Do you want to use it for environmental reasons? If so I wouldn't worry as it doesn't really make a difference.
A biological washing powder contains enzymes which break down stains and dirt whilst in the wash.
A non-biological washing powder does not contain these enzymes.
In terms of the environmental impact, neither system is perfect. Whilst the enzymes contained in a biological wash powder may take longer to disperse within the environment, the temperatures for washing can be lower than for a non-biological powder. The non-bio powder could take a higher temperature to do the same wash, which uses more electricity and water and this also has an environmental impact.
Saying that we use Proderm as its much nicer on the skin