Pilot scale investigation of zinc and sulphate removal from industrial discharges by biological sulphate reduction with molasses as electron donor

Abstract

A biological sulphate reduction process, with molasses as an electron donor, was used for the removal of zinc and sulphate from Rayon industrial wastewater. The process involved reduction of sulphate to sulphide under anaerobic conditions. The sulphide-rich effluent was used to remove zinc as zinc sulphide precipitate. The investigation was conducted at pilot scale with real wastewater from the Rayon industry as feed. The effects of sulphate loading rate and temperature of feeding wastewater were evaluated. The experimental results showed that there was no significant difference in sulphide production when the reactor was operated at 50 +/- 2 degrees C and 65 +/- 2 degrees C. Sulphide production was in the range of 500-515 mg L(-1). In addition, an increase in sulphate loading rate from 6.3 +/- 0.7 kg SO4 m(-3) d(-1) to 14.9 +/- 2.4 kg SO4 m(-3) d(-1) resulted in a dramatic decrease in sulphate removal efficiency. Furthermore, zinc sulphide precipitation at pH 7 removed more than 96% of zinc.

Recovery and Recycling of Zn(II) from Wastewater by Scenedesmus sp. MCC 26 Isolated from a Heavy Metal Contaminated Site

“…The large and middle level viscose and rayon industries generally use 10–20 g/L of ZnSO 4 in acid bath of spinning process and generate 5–50 mass% of zinc in waste effluent . The concentration of zinc in Rayon industrial waste water of Angthog Province of Thailand is reported in the range of 110–300 mg/L whereas as 85 mg/L of zinc is reported from Baroda Rayon in India .…”

“…The techniques conventionally used by viscose industries for zinc removal include precipitation with lime/caustic soda and sulfate that requires large quantities of these chemicals and generate a bulk of toxic sludge which further requires expensive procedure for disposal . Other methods such as evaporation, solvent extraction, ion exchange, membrane filtration are both energy and cost intensive .…”