BAR SCREENMATA KULIAH PBPABJURUSAN TEKNIK LINGKUNGAN

FUNGSI DAN KRITERIA DISAINberfungsi untuk menyaring benda-benda terapung dan melayang, seperti plastik, kertas, logam, bangkai binatang, daun, yang terdapat dalam air buangan agar tidak mengganggu proses selanjutnya. Selain itu juga untuk melindungi peralatan mekanis dan menghindari penyumbatan (clogging). Kriteria disain (Qasim, 1980)

KARAKTERISTIK BAR SCREENBar screens are typically at the headworks (entrance) of a wastewater treatment plant (WWTP), Bar screens are used to remove large objects such as rags, plastics bottles, bricks, solids, and toy action figures from the waste stream entering the treatment plant. Bar screens are vital to the successful operationof a plant, they reduce the damage of valves, pumps, and other appurtenances. Floatables are also removed at the entrance to a treatment plant, these are objects that "float" on the surface of the water and if aren't removed end up in the primaries or aeration tanks. It is not uncommon to see floatables hanging over the weirs of some clarifiers. Though they don't diminish the function of those processes, floatables are rather unsightly.

Coarse bar screens (or bar screens) are distinguished from fine screens by the space opening. Coarse screens usually have a spacing of 6 mm (or 0.25 in [metric system conversion]). and larger, whereas fine screens spacing is usually between 1.5 mm (or 0.059 in) through 6 mm (or0.25 in [metric to inches]). Fine screens are installed at some wastewater treatment plants that do not have primary treatment to minimized clogging of downstream liquid and solid processes. Fine screens have been used for "effluent polishing" which increases secondary effluent to tertiary effluent quality. They also are installed upstream of the trickling filters to minimize clogging and fouling of distributor nozzles.

TYPE OF BAR SCREENTypically bar screens fall under two classification, mechanical bar screens and manual bar screens (trash racks can either be manually cleaned or mechanically cleaned). Both manual and mechanical screens contain equally spaced vertical or inclinedbars that span the width of a channel. Design considerations for both mechanical and manual screens include: bar spacing, bar size, geometry of bar, channel width, angle of screen and approach velocity.

PENAMPANG MELINTANG

CONTOH PERHITUNGAN1. Disain terpilih

2. Saluran Pembawa

3. Perhitungan jarak bar dan dimensi ruang barLuas bersih yang melalui rack :

Kedalaman bersih pada rack

Terdapat 50 spasi bersih dengan ukuran 25 mmTotal lebar ruang bar = 50 x 25 mm = 1,25 mTotal jumlah bar = 50 1 = 49Lebar bar terpilih = 10 mmLebar chamber = 1,25 m + 10 mm x 49 = 1,74 mKoefisien efisiensi =

4. Perhitungan kedalaman aliran dan kecepatan di chamber pada saat aliran puncak

z1 dan z2 = ketinggian terhadap datum, mv1 dan v2 = kec. di bagian 1 dan 2, m/dtkHl = total kehilangan tekanan, md1 dan d2 = kedalaman aliran, mKe = koefisien ekspansi = 0,3Diketahui lantai/dasar chamber horizontal, reference datum = z2 = 0; Masukan dari saluran 8 cm di atas datum = 0,08 m; Ke = 0,3Dengan trial and error : d2 = 1,28 m

5. Perhitungan kecepatan (v) melalui bar rack saat clear

6. Perhitungan kehilangan tekanan melalui bar racka.

b.

7. Kedalaman dan kecepatan dalam bar rack di belakang saringan

dan

8. Perhitungan head loss melalui saringan saat 50% clogginga. Saat 50% clogging, luas bersih berkurang 50%

Dimana :d2 dan v2 = kedalaman dan kec. saat terjadi cloggingh50 = head loss saat cloggingd3 dan v3 = diasumsikan sama saat bersih (saat tdk terjadi clogging)b. Head loss saat 50% clogging

c. Kec. melewati bar rack

d. Kec. setelah melewati bar rack

e. Kedalaman dan kec. pada bar saat clogging

f. Head loss saat 50% clogging

g. Kec. melewati bar rack