What needs to be removed from industrial waste water before it is released into the environment?

The correct answer emphasizes the necessity of removing organic matter and harmful chemicals, including toxic metal compounds, from industrial wastewater before it can be safely released into the environment. This is crucial because organic matter can deplete oxygen levels in water bodies, which adversely affects aquatic life. The presence of harmful chemicals, particularly toxic metals, can contaminate water sources, harm wildlife, and pose health risks to humans. Effective wastewater treatment processes are designed to eliminate these pollutants to protect ecosystems and public health.

Other options do not address the most critical contaminants found in industrial wastewater. While removing plastic and paper waste is important for solid waste management, it is not a primary concern for treating industrial wastewater specifically. Sand and silt are sedimentary materials that can be managed through basic filtration processes but do not pose the same level of environmental risk as organic matter and toxic chemicals. The choice focusing solely on organic matter overlooks the equally significant threat posed by harmful chemical pollutants.