Certification Action Line — Answers — June 2014

June 10, 2014

b. Package plants are available from a number of manufacturers, and are perhaps most commonly supplied for filtration of turbid waters and removal of hardness, …

  1. b. Package plants are available from a number of manufacturers, and are perhaps most commonly supplied for filtration of turbid waters and removal of hardness, iron and manganese for design flows from a few hundred gallons per day to over one million gallons per day. All treatment equipment, pumps, chemical feeders and controls are usually provided in the factory-built unit so that as soon as the water pipes and electric power have been connected, the plant is ready to operate. Another advantage is that the design and equipment have been proven effective and reliable by experience, and the “bugs” have been worked out so the purchaser can have a high degree of confidence in the performance of factory-assembled package plants.
  2. False. Even automatic treatment equipment needs maintenance, repairs and occasional process control changes. Any water treatment plant can be upset by sudden or drastic changes in source water quality.
  3. a, c and d. An oxidizing agent such as chlorine, potassium permanganate, ozone or air may be used to oxidize soluble ferrous (Fe+2) iron and manganous (Mn+2) manganese to the insoluble ferric (Fe+3) and Manganic (Mn+4) forms. After adequate retention time (20 minutes to an hour depending on the chemical makeup of the water) is allowed for the oxidation reaction to be completed, insoluble precipitates of iron and manganese are formed. The precipitates can be removed by filtration.
  4. a, b, c & d. Oxidation is the process in which a molecule, atom or ion loses electrons to an oxidant. The oxidized substance (which lost the electrons) increases in positive valence.
  5. b and d. Reduction is the opposite of oxidation. Oxidation and reduction always occur together. Reduction is the acquiring of electrons (the ones lost in the oxidation process) by the oxidizing agent (the oxidizing agent is reduced in the process). Because electrons (carrying negative charges) have been acquired, reduction results in a decrease (a reduction) in positive valence.
  6. b, c & d. Certain polyphosphates (e.g., tripolyphosphate, metaphosphate and pyrophosphate) when fed into water cause a sequestering action in which dissolved ions such as those of iron and manganese are bound into the stable water-soluble phosphate polymer to prevent them from oxidizing, precipitating and staining. If the water contains less than 1.0 milligram per liter of iron and less than 0.3 milligrams per liter of manganese, the use of polyphosphate sequestrants may be effective. Other phosphate compounds (e.g. orthophosphates) form a thin passivating film on metal surfaces to control corrosion. Sodium silicate is an alternative compound that can also be used to place thin corrosion control films on metallic water pipes and fixtures. Normally a continuous dosage feed of several milligrams per liter is necessary.
  7. a. Filter aids improve filtering effectiveness by enhancing the retention of particles and/or increasing the permeability of the filter to water flow. Feeding of very small dosages of alum or the proper polyelectrolyte polymer filter aid at the inlet to filters can often make a marked improvement in the efficiency of filtration.
  8. b. inhibited.
  9. b. inhibited.
  10. b. inhibited. To achieve optimum agglomeration and filterability of suspended matter in water, the water needs to have adequate alkalinity for good coagulation with a coagulant such as alum. Any chemical reaction proceeds faster when the water is warm than when it is cold, and other chemicals such as sequestering phosphates, for example, inhibit coagulation and require larger doses of coagulant.

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