Biosorption of synthetic dyes by live and dried marine diatom Phaeodactylum tricornutum and freshwater diatom Navicula cryptocephala var. veneta.
Howard Ceaira C, Rahman Tahira Tasneem TT, Li Mingyue M, Hortin Kesler K et al.
Diatom biomass has emerged as a promising biosorbent for removing dye pollutants from dye-bearing wastewater due to its low cost, sustainability, and abundant surface functional groups. Despite interest in algal biosorption, limited studies have compared live and dried biomass across different diatom species. The relative importance of species identity, biomass state, and operating conditions therefore remains unquantified. This study addresses these gaps by investigating the adsorption of three cationic dyes: crystal violet (CV), malachite green (MG), and basic fuchsin (BF), by two diatom species, Phaeodactylum tricornutum and Navicula cryptocephala var. veneta. The effects of dye concentration, pH, temperature, and biomass state were systematically evaluated. For dry cells, adsorption capacity increased with dye concentration due to enhanced mass transfer driving force. Maximum removal efficiencies by P. tricornutum reached 91.3% for CV, 88.6% for MG, and 85.9% for BF, corresponding to equilibrium adsorption capacities of 16.7, 36.6, and 26.6 mg/g, respectively, while N. veneta showed lower removal (13.8, 31.8, and 20.3 mg/g) and earlier saturation at higher concentrations. Neutral pH yielded optimal performance. However, MG and BF exhibited strong pH dependence because of surface charge effects and dye ionization, while CV was relatively insensitive to pH. Temperature effects were strongest for MG, smaller but significant for BF, and not significant for CV. Species and biomass state were the dominant factors controlling adsorption. P. tricornutum consistently outperformed N. veneta across all dyes and conditions tested. Dried biomass achieved significantly higher removal (CV = 70% to 91%, MG = 75% to 87%, BF = 61% to 84%) than live biomass (CV = 45% to 85%, MG = 70% to 82%, BF = 49% to 79%). This may be due to the drying process removing extracellular polymeric substances and membrane barriers, exposing reactive functional groups (e.g., -COO- and Si-O-) and promoting surface-controlled electrostatic interactions. Isotherm analysis indicated adsorption onto an energetically heterogeneous surface. The concentration range examined did not reach saturation in all systems, so maximum adsorption capacities are reported only where the data constrain them. These findings establish biomass state and species identity as the dominant controls on dye biosorption under the conditions tested. This work highlights dried marine and freshwater diatoms as sustainable biosorbents for broad-spectrum dye remediation.