ebook ipal grit chamber.pdf

Desain Instalasi Pengolah Air Limbah (IPAL)

Mata Kulia Kode MK / Sks / Smtr Program Studi

Dosen

Desain Instalasi Pengolah Air Limbah (IPAL) 1309701 / 4 sks / VII Teknik Lingkungan Fakultas Teknik Sipil dan Perencanaan Institut Teknologi Adhi Tama Surabaya [ITATS} Taty Alfiah, ST.MT.

Grit Chamber

TatyAlfiah/Sabtu, 19 Oktober Oktober 2013 Hlm

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Pengertian dan Fungsi : Grit :

Fraksi organik berat dari bahan padat air limbah dengan kepadatan relatif kira-kira 2,5 sehingga punya kecepatan mengendap yang jauh lebih besar daripada bahan padat air limbah organik (kira-kira 30 mm/det) dibandingkan dengan kecepatan mengendap bahan padat air limbah organik yaitu sebesar 3 mm/det Example : Grit consists of: sand, gravel, pebbles, silt, broken glass, cinders (ash), heavy particulate matter (e.g., corn kernels, bone chips, coffee grounds, egg shells, seeds) Karakteristik grit :

• • • • • •

Tidak membusuk , anorganik Mampu mengendap sec. gravitasi BJ grit =2,65 > BJ organik = 1,02 SG range = 1,3 – 2,7 tipikal 2,65, atau 1,5 - 2,7 [Qasim] kadar air 13-65%, kadar volatil 1-56%, diamtr >= 0,2 mm Pasir, biji-2an, potongan tulang, kulit telur, dll

Most grit collected at WTTPs - nearly 90 percent on average - is larger than 70 mesh in size. In some coastal areas, smaller grit particles down to 100 mesh can be more common.

Grit Size Comparison Chart 1 Sieve Mesh #

Inches

Microns

Similarly-Sized Material

14

.0555

1400

-

28

.0280

700

Beach Sand

60

.0098

250

Fine Sand

100

.0059

150

-

200

.0029

74

Portland Cement

TatyAlfiah/Sabtu, 19 Oktober 2013 Hlm

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Grit Chamber bertujuan untuk :

•

•

• • •

(i) protect mechanical equipments from abrasion. Melindungi atau mencegah terjadinya gesekan pada peralatan mekanik dan pompa akibat adanya pemakaian yang tidak perlu dan akibat adanya abrasi (ii) reduce formation of heavy deposits in pipelines or channels. Mencegah terjadinya penyumbatan pada pipa akibat adanya endapan kasar di dalam saluran Mencegah timbulnya efek penyemenan di dasar sludge digester dan primary sedimentation tank Menurunkan akumulasi material inert di dalam kolam aerasi dan sludge digester yang akan mengurangi volume yang dapat digunakan. (iii) reduce the frequency of tank/reactor cleaning caused by excessive accumulations of grits.

Fungsi : • Grit removal is aimed on removing sand, gravel or other heavy solid materials that have subsiding velocities or specific gravities greater than those of organics in wastewater. Letak dalam IPAL/WWTP : • Grit chambers are commonly located after screening and before primary sedimentation tanks. Grit chambers are of two types: mechanically cleaned and manually cleaned. • In m e c h a n i c a l l y c l e a n ed grit chamber, scraper blades collect the grit settled on the floor of the grit chamber. The grit so collected is elevated to the ground level by several mechanisms such as bucket elevators, jet pump and air lift. The grit washing mechanisms are also of several designs most of which are agitation devices using either water or air to produce washing action. • Manually cleaned grit chambers should be cleaned atleast once a week. The simplest method of cleaning is by means of shovel.

