Bar screen

The wedge-bar screen construrtion minimizes frirtion between the screen and the advancing cake to permit the use of a relatively long screen and correspondingly long retention time for the cake without budding. 

Bar Screens These screens are generally used in handling large and heavy pieces of material. They are formed from rails, rods, or bars, suitably shaped made from rolled steel or castings fixed in parallel position and held by crossbars and spacers. Bars, which taper in thickness from top to bottom and may also taper in width from one end to the other, are recommended because they tend to avoid bhnding. 

Average Annual, 424 Maximum Month, 694 Maximum Day, 868 Headworks Bar Screen... 

The wastewater enters the plant through the headworks where it passes through a bar screen, comminutor and Parshal flume. Following the headworks, the wastewater enters the aeration basin where floating surface aerator aerate and mix... 

Headworks The facilities where wastewater enters a wastewater treatment plant. The headworks may consist of bar screens, comminutors, a wet well and pumps. Heterotroph A microorganism which uses organic matter for energy and growth. HRT Hours of Retention Time. 

Preliminary treatment The removal of metal, rocks, rags, sand, eggshells, and similar materials which may hinder the operation of a treatment plant. Preliminary treatment is accomplished by using equipment such as racks, bar screens, comminutors, and grit removal systems. 

A tmospheric-Indoor Bar screen (High H2S concentration Zinc 1... 

Unlike large hydroelectric plants, micro-hydro systems do not require a dam and reservoir, which minimize their environmental damage. A portion of the river s flow is diverted to the micro-hydro intake. A settling tank may be used to allow silt to settle out of the water. A screen or bars screen out floating debris and fish. The water then flows through a channel, pipeline,... 

Material removed by the bar-screen and in the grit chamber can cause odours if not disposed off quickly after removal. However, screenings and grit are not a major source of odours at municipal plants. 

This is a unit operation for removal of large solid matter by passing through screens. The efficiency for large solid removal is 50-99% depending on the type of coarse screen or bar screen to be used. 

Figure 9.15 DSM fiber washing unit (120° model) employing wedge-bar screening surface. (Courtesy Dorr-Oliver, Inc., Stamford, Connecticut)...

Determine the buildup of headloss, h, through a bar screen when 50 percent of the flow area is blocked off by the accumulation of coarse solids. Assume the following conditions apply ... 

Compute the clean water headloss through bar screen. Use the equation... 

Estimate the headloss through the clogged bar screen. Reducing the screen area by 50 percent results in a doubling of the velocity. 

Assuming the flow coefficient for the clogged bar screen is approximately 0.6, the estimated headloss is... 

As in the bar screen, the value of the coefficient can be easily determined experimentally from an existing microstrainer. In the absence of experimentally determined data, a value of 0.60 may be assumed for Q. Also, from the equation, as the microstrainer clogs, the value of A2 will progressively decrease thus the head loss rises to infinity, whereupon, the strainer ceases to function. Although the previous equation has been derived for microstrainers, it equally applies to ordinary screens where the approach velocity is negligible. 

Example 5.1 A bar screen measuring 2 m by 5 m of surficial flow area is used to protect the pump in a shoreline intake of a water treatment plant. The plant is drawing raw water from the river at a rate of 8 m /s. The bar width is 20 mm and the bar spacing is 70 mm. If the screen is 30% clogged, calculate the head loss through the screen. Assume Q = 0.60. 

Bar rack—Also called a bar screen, this is a device composed of large bars spaced widely far apart to separate large objects from a flowing water. 

A water treatment plant drawing water at rate of 8 mVs from a shoreline intake is protected by bar screen. The head loss across the screen is 0.17 m. The bar width is 20 mm and the bar spacing is 70 mm. Assuming that the screen is 30% clogged and using the clear space opening in Problem 5.2, calculate the value of C. ... 

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