معالجة مياه الشرب(استخدام البروم/الهالوجينات/الاوزون/مضادات الكلورة)فى معالجة المياه

BROMINE
Bromine has been used for water treatment since the 1930's
Bromine is generated commercially through the reaction of a bromine brine solution with gaseous chlorine, followed by stripping and concentration of the bromine liquid. Bromine is a fuming, dark red liquid at room temperature.
Bromine dissociates in water in the same manner as chlorine, by forming hypobromous acid and the hypobromite ion.
Hypobromous acid is a weak acid that partially dissociates to form a hydrogen ion and a hypobromite ion.
The concentration or distribution of each species at equilibrium depends on pH and temperature.
Between pH 6.5 and 9, the dissociation reaction is incomplete, and both hypobromous acid and the hypobromite ion are present.
The equilibrium ratio at any given pH remains constant.
At a pH above 7.5, the amount of hypobromous acid is greater than the amount of hypochlorous acid for equivalent feed rates.
The higher percentage of hypobromous acid is beneficial in alkaline waters and in ammonia-containing waters.
Methods of generating hypobromous acid include:
using two liquids (or one liquid and chlorine gas)

NaBr + HOCl  HOBr + NaCl
sodium bromide hypochlorous acid hypobromous acid salt
using a compressed gas
BrCl + H2O  HOBr + HCl
bromine chloride water hypobromous acid hydrochloric acid
using a solid
C5H6BrClN2O2 + 2H2O  HOCl + HOBr + C5H8N2O2
bromochloro-
dimethylhydantoin (BCDMH) water hypochlorous acid hypobromous acid dimethyl-
hydantoin


Regardless of the method used to generate hypobromous acid, the goal is to take advantage of its antimicrobial activity.
The liquid and solid methods do not require the storage of compressed gases-the major reason for gaseous chlorine replacement.
Bromine reacts with ammonia compounds to form bromamines, which are much more effective antimicrobials than chloramines.
At pH 8.0, the hypobromous acid to bromamine ratio is 8:1 in ammonia-containing waters.
Because monobromamine is unstable and because tribromamine is not formed, there is little need to proceed to breakpoint bromination.
The shorter life expectancy of bromine compounds (due to lower bond strength) lowers oxidizer residuals in plant discharges and reduces the need to dechlorinate before discharge.
HALOGEN DONORS
Halogen donors are chemicals that release active chlorine or bromine when dissolved in water.
After release, the halogen reaction is similar to that of chlorine or bromine from other sources.
Solid halogen donors commonly used in cooling water systems include the following:
1-bromo-3-chloro-5,5-dimethylhydantoin
1,3-dichloro-5,5-dimethylhydantoin
sodium dichloroisocyanurate


These donor chemicals do not release the active halogen all at once, but make it slowly available; therefore, they may be considered "controlled release" oxidizing agents.
Their modes of action are considered to be similar to chlorine or bromine, but they can penetrate cell membranes and carry out their oxidative reactions from within the cell.
These donors are being widely used because of the simplicity, low capital cost, and low installation cost of the feed systems.
In addition, because they are solids, they eliminate the handling hazards associated with gases (escapement) and liquids (spills).
Evaluated on a total cost basis, halogen donors often prove to be an economical choice despite their relatively high material costs.

OZONE
Ozone is an allotropic form of oxygen, O3. Because it is an unstable gas, it must be generated at the point of use.
Ozone is a very effective, clean oxidizing agent possessing powerful antibacterial and antiviral properties.
Because ozone is a strong oxidizing agent, it is a potential safety hazard. It has been reported that concentrations of 50 ppm of ozone in the air can cause oxidization of the lining of the lungs and accumulation of fluid, resulting in death by pulmonary edema.
consider 10 ppm immediately dangerous to life or health, and the exposure limit is a time-weighted average of 0.1 ppm.
In concentrations as low as 0.02 ppm, strong ozone odors are detectable.
Improper operation of ozone-generating equipment can produce 20% ozone, an explosive concentration.
Ozone-generating equipment must have a destruct mechanism to prevent the release of ozone to the atmosphere where it can cause the formation of peroxyacetyl nitrate (PAN), a known air pollutant.
Ozone's short half-life may allow treated water to be discharged without harm to the environment. However, the shorter half-life reduces contact in a treated water system, so the far reaches of a wa-ter system may not receive adequate treatment.
Ozone is generated by dry air or oxygen being passed between two high-voltage electrodes.
Ozone can also be generated photochemically by ultraviolet light.
Ozone must be delivered to a water system by injection through a contactor.
The delivery rate is dependent on the mass transfer rate of this contactor or sparger.
Proper maintenance of the generator and contactor is critical.
High capital costs limit the use of ozone for microbiological growth control, particularly in systems with varying demand.
DECHLORINATION
Dechlorination is often required prior to discharge from the plant. Also, high chlorine residuals are detrimental to industrial systems, such as ion exchange resins, and some of the membranes used in electrodialysis and reverse osmosis units.
Chlorine may also contribute to effluent toxicity; therefore, its concentration in certain aqueous discharges is limited.
Sometimes, dechlorination is required for public and industrial water supplies.
Reducing or removing the characteristic "chlorine" taste from potable water is often desirable.
Dechlorination is commonly practiced in the food and beverage processing industries.
Direct contact of water containing residual chlorine with food and beverage products is avoided, because undesirable tastes can result.
Excess free residual chlorine can be lowered to an acceptable level by chemical reducing agents, carbon adsorption, or aeration.
Chemical reducing agents, such as sulfur dioxide, sodium sulfite, and ammonium bisulfite, dechlorinate water but can also promote the growth of bacteria that metabolize sulfur.
Sometimes, sodium thiosulfate is used to dechlorinate water samples prior to bacteriological analysis. Common dechlorination reactions are:
SO2 + Cl2 + 2H2O « » H2SO4 + 2HCl
sulfur dioxide chlorine water sulfuric acid hydrochloric acid

NaHSO3 + Cl2 + H2O « » NaHSO4 + 2HCl
sodium bisulfite chlorine water sodium bisulfate hydrochloric acid

NH4HSO3 + Cl2 + H2O « » NH4HSO4 + 2HCl
ammonium bisulfite chlorine water ammonium bisulfate hydrochloric acid


Granular activated carbon (GAC) removes free chlorine by adsorption.
Free chlorine in the form of HOCl reacts with activated carbon to form an oxide on the carbon surface.
Chloramines and chlorinated organics are adsorbed more slowly than free chlorine.
Aeration is the least effective means of dechlorination, with effectiveness decreasing with increasing pH. The hypochlorite ion, which predominates at pH 8.3 and higher, is less volatile than hypochlorous acid.
Ultraviolet radiation dechlorinates water stored in open reservoirs for prolonged periods
by
colonel.dr
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