TY - JOUR AU - Shankar, S AU - More, SV AU - Laxman, R Seeta PY - 2010/06/18 Y2 - 2024/03/28 TI - Recovery of Silver from Waste X-Ray Film by Alkaline Protease from Conidiobolus coronatus JF - Kathmandu University Journal of Science, Engineering and Technology JA - Kathmandu University J of Sci, Engineering & Technol VL - 6 IS - 1 SE - Original Research Articles DO - 10.3126/kuset.v6i1.3311 UR - https://www.nepjol.info/index.php/KUSET/article/view/3311 SP - 60-69 AB - <p>The waste X-ray/ photographic films contain 1.5 - 2 % (w/w) black metallic silver which is<br />recovered and reused. Around 18-20% of the world's silver needs are supplied by recycling<br />photographic waste. Since silver is linked to gelatin in the emulsion layer, it is possible to break the<br />same and release the silver using proteolytic enzymes. Alkaline protease from <em>Conidiobolus<br />coronatus</em> was investigated for enzymatic hydrolysis of gelatin from waste X-ray films. At the end<br />of the treatment, gelatin layer was completely removed leaving the polyester film clean and silver<br />was recovered in the hydrolysate, both of which can be reused. Various parameters such as pH,<br />temperature, enzyme concentration, time etc on silver removal from the film were studied. Gelatin<br />hydrolysis was monitored by measuring increase in turbidity in the hydrolysate, which was<br />accompanied by release of protein and hydroxyproline. Gelatin layer was stripped completely<br />within 6 min with 1.35 U ml<sup>-1</sup> of protease at 40&deg;C, pH 10. Rate of gelatin hydrolysis increased with<br />increased in protease concentration. The enzyme could be effectively reused for four cycles of<br />gelatin hydrolysis. Silver in hydolysate was around 3.87% (w/w) based on total weight of sludge.</p><p><strong>Key words:</strong> Silver recovery; X-ray films; gelatin hydrolysis; alkaline protease; <em>Conidiobolus coronatus</em></p><p>DOI: 10.3126/kuset.v6i1.3311</p> <p><em>Kathmandu University Journal of Science, Engineering and Technology </em>Vol.6(1) 2010, pp60-69</p> ER -