ISO 11733 is titled "Water quality - Aerobic biodegradability testing for use in saline environments - Comprehensive test methods for partial and complete mineralization". The purpose of this standard is to evaluate the biodegradability of certain chemicals or water samples. This is especially important for understanding how various substances degrade in seawater.

The application of this standard is particularly important when:

- To predict the behavior of potentially pollutants in seawater.
- Evaluate the effectiveness of water treatment processes and wastewater treatment plants.
- To evaluate the environmental impact of chemicals used in seawater.
  
ISO 11733 biodegradability testing usually includes these steps:

1. The substance or sample to be tested is incubated in seawater with a culture of a particular microorganism.
2. The concentration of the substance or compound is measured by taking samples at specified time intervals.
3. The rate of degradation is calculated based on the difference between the initial concentration and the concentration after a given time.
4. The results show how quickly the substance degrades in seawater. This can be used to assess the environmental impact of the substance.

Such testing is very important for water quality and environmental protection because some substances do not biodegrade and these substances can harm the marine ecosystem. The ISO 11733 standard provides recommendations and guidelines on how to properly perform these tests.