This paper discusses the process of nanofiltration for recovering chemicals and recycling wash water used in photographic processing. Historically, recycling wash water has not been necessary in most areas of the world. However, in many countries today, the cost of water is increasing and regulatory standards are becoming more stringent. It has, therefore, become increasingly important to address the issue of recycling the water used in these processes. Two filtration techniques, which have been widely used to clean up wash water, are reverse osmosis and ultrafiltration.
Reverse osmosis is capable of producing very clean water and high concentrate retentate.
However, the process is very expensive, due to the relatively sophisticated technology it utilizes. Ultrafiltration, on the other hand, is relatively inexpensive but is not effective enough to meet stringent recycling standards. The process of nanofiltration is an effective compromise between reverse osmosis and nanofiltration. Nanofiltration utilizes membranes with pores that fall between those of reverse osmosis and ultrafiltration in size but which are still effective in removing ions from the used wash solution. Nanofiltration is easier to implement and less expensive than reverse osmosis.