomass with 100 mL of effluent and metal removal was assessed at different contact times. Biomass addition caused a pH increase, particularly in the diluted effluent (1.80 to 4.20), while in the original effluent the pH rose from 1.49 to 2.52, indicating acid-neutralizing capacity. The macroalga also showed capacity for metals removal. For Fe (4689.8 mg/L), efficiencies of 35.9–53.0% were obtained in the original effluent and 61.2–61.7% in the diluted effluent after 300 min. For Zn (1452 mg/L), removal reached 24.6–26.0% in the original effluent and 53.2–55.9% in the diluted effluent. Lower efficiencies in the original effluent reflect the higher metal load. These results show the potential of R. okamurae for removal and eventual recovery of metals from highly acidic industrial effluents. Further work is underway to optimize and separate both metals and to elucidate the underlying mechanisms, likely involving both adsorption and precipitation, to support the valorization of this invasive species for bioremediation or strategic metal recovery purposes.