Waste disposal centrifuges

Centrifugation is performed in a closed system and is therefore an excellent choice for treating volatile fluids. The liquid and solid are mechanically separated by centrifugal force. The removal of most of the liquid increases the solid concentration in, and reduces the volume of, the waste stream. The collected solid waste may then be treated and disposed of or recovered. Three types of units are available for centrifugation the solid bowl, the disk, and the basket. The first two are used in large plants, the third in smaller plants. 

During cheese making, the coagulated milk or curd is used to make cheese while the supernatant whey is a waste product rich in salts, proteins, and lactose. Whey concentration and desalting by UF produce a retentate product that can be used as an animal feed supplement or food additive. The MMV process (Maubois et al., French Patent 2,052,121) involves concentrating the milk by UF after centrifugation to remove the cream and before coagulation to improve yields and reduce disposal costs. 

Waste material snch as tank bottoms from crude oil storage tanks constitute a large percentage of refinery solid waste and pose a particularly difficult disposal problem due to the presence of heavy metals. Tank bottoms are comprised of heavy hydrocarbons, solids, water, rust, and scale. Minimization of tank bottoms is carried ont most cost-effectively through careful separation of the oil and water remaining in the tank bottom. Filters and centrifuges can also be used to recover the oil for recycling. 

NFS claims that DeHg technology offers a low-temperature alternative to other mercury recovery processes. They claim that the final waste form generated by processing passes Toxicity Characteristic Leaching Procedure (TCLP) criteria for disposal, and that centrifuge testing has proven that no free liquid mercury remains in the treated product. 

Wood, D.J., Law, J.D., Todd, T.A. 1998. Demonstration of a SREX process for the treatment of actual high activity waste at the INEEL using centrifugal contactors. Science and Technology for Disposal of Radioactive Tank Waste, Schulx, W.W., Lombardo, NJ. Eds. Plenum, New York, pp. 255-268. 

Financial losses are experienced in oil wasted, in equipment and capital charges of worn equipment in plants, and in land value of disposal ponds. Tremendous disposal ponds of discarded emulsions in Venezuela and elsewhere take up available land. In separating emulsions from tar sands, the extremely abrasive silt has ruined expensive centrifuges and makes using them impractical. 

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]. 

The philosophy of pulp mill emission control is to recover as much fiber as possible before employing other treatment measures. Recovery is obtained by sedimentation and/or flotation methods. Sedimentation may be conducted in a pond, which is periodically drained and the settled material removed (as a semibatch process). Or a clarifier (which operates in a similar manner to a thickener) may be used for continuous operation. The sediment collected contains 90-95% water plus fiber and grit solids. For disposal the waste is dewatered to 50-60% solids in a filter or centrifuge and then burned, which accomplishes both disposal and can permit energy recovery. 

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