Algal-bacterial process for the simultaneous detoxification of thiocyanate-containing wastewater and maximized lipid production under photoautotrophic/photoheterotrophic conditions

In this work, a cooperative algal-bacterial system that efficiently degrades thiocyanate (SCN^-), a toxic contaminant, and exhibits high lipid productivity, was developed. A consortium of mixed bacteria (activated sludge) and microalgae was sequentially cultivated under photoautotrophic and photoheterotrophic modes. The hydrolysis of SCN^- to ammonium (NH₄⁺)-nitrogen and subsequent nitrification steps were performed by the initial activated sludge under lithoautotrophic conditions. The NH₄⁺ and oxidized forms of nitrogen, nitrite (NO₂^-) and nitrate (NO₃^-), were then assimilated and removed by the microalgal cells when light was supplied. After the degradation of SCN^-, the cultivation mode was changed to photoheterotrophic conditions in a sequential manner. Algal-bacterial cultures containing Chlorella protothecoides and Ettlia sp. yielded significantly increased lipid productivity under photoheterotrophic conditions compared to photoautotrophic conditions (28.7- and 17.3-fold higher, respectively). Statistical methodologies were also used to investigate the effects of volatile fatty acids and yeast extract on biomass and lipid production.