Biological Approaches for Fluoride Removal from Water

Fluoride contamination in drinking water has become a critical environmental and public health concern worldwide. While fluoride is beneficial at low concentrations (0.5–1.5 mg/L) for dental and skeletal health, chronic exposure to levels exceeding the WHO guideline of 1.5 mg/L can cause dental and skeletal fluorosis, as well as damage to kidneys, the nervous system, and other organs. 

Traditional defluoridation methods—such as chemical precipitation, adsorption, ion exchange, and membrane technologies—are often expensive, energy-intensive, generate secondary pollution, and are impractical for widespread use, particularly in developing regions. In recent years, biological approaches have emerged as promising, cost-effective, and environmentally friendly alternatives. This article reviews the major biological strategies for fluoride removal from water.

Microbial Remediation

Microorganisms, including bacteria, fungi, and algae, have demonstrated considerable potential for fluoride removal through multiple mechanisms. These include biosorption, bioaccumulation, biotransformation, biomineralization, and bio-precipitation.

Biosorption and Bioaccumulation. Living or dead microbial biomass can adsorb fluoride ions onto cell surface functional groups or accumulate them intracellularly. Various bacterial species, including Bacillus strains, have been shown to effectively remove fluoride from contaminated water. For instance, Bacillus licheniformis achieved up to 97% fluoride removal from groundwater.

Microbially Induced Mineralization. A particularly promising mechanism is microbially induced calcium precipitation (MICP) and microbially induced phosphate precipitation (MIPP). In these processes, microbial metabolic activity creates local alkaline microenvironments and secretes extracellular polymeric substances (EPS) that serve as nucleation sites for mineral formation. 

Fluoride is then immobilized into stable, low-solubility mineral phases such as fluorapatite [Ca₅(PO₄)₃F] or calcium fluoride (CaF₂). Strains such as Pseudomonas sp. WZ39 and Acinetobacter LX-6 have achieved fluoride removal efficiencies exceeding 80% through these pathways. The MIPP approach also offers the added benefit of recycling phosphorus from waste sources.

Algae-Based Removal

Microalgae and cyanobacteria offer another effective biological route for fluoride remediation. These photosynthetic microorganisms grow rapidly, require few nutrients, and possess abundant surface functional groups for ion binding. 

The filamentous cyanobacterium Spirulina platensis, for example, removes fluoride through MIPP, forming fluorapatite minerals on its cell surface via ion exchange. Additionally, microalgal-bacterial consortia have been developed that simultaneously remove fluoride and nitrogen from wastewater, achieving fluoride removal rates as high as 96.8%. Even dead algal biomass, such as that of Chara vulgaris, can serve as an effective biosorbent.