Occurrence of sepiolite in Croatia and its application in phosphate removal from wastewater

Within the serpentine body near Gornje Oresje, Croatia sepiolite was found as alteration product of hydrothermal activity inside peridotitic rocks, developed as monomineral veins (10 cm wide and up to few meters long). Sepiolite was tested for the immobilization of phosphate (P)-accumulating bacteria Acinetobacter junii under sterile (synthetic wastewater) and non-sterile conditions (effluent from the secondary stage of wastewater treatment). In sterile conditions the number of immobilized A. junii was 5.60 × 109 CFU g− 1. The A. junii were successfully immobilized onto non-sterile sepiolite in the original effluent water and the prepared bioparticles contained 2.43 × 108 CFU g− 1 of A. junii and 1.19 × 108 CFU g− 1 of heterotrophs. After 24 h of incubation of bioparticles in effluent water with P concentration adjusted to 20 mg L− 1, the number of immobilized A. junii increased to 6.64 × 109 CFU g− 1. The P removal from effluent water was more efficient in a reactor with bioparticles (94.1%) than in a reactor with planktonic A. junii (73.5%).