Life cycle assessment of diatom frustule production: a multitask bio-material

Diatom frustules have gained increasing interest for their potential use as multitask biomaterials, due to their highly intricate mesoporous siliceous structure that is an attractive scaffold for a variety of special applications. To be used, the organic part must be eliminated from frustules, while preserving the peculiar structure. Four techniques are proposed in the literature, namely: i) oxidative washing with H2O2, ii) chemical treatments with oxidants and acids iii) thermal treatment and iv) plasma treatment. Only techniques (i) and (ii) can be considered of general use, as the siliceous structure is sensitive to the application of (iii), and (iv) is not suitable for some specific applications of the materials. In this paper, Life Cycle Assessment methodology was applied to assess a) the production of frustules by KMnO4-acid treatment or oxidation with H2O2, the two least aggressive techniques and potentially applicable to a larger type of frustules; b) the deep cleaning of so-obtained frustules by thermal treatment, reaching zero-residual‑carbon. LCA shows that KMnO4-acid treatment is 10 times less burdening than the H2O2-based oxidation method and that the production of diatoms generates an impact higher than the cleaning on Global warming and on all other categories. The overall production of clean frustules at lab scale results in an impact of 12 kg CO₂ eq./g of frustule, a value expected to decrease substantially with the implementation of upscaled cultivation methods. Biorefinery approach, that allows the extraction of several added-value products from diatoms, would produce an economic advantage coupled to the reduction of the impact.