Combined presentation of sodium and phosphorus
In previous presentations on this website there was a printable version of a graph (based on 1999 research) that had both sodium and phosphorus on the one graph. It is now not possible to put all the information on one graph, otherwise one would need a magnifying glass to read it. This current research (2005) has analysed the results of using 54 powder detergents in either a front loader or a top loader at the different rates of water use for the average of those types. The final result is 30 products suitable for front loaders (following respective manufacturer's recommendations) and 50 for top loaders.
Two graphs are presented, one for front loaders and one for top loaders.
In each graph the various brands of laundry detergent powders are represented by two bars - a blue bar representing the load of sodium in grams per wash, and a red bar representing the phosphorus in concentration (milligrams per litre of total wash). The reason for the two different units on the same graph is simple, sodium loads are significantly larger than phosphorus load. The sodium loads have been ranked from lowest (bottom of Y-axis) to highest (top of Y-axis). The phosphorus concentrations are unranked.
Figure F5-Na-P Combination of sodium load and phosphorus concentrations for recommended dose in front loading washing machine (75 L per wash)
Figure T5-Na-P Combination of sodium load and phosphorus concentrations for recommended dose in top loading washing machine (150 L per wash)
Assessment
The interpretation of the figures will firstly depend upon whether you use a front loader or a top loader. Where wastewater is discharged to a sewer that eventually discharges to a creek, river or lagoon, phosphorus minimisation is perhaps more important than sodium and products low in phosphorus need to be chosen (short red bar).
When the wastewater will end up on land, such as large scale reuse from municipal treatment works or small on-site domestic treatment systems (septic tanks and drainfields), the load of sodium is extremely important as the phosphorus can be utilised for beneficial purposes by plants and on many soils is immobilised and will not move provided erosion is controlled. The soil type and the plants proposed to be raised in that dispersal area have to be assessed in relation to the actual sodium load they will tolerate. If in doubt, keep to the lowest sodium load.
It is easy to use either of the two figures to choose products that are low in both sodium and phosphorus, or where you wish to utilise the phosphorus for plant nutrition, to choose products low in sodium and of varying phosphorus concentrations depending upon the area of land over which you can disperse the wastewater.
There are remedies for treating land application areas that have had too large a sodium load in previous times, however, discussion of those ameliorating factors is beyond the scope of this presentation.