Sludge dewatering operations

Dewatering is normally required prior to incineration to reduce fuel requirements. 

Dewatering reduces the cost of subsequent treatment processes, particularly thermal processes. 

Dewatering is required prior to land disposal of solids. 

Dewatering reduces the costs of transporting wastes recovered from filtration to their ultimate disposal by reducing their voliune and weight. 

In most cases, the percent solids content of a dewatered solids is set by the requirements for subsequent treatment and disposal. Each treatment technology has an optimum range of percent solid, above or below which the technology will not operate efficiently and economically, if at all. For example, combustion requires that the solid content be greater than 24 %, preferably in foe 28-30 % range for more economical operation. Particulates will vary in percent sohd depending on foe technology and application. 

Prolongation of the life of the m.aterial used as the filter may be effected by proper care. 

Such care includes washing of the filter material with the spray jets after every period of use, removal of grease and fats with warm soap solution if clogged, treatment with diluted hydrochloric acid for removal of lime encrustations, maintenance of scraper bade in careful adjustment to filter drum to prevent tearing of the filter material. 

With regard to chemical use -diluted ferric chloride solutions (10% to 20%) usually give better results in the conditioning of the sludge. A high calcium lime is preferable or sludge filtration work. One should avoid excessive use of chemicals. The quantities of chemicals used for conditioning can be frequently reduced by careful control of the 

Completely digested sludge usually filters more readily than partially digested sludge. 

The concentration of sludge to be filtered is critical as sludge with the higher solid content usually filters more readily than that with a lower solid content. 

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Dewatering technologies can be subdivided into two general processes air drying processes and mechanical processes. This chapter provides an overview of these technologies and concentrates on typical sludge dewatering operations used for wastewater treatment. 

Table 7 shows the expected characteristics for sidestreams from typical thickening and dewatering operations as applied to the conditioned sludge. 

Figure 3 in introduces the Coxsackie Sewage Treatment Plant (STP). The plant s special wastewater chlorination facility, a combined chlorine contact chamber (CCC) second-phase final settler unit, is shown in Fig. 4. This section introduces the sludge chlorination facility of Coxsackie STP and its operational data. At Coxsackie STP, data generated during 19 batches of sludge chlorination are summarized in Tables 10-12. Characteristics of the underflow from the sludge dewatering beds for nine of those...

Belt presses have the advantage of large capacity and automatic operation. The initial capital cost is also low. They were originally developed in the pulp and paper industry. Any slurry with fibers will do well in a belt press, and high-fiber material can be added to the slurry as a filter aid for belt press operation. Today, in addition to pulp dewatering, the belt press is widely used in wastewater sludge dewatering. 

Primary Sludge Primary sludge is generated during primary wastewater treatment, which removes those solids that settle out readily. Primary sludge contains 2-8% solids usually thickening or other dewatering operations can easily reduce its water content. 

Membrane Filter Press. Membrane filter presses use impermeable, flexible membranes, or diaphragms to squeeze the cake for further cake deliquoring, as shown in Fig. 15. This type of filter provides less dead time in a filtration cycle, better washing, and drier cake compared to traditional plate-and-frame and recessed plate filter presses. A comparison of a recessed press operated at 100 psi and a membrane filter operated at 25psi for sludge dewatering is shown in Table 4. ... 

Quantity and Concentration. Depending on the operating parameters, the degree of degradation, and the tightness of the liquor loop, the quantity of adipic acid required is quite small in relation to the alkali feed. At Shawnee, where a filter is normally used as the final sludge dewatering device, the adipic acid consumption rate is usually less than 10 lb/ton of limestone fed to the system, and sometimes as low as 2 lb/ton of limestone. These values correspond to only 0.6 to 3.0 tons of adipic acid per day for a 500 MW plant. 

The sludge fields are flat earth or concrete basins whose bottom is formed by dewatered filtration gravel sand. The cycle of a sludge field operation has the following stages ... 

In this basic layout, the plant experienced some operational problems, due to salt accumulation and the low final water quality. An extension was made to the plant, with the aims of increasing the settling velocity, by the use of other flocculants reducing the pollutant content in the scrubbing medium improving sludge dewatering... 

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