Design Kec. Aliran • Tipikal = 0,15 – 0,3 m/det, • terbaik 0,225 m/det  Φ 0,2 mm, sg 2,65 Kecepatan mengendap Hk Newton :

Vs =

4g(ρs − ρ)d 3CDρ TatyAlfiah/Sabtu, 19 Oktober 2013 Hlm

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Kecepatan settling Hk Stokes :

Vs =

g

18.μ

.(ρ s − ρ).d 2

dimana : vs = kec. Settling ps = densitas partikel p = densitas fluida u = viscositas fluida g = perc. Gravitasi d = diameter partikel Kecepatan scouring :

Vs =

8.β .(s - 1).g.d f

dimana : Vs = kec. Horisontal S = spesifik graviti partikel G = perc. Gravitasi D = diameter partikel β = konstanta = 0,04 – 0,06 f = faktor friksi darcy-Weisbach = 0,02 – 0,03

Secara umum ada 3 jenis tipe grit chamber, yaitu: 1. Horizontal flow grit chamber 2. Aerated grit chamber 3. Vortex Grit Chamber


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Horizontal-Flow Grit Chamber The oldest type of grit chamber for grit removal. The systems are based on a horizontal velocity of the flow equal to 0,3 m/s. • Arah alirannya horisontal • V selalu konstan untuk tiap level debit • Regulator debit : proportional weir, parshal flume, parabola flume The horizontal flow grit chamber is the oldest type of grit removal system. Grit is removed by maintaining a constant upstream velocity of 0.3 m/s (1 ft/s). Velocity is controlled by proportional weirs or rectangular control sections, such as Parshall flumes. In this system, heavier grit particles settle to the bottom of the channel, while lighter organic particles remain suspended or are resuspended and transported out of the channel.


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Desain Instalasi Pengolah ir Limbah (IPAL)

TatyAlfiah/Sabtu, 19 Oktober 2013


Aerated Grit Chamber Menggunakan proses ae asi dengan aliran spiral dan mengguna kan diffuser compressor udara

In aerated grit chambers, ir is introduced along one side of a rectan ular tank to create a spiral flow patter perpendicular to the flow through the t nk. Air flow have to be adjusted in any specific installation: • •  if air flow creates a too high velocity of roll (or agitation), grit will be carried out of the chamber • •   if air flow creates a too small velocity or roll, organic material will be removed with the g it. With proper adjustment, almost 100% f grit will be removed and the griit obtained will be well whashed (no conte t of organic matter). Some advantages of aerat d grit chambers include: • • Consistent removall efficiency over a wide flow range. • • A relatively low p trescible organic content may be remove with a well controlled rate of ae ation. • • Performance of downstream units may be improved by using pre-aeration to reduce septic con ditions in incoming wastewater. • • Aerated grit chambers are versatile, allowing for chemical addiition, mixing, preaeration, and flo culation.




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Design considerations for a erated grit chambers include the following ( WEF 1998): • Air rates typically range from 0.3 to 0.7 m3/m•min (3 to 8 f t3/ft•.min) of tank length. • A typical minimu hydraulic detention time at maximum in stantaneous flow is two minute s. • Typical length-to- idth ratio is 2.5:1 to 5:1. • Tank inlet and o tlet are positioned so the flow is perpendicular to the spiral roll pattern. • Baffles are used to dissipate energy and minimize short circu iting.



Vortex-Type Grit Chamber In vortex-type grit chambers, a vortex flow pattern is used to remove heavy particles. The vortex flow patter can be created by using a rotating turbine or by entering the flow tangentially at the top of the unit Berupa tangki silinder di mana air limbah yang masuk akan menghasilkan pola aliran vortex, gaya sentrifugal dan gravitasi sehingga tejadi pemisahan grit


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Vortex-Type Grit Chamber TatyAlfiah/Sabtu, 19 Oktober 2013 Hlm

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CONTOH PERENCANAAN : HORIZONTA L FL OW GRIT CHA MB E R DIRENCANAKAN :


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Catatan : Untuk desain kedalaman minimum grit storage=10 cm, maka untuk perencanaan ini dipakai kedalaman grit storage sebesar 10 cm namun yang terisi grit hanya sebesar 1 cm


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ebook ipal grit chamber.pdf

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