Alum - a group of hydrated double salt

Alum is a group of hydrated double salts, also known as aluminium sulfate. It is because aluminium will always mix with other elements to form a stable compound. Alum presents in some minerals, naturally. It is the third most abundant element in the earth. Alum can be produced by precipitation, evaporation to obtain crystals or treating bauxite ore with sulfuric acid and added with sulfide.

Alum is colourless, usually present in the form of white crystalline powder. It has acid taste yet odourless. Alum can dissolve in hot water and form precipitate in aqueous solution. Chemically, alum can be formed by hydration of singly charged cation and sulfates of triply charged cation of metal. Precipitation of aluminum hydroxide will occur during hydrolysis of alum too. Alum crystal

Alum is widely used in water treatment to remove impurities. It undergoes hydrolysis and formed amorphous oxides. This oxide can absorb organic matter or impurities in raw water and coagulate them into a mass which is easier for us to deal with them.

Undeniably, alum is very effective in absorbing suspended particles from raw water. This is why it is classified as good flocculating agent in water-purification plants. Besides, alum has been used as a flocculant in treating water supplies since ancient times in whole world. It is because alum plays its role effectively in removing unwanted colour and turbidity.

Alum sludge is an effective P-absorbent due to a large number of aluminium ions presented. On purpose to study the P-absorption of alum, samples of dewatered alum sludge cakes were obtained and tested with pyres columns. (Pic) Results showed that the alum sludge have a comparable P-absorption capacity to other potential wetland substrates. It removed up to 90% of influent phosphorus in farmyard. It can enhance sustained P-removal in a constructed wetland system. Alum sludge may be a treasure contributes in wastewater treatment.

Our body can absorb aluminium from our foods and drinks. Plus, accumulation of a large quantity of aluminium in our body will result in contraction of body tissues and canals. Research sponsored by WSAA (Water Services Association of Australia) has shown that about 0.4 to 1% of bioavailable aluminium comes from alum treated water. Consequently, possible health effect of alum is concerned since we take in alum from drinking water daily. It was believed a cause of Alzheimer's disease. Moreover, toxicological data for aluminium is reviewed by the National Health and Medical Research Council (NHMRC) and the World Health Organisation. They concluded that there are no strong data to set alum as No Effect Level.

Furthermore, aluminium will accumulate easily in kidney dialysis patients' blood. As a result, alum which is not removed from the water will cause dialysis dementia in them. The worse is kidney dialysis patients seemed more sensitive to aluminium in the dialysis fluid than other sources like food or antacids. It troubles them as dialysis fluids have to be treated before use.

In alum-treated litters, the mineralisation of organic nitrogen might happen due to abundant fungus population. A research is then made to study the change in total bacterial, fungal populations and urease-producing microorganisms present in litter. Bacterial population was reduced by half and bacterial urease producers were reduced by 90% within one month for the litter treated with 10% alum. However, the fungal population was extreme high in alum-treated poultry litter. The sudden change in pH also helps to inhibit bacterial populations in alum-treated poultry litter. Therefore, it concluded that organic matters can be absorbed and removed by post precipitation when the alum is used in water treatment.

The used of alum in treating raw water will unconsciously lead to environmental pollution. It was known that alum will then be filtered from treated water and forming residual cake (waste water sludge), which have to be disposed, mostly in landfills. Thus, residual cakes are consigned to landfills at huge expense known as valueless waste. Other than that, it also costs a big bomb (about three millions/pa) to recycle the landfill sludge. Another problem is insufficient of economic and well developed options to deal with the huge number of residual cakes.

In order to minimise the harmful effects of alum in treating raw water, an idea of constructed wetlands system is developed and being discussed. Its suggested idea is waste water sludge can be used as the main substrate to improve waste water treatment. Agreement and acceptance with concept of constructed wetland systems is increasing although this concept is not entirely new.

Well, alum in treated water can be removed by filtration. This can be done as alum plays its role as flocculant in a well operated water filtration plant. Thus it reduces aluminium concentrations to a concentration less than 0.1mg/L in treated water. Moreover, by utilising the conventional water treatment practices of flocculation and filtration, concentration of aluminium in treated water can be reduced effectively.

Good news for kidney dialysis patients is, reverse osmosis or deionisation units can be applied to treat dialysis water before use. As a result, aluminium concentrations are kept below 0.01 mg/L. These techniques achieved the aim of minimising the quantity of aluminium accumulated in kidney dialysis patients' blood.

According to extensive research conducted by CSIRO, the safety of alum in treatment of raw water is guaranteed. CSIRO concluded that only 1 to 2% of our daily intake of aluminium comes from water. Only little of it is absorbed and most of the absorbents are excreted through urine. However, the used of alum in treating drinking water is proved to link with Alzheimer's disease. Therefore, health authorities worldwide have said that whilst there is no epidemiological evidence to show that aluminium is a health hazard, they will keep the situation under review.

Since no new water treatment is discovered, alum should continue to be used as flocculating agent as its harmful effects are minimized, cheap enough and easy to be obtained. All in all, alum is no doubt vital for its uses as flocculating agent thus it is helpful for human daily life.

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