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Pre-Treatment From Hungerford & Terry
Hungerford & Terry, Inc.For applications where sodium increase is a concern, Hungerford & Terry produces a line of weak-acid softeners that operate in the hydrogen cycle instead of the sodium cycle
Operating in the sodium cycle, the sodium in the treated water is increased proportionately to the amount of calcium and magnesium in the untreated water. For applications where sodium increase is a concern, Hungerford & Terry produces a line of weak-acid softeners that operate in the hydrogen cycle instead of the sodium cycle. Where total hardness is numerically equal to the alkalinity in the raw water, the hardness can be economically removed using an acid-regenerated weak-acid (carboxylic) cation exchange resin. The quantity of hardness which exceeds the alkalinity will not be removed. The ion exchange mechanism in the weak-acid softening process is an exchange of calcium and magnesium ions for hydrogen ions. Therefore, no sodium is added to the treated water. Either hydrochloric acid or sulfuric acid can be used for regeneration.
During the ion exchange process with weak acid resin, carbonic acid is formed and can be stripped off using a forced draft degasifier following the softener. Also, a small quantity of sodium hydroxide can be added following the decarbonator to neutralize any remaining CO2 and to provide non-corrosive water with a neutral pH. The system can be designed for stoichiometric quantities of acid so that the waste produced does not require neutralization prior to disposal.
Clarifiers
Surface water color, turbidity, and suspended matter are effectively removed with a Hungerford & Terry clarifier. The process involves accurately flash mixing coagulant, polymer, and other chemicals in proportion to water flow and recirculaing pre-formed floc via the turbine mixer and recirculation tube. Precipitants are generated in the mixing zone of the downcomer and gradually grow larger forming a sludge blanket. Ultimately, the precipitants settle out as a floc. The clarified water rises and is collected in the launder trough located along the top of the tank sidewall. Cold lime softening uses similar equipment but is designed to remove alkalinity and the hardness associated with alkalinity to produce a water that is clear, colorless, and with reduced hardness, alkalinity, and iron. Equipment is available sized for a flow rate of 800 gallons per minute up to several thousand gallons per minute.
Gravity Filters
Following clarification or lime softening, filtration would be required to remove any floc carryover and suspended material. The H&T gravity filter system is available in single or multi-cell rectangular design or circular tanks with self-contained backwash storage. An air scour system or a surface washer can be included to ensure a high degree of agitation of the filter bed during backwashing which ensures that the filter bed is clean and that there are no areas of compaction or cementation. Underdrain systems consist of a flat false bottom plate with distribution nozzles. A full range of sizes is available from 500 gallons per minute up to several thousand gallons per minute.
