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Levi Strauss & Co.

VIBROSCREEN Unit Helps Clean Wastewater From Jean Stone-Washing Process

When jean marketers learned that product differentiation helped build sales, it wasn't long before a shrewd salesman asked his manufacturer to provide the feel and look of used jeans on some new products. From these events, the pre-washing and stone washing process began. Millions of Americans from presidents to celebrities proudly wear their comfortable jeans, but the engineers were left with an environmental challenge: how to remove pumice stones and lint from spent wash water. The following article describes how one remarkable company has meet the challenge.

Levi Strauss & Co. continues to act on its commitment to protect the environment. While some companies simple say this as they satisfy the requirement of federal and state regulations Levi Strauss & co. meets its obligations to the environment even when there are no stringent standards, which is often the case in come foreign countries where millions of other consumers have come to enjoy jeans too.

Before Levi Strauss & Co. purchased a plant for stone washing jeans in Corlu, Turkey, plans were made for the proper disposal of wastes. The U.S. Environmental Protection Agency considers secondary treatment by biological processes as the best practicable control technology for cotton finishing operations. Most textile industries direct dischargers in the U.S. use activated sludge processing.

According to an evaluation of water quality standards and treatment technologies by an environment and engineering service, the treatment system is designed to remove solids and associated Biological Oxygen Demand (BOD), to neutralize pH and to reduce the temperature of the laundry discharge. Other goals of the treatment system include that it be simple to operate and require a minimum of technical support and maintenance. BOD varies highly often nearing or exceeding 300 mg/l. Total suspended solids (TSS) loading in the laundry wastewater also fluctuates greatly. The introduction of solid material such as pumice, which is used to "stone wash" jeans, and lint – created by the process – either slows bacteria's ability to digest organic material in wastewater or required additional bacterial treatment to complete the process.

Through years of experience, Levi-Strauss & Co. has found that a certain arrangement or configuration of equipment and processes recovers water quality reasonably well for an acceptable cost. Wastewater flows by gravity from washing machines and extractor trenches into a presedimentation tank after passing through a rough screen. The sludge on the bottom of the tank is lifted to a container. Sludge is removed. The water which comes out from the sludge is returned to the inlet channel. The wastewater that flows from the pre-sedimentation tank passes through an equalization pond. Flow of the wastewater is balanced in this tank.

In Turkey and other domestic factories a pump propels the wastewater to three Kason Vibroscreen Circular screen separators. The gyrator motors of these separators impart vibratory motion to two wire screens, shaking lint and pumice across the screens to the discharge spouts. As this occurs, the water flows through the 4 mesh screen and the 120 mesh screen located below the 4 mesh screen. A cone shaped velocity breaker lengthens screen life and spreads the solids and liquid across much of the screens. Self-Cleaning Kleen Screen Rings prevents screen blinding by the solids. The solids line and pumice descend through tubes to drainable carts. Water drips down to another equalization pond in which the flow of water is controlled. Then the wastewater goes to the heat reclamation system where temperature of wastewater is reduced and the heat is regained for heating new water brought into the system. After the heat reclamation system, the water receives chemical treatment and biological treatment.

It is refreshing to know that at least one multinational company treats the environment elsewhere as respectfully as it does in the U.S. Countries such as Turkey depend on water which in many areas has a large affect on the local economy and health. Kason is proud to be a part of resource recovery for Levi Strauss & Co. .

Screen Tips - Volume 9, Number 3 Winter 1994


Kason VIBROSCREEN Circular Screen Separators help remove pumice stone and lint from spent washwater at Levi Strauss & Company's plant for stone washing jeans in Corlu, Turkey.