Electrical conductivity
As discussed previously, electrical conductivity (EC) is used as a measure of salinity. While the relationship is not direct, a simple conversion factor is often used to convert the EC reading in deciSiemens per metre (dS/m) to salinity in milligrams per litre (mg/L).
As the liquid products were mixed with deionised water (equivalent to very clean rainwater) before the EC measurement was taken, any recalculation to take account of another quality of input water (such as from a town water supply) can be added directly to the EC reading shown in the graph below, provided the dose is at the recommended dose for that particular type of washing machine.
As an example, assume you are using water from an inland NSW town water supply that has an electrical conductivity of 0.3 dS/m and using a liquid detergent that has an EC in deionised water of 0.2 dS/m, then the calculation for salinity is as follows:
EC of town
water + EC of liquid detergent in deionised water
= Final EC
0.2 dS/m
+ 0.3 dS/m
= 0.5 dS/m
Salinity
= EC of wastewater (dS/m) x
680
= 0.5 x 680
= 340 mg/L
Figure LF2-EC Effect of mixing recommended dose of liquid laundry detergent for a front loaders with water equivalent to rainwater quality.
Figure LT2-EC Effect of mixing recommended dose of liquid laundry detergent for a top loaders with water equivalent to rainwater quality.
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
The salinity of the liquid laundry detergents is generally very low and unlikely to seriously affect the growth of plants or the salinity levels in the soil. When compared with the laundry powders (Powders - EC), these liquids are very mild in terms of salinity. The average EC of powders in front loaders was 1.18 dS/m (median 1.10 dS/m) while for top loaders is was slightly lower at 0.91 dS/m (median 0.77 dS/m). For liquids the front loader average EC was 0.10 dS/m (median 0.07 dS/m) and for the top loader average was 0.10 dS/m (median 0.05 dS/m). Figure L-EC shows the frequency analysis (number of samples) in each range of EC values, noting that all are below the guidance value of 1 dS/, and most were at lower than 0.3 dS/m. That contrasts quite remarkably from the analysis of the powers.
While the average EC of liquid detergents when mixed at the recommended rate was about one-tenth that of the powders, it is possible to choose low EC products from either the liquids or the powders.