ALKALINE PROTEASE OF BACILLUS ALTITUDINIS GVC11 FOR GELATIN HYDROLYSIS AND SILVER RECOVERY FROM USED X-RAY FILMS

N. Harikrishna, S. Mahalakshmi, Y. Ranjita and Gopal Reddy*

ABSTRACT

Silver is a precious metal used in photographic/X-ray film industry. Around 18-20% of the world's silver needs are supplied by recycling of photographic waste. Emulsion layer on X-ray film contains silver and gelatin, which can possibly be broken down using proteases and release the silver into the solution. In the present study alkaline protease from Bacillus altitudinis GVC11 was studied for silver recovery from used X-ray films. Various parameters such as pH, temperature, enzyme concentration, silver recovery, reutilization of enzyme were studied. 1000 U/mL of alkaline protease removed gelatin completely within 30 min at pH 10 and 40°C. Enzyme was reutilized 6 times effectively for gelatin removal and recovery of silver from X-ray films. Loss in weight of X-ray film after treatment with enzyme was 4% and 10% of silver recovered in hydrolyzate per cycle based on the initial weight of the film.

Keywords: alkaline protease, X-ray film, silver recovery, gelatin, Bacillus altitudinis GVC11.