لماذا نعالج المياه كيميائيا3/why treated water chemically3

Dissolved Air Flotation
Dissolved Air Flotation (DAF) Units are becoming increasingly common in water treatment. In DAF units coagulant is added to the raw water or wastewater just before the flocculators. A robust floc has to be formed quickly since upon entering the DAF unit the raw water is mixed with an air pressurized stream of effluent water. The drop in pressure allows the air to be released and the bubbles float to the surface of the flocculator/clarifier.
The coagulated particles
absorb/adsorb/entrap the air bubbles and also float to the top of the vessel. A thickened sludge forms at the top which is periodically removed The coagulant has to be able to form a very robust sludge that will resist fracture in the flocculating chamber. A limitation of the DAF unit is that any sludge particles that fracture will form a very small, almost colloidal, particle that will pass through the filters and reduce the quality of the finished water. For this reason it has been found that the prepolymerized coagulants, that are hel together with chemical bonds, provide the best sludge particle and give the bes finished water quality. The alum sludges, that rely on floc collisions to build a settleable sludge tend to fracture easily. For a DAF unit, a sludge stability test is the best indicator of performance Do not be fooled by large fluffy flocs that look good in a jar test. Prepolymerized salts are often the best choice and should be screened first.

Mixing Intensity
The mixing intensity or available mixing time will have a greater effect on the performance of the chemical rather than on the choice. However, if there is insufficient mixing to optimize the coagulation process it is recommended that a sulphated aluminum or polyaluminum salt be considered. A sweep floc of aluminum hydroxide will be generated that will allow for chemical enmeshment of colloidal particles. While a true coagulation process will not have taken place, with the aid of a good flocculant, the solids should be separated from the water. If the mixing regime is satisfactory it is better to move away from the catalyzed materials and rely on hydrolysis to generate the cationic species required for coagulation and particle collisions for flocculation Chemical efficiency will be much improved and there may not be a need for a flocculant.

Sludge Disposal
Sludge disposal is becoming a very important operating parameter for many utilities. In some jurisdictions it is still possible to return aluminum sludges to a receiving water, including those that have under gone pH adjustment with Na2CO3 or Ca(OH)2. However, lime softening sludges that contain increased Ca(OH)2 concentrations and all iron based sludges have to be dewatered and sent to a land fill site. Settling lagoons and dredging or else the transfer to a municipal wastewater plant are also options for these more hazardous sludges. The type of equipment available to the utility operator, or else the capital monies allocated to plant improvement will have a significant impact on the coagulant choice.

Treatment Objective
The treatment objective will obviously have an impact on the type of treatment regime that is considered. While the processes available to all water plant owners are the same there is a difference in operating philosophy between a municipal supplier and an industrial facility. In the municipal segment the water plant serves the need to produce quality water as an end in itself. Due to public health concerns the municipal water plant operator will always strive to supply the best quality water possible An industrial facility will often treat water for use in the process of the plant Quality is determined by the needs of the process only and not by public health concerns. Economics play a very significant role in the selection of a treatment regime since water treatment is considered a cost of business. To confuse the issue, an industrial facility that only has to meet process quality guidelines may not be able to live with poor quality water for long due to the potential to manufacture off-specification product.

In summary, a municipal water plant is often run to meet regulations and community standards while an industrial process facility is run by economics (an industrial potable water plant has to meet all the government regulations If a water treatment plant operator is planning to optimize the coagulation and flocculation functions within the plant the first option is to consider all the fixed parameters, as shown above It is quite possible that by understanding the process and the chemicals available that many options will be eliminated and that a few will stand out as being good selections. A relatively easy process to select the best from all the good options can then be initiated

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].التعويم بالهواء المذاب
وحدة الداف اصبحت من اكثر الطرق المستخدمة فى معالجة المياه
حيث يتم اضافة المجلطات للمياه الملوثة قبل الدخول لوحدة الداف ثم تضاف الفلوكات داخل وحدة الداف لتكوين فلوكات منفصلة تعالج بالهواء المضغوط لتكوين فقاقيع هوائية سائلة تسمح لنمو البكتريا واتمام المعالجة البيولوجية وتنقية المياه.
الجزيئات المتجلطة
عمليات الادمصاص/الامتصاص/الفصل للفقاقيع الملوثة على سطح مياه خزانات وحدات الداف تساعد على تكوين طبقة رفيعة من السلدج على سطح المياه تتجلط بفعل المجلطات والفلوكات لتترسب داخل حجرات الترسيب
ومن مساوئ وحدات الداف هى ترسيب جزيئات سلدج صغيرة ورغوية تمر من خلال المرشحات فتقلل من كفاءة المياه المعالج بيولوجيا
ولعذا السبب يجب اضافة مجلطات بوليميرية التى تكون روابط كيميائية متعددة تجعل الجزئ كبيرا ومن ثم تجعل السلدج كبير الحجم صعب المرور من المرشحات فيصبح الماء المعالج جيد المعالجة
ولذلك يفضل استخدام البوليمرات الالومونيومية (بولى الومونيوم كلوريد) اكثر من مركبات الالومونيوم (الشبه) فى وحدات الداف وللحصول على سلدج ثابت مستقر يسهل التخلص منه جيدا.
سعة وقوة الخلاطات والقلابات
كلما كان وقت الخلط والتقليب اسرع كلما زادت عملية الترسيب والتقليب وهذا يعتمد على نوعية وتركيز المادة المجلطة ايضا
وهذا يتضح من المقارنة بين الشبه والبولى الومونيوم كلوريد حيث تركيز اكسيد الالومنيوم=15-18% فى الشبه بينما تركيز اكسيد الالومونيوم=30-50% فى البولى الومونيوم كلوريد مما يزيد من قوة الترسيب والتجلط فى زمن ترسيبى سريع مع خلط وتقليب قوى وسريع مما يحفز من التفاعلات الكيميائية وتهدرج الايونات الكاتيونية اللازمة لاتمام عمليات التجلط والفلوكات.
اخراج السلدج
عملية اخراج والتخلص من السلدج اصبحت من اهم طرق المعالجة والتخلص من السلدج الالومنيومى واعادة تدوير المياه وكذلك تظبيط الاس الهيدروجينى باضافة كربونات الصوديوم او هيدروكسيد الكالسيوم حيث يقوموا بتنعيم السلدج والتخلص الامن من المخلفات الوفيرة بالحديد والالومونيوم ودفنها باماكن الدفن المصرح بها بيئيا بدون مشاك
ل.

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» لماذا نعالج المياه كيميائيا2/why treated water chemically2
» why treating water chemically/لماذا نعالج المياه كيميائيا 1
» How is Wastewater Treated to Remove Pollutants?/كيف نعالج مياه الصرف لازالة الملوثات
» طلب مساعدة في ما يخص طرائق التحاليل المخبرية لمراقبة جودة مياه الشرب
» تحاليل المياه/water analysis