Abstract
Biogenic selenium, Se(0), has colloidal properties and thus poses solid–liquid separation problems, such as poor settling and membrane fouling. The separation of Se(0) from the bulk liquid was assessed by centrifugation, filtration, and coagulation–flocculation. Se(0) particles produced by an anaerobic granular sludge are normally distributed, ranging from 50nm to 250nm, with an average size of 166±29nm and a polydispersity index of 0.18. Due to its nanosize range and protein coating-associated negative zeta potential (−15mV to −23mV) between pH 2 and 12, biogenic Se(0) exhibits colloidal properties, hampering its removal from suspension. Centrifugation at different centrifugal speeds achieved 22±3% (1500rpm), 73±2% (3000rpm) and 91±2% (4500rpm) removal. Separation by filtration through 0.45μm filters resulted in 87±1% Se(0) removal. Ferric chloride and aluminum sulfate were used as coagulants in coagulation–flocculation experiments. Aluminum sulfate achieved the highest turbidity removal (92±2%) at a dose of 10−3M, whereas ferric chloride achieved a maximum turbidity removal efficiency of only 43±4% at 2.7×10−4M. Charge repression plays a minor role in particle neutralization. The sediment volume resulting from Al2(SO3)4 treatment is three times larger than that produced by FeCl3.
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