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Pengolahan Kimia

Learn about the process of chemical treatment to remove contaminants from water sources, with a focus on softening hard water through various chemical reactions like coagulation and precipitation.

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Pengolahan Kimia

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  1. Pengolahan Kimia

  2. Penyisihan unsur pencemar dengan cara penambahan chemical agent/bahan kimia sehingga terjadi reaksi kimia, contoh : koagulasi dan presipitasi • Prinsip dasar: perubahan bentuk terlarut/tersuspensi menjadi bentuk yang terendapkan (kecuali desinfeksi) sehingga lumpur yang terendapkan termasuk kategori B3 (perlu treatment khusus)

  3. Kelebihan pengolahan secara kimia: • Efisiensi tinggi (dapat mencapai angka yang diinginkan) • Waktu dentensi relatif singkat sehingga volume reaktor/unit pengolahan relatif lebih kecil • Kekurangan • Ada penambahan zat aditif sehingga meningkatkan konsentrasi Total Dissolved Solid (TDS). Penyisihan TDS relatif sulit dan mahal: membran atau destilasi • Meningkatkan beban pengolahan • Biaya bahan kimia cukup mahal = biaya untuk energi

  4. Softening Benno Rahardyan Faculty of Civil and Environmental Engineering - ITB

  5. Private Water System Resources

  6. Hard water

  7. What is "Hard Water"? • Perhaps you have on occassion noticed mineral deposits on your cooking dishes, or rings of insoluble soap scum in your bathtub. These are not signs of poor housekeeping, but are rather signs of hard water from the municipal water supply. • Hard water is water that contains cations with a charge of +2, especially Ca2+ and Mg2+. • These ions do not pose any health threat, but they can engage in reactions that leave insoluble mineral deposits. These deposits can make hard water unsuitable for many uses, and so a variety of means have been developed to "soften" hard water; i.e.,remove the calcium and magnesium ions.

  8. water hardness Hard water is water contaminated with compounds of calcium and magnesium. Dissolved iron, manganese, and strontium compounds can also contribute to the "total hardness" of the water, which is usually expressed as ppm CaCO3. Water with a hardness over 80 ppm CaCO3 is often treated with water softeners , since hard water produces scale in hot water pipes and boilers and lowers the effectiveness of detergents.

  9. Problems with Hard Water • Mineral deposits are formed by ionic reactions resulting in the formation of an insoluble precipitate. For example, when hard water is heated, Ca2+ ions react with bicarbonate (HCO3-) ions to form insoluble calcium carbonate (CaCO3), as shown in Equation 1.

  10. This precipitate, known as scale, coats the vessels in which the water is heated, • reduce the efficiency of heat transfer • serious effect for industrial-sized water boilers • scale can accumulate on the inside of appliances, such as dishwashers, and pipes.

  11. Softening

  12. Precipitation

  13. Neutralization CO2+Ca(OH)2 CaCO3(s) + H2O Ca+2 Precipitation at pH 10 Ca+2 +2HCO3-+Ca(OH)2  2CaCO3(s) + 2H2O

  14. Mg+2 Precipitation at pH 11 Mg+2 +2HCO3-+Ca(OH)2  2MgCO3 + CaCO3(s) + 2H2O Mg+2 + CO3= +Ca(OH)2  Mg(OH)2((s) + CaCO3(s) Ionic Balance: addnon non hardness ionic (Na+) : Mg+2 +NaOH Mg(OH)2((s) + Na + Ca+2 +Na2CO3  CaCO3(s) + 2Na+

  15. Precipitation • For large-scale municipal operations, a process known as the "lime-soda process" is used to remove Ca2+ and Mg2+ from the water supply. • The water is treated with a combination of slaked lime, Ca(OH)2, and soda ash, Na2CO3. Calcium precipitates as CaCO3, and magnesium precipitates as Mg(OH)2. These solids can be collected, thus removing the scale-forming cations from the water supply. • To see this process in more detail, let us consider the reaction for the precipitation of Mg(OH)2. • Consultation of the solubility guidelines in the experiment reveals that the Ca(OH)2 of slaked lime is moderately soluble in water. Hence, it can dissociate in water to give one Ca2+ ion and two OH- ions for each unit of Ca(OH)2 that dissolves.

  16. The OH- ions react with Mg2+ ions in the water to form the insoluble precipitate. The Ca2+ ions are unaffected by this reaction, and so we do not include them in the net ionic reaction. They are removed by the separate reaction with CO32- ions from the soda ash.

