Final answer:
Wastewater cannot be released untreated due to its contaminated and toxic nature. Wastewater treatment removes harmful bacteria, waste, excess nutrients, and heavy metals, protecting both the environment and human health.
Step-by-step explanation:
The statement that best explains why wastewater cannot be released into the environment without treatment is that it will remain contaminated and toxic. Wastewater contains harmful bacteria, oxygen-demanding waste, excess nutrients like nitrogen and phosphorus, and potentially toxic heavy metals. The purpose of wastewater treatment is to remove these contaminants and reduce pollution, thereby protecting human health and the environment. Notably, pathogenic microorganisms in untreated wastewater are a major cause of waterborne diseases, which can be deadly. Treatment processes include physical, biological, and chemical steps to clean the water before it can be safely released back into natural ecosystems or reused for purposes such as irrigation.
Furthermore, while wastewater will still become part of the water cycle, if it is discharged untreated it can lead to eutrophication, causing algae blooms and damaging aquatic life. The treatment also involves disinfection, which is crucial to remove harmful pathogens, and newer methods such as sand filtration and enhanced biological phosphorus removal to reduce nutrients that could disrupt ecosystems.