Composite samples are relatively employed for the design of wastewater treatment plants.

Explanation:
Wastewater treatment plants are designed to remove pollutants and contaminants from wastewater before it is discharged into the environment. In order to design an effective treatment system, it is important to have accurate information about the composition and characteristics of the wastewater that will be treated. This information is obtained through sampling and analysis of wastewater samples.

There are different types of samples that can be collected for wastewater analysis, including grab samples, composite samples, and integrated samples.

Grab samples:
- Grab samples are individual samples that are collected at a specific time and location.
- These samples provide a snapshot of the wastewater composition at that particular moment.
- Grab samples are useful for analyzing short-term variations in wastewater quality.
- However, they may not accurately represent the overall characteristics of the wastewater over a longer period of time.

Composite samples:
- Composite samples are created by combining multiple grab samples collected over a specified period of time.
- These samples provide a more representative picture of the average wastewater composition over that time period.
- Composite samples are useful for designing wastewater treatment plants because they provide a more accurate estimate of the average pollutant concentrations that the treatment system will need to handle.
- By analyzing composite samples, engineers can determine the appropriate treatment processes and equipment needed to achieve the desired effluent quality.

Integrated samples:
- Integrated samples are collected using automated sampling devices that continuously collect small aliquots of wastewater over a period of time.
- These samples provide a detailed picture of the variations in wastewater composition over time.
- Integrated samples are useful for studying diurnal variations in wastewater quality and for identifying peak pollutant loads.
- However, they are less commonly used for designing wastewater treatment plants compared to grab and composite samples.

Conclusion:
In conclusion, composite samples are relatively employed for the design of wastewater treatment plants because they provide a more representative picture of the average wastewater composition over a specified time period. By analyzing composite samples, engineers can design treatment systems that are capable of effectively treating the average pollutant concentrations in the wastewater.