Phosphates removal from waste water

J. Kato, K. Yamada, A. Muramatsu, Hardoyo and H. Ohtake (1993a). Genetic improvement of Escherichia coli for enhanced biological removal of phosphate from waste water. Appl. Environ. Microbiol., 59, 3744-3749. 

Sulffde Precipitants. The removal of heavy metals from waste waters using soluble sulfides has been studied extensively. Peters and Ku (13) showed that pH strongly affects the removal of heavy metal sulfides from waste water. Their data showed that the solubilities of most heavy metal sulfides, other than arsenic (HI) sulfide, decreases up to about pH 9. Since most phosphate fluid fertilizers, such as 10-34-0 and 11-37-0, have a pH in the range of 6 to 7, these data indicate that concentrations of several heavy metals in phosphate fluid fertilizers could be reduced to very low levels by precipitation with inorganic sulfide reagents. The use of soluble sulfides to precipitate heavy metals from WPA has also been reported. Both Maruyama (14) and Berglund (15) have... 

Ion flotation in the presence of surfactants for the treatment of rinses and separation of metal ions is of interest since the sixties [327, 328]. Here, we take only a few examples. The recovery of silver ions from highly diluted solutions is possible by forming a silver-thiourea complex in form of a colloidal precipitate (sublate) followed by sublate flotation with sodium dodecyl benzene sulfonate [329]. Skiylev [330] has developed methods for the removal of non-ferrous metal salts from waste waters. Subject of the investigations were 0.01 - 0.001% solutions of ferrous metal salts. Typical anionic surfactants (alkyl sulfates, alkyl phosphates, alkyl xanthogenates of potassium) or cationic surfactants (quaternary ammonium salts) were used as collectors in ion flotation from diluted solutions. At certain pH, a sublate containing a non-ferrous metal ion was formed, followed by a sublate film formation at the surface due to the rise of the complexes with air bubbles stabilised by the surfactants. 

The applications of fly ash zeolites discussed in this chapter are summarized here in brief. Fly ash zeolites A, 4A, P and 4X are suitable for detergent builder and common substitute to phosphate builders. Other types of zeolites A, Y, P, Na-Pl, 4A, X, KM, Chabazite, Herschelite and Faujasite are effective for removal of heavy metals and ammonia from waste water. Zeolite A and Faujasite are proven cation exchange materials for removal of from sewage. Zeolite Na-P,... 

Sodium alumiaate is an effective precipitant for soluble phosphate ia sewage and is especially useful ia wastewater having low alkaliaity (20,21). Sodium alumiaate hydrolyzes ia water to Al(OH)2 and Al" which precipitate soluble phosphate as aluminum phosphate [7784-30-7], AlPO. Sodium alumiaate has also been described as an effective aid for the removal of fluorides from some iadustrial waste waters (22). Combiaations of sodium alumiaate and other chemicals are being used to improve the detackification of paint particles ia water from spray-painting operations (23). 

To avoid buildup of phosphates, sulfates, and chlorides in the scrubber solution, a portion of the scrubber stream is removed from the system and evaporated to dryness. The resultant dry salts are then placed in drums for storage. The evaporation step requires large amounts of energy. The use of dual alkali scrubbing technology could avoid the need to evaporate large amounts of water to produce a solid waste. 

The aluminum chloride catalyst used in the alkylation is finally rejected from the system as an acidic aqueous solution. This by-product AICI3 is usually best used for waste water treatment. Sale or use of this material is often as an alum or copperas substitute in water clarification. It is also used in U.S. municipal sewage treatment plants, where a valuable side effect is phosphate removal. In Japan it is converted to polyaluminum chloride (PAC) and used for water treatment. Other uses for this aqueous aluminum chloride stream exist. 

A by-product aqueous stream is generated in the first washing step that contains dissolved HCl, alkylate and AICI3. The uses for this byproduct depend upon its purity. It has been used directly in industrial waste water treating and it has been shown to effectively remove phosphate from municipal sewage. In Japan it is converted to polyaluminum chloride, a highly desirable coagulant for waste water. 

Chemical pollution is the diversion of chemical elements from the natural biogeo-chemical cycles. The carbon, nitrogen, and phosphate in municipal wastes released to streams and lakes are removed from the soil-plant cycle, which is the source of the nitrogen and much of the phosphate. If those substances were instead put back directly into the soils from whence they came, much less pollution would result. Air and water only slowly convert their wastes back into their natural sites in plants and soils. Soil, on the other hand, has enormous surface area and microbial catalytic activity plus oxygen and water with which to deactivate pollutants. Soil degrades most... 

It is washed successively with 0.01 Af HNO3, 0.2 Af Na COs, 0.2 Af NaOH, and 0.02 Af HNO3. The operations are performed in mixer-settler batteries. The uranium content is reduced by a factor of 10, the plutonium content by a factor of 50, and the fission-product content by a factor of 2. Dibutyl phosphate is removed as the water-soluble sodium salt. If sodium ion in the wastes from solvent cleanup is objectionable, ammonium carbonate has been proposed as an alternative [G3]. 

It can be anticipated that various other metals will eventually be separated either from sea water or from the waste evaporator brine. Many metals are concentrated from sea water by phosphate precipitation during production of the magnesium ammonium phosphate fertilizer. Future metal recovery processes may utilize the fertilizer as a raw material. Because the evaporator brine contains a high concentration of chloride, a number of metals will be present in it as chloride complex anions (7). Many of these complex anions may be removed from the brines on an anion exchange resin such as Dowex 1 and then recovered from the resin simply by washing the column with fresh water. 

Fertilizers are a major source of phosphates entering rivers and lakes. However, domestic and industrial waste water (e.g. from detergent manufacturing) also contains [P04] and condensed phosphates, and the levels that must be removed before the waste can be discharged are controlled by legislation. In most cases, phosphates are removed by methods based on precipitation (this is the reverse of the situation for nitrate removal see Box 15.9). Fe, Al and Ca are most commonly used to give precipitates that can be separated by filtration. 

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