  17. Ion-exchange • Ion-exchange devices consist of a bed of plastic (polymer) beads covalently bound to anion groups, such as -COO-. • The negative charge of these anions is balanced by Na+ cations attached to them. When water containing Ca2+ and Mg2+ is passed through the ion exchanger, the Ca2+ and Mg2+ ions are more attracted to the anion groups than the Na+ ions. • Hence, they replace the Na+ ions on the beads, and so the Na+ ions (which do not form scale) go into the water in their place.

  18. The ion exchange process • Calcium (Ca2+) and magnesium (Mg2+) ions that cause water hardness can be removed fairly easily by using an ion exchange procedure. • Water softeners are cation exchange devices. Cations refer to positively charged ions. Cation exchange involves the replacement of the hardness ions with a nonhardness ion. • Water softeners usually use sodium (Na+) as the exchange ion. Sodium ions are supplied from dissolved sodium chloride salt, also called brine. In the ion exchange process, sodium ions are used to coat an exchange medium in the softener. • The exchange medium can be natural "zeolites" or synthetic resin beads that resemble wet sand.

  19. The exchange medium can be natural "zeolites" or synthetic resin beads that resemble wet sand.

  20. Softening Process NaZeolite + Ca2+ --> CaZeolite + Na+ and NaZeolite + Mg2+ --> MgZeolite + Na+ • Recharging Process NaCl + CaZeolite --> NaZeolite + CaCl and NaCl + MgZeolite --> NaZeolite + MgCl

  21. Ion exchange softeners replace Ca++ and Mg++ with Na+ ions. Zeolite medium is recharged with Na+ by NaCl brine when depleted.

  22. Ion Exchange Water Softeners • Exchange sodium ions for calcium and magnesium ions in water • May be dietary hazard - hypertension (adds 140 mg/l of sodium in “Hard” water) • Use potassium salt (KCl) for health reasons

  23. many people withhigh blood pressure or other health problems must restrict their intake of sodium. • Because water softened by this type of ion exchange contains many sodium ions, people with limited sodium intakes should avoid drinking water that has been softened this way. Several new techniques for softening water without introducing sodium ions are beginning to appear on the market.

  24. Types of water softening equipment available Water softeners are classified in five different categories: • Manual: There are several types of manual softeners. The operator opens and closes valves to control the frequency, rate and time length of backflushing or recharging. • Semi-automatic: The operator initiates only the recharging cycle. A button is pushed when the softener needs recharging and the unit will control and complete the recharging process. • Automatic: The automatic softener usually is equipped with a timer that automatically initiates the recharging cycle and every step in the process. The operator needs only to set the timer and add salt when needed. It is the most popular type of softener used.

  25. Types of water softening equipment available • Demand initiated regeneration (DIR): All operations are initiated and performed automatically in response to the water use demand for softened water. DIR systems generally have two softening tanks and a brine tank. While one tank is softening the other tank is recharging. • Off-site regeneration (generally rental units): A used softening tank is physically replaced with a recharged tank. Spent softening tanks are then recharged at a central location.

  26. Ion Exchange Water Softener with Sensor- Controlled Recharge

  27. Softener Selection Considerations • Required grain capacity • Daily water use (household population) • Water hardness • Desired regeneration schedule • Initial cost • Water conservation • Other (Iron removal, etc.)

  28. Ion Exchange Water Softener Capacity • Rated by grains of hardness treated between regenerations Example: Water hardness = 200 mg/l Softener Capacity = 2000 gr Household Population = 4 persons Calculate: Water Use = 4 persons x 200 l/person-day = 800 l/day Daily Hardness Treated = 800 l/day x 200 mg/l = 160 gr/day Regeneration Interval = 2000 gr/ 160gr/day = 12.5 days

  29. Recommended Softener Sizes

  30. Ion Exchange Water Softener Recharge Control Method Water Use + -Time Clock -Flow Meter -Hardness - Sensor Initial Cost - + -

  31. Water Softening • Permanent magnet water softeners don’t work • Electrostatic and catalytic descalers may “descale” water, but don’t soften it • Scale will not buildup on pipes, water heater elements, bathtubs etc. • Sudsing action of soaps is not improved

  32. Typical Programmable Water Softener Controller

  33. Reactions • CO2+Ca(OH)2CaCO3+H20 • Ca(HCO3)2+Ca(OH)2=2CaCO3+2H20 • Mg(HCO3)2+Ca(OH)2=MgCO3+CaCO3+2H20 • MgCO3+Ca(OH) 2=Mg(OH)2+2CaCO3 • MgSO4+Ca(OH) 2=CaSO4 +Mg(OH)2

  34. CaSO4+Na2CO3=CaCO3+Na2SO4 • CaCl2+Na2CO3=CaCO3 +2NaCl • MgSO4+Ca(OH)2=CaSO4 +Mg(OH)2 • MgCl2+Ca(OH)2= Mg(OH)2+CaCl2

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