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Technical Article Series
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Vibroscreen Unit Helps CleanJean Stone-Washing Process
VIBROSCREEN Unit Helps Clean Wastewater FromJean Stone-Washing ProcessWhen jean marketers learned that product differentiation helped build sales, it wasn't long before a shrewd salesmanasked his manufacturer to provide the feel and look of used jeans on some new products. From these events, thepre-washing and stone washing process began. Millions of Americans from presidents to celebrities proudly wear theircomfortable jeans, but the engineers were left with an environmental challenge: how to remove pumice stones and lintfrom spent wash water. The following article describes how one remarkable company has meet the challenge.
Kason VIBROSCREEN Circular Screen Separatorshelp remove pumice stone and lint fromspent washwater at Levi Strauss & Company'splant for stone washing jeans in Corlu,Turkey.
Levi Strauss & Co. continues to act on its commitment to protect theenvironment. While some companies simple say this as they satisfy therequirement of federal and state regulations Levi Strauss & co. meets itsobligations to the environment even when there are no stringent standards,which is often the case in come foreign countries where millions of otherconsumers 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 biologicalprocesses as the best practicable control technology for cotton finishingoperations. Most textile industries direct dischargers in the U.S. use activatedsludge processing.
According to an evaluation of water quality standards and treatmenttechnologies by an environment and engineering service, the treatmentsystem is designed to remove solids and associated Biological OxygenDemand (BOD), to neutralize pH and to reduce the temperature of the laundrydischarge. Other goals of the treatment system include that it be simple tooperate and require a minimum of technical support and maintenance. BODvaries highly often nearing or exceeding 300 mg/l. Total suspended solids(TSS) loading in the laundry wastewater also fluctuates greatly. Theintroduction of solid material such as pumice, which is used to "stone wash"jeans, and lint – created by the process – either slows bacteria's ability todigest organic material in wastewater or required additional bacterial treatmentto complete the process.
Through years of experience, Levi-Strauss & Co. has found that a certainarrangement or configuration of equipment and processes recovers waterquality reasonably well for an acceptable cost. Wastewater flows by gravityfrom washing machines and extractor trenches into a presedimentation tankafter passing through a rough screen. The sludge on the bottom of the tank islifted to a container. Sludge is removed. The water which comes out from thesludge is returned to the inlet channel. The wastewater that flows from thepre-sedimentation tank passes through an equalization pond. Flow of thewastewater is balanced in this tank.
In Turkey and other domestic factories a pump propels the wastewater to threeKason Vibroscreen Circular screen separators. The gyrator motors of theseseparators impart vibratory motion to two wire screens, shaking lint andpumice across the screens to the discharge spouts. As this occurs, the waterflows through the 4 mesh screen and the 120 mesh screen located below the4 mesh screen. A cone shaped velocity breaker lengthens screen life andspreads the solids and liquid across much of the screens. Self-CleaningKleen Screen Rings prevents screen blinding by the solids. The solids lineand pumice descend through tubes to drainable carts. Water drips down toanother equalization pond in which the flow of water is controlled. Then thewastewater goes to the heat reclamation system where temperature of
wastewater is reduced and the heat is regained for heating new water broughtinto the system. After the heat reclamation system, the water receiveschemical treatment and biological treatment.
It is refreshing to know that at least one multinational company treats theenvironment elsewhere as respectfully as it does in the U.S. Countries suchas Turkey depend on water which in many areas has a large affect on thelocal economy and health. Kason is proud to be a part of resource recoveryfor Levi Strauss & Co. .
Screen Tips - Volume 9, Number 3 Winter 1994
