Flocculation induced by homogeneous and heterogeneous acid treatments in Desmodesmus communis

•Decreasing the culture pH is an efficient method to harvest D. communis cells.•The flocculation efficiency depends by the low pH value but not by the acid source.•Solid acid carbons are cheap recyclable materials applicable for algal flocculation.•Either the supernatant or the filtered medium can be reused after flocculation.

Flocculation induced by pH decrease is here presented as a solution to pre-concentrate algal cultures of species belonging to Scenedesmaceae and preserve the integrity of the biomass, while maintaining the photosynthetic capacity of non-harvested cells. The low-pH flocculation method gives highly effective results exclusively by the strength of the acid (hydrochloric or formic) used for the treatment, and is applicable to cultures having high cell densities (> 2 g L− 1). High flocculation efficiencies (> 90%) are obtained also by using heterogeneous acids, such as solid acid carbons from naturally available compounds, which are proposed as cheap recyclable materials to be exploited for this purpose. Additionally, the potential reuse of the filtered medium (sterilized or not) and of the supernatant (containing non-harvested cells) is investigated to avoid great water losses and to re-inoculate new cultures.