In addition to washing the bed, a degradated mass containing agglomerates or fermentation zones (referred to as mud balls) can be regenerated by specific treatment techniques. Among the regeneration techniques that are usually used are sodium chloride, regeneration through application of chlorine, and treatment with potassium permanganate, hydrogen peroxide, or caustic soda. Cleaning methods based on the use of caustic soda are aimed at eliminating thin clay, hydrocarbons, and gelatinous aggregates that form in filtration basins. After the filter has been carefully washed with air and water or only with water, according to its specific operating scheme, a quantity of caustic soda is spread over a water layer approximately 30 cm thick above the filter bed. The solution is then diffused in the mass by slow infiltration. After about 6 to 12 hours, the filter is washed very carefully. Sodium chloride is used specifically for rapid filters. The cleaning solution is spread in solution form in a thin layer of water above the freshly washed sand bed. After 2 or 3 hours of stagnation, slow infiltration in the mass is achieved by opening an outlet valve for the filtered water. The brine is then allowed to work for about a 24 hour period. The filter is placed back into service after a thorough washing. Sodium chloride works on proteinic agglomerates, which are bacterial in origin.
The use of potassium permanganate (KMn04) is applied to filters clogged with algae. A concentrated solution containing potassium permanganate is spread at an effective concentration over the surface of the filters to obtain, a characteristic pink-purple color on the top of the mass and allowed to infiltrate the bed for a 24 hour period. After this operation, the filter is carefully washed once again.
PPM is the abbreviation for parts per million. A part per million is equal to a milligrams per liter. Parts per million refers to a ratio of weights. For example, one part per million is one pound in a million pounds, one ounce in a million ounces, one gram in a million grams,
Hydrogen peroxide is typically used in the range of 10 to 100 ppm. The cleaning method is similar to that used for permanganate. The addition of phosphates or polyphosphates makes it easier to remove ferruginous deposits. This method can be used in situ for surging the isolation sands of the wells. Adjunction of a reductor as bisulfite can be useful to create anaerobic conditions for the elimination of nematodes and their eggs when a filter has been infected. Hydrochloric acid solution is applied to the recurrent cleaning of rapid filters for sand, iron, and manganese removal. This operation has the advantage of causing the formation of chlorine in situ which acts as a disinfectant. Instantaneous cleaning of a filtering sand bed can be accomplished by the use of chlorine. A water layer is typically used as a dispersion medium. Further infiltration of the solution is obtained by percolation into the bed. The action goes on for several hours, after which the filter is washed. Chlorine is used from concentrated solutions of sodium hypochlorite. An alternative method involves the application of dioxide. This method has the advantage of arresting the formation of agglomerates of biological origin by permanent treatment of the filter wash water with chlorine.
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