Dewatering of the Sludge

Vacuum filtration is also common in metal finishing industries. A vacuum in this method helps to draw the sludge through filter media. Nylon or polypropylene cloth filter materials are used with fairly good results, although the best filtration is achieved when the filter belts are coated with diatomaceous earth (DE) or with paper. Sludges with 20 to 35% solids content can be produced through this method. 

Pressure filters have recently become the most widely used dewatering devices in the industry, due to improvements in the process. Polypropylene filter material is typically used. Pressures of 80 to 225 psi are employed used to force the sludge water through the filters, leaving a filter cake containing 25 to 35% solids. 

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Settling/sedimentation (followed by separation and additional dewatering of the sludge)... 

Liquid waste streams with a high-suspended solids content can be cleaned up by solids removal in clarifiers, thickeners, and liquid cyclones and by accelerated settling by inclined Chevron settlers or the like [73]. For waste streams with very finely divided solids in suspension (i.e., less than about 100 pm) dissolved air flotation techniques have been shown to be more efficient than methods employing sedimentation. Final dewatering of the sludges obtained may be carried out on a continuous filter or a centrifuge. The clarified water product can be accepted for more potential options of reuse or final disposal options than untreated water, and the separated solids may be burned or discarded to landfill, as appropriate [74]. 

Polymers normally used as coagulant aids or flocculation aids , where the main purpose is to strengthen and increase the size of floes and improve particle capture after coagulation has taken place, are the polyacrylamides of non-ionic, or low to medium cationic or anionic charge. The latter type of polymer also finds application in the dewatering of the sludges produced from clarification treatment of potable water [50]. 

Corrective Action Application In Massachusetts, a municipal wastewater treatment plant receives a number of wastestreams containing heavy metals from local industries. When tested, the dewatered sludge failed the EP toxicity test. In order to permit landfill disposal of the sludge, solidification processes were examined. A soluble, silicate-based system, developed by Chemfix, was ultimately selected which produced a product whose leachate passed the EP toxicity test (Sullivan, 1984). 

Stretford solution. Since 1987, 100% of the waste Stretford solution has been shipped to a metals reclamation facility. Vanadium is reclaimed as vanadium pentoxide. Wastewater treatment sludge. In 1987, the rehnery started a program to recycle this sludge to the coker within the refinery. At the end of 1990, 60% of the sludge was recycled to the coker. The remaining 40% was dewatered onsite at a belt filter press and then landfilled offsite or incinerated. Since 1986, the refinery has paved five plant areas to reduce the amount of dirt and debris washing into the sewer. 

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