Thiosulfate biodegradation–silver biosorption process for the treatment of photofilm processing wastewater

• Published in: Process biochemistry (1991) Vol. 38; no. 6; pp. 855 - 860
• Main Authors: Pethkar, A.V., Paknikar, K.M.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.2003
• Subjects: Biodegradation; Photofilm; Wastewater; Biodegradation; Photofilm; Wastewater
• ISSN: 1359-5113; 1873-3298
• DOI: 10.1016/S0032-9592(02)00054-7

Wastewaters emanating from photofilm processing units contain considerable amount of silver. An attempt was made to remove silver from the wastewater. It is known that these process solutions contain high concentrations of thiosulfate that interferes with silver removal by physical/biological means. Hence, a chemoautotrophic bacterium Thiobacillus thioparus tolerant to 350 mg silver l −1 was grown in 1:10 diluted wastewater. The organism oxidized thiosulfate (18.5 g l −1) to sulfate (31.2 g l −1) and sulfur (0.4 g l −1). Thiobacillus treated wastewater was then contacted with a preferentially silver biosorbing fungal culture Cladosporium cladosporioides #1 for silver recovery. Optimum parameters for silver biosorption were, pH 7–9; biomass concentration 2.5% (w/v) and contact time 20 min. T. thioparus treated wastewater was passed in continuous upflow mode through a biosorbent column containing C. cladosporioides beads. Silver (43 mg g −1) from the column was eluted in concentrated form with 0.1% alcoholic sodium cyanide solution and recovered by electrowinning. The final recovery efficiency was 70%.