Sedimentation clarifiers, treatment

The acid and alkali wastes are pumped from the acid-alkali wastewater sump [T-30] into the acid-alkali treatment module [T-31], Metering pumps controlled by pH instruments feed either acid or caustic to the module as required to maintain an acceptable alkalinity for the formation of metal hydroxides prior to discharge to the precipitator consisting of a mixing tank [T-98], a surge tank [T-99], and a sedimentation clarifier [T-101], The pH is adjusted to a value of 8.5 for optimum metal hydroxide formation and removal. 

Comparatively, the modified reduction-flotation system will have lower annual total cost (amortized capital cost plus O M cost) and will require less space, because the flotation unit is very shallow in depth and thus can be elevated. It is expected, however, that the treatment efficiency of the modified system will be higher due to the fact that the DAF clarifier can separate not only the suspended solids but also organics such as oil and grease, detergent, and so on.57-58-61 Conventional sedimentation clarifiers can separate only insoluble suspended solids. 

Figure 27.12 shows the improved activated sludge process in which a new secondary flotation is applied in series between the aeration basin and the final sedimentation clarifier for increasing the overall treatment performance and hydraulic capacity of an originally overloaded existing plant. 

For an existing conventional activated sludge treatment plant having a fungi problem, installing a DAF clarifier between the existing aeration basin and the final sedimentation clarifier (shown in Figure 27.12) will be the remedy. 

Another alternative involves the addition of a secondary flotation clarifier that parallels the existing secondary sedimentation clarifier in a conventional existing activated sludge wastewater treatment plant. 

Sedimentation clarifiers are generally used for secondary clarification of wastewater. They are characterized by having four treatment sections ... 

The data obtained are reported in figure 1. Tests were then carried out to evaluate the filter effectiveness. The clarified water, after coagulation-sedimentation pre-treatment, fed the filters. Flow was adjusted to 6.8 mh" (14.41/h). The mean results obtained are reported in figures 2 and 3, where details of the filters are given, to (Table 2). 

Secondary Treatment A wastewater treatment process used to convert dissolved or suspended materials into a form more readily separated from the water being treated. Usually the process follows primary treatment by sedimentation. The process commonly is a type of biological treatment process followed by secondary clarifiers that allow the solids to settle out from the water being treated. Sedimentation The process of subsidence and deposition of suspended matter from a wastewater by gravity. 

The pollutants of concern are the same as in wet basic oxygen furnaces, but the concentration of metals (primarily lead and zinc, but also arsenic, cadmium, copper, chromium, and selenium) in wastewater is higher because of the higher percentage of scrap charged. Wastewater treatment operations are similar to those for the wet basic oxygen furnaces, including sedimentation in clarifiers or thickeners and recycle of the water.14... 

Granular bed filters are used in porcelain enameling wastewater treatment to remove residual solids from clarifier effluent (sedimentation effluent or flotation effluent). Filtration polishes the effluent and reduces suspended solids and insoluble precipitated metals to very low levels. Fine sand and coal are media commonly utilized in granular bed filtration. The filter is backwashed after becoming loaded with solids and the backwash is returned to the treatment plant influent for removal of solids in the clarification step.10-12... 

The primary distinguishing feature of the improved activated sludge treatment system is that high-rate DAF is the secondary clarifier for separation of suspended solids from the activated sludge aeration basin effluent, as opposed to secondary sedimentation alone in a conventional activated sludge system. 

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