When we talk about "TOTAL ALKALINITY" we are not referring to whether the liquid is acid or alkaline, but measuring the buffering capacity of a liquid that is already above pH 4.5. Buffering capacity is a measure of the ability of the liquid to resist change of pH. A liquid with high total alkalinity will take a lot of acid to reduce the pH below neutral (the acid zone), whereas a weakly buffered liquid will change to lower pH with only a small amount of acid. Total alkalinity is reported in units of milligrams per litre calcium carbonate equivalent (mg/L as CaCO3). The technical details are not needed at this point.
The best example of a well buffered solution is our blood. If after eating a meal or drinking alcohol the increase of acids or alcohols in the blood would change quite dramatically if the blood was poorly buffered. Fortunately, our blood is strongly buffered and it takes large amounts of alcohol, food or drugs to change the pH outside the range that is good for us. That's important to maintain our normal function.
In the environment, the buffering capacity of water comes about because of the varying amounts of hydroxide, carbonate and bicarbonate (from carbon dioxide dissolved in the water) and hydrogen ions. Strongly buffered liquids are difficult to shift pH. Water in the natural environment has a mild buffering capacity and may be easily disturbed by the entry of small amounts of acid or alkaline substances.
Laundry detergents are, in the main, alkaline, that is their pH in water is above 7, maybe as high as 11 (strongly alkaline). We can also call them basic liquids which derive their buffering capacity from hydroxide, carbonate and bicarbonate. Sodium carbonate (washing soda), sodium bi-carbonate (baking soda) and sodium hydroxide (caustic soda) are commonly used in detergents to soften the water and increase the pH (grease, fats and food dissolve better in highly alkaline liquids). Phosphates, borates and silicates present in laundry detergents can also affect total alkalinity.
Rainwater has a very low buffering capacity (total alkalinity less than 10 mg/L CaCO3), groundwater from bores in limestone areas or under basalt landscapes may have high total alkalinity (above 500 mg/L CaCO3) from the carbonates dissolved in the water.
Good quality garden soil has a strong buffering capacity but strongly alkaline laundry water may disrupt that equilibrium.
In our reticulated water supply, the total alkalinity of the treated water is increased to about 80-100 mg/L CaCO3 to prevent the pipes dissolving in the water. That would happen if we were to be supplied with very clean water (very low buffering capacity).
When a strongly buffered laundry water (high total alkalinity) is discharged to the environment, two outcomes may result:
In the analysis of the liquid and powder detergents, the powders have higher total alkalinity than the liquids.
The following graphs show the alkalinity of laundry powders, mixed at the two rates.
INTERPRETATION: The longer the bar, the higher the total alkalinity and greater the influence the laundry wastewater will have on the natural total alkalinity of the soil and its reaction against change to the natural buffering capacity. The longer the bar, the greater the chance that the wastewater will have a detrimental effect upon the pH of the soil, particularly with repeated applications.
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4690 Armidale NSW 2350.