Thickened waste disposal

Fig. 3. The beneficiation of taconite ore on Ihe iron range requires large volumes of water in concenlrating by magnetic separation. To eliminate massive waste-disposal problems, huge thickeners, such as the 300-foot (91,5-meter) diameter caisson unit shown here, are used. This system will handle over 70 million gallons (265 million liters) per day or 50,000 gallons (189,250 liters) per minute of liquid and 250 tons per day of suspended solids. Clarifying the waste tailing stream permits reclamation of water on a large scale for plant reuse...

A thickener in a waste disposal unit of a plant removes water from wet sewage sludge as shown in Fig. E2.1. How many kilograms of water leave the thickener per 100 kg of wet sludge that enter the thickener The process is in the steady state. 

The raw potassium manganate(VI) from the secondary roaster or the Hquid-phase oxidizer contains a fair amount of insoluble material such as unreacted MnO and ore gangue. In most continuous processes, these insolubles are removed by sedimentation using thickeners or filtration and are disposed of as waste. 

Table 28-2 lists some of the currently used pretreatments and ultimate disposal methods for hazardous wastes (6). Pretreatment refers almost entirely to thickening or dewatering processes for liquids or sludges. This process not only reduces the volume of the waste but also allows easier handling and transport. 

The above-cited studies demonstrate the performance of a particular unit system for the treatment of specific type of waste stream. A particular unit system alone may not be able to treat the wastewater to a level of effluent standard prescribed for its safe disposal. Hence a number of pretreatments, such as screening, sedimentation, equalization, and neutralization, and post-treatment units such as secondary sedimentation, sludge thickening, digestion and disposal, disinfection, and so on, are extremely important for complete treatment. The effluent treatment and disposal facilities adopted by various types of pharmaceutical industries are described in the following sections. 

Figure 11.6. Thickeners for preconcentration of feed to filters or for disposal of solid wastes [see also the rake classifier of Fig. 12.2(e)]. (a) A thickener for concentrating slurries on a large scale. The rakes rotate slowly and move settled solids towards the discharge port at the center. Performance data are in Table 11.11 Brown, Unit Operations, Wiley, New York, 1950). (b) Deep cone thickener developed for the National Coal Board (UK), in a unit about lOftdia the impellers rotate at about 2rpm and a flow rate of 70 m3/scc with a solids content of 6wt%, concentrates to 25-35 wt % (Svarovsky, 1981).

Fig. 1. Schematic flowsheet of uranium processing (acid leach and ion exchange) operation. Numbers refer to the numbers that appear in the boxes on the flowsheet. Operations (3), (6), (9), and (11) may be done by thickening or filtration. Most often, thickeners are used, followed by filters. The pH of the leach slurry <4) is elevated to reduce its corrosive effect and to improve the ion-exchange operation on the uranium liquor subsequently separated, In tile ion exchange operation (7), resin contained in closed columns is alternately loaded with uranium and then eluted. The resin adsorbs the complex anions, such as UC fSO 4-. in which the uranium is present in the leach solution. Ammonium nitrate is nsed for elution, obtained by recycling the uranium filtrate liquor after pH adjustment. Iron adsoibed with the uranium is eluted with it. Iron separation operation (8) is needed inasmuch as the iron hydroxide slurry is heavily contaminated with calcium sulfate and coprecipitated uranium salts. Therefore, the slurry is recycled to the watering stage (3). Washed solids from 1,6). the waste barren liquor from (7), and the uranium filtrate from (11) are combined. The pH is elevated to 7.5 by adding lime slurry before the mixture is pumped to the tailings disposal area. (Rio Algom Mines Limited, Toronto)...

Solid-Liquid Separators. Most of the SO2 transferred from the fine gas into the liquid in the scrubber is converted to solid sulfur compounds in the scrubber and in the reaction tanks. The solid sulfur compounds and the fly ash collected in the scrubber have to be separated from the liquid and disposed of in a way that does not cause water pollution. Clarifier-thickeners, vacuum filters, ponds, etc., are being used as the solid-liquid separators. The liquid is returned to the system, and the solids are removed as waste. 

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. 

The results of the economic evaluations are presented in Tables 10 and 11. The capital investment and the first-year revenue requirement in Table 10 include the dewatering equipment (thickener and filter) but exclude the waste sludge (filter cake) disposal area. Table 11 lists separately the first-year revenue requirement for the waste sludge disposal area. 

Overview Chemical agents other than mustard were destroyed by neutralization prior to incinerating or otherwise disposing of the generated secondary waste. Mustard in all forms was destroyed by direct incineration. This was the only practical choice where the agent had aged to an intractable solid or had been thickened with polymers. 

This sludge has until now been treated by thickening, conditioning, and dewatering, and been disposed of as solid filter cake on the works-owned special waste dumps. 

The use of wet systems cause the production of a waste water flow. Which needs to be treated, a sludge fraction, which needs to be a disposed of. Some systems work without producing waste water. The sludge is thickened and, if it contains a sufficient amount of bentonite, is re-used in the moulding-sand cycle. 

---