Unlocking the Potential of Chlorella sp. Biomass: An effective Adsorbent for Heavy Metals Removal from Wastewater

Ntombiphumile Perceverence Tenza, Pr.Sci.Nat. Precious Mahlambi ^* Stefan Schmidt

• University of KwaZulu Natal, Pietermaritzburg, South Africa

Conventional wastewater treatment methods are often ineffective in entirely removing heavy metals, leading to environmental and health risks. These methods are also chemically intensive, and costly, highlighting the need for sustainable alternatives. This study explored the novel use of Chlorella sp. biomass as a sustainable and effective solution for removing heavy metals (copper, lead, and zinc) from wastewater in South Africa. The elemental composition of Chlorella sp. biomass included carbon, nitrogen, oxygen, phosphorus, and sulfur, with slightly higher nitrogen and sulfur levels than reported in the literature. Fourier Transform Infrared Spectroscopy (FTIR) identified key functional groups of Chlorella sp. biomass, such as hydroxyl, carboxyl, carbonyl, amide, and ether groups that bind heavy metal ions. . Batch culture experiments, conducted under varying conditions (biomass dosage 5-100 mg, pH 3-11, contact time 15-115 minutes, and metal concentrations 0.25-16 mg/L) at 25°C, revealed optimal removal conditions: pH 7, 60 minutes contact time, 12.5 mg biomass, and 0.5 mg/L metal concentration. In wastewater samples, Chlorella sp. biomass achieved 100% removal of copper and zinc, and 98% removal of lead. Adsorption data were best fit by the Langmuir isotherm for copper (R² = 0.9888) and by the Freundlich isotherm for lead (R² = 0.976) and zinc (R² = 0.968). The kinetics followed a pseudofirst-order model, and thermodynamic studies indicated an endothermic and spontaneous process for copper and zinc, with lead showing complete removal at all tested temperatures. Chlorella sp. biomass demonstrated high efficiency and sustainability in removing heavy metals from wastewater, presenting a promising alternative to conventional methods. Future research should focus on improved removal by using Chlorella sp. biomass in combination with biomass of other microorganisms and by scaling up to pilot applications.