pH measurement
pH is a measure of the hydrogen ion activity (electron donor). pH 7 is neutral, values lower are acid (high H+), while values above 7 are alkaline (refer back to the Laundry Products Research page)
The pH of the total wash water, that is the 75 L total load for the front loaders and 150 L for the top loaders was measured, using a freshly calibrate pH probe and meter, on the sample within one hour of mixing the detergent with the water at the dose for a normal wash as recommended by the manufacturer. The pH of your wash water may vary where you are using a town water supply that has a higher starting pH than rainwater (used in this research).
Detergent was mixed at one rate for the front loader and the other recommended rate for the top loader. Some detergents were recommended only for front loaders ( four products represented in block letters), while others were recommended for both (front and top) or for top only. Where the products were recommended for both, the results will be shown in both figures, each at the representative rate for the machine type.
The measurement of pH is important when discharging washing machine water either to the land or to a sewer. High pH (alkaline) has the ability to dissolve organic matter (sweat, blood, food) and that includes skin. One should be careful when handling the wash water when pH is above 10.
High pH liquids act as dispersing agents, causing the soil particles to separate and may lead to soil structural decline. The normal pH range for biological activity is between 5 and 9.
Figure F1-pH shows the range of pH values for 30 powders dosed at the rate recommended for front loaders.
Figure T1-pH shows the range of pH values for 50 powders dosed at the recommended rate for top loaders.
A frequency analysis is simply recording the number of products (Y-axis) that fall within a specified range (X-axis). The longer the bar, the more products in that range.
Assessment
Whether powders are used for front loaders or top loaders, the pH
of the full wash volume is generally very alkaline, that is has a pH above 8.5. Most of the powders represented in the two figures above have pH
values that are cause for concern because they fall well outside the range of
normal biological activity, and in all cases higher than desirable. While
the high pH is beneficial for removal of organic matter from clothes (food
stains, blood, sweat), it may also lead to the premature aging of clothes, that
is, they wear out because of the high pH rather than because of the washing
action.
As it is not possible to carry out normal clothes washing activities without some contact of the washing water with one's hands (be careful about splashing the wash water in your face), the potential for burns from the highly alkaline water may be high. Take care!
When highly alkaline greywater is discharged to a land application area, the high pH may interact with the soil particles and lead to dissolving organic material which can then be leached out of the soil. This is easy to demonstrate with any highly alkaline solution. The organic materials that are easily dissolved are the compounds that will, in time, degrade to become plant nutrients.
Since some plants prefer acid environments, the highly alkaline washing water may be more detrimental than any of the other compounds in the washing water. If you are using greywater on your favourite garden, it may be prudent to test a small section with the laundry water before water the whole garden with the greywater.
Unless the clothes are well rinsed (there is was no standard against which the rinsing action of washing machines could be judged until recently), the carry-over of some of the chemicals may lead to the highly alkaline salts affecting human skin with which they make contact. Whether the standard test for rinsing is satisfactory on some of the less soluble products or those high in dissolved salts has yet to be documented.