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المحاضرة 3-5

الكلية كلية الهندسة     القسم  الهندسة البيئية     المرحلة 4
أستاذ المادة محمد عبد مسلم عبد الله الطفيلي       04/07/2018 08:43:25
Ferric Chloride:

Because of the many problems associated with the use of ferrous sulfate, ferric chloride is the iron salt used most commonly in precipitation applications. When ferric chloride is added to waste water, the reactions takes place.
2 x 162.2 3 x 100 (as CaCO3) 2 x 106.9 3 x 111 2 x 44

2 FeCl3 + 3Ca (HCO3)2 2Fe (OH)3 + 3CaCl2 + 6CO2

Ferric Calcium Ferric Calcium Carbon
chloride bicarbonate hydroxide chloride dioxide
(soluble) (soluble) (insoluble) (soluble) (soluble)

Ferric Chloride and Lime:

If lime is added to supplement the natural alkalinity of the wastewater, the following reaction can be assumed to occur:

2 x 162.2 3 x 56 (as CaO) 2 x 106.9 3 x 111

2 FeCl3 + 3Ca (OH)2 2Fe (OH)3 + 3CaCl2

Ferric Calcium Ferric Calcium
chloride hydroxide hydroxide chloride
(soluble) (slightly soluble) (insoluble) (soluble)

Ferric Sulfate and Lime:

The overall reaction that occurs when ferric sulfate and lime are added to wastewater may be presented as follow:

399.9 3 x 56 (as CaO) 2 x 106.9 3 x 136

Fe2(SO4)3 + 3Ca (OH)2 2Fe (OH)3 + 3CaSO4

Ferric Calcium Ferric Calcium
sulfate hydroxide hydroxide sulfate
(soluble) (slightly soluble) (insoluble) (soluble)

JAR TEST

The jar test is the most valuable tool available for the evaluation and control of the coagulation process. A jar test apparatus is a variable speed, multiple station or gang unit that varies in configuration depending on the manufacturer. The differences, such as the number of test stations (usually six), the size (commonly 1000 mL) and shape of test jars (round or square), method of mixing (paddles, magnetic bars, or plungers), stirrer controls, and integral illumination, do not have an appreciable impact on the performance of the unit. The jar test can be run to select each of the following:
1. Type of coagulants.
2. Dosage of coagulants.
3. Coagulant aid and its dosage.
4. Optimum operating pH.
5. Sequence of chemical addition.
6. Optimum energy and mixing time for rapid mixing.
7. Optimum energy and mixing time for slow mixing.
The coagulants are rapidly mixed at a speed of 60–80 rpm for a period of 30–60 s then allowed to flocculate at a slow speed of 25–35 rpm for a period of 15–20 min. The suspension is finally left to settle for 20–45 min under quiescent conditions. The appearance and size of the floc, the time for floc formation, and the settling characteristics are noted. The supernatant is analyzed for turbidity, color, suspended solids, and pH. With this information in hand, the optimum chemical dosage is selected on the basis of best effluent quality and minimum coagulant cost (Figure N-1).
















FIGURE N-1
JAR TEST APPARATUS






Typical results from a jar test series might look like the figure below.







المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .