Influent

Another alternative involves the use of a weak acid cation exchanger in the hydrogen form. This resin is not capable of removing aH cations. It removes only the amount equivalent to the bicarbonate in the influent water. The acidity in the effluent stream is carbonic acid [463-79-6] which can be eliminated by installing a degasifter. 

In double-deck kilns, green malt is dried on the upper deck to 10—20% moisture with influent air temperature of 40—60°C during the first half of the... 

GAC may be used in fixed or moving beds and in downflow or upflow mode. Eixed beds are operated in downflow mode and as such, provide some amount of soflds filtration however, influent soflds concentration must be kept low (less than 5 mg/L suspended soflds) to prevent rapid plugging of the bed. Entered soflds are periodically removed by backwashing. Upflow beds are more tolerant of soflds because they are fluidized and expanded by the wastewater entering at the bottom. In moving beds, the flow is countercurrent and makeup, fresh carbon is added continuously at the top of the unit while an equal amount of spent carbon is removed from the bottom. 

Dissolved Air Flotation. Dissolved air flotation (DAF) is used to separate suspended soflds and oil and grease from aqueous streams and to concentrate or thicken sludges. Air bubbles carry or float these materials to the surface where they can be removed. The air bubbles are formed by pressurizing either the influent wastewater or a portion of the effluent in the presence of air. When the pressurized stream enters the flotation tank which is at atmospheric pressure, the dissolved air comes out of solution as tiny, microscopic bubbles. Dissolved air flotation is used in many wastewater treatment systems, but in the United States it is perhaps best known with respect to hazardous waste because it is associated with the Hsted waste, K048, DAF flotation soflds from petroleum refining wastewaters. Of course, the process itself is not what is hazardous, but the materials it helps to remove from refining wastewaters. 

Low concentrations of oil can be removed by dissolved air flotation (DAF). In this process, an effluent recycle is pressurized in the presence of excess air, causing additional air to go into solution, in accordance with Henry s Law. When this water is discharged to the inlet chamber of the flotation unit at close to atmospheric pressure, the dissolved air comes out of solution in the form of tiny air bubbles which attach themselves to and become enmeshed in suspended solids and oil globules. The primary design criteria is the air/solids ratio, which is defined as the mass of air released divided by the mass of solids fed. Sufficient air must be released to capture the solids in the influent wastewater. The performance of DAF for the treatment of several... 

Wastewater Coagulant, mg/L Influent on concentration, mg/L Effluent Removal, %... 

Fig. 4. Schematic of a pressurized dissolved air flotation system, (a) Influent pressurization (b) recycle pressurization.

As the sludge age is increased, more of the sludge is oxidized and the net sludge wasted is decreased. If the wastewater contains influent volatile suspended sohds, such as that in a pulp and paper mill, the soHds not oxidized in the process must be added to the net wasted. 

Recent air pollution regulations limit the amount of volatile organic carbon (VOC) that can be discharged from wastewater treatment plants. Benzene is a particular case in which air emission controls are required if the concentration of benzene in the influent wastewater exceeds 10 mg/L. 

Compounds Maximum solubiUty in water, g/L Influent concentration, mg/L Adsorption capacity, kg/m ... 

Table 1 Hsts a number of common inorganic coagulants. Typical iron and aluminum coagulants are acid salts that lower the pH of the treated water by hydrolysis. Depending on initial raw water alkalinity and pH, an alkah such as lime or caustic must be added to counteract the pH depression of the primary coagulant. Iron and aluminum hydrolysis products play a significant role in the coagulation process, especially in cases in which low turbidity influent waters benefit from the presence of additional colHsion surface areas.

Mechanically cleaned racks allow smaller clear openings because head loss does not become so high. Mechanical cleaning can be intermittent or continuous. Intermittent cleaning is cycled by float-operated switches controlled by a float in the influent channel. 

Stormwater overflow is chlorinated, and in some plants the influent may be chlorinated for odor control. 

Reverse Osmosis. In reverse osmosis (qv), a solution or suspension flows under pressure through a membrane the product is withdrawn on the other side. This process can treat dissolved soHds concentrations ranging from 1 mg/L to 35 g/L (14). The principal constraint is the requirement that the waste material be relatively nonfouling. Recent advances have been mosdy in membrane development, and pilot studies are required (15). Energy costs can be significant, and it is frequently necessary to pretreat influent in order to minimize fouhng. Reverse osmosis can deal with particles < 1 to 600 nm in size. 

Tilted-Plate Clarifiers Lamella or tilted-plate separators have achieved increased use for clarification. They contain a multiplicity of plates inchned at 45 to 60° from the horizontal. Various feed methods are employed so that the influent passes into each inchned channel at about one-third of the vertical height from the bottom. This results in the solids having to settle only a short distance in each channel before sliding down the base to the collection zone beneath the plates. The clarified liquid passes in the opposite direction beneath the ceiling of each channel to the overflow connection. 

S = influent waste concentration (mg/L) = treated waste concentration (mg/L) HRT = reactor hydraulic retention time... 

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