Custom Search

ENZYMATIC LAUNDRY WASHING IN TUNNEL WASHERS

By Nathan Schiff, Ph.D.  
Schiff Consulting

Introduction  
In the mid 1990's, London Health Linen Service (LHLS), recognized the need to off-set the use of sterile disposables in the OR (operating room). On average, reusables withstand approximately 75 launderings before being ragged. For this reason, they require, proportionately, that much less land fill to dispose of when compared to single use items. Although it was common in Europe to sterilize OR linen, no protocol to do so, existed in Canada at that time. Using FDA guidelines and some European technology, the LHLS pioneered linen sterilization in this country. In so doing, they became the first Central Laundry in Canada, outside of the hospital,  to sterilize linen packs and the Canadian Sterile Repack™ (CSR™) came into existence.   
In order to remain a viable entity, companies, including commercial laundries, are in constant need of adapting new technologies. Since new fabrics are constantly being manufactured, new methods of processing them also need to be developed, taking into account current environmental requirements and energy costs.  
This article deals with one such innovation, the use of enzymes in tunnel washers, to significantly reduce energy costs and improve detergent performance.

What is a tunnel washer  
Tunnel washers are modular machines in which batches of soiled laundry progress through a complete wash cycle, by moving from one module to the next one, where each module performs a specific portion of the cleaning process.  Tunnel washers were developed for use in high volume, continuous applications; typically processing 800 - 1000 lb of laundry per hour and using one-forth the amount of water required by conventional machines.  

What is an enzyme and how does it work  
Enzymes are specialized proteins, manufactured by living cells. They act as catalysts or agents which speed up chemical reactions. Their main function is either to help synthesize new compounds or degrade old ones. Many types of enzymes exist in nature; each one carrying out a specific function and doing so at optimal temperatures of 90 - 100^oF.  Since laundry stains often correspond to the major food categories and their digestive by-products, the enzymes developed for hospital laundry formulations include: amylases, lipases and proteases, which degrade carbohydrate, fat and protein stains, respectively. A protein stained fabric such as one containing dried blood and other bodily fluids can enzymatically be broken down within minutes, at ambient temperatures.

How LHLS Does it  
Using two - 21 chamber tunnel washers, LHLS processes the bulk of their 12,000,000 kg of laundry, annually, from 44 hospitals and clinics as well as providing (CSR™) services to 12 -13 sites of 8-9 hospitals. Each load uses one of 33 different wash formulas, depending on the soil and fabric; and has a residence time of 1½ minutes per tunnel chamber, with a maximum wash time of 32 minutes for a full wash formula. The LHLS uses several of the 21 tunnel chambers for the enzymatic phase of the wash cycle, some fortified with additional additives, to process their load. In all, a total residence time of 7½ to 8 minutes are spent in which the linens are in contact with enzymes. Since enzymes only participate in chemical reactions but are not consumed, very little product is required for optimum performance. Only 1½ to 4 oz of enzyme-containing laundry detergent is required per 100 lb of linen, to degrade stubborn soil. Only 1½ minutes of residence time per chamber is required before the laundry is transferred on to the next module where further soil removal occurs.   

Advantages of Enzymatic Washing  
Biologically derived, enzymes perform best in mild, chemical environments. The pH 9 of the wash solution provides 100 - 500 times less alkalinity than standard wash formulas use, which in turn, extends the life of the garments. Enzymatic detergents also operate at temperatures, typically 50^oF less than required of conventional detergent solutions, resulting in considerable energy savings. Enzymes are totally biodegradable, so disposal of hazardous wastes is never a problem. With an eye towards total environmental responsibility, the LHLS also introduced an alternate bleaching procedure, by replacing their chlorine containing bleach with hydrogen peroxide. The latter is an environmentally innocuous product, though somewhat more expensive, but degrades into water and oxygen, once bleaching has taken place. Toxic and carcinogenic by-products, resulting from chlorine degradation, which include: chloroform and chloroacetic acids are never generated and therefore by the use of hydrogen peroxide, pollution is a non-issue.  

Summary  
Direct costs, measured in dollars to clean 100 lb of laundry, has traditionally been the yardstick for rating the efficiency of a laundry. However, this formula doesn't take into account total costs, including those for linen replacement and energy consumption. Efficiency, as LHLS has shown, is not about chemical usage savings when operating a large, cooperative laundry.  Efficiency is about people working as a team, using the most effective detergents and procedures to achieve total quality management. Couple that with the benefits of a pleasant and air conditioned work environment for the machine operators and you wind up with a winning team. It is therefore not surprising that over 50% of the staff are long term employees with close to 30% of them having joined LHLS, 20 to 30 years ago.